UNIVERSITY OF CALIFORNIA 
 
 ANDREW 
 
 SMITH 
 
 HALLlDIft 
 
LECTURES 
 
 ELEMENTS OF BOTANY. 
 
 PART I. 
 
 CONTAINING 
 
 THE DESCRIPTIVE ANATOMY OF THOSE ORGANS, ON 
 
 WHICH THE GROWTH AND PRESERVATION OF 
 
 THE VEGETABLE DEPEND. 
 
 BY 
 
 ANTHONY TODD THOMSON, F. L. S. 
 
 MEM. OF THE ROY. COLL. OF SURGEONS, AND THE MEDICO-CHIRURG. SOC. 
 
 OF LONDON: FELLOW OF THE MEDICAL SOCIETY, OF THE ROY. PHY- 
 
 SICAL SOCIETY, AND THE SPECULATIVE SOCIETY, OF EDINBURGH: 
 
 MEM. OF THE SOCIETE DE MEDECINE DE MARSEILLES, AND 
 
 OF THE SOCIETE MEDICALE D*EMULATION DE PARIS. 
 
 VOL. I. 
 
 
 LONDON : 
 
 PRINTED FOR LONGMAN, HURST, REES, ORME, AND BROWN, 
 PATERNOSTER ROW. 
 
S. GOSNELL, Printer, Little Queen Street, London. 
 
TO 
 
 THE PRESIDENT AND THE FELLOWS 
 
 OP 
 
 THE ROYAL COLLEGE OF PHYSICIANS, 
 OP LONDON; 
 
 IN THE HOPE 
 
 THAT 
 THEIR AVOWED PATRONAGE 
 
 OF 
 
 AN ELEMENTARY WORK ON BOTANICAL SCIENCE, 
 WILL PROMOTE THE FUTURE STUDY 
 
 OF 
 
 THAT BRANCH OF KNOWLEDGE 
 AS A PART OF MEDICAL EDUCATION; 
 
 , AND THAT, 
 
 BY THUS DISPLAYING THEIR APPROBATION 
 
 OF 
 
 WHATEVER CAN ENLARGE THE VIEWS 
 OF THE STUDENT 
 
 IN 
 
 THE INVESTIGATION OF ORGANIC LIFE, 
 
 THE CHARACTER 
 
 OF THE MEDICAL PHILOSOPHER 
 
 MAY BE ELEVATED TO ITS DUE RANK IN SOCIETY; 
 
 THESE LECTURES, 
 
 WITH THEIR GRACIOUS PERMISSION, 
 ARE INSCRIBED 
 
 BY 
 
 THE AUTHOR. 
 
 u2 
 
PREFACE. 
 
 NUMEROUS works on the elementary principles of 
 Botany, and many of them very excellent pro- 
 ductions, have been published, both in this coun- 
 try and on the continent, within the last twenty 
 years: and, by pointing out the mode of inves- 
 tigating the laws of vegetable life, have done 
 much to remove an objection to the study of Bo- 
 tanical science, which had long prevailed, " that 
 " it is a pursuit that amuses the fancy and ex- 
 " ercises the memory, without improving the mind 
 " or advancing any real knowledge *." Under 
 these circumstances, the publication of a new 
 work on this subject may require some apology; 
 and it was not my intention to have placed the fol- 
 lowing Lectures before the public, had I not ac- 
 cidentally met with a manuscript copy of them, 
 
 * White** Nat. Hist, of Sclborne, 8vo. London, 1822, vol. 
 ii. p. 38. 
 
VI PREFACE. 
 
 as they were delivered to my pupils, exposed for 
 sale in a bookseller's shop*. Reflecting, therefore, 
 that any peculiar theories connected with vege- 
 table physiology, which I had taught, and of 
 which little more than outlines had been sketched 
 for the class-room, were likely to be much mis- 
 represented, and even that many of the facts 
 taken from authors might be misstated, justice to 
 my reputation required that I should rather pub- 
 lish my own opinions, than run the hazard of 
 their getting into the press in a mutilated condi- 
 tion. In revising my manuscript, however, for 
 this purpose, I found that the view of the sub- 
 ject opened before me, that one investigation led 
 on to another; and that a frequent appeal to Na- 
 ture forced me to reject much of what I had for- 
 merly regarded as truth ; so that the work im- 
 perceptibly extended far beyond the limits I had 
 allotted to it; and, now, retains little more than 
 the name and the arrangement of the original 
 Lectures. 
 
 The present volume treats of the forms and 
 the anatomy of those organs which are necessary 
 for the growth and the preservation of the vege- 
 
PREFACE. Vll 
 
 table individual; and, although it does not pro- 
 fess to enter fully into the explanation of the laws 
 which regulate the functions of these organic 
 structures, yet, much of physiology has been in- 
 troduced, both to illustrate the descriptions, and 
 to relieve the dry ness of the anatomical details. 
 The necessity of an accurate knowledge of struc- 
 ture, will be fully perceived in the perusal of the 
 physiological discussions which are intended to 
 form the subject of the second volume. I trust 
 that the plan of illustrating the descriptions 
 by the introduction of cuts into the body of the 
 letter-press, will be found of considerable assist- 
 ance to the student; and that the engraved plates, 
 although not all of equal merit in point of execu- 
 tion, will, nevertheless, be found sufficient for 
 conveying correct ideas of those parts, which, 
 from their minuteness, are necessarily microscopic 
 objects. 
 
 As an apology for errors which may be detected 
 in the volume, I might plead the interruptions, 
 anxieties, and unremitting duties of very exten- 
 sive professional occupations ; but, as I am aware 
 that no author is dragged before the tribunal of 
 
viii PREFACE. 
 
 the public against his inclination, and until he 
 declares himself prepared for trial, I do not 
 think such circumstances valid reasons for lenity 
 or favour. The work, therefore, is published with- 
 out any claim of indulgence, but with a convic- 
 tion, that, although many objections may be 
 raised to the doctrines it contains, yet, if it have 
 merit, that its faults will be lightly handled ; and 
 if it be undeserving of approbation, that even 
 the countenance of the learned body, under whose 
 patronage it is sent forth, cannot alter the sen- 
 tence which Justice should dictate. 
 
 ANTHONY TODD THOMSON. 
 
 91, Sloane Street, 
 May 30, 1822, 
 
CONTENTS. 
 
 LECTURE I. -Page I. 
 
 INTRODUCTION SKETCH OF THE RISE AND PROGRESS 
 
 OF BOTANY UTILITY OF THE SCIENCE METHOD 
 
 OF STUDYING IT, AND PLAN OF THE COURSE. 
 
 LECTURE II.~Page 39. 
 
 DEFINITION OF A PLANT GENERAL VIEW OF THE 
 
 VEGETABLE FUNCTIONS. 
 
 LECTURE III. Page 69. 
 
 GENERAL COMPONENTS OF THE VEGETABLE 
 STRUCTURE. 
 
 LECTURE IV. Page 125. 
 
 VEGETABLE ORGANIZATION. THE ROOT ITS SITUA- 
 TION, SPECIES, AND VARIETIES DIRECTION AND 
 
 DURATION. 
 
 LECTURE V. Page 189. 
 
 THE SUBJECT OF THE FORMER LECTURE CONTI- 
 NUED. OF SOILS AND MANURES. OF THE MEDI- 
 CINAL AND DIETETIC AL PROPERTIES OF ROOTS, 
 
 LECTURE VI. Page 24 1. 
 
 THE STEM ITS DIRECTION DIVISIONS AND BRANCH- 
 ING COVERING COLOUR FIGURE. CLASSIFICA- 
 TION OF STEMS. 
 
 VOL. I. b 
 
CONTENTS. 
 
 LECTURE VII. Page 284. 
 
 SUBSTANCE AND ORGANIZATION OF THE STEM AND 
 
 BRANCHES : ANATOMICAL DEMONSTRATION OF 
 
 THE COMPONENT PARTS OF THESE ORGANS THEIR 
 
 FORMATION, INCREASE, AND REPRODUCTION. 
 
 LECTURE VIII. Page 383. 
 
 ORIGIN AND ATTACHMENT OF BRANCHES ; STRUC- 
 TURE OF LIGNEOUS ROOTS; AND OF HERBACEOUS 
 DICOTYLEDONOUS STEMS. 
 
 LECTURE IX. Page 447. 
 
 OF LEAVES IN THEIR UNEXPANDED STATE, OR AS 
 
 THEY ARE CONTAINED IN THE GEM : IN THEIR 
 
 EXPANDED STATE, OR AS CONSTITUTING FOLIAGE. 
 
 LECTURE X. Page 5 13. 
 
 OF THE PETIOLE. COMPOUND LEAVES. THE SITUA- 
 TION, POSITION, INSERTION, DIRECTION, MAGNI- 
 TUDE, AND EXTENSION OF LEAVES. ANATOMY OF 
 THE LEAF. 
 
 LECTURE XL Page 599. 
 
 OF THE CUTICULAR SYSTEM OF LEAVES: USE OF 
 THE CUTICULAR APERTURES. OF THE APPEND- 
 AGES OF THE STEM AND LEAVES PUBESCENCE 
 
 THORNS PRICKLES GLANDS PROPS t USES 
 
 OF THESE APPENDAGES. 
 
EXPLANATION OF THE PLATES. 
 
 PLATE I. 
 
 Fig. 1. Section of the tubers of Orchis mascula: a. the new tuber; 
 b. the old ; e. the base of the stem of the present year's 
 herbage; d. the plantule or embryon; e. a sheath cover- 
 ing the plantule ; /. the point of conjunction of the ves- 
 sels of the stem of the old tuber, with those of the plan* 
 tule and the new tuber; g. a root. (p. 159, 161). 
 
 2. A transverse section of the new tuber, to display the vessels 
 
 injected, (p. 160). 
 
 3. A transverse section of the old tuber, to demonstrate the 
 
 effect of the absorption of the nutritious fluids on the cells 
 in the immediate vicinity of the vessels, (p. 160). 
 
 4. Longitudinal section of a potatoe : a. the central part or 
 
 pith ; b. b. b. b. the cortical part ; c. c. c. points where the 
 eyes or gems are situated ; d. point where the tuber was 
 attached to the runner, (p. 163). 
 
 5. Bulbs of Crocus sativus; a. b. the new bulbs adhering 
 
 closely to c. the old or parent bulb much shrivelled ; d. the 
 radical plate of the old bulb. (p. 167). 
 
 6. Section of fig. 5 ; d. two cords of vessels, which separate 
 
 from the general bundle immediately on entering the new 
 bulb, and pass ,on to supply nutriment to the embryons 
 e. which are forming on a. b. (p. 167, 169). 
 
 7. Bulbs of Ixia polystachia ; a. b. the bulbs bearing the pre- 
 
 sent year's herbage, partly covered with c. the reticulated 
 b 2 
 
Xli EXPLANATION OF THE PLATES. 
 
 coat of the old bulb d.; e. e. e. e. e. roots of the recent bulbs 
 protruded between them and the old bulb; /. a young 
 bulb appended by a runner, (p. 167, 168). 
 
 Fig. 8. Bulbs of Colchicum autumnale decorticated ; a. b. the new 
 bulbs ; c. c. a flattened process on each ; d. the old or pa- 
 rent bulb shrivelled up ; e. the remains of its radical plate ; 
 /. the remains of its flattened process. 
 
 9. Another view of figure 8. (p. 170, 178). 
 
 10. Section of fig. 8 ; a. the old bulb ; b. c. the new bulbs 
 (no lines should have been drawn from these letters) ; d. d, 
 the opaque portion of the new bulb ; e. e. semi-trans- 
 parent portion ; /. g. points of conjunction of the old and 
 the new bulbs h. h. herbage of the present season, (p, 
 170, 178). 
 
 PLATE II. 
 
 1. Entire bulb of Lilium candidum. (p. 173). 
 
 2. Transverse slice of one of the scales of the bulb, fig. 1. to 
 
 display the vascular bundles. 
 
 3. A. the bulb, fig. 1. denuded of its scales, to show the young 
 
 bulb : . the stem of the present year's flower; b. the young 
 bulb; *c. c. fragments of the scales of the parent bulb; 
 d. d. d. d. roots of the parent bulb ; e. e. remains of those 
 of last year's bulb. B. Section of A.: a the remains of 
 the caudex of last year's bulb ; b. caudex of this year's 
 bulb. (p. 175). 
 
 4. Bulbs of Lilium superbum: a. the bulb of the present year ; 
 
 b. that of last year ; c. the remains of that of the year be- 
 fore last ; d. the embryo of next year's bulb ; e. e. e. e. roots 
 of the bulb; /./. roots of the stem. (p. 175.) 
 
 5. The bulb, fig. 4, denuded of its scales : a. the caudex of the 
 
 present year's bulb ; b. succulent .runner bearing the em- 
 bryon bulb ; c. d. old decaying bulbs ; e. base of the stem 
 of this year's herbage;/./, roots of this year's bulb. (p. 
 175). 
 
 6. Section of fig. 4.: . the caudex of this year's bulb; b. 
 
EXPLANATION OP THE PLATES. 
 
 the base of the stem ; c. the runner ; d. the embryon bulb ; 
 e. the place where the runner of the adult bulb has sepa- 
 rated ; g. roots, (p. 176). 
 
 Fig. 7. A scale of a bulb of Lilium pomponium: a.b. two young 
 bulbs formed on it. (p. 176). 
 
 8. A portion of a scale of Lilium superbum, with a bulb formed 
 
 on its margin; a. root of the young bulb. (p. 176). 
 
 9. Congregated bulbs of Saxifraga granulata ; a. the bases of 
 
 the leaves and stem. 
 
 10. a. The plantule taken from a bulb of fig. 9. ; b. the plantule 
 in a state of vegetation, (p. 178). 
 
 PLATE III. (in two parts.) 
 
 1. A transverse section of the bulb of Narcissus Jonquilla : 
 
 a. a. two young bulbs rising between the second and third 
 layers ; b. the roots protruded from the radical plate which 
 is hid by the position of the bulb. (p. 180). 
 
 2. A bulb of Allium victorialis: a. the outer layer of the bulb 
 
 extended into the sheathing stem ; b. the reticulated layers ; 
 
 c. the caudex; d. d. the roots, (p. 182). 
 
 3. A vertical section of the bulb, fig. 2. ; a. the succulent layers 
 
 extending into the stem ; b. the old reticulated layers ; c. 
 the caudex ; d. d. the young bulbs, (p. 183). 
 
 4. A tulip bulb : a. a portion of the flower stalk ; b. the new 
 
 flower bulb ; c. c. the exterior tunic of the exhausted bulb ; 
 
 d. a lateral leaf bulb. (p. 182). 
 
 5. Transverse section of a tulip bulb ; a. the base of the flower 
 
 stalk ; b. remains of the layers of the exhausted bulb ; e. 
 the new bulb. (p. 180). 
 
 6. (Middle of the plate.) Longitudinal section of a tulip bulb; 
 
 a. the flower stem ; b. b. b. tunics of the exhausted bulb : c. 
 the young flower bulb in its tunic d. d. d. ; e. the point of 
 conjunction of the new bulb, with the parent, (p. 182). 
 
 6, 7. Bulbs of Hyacinthus orienialis: a. the body of the bulb; 
 
 b. the manner in which the layers overlap one another ; c. 
 
 b3 
 
EXPLANATION OF THE PLATES. 
 
 the radical plate; d. young lateral leaf bulbs; e. (fig. 6.), 
 a bulb which has produced leaves this season, formed with- 
 in the coats of the parent bulb. (p. 183). 
 
 Fig. 8. A longitudinal section of fig. 6. : a. the caudex; b. the young 
 bulb ; c. c. the remains of this year's plant, (p. 184). 
 
 9. A transverse section of fig. 6. (bottom of the plate): a. the 
 
 young bulb ; b. the old or parent bulb ; c. c. roots, (p. 184). 
 
 10. A bulb of Allium sativum, denuded of its outer or sheathing 
 
 tunics: a. the young bulbs; b. c. d. e. remains of the 
 sheathing layers;/, the caudex and roots, (p. 187). 
 
 11. A longitudinal section of fig. 10.: a. the caudex; b.c. d. 
 
 the sheathing layers which terminate in leaves, (p. 186). 
 
 12. A. The bulb of Fritillaria Pyreniaca : a. a. the two hemi- 
 
 spheres, which are conjoined at the caudex ; b. the flower 
 stalk rising between them ; c. the roots : B. a. a. one of the 
 hemispheres separated from the other; b.b. the young 
 bulbs; c, the flower stalk ; d. the roots, (p. 172). 
 
 PLATE IV. 
 
 t. A twig of Cullumia ciliaris. (p. 267). 
 
 2. A twig of Acacia decipiens. (p. 267). 
 
 3. A twig of Acacia alata. (p. 267), 
 
 4. A portion of the stem of Ruta graveolens. (p. 265). 
 
 6. The flower bud of CEnothera grandiflora, which is macu- 
 lated, (p. 266). 
 
 6. A perfoliate stem, as demonstrated in Chlora perfoliata, (p. 
 
 267). 
 
 7. The stem of Lathy rus latifolius; illustrative of the winged 
 
 and the stipulated stem ; a. a. a. a* stipules (p, 267). 
 
 8. A portion of the stem of Passiflora quadrangularis : a. a. 
 
 tendrils (p. 653); b.b> stipules; c.c.c. glands. 
 
 9. A portion of the stem of Lilium superbum: a. a. bulbs, (p. 
 
 268). 
 
 10, A portion of the stem of Cactus flagellifonnis. (p. 268). 
 
EXPLANATION OF THE PLATES. XV 
 
 PLATE V. 
 
 Fig. 1. Longitudinal section of Agaricus procerus: a. the stem; b. 
 the lax pith ; c. a fragment of the pileus. (p. 293). 
 
 2. Portion of the stem of Ptychosperma gracilis (from Mirbel): 
 
 a. exterior ligneous and vascular bundles; I. interior lig- 
 neous and vascular bundles, (p. 299). 
 
 3. A. A transverse slice of the stem of Trigridia pavonia, of 
 
 the natural size : B. a portion of the same magnified, (p. 
 294). 
 
 4. A longitudinal section of the scape of Typha latifolia. (p. 
 
 294). 
 
 6. A. A transverse slice of the stem of Allium molly. B. 
 a portion of the above slice magnified ; a. the cutis ; b. 
 vascular bundles : C. a magnified vertical section of the 
 above: a. the cutis; b. vascular cords ; c. c. cellular mat- 
 ter: D. the natural size of the part, of which C. is one 
 half, highly magnified. 
 
 6. Portion of a transverse slice of the stem of Juncus conglo- 
 
 meratus, highly magnified ; a. the pith ; b. the cortex ; c. d. 
 bundles of spiral vessels ; e. air cells dividing the vascular 
 cords ; /. bundles of proper vessels, forming the striae on 
 the surface of the stem : g. g. lacunae between the cortex 
 and the pith. 
 
 7. Section of a transverse slice of the stem of Hippuris vulgaris, 
 
 highly magnified: a. the exterior or cellular part; b. the 
 centre, which is vascular; c. an uncoiled vessel. 
 
 8. A. A transverse slice of the culm of Triticum astivum, 
 
 slightly magnified. B. a vertical section of one side of 
 the tube, highly magnified: a. longitudinal cells, under the 
 epidermis; b. the pith; c. a spiral vessel. C. a transverse 
 section of a portion of the above slice, highly magnified : 
 a. the cutis; b.c. vascular bundles, (p. 301). 
 
 9. Vertical section of a portion of the stem of Tradescantia 
 
 virffinica: a. a. a. a. a. a. a. vascular cords; b. b. fragments of 
 the base of the leaf, which in this plant is sheathing. 
 b4 
 
EXPLANATION OF THE PLATES. 
 
 Fig. 10. A small portion of the above, highly magnified, to display 
 the nature of the vessels : a . the kind of sheath in which 
 the rings forming the vessels, b. b. b. are enclosed. 
 
 11. The articulation of the culm of Triticum testivum split: . 
 
 the lower joint terminating in a sheathing leaf; b. the 
 new joint, (p. 300). 
 
 12. The cuticle of the culm of Triticum cestivum, to demonstrate 
 
 its respiratory pores, (p. 302). 
 
 13. The cuticle of Juncus conglomerate: a. a. portions which 
 
 cover the striae, and which are devoid of respiratory pores ; 
 
 b. portion between the striae thickly studded with pores, 
 (p. 302). 
 
 14. Transverse slice of an apple twig (copied from Mr. Knight's 
 
 plate in the Philosophical Transactions} ; a. the bark ; b. the 
 alburnum or young wood ; c. the pith. 
 
 15. A terminal twig of ^Esculus Hippocastanum split down the 
 
 middle ; a. the pith ; b. the wood ; c. the cortex ; d. e. buds 
 or gems ; /. g. the bases of the petioles of two leaves, 
 which are cut off; h i. cords of vessels connecting the pe- 
 tiole with the stem ; k. terminal leaf bud. (p. 316.) 
 
 PLATE VI. 
 
 2. A. A thin transverse slice of a twig of ^Esculus Hippocas* 
 
 tanum: B. the dark-coloured portion of the slice A, sepa- 
 rated, and very highly magnified; a. the cuticle; b. ex- 
 terior layer of the cellular integument ; c. interior layer of 
 the cellular integument; d. vascular layer of the cortex 
 
 c. liber ; * alburnum in its first stage ; /. perfect wood ; g. a 
 divergent layer; A. large vessels of the wood; t. medullary 
 sheath; k. pith. (p. 319 406). 
 
 3. A transverse slice of a twig of Sambucus nigra in the first 
 
 year of its growth, (p. 336). 
 
 4. Slice of a two years' old branch of Sambucus nigra. (p. 336). 
 
 5. Slice of a three years' old branch of Sambucus nigra. (p, 
 
 336). 
 
EXPLANATION OF THE PLATES. XV11 
 
 Fig. 6. Longitudinal section of a portion of the stem, and a branch 
 of Sambucus nigra; a. the upper part of the trunk, in 
 which c. the pith, occupies the centre ; b. the branch ; d. its 
 pith; e. the wood produced by the branch; /./. two abor- 
 tive buds. (p. 368). 
 
 7. A vertical section of the dark portion of A . fig. 2. : a. the 
 
 cortex, consisting of, 1 . the cuticle ; 2. the cellular integu- 
 ment ; 3. the vascular layer, in which the character of the 
 proper vessels is displayed ; and, 4. the liber or inner bark ; 
 
 b. the half-organized alburnum ; e. to </. the perfect wood, 
 consisting of 5. 5. 5. some porous, others entire small ves- 
 sels ; and 6. large porous vessels (p. 332) ; d. to e. the me- 
 dullary sheath, containing 7. 7. 7. spiral vessels, and 8 ob- 
 long, porous cells ; e, to/, pith; ** fragments of the cells 
 of a divergent layer, (p. 330 406). 
 
 8. A. Fragment of a transverse slice of the trunk of an old 
 
 elder tree: B. the same highly magnified ; a. a. a. a. vessels 
 of the concentric layers ; b. b. b. the concentric layers; 
 
 c. c. c. the divergent layers. 
 
 9. Longitudinal slice, from the shoot of a vine, which was laid 
 
 down to root; a. the pith; b. last year's wood; c. the pre- 
 sent year's wood in its alburnous state ; e. a root protruded 
 from the alburnum. 
 
 10. A. Portion of a thin transverse slice of an old stem of Sy- 
 
 ringa vulgaris: B. the same highly magnified; . various 
 layers of cuticle, the innermost only of which retains its 
 vitality (p. 321); b.b. ligneous layers; c.c. large vessels 
 between the ligneous layers ; d. alburnum. 
 
 11. Twig of Juglans regia split to show the diaphragms which 
 
 constitute its pith. 
 
 PLATE VII. 
 
 1. A. Magnified view of the embryon leaf-bud, in Syringa vul- 
 garis : a. the gem ; b. the lacerated base of the footstalk of 
 the removed leaf: B. the natural size of the above; c. the 
 gem. (p. 38i). 
 
EXPLANATION OF THE PLATES. 
 
 Fig. 2. Longitudinal section of fig. I.: a. section of one of the lobes 
 of the embryon bud; b. base of the petiole; c. a part of 
 the stem; d. spiral vessels entering the petiole; /. liber; 
 g.g. pith; i. alburnum, (p. 385). 
 
 3. Transverse section of fig. 1 : a. the embryon bud ; c. liber ; 
 
 d. alburnum ; e. pith. (p. 386). 
 
 4. None. 
 
 5. Wedge cut from the trunk of a lilac tree twenty years old : 
 
 . a bud not yet completely developed; b. one fully de- 
 veloped : both originated in the first year's growth of the 
 part. (p. 392). 
 
 6. Longitudinal section of a bud of Syringa vulgaris, cut in 
 
 autumn : a. rudiment of the pith of the embryon branch ; b. 
 alburnum of the embryon branch ; c. c. c. scales of the bud ; 
 d. the germ; e. cicatrix of the fallen leaf; /. rudiments of 
 spiral vessels ; g. the cortex ; h. the alburnum ; i. the me- 
 dullary sheath ; and k. the medulla of the twig bearing the 
 bud. (p. 387). 
 
 7. A. Transverse section of a branch of Philadelphus corona- 
 
 rius, eight years old : a.b.c. buds just developed, but the 
 origin of which may be traced to the first year's growth of 
 the branch (p. 392). B. a portion of the two innermost 
 ligneous circles of A, highly magnified : a.b.c. the tracks 
 of the buds conjoined, and connected with the medulla of 
 the branch. 
 
 8. Wedge from the trunk of a Lilac, ten years old : e. a blighted 
 
 bud. 
 
 9. Longitudinal section of a bud of Lilac, three weeks after the 
 
 protrusion of the branch on which it is seated : a. the em- 
 bryon of the future branch ; b. c. rudiments of the scales of 
 the bud. 
 
 10. Transverse section of a twig of Lilac three years old, made 
 
 immediately below an adventitious bud ; a. the origin of 
 the bud in the medullary sheath of the twig; b. outer 
 scales ; c. foliar scales, showing the transition from scales 
 to leaves; d. first leaf of the protruding branch. 
 
 11. Transverse section of the root of the vine: . cuticle and 
 
EXPLANATION OF THE PLATES. X15T 
 
 parenchyma of the cortex ; b. b. the divided proper vessels 
 of the cortex ; c. the divided ligneous vessels of the 
 centre. 
 
 PLATE VIII. 
 
 Fig. 1. A. The fibril of a root greatly magnified; a. the vessels id 
 the centre seen through the semitransparent cortex ; b. the 
 natural size of the fibrils : B. transverse section of A. : a. 
 the central vessels ; b. c. the cellular cortex ; d. the section 
 of its natural size. 
 
 2. A. Transverse slice of the stem of Bryonia alba: B. the 
 
 same slice moderately magnified. 
 
 3. Portion of the cuticle of the stem of Bryonia alba greatly 
 
 magnified ; a. a. green, reticulated, lozenge-shape spots on 
 it. 
 
 4. A. Transverse slice of one angle of fig. 2. highly magnified i 
 
 a. a. exterior cortical layer ; b. b. b. b. processes of the green, 
 interior, cortical layer piercing the exterior ; e. e. vascular 
 cortical layer ; d. d. cellular mass of the stem ; /. largest 
 spiral vessel of the vascular fasciculus; g. h. smaller spiral 
 vessels; e. i. entire vessels of the fasciculus (p. 415). B. 
 longitudinal section of A. : the references are the same as 
 the former, (p. 416). 
 
 6. Separated fragments of the vessels, forming the vascular 
 fasciculi in herbaceous stems, highly magnified : a. an an- 
 nular vessel ; b. a spiral vessel ; c. a membranous annu- 
 lated vessel, (p. 417). 
 
 6. A. Transverse slice of the stem of Rubia tinctorum mode- 
 
 rately magnified ; a. the cortex; b. vascular layer; c. cel- 
 lular pulp. B. one corner of the above highly magnified ; 
 a. a. exterior green cortical layer, immediately within the 
 cuticle; b.b. interior green cortical layer; c.c. layer of 
 proper vessels; d. ligneous layer containing the sap or 
 spiral vessels ; e. e. e. cellular pulp. 
 
 7. Portion of a proper or returning vessel, highly magnified. 
 
 8. Portion of a transverse slice of the stem of Hemlock ; . the 
 
XX EXPLANATION OF THE PLATES. 
 
 cuticle ; b. b. large fasciculi of proper vessels ; c. cellular 
 integument ; d. d. larger fasciculi of sap or spiral vessels ; 
 e. a smaller fasciculus of sap vessels, accompanied with 
 two fasciculi of proper vessels ; /. cellular pulp. 
 Fig. 9. Longitudinal section, passing through the centre of fig. 8. : 
 a. cellular mass of the cortex ; b. fasciculus of proper ves- 
 sels; c. slip of cellular matter; d. oblong cells; e. fasci- 
 culus of sap or spiral vessels ; /. oblong cells ; g. pith ; h. 
 condensation of the pith, forming a part of the septum in 
 this hollow stem. 
 
 10. Transverse section of the petiole in Syringa vulgaris: a. the 
 
 cortex ; b. cellular parenchyma ; c. c. small distinct fasci- 
 culi of sap vessels ; d. spiral vessels forming the central 
 fasciculus ; e. proper vessels, exterior to the sap vessels, (p. 
 
 575). 
 
 11. Transverse section of the petiole in Sambucus nigra; 
 
 a.a.a.a.a. distinct fasciculi of proper vessels; b.b.b.b.b. 
 distinct vascular fasciculi, consisting of spiral and proper 
 vessels, (p. 576). 
 
 PLATE IX. 
 
 1. A hairy stem. (p. 269). 
 
 2. A hispid stem. (p. 270). 
 
 3. A shaggy stem. (p. 270). 
 
 4. A woolly stem, Ballota lunata. (p. 270). 
 
 5. A silky stem. (p. 270). 
 
 6. A warty stem, Euonymus verrucosus. (p. 272). 
 
 7. A vesicular stem, Mesembryanthemum crystallinum. (p. 272). 
 
 8. None. 
 
 9. None. 
 
 10. Simple hairs; a. b, long flexible hairs, which produce pi- 
 lose, woolly, and shaggy surfaces, very highly magni- 
 fied, to demonstrate their articulated character ; <?. the 
 slight, subulate, inclining hair, which produces the silky 
 surface, (p. 639). 
 
EXPLANATION OF THE PLATES. XXI 
 
 Fig. 11. Subulate erect hair, also articulated, (p. 640). 
 
 12. Blunt, erect, articulated hair of Atropa Belladonna, (p. 640). 
 
 13, 14. Hooked hairs, which produce the velvety feeling of the 
 
 surface of some leaves, (p. 640). 
 
 15. A stipitate gland, (p. 636). 
 
 16. Branched hair of Marrubium peregrinum. (p. 641). 
 
 17. Stellated hairs of Althaea officinalis. (p. 641). 
 
 18. Awl-shaped bristle of Symphytum orientate, (p. 642). 
 
 19. Barbed bristle of Mimosa sensitiva. (p. 642). 
 
 20. Subulate hollow bristle of Borago officinalis. (p. 642). 
 
 21. Sting of the nettle: a. the subulate hollow bristle ; b. the 
 
 cellular bag or sponge containing the poison ; c. natural 
 size of the sting (p. 642). 
 
 22. Spindle-shaped bristle of Malpighia urms. (p. 643). 
 
 23. 24. Forked bristles, (p. 644). 
 
 25. Bristle of Humulus lupulus (p. 644). 
 
 26. Fasciculate bristle of C&ctasflageltiformis. (p. 644). 
 
 27. A papillary gland ; a. the gland, much magnified ; b. its 
 
 real size. 
 
 28. A. Two series of compound papillary glands moderately 
 
 magnified. B. one of these glands highly magnified ; a. 
 six distinct glandules ; b. the excretory pore ; c. a similar 
 pore free from obstruction, (p. 634). 
 
 29. A. A squamous gland moderately magnified : B. one of 
 
 these glands, highly magnified ; b. the scaly border; c. 
 the gland, (p. 633). 
 
 30. A cup- shaped gland, (p. 635). 
 
 31. A knob-shaped gland, (p. 636). 
 
 32. A branched pediculated gland, (p. 636). 
 
 PLATE X. 
 
 1. Part of a leaf of Cotyledon calycinum: a. a. a. a. a. young 
 
 plants springing from the serratures of the leaf. (p. 642). 
 
 2. Skeleton of the leaf of Ficus religiosa; a. the midrib; 
 
EXPLANATION OF THR PLATES. 
 
 b. b. b. b. arches formed by the inosculation of the vas- 
 cular fasciculi of the principal costae. (p. 572.) 
 Fig. 3. Appearance of the cuticular pores ; and the course of the 
 lymphatics on the inferior disk of the leaf of Hoy a 
 camosa. 
 
 4. Appearance of the cuticular lymphatics on the superior 
 
 disk of the leaf of Hoya carnosa. (p. 605). 
 
 5. Leaf of Dionaea muscipula: a. three stiff setae on the su- 
 
 perior disk of each lobe of the trap-like appendage ; 6. 
 setae on the margin of the appendage ; c. the proper leaf. 
 
 6. One of the setae of the disk of the appendage highly mag- 
 
 nified ; a. the base, which is cellular, and continuous with 
 the cuticle of the lobe on which it is seated ; b. the bristle, 
 which is rigid. 
 
 7. Transverse section of the articulation between the chan- 
 
 nelled part of the petiole and the leaf, in Phaseolus tw/- 
 garis: a. the whole of the vascular fasciculi collected into 
 one central fasciculus. 
 
 8. Transverse slice of the channelled part of the petiole, in 
 
 Phaseolus vulgaris: a. a. a. vascular fasciculi forming a 
 circle within the cutis; b.b. two distinct fasciculi, (p. 
 577). 
 
 9. Cuticle of the inferior disk of the leaf of Rumex acetosa: 
 
 a. a. cuticular pores ; b. b. lymphatics. 
 
 10. Cuticle of the superior disk of Rumex acetosa : a. cuticu- 
 
 lar pore ; b. lymphatic. 
 
 11. Transverse slice of a portion of the expansion of a leaf of 
 
 Zea Mays: a. a. cuticle; b. the parenchyma or substance 
 of the leaf; c. c. one of the visible costae ; d. e. d. e. d. fas- 
 ciculi of vessels not visible on the surface of the leaf; 
 /./. two spaces, more cellular than the rest of the leaf, 
 guarded on each side by short, subulate spines, (p. 561). 
 
 12. Transverse slice of the petiole of Trapa natans : a. a. the 
 
 vacuities, which are filled with air ; b. b. b. diaphragms 
 which separate one vacuity from another, in the length of 
 the petiole ; c. vascular fasciculi occupying the centre of 
 the petiole, (p. 596). 
 
EXPLANATION OP THE PLATES. XX1U 
 
 Fig. 13. One of the above-mentioned diaphragms separated , a. the 
 cellular sides of the vacuity ; b. the diaphragm, which is 
 slightly convex on the exposed surface, (p. 596). 
 
 14. Portion of the cuticle of the leaf of Zea Mays: a. a. the 
 
 cuticular or pneumatic pores ; b. b. the lymphatic vessels, 
 (p. 605). 
 
 15. Structure of the cuticular pore in the leaf of Zea Mays. 
 
 16. Transverse slice of a portion of the leaf of Hoya carnosa: 
 
 a. the cutis of the superior, 6. that of the inferior surface, 
 (p. 590). 
 
CORRIGENDA. 
 
 The reader is requested to make the following Corrections before 
 commencing the perusal of the volume. 
 
 Page 84, /. 12, for become read becomes. 
 
 87, /. 9, dele justly. 
 
 106, /. 12, nota, for occasions read occasion. 
 
 149, I- 21, between the words "in " and " formation," put "the." 
 178, /. 3 from bottom, for b, read a. 
 
 ib. I. 4 , for a. read b. 
 
 238, /. 5, for Athemis read Anthemis. 
 266, /. 6, for Anoethtra read (Enothera. 
 
 268, /. 25, for setaceous read setaceosus. 
 
 269, /. 2 from bottom, for 5 read 9. 
 
 270, I. 4, 16, 20, 25, for 5 read 9. 
 272, I. 6, 10, for 5 read 9. 
 
 288, /. 10, for CEnathe read (Enanthe. 
 
 392, /. 15, for 6 read 7. A. 
 
 409, I, 9, for* put -f, and /. 21 , for f put *. 
 
 416, /.I, for /./././. rearf 6. b.b. b. 
 
 424, /. 2 from bottom, for Plate 9 read Plate . 
 
 466, /. 20, for Plate 9 razrfPlateS. 
 
 406, J. 18, for Dycotyledons read Dicotyledons. 
 
 432, /. 4, for stems read roots. 
 
 464, /. 5, for woody read woolly. 
 
 495, nota, for species read specimen. 
 
 494, /. 2, for cirrose read cirrhose. 
 
 501, /. 18, for shined read shining. 
 
 517, I. 16, for seveal read several. 
 
 561, /. 22 and 26, for fig. 13 read fig. 1 1 . 
 
 562. 1. 6, for fig. 13 read fig. 11. 
 
 564, /. 3, for "is a few proper vessels surrounded by," read "is 
 
 rounded by a few proper vessels." 
 597, /. 18, for fig. 14 read fig. 16. 
 
LECTURES, 
 
 LECTURE I. 
 
 INTRODUCTION SKETCH OF THE RISE AND PROGRESS 
 
 OF BOTANY UTILITY OF THE SCIENCE METHOD 
 
 OF STUDYING IT, AND PLAN OF THE COURSE. 
 
 GENTLEMEN, 
 
 IN commencing a Course of Lectures 
 on any branch of science, the Lecturer must ne- 
 cessarily regard his auditors as totally ignorant of 
 the subject of which he is about to treat ; and must 
 endeavour not only to awaken their love for it, 
 by conveying some idea of its nature, and the 
 advantages to be derived from the study of it^ 
 but, by tracing its origin and progress, or enter- 
 ing into the details of its history, to elevate their 
 ideas of its importance, by a display of the great 
 and illustrious names that swell the catalogue of 
 its votaries, and of the estimation in which it has 
 been held by mankind in prior ages. 
 VOL. i. B 
 
2 SKETCH OF THE RISE ^LECT. I. 
 
 Whilst I acknowledge the propriety of this 
 custom, I must at the same time observe, that, 
 in following it, I do not intend to enter minutely 
 into the history of the science we are about to 
 investigate, but, tracing merely a sketch of the 
 rise and progress of Botany, rather to excite your 
 esteem for it by a display of its utility. 
 
 Botany derives its name from Borai//?, a Greek 
 word which signifies an herb. It is that branch 
 of Natural History which concerns vegetables ; 
 which teaches the knowledge of their structure, 
 habits, and properties ; and to distinguish differ- 
 ent plants from each other *. That part of the 
 science which treats of the structure, habits, and 
 properties of plants, is particularly distinguished 
 by the term PHYTOLOGY ; that which refers to the 
 classification of plants by their exterior characters, 
 so that one species may be readily distinguished 
 from another, is denominated SYSTEMATIC BOTANY. 
 The knowledge of both of these parts is requisite 
 to constitute a true Botanist. But it is further 
 my intention, in this Course of Lectures, to enter 
 upon a third branch, particularly interesting to 
 those who desire to become acquainted with the 
 economical and medicinal uses of plants; as it 
 refers to their poisonous properties, and the ac- 
 
 f Botamce est scientia naturalis, quac Vegetabilium cog- 
 " nitionem tradit." LINN^US, Phil. Bot. Introduce 4. 
 
LECT. I.] AND PROGRESS OF BOTANY. 3 
 
 tion of vegetable poisons on the animal system. 
 This branch of botanical science I would distin- 
 guish by the term VEGETABLE TOXICOLOGY. 
 
 In making a rapid sketch of the rise and pro- 
 gress of the science of Botany, I cannot avoid 
 taking notice of that wonderful love of antiquity 
 which seems to be so congenial to the human 
 mind, that whatever bears the rust of past ages, 
 appears to rise proportionally in the esteem of 
 mankind. Hence every one is anxious to date 
 the origin of the particular art or science which 
 he professes, from the earliest times ; and to in- 
 crease the respect in which he would wish it to be 
 held by impressing upon it the stamp of antiquity. 
 Thus Tubal Cain has been regarded as the father 
 of Chemistry, and ^Esculapius that of Medicine : 
 in the idle hours of the Egyptian shepherds, the 
 sublime speculations of Astronomy are supposed 
 to have commenced ; and, if we were to indulge 
 Fancy in her flights, we might with equal truth, 
 perhaps, trace Botany to a period nearly coeval 
 with the creation of the human race. But such 
 conjectures, as they are vague and fanciful only, 
 cannot be useful or satisfactory even as objects of 
 simple curiosity ; and it is impossible to say what 
 was the state of the arts and the sciences in the 
 early ages, the oral records of which, for we 
 cannot suppose that any other existed, have long 
 since passed away, and left imagination to fill 
 
 B2 
 
4 SKETCH OF THE RISE [LECT, I 
 
 up the blank. More certain data for tracing the 
 origin of art and science in the infancy of society 
 have been afforded by the discoveries of modern 
 circumnavigators. In those stages of it, which 
 their labours have opened to our view, we per- 
 ceive something like the fine arts, and some of 
 the more -useful sciences, awakening at a very 
 early period. We behold Music, Poetry, Sculp- 
 ture, and Painting, in their infant state, walking 
 hand in hand with civilization ; and, even before 
 the savage has thrown aside the deer-skin and the 
 club, their influence actuating his feelings and 
 energies, and having a principal share in the 
 formation of his character. We observe them 
 kindling by degrees the social and benevolent af- 
 fections in the human bosom ; binding man to 
 his native soil, by uniting agreeable associations 
 with locality ; forming the first medium of histo- 
 rical record ; laying the foundation of govern- 
 ment ; exciting emulation ; and sowing the seeds 
 of patriotism. In this dawn of society, something 
 like Botany is also to be seen. The plants which 
 surround the human savage are the ornaments of 
 the earth. Nature has bestowed upon them a 
 great diversity of form, of magnitude, of colour, 
 and of odour, equally fitted to attract the attention, 
 to delight the senses, and to administer to the ne- 
 cessities of mankind. The umbrageous tree, there- 
 fore, under which uncivilized man shelters himself 
 
LECT. I.] AND PROGRESS OP BOTANY. 5 
 
 from the ardour of the meridian blaze, the flower 
 which charms his eye, and the fruit that allures 
 and pleases his appetite, excite in him the desire 
 of knowing them again ; he marks some peculiar 
 feature or characteristic which he observes in 
 them ; and by these they are ever after recog- 
 nised. He even proceeds, in some degree, to 
 name and to class them. Thus, whatever may 
 be the language which is the medium of his ideas, 
 he confers a name on a fruit which he has seen 
 and tasted. Let us suppose the term he has em- 
 ployed to be plum, and that the fruit is of a 
 green colour. In a short time, meeting with fruit 
 resembling in shape and some other circum- 
 stances that which he already knows by the 
 name of plum, but of a purple colour, he names 
 this a purple plum ; and in the same manner he 
 denominates a third a yellow plum. Here plum 
 is the generic term, and green, purple, and yel- 
 low, specific appellations. In thus acting, there- 
 fore, the savage makes a step towards a science, 
 which, as such, is unknown to him ; and, without 
 intending it, performs one office of the Botanist. 
 
 But it is not till long after this period, till 
 society has attained some regular form, and till 
 men begin to perceive that a concurrence of similar 
 circumstances is necessary for the reproduction 
 of certain appearances, and that the operations of 
 nature are not the effects of fortuitous causes, 
 
 B3 
 
6 SKETCH OF THE RISE [LECT. I. 
 
 that science really begins to dawn. It was in this 
 state in Chaldea, when Botany, which is said 
 by Botanical historians to have originated there, 
 made its appearance as subservient to medicine. 
 That the sufferings, as well as the wants of the 
 human body should have given rise to the know- 
 ledge of the medicinal properties of vegetables' is not 
 surprising : for one of the unhappy but ordinary 
 effects of the advancement of society is a violation 
 of the laws of Nature, inasmuch as these regulate 
 our appetites and tastes, the natural consequence 
 of which is the production of diseases. To ob- 
 viate these evils, remedies were to be sought for ; 
 and, either by accident, or by observing the effect 
 of instinct on the lower animals, they were first 
 obtained from the vegetable kingdom. 
 
 The knowledge of plants which the Chaldeans 
 had gained for so important a purpose, was trea- 
 sured up as a rich legacy, to be handed down 
 from father to son ; and in this manner the infant 
 science was cherished till it passed into Egypt. 
 With the Egyptians, however, and even with the 
 Greeks, who received the science from Egypt, it 
 did not make any great advances. Accustomed 
 to rest too much upon genius and reflection, and 
 careless of facts, the Grecian philosophers ad- 
 vanced the most absurd doctrines regarding ve- 
 getable life. They taught that plants possess a 
 sensible and reasonable soul; have desires and 
 
LECT. I.] AND PROGRESS OF BOTANY. 7 
 
 wishes ; and are capable of experiencing pleasure 
 and pain. Einpedocles even, to whom, however, 
 is due the merit of having first hinted at the 
 sexes of plants, went so far as to assert that, 
 after a time, plants change to animals, and then 
 the sexual organs, which in the vegetable state 
 are frequently united in one individual, become 
 separated. 
 
 In Greece, for a long period, the knowledge of 
 plants was altogether confined to the Asclepiades or 
 priests of ^Esculapius, who were the physicians of 
 their time: and in the highest plenitude of the 
 taste, elegance, and learning of the Grecian Com* 
 mon wealth ; even in that happy period, when the 
 effulgence of Grecian genius burst forth in all its 
 splendour, and shone till the time of Alexander 
 the Macedonian, Botany had attained but a very 
 limited extent, among the other sciences then cul- 
 tivated. In the works of Theophrastus, who lived 
 about three hundred years before CHRIST, and in- 
 herited the learning of his great masters, PLATO 
 and ARISTOTLE, may be seen all that was known 
 at that time regarding vegetables. His History 
 of Plants, - entitled, Us^l QVTWV la-rogiag *, contains 
 the description of only five hundred species, which 
 were officinal, or used for the cure of diseases. 
 
 <PVT*V iVfyiaf, seu Historic Plantarum, lib. ix. cum 
 Comment. J. C. SCALIGERI et J. BOD.SI a Stapel. Amsterdam, 
 16*4. 
 
 B 4 
 
8 SKETCH OF THE RISK [tECT. I. 
 
 The Romans, that extraordinary people, who, for 
 the space of seven hundred years that they were 
 engaged in almost perpetual wars and commo- 
 tions, spread by the force of the sword, the bless- 
 ings of civilization over the Barbarous part of 
 the world ; and who drew all their knowledge from 
 the more refined nations over whom their arms 
 had triumphed, began to study Botany, soon 
 after their victory over Mithridates. They did 
 not, however, add much to the discoveries of their 
 instructors. The works of DIOSCORIDES, a native 
 of Anagarba in Cilicia, who flourished under the 
 tyranny of Nero, and wrote on the Materia Me- 
 dica *, contain descriptions of scarcely more 
 than six hundred plants ; and the elder Pliny -f-, 
 who flourished a short time (about sixty-four 
 years) prior to the birth of Christ, after hav- 
 ing collected all the information of his prede- 
 cessors, has described one thousand plants only ; 
 but he acknowledged there were many more, 
 which, however, as they had no names, and were 
 of no use, he did not describe. The irruption of 
 the Goths, and other northern nations upon the 
 Roman empire, drove Botany, with the other sci- 
 
 * lisp? Jxn$ iotTftxjis, de Materia Medica, lib. vi. VON 
 KOLLAR. Vienna, 1770. 
 
 f Pliny was a native of Verona : he fell the victim of his 
 scientific ardour, in endeavouring to approach the crater of Ve- 
 suvius, during an eruption, in the 56th year of his age. 
 
LECT, I.] AND PROGRESS OF BOTANY, 9 
 
 ences then known in Europe, for refuge into Asia. 
 There, however, it obtained merely an asylum ; ( 
 few or no discoveries were made ; and the works 
 of Galen, Oribasius, /Etius, /Egineta, and other 
 Asiatic writers, as well as those of Mesue, Sera- 
 pius, Razis, Avicenna, and the other Arabians, con- 
 tain little more than the names of the plants de- 
 scribed by the primitive authors. 
 
 It is melancholy to look back upon the state 
 of Europe during that period which has been 
 justly denominated the dark age. A dismal gloom 
 enveloped the whole of the civilized world: ig- 
 norance, superstition, and barbarism tyrannized 
 over learning and genius ; knowledge of any kind 
 was to be acquired only by searching among the 
 rubbish of the schools and monasteries ; fabulous 
 legends supplied the place of truth ; and the de- 
 ceptions of a crafty priesthood debased at the 
 same time that they enslaved the minds of men. 
 During this long and melancholy course of years, 
 the few scattered writings that appeared on Na- 
 tural History were the production of monks, and 
 compiled from old authors : but even these were 
 cloaked in an almost unintelligible jargon ; and 
 it was not till the middle of the sixteenth century, 
 that the sun of science again burst this thick 
 cloud, and shed its rays upon the north of Europe. 
 At this period Botany, which was exactly in 
 the same state as the ancients left it, could not be 
 
 3 
 
10 SKETCH OF THE RISK [LECT. I. 
 
 considered any tiling more than a catalogue or list 
 of the names of about one thousand plants : for, 
 although the ancients were great observers, yet 
 they did not make much use of their observations. 
 They looked at Nature rather with the eye of the 
 poet than of the philosopher ; and,, in giving the 
 reins to imagination, were too powerfully charmed 
 with her more striking beauty and sublimity, to 
 descend to a calm and patient investigation of the 
 causes of the effects which they observed. Thus, 
 they knew that the farina of the male Palm was 
 necessary to fecundate the female; but from this 
 fact they drew no inference as to the difference of 
 sex in plants : they grafted, but knew not the cause 
 of the union of the graft with the stock : they had 
 even observed the spontaneous movements of some 
 plants, but did not endeavour to discover the 
 reasons of the phenomena. Such was the state of 
 the science at the revival of learning, when it made 
 its first step towards improvement, in the repre- 
 sentation of plants by wood cuts * ; and this aid 
 to the study of Botany was soon adopted by Brun- 
 fels, a physician, at Bern, who may justly be re- 
 garded as the restorer of the science in Europe -f-. 
 
 * An Italian Flora, which was printed at Padua, in 1485, 
 is supposed to be the earliest book on Botany that was illus- 
 trated by plates. 
 
 f His work is entitled Historia Plantarum. The platee are 
 not very accurate ; but this is not much to be wondered at, 
 when we reflect that he died in 1534. 
 
LECT. I.] AND PROGRESS OF BOTANY. 1 I 
 
 To endeavour to display even an accurate sketch 
 of the progress of the science, from his time to that 
 of Linnseus, within the compass of a Lecture, would 
 be vain ; we shall notice, therefore, a few only of 
 the more remarkable occurrences. 
 
 Near the close of the sixteenth century, CJSSAL- 
 PINUS.*, a Florentine, one of the professors of the 
 University of Padua, made the first attempt at clas- 
 sification ; for, previous to his time, plants had been 
 described without any order, and the possibility of 
 simplifying the study of the science by arranging 
 them in classes, had not yet been conceived. JUN- 
 GIUS followed in the footsteps of Csesalpinus, and by 
 taking a clearer and more extensive view of his sub- 
 ject, the idea of those principles on which the 
 Linnsean system is founded, suggested itself to him, 
 and was developed in his writings : he died in 1657. 
 JOHN RAY -}-, an Englishman, succeeded Jungius, 
 whom he followed in many particulars, in preference 
 to his cotemporary the great Tournefort, whose 
 merits as a systematist were only exceeded by 
 those of Linnseus. Ray was a man of laborious 
 research. His work, entitled Hlstoria Plantarum 
 
 * This celebrated naturalist, who was born at Arezzo, ir^ 
 1519, threw great light upon the vegetable structure ; and was 
 the first of the moderns who hinted at the sexes of plants. He 
 died in 1603. 
 
 f RAY, who was a native of Essex, was born in 1628, and 
 died in 1705. 
 
12 SKETCH OF THE RISE [LECT. I. 
 
 generalis (London 1693), contains all the Bota- 
 nical learning of bis time ; and displays, in a 
 striking degree, the unwearied assiduity and ex- 
 tensive reading of its author. The first time, 
 however, that Botanists began to be really guided 
 by the light of nature in their researches, was soon 
 after the establishment of the Royal Society, 
 towards the end of the seventeenth century; when 
 Dr. GRE w,in this country, and MALPIGHI on the con- 
 tinent, began their anatomical investigations. The 
 acuteness, patience, and ardour of these celebrated 
 men, in examining the structure of plants, remain 
 yet unequalled, and their works are still standards 
 on vegetable anatomy. Towards the end of the 
 seventeenth century, CAMERARIUS first proved the 
 existence of sex in plants by observation and expe- 
 riments; GEOFFREY., and VAILLANT *, a pupil of the 
 great TOURNEFORT-}-, confirmed, and added to his 
 observations ; but this important fact had few sup- 
 porters till Linnaeus made it the foundation of his 
 system. We mentioned before, that Caesalpinus 
 
 * VAILLANT was born at Vigny, in 1669, and died at Paris 
 in 1722. His observations are contained in an Essay entitled, 
 Sermo de Slructura Florum. Lugd. Batav. 1718. 
 
 f JOSEPH PITTON DE TOURNEFORT was born at Aix, in 
 Provence, in 1656. He travelled into Greece and Asia, at the 
 expense of Louis XV.; and published a system of Botanical 
 arrangement, founding the classes on the formation of the 
 flower, while the orders were ascertained by the fruit. He died, 
 in 174-8, from an injury to his chest, occasioned by his being 
 crushed by a carriage. 
 
LKCT. I.] AND JPHOGKEfcS OF BOTANY. 13 
 
 gave the first hint of this circumstance, but he did 
 not pursue the idea ; and the honour of starting 
 this important physiological proposition has also 
 been given to Sir Thomas Millington, who is said 
 to have made the discovery in 1676. He never 
 wrote any thing, however, on the subject ; but 
 merely communicated his ideas to Dr. Grew ; and 
 the uncertainty of the claim of originality on this 
 account, detracts much from the celebrity, which 
 such a discovery would have conferred on his 
 name. 
 
 The improvements in Botanical science, that 
 had at this time gradually taken place, were much 
 forwarded by the inventions of printing and of en- 
 graving r which disseminating to a wide extent 
 every new discovery, and displaying the figures of 
 plants, in a correct and natural manner, attracted 
 men of genius in every country to the study of the 
 science. The advancement of navigation, and the 
 increase of commerce, had also a considerable 
 share in producing those beneficial effects: for by 
 their means the plants of different climates were 
 brought together; and the Botanical gardens of Eu- 
 rope enriched with the productions of every quarter 
 of the globe. It may not be uninteresting to know, 
 that the first Botanic garden was established at 
 Padua, in 1533; and that it still exists, after the 
 lapse of more than two centuries and a half, amidst 
 the changes of revolutions and the overturn of 
 
14 SKETCH OF THE RJSB [LECT. I. 
 
 states, which, in that period, have astonished and 
 convulsed Europe. At length the correct judg- 
 ment, cultivated mind, unwearied assiduity, and 
 sublime genius of Linnaeus, gave to the whole 
 science a new and more attractive aspect. It 
 would form a pleasing episode, were it consistent 
 with our plan, to enter minutely into the biography 
 of this great naturalist*. The display of his tran- 
 scendent abilities, like those of many other illus- 
 trious men, depended upon accident ; and but for 
 the kind offices of a physician of the name of Roth- 
 rnan, those of Linnseus would have been for ever sup- 
 pressed, his father having felt so much disappoint- 
 ment with his eailier studies, that he conceived he 
 was only fit for a tradesman, and destined him to 
 be a shoemaker : but this benevolent physician 
 persuaded him to allow his son to study medicine; 
 and he himself became his preceptor. The po- 
 verty of Linnaeus obliged him to struggle with great 
 hardships in his earlier years-}-. His expenses in his 
 Lapland ttfur, which, however, amounted to seven 
 pounds teu shillings sterling only, were defrayed 
 
 * LINNAEUS was born at Rashult, a village in the province of 
 Smaland) on the 3d of May, 1707. His father, Nicholas Lin- 
 naeus, was pastor of the village; and his mother, Christina Bro- 
 derson, the daughter of his father's predecessor in the church. 
 
 f When at Upsal he was glad to wear the cast-off clothes 
 of his fellow-students ; and his shoes were mended by himself 
 with the bark of trees. 
 
LECT. I.J AND frUOGUESS OF BOTANY, 15 
 
 by the University of Upsal : and he was obliged to 
 the lady who afterwards became his wife, for the 
 money which enabled him to graduate at Leyden*. 
 It was not till near the decline of his life, that his 
 sovereign conferred on him those honours, which, 
 if they could not add to his justly acquired fame, 
 were enviable marks of the admiration which his 
 talents procured for him in his own country. In 
 1735, two of his earlier publications, the Sy sterna 
 Naturce and Fundamenta Botanica, appeared ; and 
 in 1737 he published five of his works, the Cri- 
 tica Bo fan lea, Genera Plant arum, Hortus Clif- 
 fortianus, Flora Lapponica, and Methodus Sexu- 
 alis; any one of which would have been sufficient 
 to have conferred lasting celebrity on its author. 
 As his fame extended, he was invited by the King of 
 Spain to settle in his dominions, but declined the 
 invitation ; and was amply indemnified by the 
 honours which his own sovereign conferred upon 
 him. He was created a Baronet, and afterwards 
 Archiator, or Dean of the College of Physicians ; 
 and a Knight of the Polar Star, some time before 
 his death, which happened on the 8th of January, 
 1778. His system, the one which is now, with 
 some modifications, generally adopted, is founded 
 on truth and nature. It has been improved and 
 
 * This lady was Elizabeth Moreens, the (laughter of a phy- 
 sician at Fahlun. She presented him with one hundred dollars, 
 the savings of her pocket-money, to enable him to graduate. 
 
16 SKETCH OF THE RISE [LECT. I. 
 
 occasionally altered since his death, as the ex- 
 tension of the science demanded ; nor have the 
 ignorant and the unqualified refrained from mu- 
 tilating it by the most fanciful and useless varia- 
 tions : but from under the hands of both sets of 
 reformers, the principles, and the groundwork, 
 still remain, and are likely to do so, unchanged. 
 His system is not, however, the only labour for 
 which Linnaeus deserves the applause of posterity : 
 he made considerable researches in vegetable phy- 
 siology, or the doctrine of the habits and economy 
 of plants; and his endeavours to render Botany 
 useful to medicine and to agriculture, are worthy 
 of the highest praise. 
 
 It is to be lamented that biography has, 
 hitherto, conveyed to us so few notices regarding 
 the method of study pursued by those, whose cha- 
 racters as scientific men we respect and venerate ; 
 and our information, as to this particular of the 
 life of Linnoeus, is, indeed, extremely slender. We 
 know little more, than that he very early began to 
 seek nature in the fields, and to form a herbal ; and 
 that he read and studied " to the last glimpse of 
 the midnight lamp." He fortunately, indeed, lived 
 at a time when philosophy began to assume its 
 most interesting character; when its votary, 
 throwing aside the formal robe of pedantry, and 
 quitting the maze of hypothesis, laboured to apply 
 those principles which his industry, observation, 
 
LECT. I.] AND PROGRESS OF BOTANY. 17 
 
 and ingenuity had accumulated, to procure the 
 means of supplying the wants and increasing the 
 comforts of his fellow-creatures ; and of spreading 
 over the paths of ordinary life those intellectual 
 embellishments, the enjoyment of which forms the 
 most distinguishing feature of difference between 
 civilized man and the human savage. Such is cer- 
 tainly the ultimate aim of all science. How use- 
 less would have been the discoveries of astronomy, 
 had they not been applied to the purposes of navi- 
 gation ! How vain would have proved the daring 
 experiments of Franklin, in drawing lightning 
 from the clouds, to prove its identity with the 
 electrical fluid, if they had not pointed out the 
 means of securing our dwellings from the effects 
 of one of the most awfiil and dangerous of na- 
 tural phenomena ? What would have availed the 
 labours of a Newton and a Boyle, a Black and 
 a Cavendish, of Linnaeus, Hunter, Volta, and 
 Davy, did they not ultimately tend to benefit ge- 
 neral society ? Without such an object in view 
 they would be but ingenious trifles, and a very 
 straw in the balance, when weighed against the 
 efforts of the meanest artizan. 
 
 Since the days of Linnaeus, therefore, Botany, 
 also, has displayed a more important aspect than 
 it ever before assumed. The rage of making new 
 systems and arrangements of plants has passed 
 away, because these are no longer necessary : but 
 VOL. i. c 
 
18 PROGRESS OF BOTANY. [LKCT. I. 
 
 Botanists have arisen, and still live, who, besides 
 illustrating and endeavouring to perfect systematic 
 Botany, have advanced, in a great degree, the 
 more useful parts of the science, by inquiring into 
 the properties of plants, the phenomena of their 
 functions and growth, and the effects they produce 
 on the great system of nature. In this part of the 
 science an extensive field is opened for the exercise 
 of human ingenuity, the investigation of which is 
 sufficient to employ, usefully, the longest life, and 
 the highest powers of the understanding. 
 
 From the period of Linnaeus the history of the 
 science contains a long list of justly celebrated 
 names. Among these we find HALLER, an anato- 
 mist, physician, botanist, poet, and politician, the 
 friend at one time, but afterwards the rival of Lin- 
 naeus ; RUMPHIUS, who, although a physician, yet 
 was appointed to the situations of chief magistrate 
 and president of the mercantile association of Am- 
 boyna, the plants of which settlement he has de- 
 scribed in his work, entitled, Herbarium Amboi- 
 nense; (EDER, who began the Flora Damca, the 
 publication of which is still continued, under the 
 patronage of the Danish government; SCHREBER, 
 Professor at Erlangen and President of the Impe- 
 rial Academy; JACQUIN, BERGIUS; PROFESSOR 
 PALLAS; REINHOLD FORSTER, who sailed with 
 Capt. Cook ; THUNBKRG, the author of the Flora 
 Japonica, a work of unequalled merit ; JJTSSIEV, 
 immortalized by his attempt to arrange plants in 
 
LECT. I.] UTILITY OF BOTANtf. 19 
 
 a natural order ; SIR JOSEPH BANKS ; MILLER ; 
 HfiDwrc; DRYANDER; GARTNER; SIR J. E. SMITH, 
 President of the Linnsean Society ; WILLDENOW; 
 PROFESSOR VAIIL ; HUMBOLDT, the South Ameri- 
 can traveller; ROXBURGH; and many others, whose 
 names are well known and not undeservedly cele- 
 brated. 
 
 Having finished the rapid sketch of the rise 
 and progress of the science, which I proposed to 
 exhibit to you, let us now pass on to the consider- 
 ation of its utility as a branch of general know- 
 ledge. In reflecting upon this part of our subject, 
 Medicine first presents itself to our attention, as 
 deriving the greatest assistance from it. With the 
 healing art, as we have already noticed, Botany 
 originated ; and, until the period of the renowned 
 empiric Paracelsus, who introduced the use of 
 chemical remedies, almost the whole resources of 
 medicine were drawn from the vegetable kingdom. 
 Although it can scarcely be denied that the use of 
 mineral remedies has been, upon the whole, fa- 
 vourable to the advancement of the profession, by 
 putting into the hands of its practitioners very 
 powerful agents for altering and controlling, as it 
 were, the powers of the animal system ; yet it may 
 be doubted whether mankind have not suffered, in 
 some degree, by the change, inasmuch as the at- 
 tention of the medical philosopher has been di- 
 
 c 2 
 
20 UTILITY OF THE [LECT. I. 
 
 verted almost altogether from the vegetable king- 
 dom. Much certainly remains undiscovered of 
 the virtues of plants in effecting the cure of dis- 
 eases, and many excellent and very powerful salu- 
 tary agents belong to that kingdom of nature. 
 
 As civilized men are not stationary beings, but 
 are led by the thirst of gain, ambition, curiosity, 
 or enterprise, to visit every part of the habitable 
 surface of the globe, it is requisite that medical 
 practitioners should be able to generalize, and, 
 in searching for remedies to remove the morbid 
 effects of changes of climate and other contin- 
 gencies on the constitution, to know how to 
 substitute the materials within their reach for 
 those they have been accustomed to employ, but 
 which they cannot in every situation obtain. The 
 question may be reasonably asked, How is Botany 
 to teach this knowledge? Let us examine how 
 far we can satisfactorily answer it. Do we, in the 
 first place, wish to ascertain which plants are poi- 
 sonous or salutary? Botany teaches us that all 
 those arranged in the family denominated Cruci- 
 ferce, in that of the Rosacece, and in those of the 
 Malvaceae, Labiatce, and almost all the Cerealia, 
 contain no poisonous species; that the Mushroom 
 tribe, the Solanece, the Apocynece, the Tithymalce, 
 the Ranunculacece, and the Papaverce, are almost 
 all suspicious: and that the Umbellif'erce, the Ari> 
 the Polygons, contain acrid and several deleterious 
 
 3 
 
LKCT. I.] SCIENCE OF BOTANY. 21 
 
 species. It also informs us, that some plants are 
 acrid and poisonous when growing in water, which 
 appears to be their natural element, although they 
 are inert when they vegetate on dry land; and 
 that some inert land plants become acrid when 
 they accidentally spring up in water or in marshy 
 places. Do we wish to discover the probable me- 
 dicinal properties of the plants in any new situa- 
 tion, before we venture to try their effects upon 
 the animal frame? Botany informs us how to do 
 so, by arranging the plants with which we are un- 
 acquainted, into their natural families. Thus we 
 know that the Solanece are narcotic ; the Gentiance 
 yield a bitter, and sometimes a purgative principle; 
 the Laurel tribe a stimulant, which is in some in- 
 stances highly deleterious; the Gorymbiferce are 
 emmenagogue; the Rubiacea?, to which Cinchona 
 belongs, diuretic and tonic; the Crucif'erce antiscor- 
 butic; and the Malvaceae emollient. A medical Bo- 
 tanist, believing that a certain plant yields a pecu- 
 liar medicinal principle, is led to examine whether 
 the species of the same genus which are indigenous 
 to the clime that he inhabits may not contain some- 
 thing similar, if not exactly the same ; and thence 
 discoveries valuable to his country, and sometimes 
 to the human race, are effected. But this import- 
 ant method of generalizing can be practised only 
 by the Botanist; for, to one ignorant of Botany, 
 not only is the language foreign and unintelligible, 
 
 r 3 
 
22 UTILITY OP THB (JLECT. I, 
 
 but the resemblances which characterize the va- 
 rious members of the same family, and which are 
 perfectly obvious and striking to the Botanist, are 
 overlooked and cannot be perceived by an ordinary 
 observer. The advantages of a knowledge of Bo- 
 tany, also, and of the habits of plants, to the phy- 
 sician, are equally evident in the assistance they 
 afford in the cultivation of a branch of the profes- 
 sion, which has lately been much and properly at- 
 tended to; I refer to medical topography ; a subject 
 important to all, but absolutely requisite to the 
 military medical practitioner. Suppose, for ex- 
 ample, that an army is about to encamp in an 
 enemy's country, and in a situation where circum- 
 stances may require that it should remain for a 
 considerable time. The season of the year, and 
 the kind of weather prevailing at the moment, 
 may render it difficult for the medical staff to pro- 
 nounce whether the place be healthy or otherwise; 
 ^nd the information afforded by experience is too 
 }ate to prevent the impending evil, should it prove 
 unhealthy. But the very plants which cover the 
 soil clothe with a prophetic character the Botanical 
 physician, and enable him to anticipate the danger 
 which it is requisite to avoid. Yet how little has 
 this branch of study been attended to in the edu- 
 cation of professional men; who, before they pre- 
 sume to commence the performance of the duties 
 expected of them, ought at least to be acquainted 
 
LECT. I.] SCIENCE OF BOTANY. 23 
 
 with the nature and qualities of the implements 
 they are about to employ in the cure of diseases. 
 
 A remark made to me by an old and respect- 
 able physician, the late Dr. Denman, explains in 
 some degree the cause of this neglect: " I be- 
 " lieve/' said he, * that the practitioners of the 
 " present period are sensible of the inadequacy 
 " of the old method of bringing up young men 
 " to the profession, and are therefore anxious to 
 *' send out those brought up under them better 
 " instructed, and with a firmer foundation of prin- 
 " ciples than was the case forty years ago : but 
 " the ardour of youth to take an early, active 
 " share in the bustle of life, places many obstacles 
 " in the way of accomplishing their good inten- 
 " tions." The justness of the observation is too 
 obvious ; and as medical men, after they have 
 once entered upon the busy stage of life, cannot 
 well retrace their steps, happy would it be for stu- 
 dents were they to take advantage of the expe- 
 rience of their predecessors, all of whom, I will 
 venture to assert, believe that much anxiety, 
 much trouble, would have been saved to them- 
 selves, and much more pleasure and reputation 
 gained in the exercise of their profession, had a 
 few more years been spent in their education, and a 
 few more collateral studies been attended to during 
 that period. The practice of medicine is the study 
 of a lifetime ; it is entered upon the moment a man 
 
 c 4 
 
24 UTILITY OF THE [bECT. I. 
 
 begins to prescribe, and it must be unremittingly 
 continued*; but little satisfaction can be derived 
 from it, if the mind be not previously well stored 
 with principles, and enlightened by a liberal edu- 
 cation. By the force of natural genius and a 
 good address., an ignorant physician may float for 
 a while in honour's atmosphere ; if fortunate, he 
 may even be respected, and may attain wealth and 
 reputation ; but, when an unexpected difficulty oc- 
 curs, his deficiencies appear, the bubble bursts, his 
 reputation is dissipated, and he sinks neglected 
 and despised. The properly educated physician, 
 on the contrary, may rise slowly at first ; but, like 
 the sun, his strength increases as he rises ; and^ 
 although he must naturally decline with gathering 
 years, yet, when he sets, it is with equal dignity, 
 only with a milder lustre. And surely, to use the 
 language of a celebrated moralist, " to desire the 
 " esteem of others for the sake of its effects, is not 
 " only allowable, but in many cases our duty; 
 " and to be totally indifferent to praise or censure 
 " is so far from being a virtue, that it is a real 
 " defect in character "f-." Botany is one of those 
 collateral sciences, which is not only useful, but 
 
 * The following words of Linnaeus, contained in a letter to 
 Haller, should be impressed on the mind of every student: 
 " Disco adhuc ; ignoscas quod doctus, etiamnum non eva. 
 " serim." 
 
 f Dr. Blairj Sermon VI, vol. ii. 
 
LECT. I.] SCIENCE OF BOTANY. 25 
 
 adds grace to the medical character. Did I wish 
 to select examples in support of this remark, I 
 need only point to the works of Prosper Alpinus, 
 Sir Hans Sloane, Malpighi, Haller, Alston, Lewis, 
 and of our own contemporary, the indefatigable 
 Orfila. A practitioner, indeed, unacquainted with 
 Botany, may know the names of many plants and 
 their uses ; he may even gain a knowledge of the 
 physiognomy of a few of them ; but his ideas are 
 obscure and confused; his ignorance may often be 
 rendered conspicuous where he would most desire 
 to conceal it ; and it lays him open to the arts of 
 the designing, and of those who would wish to ex- 
 pose him. Of the advantages which the profession 
 has derived from the labours of Botanists, I need 
 mention a very few only of many examples that 
 might be adduced : the reintroduction of the Fox- 
 glove by Dr. Withering, as a remedy for dropsies, 
 and the recent extension to this country of the 
 Pyrola umbellata, and the Gurn Acaroides. As 
 many of the medicinal plants appear as common 
 weeds, a medical man ought to be able to distin- 
 guish these when required ; and, in the case of ve- 
 getable poisons, nothing will sink him more in the 
 opinion of others, than his appearing ignorant of 
 the plant which has occasioned the mischief; 
 while nothing will raise him more in their esteem 
 than his being able to point out its distinguishing 
 characteristics^ by which it may be known and 
 
26 UTILITY OF THK [LECT.-J. 
 
 Avoided in future. But a more important consider- 
 ation still, to a reflecting mind, is, that by the 
 degree of acquaintance which a practitioner has 
 with plants that are poisonous to the animal eco- 
 nomy, the life of a fellow-creature may be lost or 
 saved. All poisonous plants do not produce the 
 same effects, and these, consequently, require dif- 
 ferent modes of treatment ; but if the plant which 
 has caused the mischief cannot be ascertained, 
 how is the remedy to be selected ? 
 
 The utility of Botany to many of the other arts 
 is not less obvious ; and we are indebted to it for 
 a variety of our comforts, both as to food and the 
 luxuries of life. The grains so indispensable for 
 pur existence, the greater number of the fruits, 
 and the most beautiful flowers, that enrich our 
 orchards and ornament our gardens, are of foreign 
 origin ; and many of them have been brought to 
 us by Botanists whose inquiries had led them to 
 visit remote countries. The Horse Chestnut, for 
 example, now so common in our plantations, was 
 conveyed to Europe from the north of Asia, by 
 Clusius, a Botanist, in the year 1550. The Kidney 
 Bean, Phaseolus vitlgaris, was brought from the 
 East Indies : and the Nol-kol, the root of which 
 affords a large supply of wholesome nutriment, 
 has just been introduced from the same place. 
 The Crown Imperial, Fritillaria imperialis, was 
 transported from Constantinople ; the Camellia, 
 4 
 
LECT. I.] SCIENCE OF BOTANY. 27 
 
 from Japan ; many of the Roses from China , the 
 Nasturtium from South America ; and the Pelar- 
 gonium, or Geranium, as it is improperly called, 
 from the coeist of Caffreria. The Potatoe, the 
 chief support of a great majority of our poor, was 
 first described by Caspar Bauhiri in 1590 ; and 
 afterwards brought into this country, whence it 
 was dispersed over Europe*. In our own times 
 we have seen the West Indies enriched with the 
 Bread-fruit by the scientific skill of Sir Joseph 
 Banks ; and every day new plants are brought 
 home and naturalised to our climate, of great im- 
 portance both in an economical and political point 
 of view *f~. Even the arts may be benefited by a 
 knowledge of Botany. Thus, many fine statues 
 might have been preserved, had the fact been sooner 
 
 * It is very generally believed that this useful vegetable 
 was brought from Virginia by Sir Walter Raleigh ; and Willdc- 
 now states that, " in the year 1623, he distributed the first 
 " which he brought from Virginia in Ireland." Doctor Smith 
 Barton has pointed out the errors of this statement : in the first 
 place, Sir Walter never was in Virginia ; secondly, he was not 
 living in 1623; having lost his head in October 1618; and, 
 thirdly, it is by no means certain that the first exclusive depot 
 of the Potatoe was Ireland. 
 
 f The number of plants now known and systematically ar- 
 ranged amounts to 44,000; although those known by the 
 Greeks, Romans, and Arabians, did not exceed 1400; and in 
 Caspar Bauhin's time, all that indefatigable Botanist could col- 
 lect for his Pinax Theatri Botanici, a work of forty years' la- 
 bour, did not exceed six thousand species. 
 
28 UTILITY OF THE [LECT. I. 
 
 known, that the black spots which appear upon 
 them is a vegetable fungus, the Lichen niger of 
 Linnaeus. The dry rot in wood, also, is a fungus. 
 It is related that Mahomet Bey, King of Tunis, 
 was dethroned by his subjects for having the repu- 
 tation of possessing the philosopher's stone. He 
 was restored by the Dey of Algiers, upon promising 
 to communicate to him the secret. Mahomet 
 sent a plough, with great pomp and ceremony, in- 
 timating that agriculture is the strength of a na- 
 tion, and that the only philosopher's stone is a 
 good crop, which may be easily converted into 
 gold. I mention this anecdote, because it conveys 
 an impressive idea of the importance of Agricul- 
 ture ; between which and Botany the connexion is 
 so natural, and the advantages to be derived by 
 the farmer from a knowledge of it so apparent, 
 that the neglect of it as an essential part of his 
 education is, indeed, wonderful. But so blind are 
 men, often, to their true interests, that agriculture 
 in this country has, till within a few years past, 
 been regarded as an employment fit only for the 
 most uninformed part of society. Following stu- 
 pidly in the footsteps of his predecessors, and 
 guided by a few rules, which had been handed 
 down to him from the rudest ages, the agriculturist 
 was ignorant that a knowledge of the theory of 
 his operations was necessary for enabling him to 
 overcome unexpected obstacles ; to guard against 
 
LECT. I.] SCIENCE OP BOTANY. 29 
 
 the uncertainty of seasons ; and to multiply the 
 means of supplying the wants of the community 
 and enriching- himself. These mistaken notions 
 are now happily vanishing ; and the utility of Che- 
 mistry and Botany is beginning to be felt and ac- 
 knowledged by the farmer. From the more ge- 
 neral study of the economy of vegetable life, how 
 many improvements might be suggested in the cul- 
 tivation of even the most common of our useful 
 plants ! How many of those which are still re- 
 garded as useless weeds, might be found to be of 
 great importance if their properties were accu- 
 rately investigated! And certainly the nature of 
 soils would be better and more easily known by an 
 acquaintance with the different kinds of plants 
 which each variety of surface produces. 
 
 But, besides these objects of utility, to the ad- 
 vancement of which Botany unquestionably con- 
 tributes, it is likely to render a still greater service 
 to social life, by the cultivation of that branch of 
 it which assigns to each tribe of plants its altitude, 
 its limits, and its climate ; and which the French 
 designate by the tei-mGeographie Botanique. By its 
 aid nature may be in some degree subdued by art, 
 the mountains of Europe may be girt by the Cin- 
 chona, the vine may cluster upon our rocks, and 
 the high Palmetto and Coco wave on the sun- 
 ward sides of our native vales. 
 
 These examples are sufficient to show the uti- 
 
30 UTILITY OP THE [LECT. I. 
 
 lity of Botany in advancing- many of the more im- 
 portant arts ; and the study of it is no less bene- 
 ficial as a branch of general education. If the 
 intellectual enjoyments of a well-informed mind 
 be a valuable possession, whatever can augment 
 these must be considered as of great importance. 
 Many branches of knowledge have this effect; and, 
 although they cannot be considered as directly 
 advancing our interests or fortune in our inter- 
 course with mankind, yet the possession of them 
 affords a more permanent satisfaction than either 
 wealth or honour can bestow*. Botany is one of 
 
 * If we apply these observations to the fair sex, we shall 
 perhaps immediately hear of the danger of producing literary 
 women, of having wives that would leave the management of 
 their houses to pore over the page of the philosopher, and be 
 solving a mathematical problem instead of making a custard. 
 We shall be told that learned women are insupportable, and 
 use their acquirements as tyrants do their authority, making 
 them weapons of oppression rather than the instruments of 
 happiness. But a female pedant and a woman with a well-in- 
 formed mind and liberal education are two different beings ; 
 and I would answer remarks such as these in the words of 
 one of the sexf, which I think are completely convincing. 
 * c The fragile nature of female friendships," says she, " and 
 " the petty jealousies that break out at the ball-room, have 
 " been, from time immemorial, the jest of mankind. Trifles 
 " light as air will necessarily excite, not only the jealousy, but 
 " the envy of those who think only of trifles. Give them 
 " more employment for their thoughts ; give them a nobler 
 
 f Mrs. Barbauld. 
 
LECT. I.] SCIENCE OP BOTANY. 31 
 
 these; and the pleasure to be derived from the 
 knowledge of it is not confined to any period of 
 life, or any rank in society. In youth, when the 
 affections are warm and the imagination is vivid ; 
 in more advanced life, when sober judgment as- 
 sumes the reins ; in the sunshine of fortune and 
 the obscurity of poverty ; it can be equally en- 
 joyed. The opening buds of spring, the warm 
 luxuriant blossoms of full-blown summer, the yel- 
 low bower of autumn, and the leafless, desolate 
 groves of winter, equally afford a supply of men- 
 tal amusement and gratification to the Botanist. 
 
 I have thought it necessary to state these ex- 
 amples of the usefulness of > Botany and the plea- 
 sures to be derived from the study of it, in order 
 to satisfy the demands of those who consider that 
 nothing ought to be attended to which does not 
 present some immediate object of profit or of uti- 
 
 " spirit of emulation; and we shall hear no more of these paltry 
 " feuds : give them more useful and more interesting subjects 
 " of conversation, and they become not only more agreeable, 
 " but safer companions for each other." I would add, that 
 men who exclaim against learned women, often allow the sex 
 an excessive and unrestrained pursuit of pleasure ; and think 
 so meanly of their powers of mind, as to believe them fit only 
 to be amused with the fictions of romance. But, if pleasure be 
 essential for the happiness of woman, it can be obtained from 
 the pursuit of science, that knowledge which is founded on 
 truth and utility, provided an early taste for it be implanted in 
 the mind. 
 
32 GENERAL DIVISION [LEOT. I. 
 
 lity. What is the use of Botany? What can you 
 gain by it? are constant questions. We have al- 
 ready stated our opinion as to what may be gained 
 by it ; but I would further answer such inquirers 
 by an anecdote told of the Greek philosopher He- 
 raclitus. This philosopher was very poor, but 
 much respected, and visited by individuals of the 
 highest rank. One day, when certain persons 
 came to consult him, they found him paring tur- 
 nips for his supper, and warming himself in a 
 kitchen: the meanness of the place occasioned 
 them to stop ; upon which the philosopher thus 
 accosted them: " Enter/' said he, " boldly, for 
 " here, too, there are gods." 
 
 We have now to consider what mode of prose- 
 cuting the study of the science upon which we are 
 about to enter is likely to be productive of the 
 greatest benefit. 
 
 BOTANY, as we before observed, is that science 
 which teaches the knowledge of vegetables, their 
 structure, habits, and properties; and to distin- 
 guish different plants from each other ; or, it com- 
 prehends Phytology and Systematic Botany*. 
 
 * Vegetable physiology, indeed, cannot be separated from 
 systematic Botany ; for, to use the words of a French writer, 
 M. Aubert du Petit-Thouars, " it is essentially the basis upon 
 " which that science is raised ; and the more this basis shall be 
 " known, the more Botany, already so attractive in herself, 
 * will see the number of her disciples increase." 
 
LECT. f.] OF BOTANICAL SCIENCE. 33 
 
 Vegetables, like animals, are organized living 
 bodies. To the superficial observer there appears 
 no difficulty in distinguishing them from animals 
 and fossils ; but those who have examined the sub- 
 ject more minutely, find many obstacles to prevent 
 them from drawing the exact line of distinction be- 
 tween the three kingdoms of Nature. Still, how- 
 ever, vegetables possess peculiarities of structure, 
 habit, and functions, which characterize them; 
 and these are found in every plant. As plants 
 are living beings, so are they also perishable: 
 death, as is the case in animals, may either proceed 
 from innate causes, depending upon their organiza- 
 tion, or be produced by external causes. It is ob- 
 vious to our senses, that vegetables derive nourish- 
 ment from the soil in which they are fixed, and in 
 which they grow, and perfect seed capable of repro- 
 ducing the species. The researches of philosophy 
 have further informed us, that they possess irritabi- 
 lity, by which the nutriment they imbibe is progres- 
 sively moved through every part of their bodies, con- 
 verted into various secretions, and assimilated into 
 the substance itself of the plant; and that, like 
 animals, they produce certain changes on the at- 
 mosphere, and can accommodate themselves to 
 the vicissitudes of heat and cold. In the func- 
 tions of generation, also, plants have many of the 
 peculiarities of the most perfect animals. In stat- 
 ing, however, the close analogy between plants 
 VOL. i. D 
 
34 GENERAL DIVISION [LBCT. t. 
 
 and animals, we must always bear in memory that 
 they have one important function less than ani- 
 mals sensibility *. The losing sight of these cir- 
 cumstances, particularly the former, led the inge- 
 nious Darwin into a labyrinth of error ; and has 
 exposed his memory to the sarcasm of malevolent 
 wit and the derision of ignorance. That part of 
 our subject therefore, which refers to the economy 
 of the vegetable system, should first engage the 
 attention of the student. It constitutes Phyto- 
 logy, and comprehends the Anatomy and Physio- 
 logy of plants; and is the most amusing, and cer- 
 tainly not the least instructive part of the science. 
 The anatomy of plants is more difficult than that 
 of animals, from the minuteness of their parts, the 
 union of them, and the extreme difficulty of se- 
 parating them without destroying their texture. 
 If, however, it be more difficult, it is less disgust- 
 ing, and the microscope very much facilitates our 
 inquiries. Without it we can have no idea of the 
 structure of plants, and consequently no correct 
 notions of their functions can be obtained. In 
 studying the Anatomy the Terminology is acquir- 
 ed, an acquaintance with which is absolutely ne- 
 cessary for securing a knowledge of systematic 
 arrangement. By combining with these the study 
 
 * " Vegetabilia, sensatione licet destituantur, aeque taroen ac 
 *' animalia vivcre probat ortus> nutritio, <zta$, vnotus, propulsio^ 
 morbus, mors, aMstfQmia t vrganismus." Pkilos.Botanica, J133. 
 9 
 
LKCT. t.] OP BOTANICAL SCIENCE. 36 
 
 of the Physiology, on which modern Chemistry has 
 thrown the most brilliant light, the tediousness of 
 acquiring the terms of art is diminished, and 
 much interest excited in the pursuit. It is neces- 
 sary to state that Botanical Terminology is that 
 part of the science which has been less improved 
 than any other, since the time of Linnaeus. Some 
 reform, similar to that which chemical nomencla- 
 ture has undergone, is wanting, to remove the 
 rubbish with which it is encumbered ; for, although 
 arbitrary terms are less objectionable in Botany, 
 yet the terms employed should be clearly defined, 
 and comprehensive. I would recommend, on this 
 part of the subject, the perusal of Sir J. E. Smith's 
 Introduction to Physiological and Systematic Bo- 
 tany ; Rousseau's Letters on the Elements of Bo- 
 tany; Mr. Curtis* Lectures; Willdenow's Prin- 
 ciples of Botany^ which have been well translated ; 
 and, to those who read and understand French, 
 the Traite* d'Anatomie et de Physiologic Vgtales, 
 of Mirbel ; but, above all, the Philosophia Bota- 
 nica of Linnaeus, Those who wish to investigate 
 the subject more closely, will find great satisfac- 
 tion in looking into the works of Grew and Mal- 
 pighi; DuHamel, Hedwig, De Saussure, Gsertner, 
 and Spailanzani; and Mr. Keith's System of Physi- 
 ological Botany. But I will forbear, at present, 
 from loading your memories with the names of 
 authors,, and rather notice them as we proceed, 
 
 D 2 
 
36 GENERAL DIVISION [LECT, I* 
 
 when the various subjects which each has particu- 
 larly treated of come to be noticed. 
 
 By making ourselves acquainted with the 
 structure and functions of vegetables, we are pre- 
 pared to examine them as parts of a system ; and 
 thereby become acquainted, as it were, with each 
 individual of this extensive kingdom of Nature. 
 
 The astonishing diversity of form and colour 
 with which Nature lias clothed the members of the 
 vegetable kingdom, required that some mode 
 should be devised for distinguishing the different 
 kinds of plants. What is termed the natural me- 
 thod seems, at first sight, the most easy, and the 
 best ; and certainly, if it could be rendered per- 
 fect, it would undoubtedly be so ; for, in many of 
 the families of plants, such as the Grasses, Ferns, 
 Lilies, Roses, &c. there is such a natural affinity 
 between the different species of each class, and so 
 marked a distinction of the classes, as not to be 
 mistaken ; but this is not the case throughout the 
 vegetable kingdom ; and, even in some of those 
 natural classes which I have named, species are 
 found which render it exceedingly difficult to 
 know in which natural class they should be placed. 
 Many Botanists, however, have endeavoured to 
 produce systems of arrangement, according to 
 these natural affinities; but hitherto they have not 
 succeeded, not even excepting Jussieu, whose 
 very learned and valuable work is far from an- 
 
LKCT. l.j OF BOTANICAL SCIENCE. 37 
 
 swering the purposes for which it was intended. 
 Indeed, on examining the whole vegetable king- 
 dom, the attempt to divide it into natural orders 
 and families offers difficulties which, in our pre- 
 sent state of knowledge, appear insurmountable. 
 The artificial method of classification was there- 
 fore thought of; and that of Linnaeus is the best 
 and most perfect that has yet been contrived. 
 I will not now even hint at the construction of 
 this system; but merely observe, that, although 
 it is an artificial system, yet that it is founded 
 on the most correct observation of the pheno- 
 mena of the vegetable kingdom ; and plants are 
 arranged by it under Genera and Species, as the 
 individuals discover in the essential parts of the 
 flower common properties and a natural affinity. 
 This the young Botanist must study with the 
 greatest care. Without a knowledge of it no 
 one can be accounted a Botanist; and, by means 
 of an acquaintance with it, the mepiory becomes 
 capable of retaining a recollection of the charac- 
 teristic features of all the plants, which already so 
 greatly swell the vegetable catalogue; and the 
 number of which is every day increasing. This, 
 however, cannot be attained from the perusal of 
 books ; an appeal must be made to Nature, and 
 plants examined in their growing state. In order 
 to do this in a proper manner, as far as the plants 
 of our own country are concerned, the Botanical 
 
 D 3 
 
38 OBJECT OF THESE LECTURES. [LECT.-I. 
 
 student must range the fields, and find the objects 
 of his researches in their most perfect states, and 
 in those places where the hand of Nature has 
 planted them. For exotics he must have recourse 
 to the Botanic Garden; and, although he cannot 
 expect to procure the specimens in a state of per- 
 fection, yet he will obtain more information from 
 examining them, such as they are, than can be ac- 
 quired from the perusal of the best descriptions *, 
 assisted by the best plates. 
 
 Such is the outline of the plan of study I 
 would recommend ; and which I shall endeavour 
 to fill up by this course of Lectures. But I must 
 pbserve, that no lectures can convey a complete 
 knowledge of any Science. They- are intended 
 rnerely to assist the student in his inquiries, and, 
 like a pioneer, to open a path, the intricacies of 
 which must be afterwards prosecuted by himself. 
 He must endeavour to woo Nature in her most 
 secret recesses ; but he may rest assured that she 
 is not to be won without constant assiduity and 
 attention; that she is a very coy mistress, and 
 will notbesto\tf her favours upon the indolent and 
 the indifferent; while, on the contrary, on the at- 
 tentive and the industrious, she lavishes her 
 choicest treasures with an unlimited liberality. 
 
 * The best systematic works are, the Genera Plantarum of 
 Linnaeus; Persoon's Synopsis Plantarum ; Withering's Botany ; 
 Smith's Flora Britannica; and Willdcnow's edition of the 
 Species Plantarum.' 
 
?,ECT. II.] DEFINITION OP A PLANT. 39 
 
 LECTURE II. 
 
 DEFINITION OF A PI, ANT GENERAL VIRW OF TMB 
 VEGETABLE FUNCTIONS. 
 
 THE division of all natural objects into three 
 great classes is so simple and apparently so con- 
 sistent with nature, that it must have originated 
 at a very early period of society ; and the more 
 attentive observations of Philosophers, for a series 
 of ages, although they have found unexpected diffi- 
 culties in fixing the exact limit of these divisions, 
 yet, have discovered nothing to prevent altogether 
 their adoption. Philosophers, therefore, almost by 
 common consent, have classed all natural produc- 
 tions according as they appear to belong to the 
 animal, the vegetable, and the mineral or fossil 
 kingdoms. 
 
 There is no difficulty in distinguishing a mi- 
 neral from a vegetable; for, although some Lichens 
 appear to the eye more like parts of the rock or 
 the stone to which they are attached than distinct 
 organized living bodies, yet, in nothing, except in 
 the want of sensation, do the members of the ve- 
 getable and the fossil kingdoms agree. 
 
 To distinguish a vegetable from an animal does' 
 
40 bEFINITION OF A PLANT. [LECT. II. 
 
 not appear, at first sight, to be less easy. But he 
 who investigates the subject more closely finds 
 unlooked-for obstacles, arising from the unbroken 
 chain of connexion which seems to unite these 
 two classes of beings ; and is forced to acknow- 
 ledge the impossibility of fixing upon that link of 
 it, which marks the termination of the animal, 
 and the commencement of the vegetable state of 
 existence. That a perfect animal can be easily 
 distinguished from the more perfect productions of 
 the vegetable creation is undoubtedly true ; as no 
 one could hesitate, for an instant, in which of the 
 kingdoms of Nature to place a dog or a rose ; but 
 the difficulty arises when the strikingly character- 
 istic functions of each kind of life are, as it were, 
 confounded. Thus, not many years since, natu- 
 ralists were undetermined whether to consider 
 corals and corallines, polypi, and other zoophytes, 
 as vegetable or animal beings. The difficulty of 
 fixing upon the proper limits of these two king- 
 doms of Nature, and the circumstance of the 
 members of both being living organized bodies, 
 and thus differing decidedly from fossils, have in- 
 duced the moderns to propose the division of na- 
 tural objects into two classes only, INORGANIC and 
 ORGANIC: the first comprehending all those bodies 
 which submit to the general laws of chemical 
 attraction and affinity and of mechanics ; and 
 which do not possess life, as, gases, fluids, earths, 
 
LECT. II.] DEFINITION OF A PLANT. 41 
 
 salts, and raetals; the second comprehending liv- 
 ing beings, as animals and vegetables. The latter 
 is the object of our inquiries ; and, as it is of some 
 importance to mark the point of distinction be- 
 tween animals and vegetables, we shall first exa- 
 mine the truth of those definitions of a plant which 
 have been at different times delivered by Botanical 
 Philosophers; and adopt that one which, in our 
 opinion, is the least likely to mislead. 
 
 The first that we shall notice is that of Jun- 
 gius, a Botanist who, as has been already stated 
 (Lecture I.), lived about the middle of the seven- 
 teenth century, and who first hinted the principles 
 on which the Linnaean classification is founded : 
 " A plant," says he, " is a living but not a sentient 
 "body, affixed to a certain spot or seat, whence it 
 " can draw nourishment, grow, and finally propa- 
 " gate its species *." In this definition the want of 
 sensation and of locomotion, or the power of 
 changing place, are considered as the chief distin- 
 guishing characteristics of a plant ; but we shall 
 afterwards show that this definition is not to be 
 adopted, inasmuch as some animals, if a sensor tuni 
 commune, or a nervous system, is to be regarded 
 as the medium of sensation, possess no sensibility ; 
 and some are immoveably fixed to one spot. 
 
 * " Planta est corpus vivens non sentiens, seu certo loco 
 " aut certae scdi affix urn, untie nutriri, augcri, dcnique se pro- 
 " pagare. potcst." Jung. Ipagog. u,. 1. 
 
42 DEFINITION OF A PLANT. [LECT. II, 
 
 Keeping the same idea in view, Boerhaave, who 
 flourished at the beginning of the following cen- 
 tury, defines a plant thus: <c A plant is an organic 
 " body, fixed to some other body by some part of 
 " itself, by which it imbibes the matter of nourish- 
 " ment, of growth, and of life *." The same opi- 
 nion was also entertained by Ludwig, a cotempo- 
 rary of the great Linnaeus, who says, " Natural bo- 
 " dies, having always the same form, and endowed 
 " with locomotion, are called animals ; those 
 " which have always the same form but are desti- 
 " tute of locomotion, vegetables -f-." In all of 
 these definitions the want of a locomotive power 
 is chiefly insisted on as being the most peculiar 
 distinguishing characteristic betwixt a vegetable 
 and an animal: but, although we may allow that 
 plants are destitute of locomotion, yet there are 
 several genera of the molusca and testaceae, co-* 
 rals, corallines, and some of the zoophyta, which 
 incontestably belong to the animal kingdom, that 
 are immoveably fixed to a single spot ; either to the 
 bottom of the sea, or to rocks, or to shells. The 
 
 * " Planta est corpus organicum, alteri cuidam corpori 
 " cohaercns per aliquani par tern sui, per quam nutrimenti et 
 " increment! et vitae materiam capit et trahit. 1 *' Historia 
 Plant. 3. 
 
 f 4< Corpora naturalia eadem semper forma et loco-motivi- 
 " tate pracdita appellantur animalia ; eadem semper forma, scd, 
 .** loco-motivitate destituta, vcgetabilia.''-/-^^^, Vcgd. 3 t 
 
 
&BCT.-H.] DEFINITION OF A JPLANT. 43 
 
 want of locomotion, therefore, cannot, with pro- 
 priety, be regarded in a definition as a distinguish- 
 ing characteristic of vegetables. 
 
 I have already stated that Jungius mentions the 
 want of sensation as distinguishing plants ; an opi- 
 nion which Linnaeus also held : " Lapides crescunt," 
 says he, " vegetabilia crescunt et vivunt, animalia 
 " crescunt, vivunt, et sentiunt*," " Stones grow, 
 " vegetables grow and live, animals grow and live 
 " and feel." Although this opinion has been dis- 
 puted by several philosophers, and Sir J. E. Smith, 
 in his Introduction to physiological and systema- 
 tical Botany, puts the idea of vegetables being 
 sentient beings as an admissible supposition, yet 
 there is more reason for thinking that they are not 
 endowed with this principle, which seems to be the 
 peculiar attribute of animal life. We can scarcely 
 form any idea of an animal devoid of sensation ; 
 but the spontaneous movements which are ob- 
 served in some plants, and on which the opinion 
 of their sentient power is founded, may, perhaps, 
 be accounted for, independent of sensation. Sir 
 J. E. Smith, in support of his opinion, says, " Such 
 " a supposition accords with all the best ideas we 
 *' can form of the divine Creator; nor could the 
 " consequent uneasiness," adds he, " which plants 
 ^ must suffer, no doubt in a very low degree like- 
 
 Phil. Bat. 5. 
 
44 DEFINITION OF A PLANT. [LECT. II. 
 
 " wise, from the depredations of animals, bear 
 " any comparison with their enjoyment on the 
 " whole." Before perusing this passage of Sir J. E. 
 Smith's work, we thought this fanciful idea had 
 sunk into the grave with Dr. Darwin; and we 
 must acknowledge that our inflexible imaginations 
 have never yet been able so far to overcome the 
 suggestions of cooler judgment, as to lead us to 
 suppose that the general sum of enjoyment would 
 be increased by such a circumstance. It must, 
 however, be allowed, that the spontaneous move- 
 ments of some plants which we shall hereafter no- 
 tice, appear at first sight to be the effect not of 
 sensation only, but even of volition; and, although 
 the possession of that faculty by vegetables cannot 
 be proved, yet neither can it be completely dis- 
 proved. The experiments of M. Humboldt with 
 the galvanic pile upon those plants which are par- 
 ticularly irritable and are generally regarded as 
 possessing sensibility, tend, perhaps more strongly 
 than any observations that have been made on the 
 spontaneous movements of plants, to settle this 
 question. He did not succeed in rendering any of 
 them susceptible of the galvanic influence. Until, 
 therefore, further observations be made, tending 
 to confirm the opinion that vegetables are endowed 
 with sensation, or to disprove it completely, the 
 definition which mentions the want of it, as the 
 
LECT. II.] DEFINITION OF A PLANT. 45 
 
 distinguishing characteristic of plants, cannot be 
 regarded as correct. 
 
 M. Mirbel, in a late work, entitled, Trait 6 
 tfAnatomie et de Physiologic ^gdtales, has given 
 an opinion, which Sir J. E. Smith considers as con- 
 clusive on this subject. He observes, " that plants 
 " have the power of deriving nourishment from in- 
 " organic matter, which is not the case with ani- 
 a mals, who feed on animals and vegetables, and 
 " sometimes on both; but are never nourished on 
 " earths, salts, and airs. So that it should seem 
 " to be the office of vegetable life alone to trans- 
 " form dead matter into organized living bodies*." 
 This remark is, certainly, exceedingly ingenious 
 and plausible; but it contains an assumption 
 which cannot be admitted to the extent required ; 
 for, if by inorganic matter is to be understood 
 simple earths and salts, which do not form parts 
 of decaying organized bodies, the observation is 
 not just ; nor can we allow that airs are taken in 
 as food by plants. What soil can be found com- 
 
 * " C'est la faculte qu'ont les plantes de se nourrir de sub- 
 " stances inorganiques, faculte qui ne paroit pas exister dans 
 " les animaux : ils devorent des substances animales ou vege- 
 " tales, et quelquefois les unes et les autres ; mais jamais, ce 
 " me semble, ils ne se nourissent de terres, de sels, d'air et de 
 " gaz. Ainsi, les vegetaux doivent, pour condition premiere 
 " de leur existence, transformer la matiere brute en matiere 
 " organisec et vivante." Tonne i. p. 19. 
 
 4 
 
46 DEFINITION OF A PLANT. [u2CT. II. 
 
 posed of simple earths devoid of animal and vege- 
 table matter in which plants will grow? And it 
 is well known that the presence of a large quan- 
 tity of salts, even of those kinds which, in small 
 quantities, promote vegetation, is more likely to 
 kill plants than to serve as nourishment to them. 
 A plant, it is true, may be reared in pure water, 
 or in pure powdered flints moistened with water ; 
 but in this case the water is the support of the 
 vegetable ; and we know that many animals, the 
 Infusoria, for instance, are nourished and support- 
 ed apparently in water alone. As this fluid is the 
 universal solvent, whatever it contains in solution 
 may be taken up by the vegetable vessels ; and 
 the experiments of Sir Humphrey Davy have 
 proved that even distilled water may contain both 
 saline and metallic impregnations : hence we can 
 conceive from what source the alkalies, salts, me- 
 tallic oxides, and earths, even silex, which are 
 found in vegetables, have been derived; but that 
 these are directly taken in as nourishment by 
 plants is not more likely, than that lime, which 
 forms so large a portion of the animal structure, 
 is, in its uncombined state, the food of animals *. 
 
 * It is rather surprising that Sir Humphrey Davy, in his 
 late work on the Principles of Agriculture, adopts implicitly 
 the opinion of Mirbel, that saline substances form part of the 
 real food of plants ; particularly as he adds, " and supply that 
 " kind of matter which is analogous to bone in animals." Now 
 
LECT. II.] DEFINITION Otf A PLANT. 47 
 
 Salts serve to stimulate plants, and, by exciting 
 the action of their irritable fibres, promote their 
 health and growth ; part of them are taken up 
 along with the soluble vegetable matter contained 
 in the soil, and disposed of in the economy of the 
 plant, either in the simple state in which they were 
 absorbed, or forming new compounds, generally 
 neutral salts ; and this is regulated by the peculiar 
 nature of the plant, independent of any properties 
 of the soil in which it grows. The same effect is 
 produced on animals, by the saline matters taken 
 into their stomachs along with their food. Some 
 of the lower animals, as earth-worms and other 
 speciesof the vermes, feed on vegetable and animal 
 matters which have undergone decomposition, and 
 returned to that state in which they are generally 
 found in soils. Vegetables, therefore, in common 
 with these animals, although certainly in a more 
 striking manner, have the power of recombining 
 and assimilating into organized bodies those ma- 
 terials which the loss of vitality had allowed to be 
 separated by the chemical affinities of their consti- 
 tuents, or to be decomposed, but are incapable of 
 transforming matter, which has never formed any 
 part of organized bodies, into their own living- 
 
 we may ask the learned Professor, if phosphate of lime forms 
 a direct part of the food of animals, in order that bone be pro- 
 duced. 
 
48 DEFINITION OF A PLANT. [LECT. II. 
 
 organized substance. If these observations be 
 just, the remark of M. Mirbel cannot serve as the 
 means of distinguishing animals from vegetables ; 
 or of forming a correct definition of a plant. 
 
 The most satisfactory opinion I have met with 
 on this subject is that supported by Dr. Alston, 
 who was Professor of Botany at Edinburgh about 
 fifty years since, and who appears to have received 
 the idea from Boerhaave. He makes the distin- 
 guishing characteristic of vegetables to consist in 
 the want of an internal stomach, animals being 
 nourished by their internal, and plants by their 
 external surface. It is extremely difficult to find 
 any thing like an exception to this opinion ; nor 
 do we think that the proofs of it fail with respect 
 even to the Polypus, whose construction is so 
 simple, that it may be turned inside out like a 
 glove, without disturbing its ordinary functions *.. 
 Polypi seize insects that come near them with 
 feelers, which they spread out in the water, and 
 convey them by this means to their mouths ; and, 
 as their internal cavity may be regarded as one 
 entire stomach, the food is passed rapidly through 
 
 * It may not, perhaps, be unnecessary to observe, that a 
 Polypus is an aquatic animal, resembling in form the finger of 
 a glove, and, in structure, appearing to be made of particles 
 set in a gluey substance. Like those plants which can be slipped, 
 a Polypus may be cut into any number of pieces, and each di- 
 . vided portion become a new Polypus, a distinct animal. 
 
LttCT. II. j DEFINITION OF A PLANT. 49 
 
 every part of the animal, even to the extremities 
 of the feelers, which are also hollow. It is thus 
 bruised; the soluble parts are absorbed, and the 
 remainder is thrown out by the mouth, which is 
 also the anus of the Polypus. If a Polypus be 
 turned inside out, that which was the external 
 surface becomes now the stomach, and performs 
 the functions of it, but still the food is taken 
 within the animal; it is also taken at intervals 
 only, and must remain within the animal some 
 time to undergo the process of digestion, before any 
 part of it can be absorbed by the lacteals and car- 
 ried into the circulation : a Polypus, therefore, 
 cannot be said to be nourished in the same man- 
 ner as vegetables are, which is by continued ab- 
 sorption by the external surface. 
 
 If, as I suppose, no exception can be found 
 to this remark, the characteristic which it points 
 out as distinguishing animals and vegetables is 
 very striking, and may properly form the leading 
 feature in the definition of a vegetable: " A 
 " plant," I would therefore say, " is a living or- 
 " ganized body, which requires food and air for 
 " its support, grows, propagates its species, and 
 " dies: and differs from animals, in being nourish- 
 " ed by continued absorption by its external sur- 
 " face/* An objection to this definition has been 
 anticipated by Mirbel, in combating the opinion 
 of Aristotle and of Boerhaave, that plants are 
 
 VOL. I. E 
 
50 VITAL FUNCTIONS OF PLANTS. [iJSCT. .11. 
 
 animals turned outside in* " II est naturel," says 
 he, " de soup9onner que tout vestige de canal in- 
 " testinal finit par disparaitre dans les animaux in- 
 " fusoires*." But this is a mere conjecture; and 
 there is no good reason for supposing that these 
 animals have not an intestinal canal, although the 
 smallness and transparency of their bodies prevent 
 us from detecting it, even with the aid of glasses^. 
 
 Having endeavoured to give you a determinate 
 idea of a vegetable, let us now take a general 
 view of those functions which plants possess in 
 common with other organized bodies, that is, with 
 animals. 
 
 When a plant is examined with care, its struc- 
 ture is found, in many respects, to correspond with 
 that of the animal body, it is composed of solid 
 and fluid parts ; the former comprehending fibres, 
 which are endowed with elasticity and contrac- 
 tility, and vessels in which the fluids move. The 
 most perfect vegetables, however, differ from ani- 
 mals in structure, in having no stomach, heart, 
 brain, nor nerves ; but all these organs are not 
 
 * Elemens de Physiologic veg6tale, &c. t. i. p. U. 
 
 f For practical purposes, as Sir E. J. Smith observes, it is 
 sufficient for the student to know that he may always decide 
 whether " he has found a plant or one of the lower orders of 
 " animals, by the simple experiment of burning:*' the odour of 
 burning animal matter being so essentially different from that of 
 vegetable substances, as not to admit of being mistaken. 
 
LECT. II. j VITAL FUNCTIONS OF PLANTS. 51 
 
 found in every animal; for many of the lower 
 classes of animated bodies want one or more of 
 them. As is the case in animals, the organs with 
 which plants are furnished are always of the same 
 structure in every individual of the same species, 
 when in a natural and healthy state : and these 
 organs are also susceptible of the same impres- 
 sions from external agents, the circumstances being 
 in every respect equal, in every individual of the 
 same species. Thus any number of seeds of the 
 same kind of Lily will produce Lilies all resem- 
 bling each other in form and structure ; the same 
 number of parts will be evolved, and the unfolding 
 of them take place in the same manner. The dif- 
 ferences of soil, of situation, and of culture may 
 occasion varieties in colour and other unimportant 
 particulars, but the specific characters remain in- 
 variable. These facts are sufficient to prove that 
 plants are endowed with life, or possess the same 
 principle by which the existence of the organic 
 structure, the growth, and the propagation of the 
 species in animals are supported : but let us exa- 
 mine a little more closely those functions of vege- 
 tables which prove their vitality. Although vi- 
 tality cannot properly be defined, yet we know it, 
 when it is present in any object, by its effects, 
 which are never displayed by unorganized matter ; 
 and therefore we are accustomed to define it by 
 saying, it is " that property of matter connected 
 
 E 2 
 
52 VITAL FUNCTIONS OF PLANTS. [LECT. II. 
 
 " with organization, which animals and plants 
 " possess in common, of continuing life.' 1 Both 
 animals and vegetables communicate it to their 
 offspring. By viviparous animals it is communi- 
 cated to the foetus long before its expulsion from 
 the uterus; by the oviparous, to the punctum sa- 
 liens, which is afterwards the chick, before the egg 
 receives its shell ; and by vegetables, to the em- 
 bryo contained in the seed, long before this has 
 obtained perfection in point of size, and is sepa- 
 rated from the plant. In these instances the 
 functions of the new beings either immediately 
 commence, as is the case in the foetuses of vivi- 
 parous animals ; or they do not commence till the 
 necessary agents are present for evolving the proper 
 organs, as yet unformed or imperfect, as happens 
 in eggs and in seeds: but, in both cases, it conti- 
 nues for a definite time only, and is then lost. 
 During its continuance both animals and plants 
 preserve their organization, and resist those che- 
 mical attractions or affinities which subsist be- 
 tween the different component parts of their bo- 
 dies ; and which, immediately whejj life ceases, 
 act ; and, by dissolving the old combinations, pro- 
 duce new ones, by the processes of putrefaction 
 and fermentation, and render back their elements 
 to the inorganic kingdom. We do not mean, how- 
 ever, to assert that organized bodies do not admit 
 of chemical combinations, during life ; as it can- 
 not be denied that more complicated and diversi- 
 
LBCT. II.] VITAL FUNCTIONS OF PLANTS. 53 
 
 fied combinations are the direct result of the living 
 principle, than can be produced by the simple 
 power of affinity when it operates on dead matter. 
 The particular functions of vegetables that depend 
 on vitality are the germination of seeds, the nou- 
 rishment and growth of the vegetating plant, its 
 absorption, perspiration, and respiration, adapta- 
 tion to climate, and resistance of cold during 
 winter. 
 
 The seeds of plants, like the eggs of animals, 
 being endowed with vitality, many of them may be 
 kept for a very considerable time, even for a cen- 
 tury of years; and yet, when they are placed under 
 favourable circumstances, at a proper season, and 
 in a situation where they can receive a sufficient 
 supply of air, heat, and moisture, immediately 
 begin to germinate and grow. If any thing tend 
 to destroy this principle in the seed, instead of 
 germinating, when placed in a situation favourable 
 for germination, it rots ; for, although the vitality 
 which seeds thus possess does not depend on any 
 external circumstances, yet, it may be destroyed by 
 external causes. The time which it may remain 
 latent is not the same in all seeds: some will not 
 germinate unless they be put into the ground al- 
 most immediately after they be gathered ; whereas 
 leguminous seeds may be kept for ages, and yet 
 preserve their vegetative power. The vitality of 
 some seeds is indeed so permanent, that it pre- 
 
 E 3 
 
54 VITAL FUNCTIONS OF PLANTS. [LECT. II. 
 
 serves them for an indefinite period of time, when 
 under certain circumstances ; as when some of 
 the mucous-coated seeds, mustard or linseed, for 
 example, have been accidentally buried at a con- 
 siderable depth, and are again, after many years, 
 thrown upon or near the surface of the ground. 
 In this case, these seeds readily germinate, and 
 become as vigorous plants as if they had been the 
 produce of the foregoing year. It is owing to this 
 circumstance, that often, when forests are cleared 
 of the overshadowing trees, which had long pre- 
 vented the vegetation of any seeds in the ground 
 below them ; or when buildings are razed, and the 
 earth at their foundations turned up, plants sud- 
 denly appear, different from any in the immediate 
 neighbourhood, and even unknown by the oldest 
 inhabitants of the spot. If a seed, however, be 
 once exposed to the action of heat, air, and mois- 
 ture, in a situation adapted for its growth, it ger- 
 minates, and its vegetation cannot then be stopped 
 without destroying its vitality, and the seed of 
 course rots ; the continued application of the same 
 agents, which first called into action its powers of 
 life, being absolutely necessary for its future ex- 
 istence. 
 
 After the parts of a plant have been unfolded 
 from the seed, its functions depend altogether on 
 the vital principle with which it is endowed. It 
 selects from the soil its nourishment, digests and 
 assimilates it into its proper substance, and depo- 
 
LECT. II.] VITAL FUNCTIONS OF PLANTS. 55 
 
 sits in its body those secretions which render it 
 useful to mankind for economical and medicinal 
 purposes. The simple absorption of fluids by the 
 roots of plants might, perhaps, be explained on 
 mechanical principles ; but the circulation, or, 
 rather, progressive motion, of the sap, can only 
 be accounted for on the supposition that plants 
 are living beings. Various theories have been of- 
 fered to account for the ascent of the sap in plants; 
 but this is not the moment for criticising these dif- 
 ferent opinions ; it is only necessary to observe, 
 that the sap continues to rise during the life of the 
 plant, and ceases when it dies ; and that it ob- 
 viously does not depend on capillary attraction, or 
 any mechanical impetus independent of vitality. 
 If a plant in a flower-pot be kept for some time 
 perfectly dry, till vitality ceases, no supply of 
 water can again be taken up by its vessels, how- 
 ever favourable the temperature may be; for, in 
 this case, the plant having been deprived of one 
 essential agent, its vessels no longer act, and it 
 dies. Did the ascent of the sap, however, depend 
 on any other circumstance than the living action 
 of the vessels (which, I trust, we shall afterwards 
 be able to prove is not the case), it would nly be 
 necessary, in order to restore any decayed plant, 
 to supply it with moisture in a proper tempera- 
 ture. Dead plants imbibe fluids, it is true, but 
 they are not nourished by them; and the moisture 
 
 E 4 
 
56 VITAL FUNCTIONS OF PLANTS. [LECT. II. 
 
 only serves to hasten the process of decomposition. 
 When a plant has attained the natural term of its 
 life and dies, or when its death is occasioned by 
 lightning or any other accident, the absorbing 
 power of the roots and leaves is lost ; and the sap, 
 which is contained in the vessels, is evaporated and 
 dissipated ; which would not be the case did these 
 functions not depend on vitality. 
 
 To the living powers of vegetables we must 
 also revert to account for the changes of the sap 
 into the solid components, and the peculiar juices 
 of the plant. No mechanical principles can pro- 
 , duce these effects ; they are opposed to the che- 
 mical affinities which exist between the materials 
 composing the substance of the plant : nor can 
 they result from any cause, except from that prin- 
 ciple which, whilst it is present, gives life and mo- 
 tion to every being that is endowed with it ; and, 
 on being withdrawn, leaves the substance to the 
 control of those laws that regulate the combina- 
 tions of dead, inert, unorganized matter. It was 
 the opinion of Linnaeus and of many others, that, 
 although the greatest variety of plants may grow 
 at one time in the same field, yet that each of 
 them selects and takes up from the soil those par- 
 ticles of it only which are adapted to the peculiar 
 nature of their secretions; or that the soil con- 
 tained ready-formed all that is found in plants. 
 But there is no need of this supposition to explain 
 the great variety of secretions of plants retired 
 
LECT. II,] VITAL FUNCTIONS OF PLANTS. 57 
 
 in the same soil, if we admit that vegetables are 
 living beings. Is it more wonderful that plants 
 should elaborate the same nutriment into poisons 
 and wholesome food, than that venom is secreted 
 and lodged under the fangs of some species of 
 serpents, whilst nothing of the kind is possess- 
 ed by other reptiles that live on the same kind of 
 food ? In order to disprove that no such selection 
 takes place, it is only necessary to rear any num- 
 ber of different plants in water alone : each plant, 
 in growing, will assume the nature and possess 
 the qualities of the species to which it belongs, 
 whether that be poisonous or salutary : a proof 
 that the qualities of the secretions of plants, like 
 those of animals, are not dependent upon peculi- 
 arities of soil, but on the action of the vital prin- 
 ciple. 
 
 Although every vegetable is a living being, yet 
 all plants do not enjoy an equal share of vitality, 
 nor are they all equally tenacious of life. Some 
 plants die almost immediately, if they be deprived 
 of moisture; whereas others, particularly some of 
 the mosses, may be completely dried, ad pre- 
 served in this state for a considerable time, even 
 for years, and yet retain their vitality; so that the 
 application of moisture will again make them re- 
 sume their verdure and grow. 
 
 On the presence of the principle of vitality de- 
 pends the power of reproducing parts that are de- 
 stroyed. Thus, if a tree be cut down, and the 
 
58 VITAL FUNCTIONS OF PLANTS. [LECT. II, 
 
 root left in the earth, it will again shoot forth new 
 stems, branches, and leaves ; and if the bark of 
 a plant be partially cut away, it will be reproduced. 
 This power, however, is not possessed by every 
 plant, nor is reproduction observed to take place 
 in every part of any plant. All those plants which 
 may be regarded as compound beings (as trees, 
 for instance, each bud of which seems to possess 
 a distinct life), may have parts cut from them, 
 which, if stuck into the ground under favourable 
 circumstances, will throw out roots and grow, 
 and each piece become an entire plant, similar to 
 that from which it was cut. In some plants, even 
 the leaves possess such a degree of distinct vitality, 
 that any portion of a leaf, provided it contain 
 part of the margin, when stuck into the ground, 
 throws out radicles and becomes an entire and 
 perfect plant, resembling that from which it was 
 taken. The Bryophyllum calytinum is an ex- 
 ample of this fact. But those which are consi- 
 dered as simple plants cannot be much mutilated 
 without suffering. If the Cabbage, or head of a 
 Palm, for example, be cut off, the plant soon dies; 
 or if a Fir, or other resinous plant, be much prun- 
 ed or cut down, no new shoots are produced ; and 
 if a leaf of any plant be once mutilated, it never 
 again recovers that portion which it has lost. In 
 this respect plants do not differ from animals. If 
 a Polypus, and some kind of worms, be cut in 
 
 5 
 
LECT. II.] VITAL FUNCTIONS OF PLANTS. 59 
 
 pieces, each part, as happens with the slips or 
 cuttings of plants, becomes a perfect animal; and 
 jf part of a bone, or of a muscle, be taken away, 
 it is reproduced by the vital powers "of the animal; 
 but the cutis, like the leaves of plants, when once 
 destroyed, is never again restored. 
 
 Plants absorb and transpire watery fluids by 
 their surface. If a plant, or part of one, as the 
 branch of a tree, be placed in a humid air, as long 
 as either of them lives, it will absorb the moisture 
 from the air by its surface, and augment in weight. 
 On the contrary, in a dry air of an increased tem- 
 perature, it transpires fluid in the form of invi- 
 sible vapour, in the same manner as animals part 
 with what is termed their insensible perspiration. 
 The intention of this function of plants is evidently 
 to throw off the superabundant water, which is 
 necessary for keeping the nutriment absorbed by 
 the roots in a state of extreme solution ; but 
 which is no longer useful when the sap is about to 
 be exposed to the action of the air in the leaf, and 
 returned for the purposes of secretion and assimi- 
 lation. The powers of absorption of the roots, 
 therefore, must be regulated by the quantity of 
 perspiration thrown off by the leaves and surface 
 of the stems and branches ; and Dr. Hales found 
 by experiment that the quantity of transpired fluid 
 was rather more than equal to the weight of the 
 water imbibed by the roots. Plants., however, which 
 
fiO VITAL FUNCTIONS OP PLANTS. [LKCT. IK 
 
 have thick succulent leaves, as the Aloes, and are 
 natives of a warm climate, and dry arid soil, per- 
 spire very little, but absorb powerfully by the 
 whole surface of the leaves. That these functions 
 depend on vitality is evident, for both cease when 
 the plant dies. 
 
 Another function of vegetables depending on the 
 property we are treating of, is that which has been 
 termed their respiration. Air is as essential for the 
 existence of plants as of animals ; and, whether we 
 believe, with many philosophers, that they restore 
 the pure part of atmospheric air that has been 
 consumed by the breathing of animals, or join in 
 the opinion of others, who believe that they pro- 
 duce the same changes on it, to a certain extent, 
 as animals do, we know that it is during the life of 
 the plants only that any such effect is produced. 
 As the leaves are the principal organs by which 
 this function is performed, it is most vigorous 
 during the summer, while plants are clothed in 
 the full luxuriance of foliage ; and it is very much 
 diminished when the leaves drop in autumn, almost 
 ceasing in the state of torpidity of the plant in 
 winter. Still, however, as the vitality of the vege- 
 table then perpetuates its existence until the return 
 of spring ; the bare stem, and the branches, con- 
 tinue to operate the ordinary change on the sur- 
 rounding air, although in a very small degree ; 
 but when the leaves decay, and the plant 
 
LECT. II.] VITAL FUNCTIONS OF PLANTS^ 61 
 
 then, as is the case with animals, no further change 
 on the atmosphere is produced than is occasioned 
 by the process of decomposition. 
 
 Connected with this function of plants, and 
 depending on the same cause, is that power which 
 they possess in common with animals, of resisting 
 to a certain degree the alternations of temperature 
 of the atmosphere. Every animal and every 
 vegetable has a peculiar innate temperature, inde- 
 pendent of that of the surrounding air. The 
 power of the animal body in preserving this degree 
 in very low temperatures is truly astonishing; 
 nor is its power less in resisting the effects of great 
 heat. Dr. Fordyce, who was the first person that 
 accurately remarked this last property of animal 
 life in the human body, made several experiments 
 in heated rooms, assisted by Dr. Blagden, Sir Jo- 
 seph Banks, and some other gentlemen. In these 
 the rooms were heated to a degree far exceeding 
 any that can possibly take place in the natural at- 
 mosphere in any climate ; and as a clear proof that 
 it was the living principle alone which enabled 
 them to resist such extraordinary degrees of tem- 
 perature ; in one of the experiments, a beef-steak, 
 placed in the heated room with the persons trying 
 the experiment, was roasted in forty-seven minutes. 
 The power possessed by living vegetables of resist- 
 ing the changes of temperature of the external air, 
 cannot be supposed to be so great as that of ani- 
 
6*2 VITAL FUNCTIONS OP PLANTS. [LECT. IT. 
 
 mals. It is sufficient, however, to protect them 
 from the effects of frosts, that would otherwise 
 freeze the sap contained in the vessels of many of 
 them, and destroy their organization : for, we find 
 that plants live during frosts which freeze the 
 deepest lakes ; and dry up the moisture of every 
 substance not endowed with vitality. It is never- 
 theless true, that some plants may be even frozen 
 during winter, and yet be so tenacious of life as 
 to revive in the spring; but this extraordi- 
 nary circumstance is not peculiar to vegetable 
 beings, as a caterpillar, for instance, may be frozen 
 and yet live, after being thawed. The tender 
 shoots that contain much moisture, and sickly 
 branches, are however destroyed by severe frost : 
 for the vitality in the latter case is not suffi- 
 cient to preserve the innate heat ; and in the 
 former its power is not great enough to prevent the 
 freezing of the superabundant moisture contained 
 in the substance of the shoot ; and as all fluids 
 expand in the act of freezing, this effect tears 
 asunder and destroys the delicate vegetable vessels. 
 Nor can tender and sickly animals resist severe 
 frost more than vegetables, but are immediately 
 frost-bitten. When this happens, the part morti- 
 fies; and, although the vigour of the general habit 
 be supported, yet, the frost-bitten part can never 
 again be restored to its former state, but is sepa- 
 rated as a dead slough from the neighbouring 
 sound parts. The san.e effect is produced in a 
 
LKCT. It.] VITAL FUNCTIONS OP PLANTS. 63 
 
 plant ; for, if the newly evolved leaves of a tree be 
 attacked by severe frost, they also mortify, and 
 drop from the sound twig. Vegetables resist heat 
 also ; for, a vine which is nailed on a wall will feel 
 cool, when the wall can scarcely be touched on 
 account of its heat : and fruits hanging in the sun 
 remain cool, when a glass full of water placed in 
 the same situation is quickly heated*. Mr. John 
 Hunter found, by experiment, that while the 
 thermometer stood under 56 in the open air, the 
 temperature of plants, tried by placing the bulb 
 of the instrument within them, was always above 
 that degree, but under it when the weather was 
 warm. Plants are, however, very susceptible of 
 the impressions of heat ; and feel its effects, as an 
 agent acting on their vital energy, even partially ; 
 so that one part of a plant may be leafless, and in 
 a state of inaction or torpidity, whilst another part 
 is clothed with foliage. If some of the branches 
 of a vine, for example, which is growing on the 
 outside of a hothouse, be taken into the house, 
 these will be covered with leaves very early in 
 spring, whilst those that are exposed to the 
 weather remain naked, and in the same state as 
 other plants, growing in the open air, in that season. 
 
 * Mr. Forster, who sailed with Captain Cook, found the 
 ground near a volcano, in the island of Tanna, so hot as to raise 
 Fahrenheit's thermometer to 210 ; and, at the same time, 
 this spot was covered with flowers. 
 
64 VITAL FUNCTIONS OF PLANTS. [LKCT. II. 
 
 Vegetables require different degrees of tempera- 
 ture for the preservation of their vitality. The 
 plant that flourishes under the ardent beams of a 
 tropical sun, would quickly perish if exposed to 
 the keen air of a northern latitude ; while the 
 Norwegian Fir, which raises its luxuriant head 
 green amidst the waste of Arctic snows, would 
 sicken, drop its leaves, and stand a lifeless trunk, 
 if removed to the torrid zone. But living vege- 
 tables, as well as animals, gradually accommodate 
 themselves to change of climate ; although they 
 retain their old habits for some time after their re- 
 moval, and by slow degrees only are naturalized 
 to new situations. Thus a fruit-tree, for instance, 
 which has been reared in a hothouse, and after- 
 wards planted in the open air, will, in the fol- 
 lowing season, expand its buds at the same time 
 that it used to do, and so expose them to inevi- 
 table destruction ; but after a few seasons, the na- 
 tural habit of its species will overcome the acquired 
 one of the individual, and the buds will remain 
 shut up till the genial warmth of the returning 
 sun, in spring, swells and expands them into 
 leaves*. This power of plants, which naturalizes 
 them to different climates, has enabled human in- 
 
 * Rice, which is a native of the torrid zone, has gradually 
 travelled to Germany, where it is now cultivated ; but Rice 
 brought direct from the south of Italy will not vegetate in 
 Germany. 
 
. 
 
 LECT. II.] VITAL FUNCTIONS OF PLANTS. 65 
 
 dustry and ingenuity to diffuse more generally the 
 productions of every quarter of the globe over its 
 surface ; for, had this not been the case, the plants 
 of every climate must have always remained the 
 same as they were at the creation of the world. 
 
 As the vital energy of vegetables is supported 
 by the application of external agents, particularly 
 heat, the abstraction of these in part must neces- 
 sarily diminish the activity of the vegetable func- 
 tions. This is the case in winter, during which 
 season, plants, like some animals, remain in a 
 torpid state ; and, although they still live, yet the 
 powers of vegetation are at a stand ; and even in 
 those that retain their foliage and verdure, no vi- 
 sible increase of their parts takes place. That their 
 preservation during this period depends on an in- 
 herent living principle is obvious ; for, when the 
 severity of the season is sufficient to overcome its 
 preservative power, no renewal of their active func- 
 tions takes place at its termination : but, in general, 
 as soon as the animal creation begins to feel the 
 warmth of spring, the buds of trees swell, and pro- 
 trude their leaves, and the plant rapidly advances 
 in growth ; with the increasing warmth of the 
 summer sun the flowers are expanded^ and the fruit 
 arrives at perfection ; till, as it declines in autumn, 
 the leaves fall, and the state of torpidity is again 
 resumed with the cold of winter. 
 
 Thus I have endeavoured to prove that vege- 
 VOL. i. F 
 
66 VITAL FUNCTIONS OF PLANTS. [LECT. II. 
 
 tables, in common with animals, possess vital 
 energy, which distinguishes them from inert matter, 
 and displays itself by its effects. If we wish to 
 extend the inquiry beyond the examination of these 
 effects, and demand what vitality is ? we are forced 
 to pause, and acknowledge the inefficacy of human 
 means to unveil those mysteries which the Author 
 of nature chooses to conceal. We know that vi- 
 tality is attached to organization ; but it does not 
 depend on structure : it is not caloric, the cause of 
 heat, although with this agent it has the closest 
 possible connexion : nor is it chemigal affinity, for 
 it resists in organized bodies those combinations 
 which affinity produces among their components 
 when vitality ceases. The flights of imagination 
 fail us in forming any conjectures as to its nature ; 
 we search in vain for a solution of the question in 
 the schools of Philosophy; reason avails us nothing; 
 and we are forced to contemplate its effects in si- 
 lent admiration, and to regard it as an impulse of 
 the Divinity, breathed upon the organized part 
 of the creation, astonishing and incomprehen- 
 sible. 
 
 Another principle which vegetables possess in 
 common with animals, and which depends on life, 
 is irritability, or the susceptibility of being acted 
 on by external stimulants, so as to produce a change 
 in the parts, or the relative situation of the parts 
 of the body, \diich, without the impression thus 
 communicated, would not have taken place. Those 
 
LECT. II.] VITAL FUNCTIONS OP PLANTS. 67 
 
 agents which are considered as natural stimulants 
 to the animal body, as heat, light, air, and food, 
 act also on the irritability of the vegetable ; and 
 their moderate application is absolutely necessary 
 for the preservation of the life and health of a 
 plant. When they are withdrawn the irritability 
 accumulates, and the plant languishes ; when they 
 are applied in excess the vital powers are exhausted, 
 and the plant also languishes ; and if they be 
 withdrawn, and then again applied suddenly, and 
 in too great quantity, the plant dies, exactly in 
 the same manner as an animal who is killed by 
 indulging in a full meal after having been nearly 
 starved. 
 
 To bring forward examples in proof of the ex- 
 istence of this principle in plants, in this stage of 
 our inquiries, would be anticipating, our future 
 observations, nor could they be fully understood 
 without a knowledge of the structure of the dif- 
 ferent organs in which it is more peculiarly dis- 
 played; we shall, therefore, only observe generally, 
 that to it must be referred all the motions of plants, 
 both general and partial ; except such as depend 
 upon the agitation of the air, or winds, and other 
 mechanical causes, and which, like exercise to an 
 animal, are absolutely necessary for the preserva- 
 tion of the health and vigour of the vegetable. I 
 shall only now observe, that among the motions 
 depending on irritability are those observed in some 
 
68 VITAL FUNCTIONS OF PLANTS. [LECT. II. 
 
 leaves and flowers when touched ; the turning of 
 leaves to the light; the opening and closing of 
 flowers at a certain hour of the day, or, as it has 
 been termed, vigiliee florum ; and the sleep of 
 plants * ; each of which we shall minutely inves- 
 tigate in its proper place. 
 
 Plants, like animals, are destined to perform 
 their functions for a limited period only ; some live 
 for one season, others twice that period: the 
 Apple-tree flourishes through a century ; and the 
 Cedar is supposed to brave the tempests of a thou- 
 sand years : but the hand of Time sooner or later 
 presses upon all of them ; and without the aid of 
 external injury, their vegetative powers cease ; 
 and, sharing the fate of all organized beings, they 
 submit to decomposition, and crumble into their 
 primeval elements. 
 
 * Darwin (Phytologia, sect. viii. 4) ascribes these circum- 
 stances to volition ; an opinion which I shall have an opportunity 
 of combating in another place. 
 
LECT. III.] GENERAL SOLID COMPONENTS. 69 
 
 LECTURE III. 
 
 GENERAL COMPONENTS OF THE VEGETABLE 
 STRUCTURE. 
 
 IP any number of plants of the most diversified 
 forms and structure, be individually cut,, or divided 
 or torn asunder, each and all of them will be found 
 to consist of solid and fluid materials. A plant 
 may therefore, as far as structure is concerned, be 
 represented as a congeries of solids and fluids. 
 Whilst, however, regarding* it in this point of view, 
 we must always bear in mind that both constituents 
 are under the influence of the living principle; 
 that the fluid parts, often differing widely in 
 chemical properties, are not only retained within 
 certain channels, and kept from mixing with 
 each other ; b 4 ut are moved progressively by a 
 specific action of the solids through the whole body 
 of the plant ; and altered in their characters so com- 
 pletely, that the secretions which result have no 
 affinity whatever to the fluids imbibed from the soil 
 and the atmosphere from which they are formed ; 
 and that, as in the living animal body, waste and 
 repair are constantly going on in the vegetable 
 system. 
 
70 MEMBRANOUS TEXTURE. [LECT. III. 
 
 Under the solids are comprehended, i. The 
 general solid components of the vegetable organi- 
 zation ; viz. the membranous, the cellular, the 
 vascular and the glandular textures, the ligneous 
 Jibre, and the epidermis : ii. The organs necessary 
 for the preservation of the individual ; the root, 
 the trunk, the branch and the leafwiih their fulcra 
 or appendages : iii. The organs requisite for the 
 reproduction of the individual; the flower and 
 the fruit with their appendages : and, iv. Organs 
 which hold a kind of dubious character, being in a 
 certain degree both conservative and reproductive ; 
 bulbs, gems, and gongyli. 
 
 Under the fluids are comprehended the sap and 
 the proper juice ; both of which may be regarded 
 as general components. 
 
 Let us endeavour to acquire an accurate idea 
 of each of these parts, without adhering strictly 
 to the order in which they have been enumerated. 
 
 1. GENERAL SOLID COMPONENTS. 
 
 The first of these, the Membranous texture, is an 
 exquisitely thin, transparent, colourless, film-like 
 membrane or pellicle, which is found in every in- 
 dividual of the vegetable kingdom. Du Hamel, 
 and some other authors, have asserted that it is 
 composed of organic fibres, arranged parallel to 
 each other, and united by a glutinous substance ; 
 but, as Mirbel has justly remarked, " this is one 
 
LECT. III.] CELLULAR TEXTURE. 71 
 
 of those opinions by which the mind is amused, 
 when research is fruitless." Indeed, the nicest 
 microscopical examinations have not thrown any 
 light on its structure ; and we may safely aver that 
 no appearances of organization have hitherto been 
 detected in it. When placed under the microscope 
 in a moist state, it resembles the film of a soap- 
 bubble * ; but. as it can be examined only as form- 
 ing other textures, our observations must always be 
 liable to error. It is that component of the vege- 
 table structure, which constitutes its basis ; or 
 which, in its lax state, forms the cellular and the 
 glandular textures and the epidermis; a little con- 
 densed, the vascular texture, and perhaps, still more 
 consolidated, the ligneous fibre : consequently, it 
 enters into the whole of the solid materials of the 
 vegetable body. 
 
 The Cellular texture is formed from the mem- 
 branous. It presents, in the parts of a plant where 
 it is not compressed, the appearance of hexagonal 
 cells, resembling those of a honeycomb. Grew, 
 and some other botanical anatomists, had observed 
 these cells, and believed they were little bags or 
 utriculi lying contiguous to each other : he coin- 
 pares them to the bubbles on the scum of ferment- 
 ing liquor ; but, although the comparison be correct 
 
 * Mirbel asserts that it is " d'une epaisseur variable selon 
 " la nature particuliere des especes et 1'age des individus." 
 Elemcns de Physiologic vegetate, Partie l ere , p. 28. 
 
 F 4 
 
72 CELLULAR TEXTURE. [_LECT. III. 
 
 in some stages of the formation of the cellular 
 texture, yet it is incorrect, as far as regards its 
 fully organized state. Mirbel, who examined them 
 with more attention, first pointed out their real 
 nature. He discovered that they are similar to 
 the geometrical cells of a honeycomb, although 
 sometimes of a longitudinal figure, and that 
 the divisions of the membrane which forms 
 them are common to contiguous 
 cells (fig. a) ; that they communi- 
 cate with each other by means 
 of pores and slits, about the three 
 hundredth part of a line in diame- 
 ter (fig. b)*; and that through these 
 perforations the vegetable juices 
 they contain are slowly transfused. 
 The same author asserts also, that 
 these pores are surrounded with 
 borders, " petits bourrelets epais et 
 calleux ;" but this is doubtful. He 
 describes the perforations as being few and scattered 
 in the true hexagonal cells; but numerous and 
 arranged transversely in regular series, in the 
 longitudinal -f~. The membrane itself is so thin, 
 that, when examined through a microscope, with 
 
 * It must be recollected that, in these representations and 
 in all those of the vegetable internal structure which are to 
 follow, the parts are very highly magnified. 
 
 t Element de Phys. veget. Parlie l m , p. 29. 
 
LECT. HI,] CELLULAR TEXTURE. 73 
 
 the light obliquely thrown upon it, it appears 
 iridescent ; but, as it has been already stated, 
 its organization is too minute to be determined 
 by any magnifying power with which we are ac- 
 quainted. When put into water it is very quickly 
 reduced to a kind of mucilage. This solution, 
 however, takes place only when the vitality of 
 the part is extinct ; for, the cells in the living 
 plant are often turgid with aqueous fluids, and 
 yet they retain their proper consistence and 
 form. 
 
 The cellular texture, in one form or another, 
 enters into the composition of almost every vege- 
 table organ. It is dry in some parts, but in other 
 situations it receives and slowly transmits fluids ; 
 and in it, principally, the various secretions of the 
 plant are deposited. Thus, it is generally filled with 
 mucilaginous, resinous, oily, and saccharine juices; 
 but sometimes the cells contain only air. In the 
 bark of plants the cellular texture is found imme- 
 diately under the cuticle, filled with a resinous juice, 
 which is of a different colour in different species of 
 plants, but most frequently green. In this situa- 
 tion it is the seat of the colour of the bark, in the 
 same manner as the rete mucosum, or, more pro- 
 perly, the reticulated capillary membrane situated 
 under the human cuticle, is supposed to give the 
 colour to the skin ; the reddish white in the Euro- 
 pean, and the black in the African. The cells 
 
74 CELLULAR TEXTURE. - [l.ECT. III. 
 
 are filled with the same green juice in leaves, which 
 are composed of a layer of cellular substance 
 placed betwixt two layers of cuticle. The medulla 
 or pith of plants is, also, composed of these cells, 
 filled, in young and succulent plants and branches, 
 with water, or watery fluids ; but in older plants, 
 and in the trunks and branches of trees, not succu- 
 lent, they are generally empty. In the latter the 
 shape and structure of the cells are most conspi- 
 cuous, and easily observed. Thus, if a transverse 
 or longitudinal section of a twig of Spanish Broom, 
 in the second year of the growth of the twig, be 
 placed under the microscope, or even a common 
 lens, the pith of it displays in the most beautiful 
 manner the hexagonal cells, the transparent iride- 
 scent appearance of the membrane forming their 
 walls, and the situation of the communicating pores. 
 It is well seen also by the aid of the microscope 
 in the pith of many other plants. The petals of 
 flowers are almost entirely composed of cellular 
 texture, the cells of which are filled with juices 
 fitted to refract and reflect the rays of light, so as 
 to produce the brilliant and delicate tints with 
 which the pencil of Nature has embellished these 
 parts. In the same manner it enters into the com- 
 position of the stamens, the stigma, and even the 
 pollen or fecundating farina of the flower. The 
 fleshy parts also of succulent roots, and of pulpy 
 fruits, are formed of this cellular texture tilled 
 
LECT. III.] VASCULAR TEXTURE. 75 
 
 with different juices according to the nature of 
 the roots and the fruit. 
 
 When the cellular texture is compressed, the 
 cells are found forming nearly parallelograms, as 
 in the leaf-stalk of the Artichoke, in which they 
 have a somewhat tubular appearance ; and, by the 
 stretching of the membrane, the pores, which in 
 the hexagonal cells are arranged without any 
 order, are now very regularly disposed. The cells 
 are proportionally more abundant in herbaceous 
 plants than in trees ; and in the younger than in 
 the older branches. Senebier asserts that the par- 
 titions of the cells consist of a double membrane ; 
 but this is not capable of demonstration. 
 
 Such is the nature and appearance of the cel- 
 lular texture. There is every reason for believing 
 that it enters as a component into almost every 
 part of the vegetable structure ; and anatomy con- 
 firms the opinion as far as we have the means of 
 ascertaining the fact. There are indeed some 
 plants, as the Fuci and other marine vegetables, 
 which appear to be altogether composed of cel- 
 lular texture. 
 
 The next of the solids enumerated is the 
 Vascular texture. It consists of hollow tubes 
 of different forms and structure, which are 
 capable, like the vessels of the animal frame, 
 of conveying fluids. When a succulent stem 
 is cut transversely, fluids are seen issuing from 
 
76 VASCULAR TEXTURE. [ LKCT - ni - 
 
 different points; and, if the peculiar juices of the 
 plant be of a milky or coloured nature, as in 
 the Fig-tree or in any of the species of the genus 
 Euphorbia, they are still more clearly perceived 
 to issue from different points ; for instance, the 
 watery or colourless from one set, and the milky 
 or the coloured from another. This circumstance 
 leads us to conclude that the sap, or watery fluid 
 imbibed from the soil, is carried in one set of 
 vessels, and that the proper juices formed from the 
 sap by the vital powers of the plant, are conveyed 
 in another ; or, that there are conducting and re- 
 turning vessels : a fact which has been proved by 
 experiment, and which we shall afterwards fully 
 illustrate in speaking of the powers which move 
 the fluids in the vegetable body. 
 
 The minuteness of these vessels requires the aid 
 of the microscope for their examination ; and even 
 by its assistance as they are not easily seen, owing 
 to their coats being in many eases transparent, and 
 the fluids contained in them colourless, we are 
 obliged, in order to render them more evident, 
 to have recourse to coloured fluids, which are 
 readily absorbed when the cut ends of twigs or 
 branches are immersed in them ; and the course 
 of the vessels through the branch is thus marked 
 by the colour. This mode of filling the vegetable 
 vessels has been termed injecting, the intention 
 of the process being the same as that which is 
 
 2 
 
LECT. III.l VASCULAR TEXTURE. 77 
 
 aimed at by injecting coloured wax and mercury 
 into the animal vessels, when we wish to trace 
 their course. The most eligible fluids for this 
 purpose are decoctions of Brazil wood, and infu- 
 sions of the skins of black grapes ; and the plants 
 likely to yield the most satisfactory results to the 
 beginner, are the Periploca Grceca, and the Aris- 
 tolochia Sipho*. The plant or twig to be injected 
 should be cut with a very sharp knife, and its 
 divided end immediately placed in the coloured in- 
 fusion in a warm temperature : after a few hours the 
 colour, in plants favourable for the experiment, may 
 be traced into the leaves, the flowers, and even the 
 fruit. This discovers the course of the conducting 
 or adducent vessels ; and when the operation is 
 reversed, the twig being cut at its top, and in- 
 verted in the coloured fluid, we can trace that of 
 the returning or abducent vessels* By placing 
 transverse and longitudinal sections of twigs and 
 parts of herbaceous plants thus treated under the 
 microscope, we are able to ascertain the organiza- 
 tion of the coats of the vegetable vessels. Some 
 of the vessels, however, cannot be rendered more 
 visible by this means, as they refuse to admit 
 coloured fluids ; and therefore any knowledge of 
 
 * This species of Aristoloohia is a native of the Alleghany 
 mountains ; but it is now to be found in every botanical garden, 
 and in most of the nursery gardens around London. 
 
78 VASCULAR TEXTURE. [LECT. III. 
 
 their structure can be obtained only by means of 
 powerful microscopes. 
 
 Notwithstanding these facts, the existence of 
 a vascular system in plants has been altogether 
 doubted ; and the subject has given rise to much 
 controversial discussion. I might amuse you by a 
 detail of the opinions delivered on both sides of 
 the question ; but little would be gained by such 
 a display ; and it will be much more satisfactory 
 to you, to direct your attention to those facts only, 
 which have been clearly demonstrated and which 
 are generally admitted as correct. , 
 
 The Botanists to whom we are chiefly indebted 
 for the information we possess relative to the vege- 
 table vessels, are Mirbel and Mr. Knight. The 
 former examined them by means of microscopes 
 of great power, and developed their real structure ; 
 the latter made many experiments on them by 
 means of coloured fluids, which have thrown the 
 greatest light on the vegetable physiology. Let us, 
 therefore, take these two celebrated Phytologists as 
 our guides in this part of our inquiries. 
 
 The Vascular or tubular portion of the vege- 
 table structure composes a kind of net-work, 
 owing to the frequent communication or anasto- 
 mosis of the vessels with one another, which per- 
 vades almost every part of the plant. The parti- 
 cular vessels vary both in form and in the diameter 
 
LECT. III.J VASCULAR TEXTURE. 79 
 
 of their calibers. They are composed of the 
 membranous texture, are firm, comparatively thick, 
 and somewhat pellucid. Linnaeus, following Ges- 
 ner, admitted the existence of three descriptions of 
 vessels only, which he named from their supposed 
 uses. The first he called vasa succosa, because they 
 carried fluids ; the second, utriculi, on account of 
 their being receptacles for preserving the vegetable 
 juices; and the third, trachece, or air-vessels*. 
 Willdenow-f also arranges them according to their 
 supposed uses, into, 1. air-vessels vasa pneuma- 
 tophora; 2. adducent vessels v. adducentla ; 3. 
 reducent vessels v. reducentia ; and, 4. lym- 
 phatics v. lymphatica: but every arrangement 
 founded on the supposed functions of the vessels 
 must be liable to objections. I think it preferable 
 to adopt the arrangement of Mirbel, with some 
 little variations, as it is constructed altogether on 
 the forms of the vessels. He describes six different 
 kinds of vessels J; but the whole may be arranged 
 under the three following genera : 
 
 * "Constant vegetabilia triplicibus vasis: 1. Vasa succosa 
 " liquorem vehunt. 2. Utriculi alveolis succum conservant. 3. 
 " Trachea aerem attrahunt.'* Philos. Botan. 78. 
 
 f Vide Principles of Botany, trans. 236. 
 
 J " ], Les vaisseaux en chapelet ou moniliformes ; 2", les 
 41 vaisseaux poreux; 3, les vaisseaux fendus ou fausses trachees ; 
 "4, les trachees; 5, les vaisseaux mixtes ; 6, les vaisseaux 
 " propres." Elem. de Phi/s. veget. p. 31. 
 
80 VASCULAR TEXTURE. [LECT. III. 
 
 L Entire vessels. 
 
 2. Perforated vessels, 
 
 3. Spiral vessels. 
 
 1. The ENTIRE VESSELS are, as their names im- 
 port, simple tubes formed of imperforated mem- 
 brane. They are cylindrical ; and are generally 
 in bundles, regularly disposed in the cel- 
 lular part of the bark (fig. c). They are 
 found in the young shoots of almost every 
 kind of plant ; and in the fasciculated 
 state may be readily detected, and ex- 
 amined by the aid of magnifying-glasses, 
 in the leaf-stalk of the common Fern, in 
 the Arrow-head, Sagittaria sagittifblia, 
 and in the common Hemp. In order to 
 examine them individually, the bundles should be 
 steeped in spirit of turpentine for a few days, 
 by which means the vessels can be easily detached 
 from one another. 
 
 These vessels are intended to convey the proper 
 juices of the plant \ and are generally found filled 
 with oils, and resinous juices ; consequently, they 
 are more numerous in plants, the juices of which are 
 of a thick resinous nature; and these drying along 
 with the condensed vessel in the bark, are the 
 matters on which the medicinal virtues of barks 
 in general depend. They are described by Mirbel 
 under the name vaisseaux propres *, and are di- 
 
 * Element de Phys, vrg. Partie l erp , p. 31. * 
 
LECT. III.] VASCULAR TEXTURE. 81 
 
 vided by him into two species solitary and fasci- 
 culated. Those which he terms solitary, however, 
 are, in my opinion, improperly regarded as vessels, 
 being* merely oblong cells, simple receptacles of 
 secreted juices. 
 
 2. The PERFORATED VESSELS are cylindrical 
 tubes, the sides of which are pierced with minute 
 perforations variously distributed. They may be 
 divided, according to the character of the 
 
 j-i 
 
 perforations, into two species ; a. Cribri- 
 form vessels, the perforations of which are 
 simple pores, arranged in parallel series, 
 transversely and equidistant over the 
 whole surface of the tubes (fig. */, e). 
 Mirbel denominates them "poreux." He 
 asserts that each perforation is surround- 
 ed with an elevated border (bourrelet 
 saillant), as represented in fig. e ; an 
 appendage which I have never been 
 able to perceive; and observes, that they 
 must not be regarded as continuous tubes, 
 as they often separate, join again, sometimes dis- 
 appear altogether, and always terminate in cellular 
 texture. They are found in the substance of roots, 
 in the formed wood of stems, branches, leaf-stalks 
 and the central ribs of leaves ; and are most 
 numerous in hard woods, as of the Oak and the 
 Chestnut. Their pores are so extremely small, 
 that, in order to perceive them, a thin longitudinal 
 VOL. i. c 
 
82 VASCULAR TEXTURE. [LECT. Ill, 
 
 slice of the wood to be examined must be cut, and 
 placed in a drop of pure water under a powerful 
 microscope. It has not been accurately ascertained 
 what kind of fluids is contained in these vessels. 
 A modification of the perforated vessels, having 
 the appearance of a string of beads 
 (fig./,), is named by Mirbel vaisseaux 
 en chapelet, beaded vessels. It con- 
 sists, as it were, of united portions of a 
 porous tube, narrowed at the extre- 
 mities and divided from each other by 
 perforated diaphragms. This variety 
 of the perforated vessels is found fre- 
 quently in roots, and at the going off 
 of branches and the attachments of leaves, being, 
 says Mirbel, " intermediate between the large ves- 
 sels of the stem and those of the branches ; and it 
 is by their meq,ns," continues he, " that the sap 
 passes from the one set of vessels into the other*." 
 
 b. Annular vessels are so named from the per- 
 forations being transverse and oblong, as if the 
 tube were formed of rings, of the same 
 diameter, placed one above another, and 
 attached at some part of their edges, but 
 not touching throughout the whole circum- 
 ference. (Fig. g.) These vessels are in fact 
 porous vessels, with oblong transverse pores, 
 resembling in every respect, except in shape, 
 
 * Eltm. de Phys. vtgtt. 1** Partie, p. 31. 
 
 (flUK 
 
LECT. III.J VASCULAR TEXTURE. 
 
 the round pores of the last described 
 They are also surrounded by a border 
 (fig. /*), and convey resinous and oily 
 secretions. They are found in greatest 
 number in the less compact woody parts 
 of the plant. The centre of the majo- 
 rity of the species belonging to the family 
 of plants named Lycopodium contain a thick 
 cylinder, which is chiefly composed of vessels of 
 this kind. Ferns also inclose many of them, in 
 their woody threads ; and several other plants, 
 particularly the Vine, the wood of which is soft 
 and porous, contain them in great numbers. Mirbel 
 denominates them les fausses trache*es; but as 
 the analogy by which they are thus named is not 
 just, I conceive we are more correct in calling 
 them, from their structure, ANNULAR OR RINGED 
 VESSELS. 
 
 Each of these species of perforated vessels is 
 occasionally seen forming different parts of the 
 same tube ; or one portion of it may present the 
 cribriform characters, and another the annular. 
 
 3. The next set of vessels, the SPIRAL, has been 
 known to Botanists since the, time of Grew, who 
 was the first that gave his attention to the ana- 
 tomy of plants. They have been named vasa spi- 
 ralia, andjissurce spirales, from their appearance ; 
 and trachea? from their resembling the tracheae of 
 insects, and from an unfounded opinion that 
 
 G 2 
 
84 VASCULAR TEXTURE. [LECT. III. 
 
 they were the vegetable organs of respiration*. 
 They are the largest of the vegetable vessels ; and 
 in many plants their structure is visible to the 
 naked eye. Thus, if a leaf, or a green twig of 
 Dog-wood (Cornus sanguined), or of Elder (Sam- 
 bucus nigra}, or the stem of any of the Lily 
 tribe, or one of the fleshy scales of any bulb, 
 as, for example, that of the Squill, be partially 
 cut, then cautiously broken, and the divided 
 portions carefully drawn asunder, the spiral vessels 
 will be seen appearing like a screw, and their real 
 structure become apparent. They are formed of 
 a thread, turned in a spiral manner from right to 
 left ; as if, to use an illustration of Dr. Thomson, 
 a fine and slender (he should have added flat) 
 wire were wrapped round a small cylinder 
 of wood, so that the successive rings touch 
 each other, and then the cylinder be with- 
 drawn ; the form thus acquired by the wire 
 will represent the spiral tubes ~}~. (Fig. i.) 
 The thread of which they are formed is 
 elastic, opaque, silvery, shining, and flat ; 
 and in several plants, particularly the Ba- 
 nana (Musa Paradisiaca), it is sufficiently 
 strong to suspend the inferior portion of the 
 twig, or the leaf, if it be not very large ; 
 but there is no reason for believing, as 
 
 * Such was the opinion of Grew, Malpighi, Hedwig, and 
 Linnaeus. 
 
 f Thomson's Chemistry, 5th edit. vol. iv. p^ 336. 
 
LECT. III.] VASCULAR TEXTURE. 85 
 
 Willdenow and others have asserted, that it is 
 hollow, and forms a real vessel thus twisted in a 
 spiral manner; or, that the larger hollow tube 
 is an air-vessel, while the spirally twisted thread 
 is a vessel carrying fluid. For, if we consider the 
 smallness of the larger tube, and the flattened state 
 of the thread of which it is formed, the impos- 
 sibility of any fluid entering the smaller one, if it 
 really existed as a vessel, may be easily conceived. 
 According to Hedwig's observations, made with a 
 microscope which magnified 290 times, he found 
 that the apparent diameter of these air-vessels, as 
 he supposes them to be, is one tenth of an inch ; 
 their real diameter must, therefore, be the 
 290th part of the tenth of an inch, or the 2,900th 
 part of an inch. What then, I 
 would ask, must the diameter of the 
 supposed spiral vessel be, and what 
 fluid could be conducted through it ? 
 The thread is sometimes double 
 (fig. k) ; and Mirbel asserts, that 
 it is furnished with a glandular 
 border (fig. /). 
 
 These vessels are found in 
 great numbers in monocotyledonous 
 plants *, as in the centre of the ligneous threads 
 
 * These are plants, the x seeds of which have one lobe only ; 
 the term monocotyledon being a compound of the Greek word 
 /*ooj (monos), one, and x.o->v\v$uv (kotuledon), hollo\v. 
 
 G 3 
 
86 VASCULAR TEXTURE. [LECT. III. 
 
 which exist in the stems of Grasses, and in Palms. 
 They are numerous also in most herbaceous plants ; 
 and particularly in aquatics of a lax texture. They 
 are seldom detected in the root, and never in the 
 bark ; but are situated round the medulla of the 
 young shoots of trees and shrubs ; whence bundles 
 of them are given off,, and enter the middle rib of 
 leaves, to be distributed through them under their 
 upper surface. They have been detected, also, in 
 the calyx, or flower-cup, and other parts of the 
 flower ; and Gsertner asserts that they are evident 
 even in the seed-lobes. The spiral vessels, in their 
 course, proceed always in straight lines, without 
 any deviation; whereas all the other vegetable 
 vessels often take a curved direction. It is into 
 these vessels that coloured injections most easily 
 enter ; and when an annual twig of the Fig is thus 
 injected, they are seen in a transverse section of it, 
 like red dots around the pith, placed within an 
 external circle of the vessels, which contain the 
 succus proprius, or milky juice of the plant. 
 
 It cannot be affirmed that the varieties of form, 
 which we have pointed out in the vegetable 
 vessels, is of the same importance as the differ- 
 ence which exists in the structure of the arteries 
 and veins of animals. There are, indeed, some 
 plants in which three of the modifications of struc- 
 ture, according to Mirbel's observation, are found 
 in the same tube. In the Butomus unibellatus, 
 
LECT. Hi.] VASCULAR TEXTURK. 87 
 
 Flowering Rush, says that author, "I have seen 
 long portions of vessels present, at intervals, the 
 appearance of an unrolled trachea, a transversely 
 cleft vessel, and a porous vessel." 
 
 Besides these vessels, Hedwig imagined there 
 existed lymphatic, or absorbing vessels, opening 
 upon the cuticle, and forming a circle round the 
 exhaling pores : a doctrine, which has been adopted 
 by Willdenow and others ; but which Mirbel justly 
 combats, alleging " that the sides of the cells 
 which terminate in the cuticle, and the fragments 
 of which remain fixed to that pellicle when it is 
 detached, have been mistaken for lymphatic ves- 
 sels by Hedwig *." 
 
 Mirbel mentions another set of vessels, which 
 he denominates little tubes ; but they may rather 
 be regarded as tubular cells, than vessels, being 
 closed at the extremities. They resemble, very 
 much, stretched cellular substance, except that 
 the membrane composing them is less transparent, 
 and of a greater consistence. The solidity of 
 plants depends very much on the quantity and 
 density of these cells, which are filled with thick 
 and coloured, or thin and colourless juices, ac- 
 cording to the nature of the plants in which they 
 exist. 
 
 Such is the vascular system of vegetables, 
 
 * Elem. de Phys. veget. 1* Partic, p. 40. 
 
 c4 
 
88 GLANDULAR TEXTURE. [LECT. III. 
 
 As we do not intend, at present, to enter into 
 any account of the uses of the vessels we 
 have described, we will only observe, that as 
 all vegetables take up nourishment from the soil, 
 and change it into juices different from each 
 other, and which must be preserved from mingling 
 together during the life of the plant, we might 
 (a priori) suppose that plants must necessarily 
 possess a vascular system : microscopic anatomy 
 proves the fact, displays the numerous ramifica- 
 tions, and general distribution of the vessels : ob- 
 servation shows that their elongation increases the 
 bulk and growth of the plant, and that they per- 
 form the most important functions in the vegetable 
 system. I may here also remark, that whilst the 
 tubes, or vessels, which have been described, are 
 intended chiefly for the longitudinal progression of 
 fluids, the lateral transmission of the vegetable 
 juices is performed, perhaps solely, by organized 
 pores and slits, such as have been described in 
 the perforated vessels, and in the sides of the 
 cells. But the account of the manner in which 
 this function is performed, must be postponed for 
 our future consideration. 
 
 The structure of the Glandular texture, as 
 far as relates to the interior of the vegetable body, 
 is much more difficult of demonstration than that 
 of any of the general solid components which 
 have been already noticed : but, when the im- 
 2 
 
LECT. III.] GLANDULAR TEXTURE. 89 
 
 possibility of attaining an accurate knowledge of 
 the glands of the animal body, which are large 
 and visible to the naked eye, is considered, it will 
 not appear wonderful that our remarks on this 
 part of our subject are drawn rather from analogy 
 than from actual observation. When, however, 
 we reflect on the nature and diversity of the vege- 
 table secretions, and that plants possessing the 
 most opposite properties rise from the same soil, 
 there appears to be no medium by which the 
 absorbed aliment can be so altered in its characters, 
 except by that of a glandular system. I am 
 willing to admit that the simplicity of the vegetable 
 structure is astonishing ; and that effects are pro- 
 duced in plants, by means which are apparently 
 very inadequate, when we regard them with a 
 reference to the animal economy : yet, still, when 
 the eye glances over the number and variety of 
 vegetable products, there is much reason for sup- 
 posing, that the simple transfusion of fluids can 
 scarcely be sufficient for the production of these 
 changes. We know that the laws of chemical 
 affinity, in the temperature in which they take 
 place, are inadequate to the effect ; and, besides, 
 many of the changes produced, particularly those 
 which fit the sap to be assimilated into the sub- 
 stance of the plant itself, are directly contrary to 
 the laws of chemical affinity, which operate in 
 destroying these combinations, as soon as the vital 
 
90 GLANDULAR TEXTURE. [LKCT. III. 
 
 principle of the plant ceases to act. Although, 
 therefore, we cannot by demonstration prove the 
 existence of internal glands in vegetables, yet we 
 have the strongest analogical proof in favour of 
 the supposition that they do exist. The pores and 
 clefts of the cells and the vessels which have been 
 described are surrounded by opaque regular 
 borders ; and even the flat thread which forms the 
 spiral vessels is edged with a similar border. These 
 bodies are regarded by M. Mirbel as glands ; 
 and he conceives the opinion receives weight from 
 the circumstance of the mucilage, which is changed 
 into the organized tissue, being found always col- 
 lected in greatest quantity around those vessels 
 whjch are most studded with these opaque borders. 
 This supposition is extremely probable, and is one 
 of those which, if they cannot be confirmed, 
 cannot be positively denied. If, as we suppose, 
 vegetable glands exist, they must necessarily enter 
 as a general component into the structure of every 
 plant. 
 
 Besides the glands, the existence of which in 
 the interior of the plant, if not demonstrable is 
 too probable to admit of much doubt ; there are 
 also external bodies, which all Botanists have 
 agreed in considering as glands, and which, in 
 general, separate, as an excretion, some peculiar 
 fluid *. Thus, honey, or a nectarious fluid, is 
 
 * " Glandula," says Linnaeus, " est papilla humorem excer- 
 nens.*' Philosophia Botanica, 84r,- 6. 
 
LECt. HI.] LJGN f EOU8 FIBRE. 91 
 
 secreted at the base of the petals or coloured 
 floral envelopes, in the greater number of plants ; 
 on the stalks of others, a viscid substance is 
 thrown out ; and on some, little sharp bristles 
 are planted, which are -perforated, and through 
 which a very acrid fluid is ejected into the wound 
 which they make in the cuticles of animals. 
 Examples of the first are to be found in almost 
 all flowers ; we observe the second in the species 
 of the genus Silene, called Catch-fly, and in many 
 other plants ; and the bristles of the Stinging 
 Nettle supply a well-known instance of the last. 
 
 Of the structure of these glands, although 
 they are external, yet very little is known ; and 
 microscopes of the greatest magnifying powers 
 present them as masses of cellular substance only, 
 with vessels passing on to their centre, without 
 developing any other particular organization, 
 which might lead to the formation of a theory 
 explaining the mode in which they perform their 
 functions. These, however, are, in some degree, 
 obvious from their effects ; and afford more than 
 probability to the idea that vegetables possess a 
 glandular system. We shall have occasion to 
 point out, and explain, the particular forms and 
 functions of these external glands in different 
 plants, when we come to examine the parts on which 
 they are situated. 
 
 The Ligneous Jibre is a very minute, firm, 
 
92 LIGNEOUS FIBRE. [LECT. III. 
 
 elastic, semi-opaque filament, which, by its cohesion 
 with other filaments of the same kind., forms the 
 proper fibres, or layers of longitudinal fibres, that 
 constitute the grain or solid part of wood. It 
 enters, also, into the composition of another set 
 of layers, that traverse the longitudinal, named 
 divergent. It is intended to give support and 
 firmness to the vegetable body, and hence is found 
 in greater abundance in trees and other perennial 
 plants ; and according to the number of the ligneous 
 fibres in each bundle of layers and the force of 
 their cohesion, the wood of different trees possesses 
 a greater or less degree of hardness. But, 
 although wood is found of various degrees of 
 consistence, yet, as Count Rumford has suggested, 
 it is probable that the ultimate fibre is the same 
 in all plants*. 
 
 Whether the ligneous fibre be of original forma- 
 tion similar to the muscular fibre of animals, or 
 condensed membranous or cellular texture, or an 
 obsolete obstructed vessel as Hedwig supposes, 
 is yet undetermined. It is so intimately united 
 with the cellular texture containing the vegetable 
 secretions, that it cannot be procured pure for 
 examination, without the aid of chemical agents to 
 separate these adjuncts. If a thin shaving of well- 
 dried wood be first digested in boiling water, then 
 
 * Nicholson's Journal, vol. xxxiv. p. 319. 
 
LECT. III.] EPIDERMIS. 93 
 
 in alcohol, and lastly in ether, every thing soluble 
 in it will be extracted by these liquids, and the 
 insoluble part which remains be found to be com- 
 posed of interlaced fibres, easily subdivided and 
 having- some degree of transparency : these are 
 the ligneous fibres. They have neither taste nor 
 odour, and remain unaltered by exposure to the 
 atmosphere : but although insoluble in water, 
 alcohol, or ether, the fixed alkalies and mineral 
 acids dissolve and decompose ligneous fibre. The 
 relative quantity of this fibre in any plant may be 
 pretty accurately ascertained, by exposing a given 
 quantity of the wood to a moderate fire, in close 
 vessels, for a number of hours sufficient to convert 
 it into charcoal ; for, as the wood only becomes 
 charcoal and the other parts are dissipated, the 
 proportional weight of the charcoal obtained shows 
 the quantity of the ligneous fibre contained in the 
 wood. By experiments of this kind, carefully per- 
 formed on the wood of the Poplar, the Lime, the 
 Fir, the Maple, the Elm and the Oak, Count 
 Rumford ascertained that the quantity of ligneous 
 fibre in each of these trees was equal to nearly 
 nine twentieths of their wood in its natural 
 state *. 
 
 The Epidermis is that portion of the vege- 
 table structure which is exterior to all the others ; 
 
 * Gilberts Annalen der Physick, - xiv. p. 25; and Thomson's 
 System of Chemistry, 5th edit. vol. iv. p. 186. 
 
94 EPIDERMIS. [LECT. in. 
 
 at least to those which retain their vitality in the 
 vegetating state of the plant : or it is that part 
 which is interposed between the living organs of 
 the individual, and all extraneous substances. In 
 this respect it resembles the cuticle of animals ; 
 but Botanists have been too fond of tracing this 
 analogy, which has, not unfrequently, biassed 
 their observations, and led to erroneous conclu- 
 sions. It extends over the surface of every part 
 of the plant; from that of the delicate petal of 
 the flower, to that of the leaves, the branches, 
 the stem, and the root; but, except in young 
 stems and roots, it is not the exterior part of those 
 organs of the plant ; the coarse rugged surface 
 of older roots and stems being exterior to the 
 real epidermis. It is common to every kind of 
 plant, nor can we conceive that any one can 
 exist without it. Botanists, as I have already 
 stated, are very fond of drawing an analogy be- 
 tween the epidermis of plants, and the animal 
 cuticle ; and the resemblance, in many respects, 
 is conceived to be closer than it really is ; but 
 there is, nevertheless, in some circumstances a 
 very striking analogy. The vegetable epidermis 
 may be separated from the parts which it covers, 
 by raising it cautiously with a knife ; but this 
 is more easily effected by maceration and boil- 
 ing. It is more readily separated from the cellu- 
 lar substance it covers in the leaf, than in any 
 
LECT. III.] EPIDERMIS. 95 
 
 other part of the plant ; and for this purpose I 
 would recommend to the student the leaf of any 
 of the Lily tribe, before the stem shoots up ; or of 
 the Lettuce (Lactuca sativa}, or that of Sorrel 
 (Rumex acetosa) ; but even in these, some of the 
 cellular matter is always detached in separating 
 it ; and to this circumstance is perhaps to be at- 
 tributed the variety of opinions which phytologists 
 have advanced regarding its structure. 
 
 The epidermis appears at first of a green co- 
 lour on the young stems and branches of almost 
 all plants ; but it changes to different hues, ac- 
 cording to the age of the part it covers. Accord- 
 ing to Du Hamel, it is composed of fine, but 
 tough fibres, which are interwoven "together ; and 
 every where interspersed with pores, which per- 
 mit the mouths of the absorbing, transpiratory 
 and air vessels to open to the atmosphere. Com- 
 paretti also describes it as composed of fibres, in- 
 terwoven so as to form hexagonal meshes, the 
 areas of which are filled up with opaque or dia- 
 phanous vesicles, inflated as if extended with 
 air or water, and having a small black point in the 
 centre. Mr. Bauer, on the contrary, conceives 
 the structure to be altogether cellular, and vary- 
 ing in different plants*. My own observations 
 lead me to adopt the opinion of the elder Saussure, 
 
 * Tracts relative to Botany. Lond. 1805. 
 
96 EPIDERMIS. [LECT. in. 
 
 that the true epidermis is a fine, transparent, un- 
 organized pellicle *. The pores, by which the in- 
 sensible perspiration escapes, are so minute, that 
 they are quite invisible, and with difficulty permit 
 the passage of air through them. Thus, if an 
 apple be put under the receiver of an air-pump, 
 and the air withdrawn, the cuticle of the apple 
 will be lacerated by the dilatation of the air con- 
 tained in the pulp of the fruit. There are oblong- 
 pores also in the cuticle of herbaceous plants in 
 particular, as was first observed by Decandolle, 
 who named them cortical pores. The size of these 
 is considerably greater than that of the former ; 
 and varies in different plants. 
 
 The epidermis seems to be entirely destitute 
 of longitudinal vessels. In herbaceous plants, 
 and in young and succulent twigs, it is, with a 
 few exceptions, colourless and transparent ; the 
 apparent colour being produced by that of the 
 juices in the cellular substance immediately be- 
 neath it, in the same manner as that of the hu- 
 man cuticle is produced by the colour of the 
 capillary web which it covers, and which is filled 
 with different coloured fluids in different races of 
 men ; white in the inhabitants of the temperate 
 zones, and black, or brown, in those of the torrid 
 
 * Obs. stir VEcorce des Feuilles. 
 
LECT. III.] EPIDERMIS. 97 
 
 regions of the globe *. When the epidermis is 
 applied very closely to the cellular layer below it, 
 which is the case in herbaceous plants, and in the 
 young twigs of trees and shrubs, the greater por- 
 tion of the light is transmitted through the cuticle, 
 and reflected from the cellular layer, and not from 
 the substance of the cuticle ; so that the colour of 
 the herbaceous stem, or of the twig, is, in this 
 case, that of the cellular layer, and not of the 
 cuticle itself; yet in trees and shrubs, which an- 
 nually renew the cuticle, as the Plane, the Birch, 
 the Currant and many others, the epidermis, when 
 it begins to peel off, becomes more opaque and 
 does not transmit the light, but reflects it from its 
 own surface. Thus the old cuticle of the Plane is 
 dark coloured, while the new is of a light green 
 hue ; the stem of the Birch, from which layers of 
 epidermis are continually peeling off, is white, 
 while the young branches are brown ; and the old 
 branches of the Currant are dark brown, while 
 the young shoots are of a very light green hue. 
 In some plants, instead of being thrown off in 
 
 * " On peut done concevoir le corps reticulaire comrae 
 " un systeme capillaire general, entourant 1'organe cutane, et 
 " formant avec les papilles une couche intermediate au corion 
 " et a 1'epiderme. Ce systeme ne contient, chez la plupart des 
 " hommes, que des fluides blancs. Chez les negres, ces fluides 
 " sont noirs. Us ont une teinte intermediate chez les nations 
 " basanees." Bichat, Anat. Gcnerale, $c. tome 4 me , p. 657. 
 
 VOL. I. H 
 
98 EPIDERMIS. [LECT. HI. 
 
 plates^ or in layers, the old cuticle is reduced into 
 powder* 
 
 Although the epidermis is not cast off from 
 all plants in this manner, yet, it is constantly 
 renewed ; and, where it remains, the old cuticle 
 cracks as the diameter of the stem of the tree, or 
 of the branch, increases: it is then gradually 
 pushed outwards, and the accumulation of suc- 
 cessive layers, in this manner, forms the rugged 
 coats which characterize many trees^ as the Elm 
 and the Oak. This renewal of the epidermis in 
 vegetables is similar to what takes place in ani- 
 mals. The snake, for example, casts his skin an- 
 nually, as do also the crab, the lobster, the spi- 
 der and many other insects ; and the cuticle of 
 the human body often peels off, particularly after 
 some diseases, as scarlet fever for instance, and 
 on the application of acrid matters to the skin. 
 In animals, however, when destroyed, it is again 
 regenerated ; but in vegetables, this occurs on the 
 stems and branches of perennial plants only ; for 
 on annual plants, and on the leaf and flower, it 
 is not renewed after being destroyed. The ve- 
 getable epidermis is capable of extension ; but 
 this is less considerable than has been supposed ; 
 and as there is a constant renewal, there must be 
 a proportional increase or growth of its parts, so 
 that it is not simply extended to enable it to cover 
 
LECT. III.] EPIDERMIS* 99 
 
 a greater portion of surface ; but new cuticle is 
 added to produce this effect. 
 
 The use of the epidermis is to keep the parts 
 beneath it together ; and to regulate the perspira- 
 tion and absorption of the plant. It is calculated 
 also to defend the parts it covers from humidity; 
 for which purpose, it is covered with a waxy secre- 
 tion. The powers of the cuticle in regulating these 
 functions is fixed according to the nature of the 
 plant. In succulent plants, which require much 
 moisture to be retained in their leaves, the cuticle 
 is so constructed as to assist absorption, but rather 
 to prevent transpiration. Thus, if a leaf of the Aloe 
 be cut off, it will remain a very long time, even 
 when exposed to the sun's rays, before it shrivels ; 
 but, if in this state it be exposed to damp air, or 
 thrown into water, the absorption is so rapid that 
 it will regain its original plumpness and size in a 
 few hours. A fine proof of that overruling Wisdom 
 which fits every thing for the fulfilment of the 
 purposes of its creation : for, in this instance, 
 the Aloe being a native of a dry arid soil, and a 
 warm climate, it could not long exist if the per- 
 spiration from the surfaces of its leaves were con- 
 siderable, but on the contrary it draws a great deal 
 of moisture from the atmosphere by absorption. 
 Another use of the epidermis is to prevent the 
 destruction of the parts it covers : for, as it is in 
 the vessels of the inner bark, as I will afterwards 
 
 H 2 
 
100 EPIDERMIS. [LECT. nr. 
 
 demonstrate, that the greatest activity, irritability, 
 and degree of vital energy reside, if that part be 
 wounded to any considerable extent, so that the 
 external air gets access to it, exfoliation, and the 
 death of the part, and sometimes that of the whole 
 plant, follow ; the cuticle forming, as Sir J. E. 
 Smith elegantly expresses it, " a fine, but essential 
 66 barrier between life and destruction*." 
 
 Mirbel-f- combats the idea of the epidermis 
 being a distinct organ, and supposes it to be the 
 external layer of the cellular membrane con- 
 densed, and altered by exposure to the air and 
 light. But although I admit that the cuticle be 
 nearly the same as the parietes of the cellular tissue 
 which it covers, yet, it is nevertheless a distinct 
 organ. The simple exposure of the cellular mem- 
 brane will not form epidermis ; but, on the contrary, 
 when the cellular substance is exposed, it is more 
 apt to exfoliate ; and when the wound becomes 
 healthy, it is then only that cuticle is reproduced. 
 During this process the new epidermis proceeds 
 from the sides of the wound, gradually extending 
 over it, in the same manner as in a wound of the 
 human body. The very close connexion of the 
 epidermis and the cellular substance can be no 
 argument against our opinion ; for, although the 
 
 * Introduction to physiological and systematical Botany, 
 2dedit. p. 18. 
 
 f Eltmem de Pkys.^veget. l ere Partie, p. 35. 
 
LECT. III.] EPIDERMIS. 101 
 
 flakes of epidermis which are cast off annually 
 by the Plane tree, and some other trees, consist 
 of cellular substance also, yet, the cuticle is already 
 formed under the flakes before they fall, and 
 therefore it cannot be in these cases produced by 
 the action of the air, and light. On examination 
 of these flakes, the epidermis appears to be dis- 
 tinct from the plate of cellular substance which 
 separates with it. Mirbel himself, indeed, is 
 obliged to modify his objection, and adds, But, 
 although the epidermis of vegetables does not 
 resemble that of animals, and is certainly the 
 external part of the cellular substance, yet, it is 
 no less true that secondary causes modify its 
 nature, and it consequently becomes an organ 
 the functions of which are very distinct and im- 
 portant *. Such a concession is all that can be 
 demanded. That the human cuticle is a distinct 
 organ has never been denied, and yet we know 
 that it is equally without vessels and nerves. On 
 the same principle, therefore, the vegetable epider- 
 mis must be admitted to be a distinct organ ; and 
 
 * " Mais, quoique Pepiderme des vegetaux ne ressemble 
 " pas a celui des animaux, et qu'il soit forme certainement par 
 " la partid exterieure du tissu cellulaire, il n'est pas moins vrai 
 " que des causes secondaires modifient sa nature, et qu'il 
 " devient par le fait un organe dont les fonctions sont tres- 
 " distinctes et tres-importantes." Physiologic vegetate, vol. i. 
 p. 89. 
 
 H 3 
 
102 EPIDERMIS. [LECT. in. 
 
 the modifications of it in different plants are more 
 numerous than among animals. The illustration 
 of these varieties must be deferred, till we come 
 to consider the structure of the bark, of which 
 the epidermis is usually considered a layer. 
 
 Such are the principal solid components of the 
 vegetable body. Other solid matters certainly 
 enter into the structure of some plants ; but, as 
 those are not common to the vegetable race, they 
 cannot be classed amongst the general compo- 
 nents. Perhaps, also, all the parts which have 
 been examined may be resolved into modifications 
 of the membranous and cellular textures, which 
 might consequently be regarded as the only real 
 solid vegetable components ; but, although we 
 allow that the vessels, ligneous fibre, glands, and 
 epidermis most probably are composed of mem- 
 branous, or cellular texture, differently modified, 
 yet, as each of these parts possesses very distinct 
 functions, such a refinement would only throw 
 obstacles in our way towards the attainment of 
 truth; I have, therefore, considered it preferable 
 to regard them as distinct components. 
 
LECT. III.] THE SAP. 103 
 
 GENERAL FLUID COMPONENTS. 
 
 Vegetables, by their vital energy, increase in 
 bulk, and augment the quantity of solid matter 
 they contain, consequently the principles of the 
 solids must be contained in the particular fluids 
 which they select and imbibe from the soil ; but 
 in what manner the fluids are changed into solids, 
 and whether any of the solid matters be taken up 
 ready formed, or whether they result from a trans- 
 formation effected solely by the action of the 
 vegetable vessels ; are subjects of consideration 
 upon which, in the present stage of our inquiries, 
 it would be premature to enter. These fluids, 
 however, after being absorbed by the roots, enter 
 into and fill the cells and vessels of the plant, 
 and form a very considerable portion of the bulk 
 of the vegetable body. As soon as they enter the 
 plant, they constitute its SAP, or common juice, 
 to the nature of which, as it is one of the general 
 components of vegetables, we must now direct 
 our attention. 
 
 Were we about to examine the moving powers 
 by which the fluids selected from the soil, and 
 absorbed by the roots of plants, are carried for- 
 ward through the vessels, we would demonstrate 
 that although these moving powers operate at all 
 times during the life of the vegetable, yet, that 
 
 H 4 
 
104 THE SAP. [LECT. in. 
 
 their action is most energetic in spring and at 
 midsummer, at which periods, therefore, a much 
 greater quantity of fluid is found in the vegetable 
 vessels. As, however, the simple examination of 
 the sap itself is our present object, it is sufficient 
 to state the fact ; and to know that, at these sea- 
 sons, when an incision is made through the bark 
 and part of the wood of most kinds of trees, or a 
 hole is bored in the trunk, a fluid exudes in con- 
 siderable quantity. This is the sap, or common 
 juice. It is in the same situation, for the purposes 
 of the plants, as the chyle of animals is, while it 
 is yet in the thoracic duct, and before it is mingled 
 with the blood, and exposed in the lungs to be 
 fitted for the purposes of the animal. Neither is 
 in a proper state for yielding the various secretions, 
 and adding, by the process of assimilation, to the 
 growth of the plant, or of the animal ; but the 
 analogy goes no farther. In the animal, the di- 
 gestive powers of the stomach and the action of 
 the mesenteric glands so change the food taken 
 into it, that no chemical analysis of the chyle 
 produced from it could lead to an accurate know- 
 ledge of the kind of food, which had been em- 
 ployed by the animal ; but, in plants, the food is 
 already prepared in the ground before it is ab- 
 sorbed by the roots, and, therefore, were it pos- 
 sible to obtain the sap from the vessels very near 
 to the extremities of the roots, we should be en- 
 
LECT. III.] THE SAP. 105 
 
 abled to discover, with a considerable degree of 
 accuracy, the real food of plants *. This, how- 
 ever, cannot be accomplished ; and as the sap, in 
 its progress, dissolves some ready-formed vege- 
 table matter, which had been deposited at the end 
 of the former autumn, in the upper part of the 
 root and at the base of the stem, its original pro- 
 perties are thus altered ; and the farther the part, 
 which is bored in order to procure the sap, is 
 from the root, the more vegetable matter this 
 fluid is found to contain. This fact was first no- 
 ticed by Mr. Knight, who ascertained that, owing 
 to this deposition, the wood of the stem, and the 
 large branches of trees, have a greater specific 
 gravity, and contain more soluble extractive mat- 
 ter when cut down in winter, than in spring, or 
 early in summer : on this, account, although there 
 is reason for believing that the food of almost all 
 vegetables is the same, yet, the sap, in the state in 
 which we can obtain it, differs in different species 
 of plants ; and, therefore, no just idea can be 
 formed of its nature from the most accurate 
 analysis of it, when procured from any single 
 plant. Were it possible, however, to obtain the 
 
 * It has been supposed that the roots of plants absorb, in- 
 discriminatelyj all the soluble matter contained in the soil on 
 which they grow ; but were this the fact, many more sub- 
 stances would 5e found in the vegetable body, than have yet 
 been discovered in it. 
 
106 THE SAP. [LECT. HI. 
 
 sap completely free from the peculiar juice of the 
 plant, it would be very probably found nearly the 
 same in all plants. From an examination of it, 
 such as it can be obtained, we are enabled to 
 draw some general conclusions; and by comparing 
 the analysis of the sap of many different plants 
 together, we discover those components which are 
 most frequently present, and consequently form an 
 opinion, approximating to the truth, of the real 
 nature of the sap. 
 
 When a tree is wounded, in the manner we 
 have described, in the spring, it is said to bleed ; 
 and if the wound be considerable, and in the 
 principal stem, the tree being thus drained of its 
 fluid, soon dies *. Any quantity of sap may be 
 collected by this mode of wounding trees, and the 
 
 * When we reflect how early this fact must have been 
 known, it is remarkable that so. little progress has been made 
 in developing the power by which the sap is carried forward 
 through the plants. The rudest nations are acquainted with 
 the fact that trees bleed when wounded ; and from a know- 
 ledge of its consequences, the Asiatic nations, in their wars, 
 commit the greatest injuries which their opponents can suffer. 
 The Palms in Asia being as necessary for supplying the ordi- 
 nary food of the natives, as grain is in Europe ; when an 
 hostile army enters the territory of an enemy, they cut 
 notches with hatchets in all the Palms which they meet with ; 
 which occasions the sap, and the other juices of the plants to 
 run out ; and the Palms either die altogether, or are rendered 
 abortive for that season. 
 
LECT. III.] THE SAP. 107 
 
 less progress vegetation has made, it is obtained 
 in a purer state. It should, therefore, be drawn 
 very early in the spring, before the leaves expand, 
 and as near to the root of the plant as it can easily 
 be obtained, if we wish to examine its chemical 
 properties. 
 
 When the sap is thus drawn from a tree, it 
 usually appears nearly as colourless and limpid 
 as water, has scarcely any taste and no particular 
 odour. A phial containing a certain quantity of 
 sap weighs heavier than the same phial, contain- 
 ing an equal portion of distilled water ; so that the 
 specific gravity of sap is greater than that of 
 water. If it be kept for some time in a warm 
 place, it undergoes sometimes the acetous, at 
 other times the vinous, and in some instances even 
 the putrefactive fermentation. These differences 
 would indicate a great disparity in the compo- 
 nents of the sap of different vegetables ; but there 
 is every reason for thinking that they depend more 
 on the admixture of the proper juices, which, as I 
 have already stated, are always more or less mixed 
 with the sap, as we can obtain it ; and it is probable, 
 that the sap of different plants differs more in the 
 proportional quantity of these juices mixed with it, 
 than in the nature of its components. The rapid 
 vinous fermentation of some kinds of sap is taken 
 advantage of in warm climates for economical 
 purposed. From the top of the Cocoa-nut tree 
 
108 THE SAP. [LECT. in. 
 
 the natives of India extract the sap, mixed un- 
 doubtedly with the proper juice, by making an 
 incision with a sharp knife overnight, and suspend- 
 ing under it a vessel to receive the fluid as it 
 exudes. This liquor, next morning before the 
 sun is hot, is a pleasant, mild, cooling beverage ; 
 but before evening, it ferments and becomes pow- 
 erfully intoxicating. In Ceylon, arrack is distilled 
 from this fluid, which is named toddy ; ' and it, 
 also, yields a coarse black sugar, called jaggery. 
 As, however, in this case the sap is combined with 
 the proper juice of the tree, the extraordinary effects 
 of the rapid fermentation must, in a great degree, 
 be ascribed to it. It is to the same cause also, 
 as I before noticed, that we must ascribe the dif- 
 ference in different saps, particularly the saccha- 
 rine and acid qualities, which they sometimes pre- 
 sent even when newly drawn. Thus we are told 
 that sugar is extracted in the proportion of ten 
 pounds from every two hundred of the sap of the 
 Acer saccharinum,, Sugar Maple. But the sap is so 
 mixed with the peculiar secreted juices of the plant, 
 when it is drawn from the tree for this purpose, 
 that it can scarcely be considered as yielding the 
 sugar. According to the observations of Mr. 
 Knight, sap always contains a considerable por- 
 tion of air. It, also, differs in its specific gravity 
 according to the distance from the root at which 
 it is taken, the gravity increasing in the direct 
 
LECT. III.] THE SAP. 109 
 
 ratio of the distance, which appears in some degree 
 to arise from the solution of deposited matter in 
 its progress, but, perhaps, more from the transpi- 
 ration of the plant throwing off a large proportion 
 of the watery part of the matter taken up from 
 the soil. Such are the sensible qualities of sap ; 
 its chemical properties and composition are dis- 
 covered by tests and analysis by heat. I shall first 
 mention some experiments I made on the sap of 
 the Vine, and then detail the results of those made 
 on some other saps by Vauquelin a celebrated 
 chemist of the French school. 
 
 On the eighth of April, when the thermometer 
 was at 68, and a few leaves of the Vine, which 
 was the subject of experiment, had already ex- 
 panded, I cut off the extremity of the lowest 
 of the branches, and introduced the cut end of 
 the part which remained fixed to the Vine, into a 
 six ounce Apothecaries' phial. On the following 
 morning, about three ounces of a clear, limpid, 
 colourless fluid, like water, was found in it. It 
 had no perceptible taste, except a slight mucila- 
 ginous feeling on the tongue ; no odour ; and 
 weighed rather heavier than distilled water. On 
 pouring a little of the Tincture of Litmus into it, 
 it was very slightly reddened, thereby indicating 
 the presence of an acid *. The oxalic acid almost , 
 
 * Dr. Prout, who examined the sap of the Vine, found that 
 the specimen which he procured did not differ in specific gravity 
 from pure water ; nor did it alter Litmus paper. 
 
110 THE SAP. [LECT. m. 
 
 immediately rendered it milky, and threw down a 
 white precipitate. The acetate of barytes threw 
 down a white flocculent precipitate; and by acetate 
 of lead (Goulard's extract), a white curdy preci- 
 pitate was also produced. No change was effected 
 on it by the solution of ammonia, nor by that of 
 gelatin : nor was any dark hue communicated by 
 the sulphate of iron. The addition of alcohol to 
 this sap threw down a light flocculent precipitate, 
 of a mucous nature. The sulphuric acid added to 
 it, occasioned a slight effervescence, and evolved 
 the odour of acetous acid. The conclusions which 
 may be drawn from these appearances is, that this 
 specimen of the sap of the Vine contained acetate of 
 potash with perhaps an excess of acid ; carbonate of 
 lime, vegetable mucilage, some albuminous matter 
 and water. As no effect was produced by the addi- 
 tions of the sulphate of iron and the solution of 
 gelatin, we conclude that it contained neither tannin 
 nor gallic acid, and therefore possessed no astrin- 
 gent property : a proof that the sap which we tried 
 was pretty pure, for some of the secreted fluids of 
 the Vine are both very acid, and considerably 
 astringent. The small quantity of sap which was 
 obtained, owing to the rather advanced state of the 
 season, for such an experiment, prevented the pro- 
 portions of the different ingredients from being 
 ascertained. 
 
 M. Vauquelin, as I have already mentioned, 
 made the most interesting experiments, which 
 
LECT. HI.] THE SAP. Ill 
 
 yet, been attempted on sap. As he does not, how- 
 ever, mention the state of the trees, from which the 
 sap for his experiments was taken, the result of the 
 analyses affords some reason for believing, that the 
 sap was not in the purest state. He examined the 
 sap of the Elm, Ulmus campestris, collected to- 
 wards the end of April, the beginning of May, and 
 the end of May. The result of the first analysis 
 was, that 1039 parts of this sap consisted of 
 1027-904 of water and volatile matter, 9-240 of 
 acetate of potash, 1-060 of vegetable matter, and 
 0-796 carbonate of lime. The second analysis of the 
 sap collected at the beginning of May afforded a 
 greater proportion of vegetable matter, less acetate 
 of potash, and also less carbonate of lime : and 
 in the third analysis of that collected at the end 
 of May, the quantity of the acetate of potash was 
 still more diminished, and also that of the carbonate 
 of lime *. In all he found slight traces of sulphate 
 and of muriate of potash. From two different ana- 
 lyses of the sap of the Beech, Fagus sylvatica, 
 procured also at different periods of the same 
 season, he obtained water, acetate of lime, free 
 acetic acid, gallic acid, and tannin, with some 
 vegetable extractive and mucous matter -}-. In the 
 same manner he examined the sap of the Common 
 Hornbeam, Carpinus sylvestris, collected in March 
 and April, and found in it, acetate of potash, 
 
 * Annales de Chimie, t. xxxi. p. 21. 
 f Ibid, p. 26. 
 
112 THE SAP. [LECT. HI. 
 
 acetate of lime, sugar, mucilage, vegetable ex- 
 tract, and water. In the sap of the Common 
 Birch, Betula alba, he found acetate of lime, 
 acetate of potash, acetate of alumina, sugar, vege- 
 table extract, and water. In all the specimens thus 
 analysed the quantity of vegetable matter was 
 found to be greater in the sap drawn late in the 
 season, than in that collected at an earlier period 
 of it. 
 
 If we are to consider these results of Vauque- 
 lin's experiments as pointing out the real composi- 
 tion of sap, we can gain no information from his 
 labours ; as from the results of them we should 
 suppose that every different kind of tree must 
 have sap of a description peculiar to itself, which, 
 both the analogy of the animal kingdom, and the 
 knowledge we have of the nature of soils, inform 
 us cannot be the case. It is probable that the 
 water, the acetate of potash, and the carbonate of 
 lime, are taken up from the soil, and enter as general 
 constituents into the composition of sap ; but the 
 mucilage, the sugar, the extractive, the gallic acid, 
 the tannin, &c. are undoubtedly produced by the 
 vegetable system itself, and must, therefore, vary 
 in different plants. As we shall afterwards find 
 that all the productions of the vegetable system 
 can be resolved into carbon, hydrogen, and oxygen ; 
 each production' differing in its composition from 
 another in the proportion only of its components ; 
 it is easy to comprehend that, as from the water 
 
LECT. III.] THE SAP. 113 
 
 the hydrogen and oxygen may be obtained, and the 
 carbon from the acetate of potash and carbonate 
 of lime ; Vauquelin was authorized in concluding 
 that the acetate and carbonate, which are found in 
 a diminished quantity in sap drawn at an advanced 
 season, may be decomposed by the vital action of 
 the growing plant, and the carbon they yield with 
 the hydrogen and oxygen go to form the vegetable 
 matter. But although the acetates are found in 
 soils, yet they are not in any considerable quantity, 
 nor sufficient to supply all the carbon wanted for 
 the purposes of plants : it is, therefore, probable 
 that if sap could be examined in its purest state, 
 it would be found to consist of water, holding car- 
 bonaceous matter in solution, acetate of potash, 
 carbonate of lime, and now and then some siliceous 
 and aluminous particles, suspended in the so- 
 lution, and of sufficient minuteness to enter the 
 mouth of the absorbents of the root. It is pro- 
 bable, also, that there is little difference in the 
 pure sap of all plants ; but as the first changes 
 take place undoubtedly in the roots, and the modi- 
 fying power of these parts must be different in 
 different kinds of plants, the changes which occa- 
 sion the varieties of the sap, are sooner produced 
 in some plants than in others. On these differences 
 of the ascending fluid, however, the secretions 
 certainly do not depend ; for, if that were the case, 
 the grafted branch would not bear fruit and leaves, 
 
 VOL. I. I 
 
114 THE SAP. [LECT. in. 
 
 and have secretions deposited in its cells similar to 
 those of the parent, but to those of the stock. We 
 know, however, that this is not the case ; for, if the 
 branch of a Pear-tree be engrafted on an Apple-tree, 
 the Pear branch will produce leaves, flowers, and 
 fruit, and have the new wood formed on it exactly 
 the same as the Pear-tree from which it was cut, 
 although the first modifications of the nutriment 
 imbibed by the roots of the Apple stock are dif- 
 ferent from those of the parent Pear : but as soon 
 as it arrives at the secreting organs of the Pear 
 branch the alterations it undergoes are exactly the 
 same as if the branch had remained attached to its 
 parent stem ; and consequently the wood, leaves, 
 flowers and fruit, will have the characteristics of 
 its original. 
 
 The modifications which take place in the roots 
 of plants, throw considerable obstacles in the way 
 of obtaining a perfect knowledge of this part of 
 the vegetable economy; for, to obtain such a 
 knowledge of the nature of sap would require an 
 examination of that fluid in a greater number of 
 different species of plants, than the opportunities, 
 and the period of any life, permit. All that we 
 can aim at, therefore, in the present state of 
 our knowledge, is the formation of a probable 
 hypothesis, rather than the attainment of truth 
 deduced from certain experiments. In this mode 
 of viewing the subject, we may regard the sap 
 
LECT. III.] THE SAP. 115 
 
 of plants as consisting of water which is its prin- 
 cipal component, carbonaceous mattery acetate of 
 potash, and carbonate of lime*; which ingredients 
 are decomposed by the vital powers of plants, and 
 new combinations of their constituents produced 
 by the same powers, so as to form the different 
 parts of which a plant consists. The large portion 
 of vegetable matter contained in the first sap, as 
 we have already noticed, must have been previ- 
 ously deposited in the cells of the root, and taken 
 up by the water of the sap in its progress upwards : 
 and air which is also found in sap, as Mr. Knight 
 has demonstrated, is either the produce of vege- 
 tation, or is taken in by the roots dissolved in the 
 water of the soil-f~. 
 
 Such is the nature of the sap. In spring and at 
 midsummer it forms a large portion of the vegetable 
 body ; and is carried forwards through the vessels, 
 with an impetus sufficient to raise it to the summits 
 of the highest trees, until arriving at the leaves, in 
 
 * The enumeration of these ingredients as the general com- 
 ponents of sap, cannot be objected to because many other 
 saline and earthy matters are occasionally found in sap ; those 
 depending altogether on local circumstances affecting the soil. 
 
 f Sir H. Davy, in his Lectures on Agriculture, has adopted 
 the opinion of Feburier, that the sap is found in two states ; one 
 kind in the vessels of the alburnum, containing chiefly saccha- 
 rine matter, mucus and albuminous matter, and another in the 
 bark, containing tannin and extract ; but I am not inclined to 
 regard any juice found in the bark as ascending sap ; and) there- 
 fore, cannot subscribe to this opinion. 
 
 i 2 
 
116 GENERAL FLUID COMPONENTS. [LECT. III. 
 
 which it is exposed to the action of the air, and 
 light, the great quantity of water it contains be- 
 comes no longer necessary, and is thrown off by 
 perspiration ; whilst the succus proprius, or pecu- 
 liar juice of the plant, from which all its secretions 
 are formed, is produced by the changes resulting 
 chiefly from this exposure. We have, therefore, 
 next to proceed to examine the nature of this pe- 
 culiar juice, as one of the general components of 
 plants. 
 
 GENERAL FLUID COMPONENTS THE PROPER JUICE. 
 
 I should be anticipating the inquiries we have 
 to make into the physiology of leaves, were I now 
 to attempt to explain to you how the sap is con- 
 veyed into these organs, to be exposed to the action 
 of light and air ; or, by what means those changes 
 are effected in them, by which it is converted into 
 the proper juice, succus proprius : at present we 
 have to examine this fluid merely as a general 
 component. It is, however, necessary to remark, 
 that although we may admit with Malpighi that 
 the proper juice is to the vegetable system, what 
 the blood is to the animal, yet, the functions by 
 which it is prepared from the sap must be modified 
 in different kinds of plants, since it exhibits some 
 peculiar characteristics in each kind. 
 
 When a plant is cut through transversely, the 
 proper juice is seen issuing from both divided sur- 
 
LECT. III.] GENERAL FLUID COMPONENTS. 117 
 
 faces, but in greatest quantity from the open ori- 
 fices of the divided vessels in the part farthest from 
 the root ; a fact which is ascribable to the progres- 
 sion of the proper juice being invertedly to that of 
 the sap, or from the leaves towards the roots. It is 
 very often mixed with sap, and cannot be distin- 
 guished from it by colour ; but in many instances 
 it is coloured or milky. Thus, if a twig of any of 
 the species of Spurge (Euphorbia) be cut, the proper 
 juice issues from the wound in the form of a 
 resinous milky emulsion, and may be obtained in 
 considerable quantity. This juice in the majority of 
 plants is, as I have said, colourless ; it is, however, 
 yellow in some, as in the Celandine (Chelidonium); 
 red in others, as in the Bloody Dock (Rumex san- 
 guinea) and the Logwood tree (Hsematoxylon) ; 
 deep orange in the Artichoke (Cynara Scolymus) ; 
 white, as in the Spurges (Euphorbia), the Dande- 
 lion (Leontodon Taraxacum)., the Fig (Ficus), 
 &c. ; blue in the root of Pimpernell (Pimpinella 
 nigra) ; and green in the Periwinkle (Vinca). The 
 colour is sometimes changed by the exposure of the 
 exuded juice to the air. Thus Opium, which is 
 the proper juice of the white Poppy, is white and 
 milky when it exudes from the incisions made in 
 the plant for the purpose of obtaining it; but 
 changes to a yellowish brown hue by exposure to 
 the air. The plantule also of the French or Ha- 
 ricot Bean, when wounded, emits a reddish proper 
 
 i 3 
 
118 GENERAL FLUID COMPONENTS. [LECT. III. 
 
 juice, which after being exposed to the air for a 
 short time assumes a deep indigo blue tint : and 
 the juice which exudes from incisions in the leaves 
 of the Soccotrine Aloe, yields, by simple exposure, 
 according to the statement of M. Fabroni, a very 
 deep and lively purple dye, so permanent, and re- 
 sisting so completely the action of acids, alkalies, 
 and oxygen gas, that he thinks it may be used as 
 a pigment in miniature painting ; or as a dye for 
 silk, which it will effect without the use of any 
 mordaunt*. 
 
 It is necessary to mention that Mirbel, and 
 some other Botanists, have fallen into an error, in 
 confounding together the proper juice, and the 
 secretions of plants. It is from the proper juice 
 that the secretions are formed ; but it must un- 
 dergo another elaboration, something similar to 
 that which the blood of animals undergoes in their 
 glands, before it is changed into the different se- 
 cretions ; and assimilated into the substance of 
 the plant. Thus, both essential and aromatic oils 
 are found in some parts of the same plant ; muci- 
 lage, resin, tannin, extract, acids and alkalies, and 
 even silica, in other parts ; but these various pro- 
 ductions cannot be considered as the proper juice : 
 they are secretions formed from it. The proper 
 juice of plants is, therefore, " that changed state of 
 
 * Monthly Mg. 1798. 
 
LECT. III.] GENERAL FLUID COMPONENTS. 119 
 
 " the sap, after it has been exposed to the air, and 
 " light, in the leaf, and is returning from it to 
 " form the different secretions." The organs by 
 which the secretion is performed are probably 
 glands, which we have already endeavoured to 
 prove exist in vegetables ; and the secreted fluids 
 themselves are deposited in cells in different parts 
 of the plant, particularly in the bark, and the 
 roots ; these parts acquiring different medical vir- 
 tues, from the matters thus lodged in them. 
 
 It is almost as impossible to obtain the proper 
 juice of plants free from sap, as it is to procure 
 the sap free from the proper juice ; this, however, 
 in the season in which it can be obtained in most 
 abundance, is not so liable to be diluted or mixed 
 with sap as at other times ; and therefore it is in 
 the warmest times in summer, that it ought to be 
 taken for the purpose of examining its properties- 
 Some naturalists have, rather fancifully, drawn a 
 very close analogy between it and the blood of 
 animals. Thus Rafn, with a microscope magnifying 
 135 times, supposed that he could detect round 
 globules, resembling the red globules of the blood, 
 swimming in a clear fluid, in the juice of Euphorbia 
 palustris; and Fontana thought he observed them 
 in the sap of Rhus toxicodendron. But such obser- 
 vations, which are often the effect of optical decep- 
 tion, are of little value, even admitting their va- 
 lidity, in a physiological point of view. In an 
 
 i 4 
 
120 GENERAL FLUID COMPONENTS. [LECT. III. 
 
 accurate examination of the proper juice of plants, 
 Mons. Chaptal found that in no two kinds of plants 
 does it agree as far as its sensible qualities are con- 
 sidered ; but as it is in the leaf that the change from 
 sap into the proper juice occurs, so its sensible 
 qualities are modified according to the action 
 which takes place in that organ ; and that this 
 should differ is not surprising if we consider the 
 great difference of the structure of leaves. In one 
 particular, however, Chaptal found that all the 
 specimens he examined agreed. When he poured 
 into them oxygenated muriatic acid, a very con- 
 siderable white precipitate fell down ; which had 
 the appearance of fine starch, when washed and 
 dried, and did not change when kept for a length 
 of time. It was insoluble in water, and was not af- 
 fected by alkalies. Two thirds of it were dissolved in 
 heated alcohol ; and these were evidently resinous, 
 as they were again precipitated from the spiritous 
 solvent by water. The third part, which continued 
 insoluble in both alcohol and water, was found 
 by Chaptal to possess all the properties of the 
 ligneous fibre. In the seed lobes a greater quan- 
 tity of this woody fibre was found than in the 
 proper juice of the plant itself; a fact which ac- 
 counts for the rapid growth and increase of parts 
 of the young plant, before the roots are able to 
 take up from the earth the principles of nutriment. 
 The proper juices of plants, both in the seed, and 
 
LECT. III.] GENERAL FLUID COMPONENTS. 121 
 
 in the perfected plant, contain nourishment al- 
 ready properly adapted to be immediately assi- 
 milated into the substance of the plant. But this 
 preparation takes place, either during the time, or 
 after, the sap has been exposed to the action of the 
 light and air in the leaf; as no woody fibre is 
 found in the ascending sap, although the prin- 
 ciples of it are undoubtedly contained in that fluid. 
 A new chemical combination of these principles 
 takes" place ; but how this is effected, or by what 
 means the change is produced, we know not ; and 
 it is one of those mysteries of nature from which 
 human ingenuity will never perhaps be able to 
 remove the veil. In the same manner the blood 
 of animals contains the components of the mus- 
 cular fibres already formed ; and an assimilation 
 of it is constantly going on, without our being able 
 to perceive it, or even to form the most distant 
 conception of the manner in which it is performed. 
 The elementary principles of the proper juice 
 of plants and of the sap are the same ; but differ 
 in the relative proportions. These principles are 
 carbon, hydrogen, and oxygen. The same prin- 
 ciples, differently modified, form all the secretions 
 and the solid materials of the plant itself. The 
 extraneous ingredients which some plants are 
 found to contain, as part of their substance, such 
 as the alkaline and neutral salts, metallic oxyds, 
 silex and other earths, are probably obtained ready 
 
122 GENERAL FLUID COMPONENTS. [LECT. III. 
 
 formed in the soil, in a state of division sufficiently 
 minute to be suspended in water, and drunk in by 
 the absorbent vessels of the roots. This is in some 
 degree proved by the effect of change of situation 
 on plants which naturally grow near the sea. 
 Most of these plants, when burned, yield soda ; 
 but, when they are removed from the sea-shore, 
 and cultivated in an inland situation, potash in- 
 stead of soda is procured from their ashes. 
 
 As the sap undergoes the same exposure to the 
 air and light in all plants, and one product only 
 can be formed in each plant by this exposure, the 
 difference of the proper juice in different plants, is 
 a strong argument in favour of the existence of 
 vegetable glands, independent of the undeniable 
 proof afforded by the formation of the very dif- 
 ferent products, which are deposited in different 
 parts of the same plant. Unless there were glan- 
 dular organs, one product only could be produced 
 in each plant by the function of the leaves, and the 
 action of light and of air on the sap. The secre- 
 tions of plants formed from the proper juice are 
 very numerous, and known under the names of 
 gum, fecula or starch, sugar, gluten, albumen, 
 gelatin, caoutchouc, wax, Jixed oil, volatile oil, 
 camphor, resin, gum resin, balsam, extract, tan- 
 nin, acids, aroma, the bitter, the acrid and the 
 narcotic principles, and ligneous Jibre. These are 
 found in different parts of plants without any uni- 
 
LECT. III.] GENERAL FLUID COMPONENTS. 123 
 
 fonnity of distribution ; and although so nume- 
 rous and different from each other in their sen- 
 sible qualities and chemical properties., yet are they 
 all composed of different modifications of the same 
 principles, carbon, hydrogen, and oxygen. Thus 
 100 parts of gum, according to the experiments 
 of Gay Lussac and Thenard *, consist of 
 42.23 of carbon, 
 
 6.93 of hydrogen, and 
 50.84 of oxygen, the oxygen and hydrogen 
 
 being nearly in the same relative 
 
 100.00 proportions as they are contained 
 
 in water. 
 
 100 parts of common resin consist of 
 75.944 of carbon, 
 
 15.156 of a combination of oxygen and hy- 
 drogen in the same proportions as 
 they exist in water, and 
 8.900 of hydrogen in excess. 
 
 100. 
 
 100 parts of olive oil consist of 
 77.213 of carbon, 
 
 10.712 oxygen and hydrogen, as in water, and 
 12.075 of hydrogen in excess. 
 
 100. 
 
 * Recherches physico-chimigues, t. ii. p. 290. 
 
124 GENERAL FLUID COMPONENTS. [LECT. III. 
 
 The solids, also, except the earths and salts, 
 are formed from the same principles : 100 parts of 
 the ligneous fibre of the Beech and the Oak, for 
 example, consisting of 
 
 Beech. -Oak. 
 
 Carbon 51.45 . . . . 52.53 
 Oxygen 42.73 .... 41.78 
 Hydrogen 5.82 .... 5.69 
 
 100.00 100.00 * 
 
 and thus almost the whole of vegetable matter 
 may be resolved into these three simple elements. 
 
 Such are the general components of vegetables. 
 The investigation of them is yet in its commence- 
 ment only, and much must be done before their 
 real properties be fully understood. It is requisite 
 that the student keep them constantly in view, 
 for otherwise much of the more detailed part of 
 our subject will appear obscure and confused. 
 
 * Recherches physico-chimiques, t. ii. p. 294. Thomsons 
 Chemistry, fifth edition, vol. iv. p. 183. 
 
125 
 
 LECTURE IV. 
 
 VEGETABLE ORGANIZATION. THE ROOT ITS SITUA- 
 TION, SPECIES, AND VARIETIES DIRECTION AND 
 
 DURATION. 
 
 HAVING endeavoured to give you some idea of the 
 general components of the vegetable body, I have 
 now to describe to you the organs formed by the 
 combination of these constituents. 
 
 Every plant, as I have already stated, possesses 
 two sets of organs. One of these is intended 
 merely for the growth and preservation of the in- 
 dividual ; the other for the propagation, and, con- 
 sequently, the continuation of the species : or' 
 all plants are endowed with CONSERVATIVE and RE- 
 PRODUCTIVE organs. 
 
 If we dig up a tree or a shrub in the summer, 
 when it is in flower, and some of the fruit is al- 
 ready formed, an Orange-tree for example, which 
 bears flowers and fruit at the same time, we have, 
 in one plant, a complete display of these parts. 
 In the first set are comprehended the root, the 
 trunk, the branches, and the leaves, with their 
 appendages ; in the second, the flower and the 
 fruit, with their appendages. Many phytologists 
 regard those species of plants only, which possess 
 
126 CONSERVATIVE ORGANS. [LECT. IV. 
 
 all, or the greater part of these organs, as perfect ; 
 and those in which some of the more conspicuous 
 of either kind are not present, or are apparently 
 deficient, as imperfect. But we need not hesitate 
 in pronouncing this opinion erroneous ; for, as the 
 perfection of a plant consists in the power of its 
 organs to carry on its functions, and to continue 
 the species, individuals only can be imperfect. 
 
 The different organs, in whatever manner they 
 are present, assume a considerable variety of form ; 
 and as it is on that variation that Botanists have 
 founded specific distinctions ; and as it is of im- 
 portance in a physiological point of view also, the 
 student ought to make himself well acquainted 
 with the distinguishing characteristics which it 
 constitutes. In examining these, the best method 
 is to take the organs in the order in which they 
 have been enumerated: let us, therefore, com- 
 mence with the CONSERVATIVE. 
 
 a. The ROOT (Radix) is defined by Linnaeus 
 to be that part of a plant which imbibes its nu- 
 triment, producing the herbaceous part and the 
 fructification ; and which consists of a caudex, or 
 body, and radicles *. Simple as this definition ap- 
 pears to be, it is, nevertheless, objectionable, inas- 
 
 * " Radix alimentum hauriens, herbamque cum fructifica- 
 " tione producens, componitur medulla, libro, cortice; constat- 
 " que caudice et radicula" Phil. Botanica: 
 
LECT. IV.] THE ROOT. 127 
 
 much as many succulent plants in arid situations 
 do not receive their nutriment by the root ; nor is 
 the root the nutritious organ in the tribes named 
 Hepaticee *, Confervse *j~, and Fuci ; in all of 
 which it can be regarded as an attaching organ 
 only, designed to secure the individual to the soil, 
 or to the substance on which it is fixed. A less 
 exceptionable definition is that adopted by Mr. 
 Keith, which characterizes the root as " that part 
 " of the plant by which it attaches itself to the soil 
 " in which it grows, or to the substance on which 
 " it feeds, and is the principal organ of nutrition ||." 
 It might be stated, as an objection to this defini- 
 tion, that plants exist which have roots, and, yet, 
 are not fixed by them either to the soil or to 
 any other substance ; as for example, Duckweed 
 (Lemna), a small green lenticular plant, which 
 floats abundantly on the surface of our stagnant 
 pools in summer, and has unattached roots which 
 hang perpendicularly loose in the water. But all 
 plants are at first attached ; and as it is impossible 
 to frame any definition to which no exception 
 
 * A tribe of small herbaceous plants resembling the Mosses 
 found in damp shacfed places. 
 
 (- An aquatic genus, consisting of fibrous, or threadlike 
 jointed and branched parts, closely matted together. 
 
 Marine plants of various forms attached to rocks and 
 stones. 
 
 || System of physiological Botany, vol. i. p. 33. 
 
128 CONSERVATIVE ORGANS. [LECT. IV. 
 
 could be advanced, this " is perhaps/' as Mr. 
 Keith remarks, " as comprehensive as any one 
 " that can be given." 
 
 In all plants the primary root is a simple elon- 
 gation of that part which, during the germina- 
 tion of the seed, is first protruded, and is deno- 
 minated the radicle ; but as the plant continues 
 to grow, the root gradually assumes a determinate 
 form and structure, which differs materially in 
 different plants, but is found always similar in all 
 the individuals of the same species. Botanists have 
 taken advantage of this fact, and have classed 
 roots according to their forms, as seen in the 
 adult, or fully grown root ; and have availed 
 themselves of these diversities for fixing specific 
 distinctions. The classification of roots, which I 
 have ventured to arrange, differs from that which 
 is usually found in works on the elements of Bo- 
 tany ; but it is one which, I trust, will enable you 
 to form accurate ideas regarding the structure and 
 functions of these important organs. Before, how- 
 ever, entering upon the consideration of it, you 
 ought to be informed that every root, whatever 
 may be its form, consists of two distinct parts, the 
 body, caudex, and the rootlet, radicula. The main 
 part of the root, caudex *, in trees and plants that 
 
 * " Caudex descendens sub terra sensim subducit, et radicu- 
 " las profert, a Botanicis ex varia structura variis nominibus 
 " distinctus." Phil. Bot. 80. 
 
LECT. IV.] THE ROOT. 1'29 
 
 live for several yeais, is in general woody, and is 
 to the other parts what the trunk or stem is to the 
 branches and leaves ; enlarging progressively in a 
 similar manner, and giving off lateral branching 
 shoots, which spread horizontally, or in a direc- 
 tion that forms nearly a right angle with the 
 caudex. In those plants, however, the herbace- 
 ous part of which dies annually whilst the root 
 survives, and in many annuals, the caudex is 
 also a reservoir of nutriment, which is intended 
 for the renewal of the herbaceous part in the fol- 
 lowing season, or to be expended in perfecting the 
 flower and the seed. The rootlets, radiculce *, are 
 small, or threadlike productions of the caudex, 
 terminating in Jibrils, which are extremely mi- 
 nute, the real absorbing organs of the root ; and 
 are supposed by Du Hamel-f~, Willdenow^, Sir 
 E. J. Smith and others, to die annually in the au- 
 tumn with the foliage, and to be reproduced in 
 the spring ; an opinion which Mr. Knight || re- 
 gards as incorrect, as far at least as concerns the 
 terminal fibres of woody plants. My own ex- 
 
 * " Radicula est pars radicis fibrosa, in quam terminatur 
 " caudex descendens, et qua radix nutrimentum haurit pro 
 " vegetabilis sustentatione." Phil. 'Bot. 80. 
 
 f Phys. des Arb. liv. i. chap. v. 
 
 J Principles of Botany > 11. 
 
 } Introduction to physical and systematical Botany, p. 104. 
 
 Jl Phil. Trans. 1809. 
 
 VOL. I. K 
 
130 CONSERVATIVE ORGANS. [LECT. IV. 
 
 perience and observations, however, lead me to 
 
 believe that, even in woody plants, the fibrils are 
 
 annual productions. 
 
 Every root may be arranged under one of the 
 
 three following classes, i. SIMPLE ROOTS ; ii. 
 
 BRANCHED ROOTS ; iii. ARTICULATED ROOTS. 
 
 i. The SIMPLE ROOT consists either of a single 
 
 caudex furnished with fibrils only, or of one or 
 
 more rootlets with fibrils*. Considered as a genus, 
 
 it comprehends three species, the conical, the sufr- 
 
 globular, and ihejibrous. 
 
 1. The Conical root (Radix conica) (fig. a) is a 
 a. tapering caudex furnished with lateral 
 fibrils, which are situated chiefly towards 
 its smaller extremity. It is generally a 
 reservoir of nutritious matter which is pre- 
 pared in the leaves, and is the proper juice 
 of the plant, to be exhausted in the pro- 
 duction of the flower and the seed. The 
 change which takes place at the flowering 
 season in culinary roots of this descrip- 
 tion, as for example, in the Carrot, is 
 rendered very evident; by the nutritious 
 matter it contains becoming less saccha- 
 rine, diminishing in quantity, and the 
 whole root acquiring a woody consistence. 
 
 The wedgelike form of the conical root seems to 
 
 * " Simplex qua? non subdividitur." Phil. Bot. 80. b. 3. 
 
LECT. IV.] THE ROOT. 131 
 
 be particularly well adapted for penetrating per- 
 pendicularly into the ground ; but that this is not 
 the sole intention of nature in giving it this form 
 would appear from the fact, that tihe direction of 
 some conical roots is horizontal ; as, for example, 
 the Blood Root, Sanguinaria Canademis*, a North 
 American plant, which is conical, truncated, and 
 horizontal ; the root forming a right angle nearly 
 with the stem. The roots of the Carrot, Daucus 
 carota; the Parsnip, Pastinaca sativa ; the Horse- 
 b. radish, Cochlearia Armor acia ; and the 
 Dandelion, Leontodon Taraxacum ; are 
 familiar examples of the conical root. The 
 following may be regarded as its vari- 
 eties. 
 
 a. The Spindle-shaped root (Radix 
 fusiformls^c) (fig. b) differs from the real 
 conical root only, in not tapering equally 
 throughout its length, but swelling out 
 a little below its summit, like the spindle 
 or wooden pin employed by ancient ma- 
 trons in formmg the thread, which they 
 drew from the flax wrapped round the 
 distaff; whence its name. Like the pro- 
 per conical root, it is a reservoir of nu- 
 
 * .Vegetable Mat. Med. of the United States, p. 31. 
 
 f " Fusiformis quae oblonga, crassa, attenuata : ut Daucus, 
 " Pastinaca." Phil. Bot. 80. This is the definition rather of 
 the conical root than of the spindle-shaped. 
 
 K 2 
 
132 CONSERVATIVE ORGANS. 
 
 tritious secreted mattei 
 
 [LECT. iv. 
 
 and by its shape, it is 
 
 well calculated to penetrate the ground. The Ra- 
 dish, Raphanus sativus ; and the Beet, Beta vul- 
 garis ; are the best examples of this form of root. 
 b. The Abrupt or truncated root (Radix 
 c. prcemorsa *) (fig. c ) is ori- 
 
 ginally an entire conical root ; 
 but after some time the lower 
 extremity decays and drops, 
 as if it had been bitten off, 
 while numerous lateral rootlets 
 are protruded from the remain- 
 ing portion. Such is the case 
 in the root of the larger Plan- 
 tain, Plantago major, and in 
 that of Scabiosa succisa, which, according to 
 Gerarde-f*, received its common appellation 
 Devil's Bite, Morsus Diaboli (fig. c), from a su- 
 perstitious opinion connected with this appear- 
 ance of the root. 
 
 A curious modification of the Abrupt root 
 
 * " Pramorsa, quae deorsum truncata est, nee attenuate 
 " apice terminatur ; ut Scabiosa, Plantago, Valeriana" Phil. 
 Bot. 80. 9. 
 
 f The old herbalist's words are, " The greater part of the 
 " root seemeth to be bitten away : old fantasticke charmers re- 
 " port, that the devil did bite it for envie, because it is an herbe 
 " that hath so many good vertues, and is so beneficial to man- 
 kinde." Vide Herbal, p. 726. 
 
LECT. IV.] THE ROOT. 
 
 which occurs in a few herbaceous plants, and 
 which has misled some Botanists to describe it 
 erroneously in these instances, as an articulated 
 or scaly jointed root, depends on the following 
 circumstance, which was first noticed and de- 
 scribed by Dr. Grew*. In the Primrose, Pri- 
 mula veris, for example, the root is abrupt ; 
 but as the lower leaves of the plant annually decay 
 and fall, they leave a small portion of their basis 
 d. at the place of their 
 
 attachment, which 
 swells and becomes 
 more succulent ; and 
 the plant sinking in 
 the ground, lateral fi- 
 bres are protruded 
 above each of these 
 portions ; so that the 
 buried part of the root, 
 owing to a similar de- 
 cay and sinking annu- 
 ally taking place, gra- 
 dually assumes the 
 character of a long 
 caudex, and the whole 
 bears a strong resem- 
 blance to a notched 
 or articulated root. See (fig. d.) a, the present year's 
 
 * Anatomy of Plants. 
 K3 
 
134 CONSERVATIVE ORGANS. [LECT. IV. 
 
 foliage ; b. the remains of last year's, with "a 
 rootlet protruded above it ; c. c. bases of old leaves 
 converted into firm toothlike scales or processes ; 
 d. the decayed, or truncated root. The cause 
 of this decay of the lower extremity of some 
 conical roots shall be explained, when treating 
 of the physiology of these organs. 
 
 2. The Subglobular root (Radix subrotunda) 
 is an almost spherical caudex, terminating in one 
 or more small tapering points. Like the conical 
 root, it is a reservoir of nutritious matterlntended 
 for the production of the flower and seed. The 
 best example of it is the black Radish, Ra- 
 phanus sativus, var. B. niger. There are two va- 
 rieties of the subglobular root : 
 
 a. The Turnip-shaped root 
 (Radix napiformis) (fig. e) is a 
 caudex, the shape of which is the 
 intermediate of the spindle- 
 shaped and the subglobular roots, 
 bellying out suddenly above, and 
 terminating belowin along taper- 
 ing point furnished with fibrils. 
 It is scarcely necessary to quote 
 the Turnip, Brassica Rapa, as 
 an example. 
 I. The Flattened subglobular root (Radix 
 placenttf'ormis) has the appearance of a globular 
 caudex which is compressed both above and be- 
 
LECT. IV.] THE ROOT. 135 
 
 low. It has not the tapering point of the two 
 former, but a number of long fibrils which hang 
 from the centre of the lower depression. The 
 Sow-bread, Cyclamen europceum (fig. y), which 
 
 is an example of this 
 root, does not attain its de- 
 cisive character in the first 
 year of its growth ; and al- 
 though a reservoir of nu- 
 triment, yet it is not ex- 
 hausted in perfecting the 
 flower and fruit, but con- 
 tinues to increase for se- 
 veral years. 
 
 The nutriment which is deposited in the cau- 
 dices of all these species of the simple root, is not 
 that which is directly absorbed from the soil by 
 the fibrils ; but the proper juice of the plant, pre- 
 pared from the sap exposed to the action of the 
 light and' air in the leaves. The necessity of a 
 luxuriant and healthy state of the herbaceous part 
 of the plant, therefore, for increasing the quantity 
 of nutritious matter in the simple roots, which are 
 cultivated for food, is very obvious. It may be 
 thought that the practice pursued to produce earlier 
 and larger Radishes, " which is by sowing them in 
 " hot-beds in the early spring, and exposing the 
 <c tops to the cold air during the day, as this pre- 
 " vents the luxuriant growth of the summit, and 
 
 K4 
 
136 CONSERVATIVE ORGANS. JJLECT. IV. 
 
 " increases that of the root*," militates against this 
 opinion: but it maybe answered, that by exposing 
 the tops to the colii air, whilst the fibrils of the 
 roots are in a state of activity, the functions of 
 the leaves are not altogether suspended ; and the 
 only difference produced by the diminished tempe- 
 rature moderating their action, is, that less of the 
 watery part of the sap being thrown off during its 
 exposure in the leaves, the proper juice is conse- 
 quently more abundant because it contains more 
 water. It is still, however, proper juice, and is 
 conveyed from the leaves into the caudex, which is 
 necessarily enlarged ; but it is less perfectly formed, 
 and the root as an article of food wants its proper 
 flavour. 
 
 That the fibrils are the principal absorbing 
 parts of the roots we have just examined, is evi- 
 dent ; for, by merely placing the extremity or 
 tapering point of a Turnip covered with its fibrils 
 in water, the herbaceous part continues to grow 
 and put forth fresh leaves, which does not happen 
 if the caudex only be surrounded with water, and 
 the point kept dry. It is owing to this circum- 
 stance, also, that Turnips and similar roots thrive 
 and enlarge, although nearly the whole of the 
 caudex be above the surface of the ground. 
 
 3. The Fibrous root (Radix Jibrosa) consists 
 of rootlets only, which convey the nutriment ab- 
 
 *~ Darwin's Phytologia, sect. xvii. 1. 
 
LECT. IV.] THE ROOT. 137 
 
 sorbed by their fibrils directly to the basis of the 
 stem and leaves, or into what is termed a bulb. 
 Besides the bulb, which has a close analogy to 
 buds, all plants, also, that have those underground 
 organs for reproducing or rather continuing the 
 species, which have been named tubers, have 
 fibrous roots ; and although Linnaeus has fallen 
 into the error as far as regards the tuber-bearing^ 
 roots *, and the mistake concerning both them and 
 bulbs continues to be repeated in Botanical works, 
 yet, it is not the less incorrect to regard these organs 
 as roots, which, as I shall afterwards explain to you, 
 are merely appendages to some fibrous roots ; and 
 thence the terms Bulbiferous root, Tuberiferous 
 root, should be substituted for Bulbous root, Tuber- 
 ous root. In the bulbiferous roots the rootlets are 
 attached to the basis of the bulb, either directly 
 or by the intervention of a radicle plate -^ ; in the 
 tuberiferous they proceed from the basis of the 
 
 * Linnaeus defines them thus: " Tuberosa (radix) quae sub- 
 " rotundis constat corporibus in fasciculum collectis ; Pceonia, 
 " Hemerocallis, Helianthus r Solanum, Filipendula." Phil. Bot. 
 80. 6. 
 
 j- The term Bulbiferous root has already been adopted by 
 Mirbel, who thus defines it ; " Nous devons entendre par ra- 
 " cines bulbiferes, des tubercules minces, elargis en plateau dont 
 " la surface inferieure produit des filets radicaux, et dont la 
 " surface superieure porte un ognon, ou bulbed Elem. de Phys. 
 veget. t. i. p. 91. 
 
138 
 
 CONSERVATIVE ORGANS. 
 
 [LECT. iv. 
 
 stem or the herbaceous part of the plant, and are 
 ' generally above the tubers, to which they are not 
 attached. It is necessary to remark that, in 
 some instances, both in the bulb and the tuber- 
 bearing roots, the rootlets are unsupplied with 
 fibrils, performing themselves the functions of these 
 organs ; and, like them, they annually decay with 
 the foliage in the autumn, to be renewed 
 
 with it in the spring. 
 The majority of annual 
 plants and many Grasses, 
 as, for example, the Sea 
 Canary Grass, Phalaris 
 arenaria (fig. g), have 
 fibrous roots. The fol- 
 lowing are varieties of 
 the fibrous root. 
 
 a. The Filiform root (Radix filiformu) is com- 
 posed of distinct and separate threadlike rootlets, 
 as in Duckweed, Lemna. 
 
 b. The Capillary root (Radix capillarls) (fig. 
 
 h. h) consists of many very fine 
 
 fibres, as in Sheep's Fescue- 
 grass, Festuca ovina, and many 
 other Grasses. You will find, in 
 works on Elementary Botany, 
 the Tufted root (R. comosa) de- 
 scribed as a modification of 
 the Capillary root; but it is, correctly speaking, 
 
LECT. IV.] THE ROOT. 139 
 
 not a fibrous root, the hairlike tufts of which it 
 consists being attached to a caudex which fixes 
 the character of the root. The male Fern, Aspi- 
 dium 'Filix mas, affords a good example of the 
 tufted or cespitose root. 
 
 c. The Funiliform or cordlike root (Radix 
 fumliformh) is formed of thick fibres resembling 
 cords more or less fine, generally simple, but 
 sometimes slightly ramified. In the Palms which 
 have roots of this description, the cords are very 
 strong and diverging, so as to take a firm hold of 
 the ground and maintain the perpendicularity of 
 the plant, a circumstance of great importance to 
 this tribe of vegetables, many of which are simple 
 columns rising more than a hundred feet in height, 
 and bearing the whole weight of their magnificent 
 foliage at the summit. The succulent plants of 
 tropical climates also, which obtain the greater 
 part of their support by the absorbing organs of 
 the leaves and stems attracting the moisture of 
 the atmosphere, have funiliform roots, the ^chief 
 use of which is to rivet them down to the soil, and 
 secure their stability. 
 
 ii. The BRANCHED ROOT (Radix ramosa) con- 
 sists of a caudex or main root, divided into lateral 
 branches*, which are again subdivided and ulti- 
 
 * " Ramosa quae in laterales ramos dividitur.'* Phil. Bot. 
 80. 
 
140 
 
 CONSERVATIVE ORGANS. [LECT. IV. 
 
 mately terminate in absorbing fibrils ; so that the 
 
 root in its di- 
 visions resem- 
 bles the stem 
 and branches 
 inverted (fig. 
 i). This form 
 of root is the 
 most general 
 being that of 
 all trees and 
 shrubs, and al- 
 so of many her- 
 baceous plants; 
 for example, E- 
 lecampane, 
 
 Inula Helenium, and Seneka, Polygala senega. 
 
 The following are the only species : 
 
 1. The Branched root (Radix ramosa), as 
 described under the genus. 
 
 2. The Toothed root (Radix dentata) (fig. A), 
 
 k. which is a fleshy caudex with 
 
 short branches and teethlike 
 prolongations, as in Ophrys co- 
 rallorhiza. 
 
 iii. The Articulated or 
 Jointed root, (Radix articu- 
 lata) is apparently formed of distinct pieces 
 united, as if one piece grew out of another, so as 
 
LECT. IV.] THE ROOT. 141 
 
 to form a connected whole, with rootlets pro- 
 ceeding from each joint. The articulations are in 
 some instances kneed ; in others they resemble 
 nodules or beads. 
 
 The following may be considered species of the 
 jointed root : 
 
 1 . The Simple Articulated root, when the pieces 
 
 /. of which it is 
 
 composed are 
 attached lon- 
 gitudinally, or 
 nearly so, as 
 in Wild Gin- 
 ger, Asarum 
 Canadense (fig. 
 Z). 
 
 2. The Kneed root (Radix genlculata) has some 
 
 of the articulations form- 
 ing a knee ; as in Hedge 
 Hyssop, Gratiola offici- 
 nalis ; and Solomon's 
 Seal, Convallaria poly- 
 gonatum (fig. /*), which 
 is, besides, a bulbife- 
 rous root, and truncated 
 in such a peculiar man- 
 ner at the points of de- 
 tachment of the annual 
 stems, as to have given rise to its vulgar name ; 
 
142 CONSERVATIVE ORGANS. [LECT. IV. 
 
 the cicatrizations bearing a fancied resemblance 
 to impressions of a seal. 
 
 a. The Contorted root (Radix contorta), al- 
 though it cannot strictly be regarded as an articu- 
 lated root, yet, it may be classed with propriety 
 m. as a modifica- 
 
 tion or variety 
 of the kneed 
 root. TheBistort, 
 Polygonum Bis- 
 torta (fig. m), 
 affords the best 
 example of it, the 
 name of the plant 
 having originated 
 
 in the double turn which the root takes. The 
 caudex of the root, which is , perennial, is a re- 
 servoir of nutriment for the annual renewal 
 of the herbage. 
 
 3. The Necklace-like root (Radix monillformis) 
 (fig. n) is an articulated 
 root with nodular joints, 
 united together so as to 
 resemble beads in a neck- 
 lace ; as in Tall Meadow 
 Oat, Avena elatior nodosa. 
 
 Such are the general forms of roots, and the 
 
LECT. IV.] THE ROOT. 143 
 
 names by which they are known to Botanists ; and 
 under one or other of these species, with very few 
 exceptions, every variety of root may be classed. 
 One exception only is necessary to be particularly 
 noticed as it refers to a root, which is frequently 
 improperly quoted by elementary authors as an 
 example of a root bearing pendulous tubers like 
 the Potatoe; although, in fact, it is merely a 
 conical root with thick lateral rootlets swelled, near 
 the extremity of each, into a solid nodule. This 
 form of root is the Radix JUipendula of authors ; 
 as exemplified in the root of Common Dropwort, 
 Spirea Jilipendula (fig. o), which is in strict 
 
 o. 
 
 language a nodose root, the tubers or knobs being 
 perennial, actually parts of the root, and reservoirs 
 of nutriment for the use of the plant itself, pro- 
 
144 THE ROOT SCALES. ["LECT. IV. 
 
 bably, as has been suggested, to enable it to resist 
 drought ; and not at all resembling the tubers of 
 the Potatoe and other similar tuberiferous roots, 
 which are annual productions; and, as I shall pre- 
 sently explain to you, belong nearly as much to the 
 stem as to the root. 
 
 Having finished the observations I had to offer 
 on the external characters of roots, our next ob- 
 ject is to examine the APPENDAGES of these organs ; 
 which are as fixed in their forms as the roots 
 themselves, and are, consequently, taken advan- 
 tage of in describing plants. All the appendages 
 of roots may be arranged under the following 
 genera: I. Scales; 2. Suckers; 3. Knobs or 
 Tubers ; and 5. Bulbs. 
 
 1. SCALES are in many instances the remnants 
 of leaves which have decayed and fallen, as has 
 already been explained (p. 133). They more fre- 
 quently occur in roots which assume a horizontal 
 direction ; in which cases the lower part of the 
 stem which is in contact, or nearly so, with the 
 soil, gives off lateral rootlets, immediately above 
 the point of attachment of the decayed leaf ; and 
 these, dipping into the ground, drag that portion 
 of the stem under the surface of the earth, where 
 it gradually acquires all the characteristics of a 
 root. There are, nevertheless, some roots originally 
 furnished with scales, and very few or no lateral 
 
LECT. IV.] THE ROOT. SUCKER. 145 
 
 rootlets, as in Toothwort (Lathraea squamaria) 
 p. ( fig. p ) ; and it is 
 
 not improbable that 
 the scales, which 
 are generally fleshy, 
 are reservoirs of 
 nutriment for the 
 use of the plant. 
 2. The SUCKER (Stolo) is an underground bud 
 protruded from the upper horizontal branches of 
 the roots of trees, or those nearest to the surface 
 of the soil ; and which, ascending above the earth, 
 is converted into a stem, resembling the parent 
 tree ; as exemplified in the common Lilac (Syringa 
 vulgaris), the Elm, and many other trees, particu r 
 larly fruit-trees, round the stems of which, young 
 plants of the same species as the stock are seen con- 
 stantly rising ; and also in some herbaceous plants. 
 The sucker, in its earlier state, has the closest re- 
 semblance to the leaf-bud ; and in its nlore forward 
 growth to the branch, protruded from the part of 
 the plant which is above ground ; circumstances 
 which prove the affinity of the stem and the root. 
 It never detaches itself spontaneously from the 
 plant, but, if artificially separated along with a small 
 portion of the root, it may be transplanted, and 
 will grow, constituting a distinct vegetable being ; 
 although differing essentially, as I shall afterwards 
 have an opportunity of explaining to you, from 
 VOL, i. L 
 
 
146 CONSERVATIVE ORGANS. [LECT. IV. 
 
 the young plant which is the seminal production 
 of the same parent. Whilst the sucker is attached 
 to the root on which it is formed, it derives its 
 nourishment through the same organs that supply 
 the principal stem, which, consequently, must 
 become impoverished in proportion to the number 
 of suckers that surround it. 
 
 3. The KNOB or TUBER (Tuber) is a solid fleshy 
 body, attached to many fibrous-rooted plants, 
 either immediately at the basis of the stem under 
 the rootlets, or mediately by means of cords or 
 wires which proceed from the basis of the stem. 
 The tuber itself is not furnished with any rootlets 
 or fibrils ; which circumstance distinguishes it from 
 nodular and globular roots, with which it is fre- 
 quently confounded in the description of plants. It 
 is composed of cellular substance filled with a moist, 
 amylaceous fecula; is covered with a cutis vera 
 and epidermis ; and furnished with vessels, which 
 are collected at one point or at different points on 
 the surface, where a bud or gem and rootlets are 
 protruded when the tuber, has attained its full ma- 
 turity, and is placed in a situation favourable to 
 vegetation*. It is, in fact, a reservoir of nutriment 
 
 * Mirbel thus describes tubers : " Les tubercules, qui ont 
 " fait dormer le nora de tubereuse a certaines racines, sont des 
 " renflemens charnus, souvent arrondis, masses de tissu cellulaire, 
 " que parcourent quelques vaisseaux qui se rendent vers tous les 
 " points de la surface, d'ou doivent partir les filets radicaux et 
 " les turions. Les poches du tissu cellulaire des tubercles sont 
 
LECT. IV.] THE ROOT. TUBERS. 147 
 
 intended to support these buds during their evolu- 
 tion and the earlier stage of their growth as plants; 
 and thence tuberiferous plants, which are chiefly 
 annuals, are perpetuated both by a lateral and 
 seminal progeny. In this respect the buds produced 
 on tubers resemble suckers ; differing from them 
 only in not being dependent on the original root for 
 their nutriment, but obtaining it from the tuber ; 
 and in separating spontaneously from the parent 
 plant, and becoming distinct, isolated beings. They 
 resemble seeds also, inasmuch as the gems upon 
 their surfaces are endowed with vitality, like the 
 embryon or plantule enclosed in the seed, and 
 remains latent, until the tuber be placed under 
 circumstances favourable for vegetation. 
 
 Tubers are annual productions of the herba- 
 ceous part of the plant ; both the nutritious fecula 
 deposited within them, and the gems on their 
 surfaces, being formed from the descending or pro- 
 per juice, which, as you already know, is the sap, 
 or fluids taken up by the roots, changed by expo- 
 sure to the action of the air and the light in the 
 leaf. They are, in strict language, rather appen- 
 dages of the stem than of the root*; and are con- 
 
 " remplies d'une fecule amilacee." Element de Phys. veg. t. i. 
 p. 90. 
 
 * The following description by Dr. Darwin, of a variety of 
 the Potatoe raised in the garden of Major Trowel of Derby, 
 is a good illustration of this remark : " From one root there 
 " appeared to issue six or eight stems, three or four feet long, 
 
 L2 
 
148 CONSERVATIVE ORGANS. [LECT. IV. 
 
 sidered as belonging to the latter merely from the 
 circumstance of their being underground produc- 
 tions. The older phytologists regarded them as 
 roots ; and we may still speak of them, without 
 much impropriety, as appendages to these organs, 
 if we obtain, in other respects, a correct idea of 
 their nature and functions. They assume a great 
 diversity of forms, which, as they frequently enter 
 into botanical descriptions, ought to be made fa- 
 miliar to the student. In describing them I shall 
 arrange the whole under two genera: a. Closely 
 attached tubers ; b. Filipendulous tubers. 
 
 a. CLOSELY ATTACHED TUBERS are seated di- 
 rectly at the basis of the stem, or rather adhere 
 to it*, and grow in immediate contact with each 
 
 " at every joint of which were produced new Potatoes ; at the 
 " lower joints there were three of these aerial Potatoes, one 
 " large, one the size of a pullet's egg, and a smaller one on each 
 " side of it. At the upper joints only one new aerial Potatoe 
 " adhered, and these became smaller the further they were 
 " removed from the root ; and, finally, at the summit there 
 " had been a flower, as there was now a seed-vessel, called a 
 " Potatoe-apple. All these new Potatoes at the joints of the 
 " stems were green, because they had not been etiolated by 
 " being secluded from the light, but the terrestrial roots 
 " (tubers) were white.'* Darwin's Phytologia, sect. xvii. 1 , 2. 
 * This place at the basis of the stem to which these tubers 
 usually adhere is marked by a little contraction or sometimes 
 protuberance, which the French botanists call le collet, the collar. 
 ' On donne aussi le nom de collet a une espece d'etranglement 
 " ou de rebord, qui separe une tige d'avec sa racine." Diet. 
 element, de Bot. par Buttiard. 
 
LECT. IV.] THE ROOT. TUBERS. 149 
 
 other. They comprehend the following species, 
 regarding them as appendages of the root : 
 
 1. The Conjoined ovate tuber (Tuber conjunc- 
 tum ovatum) is an egg-shaped tuber, in immediate 
 contact with another, and more rarely a third, at 
 
 the point of its attach- 
 ment to the stem of the 
 plant, as in the Orchis 
 tribe (fig. q). When there 
 are three 'tubers, one of 
 them is generally shrivelled 
 almost to a skin, another 
 a little less so, and the 
 third quite plump: and when there are two only, 
 one is always somewhat shrivelled, if the root be 
 examined after the plant has flowered. The full 
 tuber is the formation of the present year, and 
 bears on it a gem for the production of the plant 
 of the following year ; but> the shrivelled one is 
 that of the preceding year, which having its nu- 
 tritious contents exhausted in formation of the 
 herb and the flowers, shrivels towards autumn ; 
 and either withers away altogether and disappears 
 in the succeeding winter, or remains a mere ske- 
 leton in the third year. The ovate conjoined tuber 
 is therefore biennial, being formed and perfected 
 in one year, and performing its functions and dy- 
 ing in the second. In fig. q are seen these three 
 states of tuber as displayed in Orchis acuminatum: 
 
 L3 
 
150 CONSERVATIVE ORGANS. [LECT. IV. 
 
 1. shows the tuber nearly shrivelled to a skin; 2. 
 the tuber of last year after the plant it bears has 
 flowered ; 3. the new tuber, the production of the 
 present year ; 4. are the real roots of the plant*. 
 r. Our conjoined ovate tu- 
 
 ber is the Radix testiculata 
 of 'authors-}-. 
 
 , 2. The Conjoined club- 
 shaped tuber (Tuber clavce- 
 1 forme conjunctum) (fig. r ) is 
 of an oblong shape, thicker 
 at the loose extremity, and 
 resembling in some degree a short club. As in 
 the former species of tuber, it is generated every 
 
 * There formerly existed a very absurd superstition con- 
 nected with the double state of these tubers. If a pair of them 
 be separated and thrown into water, the new tuber, owing to its 
 greater gravity, sinks, whilst the older one, being lighter, swims. 
 The swimming tuber, when prepared in a particular manner and 
 worn round the neck, was believed to possess the magic pro- 
 perty of securing to the wearer the strongest attachment of any 
 one he pleased ; and this belief still continues to prevail to some 
 extent among the ignorant. A more rational and useful purpose 
 to which the new tuber of the Orchis mono, and some other spe- 
 cies of the Orchidece is applied, is the manufacture of salop. For 
 this purpose the new tuber, which has attained its perfect growth, 
 is prepared by first scalding it in boiling, water to detract the 
 skin, then placing it in an oven for ten or twelve minutes to give 
 it semitransparency, and finally drying it in a moderate heat. 
 In this state it resembles sago, and constitutes a nutritious 
 wholesome article of diet. 
 
 f Quasi testiculis animalium similis. 
 
LECT. IV.] THB ROOT. TUBERS. 151 
 
 year; but there are always two or more tubers in 
 
 a state of advancement towards perfection, and 
 
 as many in that of decay. Pile-wort, Ranunculus 
 
 Jicaria, affords the best example of this form of 
 
 tuber : vide fig. r, in which 1. 1. indicates the 
 
 more recent tubers ; 2. 2. those in a state of decay. 
 
 . 3. The Fingered tuber (Tuber digitatum) (fig.*) 
 
 receives its name from 
 the tubers resembling 
 fingers. In Satyrium 
 albidum, the plant 
 exhausts two tubers 
 in one season; see 
 fig. s, in which b. b. 
 represents a pair of 
 old tubers, the origin 
 of the existing plant ; 
 a. a pair of tubers for that of the next year, 
 with a still younger pair attached to them : c. c. 
 are the real roots of the plant. 
 
 4. The Palmated tuber (Tuber palmatum) (fig. 
 
 t) also receives its 
 name from its form, 
 which somewhat re- 
 sembles the human 
 hand. There are 
 rarely more than two 
 palmated tubers con- 
 joined, as in Orchis 
 
152 CONSERVATIVE ORGANS. [t,ECT. IV. 
 
 maculata. In fig. t, 1.1. represents the roots; 
 2. the withering tuber, the origin of the present 
 plant; 3. the new tuber, the pyramidal eleva- 
 tion on the top of which marks the point, whence 
 shall germinate the plant of the ensuing year. 
 5. The Bundled tuber (Tuber fasciculatum) 
 u. (fig. u) is spindle- 
 
 shaped or nearly 
 cylindrical. Tu- 
 bers of this de- 
 scription " are 
 " "formed,andalso 
 " wither away in 
 " parcels," each 
 parcel being equi- 
 valent to a single tuber in the species already de- 
 scribed : they are well exemplified in Bird's-nest 
 Ophrys, Ophrys nidus avis (fig. u). 
 
 Such are the closely attached tubers. From 
 the circumstance of the new tuber, or the sets of 
 tubers, being always formed laterally to the old, 
 the plant appears to perform a certain degree of 
 progression ; so that in a few years it is found at 
 some distance from the spot where it originally 
 flourished*. I have used the term, " the plant," 
 
 * The cultivation of tuberiferous plants with closely at- 
 tached tubers, which are chiefly of the Orchis tribe, has always 
 been considered very difficult ; but it may be successfully ma- 
 naged as practised by the late Mr. Crowe, and thus described 
 
LECT. IV.] THE ROOT. TUBERS. 153 
 
 because, although a new plant actually rises every 
 year from the new tuber, or that one in the regu r 
 lar order of succession ; yet each is only a conti- 
 nuation of the plant raised from the seed perpe- 
 tuated by lateral production, as the buds on an 
 ungrafted tree are continuations of the original 
 tree ; and differ essentially from the seedling 
 plant, which is a real renewal of the species. 
 
 b. FJLIPENDULOUS TUBERS are attached to the 
 parent plant by underground runners, or cords, 
 which spring not from the roots but the lower part 
 of "the stem ; the roots being in this instance, as 
 in the plants with closely attached tubers, truly 
 v. fibrous. There are two 
 
 species only of the fill- 
 pen dulo us tubers ; soli- 
 tary and congregated. 
 
 I- The 5otorpen- 
 dulous tuber (Tuber so- 
 lit arium) (fig. v ) is egg- 
 shaped and attached, as 
 
 by Sir J. E. Smith : " They are best removed when in full flower, 
 " the earth being cleared completely away from the roots 
 " (tubers), which are then to be replanted in their natural 
 " soil previously dried and sifted. Afterwards they must be 
 " well watered. The bulb (tuber) for the following year has 
 " not at the flowering period begun to throw out its fibres, for 
 " after that happens it will not bear removal." Introd. to phy- 
 siological and systematic Botany t p. 110. 
 
154 CONSERVATIVE ORGANS. [LECT. IV. 
 
 at b. to the extremity of a lateral runner, proceed- 
 ing from the collar of the stem, immediately above 
 a. the old, or plant-bearing tuber. As the new tu- 
 ber makes very little progress until after the flow- 
 ering of the parent plant is over, it may escape 
 the observation of the student, if looked for be- 
 fore that period. The Musk Orchis, Ophrys 
 monorchis (fig. v), which has received its spe- 
 cific name Monorchis*, from having apparently 
 but one tuber, is the only example of this species 
 of tuber with which I am acquainted. 
 
 2. Congregated pendulous tubers (Tubera con- 
 gregata) are more generally either globular or 
 ovate, surrounding the stem, attached by runners 
 or fibres which connect them with it at different 
 distances, and in indefinite numbers. Like all 
 other tubers, they are reservoirs of nutriment 
 and moisture ; whilst the runners to which they 
 are attached perform an office similar to that of 
 the umbilical cord in animals ; conveying the pro- 
 per juice from the parent plant to the tubers, to 
 be deposited in them for the support of the suc- 
 ceeding plants; and maintaining the connexion 
 between the plant and its lateral progeny, the 
 gems on the surface of the tubers, until these are 
 perfected and endued with that vitality which en- 
 ables them to exist as independent beings. It is a 
 
 * From /uo'vos (monos), one. 
 
LECT. IV.] THE HOOT. TUBERS. 155 
 
 conjecture which is not improbable, that the final 
 cause of the length of the runners is to place the 
 tubers at a convenient distance from the parent 
 plant and from each other, in order that the new 
 plants may enjoy the advantages of a fresh and 
 unexhausted soil. 
 
 The Potatoe, which affords the best exemplifica- 
 tion of this species of tuber, has many gems on 
 its surface, all of which shoot up into stems ; and 
 from each, besides the runners for the production 
 of new tubers, rootlets are given off for the ab- 
 sorption of that portion of nutriment which is 
 required to be supplied from the soil for the sup- 
 port of^the vegetating plants. 
 
 Such are all the species of tubers which I 
 think it necessary to particularize ; and to one 
 or other of them, every known tuber may be re- 
 ferred. Other species are undoubtedly noticed by 
 authors, under the head of tuberous roots; but 
 these will be found to be varieties only of some 
 of those we have examined : even the granules 
 attached to the roots of the White Saxifrage, 
 Saxifraga granulata, are sometimes quoted* as 
 tubers, although they actually belong to the next 
 of the appendages of the root, which we have to 
 take under consideration, the bulbs. The roots of 
 several species of the Iris tribe have some resem- 
 
 * Keith's Syst. of physiological Botany > vol. i. p. 39. 
 
 4 
 
156 CONSERVATIVE ORGANS. [LECT. IV. 
 
 blance to the tuber ; but although the new caudexes 
 of these roots bear buds, which may be correctly 
 regarded as lateral progeny, yet, these caudexes 
 are nevertheless real roots, and do not accord with 
 the definition of tubers. I shall have to notice 
 them more particularly when we examine the di- 
 rection of roots. 
 
 As in tuberiferous plants, the tuber is formed 
 by the plant of the present year, and itself forms 
 that of the succeeding, which again forms a 
 new tuber or tubers, it becomes a subject of 
 rational inquiry to ascertain the part which the 
 real roots of the plant act, in producing these 
 results. That the plant is sustained to a cer- 
 tain degree by the absorbing powers of the real 
 roots, is obvious ; but it has not, yet, been deter- 
 mined to what extent or at what period it might 
 be deprived of the tuber and be supported solely 
 by the roots. In the early stage of its growth it is 
 altogether nourished by the tuber, the nutriment 
 passing directly from the tuber into the vessels of 
 the stem, and ascending through them to nou- 
 rish the plant. When the roots begin to absorb 
 from the soil, the fluid matters they take in 
 are probably mingled, in the leaf, with the already 
 formed nutriment brought from the tuber ; and it 
 is not unlikely that it is from the proper juice pro- 
 duced by the exposure of this mixture to the air 
 and light in the leaf, that the new tubers are 
 formed. That the new tubers, however, may be 
 
LECT. IV.] THE ROOT. TUBERS. 157 
 
 formed independent altogether of the nutriment 
 obtained from the tuber bearing the plant, is evi- 
 dent ; for, the first tubers of the plant raised from 
 seed are formed altogether from the nutriment 
 obtained from the soil. It should, however, be re- 
 collected, that the plant raised from seed differs 
 from that evolved from the gem on a tuber ; the 
 former being an entire new being, a renewal of the 
 species, the latter a mere continuation of the in- 
 dividual from which it springs. It may be sup- 
 posed, that although the new tubers be formed 
 from the nutriment obtained from the soil, yet 
 that the contents of the old tuber are intended 
 chiefly for perfecting the flower and the seed *, in 
 the same manner as the saccharine matter depo- 
 sited in the caudexes of the Turnip and Carrot ; 
 but, admitting this supposition, it is not the less 
 true that this nutriment may be diverted to the use 
 of the new tubers ; for those on the Potatoe plant, 
 are both enlarged and multiplied by nipping off 
 the flowers, to prevent the formation of the seed. 
 From whatever source the nutriment is obtained, 
 the healthy state of the leaf is absolutely requisite 
 to perfect the tuber ; for, the partial destruction of 
 
 * This supposition certainly obtains some support from the 
 fact, that Potatoes produced on plants raised from seed do not 
 flower in the second or third year ; the tubers apparently re- 
 quiring a greater magnitude and higher degree of perfection 
 before they can form the flower. 
 
158 CONSERVATIVE ORGANS. [LECT. IV. 
 
 these by insects or frost, or the impeding of their 
 functions by disease, as for example the curling of 
 the leaves of the Potatoe plant, is followed by a 
 decrease both in the quantity and in the size of 
 the new tubers, and also by a deterioration of 
 the nutriment deposited in them. 
 
 The runners to which pendulous tubers are 
 attached are bundles of vessels, produced from the 
 bark of the stem, and intended solely to convey 
 the proper juice from the descending vessels to 
 these knobs ; and that there are no returning 
 vessels, or, in other words, that the progression 
 of fluids through these runners is in a direction 
 from the stem to the tubers only, is rendered pro- 
 bable from the following experiment made by Mr. 
 Knight. He divided the runners connecting the 
 tubers with the stem in a Potatoe plant, and 
 immersed both portions in a decoction of Logwood. 
 The colouring matter passed along in both direc- 
 tions, but did not enter the stem, which it would 
 have done had there been any returning vessels in 
 the runners, whilst it was found to have entered 
 the tubers and filled an elaborate assemblage of 
 vessels which are situated between the bark and 
 fleshy parenchyma *. 
 
 The anatomy of tubers displays a considerable 
 difference in the structure of those which belong 
 
 * Phil. Transactions, 1803. 
 
LECT. IV.] THE ROOT. TUBERS. 159 
 
 to the tribe of plants named Monocotyledons and 
 that .denominated Dicotyledons; it demonstrates 
 also, that the organization of the tuber has the 
 closest affinity to that of the stems of the tribe to 
 which it belongs. Thus, for example, the stem of the 
 Orchis mascula, which is an annual, tuberiferous, 
 monocotyledonous plant, consists of a lax cellular 
 texture enclosed in a cutis vera and epidermis, with 
 threadlike bundles of vessels running longitudi- 
 nally through it, at equal distances. The same 
 appearance is evident in the tuber, the vascular 
 bundles or cords being larger only, and inosculating 
 with each other at the lower extremity of the tu- 
 ber, whilst at the upper they pass into a transverse 
 bundle, which seems to unite with one cord of 
 vessels descending from the stem of the plant, and 
 two cords which apparently connect the vascular 
 system of the new tuber with that of the parent 
 stem and the old tuber. This organization is quite 
 obvious to the naked eye in the half-decayed tuber, 
 and can be made so in the new tuber if the stem 
 of the plant be cut transversely through about an 
 inch from the tubers, and the portion to which they 
 are attached inverted, and allowed to remain for 
 twenty-four hours in a decoction of Brazil wood. 
 When the vessels are thus filled with colouring 
 matter, a longitudinal section of the new tuber dis- 
 plays the vessels running in cords through the cel- 
 lular texture, which is now swelled with nutritious 
 fluids (vide plate 1. fig. 1. a), whilst a transverse 
 
160 CONSERVATIVE ORGANS. [LECT. IV. 
 
 section shows them like coloured points, set in a 
 diamond form, in the white parenchyma (Ib. fig. 2). 
 In the old tuber this appearance varies ; the lon- 
 gitudinal section showing the cords of vessels sur- 
 rounded with the cells still turgid with fluids to a 
 certain distance on every side, and these enclosed 
 as it were with a wall of empty cells, which in a 
 transverse section assumes a circular or irregular 
 hexagonal figure ; or each cord of vessels appears 
 as a point in the centre of a large circle or 
 hexagon, the interior of which consists of moist 
 cellular matter, and the walls of dry or empty 
 cells (Ib. fig. 3). This appearance of the old tuber 
 can be explained only on the supposition that 
 during the exhaustion of the nutritious matter it 
 contains, the fluids pass laterally through the cells 
 towards each cord of vessels, by which they are 
 taken up and conveyed to the vessels of the stem 
 and those of the new tuber ; and consequently, 
 the more distant cells being those soonest emptied, 
 and each cord of vessels acting as the attractive 
 centre of a given space, the cells on the periphery 
 of each space, owing to the positions of the vas- 
 cular cords, must necessarily be emptied in such 
 a manner as to give the circular or hexagonal ap- 
 pearance to the transverse section. If this opinion 
 be well founded, it would appear, that the vessels 
 of the tubers of monocotyledonous plants, which 
 during the growth of the tuber convey to and 
 
LECT. IV.] THE ROOT. TUBERS. J61 
 
 deposite the nutritious fluids in the cells of the 
 parenchyma, take on a retrograde movement, and 
 acquire the functions of absorbents as soon as the 
 tuber begins to vegetate. A knowledge of the dis- 
 tribution of the vascular system of these tubers, 
 and of the manner in which the new tuber is at- 
 tached, with the appearance of the embryon plant 
 at its apex, can be readily obtained by examining 
 a longitudinal section of the base of any Orchis, 
 after the new tuber is formed ; particularly if the 
 plant be injected with a coloured fluid, as has been 
 already described *. From such an examination it 
 is evident, that, however close the attachment of 
 the new and old tubers is in the closely attached 
 tubers, the attaching organ performs a function 
 very similar to that of the umbilical cord of ani- 
 mals ; and resembles in every respect, except in 
 length, the runners which connect the pendulous 
 
 * Vide Plate I. fig. 1. which represents a longitudinal slice 
 of the tuber of the male Orchis, Orchis mascula ; a. the new 
 tuber with its longitudinal vessels, and the intermediate cel- 
 lular texture turgid with nutritious fluid ; b. the old tuber in a 
 half-exhausted state; c. the stem of the plant broken short; 
 d. t\\e plantule, which will form the next year's plant ; e. a kind 
 of sheath over the plantule> which terminates in a membranous 
 cone, and appears to be formed of a doubling of the cuticle 
 of the stem, reflected so as to unite with that of the new- 
 tuber ;f, the point of conjunction of the vessels of the stem and 
 of the old tuber, with those of the plantule and the new tuber ; 
 g. a root produced from the stem* 
 
 VOL. I. M 
 
162 CONSERVATIVE ORGANS. [LECT. IV. 
 
 tubers with the parent plant. In fact, the attach- 
 ment, when the tuber is viewed in its natural state, 
 appears much shorter than it actually is, owing to 
 the shortness of the collar of 
 the stem: but circumstances 
 occasionally occur which 
 lengthen the organ, so as 
 to give it the real character 
 of a runner, and render the 
 new tuber pendulous (fig. 
 w) *. 
 
 If we take the Potatoe to 
 exemplify the organization of 
 the tubers of Dicotyledons, we shall find that 
 they resemble, in an equal degree, the stems 
 of the tribe. When a tuber of this plant is cut, 
 either transversely or longitudinally, it appears 
 evidently to be composed of two distinct parts ; 
 one of which is internal and cellular, somewhat 
 like the pith or central part of the stern of the 
 plant, and surrounded on every side by the other, 
 which is cellular also but more dense, and bor- 
 dered with a complicated system of vessels, 
 branches from which stretch into the pith ; and 
 that it has a close affinity to the cortical part of 
 the stem. 
 
 * The plant from which this figure was drawn was raised in 
 a common garden pot, with the old tuber very near the surface. 
 a. The old tuber ; b. the new tuber ; e. the attaching process 
 extended so as to assume the form of a runner. 
 
LECT. IV.] THE ROOT. TUBERS. 163 
 
 Wherever a gem is formed on the tuber, the 
 pith or central part advances to the surface^ and 
 gives a small thread of its substance to the em- 
 bryon ; and this appears to furnish its pith : whilst, 
 in the same manner, the cortical substance, which, 
 although attenuated almost to a pellicle^ yet still 
 surrounds the thread of pith, seems to supply its 
 bark*. The vessels also of the tuber tend to each 
 point where a gem rises on its surface ; and, when 
 this begins to vegetate, they enlarge so much as 
 to become very perceptible to the naked eye ; and 
 acquire a retrograde movement, taking on the 
 functions of absorbents, and conveying the nutri- 
 tious matter deposited in the tuber to the vascular 
 system of the germe for its evolution and support. 
 
 The epidermis of tubers, to whichsoever na- 
 tural order of plants they belong, is utterly devoid 
 of either absorbing or exhaling organs ; and it is 
 this circumstance which fits tubers so admirably 
 for preserving, in an unaltered state, the nutri- 
 ment deposited in them ; the preservation of this 
 in its natural state being absolutely necessary for 
 
 * Vide Plate 1, fig. 4-. A longitudinal slice of a Potatoe : 
 a. the central part, or pith ; b. the cortical part ; c. the change 
 in the position of these parts where a gem is given off; d. the 
 point where the tuber was attached to the runner. It may 
 not, perhaps, be unnecessary to say that the points on the sur- 
 face of a Potatoe, called eyes in common language, are the 
 gems, the rudiments of the expected plants. 
 
 Mi 
 
164 CONSERVATIVE ORGANS. [LECT. IV. 
 
 enabling the germe to maintain its vitality. Finally 
 we may, with Sprengel, regard the tuber as a 
 hybernaculum, or winter habitation, for the pre- 
 servation of the embryon plants yet latent in the 
 gems which it bears *. 
 
 The BULB, the next of the radical appendages 
 which we have to examine, is a globular or pyri- 
 form, coated body, solid or formed of fleshy scales 
 or layers, and of a more or less complex structure. 
 It is not peculiarly an appendage of the root, but 
 is found also on the stem and branches of some 
 plants, and even mingled with the flowers of 
 others. As, however, the bulbs which are attached 
 to the root, have several peculiarities which dis- 
 tinguish them from those situated on the other 
 parts of the plant, it is necessary to treat of them 
 in this stage of our inquiries. 
 
 The roots of bulbs are simple fleshy fibres, 
 annual productions, which issue either from the 
 circumference of the flattened basis of a kind of 
 caudex on which the scaly and laminated bulbs 
 are seated, or from the substance of the bulb itself, 
 
 * Linnaeus defines the hybernaculum thus : " Hybernaculum 
 " est pars plantae includens herbam embryonem ab externis 
 " injuriis ;" and adds, " estque Bulbus vel Gemma." Sprengel, 
 in the edition of the Philosophia Botanica, which he has edited, 
 very properly adds the tuber. " Tuber est hybernaculum solidum, 
 " substantia marginali molliori cinctum'* 
 
LECT. IV.] THB ROOT. BULBS. 165 
 
 or from a simple scale, when it is solid ; and these 
 situations of the roots form the chief characteristic 
 of the bulb, distinguishing it from the tuber, and 
 marking out those limits between the bulb and 
 the tuber, ,the existence of which is denied by 
 Mirbel * and some other authors : for the roots of 
 the plant borne on a tuber, whether of the closely 
 attached or pendulous kind, always proceed from 
 the stem. 
 
 Bulbs, like tubers, are reservoirs of nutriment 
 for the developement and temporary support of 
 the plants formed within them ; a fact which is 
 illustrated to common observation by the growing 
 of onions, in the storeroom of the housewife. 
 Young radical bulbs, as I shall soon have occasion 
 to show you, are produced in some instances above, 
 in others below, and in others again within, or at 
 the sides of an old bulb, during the adult vegeta- 
 tion of its plant ; and are, like the gems formed 
 on the surface of a tuber, the lateral progeny of 
 the plant itself, not of the bulb. They are more 
 frequently formed previously to the flowering of the 
 parent plant; and as they preserve the plantule 
 within them, until the ensuing spring, they are re- 
 garded as winter habitations (hybernacula) by Lin- 
 
 * " II n'y a point de limites entrela bulbe et le tubercule; la 
 " transition se fait de 1'une a 1'autre, par la bulbe solide qui 
 " participe de toutes deux." Elem. de Phys. veg. l ere partie, 
 p. 135, nota. 
 
 M 3 
 
166 CONSERVATIVE ORGANS. [LECT. IV. 
 
 neeus, who points out the close affinity, except in 
 situation*, which exists between them and the 
 buds of trees. 
 
 Bulbs may be divided into solid, scaly, and 
 laminated. 
 
 I. The SOLID BULB ^ is a mass of cellular 
 substance, filled with nutritious fluids, and en- 
 closed within a thin epidermis, with vessels run- 
 ning through it from the basis to the apex. It is 
 covered with one or more coats, either of a mem- 
 branous, or a fibrous, or a reticulated texture J. 
 The solid bulb resembles the tuber in several re- 
 spects ; but differs from it in being coated, and, 
 as has been already noticed, in giving off the roots 
 from a radical plate, or from a scale at the basis 
 of the bulb, the point opposite to that from which 
 the shoot is produced. 
 
 Solid bulbs may be arranged under three spe- 
 cies, taken from the situation on the old bulb 
 where the new one is produced ; and thence they 
 may be denominated superincumbent, lateral, and 
 enclosing. 
 
 1. The Superincumbent solid bulb (Bulbus so- 
 lidus superpositus) I have so named from the new 
 bulbs being produced on the summit of the old 
 one, and appearing, even when they are fully 
 
 * " Bulbus est hybernaculum caudiei descendenti insidens." 
 Phil. Bot. 85. 
 
 f " Solidus constans substantia solida.'* Ib. 
 J Vide Plate L fig. 7. 
 
IrECT. IV.] THE ROOT. BULBS. 167 
 
 grown,, incumbent on it ; as exemplified in 
 Crocus*, Ixia^y &c. The old bulb withers, whilst 
 those which it bears are attaining maturity; but 
 it does not entirely decay away, so as to leave its 
 progeny as distinct and separate individuals, until 
 the new bulbs be formed on them. In some in- 
 stances, Crocus for example, the plants of the 
 present year, besides exhausting the old bulb for 
 their support, appear to obtain that portion also of 
 their nourishment, which is drawn from the soil, 
 through it ; the vessels that proceed from its ra- 
 dical plate passing through the centre of the 
 present year's bulbs, and sending canals even to 
 the rudiments of those formed at the basis of their 
 foliage. This is rendered evident to the naked 
 eye by dividing bulbs of Crocus sativus, taken 
 up in the latter end of May ^. In other plants, as 
 
 * Vide Plate 1 . fig. 5. Bulbs of Crocus sativus dug up in 
 May. a. b. the perfected bulbs, adhering closely to c. the old 
 bulb much shrivelled ; d. the radical plate of the old bulb with 
 roots protruded from its circumference. 
 
 f Fig 7. Bulbs of Ixia polystachia taken up, also, in May. 
 a. b. the new bulbs which bear the present year's foliage and 
 flower, partly covered with c. the reticulated coat of the old 
 bulb d. ; e. e. e. e. e. the roots of the recent bulbs, protruded 
 between them and the old bulb;,/, a small bulb appended by a 
 runner as described in the text. 
 
 J Fig. 6. The bulbs of fig. 5 dissected : a. b. the re- 
 cent bulbs ; c. the old bulb, with its vessels seen passing 
 up from its radical plate, and continued through the new 
 bulb to the basis of its foliage ; d. two cords of vessels which 
 
 M4 
 
168 CONSERVATIVE ORGANS. [LECT. IV. 
 
 Ixia for instance, although the same course of 
 vessels be perceptible, yet, very thick roots are 
 thrown out from the superincumbent recent bulbs, 
 by which the nutriment is immediately taken up 
 from the soil, without passing through the de- 
 caying bulb *. Under certain circumstances of 
 soil, also, wires are protruded from between the 
 more recent bulbs and the old bulb, with small 
 bulbs attached to them-f-, and these are some- 
 times so elongated as, to give to the lateral pro- 
 geny a pendulous character. 
 
 On dissecting this species of bulb, we find 
 that, besides the outermost coat, which is in 
 general either fibrous or reticulated, it has two 
 others more succulent and fleshy, which appear to 
 form the bases of the sheathing of the leaves, and 
 to cover the whole of the bulb terminating at the 
 plate whence the roots are protruded. Within 
 these is the solid homogeneous mass of the bulb, 
 covered with a thin, beautiful, transparent epider- 
 mis, and depressed considerably in the centre, 
 where the stem and part of the foliage are at- 
 tached ; and having cavities also at those points 
 where the young bulbs are formed. The exterior 
 leaves terminate at a kind of shoulder, which sur- 
 
 separate from the others immediately after they enter the new 
 bulb, and pass on to the embryon bulbs, forming on a. 6. e* 
 the embryon bulbs. 
 
 * Vide Plate I. fig. 7. f Ibfd. fig. 7. 
 
LECT. IV.] THE ROOT. BULBS. 169 
 
 rounds the general cavity ; and within the ex- 
 panded bases of these leaves the young bulbs are 
 seated. As in the case of tubers, although the 
 young bulbs are the production of the existing 
 plant, yet, as has been already remarked, they 
 have a vascular communication with the soil 
 through the medium both of their direct parent 
 and the old decaying bulb*. From this examina- 
 tion the following physiological conclusions may 
 be drawn ; that, in this species of the solid bulb, 
 the old bulb is exhausted in the production of the 
 herbaceous part of the plant by the functions of 
 which the bulbs immediately incumbent upon it, 
 and which bear that plant, are perfected, and by 
 which the embryon bulbs, seated on each of 
 them, are also formed. Towards the autumn, the 
 exhaustion of the old bulb is completed ; and the 
 vinculum which connects together the bulbs seated 
 on it, and which are now perfected, being thus 
 broken, they separate ; and each remains as a 
 distinct being, to be in its turn exhausted, in the 
 production of the plant of the ensuing year, and 
 of its series of bulbs. 
 
 2. The Lateral solid bulb (Bulbus solidus la- 
 teralis) is named from the new bulbs being formed 
 on each side of the old, as exemplified in Colchi- 
 cum autumnale. In this species of solid bulb, the 
 
 * Vide Plate 1. fig. 6. d. 
 
170 CONSERVATIVE ORGANS. [LECT. IV. 
 
 old bulb is completely exhausted, and the new 
 bulbs separated from it before the rudiments of 
 the next series are perceptible. The points of 
 union between the parent and its progeny are near 
 the basis of the bulb on both sides. On dissection, 
 the perfect bulb is found to consist of a mass of 
 cellular substance turgid with moist farinaceous 
 matter ; but it is not, as in the former species, per- 
 fectly homogeneous, one part being opaque, and 
 the other semitransparent. The vessels run lon- 
 gitudinally through the bulb, from the radical 
 plate to the part whence the foliage springs ; and, 
 in their dried up state, in conjunction with the 
 emptied cellular texture and the epidermis, give a 
 tough, spongy character to the exhausted bulb ; 
 which, at the time of the separation of the recent 
 bulbs, exhibits the appearance of a shrivelled 
 leathery bag, the roots having dropped from the 
 radical plate *. 
 
 * Vide Plate 1. fig. 8, 9, 10, which represent the bulbs of 
 Colchicum autumnale, dug up in May, in different points of 
 view. Fig. 8. a. b. the recent bulbs (denuded so as to show 
 their true appearance) of an irregular Pear shape, being con- 
 siderably longer on the side opposite to that by which they are 
 attached to the old bulb, and terminating in c. c. a flattened 
 process ; on the inner and upper part of which, under a pro- 
 jection formed by the termination of the shorter side of the 
 bulb, is the radical plate, whence the roots protrude. It is 
 half way above this plate, on the one side, and behind the 
 flattened process, on the other, that the new bulbs are formed. 
 
 d. The 
 
LECT. IV.] THE ROOT. BULBS. 171 
 
 The physiology of this species of solid bulb 
 closely resembles that of the other. The new 
 bulbs are produced by the plant of the bulb to 
 which they are attached, and which is exhausted 
 in the support of the foliage and fructification they 
 bear : and in partly supplying also the nutriment 
 which is deposited in them : I say partly, because 
 it must be kept in mind, that the recent bulbs, of 
 both species, have a direct communication with the 
 soil through their roots ; and consequently it is 
 probable that by far the greater part of the matter 
 deposited in them, proceeds from the nutriment 
 obtained from the soil, changed into the proper 
 juice of the plant by the functions of the leaves. 
 
 3. The Enclosing solid bulb (Bulbus solidus 
 includens), I have named from the circumstance 
 of the young bulbs being enclosed between their 
 
 d. The old bulb shrivelled up ; e. the remains of its radical 
 plate ;f. the remains of its terminal process. 
 
 Fig. 9. the back view of fig. 8. a. b. the recent bulbs ; c. c. 
 the flattened processes seen from behind ; d. the old bulb ; 
 
 e. the remains of its radical plate. 
 
 Fig. 10. a longitudinal slice of the bulbs, a. The old shri- 
 velled bulb ; b. c. the recent bulbs, in which is seen the dis- 
 similar structure of their mass ; d. the opaque portion ; e. the 
 semitransparent : the longitudinal lines in d. show the course of 
 the vessels, proceeding from the point of attachment behind the 
 process of the old bulb ; at^ and on the opposite side, from 
 that above its radical plate at g. h. h. the part of the bulbs on 
 which the foliage is seated. 
 
172 CONSERVATIVE ORGANS. fLBCT. IV. 
 
 \ - 
 
 common parents; which, in this species of bulb, 
 are two hemispheres, opposed to each other by 
 their flat surfaces, and united at their bases to the 
 radical plate, whence the stem proceeds *. Its 
 physiology is the same as that of the other solid 
 bulbs. 
 
 II. SCALY BULBS consist of fleshy scales at- 
 tached to a radical plate, and so arranged as to 
 lie over each other like the tiles of a roof. v Each 
 scale is a homogeneous mass of cellular substance, 
 thick and fleshy in the middle ; but in some in- 
 stances nearly membranous at the edge, concave 
 on one side, and necessarily convex on the other. 
 Each scale, also, is a distinct reservoir of nutri- 
 ment, and is endued with such a share of vitality 
 as not only enables it to live if detached from the 
 bulb ; but, when placed in a proper soil, to ve- 
 getate and produce an entire new bulb. There are 
 two species only of scaly bulbs, the squamous and 
 the granulated. 
 
 1 . The Squamous bulb (Bulbus squamosus ^) 
 
 * Vide Plate 3. fig. 12. The twofold bulb of cluster-flowered 
 Fritillary (F. Pyrenaica). A. a. a. the two hemispheres united 
 at the caudex ; b. the stem rising between them ; c. the roots : 
 B. a. one hemisphere separated from the other, in order to show 
 the two young bulbs b. b. produced on each side of the stem c. ; 
 the longitudinal line on each marking the place at which the di- 
 vision will take place: d. the caudex. 
 
 f " Squamosus constans imbricatis lamellis. Lilium.*' Phil. 
 Botan. 85. 1. 
 
 4 
 
LECT. IV.] THE ROOT. BULBS. 173 
 
 is well exemplified in the LiJy tribe. If we dig 
 up a plant of one of these, say the White Lily, 
 Lilium candidum, in summer, and examine its 
 bulb, we shall find that it consists of concave, 
 fleshy, overlapping scales, each of which is at- 
 tached at the base to a radical caudex, but is 
 loose at the apex*. A scale, when separately 
 examined, appears to be a homogeneous mass of 
 cellular texture enclosed in a cuticle ; the middle 
 being thick and fleshy, but the edges and the 
 apex nearly membranous; a construction, which, 
 on the convex surface, gives it a gibbous or keeled 
 character. The vessels run in longitudinal cords, 
 arranged at equal distances, through the scale ; as 
 may be seen in a transverse section of it, if the bulb 
 Have been placed for some hours in a coloured so- 
 lution-^. Removing the scales till the stem be ex- 
 posed, the new bulb is seen formed at its basis ; and, 
 by making a longitudinal section of the whole, the 
 manner in which the lateral offspring is connected 
 with the parent plant, through the medium of the 
 vascular system of the stem and of the caudex, is 
 
 * Plate 2. fig. 1. The entire bulb of the Lilium candidum, 
 as it appears, when taken up in summer, during the vegetation 
 of the stem. 
 
 f Fig. 2. A transverse slice of one of the scales, to 
 show the arrangement of the vessels in its substance. The 
 vascular bundles appear like dots ; and owing to the cellular 
 texture being more condensed in the immediate vicinity of 
 these, each bundle seems as if it were enclosed in a sheath. 
 
174 CONSERVATIVE ORGANS. [LECT. IV. 
 
 made apparent*. When the new bulb is per- 
 fected after the flowering 1 season is over, the ex- 
 terior scales of the old one decay ; and by degrees 
 the stem and a large portion of the old caudex 
 also separate ; but as the whole of the caudex 
 does not slough off, and a new portion is added by 
 each successive bulb, it becomes gradually elon- 
 gated, and at length bears some resemblance, 
 when the scales are taken off, to a cylindrical, 
 toothed, praemorse root. The new bulb, how- 
 ever, is not always found seated close to the stem, 
 in every species of this natural genus of bulbife- 
 rous plants. In Lilium superbum, for instance, 
 a very thick, succulent, lateral runner is projected 
 from the caudex of the bulb ; and, pushing aside 
 the neighbouring scales, advances considerably 
 beyond them, bearing the rudiments of the new 
 bulb on its extremity. Owing to this circumstance, 
 the plant of each successive year rises at some 
 distance from the site of its predecessor ; and as 
 the old bulbs do not soon die away, one or two of 
 these, in a decaying state, are generally found 
 
 * Plate 2. fig. 3. A. The young bulb as seen at the basis of 
 the stem, when the scales of the old bulb are removed : a. the 
 stem ; b. the young bulb ; c. the attached fragments of the 
 scales ; d. the roots of the present year's bulb ; e. the remains 
 of those of last year. B. The interior of A. divided by. a 
 longitudinal section ; a. the remains of last year's caudex ; b. 
 the caudex of the bulb of the present year, with the vessels 
 which nourish it anastomosing with those of the parent stem. 
 
LECT. IV.] THE ROOT. BULBS. 175 
 
 appended to the present year's bulb *. On taking 
 off the scales of the bulb, the manner in which 
 the runner, which bears the new bulb, is sent off, 
 becomes extremely apparent -f- ; and the connexion 
 between it and the stem and caudex of the adult 
 bulb is rendered still more obvious, by inverting 
 the cut end of the stem in a coloured solution, 
 and making a longitudinal section of the whole ; 
 for, as the vessels in this species of Lily are com- 
 paratively large, they can be readily traced, by 
 the naked eye, when filled with the colouring 
 matter, passing from the stem into the caudex, 
 thence into the runner, and through it to the small 
 scales forming on its apex J. 
 
 * Plate 2. fig. 4-. The bulb of the superb Lily, with a 
 small portion of the stem of the plant, a. The bulb of the 
 present year ; b. last year's bulb in a decaying state, with c. 
 the remains of the bulb of the prior year still attached to it : 
 
 d. the rudiments of the new bulb attached to the extremity of 
 the succulent runner, shooting forward between the scales; 
 
 e. the roots of the bulb ; f. roots given off from the stem above 
 the bulb. 
 
 f Fig. 5. a. The caudex of the bulb denuded of its scales. 
 b. the runner projected from it, and bearing the rudiments of 
 the young bulb on its extremity ; c. d. the remains of former 
 years' bulbs ; e. the cut stem of the vegetating plant ; f. the 
 roots of the adult bulb. 
 
 J Fig. 6. a longitudinal section of the caudex and lateral 
 runner of fig. 5. injected by placing the cut end of the stem 
 in a solution of extract of Logwood : a. the caudex, the coloured 
 spots in which show where the bundles of vessels passed off to 
 
176 CONSERVATIVE ORGANS. [LECT. IV. 
 
 It has been already stated, that each scale is not 
 only a distinct reservoir of nutriment ; but that it 
 is endued with such a share of vital energy, as 
 enables it, when detached from the bulb and 
 placed in a proper soil, to produce an entire new 
 bulb. In this respect, the scale resembles some 
 leaves, which I shall particularize when we treat 
 of those organs. The scales of the Canadian, 
 and those of the scarlet Pompone Lily, both of 
 which are natives of high latitudes, exhibit this 
 property more readily than any other of the tribe. 
 The young bulb rises either from a callus formed at 
 the base, or the margin of the scale * ; which gra- 
 dually decays away as the bulb enlarges ; and 
 finally separates from it as soon as a sufficient num- 
 ber of roots are produced to support this lateral 
 production as an independent being. The bulbs, 
 however, which are thus propagated, differ from 
 those formed in a more direct manner, as they pro- 
 duce leaves only ; and several successions of leaf 
 bulbs are propagated in a direct line from them, 
 
 the scales of the adult bulb; b. the stem with the vessels injected; 
 c. the runner, with the vessels running through it to supply the 
 rudiments of the young bulb on its extremity ; d. a scale of the 
 young bulb ; e. the place where the runner that supported the 
 adult bulb was broken off. ' 
 
 * Fig. 7. a scale of Lilium pomponium, with two bulbs, a. 
 and b. forming on it. Fig. 8. a portion of a scale of Lilium su- 
 perbum with a bulb formed on its edge ; a. a root already pro- 
 truded from the bulb. 
 
LECT. IV.] THE ROOT. BULBS. 177 
 
 before a flower bulb is produced. It may seem ex- 
 traordinary that no formation of young bulbs oc- 
 curs on the scales individually, when they are al- 
 lowed to remain attached to the old bulb ; but 
 when we consider that in this case their vital 
 energy, and the nutriment they contain, are ex- 
 hausted in supplying the growing plant, and aid- 
 ing the formation of its lateral progeny ; and 
 that, on the contrary, when a scale is separated, 
 the formation of the new tyulb is merely the em- 
 ployment of the same agencies, which would have 
 acted simultaneously with the other scales had 
 the separated scale been left in its original 
 state, only differently directed, the explanation is 
 obvious. Another question, however, arises on 
 this point. If, as has been stated, the young 
 bulb be the production of the joint action of the 
 bulb and the plant, how is the bulb on the solitary 
 scale formed ? I confess my inability to solve this 
 question ; and can only remark, that the bulb 
 formed on the separated scale is, comparatively, a 
 very imperfect being; and the formation of a 
 series of bulbs in a direct line from it, each pro- 
 gressively more perfect than its precursor, is 
 requisite before a bulb can be produced as perfect 
 as that one, which is the effect of the joint func- 
 tions of the plant and of the vipe or adult bulb : 
 and in this progression to perfection the plant 
 of each season necessarily plays its part. 
 
 VOL. I. N 
 
178 CONSERVATIVE ORGANS. [LECT. IV. 
 
 2. The Granulated bulb (Bulbus granulatus) is 
 named from its appearance being that of a small, 
 globular body, or grain. It is found usually asso- 
 ciated with many others, studding, as it were, the 
 root to which they are affixed ; as is beautifully ex- 
 emplified in that of grain-rooted Saxifrage, Saxi- 
 fraga granulata *. On examining a single bulb, we 
 find that it is composed of slightly curved granular 
 scales, covered with two coats -j~, and enclosing the 
 plantule, which, on vegetating, bursts the coats 
 and shoots up between the scales. As it advances, 
 these are gradually emptied, until the epidermis 
 only remains like a small shrivelled leaf; whilst 
 fresh bulbs are generated upon runners, sent off 
 from the basis of the herbage. The minuteness 
 of the scales prevents their structure being ex- 
 amined by the unassisted eye ; but, with the aid 
 of the microscope, it is perceived to be nearly the 
 same as that of those of the squamous bulb. 
 
 III. LAMINATED BULBS are composed of fleshy 
 layers, attached at the base to a solid radical 
 caudex. Each layer consists of a plate of cel- 
 lular substance, filled with secreted juices, and 
 enclosed between two cuticles. Bundles of ves- 
 
 * Vide Plate 2. fig. 9. which represents the bulbs congre- 
 gated on the runner of the plant a, 
 
 f Fig. 10. a. a bulb denuded of its coats, with the plan- 
 tule in a state of vegetation ; b. a plantuie separated from 
 the enclosing scales, attached to the radical plate, and a small 
 fragment of the tunic. 
 
LECT. IV.] THE ROOT. BULBS. 179 
 
 sels run vertically through each layer, communi- 
 cating with those of the caudex, the stem, and the 
 roots : these are entire and porous vessels ; but in 
 some of the laminated bulbs, the spiral vessels 
 are so numerous as apparently to make up the 
 greater part of the substance of the layers. There 
 are two species of laminated bulbs ; the concen- 
 tric and the nestling. 
 
 1. The Concentric laminated bulb (Bulbuscon- 
 centricus tunicosus) consists of sheathing laminae, 
 each enclosing, or nearly enclosing, the other from 
 the centre to the exterior coat or tunic. This spe- 
 cies of laminated bulb may be subdivided into two 
 sections ; the first comprehending those bulbs in 
 which the layers are entire, or in which each 
 layer is the sheath, as it were, of those within it ; 
 and the second, those in which the layers are 
 divided, or only overlap those within them, but 
 do not form an entire sheath, as in the former 
 instance. 
 
 * With entire Layers. 
 
 The most familiar examples of this division are 
 the common Onion, Allium Cepa, and the mem- 
 bers of the Narcissus tribe. In these, the cau- 
 dex is of an irregular, serniorbicular form ; and 
 consists of a central cellular part or pith, covered 
 by a more solid envelop or cortex, which is inter- 
 posed betwixt the basis of the layers and the pith, 
 and forms also the proper radical plate, whence 
 
 N'2 
 
 UNIVERSITY 
 
 OF .. 
 
180 CONSERVATIVE ORGANS. [LECT. IV. 
 
 the roots are protruded. The number of the 
 layers varies : the exterior are thin and semipellu- 
 cid, being 1 formed simply of two membranous cu- 
 ticles, with equi-distant bundles of vessels running 
 longitudinally through them : the interior are 
 more fleshy, the cells being filled with nutritious 
 juices. A transverse section of the bulb exhibits 
 the continuous character of each layer *. The 
 new flower bulb is formed nearly in the centre of 
 the old bulb, at the base of the stem ; but in 
 general, there are several leaf bulbs formed : one 
 or more within the second or the third layer from 
 the surface, and others laterally and altogether 
 exterior to the old bulb. The outer layers only of 
 the old bulb are completely exhausted in one sea- 
 son ; hence the bulb in several subsequent seasons 
 appears to be the same which originally flowered, 
 only much enlarged. The lateral bulbs separate, , 
 and, as in similar cases, maintain an independent 
 existence. In the Tulip, the bulb consists usually 
 of four concentric layers only (independent of the 
 common coat), the outermost of which may be 
 termed fleshy ; but being nearly diaphanous, the 
 longitudinal vessels are seen running through it 
 at equal distances, with the intervening spaces on 
 
 * Vide Plate 3. fig. 1. which represents the transverse section 
 of the bulb of Narcissus Jonquitta : a. a. two young bulbs 
 rising betwixt the second and third layers ; b. the roots pro- 
 truded from the radical plate, which is hid by the position of the 
 bulb. 4 
 
LECT. IV.] THE ROOT. BUJUBS. 181 
 
 the inner surface studded with opaque slightly 
 elevated glands, which produce correspondent 
 depressions on the outer surface of the next layer. 
 The other layers are fleshy and thick in proportion 
 as they approach the enclosed plantule, or centre ; 
 and, although the depressions of the glands be 
 visible on the exterior of each, yet, from the tur- 
 gidity of the cellular texture, neither these nor 
 the vessels are perceptible in them ; but by placing 
 the bulb in a coloured solution for twenty-four 
 hours, and then making a transverse section of it, 
 the latter are seen like coloured points arranged in 
 a regular series, and nearly equi-distant from the 
 enclosing epidermis of each layer*. By tearing 
 the layer longitudinally opposite to any of these 
 points, the vessels can be traced downwards 
 through the substance of the layer, and even into 
 the radical plate. 
 
 In this bulb, the stem, which bears both the 
 foliage and the flower, rises from the centre of the 
 bulb ; but as soon as the new bulb, which is 
 formed close to its base, enlarges, the enclosing 
 laminae of the old one Jbegin to lose their suc- 
 culency and plumpness ; and this exhaustion con- 
 
 * Plate 3. fig. 5. a transverse section of a Tulip bulb, du- 
 ring the flowering season, a. Section of the stem ; b. remains of 
 the exhausted layers of the old bulb ; c. the new bulb, which 
 should flower next season ; the dots in the layers showing the 
 positions of the longitudinal bundles of vessels. 
 
 N3 
 
182 CONSERVATIVE ORGANS. [LECT. IV. 
 
 tinues to keep pace with the enlargement of the 
 offspring 1 , until the layers are completely emp- 
 tied. They then decay away, and leave the stem 
 partially covered with the void cuticles on the 
 outside of the new bulb *. The stem itself, with 
 the old radical plate, next die away ; while the 
 new bulb, after remaining as it were in a state 
 of inactivity during the winter, shoots out fresh 
 roots from its radical plate in the spring, and runs 
 the same course as its predecessor. Under fa- 
 vourable circumstances, two or three new bulbs 
 are sometimes formed in the same season ; but these 
 are usually only leaf bulbs -f~. 
 
 In long-rooted Allium (Alliurn victor tails) the 
 concentric sheathing layers (each of which, as in 
 several other species of the genus, is expanded 
 into a leaf) are of a reticulated texture^; and 
 
 * Fig. 6. a longitudinal section of a Tulip bulb, during the 
 flowering season, a. Section of the stem ; b. the remains of 
 the old bulb ; c. the new flower bulb enveloped in d. its sheath or 
 exterior coat ; e. the rudiment of the caudex of the new bulb, 
 where it separated from the parent stem. 
 
 -p Plate 3. fig. 4. a bulb of the common Tulip taken up in 
 the flowering season, a. Part of the stem, which is cut off; 
 b. the exterior layers of the exhausted bulb, enveloping both 
 the new flower bulb c. and an offset, or lateral leaf bulb, the 
 stem from which is seen at d. 
 
 t Fig. 2. a bulb of long-rooted Allium. a. The outer layer 
 of the present year's bulb, extended into the sheathing stem ; 
 b. the reticulated layers, loose both at the caudex c. and 
 above ; d. the roots of the existing bulb piercing the network 
 of the reticulated layers. 
 
LECT. IV.J THE ROOT. BULBS. 183 
 
 when exhausted of the nutriment contained in 
 them, assume the appearance of lacework. In 
 this bulb, also, the young bulbs are formed within 
 the second layer of the present year's bulb *. 
 
 * * With divided Layers. 
 
 In this division of the concentric laminated 
 bulbs, the layers, as has been already stated, do 
 not form an entire sheath. In the garden Hyacinth 
 (Hyacinthus orient alls), which I select as an ex- 
 ample because it can be easily procured, they 
 comprehend two thirds only of the circumference 
 of the circle. Each layer is fleshy and thick in the 
 centre, and becomes gradually thinner towards 
 its edges until it terminates in a membranous 
 film, embracing the layers within it in the same 
 manner as the hand holds a ball which it cannot 
 completely enclose. The deficient portion of each 
 layer is always on the opposite side to that of the 
 layer immediately beneath it. The caudex has 
 the character of a segment of a hollow sphere, 
 on the convex surface of which the layers are 
 attached ; whilst a considerable number of fleshy 
 roots protrude from the circumference -j~. The 
 
 * Fig. 3. a vertical section of the same bulb. a. the suc- 
 cessive succulent layers extended into the stem ; b. the ex- 
 hausted reticulated layers ; c. the caudex ; d. the young bulb. 
 
 f Vide Plate 3. fig. 6 and 7. a. The body of the bulb ; b. 
 the manner in which the layers overlap each other ; c. the 
 radical plate, with the roots separated from one side of the cir- 
 
 N4 
 
184 CONSERVATIVE ORGANS. [LECT. IV. 
 
 vessels run in longitudinal bundles through the 
 layers ; and so numerous are the spiral vessels in 
 this description of bulb, that, in the Amaryllis 
 tribe, the Squill, and some other of the larger 
 bulbs, on breaking a layer transversely, they may 
 be drawn out to the distance of three or four 
 inches ; and from the strength of their component 
 fibres and their number, they are capable of sup- 
 porting the pendulous portion of the layer. I 
 have also been informed that the fibres of the 
 spiral vessels of the bulb of some species of the 
 Blood-flower (Haemanthus) have been spun into 
 thread and manufactured, which I can readily be- 
 lieve, from the strength of a thread which I have 
 formed from the spiral fibres of the layer of a bulb 
 of Brunsvigia toxicaria, Poison- bulb, by merely 
 twisting them in my fingers. On making a trans- 
 verse, or a longitudinal section of the Hyacinth' 
 bulb, we find one or more young bulbs seated be- 
 tween the layers * ; and that one which is nearest 
 
 cumference, to show its concavity ; d. young lateral bulbs, 
 which produce leaves, and si new bulb when detached from the 
 parent ; e. a bulb, which has produced leaves this season, formed 
 within the coats of the old bulb. 
 
 * Vide Plate 3. fig. 8. and 9.-- Fig. 8. a. The caudex, as it 
 appears in the longitudinal section of a full-grown bulb of Hya- 
 cinthus orientalis ; b. a young bulb forming with the outermost 
 fleshy layer; c. the remains of the stem and foliage of the pre- 
 sent year's plant. Fig. 9. a transverse section of another b*lb 
 of the same species of plant, showing the terminations of the 
 
LECT. IV.] THE ROOT. BULBS. 185 
 
 to the centre of the old bulb is, usually,, the real 
 flower bulb for the next season ; for, although, ow- 
 ing to a few of the outer layers only decaying, the 
 old bulb appears still to yield the flower, yet, this 
 actually springs every year from a new bulb formed 
 within the old one. Young leaf bulbs are also 
 protruded exteriorly from the base of the old bulb ; 
 and these appear to be really the production of the 
 bulb itself ; for the Dutch cut their bulbs trans- 
 versely, after they have attained a certain size ; 
 and plant the lower half, in order to multiply the 
 number of the lateral bulbs ; whilst the flower 
 bulb, as has been already stated, is evidently the 
 result of the combined functions of the plant and 
 the bulb. 
 
 No experiments, at least that I know of, have 
 been made, to ascertain whether a layer of any of 
 the concentric laminated bulbs, when separated 
 from its caudex and planted, will produce young 
 bulbs, as is the case with the scales of the squa- 
 rnous bulbs ; but I am of opinion that if an en- 
 layers, and the divided bundles of longitudinal vessels, a. 
 the lower portion of the flower stem ; b. the bulb which will 
 flower next year, gradually expanding the old bulb by its 
 growth ; c. the roots attached to the caudex, which are hid by 
 the position of the superincumbent parts. Fig. 7. another 
 bulb of the garden Hyacinth in which four young lateral leaf 
 bulbs d. are seen seated on the caudex, to show the manner 
 in which these lateral offsets generally occur. 
 
186 CONSERVATIVE ORGANS. [LECT. IV. 
 
 tire layer were carefully separated from its caudex, 
 and planted, it would produce young bulbs upon 
 its basis. 
 
 2. The Nestling bulb (Bulbus nidulans) is com- 
 posed of entire concentric layers, which termi- 
 nate in sheathing leaves, and enclose within each, 
 from the circumference to the centre, several young- 
 bulbs ; so that, when the layers are partially rup- 
 tured, the whole seems to consist of small bulbs, 
 and has a nestlike appearance *. The layers are 
 more membranous than those of the other lami- 
 nated bulbs we have examined ; and consequently 
 display, more evidently, the longitudinal equi-dis- 
 tant bundles of spiral and entire vessels. The 
 caudex is very vascular ; in form nearly an inverted 
 truncated cone, and protruding a great number of 
 long threadlike roots. 
 
 On dissecting the young bulbs, enclosed within 
 the old one, we find that those only which have 
 already shot up into leaf, contain small bulbs or 
 their rudiments within the layers ; hence, there is 
 reason for concluding that the young bulbs are in 
 this instance, chiefly the result of the functions of 
 the plant. In the bulb of Garlic, Allium sativum, 
 
 * Vide Plate 3. fig. 10. the recent bulb of Garlic, Allium 
 sativum, with the sheathing layers partially removed to exhibit 
 the young bulbs, a. The young bulbs ; b. c. d. e. remains of the 
 sheathing layers \f. the caudex. Fig. 1 1. a longitudinal section 
 of the same bulb. a. the caudex ; b. c. d. the sheathing layers, 
 which terminate in leaves. 
 
LECT. IV.] THE ROOT. BULBS. 187 
 
 the odorous, acrid, secreted juice which character- 
 izes it, is found in greatest quantity in the fleshy 
 internal layers of the young bulbs * ; and conse- 
 quently these are the parts employed both medi- 
 cinally and as a condiment ; whilst, in the mem- 
 branous layers of the old bulb, it is scarcely per- 
 ceptible either to smell or to taste. 
 
 Such are the characteristic distinctions of those 
 appendages of roots, which are denominated 
 bulbs. They have been properly regarded by Dr. 
 Darwin -f and others as subterraneous buds ; and 
 as having a close affinity with the buds on the 
 stem and branches of perennial plants : for, like 
 these, they continue rather than reproduce the 
 individual, and are liable to all the hereditary im- 
 perfections and diseases of the parent. In some 
 other particulars also this resemblance holds good; 
 for, as in all plants which are furnished with buds, 
 those produced in the first years of the plant are 
 leaf buds only, and a succession of these occur be- 
 fore flower buds are formed, so no flower bulb is 
 ever produced from seed ; the first formed being 
 always a leaf bulb, which, in many instances (as 
 the Tulip for example), produces another leaf bulb, 
 and so on for several successive generations, until 
 at length a flower bulb is formed ; after which, one 
 
 * In common language these young bulbs are termed cloves. 
 
 f Phytologia passim. 
 
188 CONSERVATIVE ORGANS. [LECT. IV. 
 
 flower bulb at least is produced every season. 
 Many circumstances connected with the physi- 
 ology of bulbs might be treated of in this place ; 
 but, as I shall have again to recur to them in no- 
 ticing those bulbs which are formed on the stem, 
 and among the flowers of many plants, I shall 
 defer at present the further consideration of this 
 part of our subject. 
 
 And being now acquainted with the forms 
 which characterize roots and their appendages, we 
 shall, in our next Lecture, finish the consideration 
 of these vegetable organs. 
 
LECT. V.] THE ROOT. 189 
 
 LECTURE V. 
 
 THE SUBJECT OF THE FORMER LECTURE CONTI- 
 NUED. OF SOILS AND MANURES. OF THE MEDI- 
 CINAL AND DIETETICAL PROPERTIES OF ROOTS. 
 \ 
 
 I HE usual situation of roots is in the ground ; 
 but many plants, although their seeds be sown 
 in the earth, yet, will not vegetate in it, their 
 proper soil being the bark of other living plants. 
 Such are named parasitical, owing to their nou- 
 rishment being obtained from those plants on 
 which they fix, and which they rob of a part of 
 their juices, often injuring them to a very consi- 
 derable degree. The Misletoe (Viscum album) ; 
 the Broom Rape^ Orobanche ; the majority of 
 Lichens ; the Mosses ; some of the Ferns ; many 
 of the Orchis tribe ; those minute fungi, which 
 produce the diseases of corn and of some grasses, 
 known by the names of rust, blight, and mildew ; 
 the Sclerotium crocorum, a sort of tuber which 
 attacks the bulb of the Saffron ; . and the Dry Rot, 
 to the destructive powers of which the noblest 
 specimens of architecture occasionally fall sacri- 
 fices ; are parasitic plants. Some of this descrip- 
 tion of plants, however, originally grow in the 
 earth, and do not lose their attachment to it 
 
190 CONSERVATIVE ORGANS. [LECT. V. 
 
 until they find another plant to lay hold of, and 
 into which they can dip their caulinar roots, or 
 rootlike absorbents, which are protruded from the 
 stem, in order to share its nutriment, and on 
 which they are afterwards supported ; as, for ex- 
 ample, the Cuscuta, or Dodder *, which may be 
 regarded as the natural parasite of our indigenous 
 Heaths and Hops. 
 
 Some plants, after they have arrived at a cer- 
 tain age, do not even require that their roots 
 should be fixed to any spot ; but maintain life on 
 what they can procure by absorption from the at- 
 mosphere. Such are the Cacti, a curious tropical 
 tribe of succulent plants ; on which account one 
 of the species, the Indian Fig, Cactus opuntia, 
 was recommended to the notice of seafaring 
 people, by the late Dr. Anderson of Madras, for 
 the purpose of supplying vegetable food on long 
 voyages ; and as a preventive of scurvy. But the 
 most curious instance of this kind is the aerial 
 flower, Epidendrum flos ae'ra-f-, an East Indian 
 parasitical plant, which continues to grow, blos- 
 soms, and even perfects its seed, when it is torn 
 
 * The Dodder germinates in the earth, and rising above it, 
 shoots out filiform stems, which twine around the neighbouring 
 plants. Its original root now decays, and a kind of warty roots 
 are formed in the stem at every point where it touches the sup- 
 porting plant by which it is nourished. 
 Aerides matutinum of Willdenow. 
 
LECT. V.] THE ROOT. 191 
 
 from the tree on which it originally grew, and is 
 suspended in the ceiling of an apartment *. Many 
 aquatic plants, also, have roots which serve no 
 other purpose than to fix them for a short time to 
 the spot where they have germinated, from which 
 they afterwards separate and float upon the surface 
 of the water; thus the common Duck Weed, 
 Lemna minor, which rises to the surface almost as 
 soon as it has germinated, has filiform roots from 
 three to six inches in length, which hang perpen- 
 dicularly in the water, and having no attachment 
 to any body, allow the plant to float freely in every 
 direction. 
 
 * Mr. Macnab, superintendent of the Botanic Garden at 
 Edinburgh, has published an account of a suspended plant of 
 Ficus Australis (Ferrugineous Fig), which had grown for 
 eight months, up to the time of publishing his paper, February 
 7th, 1820, without earth, in the stove of that garden. The plant, 
 which was originally growing in a pot in the greenhouse, on 
 being removed into the stove, and treated in a peculiar manner, 
 threw out several roots from the stem ; after which the earth 
 was gradually removed from the original roots, and the plant 
 left suspended in the air, affixed to the frame of the stove. 
 Water was, however, sprinkled over the whole plant every day. 
 " What," adds Mr. Macnab, "may appear rather remarkable 
 is, that though this Ficus is a plant by no means free in pro- 
 ducing fruit in the usual way of cultivating it, this specimen, 
 quite suspended, without a particle of earth, was loaded with Figs 
 during the months of September, October, and part of No- 
 vember. 1 * Edinburgh Philosophical Journal, vol. iii. p. 77. 
 
192 CONSERVATIVE ORGANS. [LECT. V. 
 
 All subterranean roots assume a particular di- 
 rection ; which is constant in every individual of 
 the same species of plant. They are said to be 
 perpendicular (perpendicular is) when the caudex, 
 or main body of the root,, extends perpendicularly 
 into the ground, as exemplified to the majority of 
 fusiform roots (p. 130), and in the main or top 
 root of most trees : and horizontal (horizontalis) 
 when the extension is nearly parallel to the plane of 
 the horizon, so that the root forms nearly a right 
 angle with the stem or herbaceous part of the 
 plant ; as, for instance, in Winter Green, Pyrola 
 umbellata, Sweet Flag, Acorus calamus, and in 
 the majority of the articulated roots. Many of 
 the horizontal roots, whilst they run under the 
 surface of the ground, push up stems at intervals 
 so as to multiply the plant ; tnence the appellation 
 creeping roots (R. repens) : as in common Spear 
 Mint, Mentha viridis ; Couch Grass, Triticum 
 x. repens ; Bulbife- 
 
 rous Coral Wort, 
 Dentaria bulbife- 
 ra(fig.x) 9 and ma- 
 ny other plants. 
 And this proper- 
 ty renders some 
 weeds extremely 
 obnoxious to the 
 farmer : for, if any portion of a creeping root be 
 
LECT. V.] THE ROOT. 193 
 
 left in the soil, it will throw up a new stem, which 
 in its turn produces an extension of the root. But 
 if it be injurious in some instances, it also serves 
 very important purposes in the economy of nature. 
 Thus the sand Reed-Grass, Carex arenaria, by 
 means of its creeping roots, binds together the 
 dry sand of the flats on the sea-shore where it 
 grows ; and assists not only in forming a fertile 
 soil where sterility would otherwise reign ; but 
 by preventing the sand from drifting, preserves 
 from destruction the neighbouring fields, which 
 already repay the labours of the agriculturist. 
 
 We must not, however, confound the creeping 
 with the progressive root (R. progrediens) , which, 
 in extending itself, likewise shoots up stems and 
 herbage at intervals ; since it differs in this cir- 
 cumstance, that as it advances anteriorly it decays 
 posteriorly; thus causing an obvious progression 
 of the plant ; and at the same time limiting in a 
 considerable degree its multiplication. Its direc- 
 tion also is not necessarily horizontal, like that of 
 the creeping root, but may be perpendicular ; the 
 cause of the progression in that case being the 
 production of a new root laterally : and, in this 
 respect, these roots, although the caudexes are not 
 tubers, yet have a close affinity with the attached 
 tuberiferous roots. Thus the root of officinal 
 VOL. i. o 
 
194 CONSERVATIVE ORGANS. [LECT. V. 
 
 Monkshood, Aconitum neomontanum (fig. ?/), af- 
 fords an excellent 
 example of the pro- 
 gressive conical 
 root; a. the old 
 root supporting b. 
 the lower portion 
 of the stem ; c. the 
 new root attached 
 by the lateral offset 
 d. to the basis of 
 the stem b. : so that 
 the new stem, which 
 should have arisen 
 from the bud e. 
 would have been 
 about one inch from 
 
 the old plant, had it been left in the ground. The 
 moniliform roots (p. 142), also, are progressive ; as 
 those of Paeony, Pseonia officinalis, and night smell- 
 ing Geranium, Pelargonium triste ; but in these 
 the progression is made by suckers thrown up 
 from the nodules ; such roots in this respect re- 
 sembling the tubers on the pendulous tuberiferous 
 roots. The difference, however, between the 
 progressive roots and the tuberiferous, is very ob- 
 vious; the caudexes and nodules in the former 
 being real roots, furnished with lateral rootlets 
 issuing from their surface; whilst the tubers, in 
 
LECT. V.] THE ROOT. 195 
 
 the latter, are appendages only to the real roots, 
 which are fibrous arid issue from the basis of the 
 stem, or the herbaceous part of the plant, and 
 not from the surface of the tubers. 
 
 Besides these roots which take the perpendi- 
 cular, or the horizontal direction, there are some 
 that assume an intermediate one, in which case 
 the root is said to be oblique (R. obliqua) ; but, as 
 in general, there is always an approximation either 
 to the perpendicular or the horizontal, the truly 
 oblique root is .very uncommon. In observing the 
 position of roots in the ground, it should be recol- 
 lected that it is the main root or caudex only which 
 determines this point; and that, whatever its di- 
 rection may be, that of the rootlets is always dif- 
 ferent: thus, in perpendicular roots, the rootlets 
 spread either horizontally or obliquely ; whilst in 
 the horizontal and the oblique they descend per- 
 pendicularly ; or, in every instance, they form an 
 angle more or less acute with the surface of the 
 caudex. The main root should be entire, also, be- 
 fore its direction or character can be accurately 
 ascertained ; for, if the apex be destroyed by any 
 means, the caudex no longer elongates ; but sends 
 off lateral shoots, which necessarily take an op- 
 posite direction from that which is natural to the 
 root. 
 
 The situation of the root, in regard to the 
 stem or the herbaceous part of the plant, is ge- 
 
 o2 
 
196 CONSERVATIVE ORGANS. [LECT. V. 
 
 nerally at the base ; but roots originate from that 
 part also of the stem which is above ground. Thus 
 the Strawberry throws out lateral shoots, which 
 are termed wires, from which roots descend at in- 
 tervals into the ground ; and from the stems of 
 the Ivy, the Jasmine, the Ash-leaved Trumpet- 
 flower, Bignonia radicans, and other plants which 
 fix themselves to walls and rocks, roots are pro- 
 truded,, serving equally to imbibe nourishment 
 and to give support to those climbing plants. 
 Whenever a stem is surrounded with earth, roots 
 are protruded from it. Du Hamel filled a cask 
 with earth, and boring holes through the bottom 
 of it, supported it on stakes three feet from the 
 ground. He then pushed slips of plants through 
 the earth in the barrel, and planted their ends, 
 which passed out at the holes in the bottom of the 
 cask, in the ground below it. These ends took 
 root ; the parts between the ground and the cask 
 put forth branches and leaves ; those surrounded by 
 the earth in the cask protruded roots ; and those, 
 again, above it became clothed with foliage. It 
 is, also, well known that, if a twig of a Willow be 
 bent and each end of it stuck into the ground, 
 roots will be protruded from both extremities, 
 whilst the middle or arched portion will be covered 
 with leaves and branches ; and the extremities of 
 the branches of all ligneous plants throw out roots, 
 
LECT. V.J THE ROOT. 197 
 
 if they be bent down and laid under the earth. In- 
 deed it is not absolutely necessary to lay them un- 
 der the ground to produce this effect ; for a ligne- 
 ous plant growing in a sterile soil, provided the 
 situation be shady and the air damp, will throw 
 out roots from its branches, resembling those 
 protruded by Ivy. I have in my possession a por- 
 tion of the branch of a Bay, Laurus Indica, in the 
 whole length on one side of which the bark is rup- 
 tured, owing to the protrusion of numerous short 
 rootlets. The plant from which this branch was 
 cut, was growing (in 1814) in a kind of cave, 
 formed by the intertwining roots of a noble Beech, 
 on the summit of a chalky bank, in Lord Derby's 
 grounds, near Epsom. The chalk had mouldered 
 away from under the roots of the Beech, which, 
 projecting forward as a roof, shaded the Bay that, 
 perhaps, had been originally planted close at the 
 foot of the bank : but all the soil had been long 
 since washed away from its root, which adhering 
 to the bare chalk, served no longer as an ab- 
 sorbing organ, but merely to sustain the plant in 
 its upright , position ; and as there were very few 
 leaves on the branches, the rootlets, which were 
 protruded from them, evidently maintained the 
 life of the plant, by absorbing the water held in 
 solution in the air of the shady spot where it grew. 
 On the knowledge of facts such as these, plants 
 are propagated by what are called layers, an opera- 
 
 o3 
 
198 CONSERVATIVE ORGANS. [LECT. V. 
 
 tion, which consists in bending down a branch, or 
 the s.tem of the plant, so that the knee or bent 
 portion of it can be preserved, by means of pegs, 
 under the surface of the soil. The part so treated 
 is nourished by the parent plant, until roots are 
 sent off from the part under the ground, when it 
 is cut away, and thus becomes an independent 
 plant. Some plants naturally propagate, or rather 
 extend themselves in a similar manner. Thus, 
 from the branches of the Banyan or Indian Fig- 
 tree (Ficus indica), fibres are thrown out, which 
 hang suspended like icicles, and grow thicker 
 as they reach the surface of the ground, into 
 which they strike root and become trunks, the 
 branches of which root again in the same manner : 
 and this progression of increase is continued until 
 the ground is covered to a prodigious extent with 
 an umbrageous labyrinth or grove, formed from 
 one original trunk, impenetrable to the sunbeams *. 
 One of these trees, called Cubber Burr, situated 
 on an island in the river Nerbedda, exceeded 
 2000 feet in the circumference of its shade ; and 
 in 1787, had 350 trunks. Religious festivals were 
 held under its luxuriant canopy, which was ca- 
 pable of affording shelter from the solar heat to 
 
 * Pagodas are generally built in the neighbourhood of these 
 trees; and under their friendly shade the Brahmins and de- 
 votees perform their religious rites. 
 
LECT. V.] THE ROOT. 199 
 
 7000 persons. MILTON has immortalized the 
 Banyan, by describing it as the tree under which 
 our first parents retired to hide themselves after 
 their fall : 
 
 They chose 
 
 The Fig-tree ; not that kind for fruit renown'd, 
 But such as, at this day to Indians known 
 In Malabar or Decan, spreads her arms 
 Branching so broad and long, that in the ground 
 The bended twigs take root, and daughters grow 
 About the mother tree, a pillar's shade 
 High over-arch'd, and echoing walks between : &c. 
 
 Paradise Lost. 
 
 The structure of roots does not differ materially 
 from that of the trunk and branches ; we may, 
 therefore, reserve the minute examination of that 
 part of our subject until we come to treat of these 
 organs ; and, at present, notice only their general 
 structure *. All roots are either ligneous or fleshy. 
 The ligneous belong to trees and shrubs, and are 
 composed of an epidermis or scarf-skin, a cutis 
 or bark, a vascular system, woody matter, and 
 pith. The fleshy, which belong to herbaceous 
 
 * The analogy, indeed, is so close, that a tree may be in- 
 verted so as to change the roots into branches, bearing leaves 
 and flowers, and the branches into roots producing radicles. 
 This fact has been frequently proved, by repeating the experi- 
 ment (first tried by Du Hamel) of planting a tree with the 
 branches in the ground, and leaving the roots in the air ; after 
 a season the buried branches produce radicles, and the roots 
 raised in the air give out buds, stems, and leaves. 
 
 o 4 
 
-00 CONSERVATIVE ORGANS. [LECT. V. 
 
 plants, consist chiefly of cellular and vascular 
 textures, interspersed with slender bundles of 
 woody fibre. In both the epidermis or exterior 
 covering is the same, and seemingly destitute of 
 vessels : it is present in every stage of the growth 
 of the root from its origin, on the radicle of the 
 embryon, to the tangled rugged arms which rivet 
 down the venerable monarch of the wood, the 
 pride of centuries : it serves the office of a filter, 
 and allows nothing to pass through its pores that 
 cannot enter the minute mouths of the absorbent 
 vessels which open on the surface of the bark 
 beneath it. The epidermis of roots is thus adapted 
 for its situation in the moist soil; but, in other re- 
 spects it does not differ from that which is spread 
 over the stem, branches, leaves, and every other 
 part of the plant, thejibfik, which are attached 
 to all roots, whatever may be their figure, are, as 
 has been already stated, mere bundles of vessels 
 enclosed in a cuticular membrane ; and, as they 
 take up from the earth the food of the plant, they 
 are, in fact, the real roots ; whilst the caudex may 
 be regarded as a magazine, in which the food that 
 has been elaborated into the proper juice is de- 
 posited for the particular uses of the vegetable 
 economy ; and it is this deposition which affords 
 the colour and odour which distinguish different 
 roots. 
 
 With regard to the mode of growth of the 
 
LECT. V.] THE ROOT. 201 
 
 root, Mr. Knight has advanced sufficient reasons 
 for believing that this organ is not an elongation 
 of the radicle; but is formed upon it after the 
 germination of the seed by successive increments 
 of new matter deposited at its apex ; for, whilst 
 the root never elongates by the extension of al- 
 ready organized parts, the radicle does elongate 
 throughout all its parts in the germinating seed. 
 The root, at first, consists of cellular matter only, 
 contained in an epidermis, within which the cor- 
 tical vessels are afterwards generated ; the circle 
 of vessels, says Mr. Knight, " enclosing within it 
 a small portion of the cellular substance, which 
 forms the pith, or medulla of the root ; and these 
 vessels gradually generate alburnum, which, in a 
 transverse section of the root, appears arranged in 
 wedges round the medulla." The same able phy- 
 tologist further maintains that root shoots differ 
 from stem shoots in not being emitted from the 
 alburnum ; and that the presence of the alburnum 
 is not essential is evident from the fact, that leaf- 
 stalks, which contain no alburnum, nevertheless 
 emit roots ; and these derive their existence, as in 
 all other cases, from the proper juice conveyed in 
 the returning vessels *. 
 
 All roots have originally more or less of a 
 tapering form ; which is partly the consequence 
 
 * Phil. Transactions, 1809. 
 
202 CONSERVATIVE ORGANS. [LECT. V. 
 
 of their mode of growth ; for, as has been just 
 stated, a root, in extending, is not lengthened 
 through all its parts, but by additions made to the 
 extremity, and as these, in the early stages of its 
 growth, are made more rapidly than the alburnous 
 depositions, which add to its diametrical dimen- 
 sions, its shape must necessarily be tapering. 
 That the longitudinal extension of the root is ef- 
 fected by the deposition of new matter at its ex- 
 tremity, was first ascertained by Du Ham el *, who 
 having passed small pieces of silver thread trans- 
 versely through a vegetating root, at distances 
 which were accurately measured, found that the 
 upper threads, those nearest to the stem, or herb- 
 age, retained their original and relative situation, 
 whilst that one only which was very near to the 
 end of the root was carried down ; and this is the 
 case both in succulent and ligneous roots. The 
 lateral extension, on the contrary, in succulent 
 roots, appears to depend on the deposition of ad- 
 ditional particles, throughout the whole of their 
 substance ; and in perennial and ligneous roots, 
 by the formation of an annual new alburnum, in 
 the same manner, as I shall explain to you in its 
 proper place, occurs in the stems and branches of 
 trees and shrubs. When the extremity of a root 
 is destroyed, or when the root has attained the 
 
 * Phys. des Arbres, liv. I. c, v. 
 
LECT. V.] THE ROOT. 203 
 
 natural limit of its longitudinal extension, it 
 throws out lateral branches ; and these extend with 
 most vigour in that direction in which the most 
 abundant supply of nourishment is to be found ; 
 a circumstance which has been very unaccountably 
 attributed by some to a sentient, or an instinctive 
 principle in plants. The fact is, that the influence 
 of a quantity of manure, or of richer earth, is 
 not confined to the immediate spot where it is de- 
 posited ; but extends to a certain distance in every 
 direction, diluted, as it were, by the poorer soil, 
 until its power is altogether dissipated : as soon, 
 therefore, as any branch of a root impinges upon 
 the limits of this circle, it obtains a supply of nu- 
 triment capable of exciting its vital energy in an 
 increased degree : and as this augments in a direct 
 ratio, as it extends, this branch in length and 
 vigour necessarily far exceeds those on the opposite 
 side of the main root, which have had a more 
 scanty supply of nourishment. Thus, also, if a 
 seed of a tree, conveyed by the wind, or other- 
 wise, as may accidentally happen, be planted on the 
 top of a wall, its roots will gradually extend until 
 they reach the ground ; whilst the upright growth 
 of the tree will be very scanty previous to the root 
 establishing itself in the soil. Sir J. E. Smith, in 
 referring to a fact of this kind, communicated to 
 him by the Rev. Dr. Walker of Edinburgh, regard- 
 ing an Ash, which grew on a wall in the Canon- 
 
204 CONSERVATIVE ORGANS. [LECT. V. 
 
 gate in that city, and which I have seen, explains 
 it in the following manner: " Here the vital 
 powers of the tree not being adequate, from scanty 
 nourishment, to the usual annual degree of 
 increase in the branches, were accumulated in the 
 root, which, therefore, was excited to an ex- 
 traordinary exertion, in its own natural direction 
 downwards." I would, however, say that it was 
 owing to the moisture of the earth soaking into 
 and ascending the wall, a fact which, from every 
 day's experience, we know takes place, that the 
 root extended in the direction of its natural stimu- 
 lus, the moisture ; the real exciting cause of its 
 increased exertion : and the accuracy of this 
 opinion is placed almost beyond controversy, by 
 the experiment of Mr. Knight, which I am about to 
 relate. Some Beans were placed in pots filled with 
 earth, but were half covered only with the mould. 
 The pots were then inverted on a grating of wood, 
 so as to support the earth and the Beans, in such 
 a manner, that the earth was above and the air 
 beneath each radicle as it was emitted. Water 
 was next introduced through the bottom of the 
 inverted pots : the radicles extended horizontally 
 along the surface of the mould, and in contact with 
 it ; and in a few days emitted many fibrous roots 
 upwards into it, which passed through one half of 
 the mould. We may, therefore, venture to assert, 
 Jhat although the natural direction of the radicle 
 
LECT. V.] THE ROOT. 205 
 
 is, in every instance, downwards, depending on 
 causes which have not yet been ascertained *; and 
 although roots, during their growth, assume va- 
 rious directions, which invariably occur in the 
 same kinds of roots, yet, that circumstances con- 
 nected with their mode of growth, produce devia- 
 tions, and affect the uniformity which might 
 otherwise be expected. But many roots not only 
 vary from their natural direction, but even change 
 their characteristic figure, owing to circumstances 
 connected with the state of the soil : thus, insu- 
 lated trees, that are much agitated by the wind, 
 have strong lateral roots, forming a kind of net- 
 work that adheres firmly to the earth ; whilst 
 the same description of trees, growing in a forest, 
 has long slender tapering roots. This diversity 
 may be thus explained : when a tree stands alone, 
 the soil near the surface is partially loosened by 
 the agitation of the tree by the wind, and conse- 
 quently less opposition is afforded to the extension 
 of the lateral branches of the root, than the un- 
 moved ground offers to that of its perpendicular 
 caudex ; whereas, when a tree grows in a forest, 
 the mechanical obstacles offered to the extension 
 of the lateral roots by the neighbouring roots, ex- 
 
 * The different opinion^ that have been hazarded on this 
 subject shall be noticed, when we take under our consideration 
 the germination of seeds. 
 
206 CONSERVATIVE ORGANS. [LECT. V. 
 
 ceed those which the ground offers to the per- 
 pendicular. Some Grasses, also, as the common 
 Gat's Tail, Phleum pratense, floating Fox Tail, 
 Alopecurus geniculatus, and others, which in a 
 wet situation have fibrous roots, became nodose, 
 when planted in a dry sterile soil : the cause of 
 which cannot be better explained than in the 
 words of Sir J. E. Smith. Presuming the herb to 
 be starved, he adds, " by a failure of the nutri- 
 mental fluids hitherto conveyed by the water of 
 the soil, its growth would be checked ; and when 
 checked, the same growth could not, as we know 
 by observation on vegetation in general, be in- 
 stantaneously renewed. A sudden fresh supply of 
 food would, therefore, cause an accumulation of 
 vital energy in the root, which would consequently 
 assume a degree of vigour and a luxuriant mode 
 of growth not natural to it, and become bulbous. 
 Thus, it acquires a resource against such checks in 
 future, and the herb is preserved alive, though in 
 a very far less luxuriant state than when regularly 
 and uniformly supplied with its requisite nourish- 
 ment *." 
 
 The nature of the Jibrils has been already 
 mentioned. They may be regarded as the mouths 
 of the plant : for, the extremities of their vessels 
 being open, these suck up such fluid nutriment 
 
 * Introd. to physioL and systematical Botany, p. 115. 
 
LBCT. V.] THE ROOT. 207 
 
 from the soil as can pass through the pores of the 
 epidermis, and conduct it to the caudex, or main 
 root, through the vessels of which it ascends to 
 the leaves : there it is as it were digested ; and, 
 being changed in its properties, is again conveyed 
 by another set of vessels to the caudex,, in which 
 it is deposited for the future exigencies of the 
 plant. As a proof that the fibrils are the only 
 parts of the root which take up the nutriment of 
 the plant from the soil, Mirbel remarks, that 
 " herbs perish at the foot of young trees, because 
 the fibrils issuing from the collet (the point of 
 connexion of the stem and the root) exhaust the 
 ground ; but old trees extending their vigorous 
 roots to a distance, allow the plants, which are 
 close 'to them, to subsist and destroy those which 
 are more distant." It has not yet been ascertained 
 whether the fibrils are strictly annual productions, 
 an opinion which was maintained by Du Hamel *, 
 Mirbel -f^, and Sir J. E. Smith;}:, and adopted by 
 Wildenow ; but which is doubted by Mr. Knight, 
 who, although he admits that in roots of trees, 
 or ligneous plants, crowded together in a garden- 
 pot, the fibrils are often found lifeless in the suc- 
 ceeding spring ; yet, remarks that he has "not 
 
 * Phys. des Arores. 
 
 j- Traite d'Anatomie. 
 
 J Introd. to pkysiol.and system. Botany. 
 
 Principles of Botany , Eng. trans. 260. 
 
208 CONSERVATIVE ORGANS. [LECT. V. 
 
 observed the same mortality to occur, in any 
 degree, in the roots of trees when growing, under 
 favourable circumstances, in their natural situa- 
 tion *." My own experience does not authorize 
 me to decide with confidence on this question; 
 but it rather induces me to incline to the opinion 
 that they are annual productions. 
 
 In duration, roots are either annual, biennial, 
 or perennial. Annual roots belong to those plants 
 which are produced from the seed, grow to their full 
 extent, and die in one year or season ; as, for ex- 
 ample, Barley, Hordeum secale; the White Poppy, 
 Papaver somniferum ; the common Pea, Pis urn 
 sativum ; the garden Bean, Vicmfaba, &c. : bien- 
 nial to those that live through the winter of the 
 year in which they are produced, and after flower- 
 ing and yielding seed, die in the following year, 
 as the Carrot, Daucus car of a ; the genus Teasel, 
 Dipsacus ; the Canterbury Bell Flower, Campa- 
 nula medium, &c. : and perennial to those that 
 blossom and produce seeds through many suc- 
 cessive seasons, as the majority of herbaceous 
 plants and all shrubs and trees. But the life of 
 annual and biennial roots may occasionally be 
 protracted much beyond its natural period, when 
 any circumstance occurs that can prevent the 
 plant from flowering, or, even when it does flower, 
 
 * Phil. Trans. Part 1. 1809. 
 
LECT. Y.] THE ROOT. 209 
 
 from perfecting its seed. Thus I have preserved 
 the life of a Sweet Pea until after Christmas, when 
 it was destroyed by the severity of the weather, 
 by nipping off the flowers as soon as they were 
 fully blown ; and plants of tropical climates, which 
 are naturally biennial, sometimes live for many 
 years in our hothouses ; but they all invariably 
 die after they have produced fruit. The cause of 
 this is, that the vitality of the plants of this de- 
 scription seems to be sufficient for continuing their 
 life only till after the formation of the seed, the 
 natural means of perpetuating the species ; in per- 
 fecting which, the irritability and life of the in- 
 dividual are completely exhausted; and, with the 
 plant, the root perishes. In perennial plants, the 
 fibrils only annually perish and are renewed ; they 
 decay before the leaves fall in autumn ; and are 
 again formed in the early part of spring. At least 
 this is the opinion commonly received. The 
 root, however, enjoys more vitality than any 
 other part of the plant, and can reproduce all the 
 other parts, when the tree is cut down or otherwise 
 destroyed; except in the Pine tribe and some 
 other dry resinous plants. 
 
 Such is the ROOT an organ of the greatest 
 importance, whether we consider it simply as fixing 
 the plant in the ground, and enabling it to elevate 
 its leaves and flowers in the air ; or, in a more 
 important point of view, as selecting and taking up 
 
 VOL. I. P 
 
210 CONSERVATIVE ORGANS. [LECT. V. 
 
 from the soil the materials fitted for the nourish- 
 ment and support of the vegetable body. 
 
 It is a wise provision of nature, that as plants 
 are not endued with volition and extensive loco- 
 motion, nor guided by instinct nor reason, they 
 are subject to more regular and unalterable 
 laws than the animal creation, at least than that 
 portion of it which possesses those functions which 
 have just been enumerated : their food is always 
 placed within their reach, and they enjoy good 
 health and arrive at perfection in their growth, in- 
 dependent of external accidents to which animals 
 are equally liable, when they are situated where 
 the soil contains those principles which are best 
 adapted for the various purposes of their economy. 
 The consideration of this fact suggests the ques- 
 tions, What is the composition of soils ? What 
 part of soils is taken up as food by the roots of 
 plants ? To answer them has long employed the 
 attention of the philosophical observer, and many 
 and very various opinions have been given to the 
 public ; but it is only since modern chymistry 
 made those discoveries which may justly be re- 
 garded as the most splendid triumphs of experi- 
 mental Science, that any thing rational and satis- 
 factory has been advanced. I will endeavour to 
 lay before you as clear a view as I am able of the 
 most probable conclusions which may be drawn 
 from these opinions ; and, in raising one corner of 
 
ECT. V.j THE ROOT. 211 
 
 the veil, remove much of the mystery with which, 
 to ordinary observers, the subject appears to be 
 enveloped. An investigation of this kind is as 
 useful to the physician as to the botanist and agri- 
 culturist; for, many of the exciting causes of 
 diseases, particularly of epidemics, are to be 
 looked for in the nature of the soil and other local 
 circumstances connected with the situations where 
 they originate. 
 
 The fact cannot be too often repeated and im- 
 pressed on your minds, that plants are living 
 beings, possessed of powers which enable them 
 to convert into their own material substance, 
 matters of a nature apparently very different from 
 it. Without keeping this in view, we should be 
 forced to look for all the different productions of 
 plants ready formed in the soil where they grow, 
 and to suppose that these are simply taken up by 
 their roots, and deposited in the different parts of 
 the plant : an idea too incongruous to be admitted. 
 On the contrary, they do not even take up those 
 principles which are most abundant in the soil 
 where they grow; bat select peculiar parts of 
 them, although these are not found, in general, 
 forming in their uncombined state any part of the 
 vegetable frame. Linnaeus himself, however, I 
 believe, and many others, have imagined, that 
 every soil held in it something which is peculiarly 
 the proper food of every kind of plant that can be 
 
 p2 
 
212 CONSERVATIVE ORGANS. [LECT. V. 
 
 cultivated on it ; and thus that poisonous plants 
 extract something, on which their hurtful proper- 
 ties depend, which is not taken up by wholesome 
 plants ; or, that the secretions of plants do not 
 vary in their qualities on account of the difference 
 in the action of the vessels which secrete them ; 
 but owing to their components being already pre- 
 sent in the soil. That this is not the case, how- 
 ever, has been clearly proved by the discoveries 
 of modern chymistry, which have enabled us to 
 analyse both the soil and the vegetables that grow 
 upon it. By its assistance the mode of investigat- 
 ing the subject has been simplified, and more sa- 
 tisfactory results obtained. 
 
 The ultimate components of all the various 
 substances produced by vegetables have been found 
 the same, differing only in the quantity and the 
 mode of their combination ; and the parts of 
 a soil which supply these have been found to be 
 much fewer than was previously supposed. As we 
 formerly asserted, when noticing the nature of 
 sap, if this juice could be obtained near enough 
 to the extremities of roots, or in the fibrils by 
 which the soluble part of the soil is absorbed, 
 then we should be able, by a careful analysis, to 
 ascertain the real nature of the substances ab- 
 sorbed; and, by looking for these in soils, know 
 how to supply their deficiency, or to diminish their 
 superabundance. But as an accurate knowledge 
 
 4 
 
LECT. V.] THE ROOT. SOILS. 213 
 
 of the components of sap cannot be obtained, 
 owing- to that fluid, as it advances, even in the 
 vessels of the root, dissolving some already di- 
 gested vegetable matter, which had been depo- 
 sited there in the preceding autumn, we are 
 obliged to form conclusions certainly not free from 
 error ; and to content ourselves with an approxi- 
 mation only to the truth. From the knowledge, 
 however, which we do possess I will endeavour 
 first to point out to you the known general com- 
 ponents of natural soils ; secondly, what part of 
 these is taken up as food by plants ; and thirdly, 
 in what manner, and by what means, soils are 
 improved and rendered more productive ; or to in- 
 vestigate the general nature of manures. 
 
 Every soil fit for yielding nutriment to vege- 
 tables may be supposed to consist of earth, water, 
 air, a small proportion of metallic oxyds, and de- 
 composing vegetable or animal matters, in which 
 are included salts, gases, and vegetable extracts. 
 
 Earth, which is the essential basis of all soils, 
 is, as it is commonly spoken of, a compound of 
 different earths ; the most general of which are 
 Calcareous earth, Argillaceous earth, Siliceous 
 earth, Magnesian earth, and Ferruginous earth. 
 
 1. CALCAREOUS EARTH comprehends lime, usu- 
 ally combined with carbonic acid, in the state of 
 limestone, chalk, shells, and marl which is a 
 mixture of 'carbonate of lime with clayey and 
 
 p3 
 
214 CONSERVATIVE ORGANS. [LECT. V. 
 
 sandy matters ; but lime is sometimes, also, found 
 in combination with sulphuric acid, forming a 
 substance called gypsum ; and more rarely with 
 phosphoric acid. When too much calcareous mat- 
 ter is contained in a soil, it is unfertile, owing to 
 its absorbing moisture, and consequently remain- 
 ing too dry. But the case is different when the 
 calcareous matter is mixed with silica, for then the 
 moisture absorbed remains in a free state, and not 
 so united with the chalky matter as to disappear 
 and be useless to plants. But the absorbing pro- 
 perties of all calcareous soils are not alike ; and a 
 great difference depends on the degree of com- 
 minution of the calcareous matter. Thus, 100 
 parts of calcareous sand retain, according to Pro- 
 fessor Schiibler's experiments, 29 parts only of 
 water, whilst 100 parts of the same matter in 
 the state of fine powder retain 85 per cent. In 
 the first case, when calcareous earth and silica 
 predominate in an arable field, they produce a 
 hot and dry soil; when in the second, a moist and 
 cold soil. 
 
 2. ARGILLACEOUS EARTH comprehends clay, 
 which is generally mixed with siliceous sand and 
 mineral substances, and is very retentive of mois- 
 ture. 
 
 3. SILICEOUS EARTH is almost entirely com- 
 posed of sand. The water passes so readily- 
 through it, that very little is retained for the pur- 
 
LECT. V.] THE ROOT. SOILS. 215 
 
 poses of vegetation ; and soils which contain much 
 of this earth are, therefore, barren and unpro- 
 fitable. In the form of sand it retains 25 per cent, 
 only of water ; while 100 parts of it, as it occurs 
 with clay in an arable field, retain 280 per cent, 
 of water. 
 
 4. MAGNESIAN EARTH is not so commonly 
 found as the earths we have already noticed. The 
 magnesia it contains is combined with carbonic 
 acid, and mixed with siliceous particles. It ap- 
 proaches nearest to the nature of the clayey earths 
 in its power of retaining moisture ; that power 
 enabling it to retain 4^ times its own weight of 
 water. This renders it, when it predominates, very 
 prejudicial to vegetation ; while it increases, when 
 added in moderate proportion, the fertility of a 
 dry sandy soil. 
 
 5. FERRUGINOUS EARTH consists of those oxyds 
 of iron known by the names of ochres and pyrites 
 mixed with siliceous matter. These oxyds, in parti- 
 cular the pyrites, when in any considerable quantity 
 in a soil, if it contains little calcareous matter, are 
 extremely injurious to vegetation. The pyrites is a 
 compound of sulphur and iron, and is converted by 
 exposure to air and moisture into sulphate of iron, 
 which destroys plants by over-stimulating them. 
 
 Vegetable earths have the least specific gravity, 
 and sandy soils the greatest, whether they be dry 
 or moist: the vegetable earths contain, besides 
 
 p4 
 
216 CONSERVATIVE ORGANS. [LECT. V. 
 
 vegetables in a state of decay, animal matter and 
 a large proportion of salts, which are chiefly com- 
 mon salt, sulphates of magnesia and of potash, 
 nitrates of lime, and carbonates of potash and of 
 soda. 
 
 Such are the earths generally contained in 
 soils : when any one of them abounds, the com- 
 pound earth is named after this component ; as 
 for instance, a calcareous soil, an argillaceous 
 soil, &c. 
 
 The principal difference which characterizes 
 these various kinds of earths, is their power of 
 retaining the next component of soils, WATER. 
 Water, as forming a part of soils, is either che- 
 mically combined with the earth, or merely me- 
 chanically mixed with it, and retained in combi- 
 nation by cohesive attraction. In the former 
 state it is of no use to vegetables, in the latter it 
 is essentially necessary for their support. If the 
 soil be not sufficiently retentive, the plant is 
 starved, for nothing can be taken up from the 
 earth which is insoluble ; and, as we shall show 
 afterwards, water itself is a principal part of the 
 food of plants. If the soil be too stiff and re- 
 tentive, the water remains upon its surface, and 
 does not percolate to a sufficient depth to be ap- 
 plied to the roots : and if the vegetable be of a 
 succulent kind, the herbaceous part remaining 
 constantly surrounded with moisture has its vege- 
 
LECT. V.] THE ROOT. SOILS. 217 
 
 tative powers weakened, and rots. This is par- 
 ticularly the case in winter ; for, as the vital energy 
 of the plant is then much lowered by cold, a dis- 
 ease of the vegetable takes place, similar to what 
 happens in a leucophlegmatic state of the animal 
 body, from which the plant rarely recovers. The 
 most efficient soil, as far as water is concerned, is 
 that which contains a due mixture of carbonate 
 of lime, sand, and pulverized clay, with some ve- 
 getable or animal matters ; and in which the ma- 
 terials are so mingled as to remain loose and per- 
 meable to the air. This soil is calculated not only 
 to retain the water in proper quantity ; but also to 
 absorb it from the atmosphere, which is one great 
 source of the supply that vegetables require : for 
 water, as has been already remarked, is requisite 
 for rendering the other matters in soils sufficiently 
 soluble to be taken up by the roots of plants. All 
 the earths are more or less soluble in water : thus 
 lime is taken up readily in its pure state ; and also 
 if the water contains much carbonic acid in solu- 
 tion, when the lime is in the form of chalk, or a 
 carbonate, in the proportion of about <r ir part of 
 its weight. Clay is soluble in a minute proportion 
 in rain water : silica even may be retained in so- 
 lution by the aid of carbonate of potash ; and in 
 the minute state of division in which it is preci- 
 pitated from an alkaline solution, it is soluble in 
 
218 CONSERVATIVE ORGANS. [LECT. V. 
 
 1000 parts of water : 2000 parts of pure water 
 hold one of magnesia in solution. 
 
 AIR is, also, a necessary component of soils. 
 Atmospheric air is absolutely necessary, as we 
 know, for carrying on the process of germina- 
 tion ; the more pulverulent, therefore, the soil 
 is, the more air it is capable of containing, and 
 consequently is the better adapted for support- 
 ing vegetation. But a soil which is too sandy, 
 the water not being retained, although it appears 
 to be loose, yet does not contain so much air en- 
 veloped in it as is required ; for the small par- 
 ticles of which it is composed apply more closely to 
 each other, and lie in a smaller compass than the 
 aggregated masses of a better soil, which touch 
 at a few points only, and, therefore, leave more 
 and larger interstices between them. When the 
 soil is too retentive, the water which remains on 
 its surface evaporates in summer, and deposit- 
 ing the clayey particles which it held suspended, 
 a kind of paste is left, which hardening, by 
 being baked, as it were, in the heat of the sun, 
 no air can penetrate to the parts beneath it ; nor 
 can that which has been already used in the ve- 
 getative process, and which is unfit to carry it fur- 
 ther on, escape : and we know that as atmosphe- 
 rical air is vitiated by the roots of growing plants, 
 and during the germination of seeds, a constant 
 renewal of it is requisite for supporting the vigour 
 
LECT. V.] THE ROOT. SOILS. 219 
 
 of vegetables. It is the oxygenous portion of the 
 atmospherical air contained in the soil, which is 
 vitiated by the functions of the roots of plants, I 
 shall have an opportunity of demonstrating to you 
 the importance of this agent in the process of 
 germination ; and Sir H. Davy concludes, from an 
 experiment on the vegetation of a Potatoe, in a 
 given portion of atmospherical air, at a tempera- 
 ture of 59',, " that in cases in which shoots are 
 thrown out from roots, oxygene appears to be 
 uniformly absorbed, as in the germination of 
 seeds* 1 ." Now, without stopping, at present, to 
 inquire whether the opinion that it is absorbed in 
 the process of germination be correct, it is evi- 
 dent that no accurate conclusions could be de- 
 duced from this experiment, because tubers per- 
 form nearly the same functions in evolving the 
 buds' on their surfaces, as the seed-lobes in the 
 evolution of the embryon they enclose, during 
 germination. To ascertain, therefore, the real 
 manner in which the functions of the living root 
 affect atmospherical air, I instituted the following 
 experiment: The roots of a Lilac, Syringa 
 vulgaris, were partly laid bare, and one of them 
 introduced into a cylindrical glass jar containing 
 atmospherical air, freed from carbonic acid, and 
 inverted in water. At the end of four days, du- 
 
 * Elements of agricultural Chemistry, 2d edit. p. 233. 
 
220 CONSERVATIVE ORGANS. [LECT. V. 
 
 ring which the thermometer had varied from 59 
 to 70, the root was cut from the plant, and re- 
 moved from the jar: scarcely any diminution 
 of the air was perceptible ; but lime-water became 
 instantly milky on agitating- it in the air of the 
 jar, thereby demonstrating the presence of car- 
 bonic acid gas. The quantity of the gas was not 
 ascertained in this instance. 
 
 The effect of oxygen gas, as a healthy sti- 
 mulus to roots, was ascertained by Mr. Daniel 
 Hill. He applied it to the roots of a plant of the 
 Horseshoe Geranium, Pelargonium zonale, in a 
 sickly state, and found that the plant soon revived, 
 and grew with great vigour ; and phials of oxygen 
 gas inverted in water glasses, in which Hyacinth 
 bulbs were placed, rapidly advanced the growth 
 , of the plants. 
 
 Soils contain CARBONIC ACID GAS also, inde- 
 pendent of that which is formed by the vitiation of 
 the atmospherical air. This is produced from the 
 fermentation or decomposition of vegetable sub- 
 stances ; and when it is not too abundant, it is 
 useful by loosening the soil, by its expansion when 
 first liberated: too much of it, however, checks 
 germination and impedes the growth of plants. 
 
 When the vegetable matter which the soil con- 
 tains putrefies, carbonated hydrogen gas is given 
 out ; and this is always present to a certain extent. 
 It can be useful, like the former air, by the me- 
 
LECT. V.] THE ROOT. SOILS. 221 
 
 chanical force only which it exerts in loosening the 
 soil at the moment of its formation. 
 
 These decompositions, which are continually 
 going forward in soils, evolve CALORIC ; and this is 
 retained sometimes very pertinaciously, and in 
 such quantity as to be considered as a component 
 of soils. It is certain that the earth is always 
 warmer in summer than the surrounding atmo- 
 sphere ; but this is very variable near the surface ; 
 although, at a considerable depth, the temperature 
 of the ground is almost all the same both in sum- 
 mer and winter. Soils however, which contain 
 much siliceous earth, are not favourable to these 
 decompositions ; and in these, little caloric is ac- 
 cumulated. But independent of these decom- 
 positions, some soils are more readily heated than 
 others ; and portions of different soils heated to 
 the same temperature cool with various degrees 
 of rapidity : a stiff white clay soil is heated with 
 difficulty ; and, being usually very moist, cools 
 rapidly ; hence it is properly termed a cold soil : a 
 chalky soil is heated with as much difficulty, but 
 being dryer retains its heat longer ; although it 
 should be observed, that, of perfectly dry soils, 
 those that are most readily heated by the solar 
 rays likewise cool most rapidly. Sir H. Davy 
 found " that a rich black mould which contained 
 4- of vegetable matter," was heated by exposure 
 to sunshine, from 65 to 88 in an hour ; whilst 
 
222 CONSERVATIVE ORGANS. [LECT. V. 
 
 a chalk soil was heated to 69' only under simi- 
 lar circumstances. But when removed into the 
 shade at 62', the mould lost, in half an hour, 
 15 : and the chalk only 4 U *. In many respects, 
 therefore, the considering caloric as a general 
 component of soils, is not too great a refinement 
 to be adopted. 
 
 The last component of soils which we have to 
 mention, has always been regarded as the most 
 important of the whole. We allude to animal and 
 vegetable matter in a state of decomposition, from 
 which the black mould which constitutes the rich- 
 ness of soils is almost altogether formed. But the 
 analysis of some of the most fertile soils has 
 proved, that their fertility does not depend on the 
 presence of a large proportion of these substances. 
 Thus Sir H. Davy found that the soil of a very 
 fertile field in East Lothian, contained nine parts 
 only in the hundred of decomposed animal and 
 vegetable matter ; and a soil from the low parts 
 of Somersetshire, long celebrated for yielding large 
 crops of Wheat and Beans without manure, con- 
 tained five parts of these principles only in the 
 hundred-}-. It is indeed true, that the carbonaceous 
 matter contained in plants can be derived most 
 easily from decomposing animal and vegetable sub- 
 
 * Elements of agricultural Chemistry, 2d edit. p. 179. 
 t Ibid. 
 
LECT. V.j THE ROOT. SOILS. 223 
 
 stances; but these also yield salts which prove 
 highly stimulating to growing plants ; and although 
 plants seem to attain great bulk and vigour when 
 much manure is applied, yet they are over-sti- 
 mulated, and their growth is connected with dis- 
 ease, in the same manner as in an overfed and 
 pampered animal. The natural state of both is 
 altered; premature age succeeds, and death ar- 
 rives long before the period when he should be 
 naturally expected. Those plants also which are 
 intended for the food of man and animals, when 
 reared upon soil of the kind we are now noticing, 
 yield less nutriment in the same bulk than that 
 which more healthy plants yield, and it is also of 
 an unwholesome kind. Upon the whole, we may 
 truly assert that more harm is done by loading 
 soils artificially with much animal and vegetable 
 matter, than the natural deficiency of it in soils 
 can occasion. 
 
 Such are the most general components of al- 
 most all soils ; and as it is of much importance to 
 know what is the composition of any soil, either 
 in order to ascertain the probable causes of its 
 fertility, with the view that less fertile soils may be 
 rendered similar to it ; or to estimate the value of 
 ground with which we are unacquainted, and on 
 which we have no opportunity of making experi- 
 ments by rearing plants ; we will endeavour to 
 point out how this can be done. 
 
224 CONSERVATIVE ORGANS. [LECT. V. 
 
 When a Botanist examines a space of ground, 
 he forms an estimate of the nature of the soil by 
 observing the kind of plants, or weeds as they are 
 termed, which it naturally produces, and draws 
 his conclusions from the knowledge he possesses 
 of the relation which always subsists between the 
 plant and the soil. If the plants are those which 
 have much divided roots, he concludes that the 
 soil is pulverulent and easily penetrated ; but if the 
 roots are thick and fleshy, that, as these require a 
 humid soil, it is probable that it is damp and re- 
 tentive. Some kinds of plants grow on one soil, 
 but are never found on another ; some require a 
 large supply of carbonaceous matter, or a rich 
 fertile soil ; others, he knows, glean the little they 
 require in the more barren, and soon die in richer 
 spots. But the knowledge of the Botanist, al- 
 though it is an accurate guide to a certain degree, 
 in directing his judgment as to the value of un- 
 cultivated soils ; and is valuable in preventing him 
 from making bad speculations by introducing new 
 objects of culture into a place which cannot admit 
 of them ; yet it is of little avail in examining soils 
 under the immediate influence of cultivation. 
 The experienced eye of the farmer supplies much 
 of this defect. On too loose and poor soils the 
 roots of barley and other grains are long, but the 
 stems small and weak ; but in a richer and more 
 tenacious soil the roots are short, thick, and very 
 
LECT. V.] THE ROOT. SOILS. 225 
 
 closely set with fibrils. The reason of these cir- 
 cumstances is, that the root shooting out towards 
 the spots where the stimulus of nutriment is in 
 greater quantity, exhausts the little nourishment it 
 can obtain in adding to its length, and, therefore, 
 an insufficient supply is left for the stem and 
 leaves ; but in richer soils the whole of the fibrils 
 being surrounded by nutritious matter, a greater 
 quantity is actually taken up by a much smaller 
 surface of roots, and supplies more freely the her- 
 baceous parts of the plants. 
 
 To ascertain the real nature of soils, chy- 
 mistry must lend its assistance ; and this mode 
 of examination is undoubtedly the most cer- 
 tain. Sir H. Davy has, however, justly re- 
 marked, " that the results of analyses consi- 
 " dered as affording indications of fertility must 
 " necessarily differ according to the variations of 
 " climate, situation, and other circumstances. 
 " Thus, the power of soils to absorb moisture 
 " ought to be greater in warm and dry countries 
 " than in cold and moist ones, and when the 
 " quantity of fine argillaceous earth they contain 
 " is larger. Soils likewise which are situated on 
 " declivities, ought to be more absorbent than 
 " those in the same climate situated on plains and 
 " valleys. The productiveness of soils must like- 
 " wise be influenced by the nature of the subsoil, 
 " or the earthy and stony strata on which they 
 
 VOL. I. Q 
 
226 CONSERVATIVE ORGANS. [LECT. V. 
 
 " rest. Thus, a sandy soil may sometimes owe its 
 " fertility to the power of the subsoil to retain 
 " water ; and an absorbent clayey soil may oc- 
 " casionally be prevented from being barren,, in a 
 " moist climate, by the influence of a substra- 
 " turn of sand or gravel." Notwithstanding these 
 obstacles, however, to the formation of perfectly 
 correct results in the chymical analysis of soils, 
 still, by observing the circumstances which may 
 thus alter the properties of a soil, and making 
 allowances for them, we are enabled by its means 
 to form a tolerably accurate notion of the com- 
 parative value of soils. 
 
 When any soil is to be examined, the speci* 
 men, which should never be less than three or four 
 hundred grains, must be spread out to dry, and 
 then carefully weighed. As it is of importance 
 to discover the physical properties of a soil prior 
 to its analysis, for these direct in some respects 
 the experiments that may be necessary, the spe- 
 cific gravity, colour, and consistence of the spe- 
 cimen should be next ascertained. If a phial, 
 which holds 400 grains of water, be half filled 
 with that fluid and the soil introduced until the 
 liquid rises to the mouth, and then weighed, the 
 difference between the weight of the soil and that 
 of the water (which is known) will give the spe- 
 cific gravity of the soil. Thus, if the phial filled 
 as described gains 200 grains in weight, the gra- 
 vity of the soil will be 2, or double that of water 
 
LECT. V.] THE ROOT. SOILS. 227 
 
 which is the standard ; and, if it gain 165 grains, 
 it will be 1.825, water being 1.000*. A red or 
 yellow colour indicates the presence of iron ; and 
 the scratching glass when rubbed upon it, that of 
 silex. A given portion of the soil is next to be sub- 
 mitted to a degree of heat sufficient to dissipate 
 the whole of the water it contains without consum- 
 ing the vegetable and animal matter, or extricat- 
 ing the carbonic acid gas from the lime and other 
 calcareous substances it may contain. The tem- 
 perature should not exceed 300 Fahr. ; or a piece 
 of wood may be laid in the dish in which the pro- 
 cess is conducted, and whenever it " begins to be 
 " charred, the process must be stopped." The 
 specimen should now be again weighed, and when 
 in 400 grains the loss is 50, the soil may be re- 
 garded as highly absorbent and retentive of water, 
 and to contain either much decomposing organic 
 matter, or a large proportion of clay ; but when 
 the loss is under 20, it cannot be considered as 
 either very absorbent or very retentive, and is pro- 
 bably formed chiefly of sand. After bruising in a 
 mortar the portion thus treated, the larger stones, 
 gravel, and vegetable fibres should be separated 
 by the sieve, and their weight noted down. 
 
 The sandy matter, which is insoluble, is easily 
 separated by boiling the specimen in three or 
 
 * Davy's Elements of agricultural Ckymstry. 
 Q2 
 
228 CONSERVATIVE ORGANS. [LECT. V. 
 
 four times its weight of water, and when " the 
 " soil is broken down and the water cool, by 
 " agitating the parts together and suffering them 
 " to rest for a minute or two, and then pouring 
 " off the water with what it holds suspended in it. 
 " The repetition of this elutriation will at length 
 " free the sand from all the other substances, and 
 " that being thrown on a filter and weighed, the 
 " result will give the quantity of uncombined si- 
 " lex in the soil." The water of lixiviation must 
 be preserved, as it will be found to contain the 
 saline and soluble animal and vegetable matters, 
 if any exist in the soil. 
 
 Calcareous matter is discovered by adding to 
 the portion finally deposited from the water of 
 lixiviation a quantity of muriatic acid " twice the 
 " weight of the earthly matter ; but diluted with 
 " double its volume of water :" an effervescence is 
 occasioned if lime, or any other calcareous sub- 
 stance, be present, and muriate of lime is formed ; 
 to separate which, and ascertain the quantity of 
 the lime, the whole should be thrown into distilled 
 water. The water dissolves the muriate of lime ; 
 and the solution separated by filtration being eva- 
 porated to a certain degree, carbonate of soda is 
 next to be added to precipitate the lime. The 
 weight of the precipitate, after it is washed and 
 dried, gives the quantity of calcareous matter 
 contained in the soil. If magnesia be present, it 
 
LECT. V.] THB ROOT. SOILS. 229 
 
 is known by the same process ; but the precipitate 
 must be washed with diluted sulphuric acid, by 
 which means the lime is formed into insoluble 
 gypsum, or sulphate of lime, and the magnesia 
 into soluble Epsom salt. These salts can be easily 
 separated by nitration and crystallization ; and 
 by knowing the quantity of each thus formed the 
 real quantity of lime and magnesia is ascertained 
 by the following rule : 
 
 100 parts of gypsum contain 48 of aeid, 34- of Iime,andl8ofwater. 
 100 parts of Epsom salt. . . 33 19 4-8 
 
 The organized matter, or the animal and vege- 
 table substance, is known by strongly igniting 
 what remains of the specimen, after the calcareous 
 matter is separated, in a crucible over a common 
 fire, until no blackness remains in the mass : 
 the loss of weight denotes the quantity of organic 
 matter. The clay is ascertained chiefly by sight 
 and touch ; and the ready-formed salts by the 
 evaporation of the washings of the specimen and 
 crystallization. 
 
 Such is the method of ascertaining the prin- 
 cipal contents of any soil ; and its value may be 
 computed by the knowledge we possess from the 
 experience of agriculturists, as to the capacities 
 of the different earths for retaining water and air. 
 When the examination is completed, the products 
 should be numerically arranged, and if their 
 
 Q3 
 
230 CONSERVATIVE ORGANS. [LECT. V. 
 
 quantities, added together, nearly equal the ori- 
 ginal quantity of the specimen, the analysis may 
 be considered as accurate. Many little niceties of 
 manipulation are necessary to be attended to; 
 but, for these and other particulars requisite to be 
 examined when the analysis is required to be very 
 accurate, I must refer you to Sir H. Davy's ad- 
 mirable work on Agricultural Chymistry, which is 
 the source of much of the information contained 
 in this Lecture. Let us now examine in what way 
 the components of a soil affect plants ; and which 
 of these are taken into the vegetable system. 
 
 The principal matter, undoubtedly, that plants 
 take up from the soil is water; and from the results 
 of several experiments in rearing plants in pure 
 water, this fluid has been by many supposed to be 
 the only food of plants. But when these experi- 
 ments were repeated with greater care, and the 
 water employed to moisten the pure sand in 
 which the seeds were planted was distilled, the 
 plants thus raised were found not to have gained 
 any augmentation of vegetable matter ; and sel- 
 dom or never perfected their seeds, although they 
 flowered. In some cases, however, a small ad- 
 dition of vegetable matter had been gained. We 
 have already ascertained that the elements of ve- 
 getable matter are carbon, hydrogen, and oxygen ; 
 and as we know also that water is composed of 
 hydrogen and oxygen, we can easily believe that 
 
 4 
 
LECT. V.J THE ROOT. SOILS. 231 
 
 these two elements can be obtained from the de- 
 composition of this fluid by the powers of the 
 plant; but, without the presence of any soil, 
 whence is the carbon, which is required for the 
 formation of the additional vegetable matter, ob- 
 tained ? It has been suggested that the air is ca- 
 pable of supplying this, and that the quantity of 
 carbonic acid gas it contains, although small, is 
 never wanting. It is, however, possible that it 
 may have been afforded by the water ; for although 
 it was distilled, yet, as Sir H. Davy's experiments 
 have proved, distilled water may hold many sub- 
 stances in solution, and these never can be com- 
 pletely separated from it. But, if we even allow 
 that water and air are the only sources from 
 which the vegetable matter thus gained could be 
 derived, we also know that many plants cannot 
 be supported in this manner, and yet a direct 
 supply of nutritious matter is indispensable to 
 their growth and existence. Every farmer knows 
 the fact, that many plants will grow only in cer- 
 tain soils ; and his art consists in supplying to the 
 natural soils that part which is most essentially 
 necessary for their support. As we have proved 
 that the components of all vegetable matter are 
 carbon, hydrogen, and oxygen, we must look for 
 the supply of these ingredients in the soil: and 
 it is from water and decaying organic matter 
 that they are undoubtedly obtained. From this 
 
 Q4 
 
232 CONSERVATIVE ORGANS. [LECT. V. 
 
 matter then the carbon is supplied ; and as water 
 only, and those substances which it can hold 
 in solution, can be absorbed by the mouths of 
 the roots of plants, the carbon which is con- 
 tained in the soil, separated from vegetable and 
 animal matters by decomposition, must be dis- 
 solved in the water in order to be taken into the 
 system of the plant * ; and it thus becomes their 
 proper food. 
 
 If this view of the subject be correct, the art 
 of the husbandman and horticulturist must con- 
 sist in applying those substances to the soil which 
 will promote the growth of plants without over- 
 stimulating them. The different matters known 
 under the title of manures, which are employed 
 for this purpose, must act in four ways to pro- 
 duce the effect required. 1. They must render 
 the soil of that consistence which will enable it to 
 retain a sufficiency of water; but not too much. 
 2. They must render it pulverulent to admit the 
 roots of the plants to permeate, and spread freely 
 in it. 3. They must enable it to admit and retain 
 air in its interstices : and, 4. fit it to form carbon, 
 and afford healthy stimuli to the vegetable irrita- 
 bility. The importance of a finely pulverized 
 
 * The pores in the fibrils of plants are so minute, that a pow- 
 erful microscope is required to discover them ; the extreme 
 division, therefore, of insoluble matters, which pass into the 
 vegetable system may readily be conceived. 
 
LECT. V.] THE ROOT. SOILS. 233 
 
 soil was first pointed out by Jethro Tull, in 1733 ; 
 but although his ideas on this subject extended to 
 an absurd degree, and led him to form a theory of 
 vegetation altogether mechanical, yet the direction 
 of the agriculturist to the importance of pulve- 
 rization, has been productive of the most beneficial 
 results. It allows of the easy extension of the 
 roots of plants, admits a necessary supply of air 
 during the process of germination, and assists 
 those decompositions which are requisite for ren- 
 dering manure useful. 
 
 The first place among the substances fit to 
 answer the purposes already specified, is certainly 
 due to lime. This substance acts upon soils either 
 mechanically or chymically; and on the plants 
 it acts physiologically. When in the state of a car- 
 bonate, or united with carbonic acid, it is added to 
 clayey soils, it acts mechanically by rendering 
 them more free, loose, and pervious both to air, 
 moisture, and the roots of plants : it acts chymi- 
 cally when it is deprived of carbonic acid or is in 
 the caustic state by destroying worms, and other 
 insects hurtful to young vegetables; and, by quick- 
 ening the decomposition of their dead bodies, ren- 
 ders them useful to vegetation. In either state 
 it neutralizes acids, and decomposes salts of iron 
 and other injurious saline matters often contained 
 in soils ; and by the healthy stimulus which it af- 
 fords when in the state of quicklime it invigorates 
 
234 CONSERVATIVE ORGANS. [LRCT. V. 
 
 vegetation both in young and mature plants. 
 Lime also hastens the decomposition and solution 
 of vegetable matter; and has been long known 
 as a most useful manure when applied where 
 half-decomposed vegetable matter abounds, as for 
 example, in peat soils. The best corrective, there- 
 fore, for ground that has been too much dunged 
 is lime : and peat mosses *, which consist of vege- 
 table substances, the decay of which has been sus- 
 pended by the formation of a peculiar acid in 
 them, are rendered arable and highly fertile by a 
 proper use of lime. In this operation the lime is 
 combined with the acid contained in the moss, 
 and also with carbonic acid, and remains as a 
 component of the newly-formed soil. Every kind 
 of quicklime, however, does not answer for ma- 
 nure, and particularly that which abounds with 
 magnesia; for although magnesia, when united 
 with carbonic acid, is a useful ingredient in a 
 soil, yet in its uncombined state, or as calcined 
 magnesia, which is that in which it must be, when 
 magnesian limestone is burnt into quicklime^, it is 
 
 * Peat appears to be formed by the occasional flooding of 
 places where successive generations of vegetables have grown, 
 and been allowed to decay undisturbed, until at length the de- 
 composition is stopped by the water not passing off. The 
 soil is thus rendered spongy, and an acid is generated which 
 prevents the farther production of vegetation. 
 
 f Magnesian limestones are easily distinguished by their 
 dissolving very slowly in acids ; and by their rendering weak 
 solutions of nitric acid turbid. 
 
LECT. V.] THE HOOT. SOILS. 235 
 
 injurious to plants ; as proved by the experiments 
 of Mr. Tennant. When, however, even the best 
 quicklime is too freely used, it becomes hurtful by 
 over-stimulating the growing plants ; and, there- 
 fore, the more frequent and small application of 
 it is preferable. 
 
 It would be out of place in this Lecture to 
 notice all the substances used as manures; the 
 object of all of them is either to alter the re- 
 tentive quality of the soil, or immediately to 
 supply carbonaceous matter to the plants. For 
 these purposes, as occasion has required, clay, 
 brick rubbish, limestone, marl, chalk, sand, 
 gravel, have been employed as mechanical 
 means * ; salts of various kinds as stimulants ; 
 and soot, ashes, and dung, a* affording the pro- 
 per nutriment of plants. That salts are taken 
 up ready formed from the soil by vegetables is 
 pretty certain ; Du Hamel and Cadet having 
 established the fact, that, if the marine plants, 
 which yield soda while they grow near the sea, 
 be removed to inland situations, they gradually 
 cease to yield soda, and at length potash only 
 is obtained from their ashes -\-. We shall merely 
 
 * Wet clay can be burnt to powder if put into the fire un- 
 compressed, and consequently prove useful as a manure. Me- 
 moirs of Lord Kames. Appendix, p. 224. 
 
 f Even earths, although they cannot be converted into or- 
 ganized matter, yet, when in a state of extreme division, are 
 taken up by the roots of plants, and deposited in various parti 
 of the vegetable system. Thus silica is so abundant in the 
 
236 CONSERVATIVE ORGANS. [LECT. V. 
 
 notice, with regard to dung, that when it is com- 
 pletely rotten it does not afford much soluble 
 carbon, owing to its having become as it were ox- 
 ydized and the carbon being converted into a real 
 charcoal ; other principles also, such as carbonic 
 acid and ammonia, useful both as stimuli and nu- 
 triment to plants, are dissipated during the violent 
 fermentation, which is requisite to reduce dung 
 into this state. Fresh dung, or that which is not 
 completely rotten, on the contrary, benefits not 
 only the present crop but several subsequent ones, 
 as its good effect continues as long as the process 
 of decomposition goes on. That many of the good 
 effects of fresh dung depend on the extrication of 
 heat is evident ; and I am inclined to think it 
 is to this agent, chiefly, that must be attributed 
 the great superiority of the green vegetable matter 
 used as manure, in some experiments detailed by 
 Mr. Knight, in the Horticultural Transactions * ; 
 and not, as that gentleman supposes, to the nutri- 
 ment of vegetables being more easily assimilated 
 into the substance of the living plant, the less it 
 has passed from the state of living vegetable 
 matter. 
 
 Such are some of the facts relative to soils, 
 
 epidermis of the Equisetum, Mare's Tail, that it is used by 
 cabinet-makers for polishing furniture : and it is also found 
 composing part of the epidermis of Wheat, Oats, and some 
 other grasses. 
 
 * Vide Volume 1st. 
 
LECT. V.] THE ROOT. SOILS. 237 
 
 manures, and the food of plants, which the con- 
 sideration of the structure and the use of roots to 
 the plant have suggested. It may be thought that 
 I have travelled out of the proper path, in giving 
 even the slight view of them which I have at- 
 tempted; but my object is to excite those who 
 have leisure and opportunity to examine more 
 closely a subject so intimately connected with 
 the prosperity and happiness of our country, and 
 the most essential interests of the human race. 
 
 We have noticed the importance of the root 
 as a vegetable organ, but it is not less interesting 
 as yielding medicinal agents, supplying dying 
 materials, and affording an abundant store of food 
 for man and other animals. Many of the secreted 
 juices of plants which are deposited in the roots, 
 particularly when the stems annually decay, pos- 
 sess medicinal properties. Indeed, there is scarcely 
 one of the divisions of the Materia Medica in 
 which some of the roots, or their appendages, are 
 not to be found. Thus, among the EMOLLIENTS we 
 find the roots of Marsh Mallow, Althaea officinalis, 
 of Sarsaparilla, Smilax sarsaparilla, and of Liquo- 
 rice, Glycyrrhiza glabra, yielding demulcent and 
 saccharine mucilages. Among STIMULANTS, which 
 produce their specific action on particular or- 
 gans, the bulbs of the white Lily, Lilium can- 
 didum, and of Garlick, Allium sativum, may be 
 employed to affect the skin as rubefacients and 
 
238 CONSERVATIVE ORGANS. [LECT. V. 
 
 epispastics ; the roots of the Florentine Iris, Iris 
 Florentines, and of White Hellebore, Veratrum al- 
 bum, as errhines, to stimulate the olfactory nerves 
 and promote a discharge from the nostrils ; while 
 Pellitory root, Athemis Pyrethrum, and the roots 
 of Mezereon, Daphne Mezereon, Horse-radish, 
 Cochlearia Armor acia, and Cuckow-pint, Arum 
 maculatum, contain acrid matters which, when 
 the roots are masticated, stimulate the salivary 
 glands, or act as local sialagogues. From Ce- 
 phaelis Ipecacuanha we obtain our most useful 
 emetic ; and several other roots, as those of Viola 
 parviflora, V. Ipecacuanha and V. Calceolaria, 
 Cynanchum Ipecacuanha and C. tomentosum, 
 Dorstenia Brasiliensis and D. arifolia, possess 
 also useful emetic properties. The best Cathar- 
 tics are obtained from roots, as, for example, 
 those of Rhubarb, Rheum palmatum, of Jalap, 
 Convolvulus Jalapa, Scammony, Convolvulus 
 Scammonia, Bryony, Bryonia alba ; and that fa- 
 vourite of the ancients, black Hellebore, Hellebo- 
 rus niger. The roots of Burdock, Arctium Lappa, 
 Eryngo, Eryngium maritimum, and Dandelion, 
 Leontodon Taraxacum, are diuretic, or augment 
 the urinary discharge: as remedies possessing 
 the power of increasing the natural exhalation by 
 the skin, or diaphoretics, we may mention Snake- 
 root, Aristolochia serpentaria, the roots of Contra- 
 yerva, Dorstenia Contrayerva, and of Mountain 
 
LECT. V.] THE ROOT. SOILS. 239 
 
 Arnica,, Arnica montana ; and as expectorants, Se- 
 neka-root, Polygala senega, and the bulb of the 
 Squill, Scilla maritima. That division also of the 
 class of stimulants, which comprehends those re- 
 medies that exert a general operation on the sys- 
 tem, is equally rich in roots : thus, among the 
 permanent stimuli we find the roots of Common 
 Avens, Geum urbanum, Bistort, Polygonum Bis- 
 tort a, Tormentil, Tormentilla erect a, and of the 
 Water Dock, Rumex aquaticus, employed as astrin- 
 gents ; and those of Sweet Flag, Acorus Calamus, 
 Ginger, Zingiber officinale, Sweet Fennel, Anethum 
 Fceniculum, garden Angelica, Angelica archange- 
 lica, Zedoary, Curcuma Zedoaria, Yellow Gentian, 
 Gentiana lutea, Elecampane, Inula r Helenium, and 
 Calumba, as aromatics and tonics. Among the 
 diffusible stimuli the root of Thorn Apple, Datura 
 stramonium, is narcotic, and that of Valerian, Va- 
 leriana officinalis, antispasmodic ; whilst the bulb 
 of Meadow Saffron, Colchicum autumnale, besides 
 acting as a cathartic, exerts a directly sedative 
 effect on the nervous energy. 
 
 As agents in the art of dying, the chief colour 
 that roots impart is red; in producing which, 
 those of Madder, Rubia tinctorum, and of Alka- 
 net, Anchusa tinctoria, are of great importance: 
 various shades of this colour are also obtained 
 from the roots of several species of Bed-straw, 
 Galium ; and a very beautiful, but less permanent 
 
240 CONSERVATIVE ORGANS. [LECT. V. 
 
 tint, is yielded by the slender roots of Indian 
 Madder, Oldenlandia umbellata. The proper juice 
 of the Blood-root, Sanguinaria Canadensis, is 
 bright orange, and that of the Celandine, Cheli- 
 donium majm, is yellow; but I am not certain 
 that either of these have been employed as dye 
 stuffs. 
 
 But it is in furnishing food that man has most 
 successfully exerted his ingenuity on these vege- 
 table organs. The roots of many plants, which 
 in a state of nature are small, have been enlarged 
 by cultivation, and rendered capable of yielding 
 a considerable supply of nutritious aliment ; for 
 example, the Carrot, the Turnip, the Beet, and 
 the Parsnip. Roots that are acrimonious and 
 poisonous when raw, are so altered by the art 
 of cookery, as to become mild, nutritious, and 
 wholesome food, owing to heat destroying the 
 acrimony upon which their injurious properties 
 depend : and, even by simple elutriation, one of 
 the most virulent of poisonous roots, that of 
 Jatropha manihot, is converted into Tapioca, a 
 mild fecula, well known for its nutritive qualities, 
 and universally employed as an article of diet in 
 convalescence and by persons of delicate habits. 
 By similar means many other roots, also, which 
 are now regarded as hurtful, might be rendered 
 inert ; and large additional supplies thus afforded 
 to the vegetable stores already selected for the 
 subsistence of the animal creation. 
 
LECT. VI.] THE STEM. ITS DIRECTION. 241 
 
 LECTURE VI. 
 
 THE STEM ITS DIRECTION DIVISIONS AND BRANCH- 
 ING COVERING COLOUR FIGURE. CLASSIFICA- 
 TION OF STEMS. 
 
 HAVING finished the consideration of the root, 
 I have now to direct your attention to the two 
 next divisions, in our enumeration of the parts of 
 the plant, the stem and the branches. These or- 
 gans are generally above the surface of the ground, 
 and consequently in sight : I therefore propose, in 
 order to methodize our investigation, to view them 
 in the first place, simply as they are presented 
 to the eye, in the entire plant ; then more closely 
 as regards those external properties on which Bo- 
 tanists have founded their classifications of them ; 
 and lastly, to demonstrate the anatomy of their 
 internal structure : thus preparing you to under- 
 stand more readily their physiology. You should, 
 however, be previously informed, that the stem and 
 branches are organs not essential to the vegetable 
 structure, although they are so to the plants in 
 which they are found ; for, independent of some 
 Lichens, and many species belonging to those 
 tribes of vegetables which Botanists have deno- 
 minated imperfect, they are never present in many 
 VOL. i. R 
 
242 CONSERVATIVE ORGANS. [LECT. VI. 
 
 other plants, the foliage and fructification of which 
 spring directly from the root or some of its ap- 
 pendages ; as, for example, the Meadow Saffron, 
 Colchicum autumnale ; stemless Asphodel, Aspho- 
 delus acaulis ; and stemless Artichoke, Cynara 
 acaulis, &c. These plants are nevertheless perfect, 
 and capable of performing all the functions ne- 
 cessary in their economy ; the term imperfect, as 
 I formerly observed, being applicable to indi- 
 viduals only, in which the organs necessary for 
 carrying on the functions of the plant and pro- 
 viding for the continuation of the species are de- 
 fective. 
 
 Under the general name of stem is compre- 
 hended that portion of a plant which, proceeding 
 from the upper part of the root, affords support to 
 the branches, the leaves, and the fructification *. 
 If we take a view of the vegetable kingdom, we 
 are struck with the wonderful diversity in the 
 size, direction, form, and exterior aspect of this 
 part of plants. How great is the difference 
 in strength, for example, betwixt the delicate 
 
 * " Truncus multiplicat herbas, et immediate a radice 
 " ad fructificationem ducit, vestitus foliis, terminates fructifi- 
 " catione." Phil. Bot. 81. 
 
 " Truncus folia et fructificationem profert.'* Ibid. 82. 
 
 " Tige support principal des parties du ve"ge" tal qui s'elevent 
 " au dessus de terre." Mirbel, Elemens, %c. p. 622. 
 
 Willdenow denominates it the stock (cormusj. Prin- 
 ciples of Botany, 15. 
 
LECT. VI.] THE STEM. ITS DIRECTION. 243 
 
 thread which supports the flower of the bending 
 Hairbell, and the rigid trunk of the majestic 
 Oak ! and in position and altitude, betwixt the 
 creeping Bramble and the towering Palm, rising 
 to the height of upwards of two hundred feet ! 
 Some of the climbing plants have been found, 
 when untwisted, to be five hundred feet in length : 
 and Captain Cook observed, that in parts of the 
 ocean, where the soundings were upwards of thirty 
 fathoms, the sea- weed stretched in a direct line 
 from the bottom to the surface of the waves. The 
 diversity in the thickness or diameter of the stem 
 is not less remarkable. In the Club-rush, Scirpus 
 capillaris, it is quite a hair, while Swilcar Oak, 
 on the contrary, is thirteen yards in circumference 
 round the base of the trunk, and eleven yards at 
 the height of four feet from the ground : in Ches- 
 nut trees it has been known to acquire, even in 
 Great Britain, forty feet in circumference; and 
 we are informed that the trunk of the Calabash 
 tree, Adansonia digitata, which grows on the coast 
 of Africa, although not more than twelve or four- 
 teen feet in height before it branches, is frequently 
 twenty-seven feet in diameter*. Such is the 
 amazing extent to which the stem may attain ; 
 
 * " The branches of the Adansonia, which are numerous 
 " and thick, extend from thirty to sixty feet out from it in 
 ** all directions; and the hollow trunk is often the dwelling of 
 " several negro families.'* Fam. des Plantes, Pref. ccxii. 
 
 R'2 
 
244 CONSERVATIVE ORGANS. [LECT. VI. 
 
 but the necessities of men seldom permit trees to 
 arrive at their utmost growth ; and,, to quote the 
 words of an elegant writer, " Nature preserves her 
 " magnificence in those places only, where man 
 " cannot assert his empire." 
 
 Although almost * all stems rise out of the 
 ground, yet, no minute inspection is required to 
 perceive that they do not all assume the same 
 direction. Some stand erect, elevating their 
 foliage in the air; others approach to the perpen- 
 dicular only; some, too lax even to support their 
 own weight, raise themselves by twining around 
 those which are more rigid, or climb by the aid of 
 various appendages ; while others again lie pro- 
 strate, or creep along upon the surface of the 
 earth. Each of these peculiarities has been no- 
 ticed by Botanists, and named. A stem is said to 
 be, 
 
 1. ERECT (erectus, verticalis, perpendicu- 
 laris), when its position forms nearly a right 
 angle with the surface of the soil from which 
 it rises, provided that surface be almost parallel 
 to the horizon. There are four varieties of the 
 
 * I use the word almost, because many plants that appear 
 to be stemless, have a cylindrical caudex rising from the real 
 root, which is very deep in the ground, to the surface of the 
 earth, where it gives offa tuft of leaves and flowers; as in com- 
 mon Mousetail, Myosurus minimus. This portion does not 
 perform the office of a root, and, therefore, it may be con- 
 sidered as participating of the nature of a stem. 
 
LECT. VI.] THE STEM. ITS DIRECTION. 245 
 
 erect stem,, derived from the character of the 
 line it produces from the base 
 to the apex. An erect stem is 
 a. Straight (strictus, rectus, 
 rectilineus) (fig. a), when it has 
 no natural curve in any portion 
 of its length, however] thickly 
 branched it may be ; as r for ex- 
 ample, that of the Silver Fir, 
 Pinus Picea (a), among trees ; 
 and of Spear Mint, Men t ha vi- 
 ridis, among herbaceous plants. 
 
 b. Flexuose (flexuosus) 
 (fig. b), when it is naturally 
 a regular zigzag, so as to form 
 alternate obtuse angles from 
 right to left, and from left to 
 right * ; as in Box-leaved 
 Staff-tree, Celastrus buxifolius 
 (#) ; and common Birthwort, 
 Aristolochia Clematitis. 
 
 c. Tortuous (tortuosus), 
 when it is curved or writhed 
 in different directions, but 
 not regularly as in the flex- 
 nose stems. 
 
 * " Flexuosus, secundum articulos horsum vorsum flexui ; 
 Ptclea." Phil. But. 82. 4. 
 
 R3 
 
246 CONSERVATIVE ORGANS. [LECT. VI. 
 
 d. Nodding (nutans, cernuus) (fig. c), when 
 
 near the summit 
 only it takes a di- 
 rection more or 
 less towards the 
 horizon, the low- 
 er portion being 
 quite erect ; as in 
 the Cedar, Pinus 
 Cedrus, and So- 
 lomon's Seal, Po- 
 lygonatum mul- 
 tiflora (c). 
 
 2. OBLIQUE (obliquus) is the term employed 
 to designate the elevation of a stem, the direc- 
 tion of which is diagonal to the plane of the 
 horizon. There are three varieties of the oblique 
 stem. It is said to be 
 
 a. Ascending (adscendens) (fig. d), when its 
 
 lower portion forms 
 a curve, the con- 
 vexity of which is 
 towards the earth, 
 or rests upon it, and 
 the summit rises per- 
 pendicularly ; as ex- 
 emplified in many of 
 
 the Grasses (d) ; in Common Toad Flax, The- 
 sium Imophyllum; common Clover, Trifohum 
 pratense ; small Carex, Carex dioica, &c. 
 
LKCT. VI.] THE STEM. ITS DIRECTION. 247 
 
 b. Declined (declinatus,redinatus), when the 
 lower part of the stem rises obliquely from the 
 ground ; but the upper bends towards it, form- 
 ing an arch * ; as in that of the Fig-tree, Ficus 
 carica. 
 
 c. Incurvated (incurvus), when the stem 
 rises and bends as in the former; but with 
 the apex turned inwards, as in that of the com- 
 mon Bramble, Rubusfruticosus. 
 
 3. SUPPORTED (fulcratus) (fig. e). A supported 
 
 stem appears as if 
 
 u were p r pp ed b y 
 
 a number of other 
 stems that surround 
 it, inclining towards 
 each other, at their 
 summits, until they 
 seem engrafted into 
 the base of the stem 
 which they support: 
 as in the Mangrove, 
 Rhizophora mangle^-. 
 This curious appearance is occasioned by the 
 
 * " Reclinatus, arcuatim versus terram ; Ficus." Phil. 
 Bot. 82. 6. 
 
 fThis species of Rhizophora is found in Asia, Africa, 
 and South America, growing in marshy and flooded flats, in. 
 creeks, and at the mouths of rivers. 
 
 R 4 
 
248 CONSERVATIVE ORGANS. [~LECT. V I 
 
 original trunk sending off two distinct kinds of 
 branches : those at the summit bear leaves and 
 the fructification, while the lower are leafless, 
 and bend down until they touch the ground, in 
 which they root, and are changed into real stems. 
 4. CLIMBING STEMS (scandentes) are those 
 which, being too delicate and flexible to support 
 themselves, require the aid of some perpendi- 
 cular body to enable them to elevate their foliage 
 and fructification in the air ; and this is accom- 
 plished by one or other of the following means : 
 A stem is denominated 
 
 a. Twining (volubilis), when it winds itself 
 spirally round any other plant or upright slen- 
 der body*. This motion is performed inva- 
 riably in one direction by all the plants of the 
 same species ; and is so natural to them, that if 
 it be forcibly reversed, the plants will untwine 
 themselves, and again assume the direction 
 peculiar to their species. When the twining is 
 from left to right, or following the apparent 
 motion of the sun, as in Woodbine, Loni- 
 cera Periclymenwn ; or the Hop, Humulus 
 
 * " Volubilis spiraliter adscendens per ramum alienum. 
 
 " Sinistrorsum ([ secundum solem vulgo: Humulus y 
 " Helxine, Lonicera, Tamus. 
 
 " Dextrorsum D contra motum soils vulgi ; Convolvulus, 
 11 Basella, Phaseolus, Cynanche, Euphorbia) Eupatorium." Phil, 
 Sot. 82. 5. 
 
LECT. VI.] THE STEM. ITS DIRECTION. 
 
 249 
 
 lupulus (fig. f, 1), it is termed sinistrorsum ; 
 
 and when it 
 takes the op- 
 posite direc- 
 tion, or from 
 right to left, 
 as in the Scar- 
 let Bean, Pha- 
 seolus multi- 
 Jlorus, the 
 Great Bind- 
 weed, Convol- 
 vulus sepium, 
 or smooth Pe- 
 ri ploca, Peri- 
 ploca Icevigata 
 
 (fig- "/, 2), 
 dextrorsum. 
 The cause of this spiral motion of twining 
 stems I will endeavour to explain, when we in- 
 quire into the movements of plants. 
 
 b. Radicating (radicans), when it sends 
 forth from one side short, fleshy, root-like 
 fibreSj by means of which the plant elevates 
 itself on the perpendicular surfaces of walls 
 and rocks; as in the Ivy, Hedera helix; 
 (fig. g, 1. seep. 250), Ash-leaved Trumpet- 
 flower, Bignonia radicans, &c. In general 
 
250 
 
 CONSERVATIVE ORGANS. [LECT. VI. 
 
 these root-like 
 appendages in- 
 sert themselves 
 into the cre- 
 vices of the 
 wall or rock, 
 on the face of 
 which the plant 
 climbs ; but, 
 in some in- 
 stances, they 
 operate like 
 the feet of flies, 
 and of those 
 lizards that 
 have the power 
 
 of running up smooth perpendicular walls 
 and along the ceilings of rooms ; or rather 
 like the suckers which boys employ for lifting 
 stones, and which adhere, by the closeness 
 of their application preventing any air from 
 being interposed between them and the spot 
 on which they are applied. Some Botanists 
 imagine that these caulinary radicles differ ma- 
 terially from the roots thrown out by the stems 
 of creeping plants ; and that they do not im- 
 bibe nourishment * ; but in my opinion the 
 
 * Such is the opinion of Sir J. E. Smith (see Introd. to 
 
LECT. VI.] THE STEM. ITS DIRECTION. 251 
 
 difference is more imaginary than real; for, 
 if they cannot enter into crevices, they stretch 
 down towards the earth to a considerable ex- 
 tent; for if a shoot of Ivy happen to lie 
 upon the ground, the radicles, which would 
 have remained short had it ascended the wall, 
 extend into real absorbing roots (see fig. g y 
 2, a b). They are, also, always protruded from 
 that side of the stem which is farthest from 
 the light and air, <and consequently the 
 moistest; and, thence, the opinion that they 
 do not absorb is at least problematical. 
 
 c. Climbing (scandens), when it is fur- 
 nished with tendrils, which are filiform spiral 
 appendages, that twine round the branches 
 and twigs of upright plants ; which are thus 
 enabled to elevate their foliage and fructifica- 
 tion: as in the Vine, Vitis vinifera, and all 
 the species of Passion-flower, Passiflora, &c. 
 In some climbing plants, which are not fur- 
 nished with tendrils, as for instance, purple 
 Virgins Bower, Clematis viticella, and Bitter- 
 sweet, Solanum Dulcamara, the petioles or 
 
 phys. and system. Botany, p. 118). Linnaeus, on the contrary 
 (Phil. Bot. 82, p. 8), seems to have confounded the creeping 
 with the climbing radicating stems, in the following defini- 
 tion : " Repens radiculas hinc exserens procumbendo ; Hedera, 
 " Bignonia." 
 
252 CONSERVATIVE ORGANS. [LECT. VI. 
 
 
 
 footstalks of the leaves serve the purpose of 
 tendrils, and twine round the props upon which 
 the plants climb. 
 
 5. DECUMBENT (decumbens) is a term given 
 to a stem when it rises a little upright at its 
 base ; but has its upper portion bent down towards 
 the ground, so that the greater part of it is 
 procumbent. 
 
 6. PROCUMBENT (procumbens, prostratus, hu- 
 mifusus) implies that the stem, being too weak 
 to support itself, lies flat on the ground * ; as 
 in Bearberry, Arbutus uv a ursi, Scarlet Pimpernel, 
 Anagallis arvensis, c. Many procumbent stems 
 throw out roots from the under surface, thereby 
 receiving nourishment in their progression ; and 
 this circumstance constitutes a variety, which 
 has been denominated 
 
 a. Creeping (repem) (fig. h). It denotes 
 
 * " Procumbent, horizontaliter supra terram." Phil. Bot> 
 82, p. 7. 
 
LECT. VI.] THE STEM. ITS DIRECTION. 253 
 
 that the stem extends horizontally, or on the 
 surface of the ground, and sends out roots 
 from below; as in lesser periwinkle, Vinca 
 minor (h), and Ground Ivy, Glechoma hede- 
 racea. Linnaeus, Sir J. E. Smith, and some 
 other authors, describe another variety of the 
 procumbent stem under the term trailing or 
 sarmentose (sarmentosus *) : but the sarment 
 is, properly speaking, not a stem, but merely a 
 runner which performs the same functions as 
 the underground runners, to which pendu- 
 lous tubers are attached. It is, in fact, a vas- 
 cular cord, intended to place the lateral pro- 
 geny of the plant at a convenient distance 
 from the parent, and to convey nourishment 
 to the offset until such time as it takes root 
 and is capable of supporting itself. It is at 
 first sent off from the neck or collet of the 
 root ; but, afterwards, it gives off itself roots 
 at the points where the offsets spring; and, 
 as the manner in which this is effected va- 
 ries, it is of different kinds ; but these shall 
 be demonstrated when we investigate the ap- 
 pendages of the stem. The swimming stem 
 
 * " Sarmentosus, repens, subundus est." Phil Bot. 82. 9. 
 
 " Sarmentosus, trailing. A creeping stem, barren of flowers, 
 " thrown out from the roots for the purpose of increase, is 
 " called sarmentum or flagellum, a runner.'* Smith's Intro* 
 duction, &c. p. 120. 
 
 4 
 
254 CONSERVATIVE ORGANS. [LECT. VI. 
 
 (C. natans) has a much better claim than the 
 sarmentose to be ranked as a variety of the 
 procumbent stem, as it is a real stem, and 
 lies floating on the surface of the water, throwing 
 out radicles from the under side : the Floating 
 Club-rush, Scirpus fluitans, is an example. 
 The term natans for denoting this position of 
 the stems of aquatics is of importance in a 
 systematic point of view, and is used in con- 
 tradistinction to sunk (demersus) ; which im- 
 plies that the stem lies below the surface, as 
 in common Horn wort, Ceratophyllum demer- 
 sum. 
 
 Besides the diversity which prevails in the 
 position or direction of the stems, we perceive, in 
 glancing the eye over the vegetable kingdom, that 
 they present much variety, also, with respect to 
 general form. Thus, some are simple or undi- 
 vided, while others are divided and subdivided 
 into very minute ramifications. 
 
 1. The UNDIVIDED or SIMPLE stem (C. sim- 
 plex) consists of one piece only, without any 
 branches bearing leaves; although the flower- 
 stalk may be divided ; as exemplified in knotty- 
 rooted Figwort, Scrophularia nodosa. When, 
 however, there is no division even of the flower- 
 stalk, but the whole stem is one rod or column 
 from the base to the summit, and is terminated 
 by a single flower, or a simple spike, it is 
 
LECT. VI.] THE STEM. ITS DIVISIONS. 255 
 
 then termed very simple (simplidssimus) ; as in 
 Bistort, Polygonum bistort a, the Date Palm, 
 Phoenix tkctylifera, &c. 
 
 2. The DIVIDED stem, owing to the parts into 
 which it divides being termed branches (rami), is 
 denominated branched (ramosus *) ; and the 
 manner in which this is effected produces diver- 
 sities in the general aspect of plants of great 
 importance to the systematic Botanist. It af- 
 fords, also, a kind of physiognomical character 
 to each species, by which it is immediately re- 
 cognizable to the eye of observation ; and the 
 perceiving this character, and retaining a clear 
 impression of the perception in the memory, ought 
 to be strictly attended to by the student. It af- 
 fords him a sure guide to the more particular ex- 
 amination of vegetable nature; associating the 
 minute characteristics of each species so closely 
 with its general features, as to call those up ra- 
 pidly in the memory, whenever these present them- 
 selves either to the eye or the imagination ; and, 
 in Botany, you will soon be convinced how es- 
 sential it is to fix, in as practical a manner as 
 possible, every impression which the examination 
 of plants can make on the mind. The greater 
 masters of the old schools of painting were fully 
 aware of the importance of studying the physio- 
 
 * " Ramosus est ramis lateralibus instructus." Phil. Bot. 82, 21 . 
 
256 CONSERVATIVE ORGANS. [LECT. VI. 
 
 gnomy of plants, especially of trees ; and they 
 carefully transferred it to their canvass. Thus 
 you can recognize in their landscapes, as in na- 
 ture, a Poplar, a Willow, the Cedar, an Elm, 
 an Oak, or any other tree ; whereas, the general 
 term trees is sufficient to describe the foliage, 
 which crowds in confused masses the pictures of 
 inferior artists. 
 
 The branches are evident divisions of the 
 principal trunk ; yet, in the majority of in- 
 stances, the stem can be traced, as it rises amidst 
 these divisions, from the base to the apex ; but 
 as it is, also, in some plants entirely lost, Bo- 
 tanists employ distinct terms to designate these 
 opposite states : thus, continuus is used for the 
 former, and for the latter decompositus. The 
 branching of a stem admits of several varieties, 
 each of which requires to be noticed. It is said 
 to be 
 
 a. Slightly branched (subramosus) , when the 
 number of divisions are comparatively few. 
 
 b. Much branched (ramosissimus) , when not 
 only the greater divisions are numerous, but 
 these are again divided and subdivided with- 
 out order * ; as in the Elm, Ulmus campestris ; 
 the Gooseberry-bush, Ribes Grossularia, &c. 
 
 * " Ramosissimus ramis multis absque ordine gravidus." 
 Pkit. Bot. 82. 2. 
 
LECT. VI.] THE STEM. ITS DIVISIONS. 257 
 
 Linnaeus and some others employ the term pro- 
 liferous (prolifer) to denote a modification of 
 the much-branched stem, in which the new 
 branches shoot out only from the summits of 
 the former ones *, as in the Scotch Fir, Pinus 
 sylvestris : but, as Sir J. E. Smith remarks, 
 the term is obsolete, and seldom used. 
 
 c. " Abruptly branched (determinate ra- 
 " mosus), when each branch, after terminating 
 " in flowers, produces a number of fresh shoots, 
 " in a circular order, from 
 " just below the origin of 
 " those flowers ; as in na- 
 " ked- flowered Azalea, Aza- 
 " lea nudiflora, and many 
 " of the Cape Heaths f." 
 
 d. Forked or dichotomous 
 (dichotomus) (fig. i), when 
 the divisions and subdivisions 
 are, throughout, in alternate 
 bifurcations ; as exemplified 
 in Corn Salad, Valeriana 
 locusta, Petty Spurge, Euphorbia peplus, and 
 
 * <c Prolifer ex apicis centre emittens tantum ramos ; 
 " Pinus." Phil. Bot. 82. 28. 
 
 f Smith, from whom this definition is borrowed, says that 
 the term determinate ramosus occurs frequently in the later 
 publications of Linnaeus, particularly the second Mantissa ; but 
 that he has not any where explained its meaning. Introd. p. 122. 
 
 VOL. I. S 
 
258 CONSERVATIVE ORGANS. [LECT. VI. 
 
 forked Marvel of Peru, Mirabilis dichotoma : but 
 when, instead of being bifurcated, the divisions are 
 trifid, the stem is then said to be trichotomous ; 
 as in common Marvel of Peru, Mirabilis Jalapa. 
 
 The BRANCHES themselves, whatever may be 
 their numbers or divisions, vary considerably with 
 respect to their situation on the stem ; the direc- 
 tion they assume relatively to it ; and their 
 strength, or the power they possess of support- 
 ing their own weight: and these diversities are 
 seized by systematic Botanists in forming the 
 characters of species. 
 * In situation. 
 
 Branches may be either opposite, or alternate, 
 or scattered. They are said to be, 
 
 1. OPPOSITE (oppositij, when one branch stands 
 on the opposite side of the stem to another, and 
 their bases are nearly on the same plane. Be- 
 sides this situation of branches, to which the 
 term opposite is especially applied, the two fol- 
 lowing may be regarded as varieties of it : 
 
 a. Verticillated (verticillati) , when the stem 
 is the centre of a number of branches proceed- 
 ing from it like rays on the same plane ; and 
 this occurs, in trees and shrubs, by one series 
 of the branches being always formed at the 
 extremity of the stem every year ; so that in 
 time they appear at certain distances to sur*- 
 round the stem in successive series ; as in the 
 Silver Fir, Pinus Picea (fig. a, p. 245). 
 
LECT. VI.] THE STEM. BRANCHING. 259 
 
 6. Two-ranked (distichi), when the branches 
 originating promiscuously are arranged in two 
 opposite series *, as in the Elm, Ulmus cam- 
 pestris. 
 
 2. ALTERNATE (alterni), when they stand singly on 
 each side of the stem, in such 
 a manner, that between every 
 two on one side, there is but 
 one on the opposite side ; as 
 in purging Buckthorn, Rham- 
 nus catharticus, or in the sin- 
 gular American plant, called 
 Sweet Fern, Comptonia asple- 
 nifolia^c (fig. k). 
 
 3. SCATTERED (sparsi), when 
 they are not given off from the 
 stem in any determinate man- 
 ner. 
 
 ** In direction. 
 
 Branches are, relatively to the stem, either 
 erect, or spreading. 
 
 1. ERECT (wecti), when they form a very acute 
 angle with the upper part of the stem, and, con- 
 sequently, nearly a right angle with the horizon- 
 There are three varieties of erect branches. 
 
 * " Distichus ramos situ horizontali exserit." Phil. Bot. 
 82. p. 24. 
 
 t Veg. Mat. Med.qfthe United States, vol. i. p. 224. 
 
260 CONSERVATIVE ORGANS. [LECT. VI. 
 
 a. The approximated (appressi) (fig. I), when 
 /. they rise in a direction nearly 
 
 parallel to the stem ; and are 
 closely applied to it, as in Green 
 Weed, Genista tinctoria. 
 
 b. Inflected (introflexi), when 
 the tips of the branches bend 
 towards the stem ; as in the Lom- 
 bardy Poplar, Populus dilatata. 
 
 c. Fastigiate (fastigiati), 
 when the tops of the branches, 
 from whatsoever part of the stem 
 they spring, rise nearly to the 
 same height; as in Sweet Wil- 
 liam, Dianthus barbatus. 
 
 2. SPREADING (patentes), when the angle, 
 formed by the branch and the upper part of the 
 stem, cannot be termed acute. Seven varieties of 
 this direction of branching are described by au- 
 thors. 
 
 a. Open, diffuse (patuli, diffusi*), when 
 the angle formed with the upper part of the 
 branch is about forty-five degrees ; as in great 
 Hedge Bed-straw, Gallium Mollugo. 
 
 b. Very open, horizontal (patentissimi) , when 
 the angle formed with the upper part of the 
 stem is about 90 degrees ; as in the Apple-tree, 
 
 * " Diffusus ramis patentibus." Phil. JBot. 82. 23. 
 
LECT. VI.] THE STEM. BRANCHING. 261 
 
 Pyrus Malus ; and the Asparagus, Asparagus 
 officinalis. 
 
 c. Diverging (diver gent es), when they go 
 off nearly at right angles with the stem, and 
 appear as if verticillated, without being on the 
 same plane ; as the Stone Pine, Pinus plnea. 
 
 d. Brachiate, four-ranked (brachiati *) (fig. 
 
 m), "when they spread in 
 " four directions, crossing 
 " each other alternately in 
 " pairs ; a very common 
 " mode of growth in shrubs 
 " that have opposite leaves, 
 " as the common Lilac, Sy- 
 " ringa vulgaris *f~." 
 
 e. Divaricated (dwaricati), 
 when the direction is such 
 that the angle formed with 
 the part of the stem above 
 the branch is rather more obtuse than that with 
 the part below it ; as in Fiddle Dock, Rumex 
 pulcher. 
 
 f. Close (conferti), when they are given off 
 irregularly, and stand so thick, as to have ap- 
 parently no spaces betwixt them. 
 
 * " Brachiatus raraos decussatim oppositos habet." Phil. 
 Bot. 82. 25. 
 
 f Smith's Introd. to phys. and system. Bot. 121. 
 
 s3 
 
262 CONSERVATIVE ORGANS. [LECT. VI. 
 
 g. Supported (fulcrati*), when they project 
 nearly horizontally, and give out root-like 
 shoots from the under side ; which extending 
 until they re.ach the ground, 'take root, and 
 serve as props to the branches ; as in the Ban- 
 yan tree, Ficus rellgiosus. 
 
 Such are the varied modes of branching ; but 
 many circumstances concur to alter and modify 
 the natural directions of branches in trees. Thus, 
 if a tree, which when it stands alone throws 
 out many lateral, spreading branches, be planted 
 in a thick grove, or forest, the lower branches 
 will become weak from want of air and light, and 
 fall off; and the tree, rising in height, will give 
 out top branches only: while, on the contrary, 
 a tree which is left when a wood is cut down, soon 
 throws out lateral branches, and extends in the 
 breadth of its shade, much more than it increases 
 in stature. In the Cedar also, and some other 
 trees of a pyramidal form, when, from age or acci- 
 dent, the top shoot, which is termed the runner, 
 is taken away, the lower branches drop off and 
 those of the summit of the tree stretch out broad 
 and long ; the whole aspect of the tree is changed, 
 and from a beautiful and elegant pyramid, it be- 
 comes a spreading canopy, dark, awful, and im- 
 
 * " Fulcratusy ramis descendens ad radicem ; Ficus." Phil. 
 Bot. 82. 27. 
 
LECT. VI.] THE STBM. BRANCHING. 263 
 
 pressive. The finest examples of this alteration of 
 form are the two venerable Cedars which grace the 
 Apothecaries' garden at Chelsea. Even when the 
 general character of the tree is not changed, cir- 
 cumstances occur to alter the natural direction of 
 the branches : thus, if fruit-trees, which spread 
 horizontally, be planted on a declivity, the 
 branches still preserve a direction parallel to the 
 surface of the earth, and consequently the angle 
 which is formed between them and the upper part 
 of the stem is much more acute than is natural 
 on the side next the acclivity, and much more 
 obtuse on the opposite. The steeper the declivity 
 is, the more fertile the trees are said to become; 
 which is undoubtedly owing to the position as- 
 sumed by the branches, enabling the ground to 
 operate in the same manner as a wall ; but more 
 beneficially. Cultivation, also, varies the natural 
 aspect of plants : the buds, for instance, which 
 on trees growing in a rich and cultivated soil, 
 shoot into branches, often, from a deficiency of 
 nourishment, run out into sharp-pointed thorns ; 
 and this is the case with almost every species of 
 fruit-trees in a state of nature. The changing of 
 these into branches by cultivation, is termed, by 
 Linnaeus, the taming of plants ; but many plants, 
 however, have appendages of this description un- 
 der all circumstances of situation and culture. 
 
 s4 
 
264 CONSERVATIVE ORGANS. [LECT. VI. 
 
 *** In strength, or the power they (branches) 
 possess of supporting their own weight. 
 
 In this respect branches are either sufficiently 
 thick and strong to support the whole of their 
 weight, whatever may be their relative size, 
 situations, or directions ; or they are so slender 
 as to droop in a greater or less degree. When the 
 latter state exists, the degree of drooping is de- 
 noted by specific terms. Thus they are said to be 
 
 a. Deflected, arched (deflexi), when they hang 
 down so as to describe a curve or arch, the 
 convexity of which is towards the heavens ; as 
 in the Larch, Pinus larix. 
 
 b. Pendent (reflexi), when the apex of the 
 branch droops considerably below the line of its 
 insertion; as in the Weeping Willow, Salix 
 Babylonica. 
 
 c. Pendulous (penduli), when they begin to 
 droop nearly at the point of insertion, so as to 
 hang almost parallel with the stem. 
 
 Such are the particulars connected with the 
 external aspect of stems and branches, when re- 
 motely viewed, which are noticed by Botanists ; 
 but when these organs are examined a little more 
 closely, we find many other important diversities, 
 connected with surface and figure, that are ne- 
 cessary to be demonstrated ; and without an 
 accurate knowledge of which the student cannot 
 
LECT. VI.] THE STEM. BRANCHING. 265 
 
 understand the descriptions of plants in the works 
 of systematic writers. 
 
 With regard to surface, stems are either bare 
 or covered. They are said to be, 
 
 1. BARE (nudi), when the epidermis is per- 
 fectly free from appendages of every description, 
 leaves, scales, spines, prickles, or any kind of 
 pubescence. The superficies of naked stems varies 
 considerably : it is termed, 
 
 a. Shining (lucidus, nitidus) when it glistens, 
 as if varnished ; as in shining Crane's-bill, Ge- 
 ranium lucidum. 
 
 b. Smooth (glaber), when it is free from all 
 kinds of roughness or hairiness * ; as in Peri- 
 winkle, Vinca major; Petty Spurge, Euphor- 
 bia Peplus, &c. 
 
 c. Even (Icevis), when, throughout, it is per- 
 fectly free from inequalities ; as in the Somni- 
 ferous Poppy, Papaver somniferum. 
 
 d. Punctured (punctatusj, when it is covered 
 with small yet visible perforations, either simple, 
 or surrounded, at the orifice, with a raised 
 border. In both instances, these punctures are 
 probably the excretory ducts of subcuticular 
 glands opening on the epidermis. Rue, Ruta 
 graveolens (Plate 4, fig. 4) ; and perforated 
 
 * " Glaber, superficie laevi est." Phil. Bot. 82. 18. 
 
266 CONSERVATIVE ORGANS. [LECT. VI. 
 
 St. John's Wort, Hypericum perforatum ; may 
 be taken as examples. 
 
 e. Maculated, blotched (maculosus, macula- 
 tus), when it is marked with spots or blotches ; 
 as in Hemlock, Conium maculatum, and great- 
 flowered Ancethera, Anoethera grandiflora 
 (Plate 4, fig. 5). The colour of stems is not 
 generally noticed by Botanists, unless it be 
 so remarkable and determinate as to con- 
 stitute a good specific distinction, as in the in- 
 stances just referred to ; in which the macu- 
 lated appearance of the stems is invariably 
 present. 
 
 e. Leafless (aphyllus*), when it is altogether 
 devoid of leaves, as the Dudder, Cuscuta Eu- 
 ropea. 
 
 f. Unarmed (inermis), when devoid of 
 prickles or spines. 
 
 g. Exstipulate (exstipulatus) , when without 
 stipulse ; a species of appendage of which you 
 must be supposed still ignorant,, but which 
 shall be described in the proper place. These 
 negative terms are employed chiefly to, dis- 
 tinguish those members of genera which con- 
 tain species that display opposite qualities. 
 2. COVERED (vestiti), when the epidermis is 
 
 *"Nudus 9 foliis destitutus; Euphorbia, Cactus, Slapelia, 
 Ephedra, Cuscuta. " Phil. Bot. 82. 2. 
 
LECT. VI.] THE STEM. BRANCHING. 267 
 
 clothed with some kind of appendage ; and ac- 
 cording to the nature of this, the stem is desig- 
 nated by a term expressive of its covering. It is 
 said to be, 
 
 a. Leafy (foliosus, foliatus *J, when it is fur- 
 nished with leaves from the base to the apex 
 (vide Plate 4, fig. 1,2). When the stem passes 
 through each leaf, it is denominated perfoliate 
 (perfoliatus) , as in Yellow Wort, Chlora per- 
 
 foliata (Plate 4, fig. 6). 
 
 b. Winged (alatus), when the edges or 
 angles are longitudinally expanded into leaf- 
 like borders. (Plate 4, fig. 3.) 
 
 c. Sheathed (vaginatus) (fig. o), when it is 
 
 embraced by the base of each leaf, as 
 if by a sheath ; as exemplified in the 
 Grasses ; Snake Weed, Polygonum 
 Bistort a, &c. 
 
 d. Stipulated (stipulatus), when 
 it is furnished with stipulae (organs 
 which I shall have occasion afterwards 
 to explain to you), at the axillae of 
 each leaf: as in the Common Vetch, 
 Vicia sativa, broad-leaved Everlast- 
 ing Pea, Lathy rus latifolius *\* ; &c. 
 
 e. Tendril-bearing (cirriferus), when it 
 
 * " Foliatus, foliis instructus est." Phil. Bot. 82. 3. 
 f Vide Plate 4, fig. 7, which represents the winged stem 
 of Lathyrus latifolius ; a. a. a. a. are stipulae. 
 
268 CONSERVATIVE ORGANS. [LECT. VI. 
 
 bears tendrils ; as in the Passion Flower, Passi- 
 flora * ; the Vine, Vitis, &c. 
 
 f. Bulb-bearing (bulbiferus), when it is 
 studded with bulbs in the axillae of the leaves ; 
 as in several of the Lily tribe, Lilium -f- ; Bulbi- 
 ferous Coral Wort, Dentaria bulbifera, &c. 
 
 g. Spiny (spinosus) (&g-p, l), when it is fur- } 
 
 nished with sharp 
 spines, which are 
 not productions of 
 the bark, and, con- 
 sequently, do not 
 come off with it ; 
 as in Common 
 Hawthorn, Mespi- 
 lus oxyacantha, and 
 the Sloe-tree, Pru- 
 nus spinosa, &c. 
 
 h. Prickly ( acu- 
 leatus) (fig. p, 2), 
 when it is covered with sharp-pointed bodies, 
 which separate with the epidermis ; as in the 
 Rose, Rosa centifolia, R. Eleganteria, &c. 
 
 i. Bristly (setaceous)., when its armature con- 
 sists of brushes of minute bristles, divaricat- 
 
 * Plate 4, fig. 8. A small portion of a stem of a 
 Passiflora ; a. a. the tendrils ; b. b. stipulae ; c. c. c. glands. 
 
 f Plate 4, fig. 9. A portion of the stem of Lilium super- 
 bum : a. a. the bulbs seated in the axillae of the leaves. 
 
LECT. VI.] THE STEM. BRANCHING. 269 
 
 ing from the points whence they are given off; 
 as in creeping Cactus, Cactus flagelliformis. 
 (Plate 4, fig. 10.) 
 
 k. Scaly (squamosus) (fig. q), when it is co- 
 vered, more or less, with leafy 
 scales, which are closely applied 
 to its surface, as in Broom Rape, 
 Orobanche major. When, how- 
 ever, the scales, instead of being 
 succulent and leafy, are dry and 
 membranaceous, this variety of 
 the scaly stem is termed 
 
 * Ramentaceous (ramenta- 
 ceus) (fig.r), as exemplified 
 in slender branched Heath, 
 Erica ramentacea, &e. 
 
 /. Pubescent (pube- 
 scens), when it is studded 
 or covered with hair-like ap- 
 pendages. The pubescence 
 varies very considerably, according to differences 
 of soil, climate, and exposure ; but, nevertheless, 
 there are determinate characteristics which al- 
 ways, more or less, distinguish it, even in its va- 
 riations. According to the appearance, the con- 
 sistence and the quantity of pubescence, the 
 stem on which it is found is named ; thus it is 
 termed 
 
 a. Hairy ( pilosus) (Plate 5, fig. 1), when the 
 pubescence consists of rather long separate 
 
270 CONSERVATIVE ORGANS. [LECT. VI. 
 
 hairs ; as in Mouse Ear, Myosurus minimus ; 
 Hawkweed, Hieracium pilosilla ; Meadow Sage, 
 Salvia pratensis, &c. 
 
 [3. Hispid (hispidus) (Plate 5, fig. 2), when the 
 hairs are stiff or bristly *, as in Borage, Bo- 
 rago officinalis; and Common Viper Bugloss, 
 Echium vulgare. 
 
 y. Downy (tomentosus) , when the hairs are 
 soft to the touch, like down, and so matted 
 together, that the particular hairs cannot be 
 distinguished ; as in Shepherd's Club, Verbas- 
 cum thapsus ; and round-leaved Crane's Bill, 
 Geranium rotundifolium, in which the pu- 
 besrence is white ; and Marsh Ledum, Ledum 
 palustre, in which it is of a rust colour. 
 
 S. Shaggy (villosus) (Plate 5, fig. 3), when 
 the pubescence consists of long, soft hairs ; as 
 in Villose Speedwell, Veronica villosa; and 
 downy Hedge Nettle, Stachys germanica. 
 
 s. Woolly (lanatus) (Plate 5, fig. 4), when 
 the fine hairs are long and matted ; but easily 
 distinguished from each other; as in woolly 
 Hedge Nettle, Stachys lanata, and woolly Hore- 
 hound, Ballota lanata. 
 
 i. Silky (sericeus) (Plate 5, fig. 5), when the 
 
 hairs are shining, and so arranged as to give the 
 
 stem the appearance of being covered with silk. 
 
 Instead of pubescence, the covering is in some 
 
 * " Hispidits, setis rigidis adspersus." Phil. JSot. 82. 21. 
 
LECT. VI.] THE STEM. BRANCHING. 271 
 
 instances either a dry powdery, or a moist excre- 
 tion. Of the former there are three varieties, and 
 two of the latter. A stem is denominated 
 
 a. Hoary (incanus, pruinoms), when the en- 
 tire surface is strewed over with a fine white 
 dust, which is easily rubbed off, like the bloom 
 on Grapes ; as exemplified on Dwarf shrubby 
 Orache, Atriplex portulacoides. 
 
 b. Mealy (farinosus), when the white pow- 
 der is less minute, or is mealy ; as in Bird's- 
 eye Primrose, Prinmlafarinosa. 
 
 c. Glaucous (glaucus), when the dust or bloom 
 is of a bluish green, or sea-green colour ; as in 
 the Palma Christi, (the castor oil plant,) Rici- 
 nus officinalis, &c. 
 
 d. Viscid (viscidus), when it is covered with 
 a clammy resinous exudation; as in clammy 
 Catchfly, Silene* viscosa. 
 
 e. Glutinous (glutinosus), when the exuda- 
 tion is adhesive ; but, instead of being resinous, 
 it is gummy or soluble in water ; as in clammy 
 Primrose, Primula glutinosa. 
 
 Besides being covered with the appendages we 
 have just examined, the surfaces of stems pre- 
 sent inequalities from a variety of causes ; and as 
 these are fixed and always appear in every indi- 
 vidual of a species, they are taken advantage of 
 in the formation of specific distinctions ; and, 
 therefore, require to be pointed out. A stem is 
 termed 
 
272 CONSERVATIVE ORGANS. [jLECT. VI. 
 
 a. Scabrous (scaber), when it is thickly co- 
 vered with small papillae, which are not vi- 
 sible, but can be felt on running the finger 
 along it ; as in Black Knapweed, Centaurea 
 nigra. 
 
 b. Warty (verrucosus) (Plate 5, fig. 6), when 
 it is studded over with small hard warts, or pa- 
 pillae, which can be both seen and felt ; as in 
 Warty Spindle-tree, Euonymus verrucosus. 
 
 c. Vesicular (papulosus) (Plate 5, fig. 7), when 
 the roughness depends on a small elevation of 
 the epidermis containing a watery fluid, which 
 gives the plant the appearance as if it were co- 
 vered with ice ; as in the Ice Plant, Mesembry- 
 anthemum crystallinum. 
 
 In point of FIGURE, stems are very diversified ; 
 and this is best ascertained in a transverse sec- 
 tion. When a stem is thus examined, the follow- 
 ing forms are found to exist. 
 
 a. Round, cylindrical (teres, cylindricus*), 
 / (fig. s, l). A stem is said to be round when 
 a transverse section appears nearly circu- 
 lar, for no stem is perfectly so : and the 
 term cylindrical is employed with still 
 more latitude, for all stems gradually di- 
 minish from the base to the apex. Stra- 
 monium, Datura stramonium, and Change- 
 
 * Teres cylindricus." Phil. Bot. 82. 12. 
 
 4 
 
LECT. VI.] THE STEM. FIGURE. 273 
 
 able Hydrangea, Hydrangea hortemis, may be 
 taken as examples of the round ; but the term is 
 more or less applicable to all stems which ap- 
 proach to the circular form and have no angles. 
 
 b. Half round (semiteres), (fig. s, 2), that is, 
 round on one side and flattish on the other. 
 
 c. Compressed (compressus), (fig. s, 3), which 
 implies that two sides of the stem are flat, and 
 approach each other, or that the diameter of a 
 transverse section of it is much greater one way 
 than it is the other ; as in flat-stalked Meadow 
 Grass, Poa compressa. Besides the compressed 
 stem, properly so called, there are two other 
 forms of stems, which may be regarded as va- 
 rieties of it : a. the two-edged (anceps), (fig. s, 
 4), when a compressed stem has the edges 
 sharp, like a two-edged sword ; as in striated 
 Sisyrinchium, Sisyrinchium striatum ; and @. 
 the leaf-like membranaceous (phylloideus mem- 
 branaceus), when the stem is so much flat- 
 tened as to resemble a leaf; as in Spleenwort 
 Cactus, Cactus phyllanthus. 
 
 d. Angled (angulatus), which means that 
 a stem presents several acute angles in its cir- 
 cumference. There are three principal varieties 
 of angled stems. 
 
 a. Obtuse (obtuse angulatus), when the 
 angles are rounded and the sides flat. There 
 are five sub-varieties of the obtusely angled 
 VOL. i. T 
 
274 
 
 CONSERVATIVE ORGANS. [LECT. VI. 
 
 2 
 
 'V' 
 
 stems; in designating which, the word cor- 
 nered is used, instead of obtusely angled, for 
 the sake of brevity. A stem is said to be, 
 ]. Three-cornered (trigonus), (fig. t, l, and 
 */ *> when there are three flat sides 
 A, and three rounded angles. 
 
 2. Four-cornered (tetragonus), (fig. #, 2), 
 when there are four rounded angles. 
 Sometimes the corners are bordered (fig. 
 
 *, 2). 
 
 3. Five-cornered (pentagonus), (fig. t, 3), 
 when there are five obtuse angles. In this 
 instance, also, the corners are some- 
 times bordered (fig. *, 5), and the in- 
 tervals occasionally furrowed. 
 
 4. Six-cornered 
 (hexagonus), fig. 
 t, 4), when there 
 are six obtuse 
 angles. 
 
 5. Many-cor- 
 nered (polygo- 
 
 when the angles 
 are numerous 
 and obtuse: /3. Acute (acut& angulatus), when 
 the angles are sharp, and the sides hollowed. 
 
 t " Digonus, trigonus, tetragonus, pentagonus, polygonus, 
 " precedents (anceps) species sunt." Phil. Bot. 82. 13. 
 
LRCT. VI.] THE STEM. FIGURE. 275 
 
 Of this variety of the angled stem there are, 
 also, five sub-varieties : 
 
 1. Triangular (triangular Is), (fig. u, i). 
 
 2. Four-angled (quadrangularis) , (fig. u, 
 
 2) ; 
 
 3. Five-angled (quinquangularis) , (fig. 
 U) 3). 
 
 4. Six-angled (soxangularis) , (fig. u, 4). 
 
 5. Many-angled (multangularis) *f~. In 
 many-angled stems the angles are 
 not always so acute as in the other 
 sub-varieties. 
 
 7. Three-sided (triqueter*), (fig. *, i), when 
 tliere are three flat sides forming acute angles ; 
 as in Carex acuta. 
 
 e. Angular (angulosus), implies that the angles 
 are either very obscure, and the stem, con- 
 sequently, can scarcely be placed in either 
 of the foregoing arrangements; or that the 
 angles are variable in number. There are two 
 varieties of the angular stem, which have pe- 
 culiar appellations ; viz. a. Furrowed (sulcatus) 
 (fig. *, 5), when the stem is longitudinally in- 
 dented with deep and rather broad hollows, 
 like those of a fluted column || ; as in Common 
 
 t " Triangularis, quadrangularis, quinquangularis, multangu- 
 " tarts, ex numero angulorum prominentium." Phil. Bot. 82. 15. 
 
 J " Triquetrus, latera tria plana obtinet." Ibid. 82. 14. 
 
 || " Sulcatus sulcis excavatis latis profundis exaratus." Ibid. 
 82. 16. 
 
 'T 2 
 
276 
 
 CONSERVATIVE ORGANS. [LECT. VI. 
 
 Alexanders, Smyrnium olustratum : /3. Stri- 
 ated (striatus), when it is longitudinally in- 
 dented with fine parallel lines * ; as in Sorrel, 
 Rutnex acetosa. 
 
 d. Knotted (nodosus), (fig. w, 1), implying that 
 
 the stem is divided, at 
 intervals, by swellings or 
 knots ; as in Knotty 
 Cranes'-bill, Geranium 
 nodosmn, &c. 
 
 e. Articulated (articu- 
 latus), that is, composed 
 of joints, or apparently 
 distinct pieces, united at 
 their ends-j~. It is re- 
 markable that Linnaeus, 
 in his definition of this 
 form of stem, should have confounded it with 
 the kneed stem, as he must have been well 
 aware that many articulated stems are per- 
 fectly straight or erect. In some instances the 
 articulated stems are knotted at the joints, 
 but in others they are plain. Many of the 
 Grasses afford instances of the former ; while 
 the Cactus tribe sufficiently exemplify the latter. 
 f. Kneed (geniculatus), (fig. w, 2), when an ar- 
 
 * " Striatus lineis tenuissimis excavatis inscriptus." Phil. 
 Bot. 82. 17. 
 
 f " Articulatus, internodiis geniculatus : Piper." Phil. 
 Bot. 82.31. 
 
LECT. VI.J THE STEM. FIGURE. 277 
 
 ticulated stem is more or less bent at each joint ; 
 
 as in Floating Fox-tail Grass, Alopecurus geni- 
 
 culatus; Three-flower Fescue Grass, Festuca 
 
 triflora, &c. 
 
 Such are the diversities which stems externally 
 present to the eye. But these, although in their 
 natural state they are sufficiently fixed to enable 
 systematic Botanists to employ them as distinc- 
 tive characteristics of species, which could not 
 otherwise be distinguished * ; yet, are apt to vary, 
 owing to peculiar circumstances connected with 
 situation, climate, and soil. Thus we find a stem 
 which, in its natural state, is round, assume a 
 flattened appearance as if two or more stems or 
 branches were united longitudinally side by side : 
 an anomaly which is not uncommon in the Ash, 
 several species of Daphne, the greater Nasturtium, 
 Tropaeolum majus, and many other herbaceous 
 plants ; and is denominated by authors f the clus- 
 tered stem, caulisfasciculatus. It is not easy to 
 account for this effect, since it is evidently not the 
 simple lateral union of one or more stems or 
 branches, a circumstance which might be pro- 
 duced by pressure abrading the epidermis and cel- 
 lular layer of the bark, and bringing the liber or 
 
 * " Caulis in multis plantis ita essentiales praebet differentias, 
 " ut eo demto, nulla certitude speciei." Phil. Bot. 276. 
 
 f Smith's Introduction, p. 127. Keith's System of physiolo- 
 gical Botany, vol. ii. p. 277. 
 
 r3 
 
278 CONSERVATIVE ORGANS. [LECT. VI. 
 
 innermost layer of each of the united stems into 
 contact ; for, were this the case, the pith of each of 
 these conjoined stems would be still entire, and 
 the aggregate would appear as distinct cylinders, 
 according to the number of the stems ; whereas 
 in the fasciculated stem there is one flat pith 
 only, and the other parts of the stem are, in ar- 
 rangement and number, the same as if the ano- 
 maly did not exist. The idea, therefore, of the 
 fasciculated stem arising from the pressure of one 
 or more contiguous stems, and a natural graft 
 being thus formed, as has been suggested by Mr. 
 Keith, cannot be admitted. Several other ano- 
 malies occur in the configuration of stems ; but 
 as these are generally either the consequence of 
 disease, or of some obstacle to the natural de- 
 velopment in the individual plant occasioned by 
 insects, the consideration of them may be de- 
 ferred until we come to treat of the diseases in- 
 cidental to the vegetable system. 
 
 Independent of the diversities which we have 
 already examined, STEMS have been properly distri- 
 buted into distinct species. In this classification, 
 Linnaeus and others who have copied after him, 
 enumerate six species of stems ; but among these 
 the footstalk of the leaf and the frond are impro- 
 perly included ; for, as the former is decidedly a 
 part of the leaf, and separates with it when it falls ; 
 and the latter is a peculiarity connected with the 
 foliage of distinct tribes of plants, the Palms, the 
 
LECT. VI.] THE STEM. CLASSIFICATION. 279 
 
 Algae, and the Ferns ; and is itself supported on a 
 species of real stem (which I shall soon have occa- 
 sion to describe to you), the stipe*, neither of them 
 can with propriety be classed with stems. Mirbel-f- 
 and Mr. Keith J omit the flower-stalk in their enu- 
 meration of the species of the stem, and certainly 
 with some propriety ; for, although it closely re- 
 sembles the stem in its structure, yet, in an ele- 
 mentary work, it is undoubtedly more intelligible 
 to the student to describe it as a part only of it 
 bearing the fructification, except when it proceeds 
 immediately from the root. Contemplating the 
 subject nearly in a similar point of view, I think 
 we are authorized in distributing stems into Jive 
 distinct species : the trunk, the stalk, t\\Q straw, 
 the scape, and the stipe. 
 
 1. TRUNK (Truncus) is the appellation given 
 to the stems of trees and shrubs . The trunk is 
 
 * " Frons est dilatatio vegetabilis herbacea quae arete 
 " cum cormi specie, qua sustentatur cohaeret, Palmis, Filici- 
 " bus, Algisque propria." Willdenou, Spec. Plant, tomus 
 v. Introd. p. xxi. 
 
 f Siemens de Phys. vg. p. 99 and 622. 
 
 J System of physiological Botany, vol. i. p. 43. 
 
 Linnaeus uses the term trunk in the generic sense in which 
 I have used the word stem ; and thus defines it : " TRUNCUS 
 " folia et fructificationem profert ; species ejus sunt vii. Caidis, 
 " Gulmus, Scapus, Pedunculus, Petiolus, Frans, Stipes; at 
 " ttamus pars est." Phil. Bot. 82. 
 
 T 4 
 
280 CONSERVATIVE ORGANS. [LECT. VI. 
 
 characterized by its ligneous structure, by being 
 always perennial ; generally naked at the lower 
 part; and divided and subdivided towards the 
 summit into branches and twigs, bearing leaves 
 and the fructification. It is thickest at the base, 
 and gradually diminishes to the apex ; is covered 
 with a thick, often dry and cracked bark ; and 
 internally is composed of a central pith, sur- 
 rounded by ligneous layers, the number of which 
 varies according to the age of the plant. When 
 it rises to a moderate height, like a simple 
 column, before it divides into, or gives off 
 branches, it is said to be arboreous, as exemplified 
 in the Oak, the Elm, and the majority of trees ; 
 but when the divisions or branches occur near to 
 the soil, it is termed shrubby, fruticosus ; as in 
 the Lilac, the Rosemary, and such-like. These 
 terms, however, are always to be understood as 
 having a relative signification only; for various 
 circumstances, such as change of soil, climate, 
 and the efforts of art, may metamorphose shrubs 
 into trees, or reduce these again into shrubs; 
 transitions which are by no means uncommon. 
 
 2. STALK (Caulis) is properly applicable to the 
 stems of herbaceous plants only ; although the 
 term is frequently used in a sense synonimous 
 with trunk. The specific characteristics of the 
 stalk are, that it is rarely ligneous, and lives but 
 
 4 
 
LECT. VI.] THE STEM. CLASSIFICATION. 281 
 
 one or two years in the natural state of the plant. 
 It may be divided and subdivided into branches, 
 like the trunk ; and a greater number of these 
 diversities which have been described belong to 
 the stalk rather than to the trunk. 
 
 3. STRAW (Culmus) is a name strictly con- 
 fined to the stems of the Grasses, Rushes, and 
 the gramineous cerealiae *. It is either hollow, or 
 partially filled with pith., and generally knotted, 
 articulated, and kneed ; but very rarely branched. 
 The knots are solid, confined to the articulations, 
 and give origin to the leaves, which are sheathing 
 at their base. It increases in length, tapering 
 gradually to the apex, but not in diameter, is 
 round, compressed, or triangular; and is fre- 
 quently hairy; but, as Sir J. E. Smith properly 
 observes, there is " no instance of such a scaly 
 " culm as Linnaeus has figured in his Philosophia 
 " Botanica, t. iv. f. 3f." 
 
 4. SCAPE (Scapus), strictly speaking> is a 
 flower-stalk, as it bears the parts of fructification 
 only, and is entirely devoid of leaves ; but, never- 
 theless, as it proceeds immediately from the root, 
 it may be properly classed as a stem ^. It is al- 
 
 * " Culmus truncus proprius Gramini, elevat folia fructi- 
 " ficationemque." Phil. Bot. 82. B. 
 
 f Smith's Introduction, p. 128. 
 
 f " Scapus truncus universalis elevans fructificationem nee 
 " folia : Narcissus, Pyrola, Convallaria, Hyacinthus." Phil. 
 Bot. 82. C. 
 
282 CONSERVATIVE ORGANS. [LECT. VI. 
 
 ways herbaceous; ,and is found either simple, 
 and bearing one flower only, as in common Dan- 
 delion, Leontodon taraxacum; or divided, and 
 many-flowered, as in Cowslip, Primula veris. 
 
 5. STIPE (Stipes) is the term used to express 
 the stem of Palms, Ferns, Fuci, and Fungi. It 
 is generally cylindrical ; but sometimes swollen 
 in the middle, and bears a frond, or the foliage 
 which is peculiar to it, at its summit. In the 
 Palms the stipe is in general a simple column 
 bearing a spreading plume of leaves ; and of the 
 same diameter at the summit as at the base, ex- 
 cept in a very few genera *, which throw out 
 branches. It is marked at regular distances by 
 the cicatrices of the fallen leaves ; and increases 
 in height by additions made to its summit by the 
 development of a central gem, which throws out 
 annually a new circle of leaves. In the Ferns it 
 varies considerably in form, being round, chan- 
 nelled, triangular, and quadrangular ; and is 
 either devoid of vestiture, or is chaffy, scaly, spiny, 
 or muricated, that is, covered with sharp hard 
 tubercles : and the same diversities occur in the 
 stipes of the Fuci. In the Fungi it is generally 
 fleshy or leathery ; but it varies both in substance 
 and form ; and although, in the greater number 
 of instances, it is affixed to the centre of the cap, 
 
 * Draccena, &c. 
 
LECT. Vil] THK STEM. 283 
 
 orpileus,as in the Mushroom, or nearly so ; yet in 
 others its attachment is to the side of that body. 
 
 Such are the peculiarities, connected with the 
 exterior of stems, necessary to be noticed in this 
 stage of our inquiries : in closing our examination 
 of them, this question spontaneously presents it- 
 self: why is there so great a diversity of form, 
 vestiture, and mode of branching in the vege- 
 table organs ? No satisfactory reply can be ad- 
 vanced ; and, therefore, we are left to imagine 
 that, as nature appears to delight in variety, the 
 diversified and graceful forms and appearances of 
 plants may be one source of pleasure prepared by 
 Divine Benevolence for mortals. Be this as it may, 
 man has not failed to render them accessaries to 
 his comfort, and subservient to his necessities. In 
 the cool shade of the branching arms of the Beech, 
 or under the pillared canopy of the Banyan, he 
 shuns the ardour of the meridian blaze ; with the 
 shrubby and spiny Hawthorn, or the prickly Cac- 
 tus, he encloses his fields ; while the pliant Osier 
 is woven into baskets to transport their produce to 
 the crowded city : the tall and straight Pine rises 
 a mast, on which he spreads the sail that enables 
 him to transport the riches of distant climes to 
 his native shores ; and the incurved ribs of the 
 venerable Oak, launched into the main, float, the 
 protectors of his maritime rights, and the bul- 
 warks pf his national independence. 
 
284 CONSERVATIVE ORGANS. JJLECT. VII. 
 
 LECTURE VII. 
 
 SUBSTANCE AND ORGANIZATION OF THE STEM AND 
 
 BRANCHES : ANATOMICAL DEMONSTRATION OF 
 
 THE COMPONENT PARTS OF THESE ORGANS THEIR 
 
 FORMATION, INCREASE, AND REPRODUCTION. 
 
 THE examination of the external aspects of stems 
 and branches, which we have just concluded, will 
 readily enable you to form an estimate of the im- 
 portance of the correct knowledge of terminology to 
 the systematic Botanist ; for, without a definition 
 and name for each diversity of feature, which the 
 vegetable organs present to the sight or the 
 touch, it would be impossible for him to fix these 
 specific distinctions, by which alone the different 
 members of the same family of plants can be 
 readily recognised. This diversity, as you have 
 seen, is very considerable in the external charac- 
 ter of the stem and branches ; but when we ex- 
 tend our examination to their interior structure, 
 or organization, we find it confined within very 
 narrow limits : nor will this excite our astonish- 
 ment when we reflect, that nearly the same end 
 is to be accomplished by these organs, whatever 
 may be the habits or the physiognomy of the plant. 
 
LECT. VII.] THE STEM. 285 
 
 It is now my object to direct your attention to 
 these differences, and to point out to you the cir- 
 cumstances in which they consist. 
 
 If we take a number of stems and branches of 
 different kinds of plants, and cut, or break, or 
 tear them transversely and longitudinally; we 
 shall find that some of them are easily divided, 
 whilst others resist almost all our efforts ; that 
 some are moist, succulent, and fleshy; others 
 fibrous, spongy, and dry ; and others again formed 
 of both succulent and dry parts ; the latter pos- 
 sessing very different degrees of compactness, in- 
 duration, and tenacity. But, however considerable 
 these differences may appear, the more we investi- 
 gate the subject the more we shall be convinced, 
 that, as far as respects substance, the stems and 
 branches of the whole of the vegetable kingdom 
 may be arranged under two classes, the Woody 
 and the Herbaceous. 
 
 A. WOODY stems (Caules lignosi) are those 
 which contain a very large proportion of ligneous 
 fibre ; or in which wood forms comparatively the 
 greater part of their bulk. It is found either in 
 threads or bundles which run longitudinally from 
 the base to the summit of the stem ; or is united 
 in one mass, formed of concentric circles, which 
 cohere and compress each other nearly from the 
 centre to the surface of the stem : the tribe of 
 
286 CONSERVATIVE ORGANS. [LECT. VII. 
 
 Palms affords examples of the first description of 
 ligneous stems, and all other trees of the second. 
 As far as respects substance, however, ligneous 
 stems are not arranged according to the diversity 
 of structure I have just hinted at ; but according 
 to the degree of cohesion which binds together 
 their ligneous fibres. Botanists have, therefore, 
 divided woody stems into two genera, the solid 
 and the fibrous. 
 
 1 . The solid woody stem (C. solidus) is that 
 in which the cohesion is uniform, and the 
 wood, consequently, compact and indurated; 
 sometimes to a degree on which the knife will 
 make scarcely any impression. 
 
 2. The fibrous (C.fibrosus) is that in which, 
 the cohesion being irregular, the wood is con- 
 stituted of fibrous bundles ; which, although 
 adhering to each other, can be easily separated, 
 either by tearing or by maceration. 
 
 Ligneous stems of every description are peren- 
 nial. 
 
 B. HERBACEOUS stems (Caules herbacei) are 
 those which contain a small proportion of woody 
 matter ; but are composed chiefly of cellular sub- 
 stance, and consequently can be easily cut or 
 divided. There are three distinct kinds of her- 
 baceous stems: the fleshy^ the spongy, and the 
 hollow. 
 
LECT. VII.] SUBSTANCE OF STEMS, &C. 287 
 
 1. The fleshy stem (C. carnosus) is that in 
 which the cellular substance, of which it is 
 composed, is turgid with fluids; and when 
 cut, presents a smooth, uniform moist surface, 
 similar to that of a young Cucumber when 
 transversely sliced. The common House-leek, 
 Sempervivum tectorum ; and most of the sea- 
 weeds, Algse, afford examples of the fleshy stem. 
 
 2. The spongy stem (C. spongiosus) is com- 
 posed of a compressible, elastic, cellular sub- 
 stance, contained within an epidermis ; either 
 dry, the cells being filled with air only; or 
 moist, the cells being partially filled with fluid, 
 as in a sponge. The Mushroom tribe, Fungi ; 
 Indian Corn, Zea mays ; and Great Cat's-tail, 
 Typha latifolia, have spongy stems. 
 
 3. The hollow stem (C.Jistulosus) is a suc- 
 culent or fleshy hollow cylinder, surrounded by 
 a circle of vessels and ligneous threads, imme- 
 diately under the epidermis ; and generally 
 lined with a dry white spongy layer of pith. 
 There are two varieties of the hollow stem. 
 
 a. The uninterrupted (sine septis transver- 
 sisj; when the hollow, or cavity, extends 
 from the base to the apex of the stem, as in 
 the genus Coreopsis (Coreopsis). 
 
 b. The interrupted (septis transversis inter- 
 tinctus) ; when either the longitudinal cavity 
 is divided, at regular distances, by parti- 
 
288 
 
 CONSERVATIVE ORGANS. 
 
 [LECT. vn. 
 
 tions or diaphragms (fig. a, 
 1) ; or the stem is knotted, 
 and apparently made up 
 of separate hollow por- 
 tions, shut at each ex- 
 tremity, and united at the 
 knots. The different spe- 
 cies of Horse-tail, Equi- 
 setum ; Manured Reed 
 Arundo donax; Common Water Drop wort, 
 CEnathe Jistulosa ; the Castor oil plant, Ri- 
 cinus officinalis ; and almost all the Grasses, 
 and the Cerealia, afford examples of this 
 variety (fig. a, 2). 
 
 Such is the diversity of substance of sterns 
 and branches ; we have now to examine the ana- 
 tomical construction of these organs. To the stu- 
 dent, this inquiry is not only important, as dis- 
 playing the structure of the stem itself, and 
 thereby enabling him to comprehend more per- 
 fectly its- functions and mode of growth ; but, as 
 all the parts concerned in the vegetable functions, 
 as far as the preservation of the individual is con- 
 cerned, are seen in the stem ; by a correct know- 
 ledge of its organization he becomes acquainted 
 with that also of the root, the leaves, and even, 
 in some respects, of the flowers and the fruit. In 
 this investigation it is essential to adopt some ar- 
 rangement; and although none, which has yet 
 been attempted, is free from just causes of cri- 
 
LECT. VII.] ANATOMY OP STEMS. 289 
 
 ticism, and probably none can be devised alto- 
 gether unobjectionable; yet, if by any the examina- 
 tion can be facilitated, the attempt to form one, 
 as nearly perfect as the nature of the subject will 
 admit of, is at least praiseworthy. 
 
 The only arrangements which I shall notice, 
 are those of Desfontaines and Mr. Keith. Des- 
 fontaines' method is founded on the fact, that 
 there are two grand divisions of plants, the Mo- 
 nocotyledonous * and Dicotyledonous -f~ ; each of 
 which displays a distinct and specific mode in the 
 distribution of the parts of the stem. In the in- 
 dividuals belonging to the first, the stem consists 
 of bundles of woody fibres and vessels, inter- 
 spersed throughout a cellular substance, and de- 
 creasing in solidity from the circumference to the 
 centre ; in those of the second it is composed of 
 concentric and divergent woody layers, decreas- 
 ing in solidity in the opposite ratio, or from the 
 centre to the circumference, and containing a 
 pith in a central canal J. But, as Mr. Keith has 
 justly observed, this arrangement does not ex- 
 haust the subject : as, independent of the Poly- 
 cotyledonous plants which may be classed with 
 the Dicotyledonous, there is no account taken of 
 
 * Plants, the seeds of which have one lobe only, 
 f Plants, the seeds of which have two Lobes, 
 t Vide Mem. de V Instil. Nat. tome i. 
 
 VOL. I. U 
 
290 CONSERVATIVE ORGANS. [LECT. VII. 
 
 those tribes which are altogether destitute of seed- 
 lobes ; the stems of which, in their organization, 
 exhibit neither the woody bundles of the one, nor 
 the layers of the other. Mr. Keith, in order to ob- 
 viate this objection, has arranged stems, in re- 
 ference to their internal structure, into three 
 classes : 1 . The caudex an homogeneous mass ; 
 2. The caudex an heterogeneous mass; and, 3. The 
 mass consisting of bark, wood, and pith*. This 
 arrangement is undoubtedly less exceptionable 
 and more comprehensive than that of Desfon- 
 taines ; but Mr. Keith has erred in arranging, in 
 his second division, the herbaceous stems of dico- 
 tyledonous and polycotyledonous plants ; for, al- 
 though these have no concentrical circles of formed 
 wood, such as characterize the ligneous stems of 
 those tribes, yet the distribution of the ligneous 
 matter and of the pith coincides sufficiently with 
 that of these parts in the real woody stems to 
 allow them to be classed together ; whilst it has 
 little or no affinity with that of the ligneous 
 bundles in the monocotyledonous stems with 
 which they are classed in Mr. Keith's arrangement. 
 A more perfect classification, perhaps, may be 
 formed, by adopting the first division of Mr. Keith's 
 arrangement and adding to it those of Desfon- 
 taines ; as, besides embracing the whole of the 
 subject, it leads us first to the examination of 
 
 * System of physiological Botany, vol. i. p. 287 & seq. 
 
LECT. VII.] ANATOMY OF STEMS. 291 
 
 those stems which are the simplest, because com- 
 posed of the fewest parts ; and progressively pre- 
 pares us to understand the organization of those 
 of a more compound nature. I shall, therefore, 
 attempt such an arrangement, and class stems, 
 in reference to their anatomical structure, into 
 the three following divisions : 
 
 i. Stems which display, internally, an appa- 
 rently homogeneous mass. 
 
 ii. Stems which proceed from monocotyledonous 
 seeds. 
 
 iii. Stems which proceed from dicotyledonous 
 and polycotyledonous seeds. 
 
 i. Stems which display, internally, an apparently 
 homogeneous mass, when examined by the unassisted 
 eye, seem to consist simply of an epidermis enclos- 
 ing a parenchyma, composed either of cellular 
 substance, of very different degrees of succulency, 
 sponginess, dryness, and density ; or of inter- 
 woven fibres, forming a leathery, or a felt-like tex- 
 ture, or one not a little resembling that of washed 
 animal muscle which has been macerated in spi- 
 rits. When examined, however, by the aid of a 
 good microscope, these different appearances of 
 the internal mass are all found to consist of cel- 
 lular substance, with vessels running through 
 it, and anastomosing in a variety of directions. 
 Mirbel erroneously asserts that this description of 
 
292 CONSERVATIVE ORGANS. [LECT. VII. 
 
 stems is destitute of vessels * ; for their presence, 
 at least in the stipes of the Mushroom tribe 
 (Fungi), and the stalks of many of the Algse, is 
 demonstrable by placing a small transverse slice 
 of any of them under a powerful microscope. 
 They are not, indeed, so readily distinguished in 
 a longitudinal slice, a circumstance which I am 
 inclined to ascribe to the transparency of their 
 coats confounding them with the cellular sub- 
 stance in which they are imbedded ; and which 
 consists of continuous, oblong cells, the membrane 
 forming the sides of which is of very different 
 degrees of thickness ; but, nevertheless, they 
 may be made out by any one accustomed to the 
 use of the microscope. I have never been able to 
 satisfy myself of what description these vessels are, 
 although it is evident, as Mirbel remarks, that 
 they are neither the spiral, nor the annular ; but I 
 suspect them to be the moniliform. The epidermis, 
 which cannot be separated from the cellular mass 
 it covers, is pierced with imperceptible pores, but, 
 according to Mirbel, it has no miliary glands. In 
 the different tribes of plants which afford examples 
 of this description of stems, the reproductive or- 
 gans are either altogether deficient, or so ob- 
 scure as to have eluded the researches of phyto- 
 
 * Vide Element de Phys. veget. l ere Partie, p. 37 ; and Journ. 
 de Botanique, torn. iii. p. 36* 
 
LECT. VII.] ANATOMY OP STEMS. 293 
 
 legists; and thence they have been regarded as 
 agamic. Many of them have no stem ; but among 
 those which possess it, in some it is solid, or 
 rather entire, in others hollow; and in the lat- 
 ter case, the cavity is often partially lined with 
 a very lax, dry, cellular web *. A conspicuous 
 root is rare; and, when it exists, consists of a 
 few small radical fibres only, composed of a 
 single thread, covered with a cribriform epider- 
 mis. Scarcely any facts are yet known respect- 
 ing the development and growth of this descrip- 
 tion of stem. 
 
 ii. Stems which proceed from monocotyledonous 
 seeds are more complex in their structure than 
 the preceding. They are composed of two dis- 
 tinct parts, ligneous and cellular, which assuming 
 a determinate character, enable these stems to be 
 readily distinguished, even by the naked eye. 
 They comprehend both solid and tubular, or 
 entire and hollow stems ; and as there is some 
 difference in the arrangement of the parts in 
 these varieties, we shall examine them separately. 
 
 * See Plate 5, fig. 1, which represents a longitudinal sec- 
 tion of the stem of Tall Agaric, Agaricus procerus ; a. the 
 stem ; b. its lax cellular lining, or pith, which in this example 
 nearly divides the hollow of the stem into two unequal cavi- 
 ties ; c. a fragment of the hat or pileus, to show the simplicity 
 of its union with the stem. 
 
 u3 
 
294 CONSERVATIVE ORGANS. [LECT. VII. 
 
 a. If a solid rnonocotyledonous stern, that of 
 a Palm for example, be cut, either longitudinally 
 or transversely, it is seen to consist of an epider- 
 mis enclosing ligneous bundles or cords, more or 
 less symmetrically distributed in a parenchyma or 
 medullary substance. If the section be longi- 
 tudinal, these ligneous cords are observed to run 
 longitudinally, and extend from the base to the 
 apex of the stem, sometimes in straight lines ; 
 but occasionally assuming a zigzag direction, so 
 as to touch each other at different distances : 
 closer together and firmer towards the circum- 
 ference of the stem, and more apart and softer 
 as they approach its centre *. If the section be 
 transverse, the divided extremities of the ligne- 
 
 * Vide Plate 5, fig. 2, 3, 4. Fig. 2 represents the section 
 of a transverse cutting of a Palm, the Ptychosperma gracilis 
 (copied from a plate of Mirbel) ; a. the ligneous bundles 
 closer together, more indurated, and in greater numbers than 
 in the space marked b, in which also, however, they are less 
 distant and more compact in that portion which is farther from 
 the apex of the section, than in that which is nearer to the 
 centre of the stem. 
 
 Fig. 3. A. 'a transverse slice of the scape of the Tiger- 
 flower, Tigridia pavonia, slightly magnified ; the ends of the 
 ligneous bundles being shown by the white dots, which in 
 the natural stem appear on a green ground. 
 
 Fig. 4-. A longitudinal section of the scape of Great Reed- 
 mace, Typha latifolia, showing the ligneous bundles, which 
 in this instance do not inosculate. 
 
LECT. VII.] ANATOMY OF STEMS. 295 
 
 ous bundles appear like spots, which are in some 
 instances of a dark colour, and in others white, 
 dispersed over a white or a green ground, in 
 the order just described. The epidermis adheres 
 closely to the parenchyma beneath it ; and in 
 some plants of this class, the greater density of 
 the cellular substance at the circumference gives 
 the appearance of a bark, which is never, how- 
 ever, present in this description of stem. Such 
 is the general character, and the distribution 
 of the parts, in what may be termed the lig- 
 neous solid monocotyledonous stems* ; but when 
 they have more of an herbaceous character, such, 
 for example, as the scape of Great yellow Gar- 
 lick, Allium Moly, there are no indurated lig- 
 neous cords ; but the vessels run in the midst of 
 longitudinal layers of condensed cellular matter, 
 and in a transverse section appear as white dots 
 forming a circle round the central cells, which are 
 generally much larger than those of the circumfe- 
 rence, and assume in some degree the aspect of 
 a pith *}- ; so that in the longitudinal section, the 
 
 * The student, who cannot procure the stem of a Palm, 
 may attain an excellent idea of the internal structure of the 
 solid monocotyledonous stem in the flower-stalk of the Tigri- 
 dia pavonia, which is now very common in the stoves of the 
 London florists and nurserymen; or in that of the Typha 
 latifolia, not unfrequent in ditches, flowering in July. 
 
 f Vide Plate 5, fig. 5. A. a transverse slice of the scape of 
 Allium Moly, nearly of the natural size. 
 
 u4 
 
296 CONSERVATIVE ORGANS. [LECT. VII. 
 
 diameter of the stem appears divided by two seem- 
 ingly solid cords, into three nearly equal compart- 
 ments. Mirbel, in treating 1 of this description 
 of steins, says, " their pith, instead of being en- 
 " closed in a canal, in the centre of the stem, ex- 
 " tends almost to the circumference * ;" but there 
 are exceptions to this remark, as, for instance, in 
 the Rush, Juncus, which has a perfect pith, sur- 
 rounded, however, by a cellular tube, in the sub- 
 stance of which the vascular cords characteristic 
 of the monocotyledonous stems are perfectly ap- 
 parent, arranged in beautiful order; and dis- 
 tinguish it from an herbaceous dicotyledonous 
 stem, the vessels of which, as I shall afterwards 
 demonstrate to you, are arranged in a very dif- 
 ferent manner. 
 
 Such are the appearances which, to the naked 
 eye, or to the eye aided by a common lens, the 
 solid monocotyledonous stems present. Under 
 the microscope, we perceive that each ligneous 
 cord is composed of very narrow oblong cells, 
 and of vessels which are either spiral, or annular, 
 or porous, those in the centre being always spiral ; 
 that, in the cellular substance of the more solid 
 stems, the cells are chiefly oblong, whilst in that 
 
 v " Et leur moelle, au lieu d'etre resseree dans un canal, 
 " au centre de la tige, s'etend presque jusqu'a la circonference. 1 ' 
 Element de Phys. veg. Partie 1. p. 117. 
 
LECT. VII.] ANATOMY OF STEMS. 297 
 
 of the herbaceous they form irregular hexagons, 
 except towards the circumference, and in the 
 immediate vicinity of the vascular cords*; and 
 that the membrane forming them is perforated 
 with minute pores, surrounded by a glandular 
 border. In the common Rush, Juncus conglo- 
 meratus, and some other monocotyledons, the 
 cells of the pith are of a very curious structure : 
 appearing, in a transverse section, like minute 
 heptagonal wheels or circles divided by rays 
 passing from the centre ; and these are evidently 
 filled with air *f-. In common MareVtail, Hip- 
 
 * Vide Plate 5. Fig. 3, B. represents a magnified section 
 of fig. 3, A. to demonstrate the greater density of the cellular 
 substance towards the circumference. 
 
 Fig. 5, B. a highly magnified section of fig. 5, A. a. the 
 cellular substance more condensed close to the epidermis 
 than in the heart of the stem ; b. the vascular bundles. Fig. 
 5, C. a highly magnified longitudinal section of the semi- 
 diameter of the slice A. which has the appearance of fig. 5, 
 
 d. to the naked eye: a. the cellular matter, close to the 
 epidermis, appearing as oblong cells ; I. one of the seemingly 
 solid cords, which form the circle of vascular bundles, con- 
 sisting of two spiral vessels, surrounded by oblong cells; 
 
 e. the cellular substance which constitutes the mass of the 
 stem. In this view the membrane forming the walls of the 
 cells is seen studded with points, which, under the microscope, 
 appear to be either amylaceous granules or circular apertures 
 surrounded by a border. Mirbel supposes they are pores, and 
 that the border is glandular. 
 
 f Vide Plate 5, fig. 6, which represents a magnified section 
 of a transverse slice of the common Rush : a. the pith com- 
 
298 CONSERVATIVE ORGANS. [LECT. VII. 
 
 puris vulgaris, the air-cells, which are on the out- 
 side of a central column, composed of vascular 
 and ligneous bundles, are divided from each other 
 by smaller cells, which are filled with aqueous 
 fluid : whilst, at every whorl of leaves, bundles 
 of vessels are given off from the central column, 
 and these are surrounded by condensed cellular 
 matter, which forms a kind of diaphragm ; by the 
 repetition of which the whole stem is divided into 
 compartments at regular intervals *. 
 
 posed of circular or heptagonal cells, divided by septa passing 
 from the centre of each, like rays; b. the cylinder which 
 surrounds the pith ; composed of green parenchymatous mat- 
 ter, in which bundles of spiral vessels (c. d.) run, surrounded 
 by condensed cellular matter ; e. departments consisting of air- 
 cells dividing the vascular bundles ; f. bundles, apparently of 
 entire vessels, forming the striae on the surface of the stem ; 
 g. lacunae or open spaces between the pith and its enclosing 
 tube. If I might be permitted to hazard an opinion regarding 
 the use of this organization, it would be this : that, as the Rush 
 has no leaves, the green parenchymatous tube is intended to 
 perform a function analogous to that of leaves, these organs 
 consisting chiefly of a similar substance. 
 
 * Plate 5, fig. 7, a section of a transverse slice of the stem 
 of common Mare's-tail, Hippuris vtdgaris, an aquatic plant : 
 a. the exterior, or cellular part (enclosed merely by the epi- 
 dermis), consisting of large air-cells, each surrounded by 
 smaller cells, which are generally found turgid with aqueous 
 fluid ; b. the central column, which consists chiefly of spiral 
 vessels, one of which is drawn out at c. All aquatic plants 
 contain very large air-cells ; which are most abundant in their 
 stems, if their leaves be few or comparatively small, or the 
 greater number of them is above the surface of the water ; and 
 
LECT. VII.] ANATOMY OF STEMS. 299 
 
 It is necessary to notice, particularly, the 
 structure of one variety of the solid, herbaceous, 
 monocotyledonous stems ; as it constitutes the 
 link betwixt the solid and the fistular monoco- 
 tyledons. It is articulated, giving off leaves at 
 the joints only ; and these are sheathing or em- 
 brace the stem. On dissection, we find the vas- 
 cular bundles, which can scarcely be called lig- 
 neous, enclosed in a cellular parenchyma, and 
 running in straight lines between the joints ; but 
 at these they inosculate in arches, and send off 
 horizontal branches, some of which terminate in 
 the leaves and others in the lateral shoots that 
 originate at their basis. This structure is beau- 
 tifully displayed in the stem of Spiderwort, Trade- 
 scantia Virginica, in which the circles forming 
 the annular vessels being nearly opaque, the 
 course of the vascular bundles is readily traced ; 
 and the manner in which the vessels are given off, 
 and inosculate, distinctly seen by the aid of the 
 microscope *. 
 
 in the leaves, if these be large or mostly immersed, as for in- 
 stance the Common Reed-mace. 
 
 * Vide fig. 9 and 10, Plate 5. Fig. 9, a. a. a. a. a. a. the 
 vascular cords, as seen by means of a good lens by reflected 
 light, forming arches at the joint ; b. 6. the base of the leaf, 
 with the vessels which supply it proceeding nearly from the 
 centre of the joint ; d. the fragment of a lateral shoot, the 
 vascular bundles connected with which are seen originating 
 from the same spot as those of the leaf. Fig. 10, a Small por- 
 tion of the joint highly magnified, to display the structure of 
 
300 CONSERVATIVE ORGANS. [LECT. VII. 
 
 b. The hollow or fistular monocotyledonous 
 stems are composed of distinct portions, united by 
 knots ; at each of which the cavity is divided by a 
 diaphragm : or, rather, each portion may be re- 
 garded as a distinct individual, which takes its 
 origin from one knot, and terminates in another, 
 out of which again a new individual arises, and so 
 on in succession, as I shall more particularly de- 
 scribe in explaining the mode of growth of these 
 stems. The general structure of this description 
 of stems is best exemplified in the Grasses. Thus, 
 in Wheat we perceive the upper articulation rising 
 within the knot, in which the lower has termi- 
 nated ; with the leaf which infolds it crowning 
 the embracing knot*. The organization of this 
 variety of the monocotyledonous stem cannot be 
 readily distinguished without the aid of the mi- 
 croscope. It is seen, in a longitudinal section, to 
 consist of several layers of narrow oblong cells, 
 which constitute its exterior and more solid part ; 
 and of an interior more open cellular substance, 
 
 the vascular cords and the inosculation of the vessels, a. The 
 bed or sheath in which the vessels run ; b. the vessels themselves 
 apparently composed of separate rings, held together by small 
 spicular bodies, which appear as lines on the surface of the 
 vessels, within the transparent sheaths ; when detached, they 
 appear like acicular crystals. The cells are studded with amy- 
 laceous granules. 
 
 * Vide Plate 5, fig. 1 1. a. the knot of the straw bearing a 
 fragment of its leaf; b. the new articulation rising within the 
 knot. 
 
LECT. VII.] ANATOMY OP STEMS. 301 
 
 enclosing vascular, ligneous cords, composed of 
 oblong cells like those on the circumference, sur- 
 rounding spiral and annular vessels. In the trans- 
 verse section the divided extremities of these cords 
 appear as clustered vascular spots in the cellular 
 substance *." 
 
 The bark, if the surface of the stem can be 
 so named, of the more solid monocotyledons 
 is formed of the footstalks of the leaves; but 
 the real epidermis of both the ligneous and 
 herbaceous stems of this tribe, is always, as has 
 been already stated, so closely applied to the 
 part which it covers, as to be inseparable from 
 it by any means. Owing to this circumstance 
 it appears of a cellular structure, and its cha- 
 racter is regulated by the nature of the parts it 
 immediately encloses. In those plants, in which 
 it can be readily examined, it displays, under the 
 microscope, a regular series of organic exhaling 
 pores, each apparently surrounded by a glandu- 
 
 * Vide Plate 5, fig. 8. A. B. C. A. represents the transverse 
 slice of a stem of Wheat, as seen through a good lens ; B. a 
 longitudinal section of the slice highly magnified ; a. the outer 
 cellular substance, composed of oblong cells and entire vessels ; 
 b. the interior cellular lining of the cylinder of the stem ; c. 
 a vascular bundle, consisting of a spiral vessel surrounded by 
 oblong cells ; C. a transverse section of the slice ; a. the tu- 
 bular cells immediately under the epidermis ; b. the common 
 cellular substance ; c. the vascular bundles. 
 
 3 
 
302 CONSERVATIVE ORGANS. |~LECT. VII. 
 
 lar border ; as is beautifully demonstrated in the 
 culm of Wheat * : but in some plants, as, for in- 
 stance, the Common Rush, these apertures are 
 perceptible in the furrows only between the striae, 
 the elevations being apparently free from any 
 exhaling pores-f~. In some of the herbaceous dico- 
 tyledons, silex is found deposited in, or rather 
 immediately undeiv the epidermis. 
 
 Monocotyledonous stems, those even of the 
 largest diameter, display no medullary rays, such, 
 as I shall soon have occasion to demonstrate, as 
 characterize the dicotyledonous ; nor do such ap- 
 pear to be necessary, owing to the extensive dis- 
 tribution of the cellular matter throughout the 
 substance of these stems. The woody bundles, 
 however, become indurated by age, and the more 
 external being enlarged by the deposition of new 
 ligneous matter, they at length occasionally touch 
 each other, and form a circle of continuous wood ; 
 but the interior bundles never attain this state, 
 and are always sufficient to distinguish the stem 
 as a monocotyledon. 
 
 Monocotyledonous stems increase in length 
 or height ; but, with very few exceptions, not in 
 diameter. As I have had no opportunity of tracing 
 the manner in which this is effected, in the ligneous 
 
 * Vide Plate 5, fig. 12. 
 
 t Vide Plate 5, fig. 13. a. the appearance of the cuticle over 
 the ridges ; b. its cribriform appearance in the furrows. 
 
LECT. VII.] ANATOMY OF STEMS. 303 
 
 monocotyledons, I shall follow the description of 
 Mirbel, in explaining to you the growth of a Palm. 
 When the young plant, rising from the seed, ap- 
 pears at the surface of the ground, the leaves, 
 originally folded up and sheathed within each 
 other, separate themselves, increase in number, 
 and form a sheaf-like group. Those on the cir- 
 cumference now spread out, perform their func- 
 tions, and are detached ; but their bases re- 
 maining, form a solid or ligneous ring, which 
 is the origin of the stem. Within this circle the 
 sheaf of leaves rises vertically ; owing, perhaps, 
 to the resistance at the circumference ; and the 
 exterior ones having spread out on every side in 
 the same manner as the former, drop after a time, 
 also, and leave their bases to form another circle ; 
 within which the sheaf still rising, again spreads 
 out another range of leaves ; and in this way the 
 stem is gradually formed by the evolution of the 
 terminal leaf-bud, and the induration of the 
 footstalks of the fallen leaves. The whole stem 
 displays the cicatrices of the successive circles of 
 detached leaves, and these becoming hardened 
 by their exposure to the air, and the ligneous 
 bundles within them being older, in a direct ratio 
 as they are nearer to the surface (the development 
 of parts always taking place in the centre), the 
 substance of the stem is necessarily softer within, 
 and harder as it approaches the circumference. 
 
304 CONSERVATIVE ORGANS. [LECT. VII. 
 
 Owing to the mode of growth, also, which has 
 just been described, the stem is always naked, 
 columnar, and terminated with leaves and fruc- 
 tification in the form of a magnificent crown, as 
 exemplified in the Palms. The stipe, therefore, 
 or this kind of monocotyledonous stem, may be 
 regarded as a fasces of ligneous vascular rods 
 imbedded in cellular substance, and terminating 
 in leaves * : and its vitality being, in a great de- 
 gree, dependent on the herbaceous part, if the 
 central bud, or cabbage-}-, as it is commonly 
 called, be cut off, the whole plant immediately 
 dies. In tropical climates, some kinds of Ferns 
 rise with a stipe resembling that of the Palms ; 
 but this appears to be, according to Mirbel, " a 
 
 * The height to which some Palms arise, without increasing 
 in diameter, is truly astonishing. Thus the Ptychosperma 
 gracilis rises more than sixty feet above the surface of the 
 ground, with a stem not four inches in thickness. The eleva- 
 tion of the Areca oleracea is often not less than one hundred 
 and eighty feet ; and " although," says Mirbel, " its diameter 
 " is greater than that of the Ptychosperma, yet, it is certain 
 " that it never increases in thickness." Elem. de Phys. veg. 
 t. i. p. 12. Its stem is, nevertheless, thicker in the middle 
 than either at the base or the summit, when the Palm has 
 attained to a certain age ; which is justly ascribed to its vegeta- 
 tive powers being more vigorous at the middle period of its ex- 
 istence. 
 
 f The terminal bud of the Areca oleracea is boiled and 
 eaten as a delicacy, under the name of Cabbage ; and the plant 
 is called the Cabbage Palm. 
 
LECT. VII.] ANATOMY OF STEMS. 305 
 
 " simple fasces of petioles, or leaf-stalks * ;" al- 
 though circumstances occasion these to unite in 
 the interior of the stipe, and form masses of com- 
 pact wood. This variety of stipe does not increase 
 in diameter. 
 
 The Aloes, the Yucas, and the Dracaena differ 
 in their mode of growth from the Palms, inas- 
 much as they give off branches and increase in 
 the diameter of their stems. From the observa- 
 tions of M. Aubert du Petit-Thouars -f- , who traced 
 the mode of branching, and the consequent in- 
 crease of diameter in the stem of the Dracaena, 
 it appears that the branch originates in a small 
 protuberance under the epidermis, which it soon 
 ruptures ; and extending, first unfolds some scales 
 and then leaves, the result of the successive de- 
 velopment of which is a cylindrical branch com- 
 posed of ligneous cords, similar, in every respect, 
 to the parent stem, and seated upon it like a graft. 
 The ligneous cords, at the point of their junction 
 with the adult stem, spread out at first like rays, 
 and then extend, in an opposite direction to the 
 growth of the branch ; the exterior descending in 
 straight lines towards the earth, whilst the others, 
 after ascending a little at first, soon, also, bend 
 down and take the same course, which the whole 
 
 * ElSmens de Phys. vSget. 1. p. 121 . 
 
 f Essais sur la Vegetation, &c. Paris, 1809, p. 1. 
 
 VOL. I. X 
 
306 CONSERVATIVE ORGANS. [LECT. VII. 
 
 preserve until they are lost in a mucilaginous sub- 
 stance, secreted under the detached epidermis. 
 A layer of new ligneous cords is thus applied over 
 those of the old stem, and the development of 
 other branches still adding fresh layers, the stem 
 is gradually increased in diameter. M. Aubert 
 du Petit-Thouars thinks that, for the formation of 
 branches in these plants, a vital point (un point 
 vital) exists at the axilla of each leaf; but re- 
 mains latent and inactive, unless peculiar circum- 
 stances occur to call it into activity ; and this, he 
 conceives, constitutes the difference between these 
 gems and the buds which appear in the axillae of 
 the leaves in the great majority of dicotyledonous 
 plants. I shall, however, soon have an oppor- 
 tunity of demonstrating to you that the same 
 circumstance occurs in dicotyledonous stems ; on 
 which buds sometimes appear, that have existed 
 in a latent state for many years; and can be 
 traced back to their origin in the change of or- 
 ganization, occasioned by the frustrated effort to 
 develop them, in the successive layers of wood 
 which have annually added to the diameter of the 
 stems, on which they are ultimately developed. 
 
 The development and growth of the herba- 
 ceous, solid, monocotyledonous stem is nearly the 
 same as that of the ligneous, except that the parts 
 are more rapidly evolved. If we trace the growth 
 of the stem of the White Lily, for example, 
 
LECT. VII.] ANATOMY OF STEMS. 307 
 
 springing from a full-grown adult bulb, we per- 
 ceive that it first appears on the surface of the 
 ground like a large naked leaf-bud, which, when 
 dissected and minutely examined, consists, not only 
 of leaves overlapping each other, but also of the 
 rudiments of the flower and fructification. Before 
 this has risen much above the earth, the exterior 
 leaves separate at their apex from the others and 
 spread themselves out to the air and light, to 
 form those secretions which are partly deposited 
 in the portion of the stem below them, for the 
 purpose of affording it firmness and solidity; 
 whilst the more succulent portion above them 
 extends, carrying with it the bud, until the 
 leaves, next in succession, spread out and har- 
 den it in its turn. As the stem continues to ex- 
 tend and the leaves alternately to expand, it thus 
 attains the summit of its height. In this pro- 
 gress, the stem, as it advances, gradually loses a 
 portion of its diameter ; and a transverse section , 
 of it, near the summit, displays very few ligneous 
 vascular cords, compared with those of one near 
 the base ; and, consequently, contains less lig- 
 neous matter. At the point, however, where the 
 flower-stalks spring, it again thickens ; and the 
 attachment of these closely resembles that of the 
 branches of the Dracaena. 
 
 In our demonstration of the anatomical struc- 
 ture of the stems of this tribe of plants, we stated 
 
308 CONSERVATIVE ORGANS. [LECT. VII. 
 
 to you that those which are articulated, or knotted 
 and nevertheless solid, form the link between the 
 more common solid herbaceous, and the hollow 
 or fistular monocotyledonous stems. As they 
 display something in common with each, and yet 
 differ from both, in some degree, in structure, so, 
 also, they differ from both in the development of 
 their parts. The leaves are given off at the joints, 
 or knots only, and in general embrace the stem, 
 or are sheathing to a certain extent: and when 
 they protrude branches, these originate in gems 
 formed at the joints, between the stem and the 
 leaf, in a manner very closely resembling that in 
 which young lateral bulbs are formed on the ex- 
 terior of the laminated bulbs. These productions, 
 indeed, may be almost regarded as lateral pro- 
 geny, rather than real branches ; for they shoot out 
 radical fibrils at the lower part of a knee which 
 they often form with the main stem ; and, taking 
 root in the earth, perpetuate the existence of the 
 plant after the decay of the original stem. The 
 parts of the stem below these lateral shoots increase, 
 in a small degree, in diameter, from causes similar 
 to those which have been already detailed as pro- 
 ducing the increased diameter of the stem of the 
 Dracsena; and it is in this respect chiefly that 
 this stem differs in the manner of its growth from 
 the culm or fistular monocotyledonous stem. This 
 description will be better understood by refer- 
 
LECT. VII.] ANATOMY OP STEMS. 309 
 
 ing to the marginal cut, in which 1. represents 
 J 2 a portion of the stem 
 
 of Trad escan ti a Virginica, 
 with two lateral shoots 
 or branches : a. a young 
 shoot, partially envelop- 
 ed in its sheath b. and 
 its origin fully displayed 
 by the removal of the leaf 
 in the axilla of which it 
 is seated ; c. another shoot, 
 but covered by the base 
 of the leaf, the upper 
 part of which is cut away 
 at d. In 2, which represents the same portion 
 of stem divided longitudinally, the manner in 
 which the buds a. b. c. are given off is rendered 
 more obvious. The white longitudinal lines are 
 the vascular cords, which always appear white 
 amidst the green parenchyma; whilst the trans- 
 verse septa between each articulation, being 
 formed by the branches of these vessels assum- 
 ing an oblique direction, appear, also, of a white 
 colour. The vascular cords, from which the ves- 
 sels of the shoots originate, are easily distin- 
 guished by their greater* size, and by passing di- 
 rectly to the base of each shoot. 
 
 The Culm, as has been described, consists of 
 x3 
 
310 CONSERVATIVE ORGANS. [LECT. VII. 
 
 hollow articulations connected by knots; which 
 in their growth appear to rise from within each 
 other ; the new one always carrying with it the 
 central bud, which in the last of the series termi- 
 nates in the inflorescence. The leaves are sheath- 
 ing and given off only at the knots, which are 
 solid, or rather are filled up with a dense cellular 
 substance, containing at first a saccharine nutri- 
 tious juice, which Darwin asserts to be essential 
 to the growth of the next joint, for it is absorbed 
 or at least disappears as that is perfected. The 
 vascular cords, which run in straight lines 
 throughout the length of each joint, divide as they 
 approach the knot, forming an inosculated plexus, 
 and send off branches to the leaf and to the new 
 articulation, to which the cellular substance, that 
 forms the diaphragm interposed between the 
 cavity of each articulation, actually belongs ; 
 giving to the basis of the new joint the appearance 
 as if it rose from a bulb. It was this appearance, 
 as seen by the naked eye, which suggested the 
 theory advanced by Dr. Darwin, that each joint 
 of these stems is a distinct individual; and that 
 the whole of a stem of any grass, Wheat for ex- 
 ample, is a successive series of leaf-bulbs and 
 leaf-buds produced in one year, and terminating 
 in a flowering bulb. " At the first joint of the 
 " stem of Wheat," says the Doctor, " on or 
 
LECT. VII.J ANATOMY OF STEMS. 31 L 
 
 " within the surface of the earth, a leaf is pro- 
 " duced ; from which rises the principal or central 
 " bud, and around it many new buds, which 
 " strike their roots into the soil. After this cen- 
 " tral bud, and those around it, have risen six or 
 " eight inches, a new leaf and a new leaf-bud 
 " rises on each of them, producing a second joint of 
 " the stem ; and lastly a flower-bud is generated 
 " at the summit, which are all evidently distinct 
 " vegetable beings, as there is a division across 
 " the stem at each joint, which shows there is no 
 " connexion of the pith or brain, or spinal mar- 
 " row, between the lower and upper joints. That 
 " a new bud thus constitutes each joint of the 
 " stem of Wheat and other grasses is further 
 " evinced ; first, by the existence of a leaf at each 
 " joint without a lateral bud in its axilla, as oc- 
 " curs in other vegetables : secondly, because for 
 " the nourishment of this new leaf-bud a reservoir 
 " of sweet juice is prepared in the new joint ; as 
 " in the bulbs of many plants : and thirdly, be- 
 " cause the lower leaf dies, and the sweet juice is 
 " absorbed, as the upper leaf becomes vegete *." 
 Setting aside the fanciful allusions to the brain and 
 spinal marrow, there is much plausibility in this 
 theory ; and it even appears supported by the ana- 
 tomy of the knots of these stems, as far as that can 
 
 * Phytologia, sect. ix. 3, 1. 
 
 x4 
 
312 
 
 CONSERVATIVE ORGANS, 
 
 [LECT. vn. 
 
 be perceived by the naked eye, or by the aid of an 
 ordinary lens ; but when the microscope is em- 
 ployed, the vessels can be traced from one joint 
 to the other, passing through the spongy cellular 
 diaphragm, and pursuing their course to the sum- 
 mit of the stem. To illustrate this, I have ad- 
 joined (see marginal cut) a 
 plan of the vessels in the knot 
 of the Wheat stem, as dis- 
 played by the microscope, in 
 a longitudinal slice of a straw. 
 In this plan the white lines 
 a. . represent the course of 
 the vessels in the cylindrical 
 part of the old joint running 
 in a perpendicular direction, 
 which they preserve up to the 
 point b. b. where the leaf se- 
 parates from the new articu- 
 lation c. which is sheathed within it. At d. d. and 
 between that point and b. b., branches are given 
 off, which meet in the centre of the cellular matter 
 of the knot, and again join the vessels a. a. at . 
 b. b. where they enter the leaf f.f. in which they 
 terminate. A little lower, however, opposite g. g. 
 vessels are sent off, which at first are curved in- 
 wards, but soon acquire a perpendicular direction 
 and constitute the vessels of the new joint as seen 
 
LECT. VII.] A N ATOM Y OF STE M S . 313 
 
 at i. 2. The density of the cellular substance 
 around the inosculating vessels constitutes the 
 diaphragm, which is interposed between the arti- 
 culations of this description of stem : and the new 
 joint does not appear hollow at first, the cellular 
 substance filling up its cavity as at k. for a short 
 space above the knot. There can be, therefore, 
 little doubt that the articulated culm is as much 
 one individual as the stipe ; and the truth of this 
 opinion is not shaken by our inability to explain 
 the object of its articulated structure. But if it 
 be allowable to hazard a conjecture, I would say, 
 that as the cords of vessels run in straight lines, 
 and are comparatively remote from the surface in 
 these stems, the enlargement at the knots is partly 
 intended to afford space for permitting branches 
 from these vessels to be given off to supply 
 the new joint which originates there: accord- 
 ingly we see branches added to the vascular cords 
 as they arrive at the knots; and these, after 
 passing through it, approach each other and dis- 
 appear in the vascular cords again pf the new 
 joint ; the necessity for the branches no longer ex- 
 isting. The original cords of the old stem ac- 
 tually terminate in the leaf, which is the limit of 
 the growth of the joint ; and in this respect gives 
 some colour of truth to Darwin's theory of the 
 individuality of the articulations. The cellular 
 substance itself, in the knot, is probably intended 
 2 
 
314 CONSERVATIVE ORGANS. [LECT. VII. 
 
 partly for supporting these additions to the vessels, 
 and partly for the development of the new bud 
 in the axilla of the leaf ; which, notwithstanding 
 the assertion of Dr. Darwin, occurs in the grasses 
 in the same manner as in other plants, although 
 in our climate it is not always evolved *. The 
 saccharine juice, also, secreted in the knot, is more 
 likely to be required as the first nutriment of the 
 embryon bud (in some degree a new being -f-), 
 which may be developed at this point, than to 
 forward the growth and extension of the next 
 joint ; which is already so constituted as to be 
 able to make use of the nutriment with which it 
 is supplied from the soil, through the medium of 
 the roots. 
 
 Such is the structure and the mode of growth 
 of monocotyledonous stems. The positive features 
 which chiefly characterize them in point of struc- 
 ture, are the separate vascular ligneous cords, and 
 intermixed cellular parenchyma; but they are 
 distinguished more strikingly by negative qualities ; 
 as, for example, those of having no proper bark, on 
 
 * In tropical climates almost all the grasses give off branches 
 from buds formed in the axilla of the leaves ; and even in this 
 climate this occurs in Nodose Canary Grass, Phalaris Nodosa, 
 and several other perennial grasses. 
 
 f I have said, " in some degree," because, even allowing 
 the bud to be lateral progeny, yet it is, strictly speaking, an 
 extension only of the parent, and not a new being, in the 
 sense in which this term is properly applied to seminal progeny. 
 
LBCT. VII.] ANATOMY OF STEMS. 315 
 
 liber, no alburnum, and no medullary rays; parts 
 which, as I shall soon have occasion to demon- 
 strate to you, belong, exclusively, to the dicoty- 
 ledonous and polycotyledonous stems. I do not, 
 at present, attempt to detail to you either the 
 opinions of others, or my own conjectures, re- 
 lative to the manner in which the various parts of 
 these stems are formed; nor to trace their par- 
 ticular functions ; as we shall enter fully into this 
 part of our subject, when we arrive at the proper 
 moment for taking into consideration the combined 
 functions of the root, stem, and leaves. 
 
 iii. Stems belonging to plants, which are pro- 
 duced from dicotyledonous and polycotyledonous 
 seeds, are in every respect alike in point of struc- 
 ture ; and, therefore, for the sake of brevity, I 
 shall describe both under the single appellation of 
 Dicotyledonous stems. In treating of these, their 
 natural division into woody and herbaceous imme- 
 diately presents itself to our attention. 
 
 A. WOODY DICOTYLEDONOUS STEMS consist of 
 three distinct parts, the bark, the wood, and the 
 pith. They are best exemplified in trees and 
 shrubs ; but as the structure of each of these parts 
 differs according to the age of the plant, it is re- 
 quisite to examine them, both as they appear in 
 the young plant or the shoot one year old only, 
 and in the trunk and branches of older subjects. 
 If the young shoot of any tree or shrub, the 
 
316 CONSERVATIVE ORGANS. [LECT. VII. 
 
 Horse Chesnut for example, be cut either trans- 
 versely or longitudinally, the parts which have 
 been enumerated, are rendered evident to the na- 
 ked eye. If the section be transverse, it is seen 
 to consist of a central spongy or cellular portion, 
 which is the pith, enclosed within a ring of more 
 solid consistence, which is the wood; and this, 
 again, is environed by another circle of an in- 
 termediate degree of firmness, which is the bark. 
 If the section be longitudinal these parts are seen, 
 in the same order (vide fig. 1, Plate 6), extending 
 the whole length of the shoot ; the pith a. appears 
 like a central column, guarded on every side by 
 the wood b. y and this bounded by the bark c., 
 which forms the exterior envelope of the whole. 
 Running the eye, however, along the section, 
 we perceive that the bark is not continuous ; but 
 where the buds d. e. project, it appears as if re- 
 flected over them, while the exterior fibres of the 
 wood enter into their substance. At the bases of 
 the leaf-stalks,/*, g. this is not the case ; for these 
 appear as if seated upon the bark, connected with 
 the shoot merely by the cords of vessels h. i. which 
 penetrate the wood, and are apparently lost on 
 the surface of the pith. At the summit of the 
 shoot the pith appears to terminate, enclosed by 
 the wood as if by an arch ; whilst the bark still 
 covering the wood mingles with the substance of 
 the leaves which form the terminal bud k. In 
 
LECT. VII.] ANATOMY OF STEMS. 317 
 
 pursuing our inquiries, we find that the bark is 
 readily detached from the wood, b. and is sepa- 
 rable into three layers ; that the wood is fibrous 
 and more compact and harder within than in its 
 exterior part ; and that the pith is evidently com- 
 posed of cells, which, ,in the more succulent parts 
 of the shoot, are filled with an aqueous fluid, and 
 in the drier with air. Such is nearly the sum of 
 the information we can obtain from an examina- 
 tion with the naked eye ; to secure, therefore, an 
 accurate knowledge of these parts, we must call 
 in the aid of the microscope ; and, with its as- 
 sistance, let us examine each of them in the order 
 in which they present themselves in the shoot 
 under our inspection, beginning with the bark. 
 In taking this course, we shall confine our actual 
 demonstrations to this shoot : pointing out, how- 
 ever, and illustrating as far as possible, the va- 
 rieties which have been remarked in each part, in 
 different ligneous stems, both in their first year's 
 growth, and in the after-periods of their ex- 
 istence. 
 
 a. The BARK. In the shoot we are now ex- 
 amining, which has been cut in the autumn, the 
 bark when separated from the wood is about the 
 sixteenth part of an inch in thickness, and ap- 
 pears, to the naked eye, to be composed of four 
 very distinct parts. 1. A dry, leathery, fawn- 
 coloured, semi-transparent, tough membrane, 
 
318 CONSERVATIVE ORGANS. [LECT. VII. 
 
 which is the cuticle ; 2. a cellular layer which 
 adheres, although not very firmly, to the cuticle, 
 and is named the cellular integument ; 3. a vas- 
 cular layer ; and 4. a whitish layer, apparently 
 of a fibrous texture, which is the inner bark ; and 
 which, as we shall afterwards find, is of a more 
 complicated structure than the other layers. We 
 shall now view these parts separately under the 
 microscope. 
 
 1. The Cuticle. Before demonstrating the 
 structure of this part, it is necessary to remark, 
 that I prefer the term cuticle to that of epider- 
 mis, in reference to the exterior covering of stems 
 and branches, in order to distinguish it from the 
 thin unorganized pellicle which has already been 
 described (page 93) under the name Epidermis, 
 as one of the general components of the vege- 
 table structure; and which is, in fact, the ex- 
 terior part of the cuticle. 
 
 The cuticle may be raised from the cellular 
 integument by the point of a knife, and this is 
 the best method to obtain it for minute examina- 
 tion *. When thus separated and placed under 
 the microscope, it appears, to consist of two layers ; 
 
 * Some authors recommend boiling the shoot or cutting, in 
 order to separate the cuticle ; but although it is thus readily 
 separated, yet, the boiling coagulates and thickens its sub- 
 stance, rendering it opaque and destroying its natural structure. 
 
LECT. VII.] ANATOMY OF 8TEMS. 319 
 
 the outer being the unorganized pellicle of true 
 epidermis, and the inner a vascular texture, com- 
 posed of minute vessels which terminate externally 
 at the surface of the stem, and internally in the 
 cellular integument *. These are, apparently, an- 
 nular vessels with oblong pores ; and, although 
 I have never been able completely to satisfy myself 
 that they penetrate the real epidermis, yet, they 
 probably do so to perform the office of exhalants 
 or of absorbents. The abrupt manner in which 
 these vessels terminate in the cellular integument, 
 readily accounts for the facility with which the 
 cuticle separates from that portion of the bark -f-. 
 Such is the cuticular portion of the bark of the 
 Horse Chesnut ; but the structure of this part 
 is not the same in all ligneous dicotyledonous 
 stems. In that of the Pear, Pyrus communis, it 
 consists rather of transverse cells than of vessels, 
 the outer series of which is covered by the real 
 epidermis: this is the case also in the lesser Pe- 
 riwinkle, Vinca minor, in which there are three 
 series of such cells ; in the Laburnum, Cytisus 
 
 * Vide Plate 6, fig. 2, a. 
 
 f It was probably this vascular part of the cuticle, which 
 led Du Hamel (Phys. des Arbres, liv. 1. c. ii.) to describe the 
 vegetable epidermis as a tissue of delicate parallel fibres inos- 
 culating at regular intervals, or united by lateral fibres, so as 
 to constitute a network, the meshes of which are filled up 
 with a thin, transparent pellicle. 
 
320 CONSERVATIVE ORGANS. JJLECT. VII. 
 
 Laburnum, it is composed of the epidermis simply 
 covering a layer of an irregularly cellular or 
 spongy character ; in the Laurustine, Viburnum 
 Tinus, of one layer of cells covered by the epider- 
 mis ; and the same is the case in the Vine, except 
 that the cells are extremely minute, and oblong in 
 the length of the stem, having the appearance of 
 vessels in the transverse section. These and similar 
 varieties in the structure of the cuticle account 
 for the want of coincidence in the descriptions of 
 authors. 
 
 The true epidermis or exterior layer of the 
 cuticle is necessarily cribriform, whether it act as 
 an exhaling or an absorbing surface ; and the man- 
 ner in which the pores are arranged, does not 
 differ less, in different plants, than the structure 
 of the interior layer. It is frequently studded 
 with hairs, glands, and prickles ; but, as these 
 are not peculiar to stems, their particular struc- 
 ture shall be demonstrated, when we treat of the 
 general vegetable appendages. In young and 
 succulent shoots, the cuticle is generally almost 
 colourless, and semi-transparent, transmitting 
 the green colour of the exterior part of the cel- 
 lular integument over which it lies; but it becomes 
 opaque and coloured by age, or rather on losing 
 its vitality ; for, as it is annually reproduced, on 
 the ligneous stems under consideration, the old 
 layer, if it does not fall off, cracks and is pushed 
 
LECT. VII.] ANATOMY OF STEMS. 321 
 
 outwards by the increase of the diameter of the 
 stem ; and the accumulation of such layers forms 
 the rugged surfaces of stems, as for example of 
 the Elm, the Oak, and the majority of trees *. 
 In the greater number of instances it cracks verti- 
 cally, and is pushed outwards with a portion of the 
 cellular integument by the new epidermis, which 
 can be brought into view by removing these 
 rugged portions. In others it splits horizontally, 
 and the new cuticle is formed immediately under 
 the old, which, after a time, detaches itself in 
 fragments ; or, there is a succession of cuticles, 
 which, although one is formed every year, yet 
 do not separate annually, but occasionally only, 
 in multiplied layers, that can, however, be readily 
 detached from each other, as in the Currant and 
 the Paper Birch. Some trees, the Plane for ex- 
 ample, annually throw off the cuticle at once, in 
 large flakes ; and in this respect, such plants re- 
 semble those reptiles that cast their skins or their 
 crusts, as the snake, the spider, and the lobster. 
 
 2. The Cellular integument. On carefully 
 raising the cuticle of the young shoot of the Horse 
 Chesnut, we find under it a cellular layer ; which, 
 in a transverse section of the stem placed under 
 
 * In Plate 6, fig. 10. a. represents a microscopic view of the 
 various layers which form the rough cuticle of an old stem 
 of the Lilac, Syringa imlgaris ; the innermost only of which 
 retains its vitality. 
 
 VOL. I. Y 
 
32*2 CONSERVATIVE ORGANS. [LECT. VII. 
 
 the microscope, is seen to consist of two distinct 
 parts, both cellular, but nevertheless different. 
 The exterior, or that on which the cuticle imme- 
 diately reposes, appears to be composed of a dark 
 green, semiorganized pulp, in which the cells are 
 irregular both in their dimensions and form (vide 
 Plate 6, fig. 2, 6.), and has somewhat of the as- 
 pect, as Mr. Keith aptly expresses himself, of " a 
 " distinct and separate epidermis in an incipient 
 " state, rather than a true and proper pulp :" 
 while the interior is less coloured and composed 
 of regular hexagonal cells (Plate 6, fig. 2, c.), 
 the sides of which are perforated and frequently 
 studded with small granular bodies. It is the ex- 
 terior layer of the cellular integument, which is 
 the seat of colour of the young twig, and the 
 green hue of which is transmitted through the 
 yet semitransparent cuticle : its appearance, and 
 the fact that it is annually reproduced, led Mr. 
 Keith to believe that it is really the next year's 
 cuticle in an incipient stage of organization. But 
 the vertical direction of the cells, while those of 
 the cuticle are horizontal, is sufficient to overturn 
 this opinion, (Plate 6, fig. 7, a. I. 2.) These two 
 portions of the cellular integument are particu- 
 larly noticed by Mirbel, who denominates the 
 exterior the herbaceous tissue, and the interior 
 the parenchyma ; and conceives, with much pro- 
 bability, that the deeper green colour of the latter 
 
 2 
 
LECT. VII.] ANATOMY OF STKMS. 323 
 
 depends on the exposure of its juices to the light 
 and on the resinous nature of these juices. He re- 
 gards the whole of the cellular integument, also, 
 as a glandular body serving to separate the trans- 
 pirable matter from the other fluids * ; an opinion 
 which I shall have occasion to notice more par- 
 ticularly when we investigate the functions of 
 the stem. The cells of the interior portion, in 
 the young shoot of the Horse Chesnut, are very 
 regular hexagons, except in those places where 
 there is any pressure, or where the adjoining 
 parts require a variation of form, when a change 
 takes place; but, independent of these circum- 
 stances, the pure hexagonal form does not prevail 
 in the stems of every species of the natural tribe 
 of plants under examination. Thus in Privet, 
 Ligustrum vulgare, the cells are variously formed, 
 some being nearly circular, others rudely ellip- 
 tical, and some very obscurely heptagonal : in the 
 Elder, Sambucus nigra, they are equally irregu- 
 lar ; in the Common Lilac, Syringa vulgaris, the 
 proportion of real cellular matter compared with 
 that of the semi-organized pulp is small, and the 
 cells, which are of an oblong figure, are com- 
 pletely filled with minute amylaceous granules ; 
 and this is the case, also, in the Laburnum, 
 Cytisus Laburnum, in which, however, they 
 
 * Elemens de Physiologic vegetate, l ere par tie, p. 103. 
 
 Y-2 
 
324 CONSERVATIVE ORGANS. [LECT. VII. 
 
 are regular hexagons : in the Pear, Pyrus com- 
 munis, they resemble globular utricles : and in 
 the Rock Rose, Cistus Ledon, they are irregu- 
 lar oblong hexagons. Such are the diversities 
 of figure of these cells ; but it is still a ques- 
 tion whether the membrane of which they are 
 composed be single or double, as I formerly re- 
 marked (page 75), in describing the cellular tex- 
 ture among the general vegetable components? 
 Senebier and Link are both of opinion that each 
 cell is a separate utricle, completely distinct from 
 those which are in contact with it, and conse- 
 quently that the partitions are double on every 
 side. Link further contends * that there are no 
 visible organic pores in these partitions, the fluids 
 passing from the one to the other by a double fil- 
 tration ; and that the appearance of pores is occa- 
 sioned by small amylaceous granules scattered over 
 their surfaces. It is certainly not easy to deter- 
 mine this question as far as regards the double or 
 single nature of the cellular membrane, although 
 I am disposed to believe it is double ; both from 
 the appearance which it presents under the micro- 
 scope, and also from the greater facility which 
 such a supposition affords of explaining the origin, 
 and the hexagonal figure of the cells, a point which 
 shall be discussed in its proper place ; but, if 
 
 * Vide ROMER, Collect. Botanic, facs. 1. p. 163. 
 
LECT. VII.] ANATOMY OF STEMS. 325 
 
 any confidence is to be placed in the microscope, 
 there can be no doubt of the existence of the cel- 
 lular pores. That many of the cells, however, are 
 filled with minute particles, is perfectly evident ; 
 and the number of these is always greater where a 
 branch is given off. Their use is yet unascertained, 
 but it is not improbable that they are of a nutri- 
 tive nature, and deposited in the cells to be dis- 
 solved by the ascending sap for the evolution of 
 new parts. Independent of these particles, the 
 cellular integument is filled both with coloured 
 and colourless secreted juices ; and it is very pro- 
 bable that this part performs some changes on the 
 sap thrown into its cells, similar to those effected 
 in the leaf. 
 
 The cellular integument is partially destroyed, 
 and reproduced, a great part of the old portion 
 being pushed outwards with the cuticle which 
 is annually detached ; while new cells are added 
 to that which remains at the time the new cuticle 
 is produced. 
 
 3. Vascular layer. Imbedded in the cellular 
 integument and impinging on the internal sur- 
 face of the bark, are distinct bundles of entire 
 vessels, each of which is so arranged as to pre- 
 sent, in the transverse section of the stem under 
 consideration, a semilunar aspect * ; and, in the 
 
 * Vide Plate 6, fig. 2, d. 
 Y3 
 
326 CONSERVATIVE ORGANS. [LECT. VII, 
 
 longitudinal section, that of a fascis of flexible 
 cords, readily separable from each other, and 
 from the surrounding cellular substance * ; which 
 is condensed where it comes in contact with these 
 bundles. These vessels are supposed to convey 
 downwards the proper juice of the plant, ela- 
 borated from the sap, by the action of the light 
 and air in the leaf; and this opinion is supported 
 by the fact, that it is from them the milky 
 juice of the Fig-tree and the coloured juices of 
 other plants exude, when the stem is trans- 
 versely divided. In some stems, as, for example, 
 that of Laburnum, Cytisus Laburnum, the vascu- 
 lar bundles coalesce, and form nearly one conti- 
 nuous layer or circle around the wood ; and in 
 others, although they do not actually coalesce, 
 yet, they approach so close as almost to assume 
 the same character. As the stem increases, these 
 vascular bundles become impervious, and are 
 pushed outward with the cellular integument, giv- 
 ing place to a new layer which is annually pro- 
 duced. 
 
 4. Inner bark. Immediately under the vascu- 
 lar bundles, we find another layer -f- which consti- 
 tutes the internal boundary of the bark. In the 
 transverse section of the stem of the Horse Ches- 
 nut now before us, it appears under the microscope 
 
 *Vide Plate 6, fig. 7, a. 3. 
 
 t Plate 6, fig. 2, e. and fig. 7, a. 4. 
 
LBCT. VII.] ANATOMY OF STEMS. 327 
 
 to consist of the extremities of longitudinal fibres 
 closely united together ; and, in the tangental 
 section, these fibres are seen running in a waving 
 direction and touching each other at certain points 
 only so as to form oblong meshes, which are filled 
 with cellular matter. The nature of this structure 
 will be better understood by referring to the mag- 
 nified marginal plan, in which 
 a. a. a. represent the reticular ar- 
 rangement of the longitudinal fi- 
 bres, and b. b. b. the cellular meshes. 
 This layer is denominated LIBER, 
 a name imposed from its having 
 been employed to write on before 
 the invention of paper. As the network formed 
 by the dividing threads of the meshes is not 
 readily dissolved in water, whilst the cellular 
 matter which fills them up is remarkably soluble, 
 the liber of some plants, for example the Daphne 
 lagetto, when soaked in water and afterwards 
 beaten, forms a very beautiful vegetable gauze ; 
 which may be used as an article of dress. A 
 coarser specimen of this gauze, or lace, is seen 
 in the bark of many of our indigenous trees, par- 
 ticularly the Oak, when it has been long exposed 
 to the weather, after being separated from the 
 trunk. This regular arrangement, however, of 
 the longitudinal texture of the liber, is not found 
 in every instance ; for in the Fir and some other 
 
 v4 
 
CONSERVATIVE ORGANS. [LECT. VII. 
 
 trees the longitudinal threads are seen lying 
 nearly parallel to one another, without any meshes 
 or intervening cellular matter. Like the other 
 parts of the bark, the liber is annually reproduced. 
 The old layer loses its vitality, and is pushed out- 
 wards by the new ; the accumulation thus formed 
 constituting what botanical writers have called 
 the cortical layers, which Malpighi supposed de- 
 rived their origin from the older bark. 
 
 The vitality of the stem of dicotyledonous 
 plants is more conspicuous in the liber than in 
 any other part. If the bark be wounded, or a 
 portion of it be removed, layers gradually extend 
 themselves from the liber on each side of the 
 wound until it is closed up ; but, as this is not ef- 
 fected in one year when the wound is extensive, 
 and as the new layers are thrown out by the liber 
 only which is annually renewed, the cicatrix, if 
 the healed portion can be so named, always re- 
 sembles a hollow cone, the base of which is the 
 exterior of the trunk. The union of a graft, or of 
 a bud taken from one tree and implanted on ano- 
 ther, succeeds only when the liber of the bud, 
 or the graft and that of the stock is placed in 
 immediate contact ; the union in these instances 
 closely resembling that which occurs when two 
 raw surfaces of a living animal body, or of two 
 distinct animals, are retained for some time in con- 
 tact. Grew, Malpighi, Du Hamel, and others 
 
LRCT. VII.] ANATOMY OF STEMS. 329 
 
 supposed that the liber annually changes, by hard- 
 ening, into the alburnum or young wood, an 
 opinion which is still maintained by some of the 
 ablest phytologists * ; but which I shall afterwards 
 prove to you is founded upon mistaken principles. 
 It is through the liber, however, that the matter 
 in which the new wood is formed, which annually 
 augments the diameter of the trunk and branches, 
 is secreted; and hence the importance of this 
 portion of the bark. 
 
 Such is the structure of the bark of the stems 
 of woody dicotyledons ; and that of the root does 
 not materially differ from it; any difference de- 
 pending, perhaps, altogether on the medium in 
 which these two parts are situated. In the bark 
 the secreted juices of plants, and consequently 
 their medicinal qualities, are chiefly deposited; 
 but the consideration of the functions of this part 
 and its properties must be deferred, until the 
 whole of the structure of the stem has been de- 
 scribed. 
 
 b. The WOOD. Pursuing our investigation in 
 the young stem of the Horse Chesnut ; when the 
 whole of the bark is removed, we find, imme- 
 diately under and slightly adhering to it, a 
 firmer and more compact substance, which, both 
 in a longitudinal and a transverse section, ap- 
 
 * " Le liber endurcie, de verdatre qu'il etait, devient blanch- 
 " atre, et prend le nom d'aubier." MIRBEL, Element de Phys. 
 vcg. t. i. p. 106. 
 
330 CONSERVATIVE ORGANS. [LET. Vlt, 
 
 pears to constitute a cylinder, enclosing a co- 
 lumn of spongy cellular matter or pith. This is 
 the wood. It has been regarded 1 , in reference to 
 the vegetable, as answering the same end as bone 
 in the animal body ; but, except in its property of 
 giving firmness and support to the plant, the ana- 
 logy does not hold good. It is at first soft and 
 vascular, and is then called Alburnum ; but it af- 
 terwards becomes hard, and, in some trees, is of 
 a density almost equal to that of iron. In a trans- 
 verse section of our stem of Horse Chesnut, it ap- 
 pears, to the unassisted eye, a continuous circle 
 of a homogeneous structure, of a very light straw 
 colour exteriorly or near the bark, and greenish 
 interiorly, or where it is in contact with the pith ; 
 but in some other trees, as for example the La- 
 burnum and the Elder *, this circle appears tra- 
 versed, at nearly regular distances, by rays of an 
 evidently different structure. These are found, 
 however, to exist also in the stem of the Horse 
 Chesnut, and in every other woody dicotyledon 
 when it is examined by a magnifying glass; and 
 they are observed in the soft wood, or alburnum, 
 as well as in the hard and most perfect wood. 
 These two distinct parts, which constitute the 
 wood, may be described under the names Concen- 
 tric and Divergent layers ^. 
 
 * Vide Plate 6, fig. 3. 4. 5. 
 
 f These names are adopted by Mr. Keith (System of physio- 
 logical Botany ) y and are more expressive of the parts they are in- 
 tended to designate, than any others which have been employed. 
 
LECT. VII.] ANATOMY OF STEMS. 331 
 
 Placing a very thin transverse section of the 
 stem of Horse Chesnut under the microscope, the 
 wood no longer appears solid and compact ; but of 
 an irregular reticulated texture -f-. In this state, 
 however, the concentric and divergent layers are 
 readily distinguished; the open spaces in the 
 former being evidently the transverse orifices of 
 divided longitudinal or vertical cells and vessels, 
 whilst those in the latter are the lateral openings 
 of horizontal cells ^. Let us now examine se- 
 parately the minute structure of each of these 
 parts as they appear in the stem of one year's 
 growth. 
 
 1. The Concentric layers consist apparently of 
 longitudinal fibres, which are, however, appa- 
 rently not solid, but narrow tubes or oblong cells, 
 the sides of which are thick and nearly opaque, 
 and of vessels of different kinds. These are ar- 
 ranged parallel to each other, except where they 
 are separated by the divergent layers, as may be 
 seen in a thin tangental section 
 of any stem placed under the 
 microscope ; and is rudely dis- 
 played in the marginal plan, 
 in which a. a. a. a. a. represents 
 
 t Vide Plate 6. Fig. 2. * represents the first state of the soft 
 wood or alburnum,/, the more perfect wood, and h. the orifices 
 of the large vessels of the wood. 
 
 J Vide Plate 6, fig. 2.g. 
 
332 CONSERVATIVE ORGANS. [LECT. VII. 
 
 the longitudinal fibres or oblong cells ; c. c. c. the 
 vessels which in the Horse Chesnut are porous, 
 and b. b. b. the exterior ends of divergent layers. 
 In the alburnum, the walls of the concentric tubes 
 are tender and transparent ; but by the deposition 
 of ligneous matter in the membrane of which 
 they consist, and in the tubes themselves, they 
 become opaque and firm ; and according to the 
 degree of this, the wood is more or less dense, 
 hard, and tenacious. Other matters, also, are 
 deposited in this part of the woody texture ; such 
 for example as Guiaic in that of the Guiacum 
 officinale, colouring matter in the Logwood, 
 Haematoxylon Campechianum, and even silex, 
 which has been extracted from the Teak wood, 
 Tectona grandis, by Dr. Wollaston. The vessels 
 of the concentric layers are chiefly porous and an- 
 nular, and their section produces the openings ob- 
 served in the transverse section of any stem* ; but 
 besides these, in the circle of the wood of the first 
 year's growth, a circle of spiral vessels surrounds 
 the pith *f~. These are, however, justly regarded by 
 
 * Vide Plate 6, fig. 2. h. and fig. 8. a. a. a. The tubular 
 nature of the oblong cells, forming the concentric layers, is 
 rendered evident in this section of the common Elder, fig. 8. at 
 b. b.; and the distinct character of the divergent layers at c. c. 
 Leuwenhock, in 1680, first delineated the porous vessels of the 
 wood. Vide his Epist. Physiolog. p. 14-. 19. 
 
 f Vide Plate 6, fig. 7. d. e. 7, 7, 7. In this figure, also, the 
 first, or half-organized state of the alburnum, is represented 
 between b. c. ; and the vascular structure of the perfect wood 
 
LECT. VII.] ANATOMY OF STEMS. 333 
 
 Mirbel not as vessels of the wood ; but of a dis- 
 tinct sheath lining the wood, which he has deno- 
 minated F6tui me*dullaire ; and there is un- 
 doubtedly some reason for this distinction, inas- 
 much as these vessels have not been detected in 
 the wood, but always in immediate contact with 
 the pith. I shall more particularly examine this 
 opinion before describing the structure of the pith. 
 2. The Divergent layers * consist of flattened 
 masses of cellular substance, which cross the con- 
 centric layers at different parts, and, separating 
 the bundles of longitudinal tubes of which they 
 consist from each other, produce the reticulated 
 arrangement seen in the tangental section of any 
 steal ; the oblong tubes and vessels forming the 
 tissue of the network, the meshes of which are 
 filled up by the cells of the divergent layers. The 
 individual cells, which are narrow and horizontal 
 in their length, extend in series from the centre 
 to the circumference of the wood; and conse- 
 quently form nearly right angles with the tubes 
 of the concentric layers^. They communicate 
 with each other by pores ; so that fluids may 
 readily pass through the whole series, and of 
 
 between c. d., the smaller vessels being marked by the figure 
 5, and the larger by 6, showing distinctly their porous and an- 
 nular structure. 
 
 * Dr. GREW was the first author who described these layers 
 under the name of insertions. 
 
 f Vide Plate 6. fig. 7. *. *. 
 
334 CONSERVATIVE OKGANS. [LECT. VII. 
 
 course transversely through the wood ; and Mirbei 
 remarks that, " in many coniferous trees the di- 
 " vergent rays are not cellular ; but consist of ho- 
 " rizontal tubes which extend from the medulla or 
 " pith to the bark*." Whether they are cellular or 
 tubular, the layers, or masses, are flat, or in plates, 
 with the edges placed vertically, and thicker in 
 the centre than either above or below, appearing 
 therefore of a lozenge shape (see marginal plan, 
 p. 331) when vertically divided ; whilst in their 
 transverse section they display a slight inclination 
 to the wedge form -J-. They are much more deli- 
 cate in their structure than the concentric layers ; 
 and readily dissolve, like the common cellular 
 texture, so that when a thin tangental slice of 
 wood is macerated in water, the divergent layers 
 are decomposed and leave the meshes of the con- 
 centric layers empty, displaying the appearance 
 of a network or lace similar to that formed by 
 the macerated liber. 
 
 From the cellular texture of the divergent lay- 
 ers, they are regarded by some authors as pro- 
 cesses of the pith or medulla ; and hence have 
 been named medullary rays ; and Mr. Keith ob- 
 serves, they are " apparently nothing more than 
 " the vesicles or cellular tissue of the pulp that 
 " originally existed in the alburnum now deprived 
 
 * Elemens de Phys. veg. l re partie, p. 110. 
 t Vide Plate 6, fig. 2. g. 
 
LECT. VII.] ANATOMY OF STEMS. 335 
 
 " of its parenchyma ; but still filling up the in- 
 " terstices of the concentric layers, and binding 
 u them together like a cement.** But there is 
 little difficulty in demonstrating the error of both 
 these opinions ; for, examining the alburnum in a 
 very early stage of its formation at the moment it 
 is passing from the gelatinous state in which it is 
 first deposited, we find the rudiments of both the 
 concentric and divergent layers already assuming 
 the form which they afterwards maintain. Were 
 any further reason required to prove that the diver- 
 gent layers do not originate in the pith, it would 
 be found in the fact, that many of them cannot be 
 traced to the pith ; although the more conspicuous 
 of them traverse the whole of the wood, from the 
 pith to the bark. 
 
 Such is the structure of wood in the stems of 
 one year's growth of ligneous dicotyledons ; and 
 it is found nearly of the same structure in the root : 
 a fact, which is rendered evident, not only by the 
 microscope, but also to the unassisted eye, by the 
 decomposition of the divergent layers in the ligne- 
 ous part of roots which have been dug up and long 
 exposed to the action of the atmosphere. The 
 concentric layers, longer resisting the action of 
 the weather, remain after the divergent have dis- 
 appeared, and display a beautiful network, more 
 or less open in its meshes, according to the den- 
 sity or sponginess of the wood. 
 
336 CONSERVATIVE ORGANS. [LECT. VII. 
 
 Wood in its soft state, or that in which it 
 forms the outer circle in every ligneous dicotyle- 
 donous stem and branch, is, as has been already 
 mentioned, named alburnum. While it con- 
 tinues so, it is endowed with nearly as much ir- 
 ritability as the liber; and, as shall be after- 
 wards fully described, performs functions of 
 great importance in the vegetable system ; but 
 when it becomes hard these functions cease, and 
 in time it loses even its vitality ; not unfrequently 
 decaying in the centre of the trunk of trees ; 
 which, nevertheless, still flourish and put forth 
 new shoots as if no such decay existed. To 
 carry on, therefore, the functions of the wood, a 
 new circle of it is annually formed over the 
 old ; and thus, also, the diameter of the trunk 
 and branches present, by the number of these an- 
 nual zones, a pretty correct register of their age, 
 each zone marking one year in the life of the 
 part*. There are, however, exceptions to the 
 criterion thus afforded of the age of the plant, for 
 circumstances may occur to prevent the zone from 
 being formed of a thickness which will be per- 
 ceptible after a few years have passed over, and it 
 is pressed between other zones. If the summer 
 
 * Vide Plate 6, figures 3, 4, 5, which represent sections of 
 the same stem, in the first, second, and third year of its 
 growth ; and fig. 6. which displays two zones, as they are seen 
 in a longitudinal section of the stem of the Elder. 
 
LECT. VII.] ANATOMY OF STEMS. 337 
 
 be unusually cold, or if the leaves of the tree or 
 the shrub happen to be much devoured by caterpil- 
 lars, it gains very little that season in diameter. 
 From the same cause the zones are also of un- 
 equal degrees of hardness : but, independent of 
 the comparative density of each, the hardness of 
 the whole increases with the age of the tree, so 
 that they are hardest in the centre, and less and 
 less hard as they approach the circumference. 
 The outermost layer, being alburnum, is always 
 soft, and continues so until another layer is formed 
 over it ; but if the tree be barked the alburnum 
 assumes the apparent character of wood in the 
 same year ; and hence it has been recommended 
 to bark trees the year before they are intended to 
 be cut down. "The German foresters," how- 
 ever, " have proved that wood treated in this 
 " manner is less elastic, and is more easily in- 
 " jured by humidity and insects * ;" which I 
 conceive is owing to the natural change of al- 
 burnum into wood not depending on a simple 
 hardening or condensation ; but on such a de- 
 position of ligneous and other particles in its tex- 
 ture, as tends to increase the cohesive attraction 
 of all its parts, and consequently to augment 
 both its hardness and its elasticity ; while the ex- 
 posure of the alburnum, by stripping off the bark, 
 
 * Mirbel, Elemens de Phys. veg, l cfe partie, p. 110. 
 VOL. 1. Z 
 
338 CONSERVATIVE ORGANS. [LECT. VII. 
 
 produces merely a simple condensation of the solid 
 matter, a hurried crystallization of the salts, and 
 a hasty consolidation of the other secretions. In- 
 deed, when wood acquires its firmness by the na- 
 tural means connected with its growth, it is a well- 
 known fact that the hardest is always of the slow- 
 est growth; as exemplified in the comparative 
 hardness of the wood of the Oak, which is of very 
 slow growth, compared with that of the Willow or 
 Horse Chesnut, which are trees of rapid growth ; 
 and even in that of the wood of the same tree 
 when growing in a dry and in a moist situation. 
 
 Much difference of opinion has existed among 
 Phytologists regarding the origin of each suc- 
 cessive layer of wood. Linneus conceived that 
 it is formed from the pith, and added internally ; 
 but the absurdity of this opinion must be imme- 
 diately obvious to any one who examines the trans- 
 verse section of any stem or branch more than 
 two years old. Dr. Hales supposed that it is 
 formed from the zone of the prior year, by the 
 horizontal dilatation of the vessels, and "the 
 " shooting of the longitudinal fibres lengthways, 
 " under the bark, as young fibrous shoots of roots 
 " do in the solid earth * ;" an hypothesis which 
 has had almost as few followers as that of Linneus. 
 Malpighi taught that the liber is annually trans- 
 
 * Vegetable Staticks, p. 340. 
 
LRCT. VII.] ANATOMY OF STEMS. 339 
 
 muted into alburnum * ; an opinion which was af- 
 terwards supposed to be fully established by the 
 experiments of Du Hamel and of Dr. Hope, and 
 is still maintained by Mirbel^. The first ob- 
 ject of Du Hamel was to ascertain whether the 
 new layer of wood was formed by the bark, or by 
 the former layer of wood. He raised a portion of 
 the bark of a growing tree, and introduced under 
 it a piece of tin foil, over which he carefully bound 
 down the bark ; and, after the wound was healed, 
 allowed the tree to remain in the ground for some 
 years. He then cut it down, and found layers of 
 wood on the outside of the tin foil ; but none had 
 been formed between the foil and the wood with 
 which it had been placed in contact ^. This experi- 
 ment, although it was decisive of the fact, that the 
 new layer of wood is not formed by the old layer 
 which preceded it, yet has been justly objected to 
 by Mr. Knight as by no means confirming the opi- 
 nion of Malpighi regarding the transmutation of 
 the liber into wood; and the same objection may be 
 applied to the following experiment of Dr. Hope, 
 detailed by Sir J. E. Smith, on the authority of his 
 son, Dr. Thomas Hope. " A longitudinal incision 
 
 * Anat. Plantarum. 
 
 f " La transformation du liber en aubier est prouvee par 
 " Tobservation microscopique et par 1'experience." Elemens de 
 Phys. veg. p. 106. 
 
 J Phys. de Arbres, 1. iv. c. 7. 
 
 z 2 
 
340 CONSERVATIVE ORGANS. [LECT. VII. 
 
 " several inches in length was made in the bark of 
 " a branch of Willow, three or four years old, and 
 " the bark loosened, so that it might be slipt 
 " aside from the wood in the form of a hollow 
 " cylinder, the two ends being undisturbed. The 
 " edges of the bark were then united as carefully 
 " as possible, the wood covered from the air, and 
 " the whole bound up to secure it from external 
 " injury. After a few years, the branch was cut 
 " through transversely. The cylinder of bark was 
 " found lined with layers of new wood, whose num- 
 " ber, added to those in the wood from which it 
 " had been stripped, made up the number of rings 
 " in the branch above and below the experi- 
 " ment *." But if these experiments do not prove 
 the truth of Malpighi's opinion, they completely 
 disprove the hypothesis of Hales; and throw great 
 light upon the fact, that the alburnum is actually 
 formed from the secretion deposited by the vessels 
 of the liber ; an opinion which has been fully es- 
 tablished by the experiments of Mr. Knight*)-. 
 
 * Introduction to physiological and systematical Botany , 
 chap. iv. 
 
 f It is but justice to say, that although Dr. Hales states it 
 as his opinion that " the new zone of wood is formed by the 
 " shooting of the longitudinal fibres lengthways under the bark, 
 " as young fibrous shoots of roots do in the solid earth ;'* yet 
 that he afterwards remarks, " we may observe that nature has 
 " taken great care to keep the parts between the bark and wood 
 
LECT. VJI.J ANATOMY OF STEMS. 34l 
 
 Before, however, entering into the details of Mr. 
 Knight's doctrine, it will be proper to notice that 
 of Dr. Grew, who conceived that a new ring of 
 sap-vessels is first generated in the mucilage 
 thrown out between the bark and the wood, to 
 which he gave the name of Cambium; and this 
 ring of vessels, lining the inner surface of the 
 liber of the former year, is converted into a new 
 layer of liber that ultimately splits into two por- 
 tions, the outer of which forms the new layer of 
 bark, and the inner the new layer of wood. Not- 
 withstanding the inconsistency of this hypothesis, 
 in supposing that the mere separation of the two 
 portions of the liber could produce, in one of 
 these, a new organization and properties, so dis- 
 tinct as those which the wood possesses from the 
 liber, yet it has been characterized, by a late able 
 writer on vegetable physiology, as " perhaps more 
 " conformable to fact" than any other *. Du 
 Hamel made several experiments to ascertain 
 its truth. He passed threads of fine silver wire 
 through the bark of a tree, some near the outer 
 part, or towards the epidermis; others near 
 the liber, others through the liber itself; and 
 others between the wood and the liber. After 
 
 " always very supple with slimy moisture, from which ductile 
 " matter the woody fibres, vesicles and buds are formed." Ve- 
 getable Staticks, p. 340. 
 * Mr. Keith. 
 
342 CONSERVATIVE ORGANS. [LECT. VII. 
 
 some years, when the tree was cut down, those 
 that were placed towards the epidermis were found 
 covered by a thin, decayed, and friable crust 
 only ; those that were placed near the liber were 
 now among the external cortical layers ; those 
 that were passed through the liber were now im- 
 bedded in the wood ; as were those, also, that had 
 been placed between the wood and the liber *. At 
 first sight this experiment appears perfectly con- 
 clusive of the truth of Grew's opinion ; but, when 
 we consider the probability that the wood and 
 the liber are formed at the same time ; for the vi- 
 tal action which is capable of forming the one is 
 undoubtedly equal to the generation of both ; the 
 difficulty of drawing an accurate inference from 
 such an experiment is obvious : and if our reason- 
 ings must be hypothetical, there is certainly more 
 wisdom in deciding in favour of that conjecture, 
 which explains the effect by simple and direct 
 means, than of that which supposes two causes, 
 the one consequent on the other ; and the second 
 involving a difficulty as great as that which it is 
 intended to explain. 
 
 But the true explanation of the phytological 
 fact under consideration, was reserved for Mr. 
 Knight, whose experiments and observations have 
 settled almost every doubt upon the subject. Mr. 
 Knight could not avoid admitting that the ex- 
 periments of Du Hamel and of Dr. Hope were 
 
 * Physique des Arbres t 1. iv. c. 7. 
 
LECT. VII.] ANATOMY OF STEMS. 343 
 
 sufficiently satisfactory, so far as regarded the 
 fact that the presence of the bark is necessary for 
 the formation of the new zone of wood ; but he 
 denied their conclusions ; and it was still essential 
 to ascertain, whether the wood is transmuted liber ? 
 or, if not, whether the matter of which it is 
 formed be a secretion from the bark, or supplied 
 by some other of the vegetable organs ? That it is 
 not transmuted liber is evident from the dissimi- 
 larity of the liber and the alburnum. Thus, accord- 
 ing to Mr. Knight *, the commencement of the 
 alburnous layers in the Oak is distinguished by a 
 circular row of very large tubes, which appear in 
 spring, arranged in ridges in a gelatinous mass, 
 beneath the cortical vessels ; but such tubes are 
 not found in the bark of the tree, which would be 
 the case were the alburnum a transmutation of the 
 liber. The bark of the Wych Elm (Ulmus monta- 
 na) also is so fibrous and tough that it may be 
 formed into cords, while that of the Ash (Faxinus 
 excelsior) is very fragile and not at all fibrous; ne- 
 vertheless the wood of both these trees> and conse- 
 quently the alburnum, is nearly alike-f-. As con- 
 vincing a proof also is the simple fact, that the 
 layer of alburnum is often more than twice the 
 thickness of the bark. But the question was set- 
 tled by the following experiment of Mr. Knight. 
 
 * Phi Intophical Transactions, 1805. f Ibid. 1808. 
 
 z4 
 
344 CONSERVATIVE ORGANS. [LECT. VII. 
 
 He cut out a ring of bark from the stern of an 
 Apple tree, and another from that of a Crab tree, 
 which were particularly distinguished from each 
 other by the colour of their wood. He then trans- 
 posed these rings, applying and fixing, by means 
 of a firm bandage, the bark of the Crab tree quite 
 round the uncovered part of the stem of the Apple 
 tree, and that of the Apple tree round the stem 
 of the Crab tree. The air was excluded from 
 both by a plaister of bees wax and turpentine, 
 and covered with well-tempered clay. The in^ 
 ner surface of the Crab tree bark had sinuosi- 
 ties that corresponded with elevated parts of the 
 alburnum of the tree from which it was taken, 
 occasioned by the former extension of many 
 branches ; but that of the Apple tree bark was 
 smooth. In a short time a vital union took place 
 between the applied pieces of bark of both trees, 
 and the bark and alburnum of the trees on which 
 they were bound ; and before the end of the ensu- 
 ing autumn "it appeared evident that a layer of 
 " alburnum had been, in every instance, formed 
 " beneath the transposed pieces of bark, which 
 " were then taken off." " Examining," conti- 
 nues Mr. Knight, ".the organization of the albur- 
 " num, which had been generated between the 
 " transposed pieces of bark of the Crab tree, and 
 " which had formed a perfect union with the al- 
 
LECT, VII.] ANATOMY OF STEMS* 345 
 
 " burnum of the Apple tree, I did not discover any 
 " traces of the sinuosities I had noticed ; nor was 
 " the uneven surface of the alburnum of the Crab 
 " tree more changed by the smooth transposed 
 " bark of the Apple tree* The newly generated 
 " alburnum, beneath the transposed bark, ap- 
 " peared perfectly similar to that of other parts of 
 " the stock, and the direction of the fibres and 
 " vessels did not in any degree correspond with 
 " those of the transposed bark *." Nothing, in 
 my opinion, can be more decisive of the ques- 
 tion than this experiment ; for, although Mr. 
 Knight himself modestly suggests that it is not 
 " calculated to prove that the newly generated 
 " bark was not converted into alburnum ;" yet it 
 is not probable that the merely transposing the 
 bark of one tree to another would alter the ori- 
 ginal features of the liber of the transferred por- 
 tion in so short a period as one season, if such a 
 change should even afterwards occur ; of which, 
 however, we have no evidence. The obvious con- 
 clusion therefore to be drawn from this experiment 
 is, that although the alburnum is generated 
 through the medium of the bark, yet, it is deci- 
 dedly not transmuted liber. 
 
 The opinion of Mr. Knight is, that the bark 
 deposits the alburnous matter ; but that the leaves 
 
 * Phil. Trans. 1808, Part I. p. 104-5. 
 3 
 
346 CONSERVATIVE ORGANS. [LKCT. V1L 
 
 are the organs in which this matter is elaborated 
 from the sap ; or, in other words, that the albur- 
 num is generated from the cambium, which is 
 part of the proper juice of the plant, formed by 
 the exposure of the sap to the light and air in the 
 leaf, and returned from it by the vessels that pass 
 down from the leaf into the interior bark, by which 
 it is deposited. To determine this point, he re- 
 moved narrow circles of bark from shoots of Apple 
 trees, " leaving a leaf between the places where 
 " the bark was taken off; and on examining them 
 " frequently during the autumn," he found that 
 the diameter of the shoot between the insertion of 
 the leaf-stalk and the lower incision was as much 
 increased as in any other part of the tree ; but 
 when no leaf was left " on similar portions of in- 
 " sulated bark, on other branches of the same 
 " age, no apparent increase in the size of the wood 
 " was discoverable*." No other inference, than 
 that the leaf is the essential agent in producing 
 the increased diameter of the wood, could be 
 drawn from this experiment: and Mr. Knight 
 further found that where the deposition of the 
 proper juice returned from the leaf is greatest, 
 that is, at the points where the returning vessels 
 enter the inner bark, there the formation of al- 
 burnum is observed to take place in ridges cor- 
 
 * Phil. Trans. 1801, P. I. p. 2, p. 335. 
 
LECT. VII. ] ANATOMY OF STEMS. 347 
 
 responding to the number of the vascular 
 bundles. The fact, indeed, that the leaf is es- 
 sential for the formation of wood, had been ob- 
 served by Dr. Hales, who took off circles of 
 bark half an inch in breadth, at several places, 
 from two thriving shoots of a dwarf Pear tree, 
 leaving on all the remaining intervening ringlets 
 of the bark, except one, a leaf-bearing bud, which 
 produced leaves the following summer. Each 
 ringlet, on which a bud was left, grew and swelled 
 below the bud, or at its lower edge ; but that one 
 on which no bud was left " did not increase at 
 " all * :" but he drew a very different and less pro- 
 bable conclusion from his experiment, which it is 
 unnecessary to mention in this place. 
 
 The above-mentioned experiments of Mr. 
 Knight readily explain why trees and shrubs, 
 the leaves of which are destroyed by caterpil- 
 lars, form scarcely any new wood in that sea- 
 son ; and, indeed, every one who has ever pruned 
 a tree, or shortened a growing twig, must have 
 observed that the part above the last leaf al- 
 ways shrivels and dies, while all below it con- 
 tinues to live and increase in diameter: and we 
 observe the same thing in the lower part of the 
 stem of a young tree, when a portion of the bark 
 has been gnawed off by sheep, or accidentally de- 
 stroyed. The part above the wound continues to 
 
 * Vegetable Staticks> p. 145, fig. 28, 29, 30. 
 
348 CONSERVATIVE ORGANS. [LKCT. VII 
 
 augment in diameter, as represented at a in the 
 marginal cut, because it is supplied 
 by the alburnous matter furnished 
 from the leaves ; but that below it, b, 
 ceases to grow, and continues in the 
 same state, the communication by the 
 interior bark between it and the foli- 
 age being completely destroyed. From 
 the same cause, also, the pith of a 
 stem is thrown apparently out of its 
 centre, for some distance below the 
 point where a branch is given off; a circumstance 
 which I shall very soon have occasion more par- 
 ticularly to notice *. 
 
 The only objection of any weight which has 
 been advanced against Mr. Knight's theory, is 
 founded on the fact, that when a stem is wholly, 
 or in the greater part stripped of its bark, and 
 the denuded surface excluded from the action of 
 the air, a glary fluid is exuded from the albur- 
 num, or soft wood, which gradually becomes or- 
 ganized and cellular. Detached spots of bark 
 are thus reproduced, and, gradually extending, 
 coalesce, until the stem is again clothed with 
 
 * Vide Plate 6, fig. 6. which displays, moderately mag- 
 nified, a longitudinal section of an Elder (Sambucus nigra) of 
 two years growth, with a luxuriant branch of the same age : 
 a. the trunk has the pith c. in the centre, except below the 
 branch b. where the additional wood e. [augments the diameter 
 of the stem on that side, 
 
LECT. VII.] ANATOMY OF STEMS. 349 
 
 a new bark, capable of performing all the func- 
 tions of the original. This fact was first observed 
 by Du Hamel. But Dr. Hope's experiment proves 
 that a similar matter is exuded from the liber, 
 when the bark is detached from the wood ; and 
 Mr. Knight observed that in this case it becomes 
 sooner organized than when it is exuded from al- 
 burnum ; and as we cannot conclude that the new 
 bark is first generated from the former year's al- 
 burnum, and then the new alburnum from this 
 newly formed bark, the only mode of getting over 
 the objection is, by supposing that, under that 
 state of circumstances which as it were obliges 
 the wood to form a new bark, the descending 
 juice from the leaves being impeded in its course 
 downwards through the bark, finds its way into 
 the alburnum in much greater quantity than is 
 required for the ordinary purposes of the plant 
 in that part of its structure ; and the alburnous 
 vessels taking on a retrograde action, it is thrown 
 out in the manner described at different points 
 over the denuded trunk. This opinion is sup- 
 ported by analogy in the animal body, on which, 
 when one organ is destroyed, its function is per- 
 formed by another. We are, therefore, fully war- 
 ranted in adopting Mr. Knight's theory, as far as 
 it maintains that the wood is formed from the 
 proper juice which descends from the leaf through 
 the inner bark ; but, in doing so, there are some 
 
350 CONSERVATIVE ORGANS. [LECT. VII. 
 
 points which have been overlooked by Mr. Knight, 
 and to which it is necessary to direct your at- 
 tention. 
 
 In explaining his theory, Mr. Knight seems to 
 .imply that the whole of the change which the sap 
 undergoes is effected in the leaf, and that the 
 liber is the mere medium of transmission of the 
 alburnous matter. But if, as we must admif is 
 most probable, the whole of the secretions of the 
 plant are produced from the same proper juice 
 elaborated from the sap, by its exposure to light 
 and air in the leaf; and consider the great diver- 
 sity of these ; it is more likely that some altera- 
 tion takes place in the bark, previously to the 
 cambium being thrown out by its vessels ; and, con- 
 sequently, we must admit the force of Mr. Keith's 
 suggestion, that it is " possible the proper juice 
 " may receive its final degree of modification in 
 " the bark itself*." It is by such an admission 
 only that we can satisfactorily explain the fact 
 observed by Mr. Knight in one of his experiments, 
 that a small quantity of wood was generated even 
 at the lower lip of an insulated portion of bark, on 
 which there was neither bud nor leaf -f~. It is also 
 necessary for the sake of those unacquainted with 
 physiological reasonings, to remark that it is not 
 
 * System of physiological Botany -, vol.ii. p. 229. 
 f Phil Trans. 1803. 
 
LECT. VII.] ANATOMY OF STEMS. 35 1 
 
 to be supposed, from the term deposition of albur- 
 nous matter which Mr. Knight employs, that no- 
 thing more is necessary for the formation of the al- 
 burnum than the deposition of that matter. For 
 although alburnous matter may be justly said to be 
 generated from the sap after its elaboration in the 
 leaf, whether we designate it by the term alburnous 
 matter, or cambium, or proper juice, yet it is merely 
 the pabulum ; the organization of the alburnum, 
 or the transmutation of the cambium into its cel- 
 lular and vascular texture, being the result of the 
 vital principle operating upon it, in a manner which 
 we do not understand, and not of any simple coa- 
 gulation, or attraction, or chemical affinity of its 
 parts, in any way similar to what would take place 
 in the same matter, wherever deposited, if de- 
 prived of vitality. The simple fact, therefore, is, 
 that the sap is changed into proper juice in the 
 leaf, and returned into the bark, where part of it 
 being poured out in a gelatinous form between the 
 liber and the wood, there becomes the raw material 
 from which the new zone of wood, in its state of 
 alburnum, and the new layer of liber, are ma- 
 nufactured by the vital principle inherent in the 
 living plant. 
 
 Such is all that is necessary to be known, in 
 the present stage of our investigation into the 
 origin of the annual zones of wood, by which 
 the diameter of ligneous dicotyledonous plants is 
 
352 CONSERVATIVE ORGANS. [LECT. VII. 
 
 augmented. Many important points, indeed, re- 
 lating to the inquiry, and involving other hypo- 
 theses, still remain to be examined ; but these 
 must be deferred until I again bring the question, 
 as it is connected with the general theory of the 
 growth of the vegetable body, under your consi- 
 deration *. The following simple facts, therefore, 
 
 * Although it is unnecessary to load the text with any fur- 
 ther details of the various hypotheses, which have been ad- 
 vanced in explanation of the origin of the annual zones of 
 wood, which increase the diameter of ligneous dicotyledons, 
 yet it may not be improper to give here a slight sketch of that 
 of M. Aubert du Petit Thouars, which has for some years past 
 divided the opinions of the French Botanists. He regards 
 each gem which exists at the axilla of a leaf, as an em- 
 bryon resembling, in some respect, that contained in the seed ; 
 and which, to effect its evolution, draws its nourishment from 
 the succulent parenchyma on the bark on which it is seated, 
 and with which he supposes it to have an immediate communi- 
 cation. As soon as the gem begins to be evolved, it sends 
 down fibres, which our author regards as the roots (veritables 
 racines) of the gem ; and these growing and extending by 
 the organic power (qui, comme I'electricite et la lumiere, 
 semble ne point connoitre de distance), pass down between the 
 wood and the bark from the gem whence they originate to the 
 roots of the tree, taking up, as nutriment (la matiere de leur 
 accroissement), in their passage the viscous fluid, or cambium, 
 which at this season is found between the wood and the bark. 
 The sum of these radical fibres constitutes the new layer of 
 wood, which appears in a concentric circle, owing to the 
 leaves, and consequently the gems, whether they are opposite 
 or alternate, rising on every point of the circumference of the 
 
LECT. VII.] ANATOMY OF STEMS. 353 
 
 relative to the origin and increase of the concen- 
 tric zones of wood, observable in the transverse 
 section of any tree or shrub of more than one 
 year's growth, and which has sprung from a seed 
 
 stem or shoot. In the same manner, he supposes the liber is 
 formed by an equal elongation of the fibres df the interior 
 bark of the gem ; so that each gem has thus a double commu- 
 nication with the root of the tree. The latter part of our au- 
 thor's opinion closely resembles that promulgated by Dr. Dar- 
 win, who supporting the theory of the individuality of buds, 
 thus expresses himself: "The bark is only an intertexture 
 " of the caudexes of the numerous buds, as they pass down 
 " to shoot their radicles into the earth" (Phytologia, 4to. 1800, 
 chap. i. 1, 2. 3) ; but he also so far maintained the opinion of 
 Du Hamel, as to suppose that as these caudexes form a new 
 bark over the former one, that of the last year is transmuted 
 into alburnum. M. Aubert Du Petit-Thouars explains the 
 formation of the medullary rays by supposing that the fibres 
 which, according to his doctrine, constitute the new layers of 
 wood and liber, determine the formation of a certain quantity 
 of parenchyma, which is deposited interiorly by the ligneous 
 fibre, and exteriorly by the fibres that form the new liber. 
 (Essais sur la Vegetation consider ee dans le Developpement des 
 Bourgeons, Paris, 1809, 2 e Essai.) I shall not endeavour to 
 point out the very hypothetical nature of this doctrine ; but 
 merely observe, that, with the exception of the remark that 
 each gem is a distinct embryon, the whole is founded upon 
 assumption ; and that it is utterly destroyed by the simple fact, 
 that isolated spots of bark and alburnum are formed on de- 
 corticated stems, which cannot be the roots descending from 
 the gems, unless we suppose that these have penetrated the 
 wood and again protruded at the points where the new patches 
 of bark and alburnum appear. 
 
 VOL. I. A A 
 
354 CONSERVATIVE ORGANS. [LECT. VII. 
 
 with two or more cotyledons, are to be regarded 
 as fully established : 
 
 1. That the proper juice descending from the 
 leaf through the vessels of the bark, and poured 
 out between it and the wood of the preceding 
 year, is the material from which the new wood or 
 alburnum is formed. 
 
 2. That the organic power, or vital principle, 
 inherent in the plant, transforms this viscous 
 fluid into cells or vessels, or regularly organized 
 alburnum ; the divergent layers being formed at 
 the same time as the vertical or concentric layers. 
 
 3. That under certain circumstances, such as 
 the entire decortication of a stem, the lateral com- 
 munications, which exist throughout the vegetable 
 structure, may conduct the descending juices 
 through the wood, so as to be thrown out in 
 detached spots on its surface ; and there be trans- 
 formed into new bark and alburnum. 
 
 The use of the wood to the plant, exclusive of 
 its power of supporting and elevating the buds 
 with their leaves and fructification in the atmo- 
 sphere, is chiefly confined to its soft or alburnous 
 state. In this state it is endowed with a high 
 degree of irritability. But if it be freely exposed 
 to the atmosphere during a few hours only, all 
 vegetation for ever ceases on that surface ; and, 
 although the bark may close above it, and new 
 wood be formed over it, yet, no vital union 
 
LECT. VII.] ANATOMY OP STEMS. 355 
 
 takes place, and the new wood will always remain 
 distinct*. In this state, also, through its tubes 
 the sap is raised to the summit of the highest 
 trees ; and, according to Mr. Knight, when this 
 function ceases in winter, it becomes " a reservoir 
 " of the sap or blood of the tree, as the bulbs of 
 " the Hyacinth and Tulip, and the tuber of the 
 " Potatoe certainly do of the sap or blood of these 
 " plants ;" an analogy which is good ; but we must 
 remark, in making this admission, that it is not 
 the sap, but the proper juice (succus proprius), 
 which is there laid up, and is dissolved by the 
 first ascending sap in the spring. 
 
 The alburnum does not attain its entire thick- 
 ness at once ; but continues to increase during 
 the greater part of the summer, at least till after 
 the midsummer shoots are protruded ; and even, 
 if circumstances occur to stop its progress, such 
 for example as a week of very cold weather 
 in the middle of the season, two layers may be 
 formed in the same year ; an event not unlikely to 
 happen in this variable climate, and which throws 
 an uncertainty on the mode, which has been al- 
 ready alluded to, of determining the age of trees 
 by counting the number of the concentric zones of 
 
 * In this new wood the divergent rays are distinctly seen ; 
 a sufficient reason, as Mr. Knight remarks, for believing that 
 they are not processes of the pith. 
 
 AA2 
 
356 CONSERVATIVE ORGANS. [LKCT. VII. 
 
 wood displayed in the transverse section of a stem. 
 As the alburnum changes into wood it loses its 
 irritability; but an unexceptionable theory of the 
 means by which this change is effected, is still a 
 desideratum in vegetable physiology. The opinion 
 that the lignification is the consequence of the 
 mere loss of fluid parts, and the approximation of 
 the solid, cannot be admitted as correct; because, 
 in this case, the drying of the alburnum even after a 
 tree is cut down, would give it the consistence and 
 characteristics of perfect wood, which is not the 
 fact. I am inclined to believe, that the ligneous 
 matter is deposited in a manner somewhat ana- 
 logous to the deposition of the phosphate of lime 
 in bones ; and that this deposition continues to be 
 effected long after the alburnum assumes the cha- 
 racter of wood. The heart wood, even of an old 
 tree which is sound, contains some moisture as 
 long as the tree continues to grow, which can only 
 be accounted for by supposing that it still lives *, 
 and, consequently, is in some degree under the 
 control of the organic power ; and, as a lateral 
 communication is preserved between the exterior 
 and the interior of the stem by means of the diver- 
 gent rays, there is no improbability in supposing 
 that a sufficient supply of proper juice finds its 
 
 * Darwin (Phytologia, xviii. 2, 12.) asserts that the 
 heart or internal wood is not alive ; but this is not the case, for 
 the whole is alive whilst the tree remains sound. 
 
LECT. VII.] ANATOMY OF STEMS. 357 
 
 way to the innermost layer of wood, until that 
 has received its final degree of induration. I know 
 of no observations which tend to prove that the 
 concentric zones are diminished in thickness as 
 they increase in solidity and density, which would 
 be the case, did they shrink or suffer any com- 
 pression ; and if it be true that no such change 
 takes place, their progressive induration can be 
 explained only by admitting that there is a con- 
 tinual deposition of new matter. The truth of 
 such an opinion is further confirmed by the change 
 of colour, which the alburnum undergoes in pass- 
 ing into the state of perfect wood. With regard 
 to the period at which the wood attains its final 
 degree of induration, I would say> with Mr. 
 Keith, that perhaps no layer has acquired this 
 state until " such time as the tree has arrived at 
 " its full growth*." 
 
 Returning to our shoot of Horse Chesnut, if 
 we scoop out the pith from the ligneous cylinder 
 that encloses it, we perceive this is lined with a 
 thin green layer or coating; which, to the un- 
 assisted eye, appears to resemble in its structure 
 rather the cellular integument of the bark than 
 any part of the surrounding wood. This is the 
 MEDULLARY SHEATH (etui mtfdullaire) of Mirbel 
 and the French Botanists : for, although it was 
 
 * System of physiological Botany , vol. ii. p. 230. 
 AA3 
 
358 CONSERVATIVE ORGANS. [LECT. VII* 
 
 first noticed by Dr. Hill, who named it Corona, 
 yet, it has been overlooked or confounded with 
 the wood, or the alburnum, by almost every suc- 
 ceeding British Phytologist, until Mr. Knight's at- 
 tention was directed to it in searching for his cen- 
 tral vessels. It is readily distinguished, in either a 
 transverse or a longitudinal section of many stems, 
 by its green colour, which appears deeper as con- 
 trasted with the dead white, the more usual hue of 
 the pith which it surrounds ; but it is also easily 
 traced in the succulent dicotyledonous stem as 
 soon as it is evolved from the seed, separating the 
 pith from its herbaceous investiture. 
 
 When viewed under the microscope the me- 
 dullary sheath appears to be composed of a cel- 
 lular substance, in which are imbedded longi- 
 tudinal layers of spiral tubes *. It is not easy 
 to comprehend the meaning of Mr. Knight, when 
 he speaks of another description of vessels as 
 being found here, to which he says " the spiral 
 " vessels are every where appendages," and which 
 he names central vessels, " to distinguish them 
 " from the spiral tubes and the common tubes of 
 " the wood-f~." In the stems which I have exa- 
 
 * Vide Plate 6, fig. 7. in which the space from d. to e. re- 
 presents the appearance of the medullary sheath in a longitudi- 
 nal section of an annual twig of Horse Chesnut ; 7. 7. 7. the 
 bundles of spiral vessels ; and 8. the parenchyma, or green cel- 
 lular lining of the sheath. 
 
 f Phil. Trans. 1801. 
 
LBCT. VII.] ANATOiMY OF STEMS. 359 
 
 mined, the spiral vessels are seen in some instances 
 detached, or not immediately accompanied by any 
 other description of vessels, and in others they are 
 accompanied by either cribriform or annular ves- 
 sels according as the one or other of these are the 
 common vessels of the alburnum and wood. Thus, 
 in longitudinal and in tangental sections of the 
 medullary sheath of the Horse Chesnut, the spi- 
 ral vessels are accompanied with the cribriform 
 vessels only of the wood ; and such is, also, the 
 case in the Elder (Sambucus nigra), and in the 
 Lilac (Syringa vulgaris). In the Elastic-gum Fig 
 tree (Ficus elastica), the sheath of which is not dis- 
 tinguishable by colour, the spiral vessels are seen 
 close to that part of the first year ! s wood, which 
 touches the pith, and consequently in the situation 
 of the sheath ; but they are not immediately ac- 
 companied by any other vessels : those nearest to 
 them, however, are cribriform, like the larger 
 vessels of the wood. In the Medlar (Mespilus), 
 in which there is, likewise, no evident medullary 
 sheath, the spiral tubes, which are very numerous, 
 are accompanied by the common vessels only of 
 the alburnum : and in the Cinnamon (Laurus 
 Cinnamomi) the accompanying vessels are annular, 
 such being the vessels of the alburnum and the 
 wood. The cells of the medullary sheath (Plate 
 6, fig. 7, d. e. 8.) are narrow and oblong ; and, 
 therefore, when it is not coloured it is scarcely 
 
 A A4 
 
360 CONSERVATIVE ORGANS. [LECT. VII. 
 
 distinguishable from the wood, except by the spi- 
 ral vessels ; which have not yet been discovered 
 in any layer of formed wood subsequent to the 
 first; for their apparent existence in stems and 
 branches of several years' growth, is owing to 
 the lignification of the medullary sheath. Grew 
 and Hedwig, however, have represented them as 
 existing in the wood ; but, although I have 
 searched for them in every species of wood, yet 
 I have not been able to detect them ; and as the 
 same result has followed the investigations of Du 
 Hamel, Mirbel, Knight, Mr. Keith, and others, I 
 am inclined to regard my conclusion as correct. 
 The cells which are between the layer of spiral 
 vessels and the pith (Plate 6, fig. 7, d. e. 8.) ; and 
 which are the site of the colouring matter, when 
 this part of the stem is green, as it is in the 
 example now before us, have a cribriform struc- 
 ture. 
 
 The spiral vessels of the medullary sheath vary 
 in their arrangement, and thus the widely separated 
 bundles they form in the Elder, give the canal of 
 the pith a furrowed character; in the Pear tree their 
 arrangement produces an irregular pentagon ; and 
 this is, also, the case in the Oak ; while in Laurel- 
 leaved Magnolia, M. grandiflora, the bundles are 
 seen at the distance of four or five diameters from 
 each other^ and projecting forwards, so as to seem 
 imbedded as it were in the pith. But, whatever 
 
LECT. VIJ.] ANATOMY OF STEMS. 361 
 
 may be the arrangement, it appears to be in a 
 great degree regulated by the disposition of the 
 leaves, into which the spiral vessels in every in- 
 stance direct their course, leaving for that pur- 
 pose the medullary sheath, and traversing the 
 wood, a little below the insertion of each leaf. 
 
 As the medullary sheath forms the only parti- 
 tion between the bark and the pith in the tender 
 succulent shoot, before the ligneous matter is de- 
 posited, and is in its texture lax, and incapable of 
 affording sufficient support to the delicate coats 
 of vessels, such as are found in the alburnum, if 
 these were distended with ascending sap, the 
 vessels that run through it are of a different 
 structure from those of any other part of the ve- 
 getable. The elastic thread of which these spiral 
 vessels are formed is tough, and possesses irrita- 
 bility ; and being stimulated to action by the effort 
 of the sap to dilate the diameter of the vessel, 
 contracts in its length in each coil alternately, and 
 after each contraction again returns to its first 
 state, producing a vermicular motion, which 
 enables these vessels to conduct forward the sap. 
 Thus : the contraction in length of the portion of 
 the thread which forms the first coi}, lessens the 
 diameter of that portion of the tube, and hence the 
 fluid contained within in it will be displaced and 
 moved either upwards or downwards ; but as the 
 resistance opposed to its return, or movement 
 
362 CONSERVATIVE ORGANS. [LBCT. VII. 
 
 downwards, is the greater owing to the pressure 
 of the ascending sap, it must necessarily advance ; 
 and this contraction being repeated in every suc- 
 cessive coil, the fluid is moved forward with a suf- 
 ficient impetus ; while the new quantity of sap 
 which supplies the place of that carried forward, 
 and which rushes into the coil at the instant of its 
 relaxation, forming the basis of resistance to the 
 return of the portion before it, and at the same 
 time exciting a renewal of the contraction, its pro- 
 gression must be uninterrupted. I should be an- 
 ticipating what I have to say on the general ascent 
 of the sap (or, as it has been erroneously termed, 
 its circulation), were I now to explain the means 
 by which this fluid is raised through the ligneous 
 parts of a tree, until it arrives at the succulent 
 twigs, in which alone the spiral vessels are active ; 
 and it is, therefore, here merely necessary to add, 
 that I believe these to be the only vegetable vessels 
 endowed with contractility, or which act in any 
 manner analogous to the arteries of animals. If 
 this hypothesis be maintainable, the spiral vessels 
 are the sap vessels of the succulent stem and the an- 
 nual shoot of dicotyledonous ligneous plants ; and 
 their spiral structure is essential for the performance 
 of their conducting function, in the spongy medul- 
 lary sheath, or cellular parenchyma in which they 
 are imbedded. How long they continue to act as 
 sap vessels it is impossible to conjecture ; but they 
 
LKCT. VII.] ANATOMY OF STEMS. 363 
 
 may maintain their irritability, and consequently 
 their contractility, for two or more seasons, or as 
 long as the medullary sheath remains succulent ; 
 although, as it is not necessary for the progression 
 of the sap that they should act by alternate con- 
 traction and dilatation, after the alburnous or lig- 
 neous vessels are completed, it is probable that 
 they lose these properties, after the first year of 
 the life of the stem or of the twig. 
 
 If we inquire what are the opinions of other 
 phytologists respecting the functions of the spiral 
 vessels, we find Malpighi regarding them as bron- 
 chia, or air-vessels *, and the same opinion is 
 supported by Grew*f~, Hales |, and Du Hamel. 
 Grew, however, believed that they acted as sap- 
 vessels in the wood ||, in which, as I have already 
 stated, he fancied he had detected them ; and Du 
 Hamel once suspected that they might contain 
 highly rarefied sap. The supposition that they are 
 air-vessels, probably originated from their always 
 appearing empty when examined ; but on the same 
 account the animal arteries were regarded as air- 
 vessels by the ancients and their followers, until 
 
 * Anal. Plantarum. 
 f Anatomy of Plants, fol. edit. 
 \ Vegetable Statics, chap. v. 
 Physique des Arbres. 
 
 || His words are, " in the wood the sap ascendeth only by 
 4< the air-vessels." Veg. of Trunks, chap. i. 
 
364 CONSERVATIVE ORGANS. [LECT. VII. 
 
 the discoveries of the immortal Harvey demon- 
 strated them to be blood-vessels. The opinion 
 that they contain air only, is still maintained by 
 Mr. Knight, who supposes them to be appendages 
 to another set of vessels, which he denominates 
 central, and through which he supposes the sap 
 ascends as soon as it arrives at the bud or suc- 
 culent shoot, " aided by the spiral vessels *." 
 I have however demonstrated to you that the 
 spiral vessels are unaccompanied by any others, 
 at least in all those trees which I have examined, 
 and are even at some distance from the alburnous 
 vessels in the annual shoot of many plants. 
 Mr. Knight, it is true, in another essay-}-, en- 
 deavours to explain the meaning of his term cen- 
 tral Vessels, by saying that they are the same 
 as the tubular tissue of M. Mirbel ; but, as the 
 spiral vessels form part of Mirbel's tubular tissue, 
 which besides comprehends all the other species 
 of vegetable vessels, this attempt at explanation 
 only renders the subject more confused. Mr. 
 Keith, in criticising Mr. Knight's explanation, has 
 fallen into a curious mistake regarding Mirbel's 
 opinion of the vessels which carry the sap. He 
 says, " If we regard their (the central vessels) re- 
 " spective functions, they can correspond only to 
 " the small tubes, as it is by them alone, accord- 
 
 * Phil. Trans. 1801. f Ibid. 1807. 
 
LECT. VII.] ANATOMY OF STEMS. 365 
 
 4 
 
 " ing to M. Mirbel, that the sap ascends." (Syst. 
 of phys. Bot. vol. ii. p. 119.) Now, Mirbel's 
 words are, " la seve monte par les gros vaisseaux." 
 (EUmens, t. i. p. 208.) The cells of the medul- 
 lary sheath are, indeed, oblong", and, therefore, 
 somewhat tubular, and to these probably Mr. 
 Knight refers ; but, admitting this, we cannot see 
 in what manner the ascent of the sap through 
 these cells can be aided by the spiral vessels, the 
 bundles of which are, in many instances, placed 
 at the distance of three or four diameters from 
 each other, and consequently the intermediate 
 cells are beyond the sphere of their influence. Mr. 
 Knight's opinions on this subject have certainly 
 much less weight than they usually and most de- 
 servedly possess. 
 
 Grew, as I have already stated, first suggested 
 the idea of the spiral vessels acting as sap vessels, 
 and Du Hamel supposed he had detected them in 
 the performance of this function. Hedwig * also 
 asserts, that he observed the sap issuing from the 
 orifices of the spiral vessels in a horizontal section 
 of the stem of the Pumpkin, Cucurbita Pepo, and 
 the squirting Cucumber, Momordica Elaterium ; 
 and Senebier ^, more lately, remarked the same 
 occurrence in a section of the stem of the Sago 
 
 * Fundamentum Hist. Nat. Muscorwn Jrondosoruntj Lip. 
 1732, p. 55. 
 
 f Phys. veg. t. i. p. 107. 
 
 4 
 
366 CONSERVATIVE ORGANS. [LKCT. VII. 
 
 Palm, Sagusfarinifera. Dr. Darwin may perhaps, 
 however, be regarded as actually the first who 
 taught that the spiral vessels convey fluids ; and 
 he suggested the idea, which, with some modifi- 
 cations, I have adopted, of the manner in which 
 they carry forward their contents. " It is easy," 
 says he, " to conceive how a vermicular or peri- 
 " staltic motion of the vessel, beginning at the low- 
 " est part of it, each spiral ring contracting it- 
 " self, till it Jills up the tube, must forcibly push 
 " forward its contents without the aid of valves *." 
 He, however, considered them absorbent vessels ; 
 and erroneously supposed that they pass down the 
 trunks of trees from the caudex of each bud, to 
 the roots. Finally, Mirbel-j- regards the spiral 
 vessels as sap vessels ; whilst Mr. Keith considers 
 the reformed opinion of Grew the most correct, 
 namely, that they transmit not only air but sap \. 
 c. The MEDULLA or PITH. Returning to our 
 shoot of Horse Chesnut, we find the tube which 
 is formed by the wood and lined with the medul- 
 lary sheath, as has been already described, filled 
 with a white, dry, very compressible, spongy sub- 
 stance : this is the Medulla or Pith. In the suc- 
 culent state of a stem or a twig, it is turgid with 
 aqueous fluid ; but before the wood is perfected it 
 
 *Phytologia, sect. 11, 8. 
 
 t Eltmens de Phys. veg. l ere partie, p. 205. 
 
 J System of phys. Botany, vol. ii. p. 120. 
 
LKCT. VII.] ANATOMY OF STEMS. 367 
 
 becomes dry and spongy ; except near the termi- 
 nal bud, or where branches are given off, in which 
 places it long retains its moisture. 
 
 The form of the pith is regulated by that of the 
 cavity it fills, which in the majority of instances 
 is nearly circular ; but to this there are many ex- 
 ceptions. Thus, in a horizontal section of a young 
 stem or twig of the Elder, Sambucus nigra, and 
 the Oriental Plane, Platanus orientate, we find 
 it circular, but furrowed by the bundles of spiral 
 vessels of the medullary sheath. It is oval in the 
 Ivy, Hedera Helix, and the Ash, Fraxinus ex- 
 celsior ; irregularly oval and furrowed in the Ori- 
 ental Plane, Platanus orientalis ; triangular in 
 the Oleander, Nerium Oleander; pentangular in 
 the Oak, Quercus Robur ; four-sided, with the 
 angles obtuse or tetragonal, in common Lilac, Sy- 
 ringa vulgaris, and yellow flowering Horse Ches- 
 nut, ^Esculus flava ; pentagonal in the Walnut, 
 Juglans regia, and hexagonal in the common Dog- 
 wood, Cornus sanguined. M. de Beauvois is of 
 opinion that the situation of the leaves on the 
 stem regulates the form of the tube which the 
 pith fills, an opinion which M. Mirbel * regards as 
 fallacious ; but it is nevertheless true, that in 
 the horizontal section of many stems, the form of 
 the medulla differs at, and immediately under the 
 
 * Etemens de Phys. v(g. 1 partie, p. 111. 
 
368 CONSERVATIVE ORGANS. [LRCT. VII. 
 
 places where the leaves are seated, from what it 
 is in the intermediate spaces. In the Lilac, for 
 example, the obtuse tetragon becomes an ellipsis 
 near the insertions of the leaves, which are op- 
 posite; while each angle of the Oleander is length- 
 ened into a horn or process. But besides these 
 diversities of form, the pith varies in diameter 
 in other respects. In the young tree, of a few 
 inches in height, it is smallest at the basis of the 
 stem, largest in the middle, and smaller again 
 at the summit ; and in the growth of each future 
 year, nearly the same variations in its diameter 
 are observable. 
 
 The pith, in the majority of ligneous dicotly- 
 ledons, is longitudinally entire; but in some, 
 the Walnut for instance, it consists of a succes- 
 sion of transverse diaphragms intersecting the 
 hollow cylinder of the wood, with the interven- 
 ing spaces empty *. In others the continuity of 
 the medullary column is broken by ligneous plates, 
 which proceeding from the side of the central 
 tube, either partially intersect it or completely 
 partition off portions of it, as in several of the 
 Magnolias ; while in others, again, it is merely a 
 spongy sheath, lining the interior of the cavity, 
 as in the stem and branches of Woodbine, Loni- 
 cera Periclymenum. Where the branches are 
 
 *Vide Plate6, fig. 11. 
 
LECT. VII.] ANATOMY OF STEMS. 369 
 
 given off from a stem, a thread of medulla, in 
 some instances, separates from the central column, 
 and entering the branch, is gradually augmented 
 to a diameter proportionate to that of the 
 branch *. Such a circumstance led M. Aubert Du 
 Petit-Thouars f to describe the medulla at the base 
 of every bud, as an inverted cone, the apex of 
 which originates from the pith of the branch on 
 which the bud appears ; but in general this is not 
 the case, the pith commencing in the bud itself, 
 which originates at the surface of the stem ; 
 and hence no direct union exists between the 
 pith of the branch and that of the stem 
 (see marginal figure). In the annual 
 shoot, the wood shuts up the canal of the 
 pith at its extremity, as soon as it ceases 
 to grow for the season, as is seen in the 
 longitudinal section of our shoot of Horse Ches- 
 nut, immediately under the terminal budj; and 
 thus isolates it from the shoot of the next year. In 
 many plants this forms a kind of woody partition, 
 which marks the limit of the growth of each year 
 in the length of the stem ; but in others it is ab- 
 sorbed, the continuity of the pith being, appa- 
 
 * Vide Plate 6, fig. 6. representing a cutting of the common 
 Elder; in which d. the pith of the branch b. is united by a 
 small thread to e. the pith of the main stem a. 
 
 f Histoire d'un Morceau de Bois, p. 153. 
 
 t Vide Plate 5, fig. 15. 
 
 VOL. I. B B 
 
370 CONSERVATIVE ORGANS. [LECT. VII. 
 
 rently, uninterrupted from the root to the apex of 
 such stems. Those partitions are almost always 
 present when the pith is composed of distinct 
 plates, as in the Walnut, or of a spongy sheathing 
 membrane, as in Woodbine. 
 
 The colour of the pith, in the succulent shoot 
 or in the young plant, is green, which, as the cells 
 empty, changes to white; but to this there are 
 some exceptions. Thus it is yellow in the Bar- 
 berry, Berberis vulgaris ; pale brown in the Wal- 
 nut, Juglans regia ; fawn-coloured in the Sumach, 
 Rhus Coriaria ; and pale orange in yellow-flow- 
 ered Horse Chesnut, yEsculus flava; but it is 
 more frequently coloured in the caudex of the root 
 than in the stem. 
 
 Placing a thin slice of pith, taken either from 
 a vertical or a horizontal section of our shoot of 
 Horse Chesnut, or of any other plant, under the 
 microscope, it appears to consist of hexagonal 
 cells *, which are larger and more regular in the 
 centre than near the circumference -j~. In very 
 young stems and succulent shoots, these cells are 
 filled with an aqueous fluid, and closely resemble 
 the cellular integument % ; but, in older stems and 
 twigs, they are found empty, or, more accurately 
 
 * The cellular structure of the pith was first pointed out by 
 Grew in his work on the Anatomy of Plants, fol. 1682. 
 t Vide Plate 6, fig. 2, k. 
 J Vide Plate 6, fig. 2, c. 
 
LECT. VfJ.J ANATOMY OF STEMS. 371 
 
 speaking, filled with air. The cells retain the hex- 
 agonal form in their empty state ; but in some, as 
 the Walnut, this is destroyed in the lamellae, into 
 which the pith then separates; and the same oc- 
 curs in the interior of the medullary sheath of 
 Woodbine, and similar hollow stems. In the' 
 greater number of plants no vessels are percep- 
 tible in the pith ; but in some, entire vessels con- 
 veying proper juice are present, as in the Gum- 
 elastic Fig tree, the proper juice of which is seen 
 exuding from different points of the pith in a hori- 
 zontal section of the stem : and, in all plants, the 
 cells communicate with each other by means of or- 
 ganized pores, which are visible under the mi- 
 croscope. M. Aubert Du Petit-Thouars has lately 
 affected to regard the medulla as deserving that 
 name only after the cells become empty, naming it 
 parenchyma in the early or succulent stage of its 
 existence * : but this is at best a useless refinement ; 
 for, although I am not prepared to admit, with Mr. 
 Keith -f-, that there is an essential difference be- 
 tween the membrane composing the cells of the 
 parenchyma or pulp, and that forming those of the 
 pith, yet the insulated and enclosed situation of 
 the pith is sufficient to obtain for it the dignity of 
 
 * " Ce n'est que par 1'extraction des sues qu'elle (la Mo- 
 " elle) contient qu'elle est devenue Moelle." Essais stir la 
 Vegetation, p. 205. 
 
 f System of phys. Bot. vol. i. p. 324. 
 B B 2 
 
372 CONSERVATIVE ORGANS. [LECT. VII. 
 
 being a distinct organ in every stage of its ex- 
 istence. 
 
 To enter at present upon the explanation of 
 the formation of the pith, would be anticipating 
 our inquiries into the general theory of vegetation, 
 a part of our subject for the discussion of which 
 we are not yet fully prepared. Regarding, how- 
 ever, the mere mechanical causes which possibly 
 operate in producing the hexagonal form of the 
 cells, I may remark that, if the ,gelatinons pulp, 
 which constitutes the earliest state of the pith, as- 
 sumes the form of globules as the first effect which 
 the operation of the vital organizing influence pro- 
 duces on it ; it is easy to conceive that, from the 
 individual inflation of these occasioning them to 
 press in every direction upon one another, within a 
 certain limit, each globule will necessarily acquire 
 an hexagonal form. In this state the flat surfaces 
 of the enclosing membrane of each globule which 
 are in immediate contact, uniting and acquiring 
 firmness, while the contained fluid is dissipated 
 and air admitted, the cavity it occupied will re- 
 main as an hexagonal cell ; and of such is the dry 
 pith constituted. To produce this effect, how- 
 ever, the following circumstances are necessary: 
 1. The membrane which divides each cell from 
 those adjoining it, must be double, which Link * 
 
 * Secunda Dissert, in Homer's Collect. Bot. fascic. i. p. 163. 
 
LECT. VII.] ANATOMY OF STEMS. 373 
 
 and Kieser * have demonstrated to be the case-f-. 
 2. This membrane must be cribriform, such as I 
 have described it, when seen under the microscope, 
 to permit the aqueous fluid to pass readily through 
 it, and to admit the air into the cells to supply its 
 place. But it is necessary to remark here, that 
 this fact, although supported by the observations 
 of Sprengel, Mirbel, and others, is positively de- 
 nied both by Link and Kieser ; but, as it was re- 
 quisite for those who denied the porosity of the 
 membrane to state how fluids can be transmitted 
 from one cell to another, Link has advanced the 
 unphilosophical suggestion, that this is effected by 
 a double filtration through invisible pores: and 
 the ingenious Mr. Ellis, who gives credit to Kieser's 
 observations, is forced to admit that this filtration 
 can be accomplished, " consistently with the in- 
 " tegrity of the cellular texture, only by the ex- 
 " ercise of the alternate functions of secretion and 
 " absorption J." 3. The mass must be free from 
 any external pressure, which would, eventually, 
 destroy the regular form of the cell. 
 
 It is not easy to conjecture by what means 
 
 * Mem. sur I' Organization des Plantes, p. 91. 
 
 f We may also regard as an analogical proof a fact lately 
 ascertained by Dr. Barclay, that each side of every cell in the 
 honeycomb is double, or composed of two plates of wax. Vide 
 Wernerian Trans, vol. ii. 
 
 J Supplement to the Encyclop. Brit. vol. i. Part 2. 
 BB3 
 
374 CONSERVATIVE ORGANS. [jLECT. VII. 
 
 air is introduced into hollow ligneous stems ; but, 
 probably, in those in which the pith is sheathing, 
 as in the Woodbine, the union between the utricles 
 may be less intimate in the centre, and the air 
 insinuating itself between them, while the cells 
 are emptying themselves, compresses their sides 
 together and separates them ; and extending itself 
 in the length of the stem, forms it into a hollow 
 tube. In others, as the Walnut, it may be intro- 
 duced laterally, in separate quantities, at dif- 
 ferent points at the same time, and these dilating, 
 compress the horizontal portions of the emptying 
 cells between them, so as to produce the medul- 
 lary plates, which characterize that and similar 
 stems. 
 
 Phytologists have not differed more on any 
 subject than in assigning the functions of the pith. 
 When we reflect that Caesalpinus, who lived in 
 the sixteenth century, taught that the pith is less 
 essential to the life and growth of a tree than 
 the bark *, it is astonishing that writers of so re- 
 cent a period as Dr. Darwin and Sir J. E. Smith, 
 should be found maintaining the accuracy of the 
 ancient opinion, that the pith is to the vegetable 
 what the brain and spinal marrow are to the 
 animal body-}-. Darwin's imagination led him 
 
 * De Plantis. Flor. 1583. 
 
 f Such was also the opinion of Linnaeus, Amcen. dead. 
 vol. iv. p. 372. 
 
LBCT. VI 1.] ANATOMY OF STEMS. 375 
 
 even so far as to believe that it furnishes "the 
 " power of motion, as well as of sensation to the 
 " various parts of the vegetable system *." Hales 
 and Linnaeus also regarded it as the seat of the 
 vital energy of the plant -f~ ; and Mr. Lindsay, of 
 Jamaica, " thought he demonstrated the medulla 
 " in the leaf-stalk of the Mimosa puclica, or Sen- 
 " sitive Plant, to be the seat of irritability ;" nor 
 " can I," says Sir J. E. Smith, " see any thing 
 " to invalidate the opinion J." It would, never- 
 theless, be no difficult task to prove the unte- 
 nable nature of these doctrines, were they not com- 
 pletely destroyed by the experiment of Mr. Knight, 
 who abstracted more than an inch of the pith from 
 the shoot of a vine, above and below a leaf and 
 bud ; both of which, " with the lateral shoot an- 
 " nexed, continued to live, and did not appear to 
 " suffer much inconvenience ; but faded a little 
 " when the sun shone strongly upon them ." Now 
 the life of the shoot, even admitting with Darwin, 
 for the sake of argument, that each bud has a sen- 
 
 * Phytologia, xviii. 2, 13. 
 
 f Linnaeus, like Darwin, compared it to the spinal marrow. 
 
 J Introd. to phys. and syst. Bot. chap. vii. 
 
 Phil. Trans. 1801, p. 338. 
 
 Mr. Keith gives a quotation from Theophrastus to show 
 " that this experiment had been performed, and the result as- 
 " certained," even in the time of that naturalist. System of 
 phys. Bot. vol. ii. p. 211. 
 
 B B 4 
 
376 CONSERVATIVE ORGANS. [LECT. VII. 
 
 sorium of its own ||, could not be supported un- 
 der such a circumstance, did any analogy exist 
 between the medulla of plants and the spinal 
 marrow of animals. Grew and Malpighi believed 
 that the functions <jf the pith are the same as those 
 of the cellular integument, which they regarded 
 as the organ for elaborating the sap into nourish- 
 ment for the support of the plant, and to give 
 origin to future buds; an opinion which Mr. 
 Keith regards as the best founded of any yet ad- 
 vanced, with the exception of that part of it 
 which relates to the origin of buds. Du Hamel, on 
 the contrary, considered the pith in common with 
 the general cellular texture, as merely intended to 
 hold together the various parts of the plant ; and 
 lastly, Mr. Knight has supposed that " it forms a 
 66 reservoir to supply the leaf with moisture, when- 
 " ever an excess of perspiration puts that in a 
 " state to require it ;." There is certainly much 
 plausibility in Mr. Knight's suggestion ; and it is 
 not, in my opinion, destroyed, as has been sup- 
 
 || " The pith,'' says Darwin, " communicates to the leaves 
 " on each side of it, but not to the new buds in the bosoms of 
 " those leaves ; because those new buds are each an indi- 
 " vidual being, generated by the caudex of the leaf, and must, 
 " therefore, possess a sensorium of its own.'* Phytologia, 
 xviii. 2, 13. 
 
 | Phil. Trans. 1803, p. 349. A similar opinion is advanced 
 by Plenck, in his Physiologia Plantarum. 
 
LKCT. VII.] ANATOMY OF STEMS. 377 
 
 posed, by the remark of Sir J. E. Smith, that 
 " all the moisture in the medulla of a whole 
 " branch is, in some cases, too little to supply 
 " one hour's perspiration of a single leaf * ;" for 
 Mr. Knight could never mean to assert that the 
 fluid in the medulla is intended to supply the 
 entire loss of moisture from perspiration in the 
 leaf, although it might make up the excess. But 
 a more tenable objection to this hypothesis may 
 be deduced from the fact, that the succulent twig 
 perspires nearly as much as the leaves themselves ; 
 droops also, like them, from an excess of perspira- 
 tion in sultry weather ; and is again, in the same 
 manner, revived by the check given to that excess 
 in the night, or by a fresh supply of moisture to 
 the roots. What then, it may be asked, is the use 
 of the pith ? 
 
 In answering the above question, I may re- 
 mark, that as it is more easy to discover the de- 
 fects of an hypothesis, than to suggest one ; and 
 as none is so unlikely to discover the errors of a 
 new opinion, as its proposer, it is very probable 
 that that which I am about to hazard on this sub- 
 ject, may be found as defective as any of those 
 we have criticised. 
 
 * Introd. to phys. and syst. Bot. p. 41. Mr. Keith con- 
 curs in the objections of Sir J. E. Smith, regarding them as 
 " fatal to Mr. Knight's hypothesis.*' Syst. of phys. Bot. vol. 
 ii. p. 21. 
 
378 CONSERVATIVE ORGANS. [_LECT. VI t. 
 
 If we examine a tree in the first stage of its 
 growth, or a fresh shoot, we shall be satisfied 
 that the alburnum and bark form so very small 
 a portion of their diameter, that, were there not 
 some means of extending the surface of these 
 parts, there would be neither sufficient space for 
 the formation and arrangement of the vessels 
 essential to their future existence ; nor a suf- 
 ficient support to maintain the plant in its erect 
 position, or the shoot in its projection. To supply 
 these purposes the pith is given to young plants 
 and shoots ; for, its cells being filled with an 
 aqueous incompressible fluid, both extension and 
 support are thus afforded by it, as long as these 
 are required, or until the first ligneous zone is fit 
 to allow the next zone of alburnum to be formed 
 on it, and consistent enough to afford sufficient 
 stability to the plant. When this takes place, the 
 moisture passes from one cell to another until it is 
 altogether carried off, leaving the pith in the dry 
 spongy state in which it is found in the older stems 
 and branches. The comparative diameter of these 
 stems and branches depends equally on the evo- 
 lution of the pith ; for, in moist seasons, when these 
 push out thicker and more vigorous than usual, 
 we find their mass consist chiefly of pith ; and the 
 ligneous circle, although much widened, yet, not 
 containing a proportionate increase of substance. 
 In such shoots also we have another proof that 
 it is the turgidity of the medullary cells with 
 
LECT. VII.] ANATOMY OF STEMS. 379 
 
 aqueous fluid, which gives them firmness, and 
 enables them to rise to the great height to which 
 they often attain in so short a period, without 
 any curvature; for, on examining the pith, the 
 cells are found not more numerous, but merely 
 larger than in an ordinary shoot. As soon, how- 
 ever, as the first circle of wood is formed, no sub- 
 sequent increase of diameter can be attributed to 
 the pith. If these remarks be correct, the follow- 
 ing must be regarded as the functions of the 
 pith: 1st, to afford the surface necessary for the 
 formation of the first layer of wood ; and 2d, to 
 give a degree of firmness to the succulent stem 
 and recent shoot, which they would not other- 
 wise possess, before the bark and alburnum ac- 
 quire sufficient consistence for that purpose. 
 
 But is the pith of use only in the succulent 
 shoot ? If my idea of its functions be correct, its 
 utility to the plant must cease as soon as the first 
 circle of wood is perfected ; and it is indeed not 
 easy to conceive in what manner it can be useful 
 after it has become dry. Mr. Keith remarks, " it 
 " is essential to vegetation in all its stages * ;" but 
 even admitting that it is, as he and Malpighi be- 
 lieve, an organ of elaboration, we must suppose 
 that all vegetation ceases in every annual shoot at 
 the termination of the season in which it is 
 
 * Syst.of phys. Bot. vol. ii. p. 213. 
 
380 CONSERVATIVE ORGANS. [LECT. VII. 
 
 evolved, before we can accord with his position; for 
 it is during that period only that the pith is es- 
 sential in trees and shrubs. But although its 
 functions cease, yet the pith still remains a part of 
 the trunk of the oldest trees, as long as these re- 
 main sound. Some authors, among whom we find 
 Willdenow *, Mr. Keithf , and Sir J. E. Smith +, 
 assert that it disappears altogether, obliterated 
 " by the increasing solidity of the wood." Darwin $ 
 supposes that it is either absorbed or imbued with 
 ligneous matter, so as not to be distinguishable 
 from wood; an opinion which Mr. Knight com- 
 bats, affirming that its place " is never filled with 
 " wood || ;" while others contend that it never va- 
 ries, being the same in the old trunk as in the 
 young branch. Let us examine in what these 
 opinions are correct. 
 
 In stems, the wood of which is of a close 
 texture, and the divergent layers very thin, no 
 obliteration of the pith can take place, nor even 
 any compression of it occur, after the case of 
 wood which encloses it is perfected ; and, on 
 close examination, it can readily be detected in 
 the oldest sound stems of this description ; but, 
 
 * Principles of Bot. trans, p. 251. 
 f Syst. of phys. Bot. vol. ii. p. 213. 
 J Introd. to phys. and syst. Bot. p. 39. 
 Phytologia, xviii. 2, 13. 
 I] Phil. Trans. 1803. 
 
LECT. VII.] ANATOMY OF STEMS. 381 
 
 as in almost every old stem, it has acquired the 
 colour of the wood, and is comparatively so small 
 a point in the diameter of a large trunk, it is 
 easily overlooked. In a transverse slice from the 
 centre of a very old Oak, now before me, the 
 medulla is distinctly seen of the same size and 
 figure usually found in the young stem, although 
 its colour is nearly as dark as that of the surround- 
 ing wood, and the cells are altogether obstructed ; 
 and in the stem of a Nectarine, twenty years old, 
 also now before me, the same state of the pith is 
 observable. In both, the cells appear obliterated, 
 even when examined by a good lens ; but when 
 a very thin slice is placed under the microscope, 
 in a drop of pure water, the hexagonal character 
 of the cells is perfectly distinguishable if the 
 section be transverse ; while, if longitudinal, not 
 only the difference of form between the real pith 
 cells and those of the medullary sheath is per- 
 ceptible, but the spiral vessels are seen, filled 
 with a dark-coloured resinous matter. In such 
 stems, therefore, the pith is neither compressed, 
 obliterated, nor converted into wood. But when 
 the ligneous matter is of a loose texture, or, in- 
 stead of forming a continuous circle, it is in 
 separate columns, as in broad-leaved Birth- wort, 
 Aristolochia Sipho, and the divergent rays are very 
 large, the pith, although it is never completely 
 obliterated, yet, is considerably compressed and 
 
 2 
 
382 CONSERVATIVE ORGANS. JJLECT. VII. 
 
 altered in form, in stems even of a few years' 
 growth. The future state of the pith, therefore., 
 varies; and is altogether regulated by the cha- 
 racter of the wood which encloses it. 
 
 Such is the general anatomy, or, more strictly 
 speaking, phytotomy of ligneous dicotyledonous 
 stems. Almost every species of tree and shrub, 
 however, has something peculiar to itself, but 
 these are more connected with the arrangement, 
 than with the structure of the parts. 
 
383 
 
 LECTURE VIII. 
 
 ORIGIN AND ATTACHMENT OF BRANCHES; STRUC- 
 TURE OF LIGNEOUS ROOTS; AND OF HERBACE- 
 OUS DICOTYLEDONOUS STEMS. 
 
 WHETHER we regard branches merely as divi- 
 sions and subdivisions of the stem, or more cor- 
 rectly, at least as far as regards their origin,, as 
 distinct individuals, its lateral progeny, we find 
 their structure to accord in every particular with 
 that of the stem. The description of the struc- 
 ture of the trunk is consequently applicable to the 
 branches ; and we have now, therefore, only to 
 investigate the nature of the connexion between 
 these parts : tracing the branch from its earliest 
 state, or long before it is visible to the eye, till 
 it is fully extended, and has itself become the 
 parent of future branches. 
 
 Every branch is formed in a bud or gem ; and 
 every bud, except perhaps the terminal one, and 
 such as appear on roots, and constitute suckers, 
 originates in the axilla of a leaf*; to trace, there- 
 fore, the origin of the branch, is in fact to trace 
 
 * Some buds, as, for example, those of the Plane and the 
 Sumach, are generated in the centre of the base of the foot- 
 stalk of the old leaf; but this is a mere modification of the 
 axillary bud. 
 
384 CONSERVATIVE ORGANS. [LECT. VII [. 
 
 that of the axillary bud ; and this may be done 
 most readily in the succulent shoot of any tree or 
 shrub in early spring, as, for example, of the 
 common Lilac, which is at this time (March 26th) 
 just expanding its leaves. 
 
 In the shoot now under consideration, one 
 inch only in length, and on which none of the 
 real leaves, except the three first pairs, are yet 
 expanded, we cannot perceive, on pulling off 
 those nearest the base, that is, the intermediate 
 between the scales of the bud from within 
 which the shoot has protruded and the real 
 leaves-}", any appearance of a bud in their axillae, 
 even when the sight is aided by a good lens : 
 neither is any seen at the attachments of the 
 second pair. At the third, however, we observe 
 by the aid of the lens, immediately above the la- 
 ceration produced by tearing off the leaf, a mi- 
 nute elevation, resembling a semitransparent 
 vesicle depressed in the centre ; which, under the 
 microscope, appears to be a lobular body, with 
 a small green speck in the central depression (see 
 Plate 7, fig. 1, a) %. This is the rudiment of the 
 
 f The distinguishing characteristics of real leaves, and of 
 those which appear first on a new shoot, shall be pointed out 
 when we examine the external structure of buds. 
 
 J In this figure, which represents a thin tangental slice of 
 the shoot very highly magnified, a. displays the appearance of 
 the embryon germ within the bud ; and b. the lacerated base of 
 the footstalk of the removed leaf: c. is the natural size of the 
 
LECT. VIII.] ORIGIN OF BRANCHES. 388 
 
 bud and germ *, and consequently of the future 
 branch. To examine the structure minutely, let 
 us place a longitudinal and a transverse slice of 
 the shoot under the microscope. 
 
 In the portion of the longitudinal slice of 
 which a highly magnified drawing is now before 
 us (see Plate 7, fig. 2), we perceive the section a. 
 of one of the lobes, situated at the point where' 
 . the footstalk of the leaf b. separates from the stem 
 c. The small speck at the base of the lobe ap- 
 pears now an obtuse, pyramidal, insulated body ; 
 while nearly all the cellular matter above e^ which 
 is apparently the line of separation between the 
 system, if I may be allowed the expression, of the 
 bud and that of the leaf, seems directed towards 
 it. The bundle of spiral vessels, d., passes up- 
 wards to supply the leaf; but neither the lobe 
 nor the speck has any vessels, unless we suppose 
 that some from the liber^. above it, are given off 
 for its supply ; a circumstance which, however^ 
 is conjectural only, as none is perceptible. The 
 whole of the cellular substance, connecting the 
 
 slice. The whole of the cuticle in this young state of the 
 branch is studded with small pedicillated glands, which exude 
 a viscid tenacious fluid. 
 
 * It is necessary, before proceeding, to explain the meaning 
 of these terms. The bud or gem is the pyramidal body, as it 
 appears on the surface of the stem or branch covered with its 
 scales ; the germ is the rudiment of the young branch, and 
 leaves contained within these scales. 
 
 VOL. 1. C C 
 
386 CONSERVATIVE ORGANS. [LKCT. VIII. 
 
 lobes with the pith g. is more opaque than in any 
 other part, from its cells being filled with small 
 amylaceous granules ; but whether these are de- 
 posited by the vessels which convey the proper 
 juice from the leaf above then), it is impossible to 
 decide. The chief fact established by this view of 
 the parts, is the connexion between the cellular 
 matter of the lobes of the gem, and that of the pith, 
 the medullary sheath, the bark, and the liber, in 
 the succulent shoot ; while, nevertheless, the germ 
 itself appears a distinct body. In the transverse 
 section (Plate 7, fig. 3) this connexion betwixt the 
 lobes a. and the pith e. is still more apparent ; for 
 neither the spiral vessels d. which appear like 
 a circle of dark spots surrounding the pith in 
 every other place ; nor the alburnous matter c. 
 which accompanies them, interfere to prevent this 
 union. In this section, also, the distinct nature 
 of the germ, notwithstanding its connexion with 
 the surrounding parts, is rendered very evident. 
 As the bud advances in growth, it gradually as- 
 sumes somewhat of a pyramidal form; and the 
 organization of the germ within it, that is, of the 
 new branch and leaves, commences. Towards the 
 end of summer, the lobes begin to appear as op- 
 posite scales, from amidst which the apex of the 
 germ, covered by other scales, is observed pro- 
 truding; whilst in a longitudinal section placed 
 under the microscope, the rudiments of the new 
 
LECT. VIII.] ORIGIN OF BRANCHES. 387 
 
 branch can be traced; for it is now obscurely 
 marked by the deposition of alburnous matter, 
 which being paler and more transparent than the 
 rest of the bud, is seen separating the cellular 
 substance to constitute the future pith (see Plate 
 7, fig. 6, .), from (b.) that which is to form the 
 bark. But no spiral vessels are yet perceptible; 
 the alburnous circle is mere semitransparent mat- 
 ter ; and the pith is distinguishable from the cel- 
 lular substance in which the germ is formed only 
 by the paler alburnous matter surrounding it*. 
 The progress of the organization advances a little 
 in autumn ; but is not perceptible during winter, 
 and it is not until the following spring that the 
 embryon branch is very conspicuous. At this 
 period, in the Lilac, the plant before us, it is seen 
 rising as it were from the medullary sheath, in 
 which the spiral vessels seem to originate ; and 
 
 * In this figure { Plate 7, fig. 6) the germ d. is seen separat- 
 ing the exterior scales c. which were originally the lobes. It 
 appears to consist of the rudiments of four leaves, which are 
 not, however, the true leaves ; but those intermediate between 
 the lobular scales and them, the true leaves being yet latent. 
 The pith of the new branch originates from a. : the pale space 
 between this and b., the bark of the embryon branch, is alburnous 
 matter : e. is the eschar, formed by the fall of the leaf in au- 
 tumn, with the spiral vessels which supplied the leaf, now ob- 
 structed ; f. the rudiment of a spiral vessel belonging to the 
 scale c. ; g. the bark of the portion of the shoot above the 
 bud ; h. the alburnum ; . the medullary sheath j k. the medulla, 
 
 cc2 
 
388 CONSERVATIVE ORGANS. [lECT." VIII. 
 
 whence, passing up, they distribute bundles to 
 each of the leaves, which appear now completely 
 organized, although extremely small and com- 
 pressed within the scales of the bud. As the sea- 
 son advances, the bud lengthens ; and at the mo- 
 ment of its opening, the young branch is seen 
 stretching forwards clothed with its leaves, which 
 gradually unfolding themselves, display in their 
 axillae the rudiments of future buds, destined to 
 run the course which has just been described; 
 and become in their turn the parents of another 
 series. 
 
 If the young' branch be now dissected, it is 
 found to possess exactly the same structure as the 
 stem in the early stage of its growth ; that is, to 
 consist of a central pith turgid with fluid, sur- 
 rounded by the medullary sheath, around which 
 the spiral vessels appear in distinct longitudinal 
 bundles ; and beyond them a layer of semior- 
 ganized alburnum, bounded by the liber : the 
 vascular fasces of the bark are embedded in the 
 cellular integument, and the whole enclosed by 
 the epidermis, which at this period is generally 
 covered with excretory glands or some kind of 
 pubescence. But after the leaves have expanded 
 and performed their functions for some time, if 
 the branch be again examined, by carrying a lon- 
 gitudinal section into the stem, we perceive its 
 alburnum, now fully organized and continuous 
 
LECT. VIII.] ORIGIN OF BRANCHES. 389 
 
 with the new layer in the stem, deposited over 
 that of the former year, which has already be- 
 come wood : and, as the branch increases an- 
 nually by new layers, in the same manner as the 
 stem, a similar section made at any subsequent 
 period displays its connexion with the stem, form- 
 ing a cone, the apex of which touches the me- 
 dullary sheath of the stem, and the base its sur- 
 face whence the branch projects. This conical 
 appearance is rendered more 
 evident by the marginal cut; 
 in which a. represents a stem 
 five years old ; and b. a branch 
 three years old projecting from 
 it. At the points of union 
 (c. c.) a kind of raphe is formed 
 above and below the branch 
 owing to the descending albur- 
 nous matter of the branch 
 meeting that of the stem. 
 
 Such are the appearances which mark the 
 origin of the branch and its connexion with the 
 trunk in the Lilac ; and the same, with some 
 modifications, are perceptible in all ligneous dico- 
 tyledons. The principal of these modifications is 
 seen in those ligneous stems, the pith of which is 
 interrupted at the points where the buds are 
 formed, as for example in that of the Vine. In it 
 a process from the medullary sheath extending di- 
 
 c c 3 
 
390 CONSERVATIVE ORGANS. [LECT. VIII. 
 
 rectly across the ligneous cylinder of the stem, 
 forms an apparently solid diaphragm ; and swell- 
 ing externally affords a base a. (see 
 marginal cut) on which the bud, 
 and consequently the new branch, 
 are seated. This appearance was er- 
 roneously supposed by Grew* to 
 be occasioned by the shooting of 
 the branch across the pith ; but, it 
 is obviously a process of the medullary sheath; 
 for, when placed under the microscope, it dis- 
 plays the same structure ; and the cells of which 
 it is composed are crowded with small granules, 
 as is generally -the case in those of the medullary 
 sheath. The colour, which is green like the me- 
 dullary sheath, distinguishes it from the pith, 
 which is of a fawn colour in the vine. It is not 
 always, however, thrown completely across the 
 pith; for, when neither a bud nor a tendril rises 
 from the opposite side of the stem, it never 
 stretches entirely across, but leaves 
 a free communication between the 
 pith above and below it, at least 
 one third of the circumference of 
 the ligneous cylinder. The plans in 
 the margin illustrate, more clearly, 
 this fact : thus, where the tendril is 
 
 * Anatomy of Plants^ t, 19. 
 
LECT. VIII.] ORIGIN OF BRANCHES. 391 
 
 ^^ given off, as at a. the diaphragm 
 
 *mi$[ IS Com pl ete 5 but at ^ (P- 390), 
 
 where there is a bud only, it is in- 
 complete; and this is farther dis- 
 played at c. in a transverse section of the shoot. 
 
 We are now prepared to consider the phy- 
 siology of the parts that have been just demon- 
 strated. We have seen that the rudiment of the 
 bud is perceptible, in the axilla of the leaf, on 
 the young branch at the moment of its protrusion 
 from the bud in early spring; and that at this 
 period, at least, it is an isolated body, distinct, 
 as Gaertner has correctly asserted, from the pro- 
 per and permanent members of the plant *. The 
 question thence occurs, When and how are buds 
 formed ? Du Hamel supposed that they originate 
 in what he terms preorganized germs, which are 
 deposited by the proper juice in its descent from 
 the leaves, and pervade every part of the plant -f-: 
 but, although it is impossible to demonstrate the 
 fallacy of this opinion ; yet, if it can be shown 
 that buds, on whatever part of a stem or branch 
 they are found, or at whatever period of the 
 growth of these members they appear, can be 
 traced to their origin in the first year's growth of 
 
 * De Fructibus. Introd. 
 f Phys. des Arbres, torn. i. 
 
 c c 4 
 
392 CONSERVATIVE ORGANS, [LECT. VIII. 
 
 the part on which they appear, it will be at least 
 rendered improbable, To effect this, we have 
 only to saw out a portion of any trunk or branch 
 on which a young bud appears ; and carrying our 
 incision down to the pith, and by carefully slicing 
 the portion horizontally, or in a right angle to the 
 surface of the stem, till we divide the bud to its 
 centre, we shall find a white line extending from 
 it, through every concentric layer of the wood, 
 till it touches the medullary sheath. Thus, in the 
 wedge, represented in Plate 7, fig. 5, cut from 
 the trunk of a Lilac twenty years old, we can 
 trace the buds a. b. to their very point, which ter- 
 minates at the pith of the plant ; and the same is 
 the case with the three buds a. b. c. of fig. 6, 
 in the same plate: for, although a. appears to 
 spring from the surface of the third circle of the 
 stem when examined with the naked eye, yet, un- 
 
 ^ 
 
 der the microscope (see fig. 7), it is seen to stretch 
 to the medullary sheath, in conjunction with its 
 fellows. It is argued, however, that if an Oak, 
 or any old tree, be cut down in winter, leaving 
 the root in the ground and a foot or two of the 
 trunk, we shall find on the margin of the stump 
 multitudes of buds protruding in the following 
 spring. I admit the fact; but deny the con- 
 clusion inferred from it, that these buds originate 
 on the surface where they appear ; for, if they do 
 not all push out on the same plane, which is 
 
LECT. VIII.] ORIGIN OF BRANCHES. 393 
 
 the fact, I have no doubt that each could be 
 traced to the centre of the trunk ; as I have found 
 to be the case in the Willow and some other soft- 
 wooded trees, which after being cut down, have 
 displayed the same appearances as the Oak ; and 
 although I have had no opportunity of examining 
 the Oak, yet, there is no reason for supposing it 
 an exception. If buds, therefore, be pre-organ- 
 ized germs, they can be deposited only in the first 
 year's growth of the stem or branch, the admission 
 of which would defeat the object of Du Hamel's 
 hypothesis. 
 
 These facts, also, render less tenable the 
 doctrine of Mr. Knight, that buds proceed from 
 the alburnous vessels, which he supposes have 
 the power to generate central vessels *: for, if 
 this were the case, buds could be traced no 
 deeper than the alburnum of the season in which 
 they appear. Neither is the opinion strengthened 
 by the fact, that if buds be destroyed in early 
 spring, others appear ; for, in this case, either the 
 buds are such as have not been cut or rubbed off 
 at a depth sufficient to extinguish their vitality, 
 and prevent them from shooting forth again la- 
 terally, or by destroying the already protruded 
 buds, those that remain latent, two or more germs 
 being often present in the same vital stream, if I 
 
 * Phil. Transactions, 1805. 
 
394 CONSERVATIVE ORGANS. [LECT. VIII. 
 
 may be allowed the expression (see Plate 7, fig. 
 7, a. b. c.); receive a new impulse, sufficient to 
 call into action their dormant powers, and enable 
 them to protrude and evolve their leaves, in the 
 same season ; which, had the other buds been 
 left, might not have happened for many years 
 to come. 
 
 This fact is practically known to nurserymen 
 and gardeners, who, without any theory, but 
 guided by their experience, act upon it in order 
 to obtain a clean Cherry tree stem. No tree 
 is so apt to throw out adventitious buds as the 
 Cherry tree; but as this would deform and injure 
 the plant, the nurserymen cut them off close to 
 the bark. A second crop of shoots, very soon af- 
 terwards, makes its appearance, which is also 
 taken away by the knife, after which no other 
 appears; and, if the stem be now cut through 
 under the existing branches, it ceases to grow. 
 I am of opinion that the same circumstance would 
 take place in forest trees, were all the lateral 
 buds of the leading shoot annually rubbed off, 
 so as to bring forward every latent germ ; and, 
 by destroying the successive crops of buds as 
 they are evolved, a clean stem perfectly free from 
 knots might always be insured. That the buds, 
 when they first protrude, receive their nourish- 
 ment from the descending proper juice, is ex- 
 tremely probable ; but this would also be the case 
 
LECT. VIII.] ORIGIN OF BRANCHES. 395 
 
 did they arise from the pre-organized germs of 
 Du Hamel. If this reasoning be correct, the first 
 division of our question is already answered ; and 
 we may conclude that all stem buds originate 
 when the young stem is evolved from the seed, and 
 all branch buds at the time that the young branch 
 is formed in the axilla of the leaf. They are not, 
 however, all protruded during the succulent state 
 of the stem and branch, but many remain latent, 
 performing so much of their functions only as is 
 requisite to organize to their proper structure a 
 certain portion of each successive annual layer of 
 wood, and carry them forward in the einbryon 
 state; until circumstances occur favourable to the 
 completion of their organization and protrusion on 
 the surface of the stem ; or until some accident 
 destroys them*. 
 
 If buds be not pre-organized germs, nor 
 formed from the descending proper juice; how 
 then do they originate ? I reply, in vital points 
 (puncta vitalia) generated, in the first period of 
 the growth of the stem and the branch, in the 
 axillae of the leaves : or that they are, to use the 
 language of Darwin, distinct individuals, the 
 lateral or viviparous progeny of the. parent upon 
 
 * In Plate 7, fig. 8, a. represents a bud which has been 
 destroyed in the fourth year of the growth of the stem ; and 
 over which the subsequent layers of wood have formed. 
 
396 CONSERVATIVE ORGANS. [LECT. VIII. 
 
 whose surface they appear*. The individuality of 
 buds must have been suspected as early as the 
 discovery of the art of budding ^ ; and it is fully 
 proved by the dissection of plants, as we have 
 seen in the demonstrations before us. The vital 
 energy, however, which commences the process 
 of organization in the bud, is not necessarily con- 
 fined to the germ, nor distinct from that which 
 maintains the growth of the entire plant ; but it is 
 so connected with organization, that when this 
 has proceeded a certain length, the bud may be 
 removed from the parent and attached to another, 
 where it will become a branch the same as if it 
 had not been removed ; or, with proper care, it 
 may be made to grow in the earth, and become 
 an entire plant, with all the properties and phy- 
 siognomical characters of the parent. 
 i 
 
 * Malpighi taught that the gems are formed in the pith, 
 which he regarded as a viscus intended for this purpose and the 
 elaboration of the sap. Thummig, a German author who wrote 
 in the 18th century, imagined that the medulla contains the 
 rudiments of the gems : Darwin suspected that the embryons 
 of the buds are secreted from the " vegetable blood " at the 
 footstalk of each leaf; while Mr. Knight supposed that they 
 are generated by the alburnous vessels from the descending 
 proper juice. 
 
 f Budding is that operation in gardening, by which a bud 
 taken from one tree is transferred to another, with which it 
 unites and becomes a branch. It is founded on the fact, that 
 the bud, which is a branch in embryo, is a distinct individual. 
 
LKCT. VIII.] ORIGIN OF BRANCHES. 397 
 
 The ingenious Bradley supposed that a bud 
 takes root in the body of a tree in the same 
 manner as a seed takes root in the earth * ; an 
 idea which evidently suggested Darwin's theoiy of 
 the individuality of buds, and the augmentation of 
 the diameter of the trunk and branches by the 
 extension of their radicles, as has been already 
 noticed ; and which has since been illustrated, and 
 given to the world as his own, by a celebrated 
 French phytologist, M. Aubert Du Petit-Thouars-f-. 
 But, although a bud will send out roots and grow 
 if planted in the ground, the analogy does not 
 apply to the bud attached to the original parent, 
 nor even to that which is budded. 
 
 Before organization commences in the germ, 
 it is, as we have seen, an insulated speck, covered 
 by the epidermis only, and connected with the 
 other parts of the stem or branch, in which it is 
 seated, merely by cellular matter. The effect of 
 the organic power on it is the addition of new 
 matter, and the consequent evolution of its parts; 
 till gradually extending in the direction of its 
 axis, it unites with and becomes a permanent part 
 
 * Discourses on the Growth of Plants, 1727, p. 56. 
 
 f This is rendered evident by comparing the theory de- 
 livered in his work, entitled Essais sur la Vegetation consideree 
 dans le Developpement des Bourgeons; which was published in 
 1809, with that in the Phytologia of Darwin, which appeared 
 in 1800. 
 
398 CONSERVATIVE ORGANS. [LECT. VIII. 
 
 of the plant. The quantity of amylaceous gra- 
 nules contained in the cells surrounding the germ, 
 renders it probable that it receives its first nou- 
 rishment from this source ; and it is not less pro- 
 bable that the lobes which surround it, perform 
 for it a similar function to that of the cotyledons, 
 or seed-lobes, as connected with the embryon en- 
 closed within them, or that of the leaves in re- 
 ference to the stem and branch ; which we shall 
 afterwards prove to be analogous to that of the 
 lungs in animals. But it is, also, probable that 
 the leaf above the bud supplies part of the pabu- 
 lum which is elaborated into the new branch ; for, 
 until its own leaves are expanded in spring, and 
 capable of producing that change on the sap which 
 converts it into proper juice, no alburnous mat- 
 ter can be formed by them. The descending juice, 
 however, from the leaf above the germ, is not 
 conveyed to it by any vascular communication, but 
 deposited in the cellular mass or placenta, if it may 
 be so termed, on which it is seated; and by which 
 alone it is connected with the medullary sheath of 
 the parent shoot. In the germ or vital speck, thus 
 situated and supplied with nutriment, the organiza- 
 tion of the branch commences as from a centre. It 
 is not probable that we shall, ever, be able to trace 
 every minute change, which occurs from this period 
 until the first rudiment of the new branch is per- 
 spicuous, even by the aid of the best microscopes ; 
 
LECT. VIII.] ORIGIN OF BRANCHES. 399 
 
 but the first part that can be distinctly recognised 
 is the pith, which, in a longitudinal section of the 
 green twig of the Lilac, made three weeks after its 
 protrusion from the bud, and the appearance of 
 the gem on its surface, resembles a more opaque 
 spot of a greenish hue ; with lines running in a 
 direction from the centre of the parent branch to- 
 wards the apex of the gem. These are the first 
 traces of the spiral vessels of the future branch 
 (see Plate 7, fig. 9, a.). The cellular matter, in 
 the part of the bud above the vital speck, which 
 now appears as at c. displays also at this period a 
 more regular form, and indications of its separa- 
 tion into scales are already perceptible at b. ; but 
 the whole bud is still a completely insulated body. 
 As the organization proceeds, new scales are seen 
 separating from the mass of parenchyma, the 
 medulla enlarges in every direction, and in au- 
 tumn the whole presents a pyramidal appear- 
 ance ; in which state the bud remains nearly sta- 
 tionary until the ensuing spring. 
 
 As the cessation of the vegetative power in 
 winter increases in a great degree the excitability 
 of plants which outlive its severity, the genial in- 
 fluence of spring is very early visible on their 
 buds, in which the whole vital energy of trees and 
 shrubs may be supposed at this period to reside; 
 and it is only by the visible change which rapidly 
 occurs in them, that we can pronounce upon the 
 
400 CONSERVATIVE ORGANS. [LECT. VIII. 
 
 life of the entire plant. If a longitudinal section 
 of a twig be examined at this time, although the 
 pith be, generally speaking, a dry spongy mass, 
 yet, a little above and below the parts where the 
 buds appear, it is succulent and green. This can 
 be explained only by supposing that the increased 
 vital energy of the buds is extended around them 
 to a certain degree, maintaining the lateral com- 
 munication through the pores of the cells, while 
 these have now become impervious in other parts; 
 and by this effect a sufficient supply of nutriment 
 is provided for the bud, which, enlarging in every 
 direction as the spring advances, at length opens 
 its scales and pushes forwards, into the light and 
 air, the young branch with its leaves and flowers. 
 On examining now the connexion of the shoot with 
 the stem or branch, we find it no longer, an iso- 
 lated individual, but seated closely upon the me- 
 dullary sheath of the parent; and the alburnous 
 matter which is deposited between its bark and 
 pith, continuous with that thrown out from the 
 liber of the old bark, already giving origin to a 
 ligneous layer, that forms both a connecting vin- 
 culum between the tree and the new branch, and 
 a support to the latter in its projecting position. 
 
 I suspect that Hill confined his examination 
 of buds to the autumn, and before they were 
 ready to open in spring; and thence he was led 
 to adopt the opinion that the branch originates 
 
LECT. VIII.] ORIGIN OF BRANCHES. 401 
 
 from the vessels of the medullary sheath, which, as 
 I have already remarked, he termed the corona, 
 holding it to be the most important part of the 
 plant *. The difficulty of explaining the appear- 
 ance of adventitious buds on such a supposition, 
 led to the rejection of his theory ; and I am sur- 
 prised to find that a late ingenious writer -f- sup- 
 ports the fallacy of it by this remark : " it is no- 
 torious, that trees in which not only this first 
 circle, but almost every other circle of vessels 
 has perished, produce leaves and shoots from 
 the trunk where the bark is entire, as this au- 
 thor himself admits, p. 44 of his work : " for, in- 
 dependent of the absurdity of imagining that the 
 life of the tree could be supported at all, if every 
 circle of vessels had perished, the objection dis- 
 plays an unaccountable neglect of investigation. 
 
 I trust enough has been demonstrated, in ,the 
 dissections laid before you, to establish the fallacy 
 of Hill's theory; but on different grounds from 
 those taken up by the author above quoted ; and 
 I have now only to explain how the appearance of 
 adventitious buds on hollow trees does not militate, 
 in any degree, against the theory I have advanced. 
 In doing so, I must recur to my position, that 
 every bud originates with the branch or stem on 
 
 * Hill on the Construction of Timber, p. 21 . 
 
 f Mr. Ellis : see the article Vegetable Anatomy^ in the Sup- 
 plement to the Uh and 5th editions of the Encyclopedia Bri- 
 tannica t vol. i. Part 2. p. 335. 
 
 VOL. I. D D 
 
402 CONSERVATIVE ORGANS. [LECT. VIII. 
 
 which it appears, but is not always evolved in the 
 season in which it is generated. When it appears 
 at any future time, therefore, although it is, as 
 I have demonstrated, traceable from the medul- 
 lary sheath to the surface on which it appears, 
 yet, the maintaining a communication with that 
 sheath has long ceased to be requisite, either for 
 its preservation or its nourishment ; and, conse- 
 quently, it is not affected by the destruction 
 of that part, or of the circles of wood interme- 
 diate to it and the bark. The pale streams of pa- 
 renchyma traversing these circles, only mark the 
 track in which the vital speck or germ has ad- 
 vanced to the surface of each annual zone, where 
 it was ready to be developed, had circumstances 
 been favourable for that event ; but this streak of 
 parenchyma is altogether useless as far as regards 
 the gem, except in the zone on the surface of 
 which it is seated, and with the life of which its 
 vitality is, indeed, intimately connected. De- 
 stroy this zone, and the latent germ becomes 
 extinct; increase its vital energy by any means, 
 as, for example, by lopping off a branch, and 
 the germ is evolved into a perfect bud and 
 branch; but leave the parts as they are, and 
 the vital speck advances to the surface of the next 
 zone which is formed over the present, and so on 
 progressively, until it is ultimately evolved, or 
 perishes with the destruction of the tree. The bud, 
 therefore, which appears on the surface of a hoi- 
 
JLECT. V1JI.] ORIGIN OF BRANCHES. 403 
 
 low tree, is still to be regarded as having originated 
 in the first year of the life of that trunk, however 
 old it may be : and its progress may be traced 
 through the shell of wood which still remains free 
 from decay. 
 
 In general the latent germ passes in a straight 
 line through each concentric layer of wood ; but 
 when a branch, which is given off at an acute 
 angle, coalesces with the trunk, its direction 
 is changed to a curve, so as to continue it in 
 the wood of the stem or branch in which it 
 originated. Thus in the horizontal section of a 
 Willow, now before us, which was cut a little 
 below the bifurcation of a branch, that had co- 
 alesced with the trunk, we find the bud a. trace- 
 able in a direct line from the centre of the trunk ; 
 but b. as soon as it enters the zone c. where the 
 coalescence occurs, turns aside, and instead of 
 being protruded at/, which would have been the 
 case had it continued its course in its first direc- 
 tion, it appears at b. In this section, d. marks 
 
404 
 
 CONSERVATIVE ORGANS. 
 
 [LECT. vin. 
 
 the last independent ligneous zone of the branch, 
 and e. that of the trunk : but it must be re- 
 marked that the other zones, common to both, 
 are the result of alburnous matter furnished by 
 each in particular. 
 
 A very clear idea of the origin and connexion 
 
 of branches may be ob- 
 tained by the aid of a 
 diagram, similar to one 
 which was employed by 
 Du Hamel to illustrate 
 the opinion he entertain- 
 ed, although that was 
 directly opposite to the 
 theory I have advanced. 
 Let us imagine the fi- 
 gure in the margin to 
 be a tree four years old ; 
 the cone a. representing 
 the first year's growth, 
 fc. b. the second, c. c. the 
 third, and d. d. the fourth. The buds furnish- 
 ing the branches e.f. g. h, are all generated on the 
 surface of a. in the spring of the first year ; but in 
 that year e only sprouts into a branch; on the 
 surface of which is generated i. } which in its turn 
 generates k. In this series, each branch has sprung 
 in regular succession from that of the former year ; 
 the age of the branch being marked by the num- 
 
 "bed 
 
LECT. VIII.] ORIGIN OF BRANCHES. 405 
 
 her of ligneous layers : thus k. which is one year 
 old, is covered with one ligneous layer; i. with 
 two, and e. with three ; while the original trunk 
 has four, which give the age of the germ, whence 
 e. originated. But g. has two layers only, and 
 f. h. no more than one, although shooting from 
 the same surface as e. which is thus explained. 
 The branch g. sprung from an adventitious bud, 
 which protruded in the second year of the growth 
 of the stem ; and, therefore, although the germ 
 whence it originated is as old as that of e. yet it 
 is covered with two ligneous layers only ; and the 
 branch /. which it has produced in regular succes- 
 sion has but one, or is no older than k. the third in 
 succession on e. In the same manner the branches 
 f. and h. which have also sprung from adventitious 
 buds, are of the same age as k. although their 
 germs were generated on a. and are consequently 
 coeval with the first development of the trunk. 
 
 Such are the observations which I have 
 thought necessary to be laid before you to illus- 
 trate the origin of branches and their connexion 
 with the trunk ; from which the following conclu- 
 sions maybe drawn: 1. That every branch ori- 
 ginates in a bud or germ. 2. That every bud or 
 germ is a distinct isolated individual, the lateral 
 progeny of the plant, and generated at the first 
 development of the stem or branch on which it 
 appears; but, after some time, increasing by 
 
 DD3 
 
406 CONSERVATIVE ORGANS. [LECT. VIII. 
 
 its own organic powers it forms a branch, and 
 becomes a part of the tree or shrub which has 
 produced it. 3. That every adventitious bud, or 
 bud appearing at any after period, originates in a 
 germ generated at the development of the stem or 
 branch on which it appears, although it has 
 hitherto remained latent. 4. That every latent 
 germ is annually carried forward, in a horizon- 
 tal direction, through every concentric zone of 
 wood, intermediate to the medulla and the sur- 
 face on which it will sprout. into a branch; leav- 
 ing behind it a substance of a peculiar structure, 
 somewhat resembling a white cord penetrating the 
 ligneous zones, by which its progress can be 
 traced. 5. That every branch when fully deve- 
 loped, displays the same structure as the stem. 
 
 In examining the structure of the ROOT in 
 ligneous Dycotyledons, it will be useful to follow 
 the division of this organ into caudex, radicles, and 
 ^fibrils, which I adopted in describing the external 
 characters of roots in general; and to examine 
 each part separately, beginning with the caudex. 
 
 a. The Caudex. Taking the Horse Chesnut 
 still as the subject of our examination, we find 
 that the caudex of the root consists of the same 
 parts as are found in the trunk of the tree, ar- 
 ranged in the same relative order, and that each 
 
LECT. VIII.] STRUCTURE OF LIGNEOUS ROOTS. 407 
 
 part, when placed under the microscope, displays 
 nearly the same structure as the corresponding 
 part above ground. Thus in the bark we find the 
 cuticle with its horizontal vessels terminating in the 
 parenchyma; the cellular Integument consisting 
 of regular hexagonal cells ; and the liber display- 
 ing its reticular meshes. The cells, however, are 
 larger than those of the caulinar bark, and are 
 filled with a fawn-coloured instead of a green 
 fluid. The circle of alburnum and of wood differ 
 in nothing from those of the stem ; except that the 
 vessels, which are also cribriform, and the cells 
 of the divergent layers contain numerous trans- 
 parent granular bodies, which are likewise found 
 crowding the cells of the medullary sheath and 
 those of the pith. I have not been able to dis- 
 cover any spiral vessels in the medullary sheath of 
 the root-caudex, even in the youngest trees ; in 
 which particular, therefore, the root differs from the 
 stem. The pith, which is larger than that of the 
 stem, consists of hexagonal cells, turgid with fluid, 
 and so crowded with the granular bodies already 
 described, as to obscure their hexagonal structure, 
 which, however, can be distinctly observed in a 
 very thin section. 
 
 Such is the root-caudex of the Horse Chesnut 
 in the second or third year of its growth; and it 
 may be taken as an example of the structure of this 
 
 D D 4 
 
408 CONSERVATIVE ORGANS. [LECT. VIII. 
 
 part in the majority of ligneous dicotyledons. 
 While it remains entire, the young tree may be 
 regarded as composed of two similar cones united 
 at their bases ; the one rising vertically, or nearly 
 so, above the surface of the soil, and the other, 
 which forms the root, taking the opposite direc- 
 tion and penetrating the earth by constant ad- 
 ditions made to its apex. The place of their 
 union is distinguished externally by an im- 
 pression as if a cord had been tied very tightly 
 round the stem ; and is that part which the French 
 term collet, in the first evolution of the plant in 
 the germinating seed. If the apex be destroyed, 
 it ceases to elongate in the direction of its axis, 
 and shoots out lateral branches ; but these are 
 given off at various other parts also during its ex- 
 tension, and form divisions resembling those of 
 the trunk and the branches above ground. 
 
 b. The RADICLES. The medulla disappears in 
 the radicles, whether they be given off from the 
 caudex or a branch ; but something like the me- 
 dullary sheath is still present. The radicle, there- 
 fore, consists of a spongy centre, resembling the 
 medullary sheath devoid of spiral vessels, sur- 
 rounded by a circle of ligneous vessels, which are 
 either cribriform as in the Horse Chesnut, or annu- 
 lar as in the Vine (the character of the vessels in 
 the radicle being always the same as that of those 
 in the stem and branches) ; and a bark, which is 
 
LECT. VIII.] STRUCTURE OF LIGNEOUS ROOTS. 409 
 
 much thicker than that of any part above the soil. 
 The vessels are so arranged as to give a radiated 
 appearance to a transverse section, and I have 
 been able to trace the presence of divergent rays ; 
 but I am doubtful whether these are always present 
 in the smaller radicles. In the Vine we sometimes 
 find the bark running inwards, and dividing the 
 vessels into distinct wedge-like bundles (see Plate 
 7, fig. 11. *) ; and this may be the case, also, in 
 other radicles, to supply the place of other diver- 
 gent layers. 
 
 The radicles given off from the caudex appear 
 to proceed from the medullary sheath and the first 
 ligneous layer ; and, - like the branches above 
 ground, originate in the first year's growth of 
 each additional length of the root, for they can 
 be traced to the medullary sheath in the thickest 
 caudex. When, however, they are given off from a 
 stem or a branch which has been laid down in the 
 ground, they originate in the alburnum of that 
 season (see Plate 6, fig. 9 -}-) ; and this is also the 
 
 *In this figure, a. marks the pith in the slice of a shoot which 
 had been laid down and had rooted ; It. the first year's wood ; 
 c. that of the present year whence the radicle e. has shot forth ; 
 and d. the bark, the cuticle of which is seen uniting with that 
 of the radicle. 
 
 f In this figure, which displays the transverse slice of a 
 Vine radicle magnified 750 times, a. marks the cuticle and the 
 parenchyma of the bark ; b. the divided orifices of the proper 
 vessels of the bark ; and c. those of the ligneous vessels. 
 
410 CONSERVATIVE ORGANS. [LECT. VIII. 
 
 case in those radicles which shoot out above the 
 caudex when the soil is heaped up around the 
 stem. From whatever part the radicles proceed, 
 they are always given off in such a direction as to 
 form a right angle with the surface of the part, 
 which would not be the case did they descend 
 from the stem buds, as Dr. Darwin and M. A. 
 Du Petit-Thouars assert ; for, were their opinions 
 correct, the radicles would be given off from the 
 caudex in the same manner as a few threads are 
 separated from a skein of thread. The radicle, 
 on the contrary, receives vessels from the layer 
 of the caudex on which it originates, from both 
 above and below the point whence it shoots. 
 I have not been able to trace the origin of the 
 radicle ; but it is probable that every layer of al- 
 burnum is capable of producing radicles; for it 
 is only necessary to apply moist earth round any 
 part of a stem or branch to make them protrude, 
 c. The Fibrils *, soon after they are visible on 
 the radicles of the Horse Chesnut, are 
 minute, ovate, semitransparent bodies 
 (see a. marginal cut, which represents 
 a fibril considerably larger than in na- 
 ture), and, when placed under the 
 microscope, appear to consist of a 
 spongy mass of cellular matter, en- 
 closed in a thin transparent pellicle, 
 
 * These are the capillame.nta of Malphigi, Anat. Plants, p. 14-5. 
 
LECT. VIII.] STRUCTURE OF LIGNEOUS ROOTS. 411 
 
 perforated with absorbing pores: such is their 
 earliest character in every dicotyledonous root I 
 have examined. At this period they are productions 
 of the bark only of the radicle ; but a few ligne- 
 ous vessels soon shoot into their centre, and they 
 begin to lengthen (see Plate 8, fig. A. B*); always, 
 however, retaining a clubbed appearance at the 
 apex (see b. b. marginal cut). They shrivel up in a 
 few seconds after the root is taken out of the 
 earth, and then appear as represented at c. c. 
 (marginal cut) ; but so great are their absorbent 
 powers, that, when perfectly dry, if thrown into 
 water, they expand again in a few seconds to their 
 original size. The minuteness of these pores ren- 
 ders it impossible, even by the aid of the most 
 powerful glasses, to obtain a knowledge of their 
 structure ; and although the fibril shrivels so 
 quickly, yet the smallness of the parts prevents 
 us from determining whether this shrivelling be the 
 consequence of exhalation, or of the fluid being 
 carried forwards into the radicle. Whatever may 
 be the structure of these pores, they are evidently 
 
 * Fig. 1 A. represents, greatly magnified, the entire fibril 
 soon after it begins to lengthen ; the dark shade a. in the centre 
 being produced by the ligneous vessels, which are more opaque 
 than the cellular matter; b. is the real size of the fibril. Fig. 
 1, B. is a transverse section of the same fibril; a. the vessels, 
 b. c. the cellular matter filled with transparent granules, which 
 are much more numerous in the exterior circle b. ; d. the real 
 size of the section. 
 
412 CONSERVATIVE ORGANS. [LECT. VIII. 
 
 the absorbent mouths of the root, and must either 
 possess a valvular apparatus, or a power of c,on- 
 tracting strongly, so as to enable them to retain 
 the fluid they imbibe, until it is taken up by 
 the ligneous vessels. From their forming on 
 the radicles and their divisions, and seldom or 
 never on the caudex, they are placed at a dis- 
 tance from the trunk of the tree ; and conse- 
 quently seeds and small plants thrive better close 
 to trees, than at a little distance, the earth being 
 less exhausted in the vicinity of the larger roots 
 than where the radicles spread. 
 
 I have already stated (p. 129) the opinion of 
 Du Hamel and some other phytologists, re- 
 garding the annual death and reproduction of 
 the fibrils ; and the objections to it urged by Mr. 
 Knight. My own observations induce me to be- 
 lieve that fibrils are annual productions in all de- 
 ciduous trees and shrubs, although they are 
 perennial in evergreens. Were I called upon to 
 suggest a reason for this distinction, I would say, 
 that, as the fibrils do not appear until the leaves 
 begin to expand, they are produced for the pur- 
 pose of maintaining a due balance between the 
 absorption and the exhalation of the plant, and to 
 secure a supply of nutriment in proportion to the 
 demand, which must always depend on the energy 
 of the leaves in which it is converted into the 
 proper juice of the plant ; and, therefore, when the 
 
LECT. VIII.] STRUCTURE OF HERBACEOUS STEMS. 413 
 
 leaves decay and fall in autumn, the function of 
 the fibrils being no longer required, they also decay 
 and separate from the radicles ; but in evergreen 
 shrubs, the office of the leaves being permanent, 
 the new set always appearing before the old set 
 falls, the continued presence of the fibrils becomes 
 also requisite. 
 
 Such is the root of ligneous dicotyledons. Its 
 similitude both in structure and functions to the 
 portion of the tree above ground is very obvious, 
 the caudex resembling the stem, the radicles the 
 branches, and the fibrils the leaves ; *and hence 
 trees have been inverted and yet have lived ; the 
 buried stein and branches being converted into 
 roots, whilst the roots elevated into the air and 
 light have assumed the characters and performed 
 all the functions of the organs, the place of which 
 they now supply. 
 
 B. HERBACEOUS DICOTYLEDONOUS STEMS are so 
 much diversified in structure, particularly as far 
 as relates to the arrangement of the parts, that it 
 is impossible to form as accurate an idea of their 
 anatomy from the examination of one or two spe- 
 cimens, as we are enabled to do of that of the 
 stems of dicotyledons. To obviate, however, in 
 some degree, this objection, I shall divide them into 
 two classes, comprehending under the first A. those 
 which have no central cavity^ or are entire, and 
 
414 CONSERVATIVE ORGANS. [LECT. VIII. 
 
 under the second, B. those which are hollow; so 
 that by again subdividing these, I shall be able to 
 convey to you some general ideas of the prominent 
 characters which constitute the diversities. 
 
 A. The entire stem has no conspicuous internal 
 cavity, but the whole of that space which is filled 
 with the medulla in solid ligneous dicotyledons, 
 is made up of cellular matter turgid with fluid. 
 The stem, indeed, consists chiefly of similar cel- 
 lular texture, with detached bundles of vessels re- 
 gularly arranged through it, and the whole en- 
 closed by a bark. As the difference in point of 
 structure in this class depends on the arrangement 
 of the vascular bundles, it may be divided into 
 two genera ; ihejirst, a. comprehending all those 
 herbaceous dicotyledonous stems in which the dispo- 
 sition of the vascular bundles approaches to that 
 characterizing monocotyledonous stems ; and the 
 second b. those in which it resembles, in some de- 
 gree, the concentric circles oj ligneous dicotyle- 
 dons: each of these genera necessarily including 
 many species and varieties. 
 
 a. To illustrate the first of the genera of stems 
 just defined, I have selected the stem of the 
 White Bryony, Bryonia alba, because it is a plant 
 very readily procured. 
 
 If we examine with the naked eye a thin 
 transverse slice of the stem of Bryony, placed on 
 a dark surface, we perceive that it consists of a 
 
LECT. VIII.] STRUCTURE OF HERBACEOUS STEMS. 415 
 
 pale green opaque bark, enclosing a transparent 
 parenchyma studded with fourteen opaque ovate 
 spots of the same colour as the bark, and having 
 a white dot in the centre of each spot (see Plate 
 8, fig. 2, A) . Placing the same slice under a mi- 
 croscope of a moderate power, we find that the 
 transparent portion is formed of hexagonal cells of 
 different sizes; and each spot consists of the divided 
 orifices of two clusters of oblong cells and entire 
 vessels, surrounding one large and several small 
 sap vessels. The bark appears to consist of a 
 cuticle and three distinct cellular bands, the cen- 
 tral one of which is filled with a green fluid, and 
 may be regarded as equivalent to the green cel- 
 lular integument in ligneous dicotyledons ; except 
 that it penetrates the outer band to the cuticle at 
 nearly equal distances (Plate 8, fig. 2, B). If we 
 take a small portion of this section, and also of 
 a longitudinal slice of the stem, and examine 
 them under the highest power of the microscope, 
 we shall find the real structure of this kind of stem 
 to be as follows. The cuticle is irregularly reti- 
 culate and streaked with green cellular lozenge- 
 shaped spots (Plate 8, fig. 3, a. a.) 9 which are the 
 processes of the middle band of the bark ; the 
 outer cortical band, or that immediately within 
 the cuticle, consists of narrow tubular cells (see 
 a. a. fig. 4, A and B. Plate 8); the second of 
 shorter and wider cells (b. b.) y filled with the green 
 secretion already noticed, and penetrating to the 
 
416 CONSERVATIVE ORGANS. [LECT. VIII. 
 
 cuticle at /. /. /. /. (Fig. 4, A.), so as to give the 
 stem its striated aspect ; and the third band (c. c.) 
 is composed of entire vessels. Although we may 
 regard the part just described as analogous in 
 some respects to the cortex in ligneous stems, yet 
 in others it differs materially from that organ; and 
 it can neither be separated entire from the parts 
 beneath, nor can the bands be detached from 
 each other without destroying the organization. 
 Immediately within the vascular band of the 
 cortex we find the cellular mass d. d. d. d. com- 
 posed of cells which appear more or less regular 
 hexagons in the transverse section (Fig. 4, A) ; 
 but in the longitudinal (B) their length is seen to 
 be more than twice the sum of their diameter. 
 They are larger and more regular in the centre of 
 the stem ; and the hexagonal shape is sometimes 
 lost, in order to accommodate them to the forms 
 of the vascular fasciculi. The cells are filled with 
 a thin mucilaginous fluid, which is more viscid in 
 the vicinity of the vascular band of the cortex 
 and the vascular fasciculi; but, as the season ad- 
 vances, it almost disappears in the central cells, 
 which then assume the character of the pith in 
 dicotyledons. All the cells are perforated. The 
 vascular fasciculi contain from seven to ten cen- 
 tral vessels ; one of which (//) is very large, 
 and the others (g. g. h. h.) smaller in a regu- 
 lar ratio as they are distant from it, or towards 
 
LECT. VIII.] STRUCTURE OF HERBACEOUS STEMS. 417 
 
 the centre of the stem : these are surrounded by a 
 double cluster of entire vessels, which in the trans- 
 verse section appear like small hexagonal cells 
 (Fig. 4, A. e. i.) ; but in the longitudinal (B. e. i.) 
 they display their proper character, although it is 
 not improbable they are divided, at certain dis- 
 tances, by diaphragms which the transparency of 
 their coats conceals. The central vessels are not 
 all of the same structure, the larger being an- 
 nular, with oblong pores (Fig. 5, a.) ; the next size 
 spiral, with the fillet either punctured or studded 
 with glands (Fig. 5, b.), for I have not been able 
 to satisfy myself on this point; and the smallest 
 (Fig. 5, c.) of the same structure as those vessels, 
 which I have already described as existing in the 
 stem of Tradescantia and of some other her- 
 baceous monocotyledons. These consist of iso- 
 lated rings, separated from each other by a space 
 equal to their own diameter, which are apparently 
 intended as a frame- work to keep extended a 
 simple membranous tube in which they are en- 
 closed (Fig. 5, c.). 
 
 Mr. Kieser is the only phytologist who has 
 published any description of the last-mentioned 
 form of vessel; but he regards it merely as the 
 substratum or origin of the annular punctuated 
 spiral*; and, had I seen it in the stem under 
 
 * Mem. stir I* Organisation des Plantes, Haerlem, 181 4-. 
 VOL. I. E E 
 
418 CONSERVATIVE ORGANS. [_LECT. VIII. 
 
 consideration only, I should have adopted his 
 opinion, as it is the innermost and apparently 
 the least perfect of the series in each fasciculus: 
 but having seen it, in a more perfect form, in 
 the Tradescantia ; and not being able to con- 
 ceive why those distinct rings should exist only 
 to be transmuted into punctuated spirals, I am 
 inclined to consider it a distinct vessel. It is 
 true, as Kieser has observed, that the mem- 
 branous vessel, or intervening membrane as he 
 terms it, is punctuated ; but he appears to have 
 overlooked the fact, that the rings are retained 
 in their places by minute acicular bodies, which 
 I have separated from the vessels in Tradescan- 
 tia, although I have not succeeded in doing so 
 from those in the Bryony. No such bodies are 
 seen attached to the real annular vessel ; and in 
 the spiral vessel (Plate 8, fig. 5, #.), which is the 
 intermediate of the large annular vessel and the 
 ringed membranous vessel in the Bryony, the 
 * flattened fibre or fillet forming the spirals is 
 itself punctuated. Notwithstanding, therefore, 
 the apparent probability and simplicity of Kieser's 
 theory of the transformation of the ringed mem- 
 branous vessel into the punctuated spiral ; and 
 this into the annular, in the description of stem 
 now under consideration ; I am still of opinion 
 that the central vessels, in the vascular fasciculi in 
 the stem of Bryony and of similar plants, are of 
 
LECT. VIII.] STRUCTURE OF HERBACEOUS STEMS. 419 
 
 three distinct kinds, t as I have represented them 
 (Fig. 5, plate 8), viz. the annular, the punctuated 
 spiral, and the ringed membranous. 
 
 Such is the general structure of those her- 
 baceous dicotyledonous stems, which approximate 
 in some of their characters to monocotyledonous 
 stems, particularly in the arrangement of the vas- 
 cular fasciculi through the parenchyma. But, in 
 regarding the Bryony as a good specimen of the 
 structure of this our first division of herbaceous 
 dicotyledonous stems, we must bear in mind that 
 the division admits of many modifications. In all, 
 however, the fasciculi are distinct, as in the stems 
 of monocotyledons ; the chief feature that distin- 
 guishes them from monocotyledonous stems, being 
 the presence of a decided cortex, more or less ap- 
 proaching the characters of that which is always 
 present in ligneous dicotyledons; while the stem of 
 the monocotyledon is a fascis of vascular fasciculi, 
 interspersed with cellular matter and covered only 
 by a simple cuticle, 
 
 b. The structure of the entire herbaceous stem, 
 in which the arrangement of the parts approaches 
 to that in trees and shrubs, is well illustrated in 
 the Madder, Rubia tinctorum. In a transverse slice 
 of the stem of this plant, which is hexangular, 
 we find the following parts: 1. a cortex a. (Plate 
 8, fig. 6) easily separable from the parts beneath 
 it; 2. a vascular layer, b. resembling in its con- 
 
 EE2 
 
420 CONSERVATIVE ORGANS. [LECT. VIII. 
 
 tinuity the first concentric woody circle in a ligne- 
 ous stem, and 3. a cellular pulp, c. which gra- 
 dually loses its aqueous contents, and assumes the 
 characters of a- real pith. By the aid of the mi- 
 croscope, we find that the cuticle consists of a 
 thin, transparent, cribriform membrane ; and en- 
 closes a cellular cortex (Plate 8, fig. 6, B.), the se- 
 cond layer of the cells of which a. is filled 'with 
 a green coloured fluid, which extends over four 
 or five layers at each angle, and is the source 
 of the colour of the stem. Beneath this green 
 secretion the cells contain a pale yellow fluid, 
 which gradually deepens towards the interior of 
 the cortex, where we find its source, the proper 
 juice, filling a range of narrow oblong cells b. 
 which are situated close to c. the layer of return- 
 ing vessels. In these, the proper juice is much 
 paler than in the adjoining cells, which is pro- 
 bably owing to its dilution, in consequence of the 
 greater fluidity which is necessary for permitting its 
 motion in the vessels, through the cribriform 
 coats of which it passes into the adjoining cells, 
 where it is inspissated by rest, slowly spreading 
 its colour outwards by the lateral communication 
 of the cells. In d. which may be termed the 
 woody layer, and which consists of the large or 
 sap vessels embedded in a green pulp, we find 
 the vessels arranged like wedges pointing in- 
 wards, separated by cellular septa, and thus form- 
 ing a continuous band enclosing the cellular pa- 
 
LKCT. VII I.] STRUCTURE OF HERBACEOUS STEMS. 421 
 
 renchyma e., . and which is altogether composed 
 of hexagonal cells, that become larger and more 
 regular as they approach the centre; and supply 
 the place of the pith. The green secretion in the 
 pulp of the woody layer slightly tinges the fluid 
 in the cells of the pith to some distance from the 
 circumference ; but, the colour being more and 
 more diluted, the central cells are completely co- 
 lourless. The sap vessels are spiral, each being 
 composed of three distinct filaments. The proper 
 or returning vessels are cribriform and extremely 
 delicate. 
 
 As in the former division of this description of 
 herbaceous stems, there are many modifications of 
 structure, so, in some instances, in this division, it 
 approaches more closely to, and in others recedes 
 more widely from, the characters of that of trees. 
 Thus, in the stem of Endive, Chicorium Endivia, 
 which Malpighi has described *, the vessels near 
 the circumference are disposed in lines directed 
 towards the centre, and are separated by small 
 septa of compressed cellular substance; but the 
 interior, which are also the larger, extend in 
 rays a considerable way through the pith. In the 
 stem of Lettuce, Lactuca sativa, which may be 
 regarded as the intermediate of the two divisions 
 already noticed, the sap vessels being in distinct 
 fasciculi like those of the first, but arranged in 
 
 * Anatomia Plantarum, p. 25. 
 EE 3 
 
422 CONSERVATIVE ORGANS. [LECT. VIII. 
 
 one circle only round a pith, like those of the 
 second, I find that the fasciculi resemble those 
 in the Bryony, with the sap vessels, however, ar- 
 ranged in distinct divergent rays in each fasciculus. 
 The divergence, also, being on that circumference 
 of each fasciculus which is towards the centre of 
 the stem, and all the rays pointing more or less 
 to that centre, they are necessarily of very differ- 
 ent lengths: the longest rays generally containing 
 from six to ten vessels, whilst the number in the 
 shortest seldom exceeds two or three. Between 
 each ray we find the same condensed cellular septa 
 which Malpighi has described as existing in the 
 Endive. The sap vessels are all punctuated spirals; 
 but I have not been able to ascertain satisfactorily 
 the structure of the returning vessels, their deli- 
 cacy, transparency, and the milky nature of the 
 juice they convey rendering it impossible to make 
 out their characters distinctly, even under a mi- 
 croscope of the highest power. I have some rea- 
 sons for believing v that they are membranous and 
 cribriform. 
 
 In concluding the view I have taken of this 
 division of herbaceous stems, it is necessary to 
 point out an exception to the general rule, that 
 all ligneous stems are necessarily perennials, and 
 all the herbaceous either annuals or biennials. In 
 the Thorn Apple, Datura stramonium, which is 
 an annual, generally described as herbaceous, 
 and which contains a large proportion of a very 
 
LECT. VIII.] HOLLOW HERBACEOUS STEMS, 423 
 
 spongy, lax, pith, the stem, when examined un- 
 der the microscope, displays every character of 
 the real ligneous stem; resembling particularly 
 that of the Elder, except that the cells of the di- 
 vergent rays in the Thorn Apple are nearly 
 square, whereas those of the Elder are oblong. 
 The stem of Thorn Apple is in fact a soft ligneous 
 stem ; and, consequently, has been hitherto in- 
 correctly classed as herbaceous. The softness of 
 the stem is no argument against this decision, and 
 only demonstrates the great diversity, with re- 
 spect to induration, which wood displays. 
 
 B. Hollow herbaceous stems may, also, be de- 
 scribed under two subdivisions ; a. thejistulous or 
 unpartitionedy and b. the partitioned. 
 
 a. In internal structure there is little to dis- 
 tinguish the Jistulous or unpartitioned hollow 
 stems from those of the last division, except the 
 deficiency of the pulp or pith which constitutes 
 the hollow ; some of them, in every other respect, 
 resembling closely the Bryony, or those of the 
 first subdivision ; and others those of the second. 
 With regard to the cavity in the centre of the 
 stem, in some it is apparently the consequence 
 of an original deficiency of cellular matter; for 
 that which exists has evidently undergone no com- 
 pression; whilst in others it is evidently com- 
 pressed, and the hollow seems to be the result 
 
 E E4 
 
424 CONSERVATIVE ORGANS. [LECT. VIII. 
 
 of air introduced into the centre of the stem 
 at a period subsequent to the formation of the 
 pith, which at first fills up the whole of the space 
 within the vascular circle. Whether the air con- 
 tained in these stems be introduced from without 
 or generated in the stem as a secretion, is still 
 a question in phytology. Examining it eudiome- 
 trically, I found that the stem of Cow Parsnep, 
 Heracleum sphondylium, contains a little more 
 carbonic acid gas, than atmospherical air, from 
 which it differs in no other respect. But if it be 
 a secretion, the components will probably vary in 
 different stems *. 
 
 b. The internal structure of the partitioned 
 hollow stems is the same as that of the fistulous, 
 except at the knots where the partitions are si- 
 tuated. In selecting the stem of Common Hemlock, 
 Conium maculatum, to illustrate this part of their 
 structure, I shall point out to you a variation in 
 the arrangement of the fasciculi of descending ves- 
 sels, which is peculiar to this plant and a few others 
 of the same natural order of the umbelliferae. 
 
 If we place a transverse section of the stem 
 of Hemlock under the microscope, we find the 
 cortex to consist of a cuticle composed of a thin 
 cribriform epidermis,, covering two rows of square 
 cells 0. (Plate 9, fig. 8) ; and a cellular integu- 
 ment, c., through which the proper vessels descend 
 
 * This part of our subject shall be fufly discussed in its pro- 
 per place. 
 
LECT. VIII.] HOLLOW HERBACEOUS STEMS. 425 
 
 in large flattened fasciculi b. b. placed near the 
 cuticle. Immediately beneath the cuticle, round 
 the fasciculi of proper vessels, and bordering the 
 cellular integument interiorly, the cells are irre- 
 gular, smaller than in the centre, and filled with 
 a green secretion, which gives the green colour to 
 the stem; but the colouring matter forming the 
 blotches or maculae is deposited in the cells of the 
 cuticle. Within the cortex, the principal bundles 
 of sap vessels, d. d. with their accompanying de- 
 scending vessels, are placed at equal distances 
 round the circle, and stretch inwards, affording in 
 the transverse section a form not unlike the print 
 of the human foot. These alternate with smaller 
 fasciculi, e. each of which is accompanied by three 
 clusters of descending vessels ; the circumstance 
 in which the peculiarity of this stem consists. 
 The cellular matter is composed of irregular hex- 
 agonal cells, turgid with a colourless mucilaginous 
 fluid, which becomes firm and elastic when the 
 part is placed in cold water. 
 
 The nature of the septum or partition, which 
 interrupts the cavity of the stem at each knot, 
 in this description of stem, is readily seen in a 
 longitudinal section. By the aid of a common 
 lens, the vascular bundles are easily traced, by 
 their whiteness and opacity. Thus in the mar- 
 ginal figure (see next page) the white line a. is a 
 bundle which runs uninterruptedly upwards on 
 
426 CONSERVATIVE ORGANS. [LECT. VIII. 
 
 the side of the stem where no leaf is given off; 
 but b. when it arrives at the base of 
 the leaf c. divides, and one part d. 
 enters the leaf, while the other, curv- 
 ing inwards, continues its course 
 along the stem : it then gives off a 
 bundle a little higher up, which ana- 
 stomozing with a bundle from d. forms 
 part of the fasciculi for supplying the new shoot, 
 originating in the axilla of the leaf. The sep- 
 tum is not a thin plate or diaphragm traversing 
 the hollow of the stem ; but a mass of cellular 
 substance, which, in the example before us, oc- 
 cupies the space from e. tof. and is condensed in 
 the centre where it appears white and opaque. In 
 a thin longitudinal slice examined under the mi- 
 croscope, we find that the cellular matter forming 
 the septum is the same as that of the other parts, 
 except where it is condensed in the centre (Plate 
 9, fig. 9, h. *), at which place the cells assume a 
 .horizontal position, as if the cellular texture in the 
 parts above and below terminated at that spot, 
 
 * In this figure (which represents a longitudinal section, 
 passing through the smaller vascular fasciculus marked e. fig. 8), 
 a. is the cellular matter of the cortex ; b. a bundle of proper 
 vessels separated by a slip of cellular substance from the sap 
 vessels e. which are simple spirals, surrounded by a few oblong 
 cells d.f. : the cells g. which supply the place of the pith, are 
 condensed at h. forming the real septum in the hollow parti- 
 tioned stem. 
 
LECT. VIII.] HOLLOW HERBACEOUS STEMS. 427 
 
 and the boundary of the one compressed that of 
 the other; each mass exceeding in length the 
 space it is intended to occupy. In the old stem, 
 however, when the pulp which constitutes the pith 
 becomes dry and the cells empty, the diaphragm 
 is condensed to a thin opaque plate. 
 
 In both kinds of hollow stems, the sap vessels 
 are spirals, formed of one or two flat, entire or 
 punctured threads ; while the proper vessels, as far 
 as I have been able to observe them, are simple, 
 transparent, cribriform tubes. The number of 
 vessels varies in each fasciculus, generally in- 
 creasing with the growth of the plant, and conse- 
 quently the same fasciculus consists of a differ- 
 ent number of vessels, according as the part in 
 which it is situated is nearer to, or farther from 
 the root. Thus, in a mature stem of the Gourd, 
 M. Kieser, who took the trouble of counting the 
 sap vessels, says the number in each fasciculus, 
 near the top of the stem, seldom exceeds six or 
 seven, but below the second knot it is nineteen, 
 and still greater below the third. In the centre of 
 the stem the number of vessels in each fasciculus 
 is twenty-three, and near to the root twenty-nine, 
 if the stem be examined in autumn. But besides 
 this diversity with respect to number, Kieser as- 
 serts that the size and general characters of the 
 vessels vary. At an early period, or near the sum- 
 mit of the plant, he says they are simple spirals ; 
 lower down they are of a larger size and annular 
 
428 CONSERVATIVE ORGANS. [LECT. VIII. 
 
 spirals ; in the third internodial space they are still 
 larger, and two or three of them have become 
 punctuated spirals ; and the number of these in- 
 creases as we descend in the examination of the 
 stem. In the mature stem, near the centre, each 
 fasciculus contains six large punctuated spirals, and 
 near the root only six of the twenty-nine vessels in 
 each fasciculus are simple spirals, all the rest being 
 punctuated. The same phytologist also asserts, 
 that as these vessels enlarge, their sides become 
 thicker and more opaque, and a sort of cellular 
 tissue is formed within them *. A similar variety 
 in the number of the vessels which compose the 
 fasciculi of sap vessels, occurs in almost all her- 
 baceous plants ; and my observations tend, also, 
 to confirm Kieser's remarks respecting their aug- 
 mentation in size ; but I have not been able to 
 satisfy myself of the correctness of his opinion, 
 that the transformation of the simple spiral vessels 
 is the cause of the diversity of character of the 
 vessels in the different parts of the stem. I 
 have not examined the Gourd ; but in the stems 
 of Bryony and of the Cucumber, which belong 
 to the same natural order of plants, I have found 
 the three distinct kinds of sap vessels, which 
 I demonstrated to you in our examination of the 
 structure of the stem of Bryony, in every part of 
 
 '* Mem. sur I' Organisation des Planles, p. 134-. 
 
LECT. VIII.] HOLLOW HERBACEOUS STEMS. 429 
 
 the stem. We must, also, bear in mind, that, in 
 his explanation of these diversities, Kieser has a 
 favourite theory to support ; and believes that the 
 simple spiral is the original form of every ve- 
 getable vessel, whether annular or cribriform, and 
 whether existing in trees and shrubs or in herba- 
 ceous plants. But the fallacy of this opinion is 
 easily proved by a good microscope and attentive 
 observation. I am even satisfied that the exa- 
 mination of the vessels in their united state in 
 the fasciculi of herbaceous stems, often leads to 
 erroneous conclusions; for, as the thread form- 
 ing the spiral is more opaque than the membrane 
 forming the membranous cribriform vessels, if 
 one of these be mixed with several spiral ves- 
 sels, it assumes a ribbed character owing to the 
 spirals situated below or behind it being ob- 
 scurely seen through its coat ; thence we con- 
 clude that it is an annular vessel ; and the error 
 is detected only when we can fortunately separate 
 the vessels from each other, and from the sur- 
 rounding cellular matter, an operation which is 
 extremely difficult. Thus, in my dissections of the 
 stem of Bryony, the large vessels in each fasciculus 
 always appeared as punctuated annulars, until 
 accident enabled me to detach one of them from 
 the connecting parts. It appeared, evidently, to 
 be composed of a simple membranous coat, punc- 
 tured in circles round the vessels (see Plate 9, fig. 
 7). With regard to the rigid membranous vessel, 
 
430 CONSERVATIVE ORGANS. [LECT. VIII. 
 
 which Kieser has named the annular spiral, I can 
 form no idea of the possibility of its transformation 
 from the spiral, the rings being entire and placed 
 at the distance of their diameter from each other; 
 whereas the spires of the simple spiral are in con- 
 tact, and never appear otherwise unless the fibre 
 be drawn out, which is very frequently the case in 
 preparing the section of a stem for the microscope. 
 The hypothesis of Kieser is certainly very im- 
 posing, from the simplicity with which it accounts 
 for the varied form of the sap vessels in the fasci- 
 culi of herbaceous stems ; but my observations 
 prevent me from adopting his conclusions. 
 
 The proper or descending vessels are also of 
 two different kinds, at least in respect of diameter, 
 as is evident in the portion of a transverse section of 
 the stem of Hemlock represented in Plate 9, fig. 
 8 ; but I have not been able to make out satis- 
 factorily the characters of either, except that both 
 are cribriform. Indeed, we can scarcely conceive 
 in what manner these vessels could perform their 
 functions, were their coats completely impervious; 
 for, as they convey the sap, altered in its proper- 
 ties in the leaf, or converted into proper juice, 
 or that fluid from which all the other secre- 
 tions, and even the woody fibre, are produced, 
 there must be some means of communication be- 
 tween them and the cells, in which these secre- 
 tions are deposited: and this would be necessary 
 
LECT. VIII.] HOLLOW HERBACEOUS STEMS. 431 
 
 although the ultimate changes may take place in 
 the cells ; an hypothesis, however, which I am by 
 no means prepared to admit. 
 
 Pursuing our inquiries into the structure of 
 herbaceous roots, we find that the analogy be- 
 tween these organs and the stem is less close 
 than in ligneous plants. This arises in many in- 
 stances from the difference in the duration of the 
 life of these parts in herbaceous plants ; for the 
 root may be biennial or perennial, when the stem 
 or stems are annual only, or dying in the autumn 
 and giving place to others, which rise from the 
 same root in the succeeding spring. 
 
 When the root is annual only, as, for ex- 
 ample, that of the Sweet Pea, Lathyrus odoratus, 
 it consists of a cuticle enclosing a thick cellular 
 cortex, apparently devoid of vessels; and a cen- 
 tral part, which is composed of a bundle of sap 
 vessels, or rather of several bundles, arranged so 
 as to form an irregular six-rayed star, embedded 
 in a mass of small oblong cells, through which 
 six fasciculi of proper vessels descend, almost 
 touching the cortex, and situated in the spaces 
 formed by the rays of the central fasciculus of 
 sap vessels. The sap vessels are all punctuated 
 spirals * ; but those in the centre are smaller 
 
 * This is the only form of sap vessel I have observed in an- 
 nual roots ; and as Kieser, also, found punctuated spirals only 
 
432 
 
 CONSERVATIVE ORGANS. 
 
 [LECT. vin. 
 
 than those which constitute the rays of the fas- 
 ciculus (see marginal cut). Such 
 is the general structure of the 
 majority of strictly annual stems ; 
 but they vary as far as regards 
 the number of the rays of the 
 s.ap vessels and the situation of the proper vessels. 
 The cells of the bark are, commonly, hexagonal, 
 varying however in size ; and those of the central 
 part oblong, and apparently transversely fur- 
 rowed ; but the transparency of their coats ren- 
 ders it difficult to ascertain whether this furrowed 
 appearance arises from oblong slits, opening from 
 one cell into another, or from elevations perhaps 
 of a glandular nature. In -all the annual roots 
 belonging to herbaceous plants, which secrete a 
 white opaque proper juice, as, for example, the 
 PPP V > P a P aver somniferum, nearly the whole of 
 the cells are oblong, or rather tubular ; and are ar- 
 ranged with great symmetry, 
 in the manner figured at a. (see 
 marginal cut). A few cells 
 very highly magnified are fi- 
 gured at b., chiefly to show the 
 appearance of the lateral fur- 
 rows or transverse slits, which 
 
 in the root of the Gourd, I am disposed to believe that, the 
 simple spiral is rarely, if ever, found in the annual root. 
 
 3 
 
LECT. V1IJ.] STRUCTURE OF HERBACEOUS ROOTS. 433 
 
 are very conspicuous in these cells. I have not 
 been able to detect any fasciculi of proper vessels 
 in roots of this description, and I am, therefore, 
 disposed to believe that these tubular cells are not 
 only the reservoirs, but the conductors of the 
 proper juice. That they are endued with con- 
 tractility, and communicate freely with each 
 other, is evident: for, by making a horizontal 
 section of the root, the exudation of juice is much 
 greater than can be contained in the range of cells 
 which is divided ; and, by placing a longitudinal 
 slice of the root under the microscope, we find 
 the cells of several successive ranges empty and 
 shrunk. That this longitudinal communication 
 is regulated by valves, or something of a similar 
 nature, is probable; for, the exudation of the 
 juice is much more considerable on the divided 
 surface, and the shrinking of the cells extends to 
 more distant ranges, in the portion of the divided 
 root which remains attached to the plant, than in 
 that which is separated from it. 
 
 The disposition of the parts of the root is more 
 varied in biennial than in annual roots. Taking 
 the root of Burdock, Arctium lappa, as an ex- 
 ample, we find that, in the first season of its 
 growth, or in the seminal plant, it consists of a 
 thick cellular bark, the cells of which are irre- 
 gular hexagons arranged in concentric circles 
 around a large central part, which is composed 
 
 VOL. I. F F 
 
434 CONSERVATIVE ORGANS. [LECT. VIII. 
 
 chiefly of oblong cells, or rather short hexa- 
 gonal tubes. These tubes in the transverse section 
 appear arranged in beautiful rays proceeding from 
 the centre to the circumference, and, in the lon- 
 gitudinal section, show nearly the same symme- 
 trical ranks that have been described as exist- 
 ing in the Poppy root. The sap vessels are com- 
 paratively few in number, and are arranged in rays 
 through the central part. They are larger than the 
 cellular short tubes, which are condensed in the 
 line of each ray of sap vessels, so as to produce a 
 very beautiful appearance in a transverse slice of 
 the root examined under the microscope. All the 
 sap vessels are punctuated, but I have not been 
 able to satisfy myself that they are spiral. In the 
 second year, a new circle of short tubes is formed 
 with Some additional sap vessels interspersed 
 through it, both preserving the radiated arrange- 
 ment ; the old bark appears lacerated, shrivelled, 
 and pushed outwards, whilst the space betwixt it 
 and the new central matter, is filled up with fresh 
 cortical cells. 
 
 The short tubes appear to be the principal re- 
 servoirs of the mucus, with which this root 
 abounds ; but it is present in the cortical cells also, 
 a lateral communication existing between these 
 and the hexagonal tubes. It is apparently in- 
 tended for advancing the fructification of the 
 plant, being gradually absorbed as that process is 
 
LECT. VIII.] STRUCTURE OF HERBACEOUS ROOTS. 435 
 
 perfected; at which time the short tubes are 
 emptied, and their sides gradually become ligne- 
 ous and opaque. 
 
 The root of the Carrot, Daucus carota, re- 
 sembles that of the Burdock in general structure, 
 but the sap vessels are comparatively more nu- 
 merous, and the cellular rays more condensed. 
 The cells and short tubes are rather four-sided 
 than hexagonal; and there is no symmetrical ar- 
 rangement of the latter. The sap vessels are all 
 punctuated, even the smallest and most recently 
 formed, which militates against Kieser's opinion of 
 transformation. 
 
 In the root of Hemlock, Conium maculatum, 
 the sap vessels are situated chiefly in the centre, 
 in fasciculi, interspersed with cellular matter, dis- 
 posed in narrow wedgelike masses, divided by 
 more condensed cellular matter, closely resem- 
 bling the divergent rays in the roots of trees. The 
 cortex is thick, and contains various fasciculi of 
 proper vessels, disposed at regular distances, so 
 as to form a kind of double circle. The sap vessels 
 are punctuated spirals. 
 
 Such is the structure of these three biennial 
 roots. The diversity they display is sufficient to 
 demonstrate the variations in the position of the 
 parts, which occur in biennial herbaceous roots. 
 In all of them the proper vessels constitute the 
 greater part of the bulk of the root ; and appear 
 
 FF2 
 
436 CONSERVATIVE ORGANS. [LECT. VIU. 
 
 to be chiefly reservoirs of the proper juice formed 
 by the first year's foliage, which is expended in 
 the formation and perfecting of the flower-stem 
 and the fructification, the productions of the second 
 year. 
 
 As the growth of the flower-stem, therefore, 
 and the evolution of the flower advance, the root, 
 instead of increasing in bulk, gradually shrivels, 
 and becomes of a more ligneous texture, owing 
 to the absorption of the proper juice and to the 
 emptied state of the short tubes. On this account 
 we find that those biennial roots, the Carrot and 
 Turnep for example, in which the art of cultivation 
 has so much increased the deposition of nutritious 
 matter, as to render them important as articles of 
 food to man and other animals, cease to be fit for 
 this purpose very soon after the flowers of the 
 plants to which they belong make their appearance. 
 
 The perennial herbaceous roots are still more 
 varied in structure, as far as regards the proportion 
 and arrangement of the vascular parts, than either 
 the annual or the biennial. It would be impossible 
 in this place to demonstrate even a very small pro- 
 portion of those diversities : and these roots have 
 been too little examined to admit of any classifi- 
 cation founded on structure. I shall venture, how- 
 ever, to arrange them into two classes, the first 
 comprehending those which, besides sap and pro- 
 per vessels, are composed chiefly of short tubular 
 
LECT. VIII.] STRUCTURE OF HERBACEOUS ROOTS. 437 
 
 cells, which appear symmetrically arranged in the 
 longitudinal section of the root: the second, those 
 which consist of sap and proper vessels, and com- 
 mon cellular matter only, exhibiting no peculiar 
 symmetry of arrangement in the longitudinal sec- 
 tion. 
 
 1. Perennial herbaceous roots composed 
 chiefly of tubular cells symmetrically arranged. 
 As examples of this class, we may select the roots 
 of Dandelion and of Marsh Mallow; because the 
 principal secretion in the one is an opaque, white, 
 glutinous fluid, and that in the other a transparent 
 colourless mucus. 
 
 If we place a transverse and a longitudinal slice 
 of the root of Dandelion, Leontodon Taraxacum, in 
 the first year of its growth, un- 
 der the microscope, it appears 
 composed of a cellular pith a. 
 (see marginal cut), surrounded 
 
 by ten fasciculi of sap vessels 
 b. ; and a very thick cortex, 
 which consists, interiorly, of a 
 concentric layer of smaller cells 
 arranged in rays, through which run numerous 
 fasciculi of proper vessels, c. arranged so as to 
 form three concentric circles ; and exteriorly of a 
 mass of hexagonal cells, the same as the pith 
 covered with a thick cuticle, d. The sap vessels are 
 punctuated, the perforations being oblong trans- 
 
 FF3 
 
438 CONSERVATIVE ORGANS. [>ECT. VIII. 
 
 verse slits; and the radiated cells are tubular 
 and arranged in symmetrical order. The cha- 
 racter of the proper vessels can scarcely be made 
 out, owing to their transparency and the white 
 juice with which they are filled; but they are evi- 
 dently perforated and communicate laterally with 
 the tubular cells, into which the juice they convey 
 is filtered, to be preserved for the purposes of 
 the plant. This juice probably undergoes some 
 change in its passage, as it appears to be more pel- 
 lucid in the tubular cells, than in the proper 
 vessels. 
 
 As the root advances in age, additional vessels 
 are added to the fasciculi of sap vessels, until the 
 whole of the central part of the stem is nearly oc- 
 cupied with them ; and, the original cellular matter 
 being closely compressed between the fasciculi, 
 the vascular portion assumes the aspect of one 
 large fasciculus. Vessels are added exteriorly also ; 
 but these are much fewer in number, although 
 they are larger and more distinct than those within 
 the original circle. In the same manner a new 
 layer of cellular tubes and of proper vessels is an- 
 nually added to the bark, so that a transverse 
 section of an old root appears to the naked eye to 
 consist of an opaque woody central part sur- 
 rounded with concentric circles, alternately 
 opaque and transparent. The old cuticle, with a 
 portion of cellular matter adhering to it, is annu- 
 ally pushed outwards, as in the trunks of trees, 
 
LECT. VIII.] STRUCTURE OF HERBACEOUS ROOTS. 439 
 
 and its place is supplied by a new one ; but in 
 this plant the cellular matter, which is found 
 situated immediately under the cuticle in the 
 young*, is deficient in the old root. 
 
 The transverse section of the root of Marsh 
 Mallow, Althaea officinalis, displays a kind of 
 pith composed of one large fasciculus of sap vessels 
 in the centre, surrounded by a mass of cells ar- 
 ranged in rays, having a few small fasciculi of sap 
 vessels dispersed through it; and several larger 
 on its verge, forming an interrupted circle round 
 it. The cortex is thick, cellular, and contains clus- 
 ters of proper vessels arranged in a radiated form* 
 In the longitudinal section we find that the sap 
 vessels are punctuated, but not spiral; and the 
 tubular cells are comparatively much shorter and 
 wider than those in the root of Dandelion ; a cir- 
 cumstance which appears almost to be essential, 
 when we consider the nature of the mucilaginous 
 secretion deposited in them. 
 
 In both these roots the central part readily se- 
 parates from the cortex; and, except in very 
 young roots, it is from the latter only that we can 
 extract the secretions on which their value as me- 
 dicinal agents depends. 
 
 2. Perennial herbaceous roots composed chiefly 
 of common cellular matter. The root of Deadly 
 Nightshade, Atropa Belladonna, may be taken as 
 
 FF4 
 
440 CONSERVATIVE ORGANS. [LECT. VIII. 
 
 an example of the general structure of this di- 
 vision. It is composed of a central part and a 
 very thick bark. Placing a transverse section of 
 the young root under the microscope, we find that 
 the central part consists chiefly of cellular matter 
 postured in a radiated manner, with one large 
 fasciculus of sap vessels in the centre, and several 
 smaller fasciculi interspersed through it, forming 
 nine or ten indistinct, interrupted rays. In the 
 root of the second year, the additional sap vessels 
 appear as an interrupted circle bounding the cen- 
 tral part; and in older roots, as new circles are 
 annually added, the transverse section resembles, 
 in some degree, that of a ligneous stem ; or it ap- 
 pears to consist of a pith, concentric circles of 
 wood traversed by divergent rays, and a bark. In 
 the longitudinal section we perceive that the sap 
 vessels are punctuated, but certainly not spiral; 
 and that the cells are oblong, but not arranged in 
 the symmetrical manner, which characterizes the 
 former division of the roots under examination. 
 Decorticating the root, we perceive, also, that the 
 fasciculi of sap vessels do not run in straight lines, 
 but take a waving course; and by vessels separat- 
 ing from one fasciculus coming in con- 
 tact with those separated from another, 
 the whole appears like a reticulated tex- 
 ture on the surface of the central part 
 (see marginal cut); a circumstance, 
 however, which is not peculiar to this root, but is 
 
LECT. VIII.] STRUCTURE OF HERBACEOUS ROOTS. 44l 
 
 general to all herbaceous roots in which the cen- 
 tral part consists of rather more cellular than 
 vascular matter. 
 
 Such is the general structure of herbaceous 
 roots. The main caudex in every instance is more 
 or less of a spindle shape ; but it frequently be- 
 comes forked near the apex, in which case there is 
 a separation of the sap vessels, in the same man- 
 ner as occurs in dividing a skein of threads into 
 two or three parcels; each fork of the root con- 
 taining a portion of the vessels belonging to the 
 main body of the root. In the lateral branches or 
 rootlets, however, this is not the case. These are 
 generally given off at right angles with the main 
 root; and each is composed of one large fasciculus 
 of sap vessels enclosed in a cellular cortex ; but 
 very few of these vessels are given off from those 
 of the caudex; the majority being new vessels ge- 
 nerated in the puncta vitalia; in which the rootlets 
 originate. Whether these new vessels anastomose 
 (using the expression as it is employed in speaking 
 of animal vessels) with the vessels of the main 
 root, I have not yet been able to satisfy myself; 
 they are evidently closely applied to and lost on 
 the surface of the fasciculus of the caudex whence 
 they originate, and pour their contents into it; 
 but this might be effected without an anastomosis, 
 by the lateral transmission through the punctures 
 in the coats of the vessels. 
 
442 CONSERVATIVE ORGANS. [LECT, VIII. 
 
 In general, the lateral rootlets extend in the 
 direction of their axis, and display an uniform 
 structure throughout their length ; but this is oc- 
 casionally altered by the nature of the soil. Thus, 
 on the root of the common Sweet-pea, Lathyrus 
 odoratus, when cultivated in a dry soil, we fre- 
 quently find that the rootlets, instead of extending 
 as fibres, swell and assume all the external charac- 
 ters of knobs; which, however, differ from tubers 
 in being merely reservoirs of nutriment, without 
 containing the germs of future buds. When one 
 of these is dissected, the vessels are seen to origin- 
 ate as in the other rootlets, but they soon divide, 
 and embrace the cellular mass which 
 contains the nutritious matter, of which 
 the knob is the reservoir (see marginal 
 cut, in which a. represents the knob, 
 and b. b. b. the natural radicles). The 
 explanation of the formation of these 
 occasional knobs on herbaceous roots, 
 advanced by Sir J. E. Smith, does not 
 now appear to me so satisfactory as I 
 formerly supposed it to be (page 206) ; 
 for I find that they appear on the roots when 
 " no sudden fresh * supply of food is furnished." 
 It is probable, also, that such a supply, if made 
 to a half-starved plant, the roots of which as 
 yet display no knobs, would occasion the na- 
 tural extension of the rootlets, instead of producing 
 
LECT. VIII.] STRUCTURE OF HERBACEOUS ROOTS. 443 
 
 knobs. It appears to me, that when an herba- 
 ceous plant is partially stinted of moisture and 
 nutriment in the soil, the functions of some of the 
 rootlets are destroyed, owing to the sap vessels 
 losing their irritability and becoming obstructed; 
 while at the same time the absorbing orifices of the 
 cuticle become also impermeable. But as the other 
 rootlets still continue in a natural state, the plant 
 is kept alive; and as the proper juices are se- 
 creted, the usual supply is sent to the affected 
 rootlets, which, however, not being able to assi- 
 milate it, the cellular matter in which it is depo- 
 sited swells, and the rootlets assume the cha- 
 racter of the knobs in question *. 
 
 From the examination of the structure of her- 
 baceous roots, which we have just concluded, se- 
 veral practical hints may be obtained. Thus it ap- 
 pears probable, that those roots, containing bland 
 saccharine or amylaceous secretions, which possess 
 a moist cellular central part, are the best adapted 
 for rewarding the skill of the horticulturist, in 
 converting them into articles of food for man and 
 other animals. We also discover the reason that 
 
 * Mr. Keith says, " This anomaly seems to be merely the 
 " result of a provision of Nature, by which the plant is en- 
 " dowed with the capacity of collecting a supply of moisture 
 " suited to existing circumstances, and hence of adapting itself 
 to the soil in which it grows." Syst. of Phys. Bot. vol. ii. 
 p. 271. 
 
444 CONSERVATIVE ORGANS. [*,ECT. VIII. 
 
 the central parts of some medicinal roots are as 
 valuable as the cortical; although, in general, 
 the bark is that part of the root which is most 
 richly stored with the proper juices of the plant. 
 In examining unknown roots, when we find the 
 central part woody, we may always conclude that 
 it consists entirely of sap vessels, and therefore is 
 useless either as food or as medicine; but when it 
 is composed chiefly of a moist, cellular substance, 
 we may expect to find it useful, from having some 
 of the proper juice and secretions of the plant de- 
 posited in it. The ignorance of this fact, led 
 Pharmacopolists, until very lately, to expend un- 
 necessarily much labour and time in preparing 
 several vegetable decoctions and extracts, as, for 
 example, the decoction of sarsaparilla ; for the 
 preparation of which the root underwent long 
 macerations and much boiling, from an idea that 
 its virtues were contained in the ligneous central 
 part ; whereas the saponaceous mucus for which 
 it is valued, is deposited solely in the cortical 
 part, and can be entirely extracted by cold water. 
 In selecting the proper period for digging up 
 roots for medicinal purposes, it ought to be re- 
 collected that, as the proper juices which are 
 stored up in the roots of such plants as produce 
 leaves only in one year, and then flower and die in 
 the second, are expended in the process of fructi- 
 fication ; biennial roots should be taken up at the 
 
LECT. VIII.] STRUCTURE OF HERBACEOUS ROOTS. 445 
 
 end of the first season of their growth, for then 
 the cells are turgid with the secretions. Perennial 
 roots, also, should be dug up before the central 
 part becomes ligneous.; for, as these roots increase 
 in diameter by annual additions to both their cen- 
 tral and cortical parts, in the same manner as the 
 stems of trees, the interior of the central part be- 
 comes every year more and more inert, and ul- 
 timately decays; so that, in employing such roots, 
 when old, even before they decay, the active 
 principle they contain becomes too largely diluted 
 with the inert matter to answer the purposes 
 expected from them as drugs. 
 
 In closing our researches into this part of Phy- 
 totomy, the anatomy of stems and roots, I may 
 observe that the subject has, hitherto, been 
 imperfectly examined; although the fieJd of in- 
 vestigation is very extensive, and the harvest it 
 contains calculated to repay amply the toil of the 
 most assiduous labourer. The improvements which 
 are daily making in the construction of the micro- 
 scope, are likely soon to set aside all the obstacles 
 depending on the minuteness of the parts; and a 
 very little experience is sufficient to make the stu- 
 dent 'expert in the use of this instrument. The 
 best authors to be consulted on the subject are 
 Grew, Anatomy of Plants; Malpighi, Anatome 
 Plantarum; Rudolphi, Anatomic der Pflanzen; 
 Kie&er, Me*moire sur FOrganisation des Plantes; 
 
446 CONSERVATIVE ORGANS. [iJSCT. VIII. 
 
 Mirbel, ElSmens de Physiologic v6g6tale; Corn- 
 par etti, Prodromo de Fisica vegetabile; Du 
 Hamel, La Physique des Arbres; Hill on the 
 Construction of Timber; Krocker, Diss. de Plan- 
 tarum Epidermide; Bauer, Tracts relative to 
 Botany, London, 1809; Bolimer de Vegetabilium 
 celluloso Contextu ; Reichel de Vasis Plantarum 
 spiralibus ; Histoire d'un Morceau de Bois, &c. par 
 A. A. du Petit Thouars; Keith's System of phy- 
 siological Botany ; Supplement to the Encyclo- 
 paedia Britannica ; and Mr. Knight's papers in the 
 Philosophical Transactions. 
 
LECT. IX.] HYBERNACULA. 447 
 
 LECTURE IX. 
 
 OF LEAVES IN THEIR UNEXPANDED STATE, OR AS 
 
 THEY ARE CONTAINED IN THE GEM: IN THEIR 
 
 EXPANDED STATE, OR AS CONSTITUTING FOLIAGE. 
 
 HAVING concluded our examination of roots, 
 stems, and branches, we are now prepared to in- 
 vestigate the structure of leaves. 
 
 In winter, while the power of vegetation is 
 inactive, and the groves and forests present the 
 desolate appearance of naked stems and branches, 
 the majority of trees, shrubs, and many other 
 plants may be regarded as existing in a state of 
 torpor, similar to that which some animals expe- 
 rience in the same season. During this period the 
 leaves are enclosed in small pyramidal bodies, 
 either projecting from the surface of the stem and 
 branches, or seated upon the roots; and in this 
 state they remain until the warmth of the vernal 
 sun, again rousing into action the vegetable func- 
 tions, enables them to burst open their coverings, 
 and clothe the woods anew in all the luxuriance of 
 foliage. In our examination of leaves, therefore, we 
 must regard them both as they are shut up in these 
 
448 CONSERVATIVE ORGANS. [LECT. IX. 
 
 hybernacula, or winter habitations, and in their 
 expanded state. 
 
 The pyramidal bodies which I have just no- 
 ticed are well known by the name of buds; and 
 the appellation is so universally applied in this 
 country in reference to their appearance on trees 
 in early spring, that it would be pedantic to re- 
 ject it ;. besides, I have already used it in speaking 
 of the origin of branches. But as the term bud is 
 also employed to denote the separate flower before 
 it blows, and as the purposes of science are better 
 attained by using a word applicable to the object 
 only which it is intended to present to the mind, 
 I shall employ the term hybernaculum as syno- 
 nimous with bud, in treating of this part of our 
 subject. 
 
 A HYBERNACULUM may be defined : an organic 
 body which sprouts from the surface of different 
 parts of a plant, enclosing the rudiments of the 
 new shoot ; and which is capable of evolving a new 
 individual perfectly similar to the parent. This is a 
 modification of the definition of Gsertner *, which 
 
 * " An organic body generally sprouting from the surface 
 " of a plant, without previous fecundation ; in the beginning 
 " distinct from the peculiar and permanent membranes of the 
 " plant ; but which, in a certain time, either becomes a part 
 " of the parent, or separates from it, and by the increase of its 
 " own substance becomes a new plant, closely resembling the 
 " parent." Gartner de Fructibus Plant, p. 3. 
 
LECT. IX.] HYBERNACULA. 449 
 
 is objectionable only in expressing an opinion, as 
 to the early state of the bud, that may be dis- 
 puted*. Some hybernacula remain attached to 
 the parent ; others detach themselves after a cer- 
 tain period, but both kinds are to be regarded as 
 the lateral progeny of the plant ; for even that 
 which remains attached possesses, in a certain de- 
 gree, a separate or distinct vitality, by which it is 
 enabled to exist when forcibly detached from the 
 parent. Thus a bud taken from a tree, and pro- 
 perly planted in the ground, covered with a glass 
 to prevent too great an exhalation of its natural 
 moisture, will grow and become a tree resembling, 
 in every respect, that from which it was taken. 
 But still the plant, whether raised from a bud 
 thus forcibly detached, or from one which na- 
 turally detaches itself, is an extension only of the 
 parent, displaying all its individual peculiarities 
 the effects of soil or culture, and inheriting all its 
 diseases; whereas a plant raised from a seed is 
 a new individual, displaying the generic and 
 specific characters only of the parent. From 
 the same cause, also, plants which are natives of 
 a warm climate, when taken to a colder, and pro- 
 
 * " Hylernaculum est pars plantae includens herbam em- 
 " bryonem ab externis injuriis." Phil. Bot. 85. The ad* 
 mirable simplicity which characterizes all Linnaeus 's defini- 
 tions is here conspicuous ; but the definition is objectionable in 
 being equally applicable to the seed as to the hybernaculum. 
 
 VOL. I. G G 
 
450 CONSERVATIVE ORGANS. [t,ECT. IX. 
 
 pagated by slips or buds, never become so com- 
 pletely naturalized as to bear all the variations 
 of the new climate with impunity; but plants 
 which are propagated by seeds, although natives 
 of very warm climates, yet, become perfectly na- 
 turalized to colder in a certain number of genera- 
 tions. 
 
 Botanists enumerate three kinds of sponta- 
 neously separating Hybernacula, the Propago, 
 the Gongylus, and the Bulb; and one which does 
 not spontaneously separate from the parent, the 
 Gem. 
 
 The PROPAGO * is thus denned by Gaertner : 
 " A simple leafless, polymorphous, or variously 
 " shaped germ, in some instances naked, in others 
 " enclosed in a cortical sheath^ which sponta- 
 " neously separates from the parent, and is scat- 
 " tered in the manner of seed." It is a small 
 pulpy or cellular body of no regular shape ; and 
 is sometimes covered with an epidermis. It is 
 readily found in dividing the tubercles and 
 shields or saucerlike bodies, which appear on the 
 surfaces of Lichens, in an early stage of their 
 
 * This term was used by the ancients chiefly to denote a 
 cutting of the Vine, when buried in the ground to throw up 
 new shoots ; but it was applied also to cuttings of other plants. 
 Arbores aut semine proveniunt, aut plantata radice, aut propa- 
 gine, aut avulsione, aut surculo, aut insito et consecto arboris 
 trunco. Pliny, 1. 17. c. 10. 
 
LECT. IX.] HYBERNACULA. 451 
 
 growth. According to Gaertner all the Algee are 
 propagated by the propago, and not by seeds 
 as Hedwig and other phytologists have asserted. 
 With such names as contending authorities on this 
 subject, may we venture to suggest, that al- 
 though the sexual organs of these plants have not 
 yet been discovered, and although they throw off 
 the propago as lateral progeny, yet they may, 
 also, produce real seeds ? Many of the more per- 
 fect plants are propagated in both ways ; and 
 we know that this occurs even in the animal 
 kingdom ; for the aphis which is first propagated 
 by sexual intercourse continues its species, through 
 several successive generations, by lateral offsets. 
 
 " The GONGYLUS," according to Gaertner, " is 
 " a simple, leafless, somewhat globular, solid 
 " germ attached to the parent under the bark, 
 " and separating spontaneously from it." He ob- 
 serves that it has a close affinity to the tubers 
 found on roots; but differs inasmuch as the tu- 
 ber possesses as it were a multiplied life, so that 
 it may be divided into as many pieces as there are 
 foliaceous gems on its surface, from each of which 
 a new plant will arise. The gongylus consists of 
 cellular matter like the propago, but of a much 
 firmer and more solid consistence, and is always 
 covered with an epidermis. Gaertner supposes that 
 the Fungi, or Mushroom tribes, are altogether pro- 
 pagated by gongyli : but Michelius, Hedwig, and 
 
 G G 2 
 
452 CONSERVATIVE ORGANS. [LECT. IX. 
 
 Bulliard detected their seeds ; and there is every 
 reason for believing that these and many of the 
 other tribes of lower plants produce both seminal 
 and lateral progeny. 
 
 The BULB having been already denned (p. 164), 
 and also described as it appears attached to the 
 roots of plants ; we have now to examine it only 
 as it appears upon the stem *. It is found on the 
 stems of several species of the Lily, on that of bul- 
 biferous Coralwort, Dentaria bulbifera, and of 
 drooping Saxifrage, Saxifraga cernua, &c.*f- seated 
 in .the axilla of the leaves (Plate 4, fig. 9, a. a.). 
 If we take the Tiger Lily, Lilium tigrinum, as 
 an example, we shall find the bulbs appearing 
 like a white speck in the axilla of the leaves long- 
 before these expand. A few days, however, after 
 the expansion of the leaf the bulb assumes a py- 
 ramidal form, which gradually enlarging and 
 swelling in the centre, at length appears of an 
 ovate or nearly globular shape, with a keel ter- 
 minating in a point. During this transformation 
 
 * Mirbel denominates the caulinar bulb, Bulbille, Bulbillus, 
 and thus defines it : " Petite bulbe qui nait sur differentes par- 
 " ties de la plante hors de terre, se detache et prend racine." 
 Element de Phys. veg. Partie 2, p. 634. 
 
 I Sir J. E. Smith says he has seen bulbs form on the flower- 
 stalk of three-coloured Lachenalia, Lachenalia tricolor, whilst 
 lying for many weeks between paper to dry ; and these on being 
 put into the ground have become perfect plants, though of 
 slow growth. Infrocl, to Botany, p. 112, note. 
 
LECT. IX.] HYBERNACULA CAULINAR BULBS. 453 
 
 it also acquires colour on that part of the surface 
 exposed to the light; passing first from white to 
 green,, then to light brown, and lastly to a very 
 deep shining jet brown. On attaining this degree 
 of maturity it separates from the stem on the 
 slightest touch, or it spontaneously loses its hold ; 
 and, dropping to the ground and vegetating, 
 throws out roots and acquires all the characters of 
 a root bulb. Linnaeus, nevertheless, regarded the 
 caulinar bulb as a gem, and denominated it Gem- 
 ma decidua* ; but, independent of its spontane- 
 ously separating from the parent, which the real 
 gem never does, it differs in other essential cha- 
 racters from the gem. 
 
 Examining one of these bulbs in a mature 
 state, we find at its lower part a depression re- 
 sembling the hilum or scar, which on a seed 
 points out the place of its attachment in the seed- 
 vessel. It consists, in the bulb, of a depression 
 enclosing three elevated points, which indicate 
 the place where the vessels connecting it with the 
 parent entered. The bulb itself consists of two 
 outer scales, the uppermost large and embracing 
 the lowermost, which projecting forms the keel of 
 the bulb, and embraces another scale within it, 
 which in its turn embraces a fourth, and so on to 
 
 * Species Gemmarum variae sunt, Deciduce in Dentaria, 
 Ornithogalo, Lilio, Saxifraga. Phil. Bot. 85. 
 
 G G3 
 
454 
 
 CONSERVATIVE ORGANS. 
 
 [LECT. IX. 
 
 the germ or embryon. This struc- 
 ture is illustrated in the marginal 
 cut, which displays a transverse 
 section of the bulb very consider- 
 ably magnified : a. is the upper- 
 most or largest scale., composed of 
 a mass of cellular matter enclosed in a cuticle, 
 with seven fasciculi of vessels, as marked by the 
 dots where they are divided, running through it ; b. 
 the second or lowermost, or keel scale, with its 
 vessels; and within it are the third, fourth, and 
 fifth scales, each embracing the one within it. The 
 whole of the cells are filled with minute amylace- 
 ous granules, mingled in a clear, viscid mucilage ; 
 the opacity of the fluid being greater in the outer 
 scales and diminishing in a direct ratio as these 
 approach the centre of the bulb. Each scale is 
 covered with a beautiful, readily separating epider- 
 mis. 
 
 Making a longitudinal section of the stem of 
 the Lily, so as to divide a bulb, 
 in situ, directly through its 
 axis, we find that the fasciculus 
 of vessels a. (see marginal cut) 
 which nourishes it, and which 
 may be regarded as its um- 
 bilical cord, is a portion of the 
 bundle b. which is given off to 
 supply the leaf. As it ap- 
 
LECT. IX.] HYBERNACULA CA.ULINAR BULBS. 455 
 
 preaches the bulb, it divides into three fasciculi, 
 one of which enters the upper scale c. where it 
 splits to form the seven fasciculi that run through 
 it, as has been already demonstrated ; another 
 passes into the keel scale d. and the third subdi- 
 vides to supply the interior scales and the em- 
 bryon. The conducting vessels are all simple 
 spirals; but I have not been able to determine the 
 character of the returning vessels. When the bulb 
 is perfected it separates from the stem, as has been 
 already mentioned, in the same manner as ripe 
 fruit falls, the umbilical vessels dividing at the 
 point of attachment. 
 
 Caulinar bulbs when planted produce leaves 
 only, like those formed on the separated scales, 
 or raised from the seeds of the Lily; and like 
 these, also, they exhibit all the peculiarities and 
 diseases of the parent. 
 
 From the analogy which we recognise between 
 the sexual progeny of animals, and the seminal 
 progeny of vegetables, we are accustomed to re- 
 gard the distinct vitality of seeds and their reten- 
 tion of 1 life as a matter of course; and even per- 
 suade ourselves that we comprehend the manner 
 in which the principle of vitality is conveyed to 
 the embryon ; but, although bulbs resemble seeds 
 in many respects, yet as they are not the result of 
 the sexual functions, we find much difficulty in 
 comprehending how they acquire and maintain 
 
 G o 4 
 
45 6 CONSERVATIVE ORGANS. [LECT. IX. 
 
 that individual vitality, which is necessary for pre- 
 serving them in a state fit for vegetating, after their 
 separation from the parent, and before they are 
 planted in the ground. It would be anticipating 
 the arguments I have to advance on the causes of 
 vegetable reproduction, were I to enter largely into 
 the consideration of this subject at present; but I 
 may observe that, whether the progeny be direct 
 or lateral, a certain organization, whatever that 
 may be, peculiar to the species to which the indi- 
 vidual belongs, is requisite for retaining the vital 
 principle in conjunction with matter, and this is 
 found in the bulb as well as in the seed. In both, 
 the embryon is to be regarded not as a part only, 
 but as a compendium of the whole of the parent; 
 and the organization is so complete in every part, 
 that the separation from the parent effects no 
 change in it; and, consequently, as long as no 
 change occurs, both the bulb and the seed continue 
 fitted for commencing the vegetating process, when 
 placed under circumstances favourable for that 
 event. But it may be argued that a small portion 
 of a polypus will increase and become a perfect 
 animal, and twigs of the Willow, the Vine, and 
 of some other plants, after being separated for a 
 considerable time from the parent, will vegetate 
 if thrust into the ground and left there. We know 
 too little of the nature of polypi, to explain the 
 multiplication of the animal from cuttings, but it 
 is probable that the vegetation of the twigs re- 
 
LECT. IX.] HYBERNACULA CAULINAR BULBS. 457 
 
 ferred to, depends on the organization of the germs 
 contained in the buds of these plants approaching 
 to that degree of perfection which is found in bulbs 
 and seeds. It may, however, still be demanded 
 how is this perfect organization accomplished in 
 bulbs ? In seeds, while in the state of ovula, the 
 peculiar stimulus of the pollen may produce a 
 specific action capable of evolving all the parts of 
 that peculiar structure, with "which we find vitality 
 connected; but in bulbs we can scarcely sup- 
 pose that the vital action which completes their or- 
 ganization differs from that by which a gem, or 
 branch bud, is formed ; and yet buds, when sepa- 
 rated from the parent stem, will not live, unless 
 they are either immediately planted, or inserted 
 into another stock of a structure resembling that 
 of the parent. A question thence occurs (admit- 
 ting that all plants which throw off lateral pro- 
 geny as bulbs, propagines, and gongyli, possess 
 sexual organs, and, therefore, are capable of being 
 also propagated in a direct way), namely, can any 
 of the impulse communicated by the sexual func- 
 tions influence the lateral progeny? That such 
 an influence exists is probable, if it be allowable 
 to reason analogically and refer to the animal 
 kingdom; for we find that from the egg of the 
 aphis, which is laid in the autumn, and is the re- 
 sult of the sexual intercourse of males and fe- 
 males, a young insect is produced in the spring ; 
 which after casting its skin once or twice, pro- 
 
I 
 
 458 CONSERVATIVE ORGANS. [LECT. IX. 
 
 duces a living progeny without sexual intercourse ; 
 and " this offspring produces others by this solitary 
 "propagation, till the tenth generation; then a 
 " sexual progeny of males and females is produced," 
 and eggs are laid from their copulation*. Now, 
 although no experiments have been made to ascer- 
 tain how long a bulbiferous plant may be propa- 
 gated by bulbs only, checking every effort for the 
 production of seed, yet, we know that in bul- 
 biferous plants, when the production of bulbs is 
 considerable, the seeds are seldom ripened, and 
 even the sexual organs are often defective; and the 
 reverse happens when the production of bulbs is 
 either scanty or defective. The analogy between 
 the successive lateral generations of the aphis, 
 before males and females are formed to recom- 
 mence the propagation by eggs, and the pro- 
 gressive formation of bulbs before a flower-bulb is 
 the result, is still more striking. The bulb, which 
 is raised from the seed, produces one or two leaves 
 only, and bulbs one degree more perfect than it- 
 self; which in their turn yield stronger plants and 
 more perfect bulbs; and in this manner a suc- 
 cession of leaf-bulbs are annually evolved for four 
 or five years, till at length a flower-bulb and a 
 seminal progeny are produced. The vegetable, 
 however, differs from the animal in producing, 
 at the same time with the flower-bulb, other 
 
 * Amcenit. Academ. vol. vii. Darwin's Phytologia, ix, 3, 1. 
 
LECT. IX.] HYBERNACULA CAULINAR BULBS. 459 
 
 leaf-bulbs also; so as still to secure its preserva- 
 tion should its flowers be accidentally destroyed. 
 
 Such are the separating Hybernacula. Al- 
 though they resemble seeds in containing within 
 them a perfect embryon, yet, like that contained 
 in the attached buds, which we are now about to 
 examine, it is an offset or continuation only of the 
 parent, and not a renewal of the species. Many 
 of these plants which have been improperly named 
 imperfect, as for example the Confervas and 
 Lichens, are supposed to be propagated by no 
 other means; but as the plants thus produced dis- 
 play not only the essential, but the accidental cha- 
 racteristics of the parent, I am disposed to believe, 
 as I have already stated, that the " propagation 
 " by seed is, in their case," by no means, " out 
 " of the question *." 
 
 The attached Hybernaculum, or bud, or 
 GEM -|~, as it is more generally termed, is a small 
 oval or pyramidal body, enclosing the rudiments 
 
 * Elements of the Philosophy of Plants, by A. P. Decan- 
 dolle and K. Sprengel, 302, Eng. Trans. 
 
 f The ancients used the terms Germen and Oculus to denote 
 those buds which contain the rudiments of branches and leaves, 
 and Gemma those in which flowers only are contained ; but by 
 the moderns, Germen has been applied to denote the rudiment 
 of the fruit ; thus, Linnaeus, Germen rudimentum fructus im- 
 maturi in flore (Phil. Bot. $96), or as a generic term for all 
 buds (see Gaertner de FructibusJ, while Gemma is employed 
 exclusively to indicate caulinar buds. 
 
460 CONSERVATIVE ORGANS. j^LECT. IX. 
 
 of branches and leaves, and sometimes flowers, 
 and never separating from the parent *. 
 
 Gems are found on all trees and shrubs in 
 temperate climates. In the majority of instances 
 they are visible from the first, in which case they 
 are axillary, that is, seated in the axillae of the 
 leaves, or the angle which the upper part of the 
 footstalk of the leaf makes with the surface of the 
 stem ; and terminal, or at the extremities of the 
 branches : but in some instances, for example, 
 the Sumachs, Rhus, and the Planes, Platanus, 
 they are latent ; being hid within the base of the 
 footstalk, and never seen until the fall of the 
 leaf. In the marginal cut, a. repre- 
 sents the footstalk of a leaf of the 
 Oriental Plane, Platanus orienfalis, 
 split longitudinally to show the ca- 
 yity b. in which is seated c., the 
 gem. Gems are, however, some- 
 times protruded from the trunk, 
 long after it has ceased to produce 
 
 * The above definition is a modification of that of Gaertner, 
 who thus defines the gem, " a compound subulate or pyramidal 
 " germ, with manifest herbaceous leaflets, containing the rudi- 
 " ments of branches, and never separating from the mother." 
 Linnaeus's definition is less correct, " Gemma est hybernaculum 
 " caudici adscendenti insidens. Constat vel stipulis, vel 
 " petiolis, vel foliorum rudimentis, vel squamis corticalibus/' 
 Phil. Bot. 85, 2. 
 
LECT. IX.] HYBERNACULA GEMS. 46 1 
 
 leaves, as in the case of adventitious buds, already 
 treated of; they are also situated on roots, and on 
 tubers; but in these cases they are usually deno- 
 minated eyes, oculi. Annual plants are supposed 
 not to be furnished with gems; but although they 
 are devoid of covered gems, yet their lateral shoots 
 proceed from naked buds, which immediately 
 spread into foliage. 
 
 The relative position of axillary gfcms is ne- 
 cessarily regulated by that of the leaf; and there- 
 fore we find them, 1. opposite, or placed exactly on 
 the same line on opposite sides of the stem or the 
 branch; 2. alternate, or placed alternately, al- 
 though on opposite sides; and 3. spiral, that is, 
 placed round the stem or the branch in such a 
 manner, that a cord wound in a spiral manner round 
 it would touch each gem. They are said to be 
 simple or solitary, when one gem only is seen in the 
 axilla of each leaf, as in the greater number of in- 
 stances ; and aggregate, when, as in some plants, 
 two, three, and even more, are protruded at the 
 same time: thus we find two on the common 
 Elder, Sambucus nigra, three on broad-leaved 
 Birth-wort, Aristolochia sipho, and on Blue-ber- 
 ried Honeysuckle, Lonicera ccerulea, and many 
 on common Toothach tree, Zanthoxylum fraxi- 
 neum ; but as these are natives of cold countries, 
 it is supposed that the intention of Nature in this 
 double and triple supply is to secure the plants 
 
462 
 
 CONSERVATIVE ORGANS. 
 
 [LECT. ix. 
 
 against the effects of frost, and other accidents of 
 climate to which their situation exposes them. In 
 this climate, however, one of the additional buds 
 is always evolved the same season in which it is 
 protruded. 
 
 Du Hamel first noticed the fact, that stems 
 and branches furnished with 
 alternate axillary gems, have 
 generally one terminal gem 
 only, and those with opposite 
 have generally three terminal 
 gems. In the Horse Chesnut 
 the middle terminal gem is the 
 largest (see a. in the marginal 
 cut), and bursts soonest into 
 foliage; while those on its 
 sides (b. b.) are much smaller, 
 and sometimes never open, but 
 decay and drop from the 
 branch. In the Lilac, on the contrary, the middle 
 terminal gem is always the smallest, and scarcely 
 ever pullulates. In some trees, as for example the 
 Pine tribe, all the gems are terminal. 
 
 The gems on most trees and shrubs rise with a 
 broad base from the surface where they are pro- 
 truded, and, consequently, being in close contact 
 with it, are said to be sessile (sessiles) ; but they 
 are distant or stalked on some; as for example, 
 the common Alder, Alnus glutwosa, on which 
 
LKCT. IX.] HYBRRNACULA GEMS. 463 
 
 they are supported on a short footstalk, and are 
 then termed stalked (pedicillatce) . In employing 
 these terms, however, the student must bear in 
 mind, that they refer to the entire gem ; for a 
 writer of great merit, in describing the gem, says, 
 it " is connected with the stem or branch by means 
 " of a short and fleshy pedicle, in which the 
 " scales originate * ;" whereas this is merely the 
 base of the young branch it encloses. The angle, 
 also, which gems form with the stem or branch, 
 varies considerably in different trees ; thus on the 
 Willow they lie almost parallel to it, while on 
 Apple and Pear trees they project so as to form 
 nearly a right angle with it ; but by this the di- 
 rection of the future branch is regulated. 
 
 Let us detach a gem from any tree, for in- 
 stance the Horse Chesnut, which affords the most 
 magnificent specimen of a gem known in this 
 country, and examine its structure. We find that 
 it consists exteriorly of eight pairs of hollow scales, 
 each pair consisting of scales of the same form and 
 magnitude, placed directly opposite to each other, 
 in such a manner as to cover the opposing edges of 
 the pair within them. The inner scales are longer, 
 and more tender and succulent than the outer, 
 which are hard and covered with a viscid resinous 
 exudation, that unites them together, and is found 
 
 * Keith's Syst. of phys. Bot. vol. i. p. 65. 
 
464 CONSERVATIVE ORGANS. [tECT. IX. 
 
 on the inner scales also; but of a thinner and 
 more transparent quality. On removing all the 
 scales, the rudiments of the young branch and the 
 leaves are discovered, embedded in a soft hairy or 
 woody substance. If this examination be made, 
 by dividing a terminal gem longitudinally, in the 
 very early part of spring, before the buds begin to 
 swell, we find (see Jc. fig. 15, Plate 5) the rudi- 
 ment of the new branch apparently quite distinct 
 from the old ; separated by a partition which, as 
 the season advances and the scales begin to open, 
 is gradually obliterated, while at the same time 
 the quantity of woolly matter surrounding the 
 leaves is greatly increased, and these acquire their 
 determinate forms, folded up, however, so as to 
 occupy the smallest possible space. But although 
 the examination of any gem will afford a general 
 idea of the structure of all, yet, gems differ very 
 considerably in the number and characters of the 
 enclosing scales, their contents, the folding up of 
 the leaves within them, and the manner in which 
 these are evolved in the spring. 
 
 a. The scales which constitute, in fact, the hy- 
 bernaculum, differ, as has been already stated, in 
 size and texture even in the same gem ; in the 
 gems of different plants they differ also in num- 
 ber and in the nature of their coverings. Some 
 gems, indeed, are entirely destitute of scales, for 
 example, those of annual plants, and of many 
 
LKCT. IX.] HVBKKNACULA GEMS. 465 
 
 perennials of tropical climates, in which the in- 
 terval between the formation and the evolution of 
 the bud is so short as to require no protection for 
 the young shoot. 
 
 The scales in some instances are smeared with 
 a resinous matter ; in others they are perfectly free 
 from any moist exudation, but are smooth and 
 polished, being covered with a dry gummy var- 
 nish ; or they are externally hairy, or enveloped in 
 a velvety down. In their organic structure, they 
 closely resemble the scales of bulbs, being com- 
 posed of a layer of cellular substance, enclosed in 
 an epidermis, and containing fasciculi of ves- 
 sels running in lines from the base to the apex. 
 The vessels enter the scale in distinct fasciculi ; 
 and to this arrangement is attributed the differ- 
 ence in figure which always exists between the 
 scale and the real leaf, into the latter of which the 
 vessels enter in one fasciculus only, from which, 
 as from a common centre, they are distributed 
 through the leaf. 
 
 The inner scales perform the functions of the 
 leaves until several of these are expanded, and then 
 they generally drop off; displaying in this respect 
 a striking analogy to seed lobes, which, in many 
 seeds, rise above the surface of the ground, and 
 become green, executing all the functions of 
 leaves until these attain a certain degree of ma- 
 turity; after which they shrivel and fall. The 
 
 VOL. I. H H 
 
46(5 CONSERVATIVE ORGANS. [LKCT. IX. 
 
 period at which the scales drop, differs in different 
 plants; in some, as the common Lilac for instance, 
 the more succulent inner scales remain attached 
 until the shoot has attained to a considerable 
 length ; whereas in the Lime tree, Tilia Europea, 
 they drop before the leaf is fully expanded. Gems 
 are scarcely ever formed in the axillae of the scales. 
 
 Gems differ in their characters in the same 
 family of plants * 3 and even when found on the 
 same tree; and, as the external form of the gern 
 indicates the nature of its contents., Botanists have 
 arranged them into three species, leaf-gems, flower- 
 gems, and mixed gems. 
 
 1. Leaf-gems, or buds ( Gemmce foliiferce), 
 are long, slender, tapering, and acute, generally 
 containing, besides leaves, the rudiments of a 
 shoot, on which account they are also termed 
 wood buds; and are, in truth, embryon branches^. 
 
 * " Gemmae in eodem genere saepe diversissimae, uti constat 
 " ex genere Rhamiii, ubi Cervispina, Alaternus^ Paliurus, 
 " Frangila, gemmis diversae sunt.'' Phil. Bot. 278. 
 
 f On this fact is founded the process of budding or inocula- 
 tion, which is generally performed in July and August, and is 
 preferred to grafting for such trees as are liable to exude much 
 gum. To perform the operation, a transverse incision is 
 made in the bark of the stock through to the wood ; then a 
 longitudinal one downwards, so that the two incisions shall re- 
 semble the letter T; and, lastly, the bark on each side of the 
 longitudinal incision, is gently raised with a flat instrument, or 
 the handle of the pruning-knife. The bud to be inserted should 
 be selected from the middle of a shoot, and being separated 
 with a slice of the bark about an inch above and below it, the 
 
LUCT. IX..] HYBERNACULA GEMS. 467 
 
 2. Flower-gems ( Gemmce ftoriferce vel fructi- 
 feros) are short, thick, swelling and rounded at 
 
 the apex. Whenever the fruit ripens, all the parts 
 protruded from a flower-bud die, but those from 
 a leaf-bud give a permanent addition to the tree. 
 
 3. Mixed gems (Gemmae mlxtcc vel foliif'ero- 
 florlf'erce) are intermediate in respect to form ; but 
 generally larger than either of the other kinds-^. 
 
 The Peach tree, Arnygdalus Persica, the 
 Mezereon, Daphne Mezere- 
 um, and many other plants, 
 afford examples of distinct 
 leaf and flower gems ; the 
 Lilac and the Horse Chesnnt 
 of mixed gems; and Pear 
 and Apple trees of both leaf 
 and mixed gems. The mar- 
 ginal cut represents the twig 
 of a Pear tree, in which . is 
 
 leaf is then to be cut off, leaving half an inch of the stalk ; 
 and any wood that may remain attached to the bark, must be 
 stripped off by pulling it downwards. The lower part of the 
 bark, attached to the bud, is now to be introduced into the cross 
 incision in the stock, and pushed downward*: and, the upper 
 part being cut across, the bark of the bud and that of the stock 
 are brought into close contact. A piece of bass tied round the 
 stock over the incision is the best mode of securing the bud 
 in its place; and on loosing it, about three weeks after the 
 operation, if the bud appear swelled and the footstalk of the 
 leaf drop off, the operation has succeeded. 
 
 f Linnaeus enumerates seven species of gems: "Deciduae, in 
 H H2 
 
CONSERVATIVE: ORGANS. [LECT. ix. 
 
 a leaf or branch gem ; and b. b. are gems which 
 produce a small tuft of leaves terminated by a 
 bunch of blossom. The information afforded 
 by the external characters of gems is import- 
 ant to the practical gardener, in pruning fruit- 
 trees in winter and in early spring ; for, without it 
 the whole of the floriferous gems might be de- 
 stroyed, and the expectations of the cultivator al- 
 together disappointed. But change of soil or of 
 climate, the art of the horticulturist, and many 
 accidents, may change one kind of gems into the 
 other kinds. Thus a Solandra, Solandra grandi- 
 flora, in the Kew garden, which had never flow- 
 ered, being by an accidental neglect left without 
 water, the too luxuriant growth of the plant was 
 checked, and flower-buds were formed in the en- 
 suing summer *. From the same cause, a tree 
 newly transplanted, is often covered with blossoms, 
 although it be nearly destitute of foliage. 
 
 The leaves, as has already been mentioned, 
 are variously folded up, so as to occupy the 
 smallest possible space within the hybernaculum. 
 This regulates the expansion of the leaves when 
 
 / Deritraria, Ornithogalo, Lfiio, Saxifraga. Foliiferce, nonjlo- 
 " rifercK : Alnus. Foliiferce, et Jloriferce distinct^ : Populus, 
 " Salicis species, Fraxinus. Foliiferce et Jloriferce jeminece : 
 " Corylus, Catfpinus. Foliiferce et jloriferce mascultB : Pinus, 
 " Abies. Foliiferce etjlorifera hermaphrodite : Daphne, Ulmus, 
 " Cornus, Amygdalus. Foliifero-Jlorifera:, ut pleraeque ar- 
 4< bores." Phil. Boi. 85. * Smith's Introduction^ p. 190. 
 
LECT. IX.] HYBKRNACULA GEMS. 469 
 
 the gem opens in spring; and it is invariably 
 the same in individual plants of the same spe- 
 cies. The process is termed FOLIATION *, and the 
 figures which the leaves assume at the time, 
 have received different appellations. In noticing 
 these I shall arrange them under the three fol- 
 lowing heads : Folded, jo Overlapping, and y 
 Rolled; and mention the varieties of each kind. 
 The best method of ascertaining the character of 
 a gem, as respects its foliation, is to cut it across 
 while it is opening, and to examine the sections 
 of the leaves. 
 
 oc. Folded. This kind of foliation displays the 
 leaf- or its parts variously doubled together. 
 There are two varieties of it : the doubled and the 
 plaited. 
 
 1. In the doubled (condu- 
 plicata), the two sides of the 
 leaf lie parallel to each other, 
 as exemplified in the Oak, the 
 Walnut, the Cherry, the Beech, 
 the Rose, &c. In the marginal 
 cut, a. shows the section of a 
 leaf, and b. the entire opening 
 gem of the Lime tree, Tilia 
 Europea, which is an excellent 
 illustration of this variety. 
 
 * FOLIATIO est complicatio ea, quam servant folia, dum 
 intra Gemmam aut Asparagos plantarum latent. Phil. Bot. 
 163, iv. 
 
 H H 3 
 
470 CONSERVATIVE ORGANS. [LECT. IX. 
 
 2. In the plaited (Plicata), the 
 leaf is folded up like a fan ; as ex- 
 emplified in many of the Palm tribe; 
 in the Birch, Betula alba, and La- 
 dy's-Mantle, Alchemilla. In the mar- 
 ginal cut, a. represents an unexpanded 
 leaf of Alchemilla alpina ; b. its trans- 
 verse section. 
 
 Overlapping. Under this head are ar- 
 ranged those gems in which the margins of the 
 leaves overlap those within them, or opposite -to 
 them, without being rolled. It comprehends the 
 three following varieties. 
 
 1 . The Imbricate (Imbricata), in which the 
 
 edges of two opposite leaves touch each 
 other, embracing those within them, 
 which they cover like tiles. In some 
 instances the edges of the one leaf ex- 
 tend a little over those of that to 
 which it is opposed ; while in others 
 the opposed edges scarcely touch. This 
 variety is exemplified in Privet, Ligus- 
 trum vulgar e, and Lilac, Syringa vul- 
 garis, &c. In the marginal cut, a. 
 represents the opening gem of Lilac, 
 and b. its transverse section. 
 
 2. The Equitant (Equitantia), in which 
 the leaf is so folded, that the two sides 
 
LECT. IX.] HYBERNACULA GEMS. 471 
 
 deeply embrace the opposite leaf, 
 which in its turn encloses the one op- 
 posed to it ; and so on to the centre of 
 the bud. It is beautifully exemplified 
 in Day Lily, Hemerocallis ; in the 
 Iris family ; and in Solomon's Seal, 
 as represented in the marginal cut, in 
 which fig. 1. shows the character of the 
 entire bud, with the leaf a. embraced 
 by the opposite one b. ; and fig. 2. the 
 transverse section in which a. b. and 
 the other leaves are drawn slightly 
 asunder, so as to show more distinctly 
 their arrangement. 
 
 3. The Ob volute (Obvoluta), in which one 
 leaf, doubled lengthways, embraces 
 within its doubling one half of the 
 opposite leaf, folded in the same manner ; 
 as in the genus Valerian, Valeriana ; 
 Scabious, Scabiosa; Teasel, Dipsacus ; 
 and Sage, Salvia. In the marginal 
 cut, a. represents the opening bud of 
 Common Sage, b. its transverse sec- 
 'tion. 
 
 Rolled. This division contains all those 
 gems in which the leaves are rolled, either on their 
 lateral margins, or from the apex to the, base. 
 There are five varieties of this form of foliation. 
 l.The convolute (Oonvoluta}, in which the leaf 
 
 H H 4 
 
 7- 
 
472 
 
 CONSERVATIVE ORGANS. [LECT. IX, 
 
 is rolled lengthways in a spiral manner, one mar- 
 gin forming the axis round which the other turns, 
 as in the Plum genus, Prunus ; the Lettuce 
 tribe, Lactuca ; the Cabbage, Brassica, and many 
 Grasses, &c. In the marginal cut, g. displays this 
 form of foliation in a section of the unrolled leaf 
 of Indian Corn, Zea Mays. 
 
 2. The Involute (Involuta), in which each 
 lateral margin of the leaf is rolled in- 
 wards ; as in the gems of the Honey- 
 suckles, Lonicerae ; and the Violets, 
 Violae, &c. In the marginal cut, e. 
 is a section of the unexpanded leaf 
 of the Yellow Water Lily, Nuphar 
 lutea. 
 
 3. The Re volute (Revoluta), in 
 which the lateral margins are rolled 
 as in the gems of Rosmary, Ros- 
 marinus officinalis; and of the Primrose genus, 
 Primula, &c. In the marginal cut, f. is a sec- 
 tion of the unexpanded leaf of Patience Dock, 
 Rumex patientia. 
 
 4. The Circinal (Circinata), in which the leaf 
 ^ is rolled from the apex to the base, as 
 in the Ferns, Filices; the divisions of 
 the leaf, as represented at a. a., in 
 the marginal cut, being rolled upon 
 the mid-rib, which is also rolled from 
 to c. carrying the divisions in its turns. 
 2 
 
 outwards 
 
LECT. IX.] HYBERNACULA GEMS. 473 
 
 5. The Turned down (Redinata), in which 
 the leaf hangs down and is wrapt 
 round the footstalk, as in the buds 
 of officinal Wolfsbane, Aconitum neo- 
 montanum ; the genus Anemone, &c. 
 In the marginal cut representing an 
 unexpanded leaf of Duck's-foot, Po- 
 dophyllum peltatum, a. a. shows the 
 leaf wrapped round the footstalk b. c. 
 
 As the gems open, the leaves gradually unfold 
 themselves, and assume their natural forms ; but 
 the opening of the bud does not, in every in- 
 stance, immediately set free the leaves; for, in 
 some gems, each leaf is separately enclosed in a 
 membranous cover, which opens either laterally 
 or at the apex, and permits the leaf to expand. 
 This covering is generally regarded as a stipule 
 (stipula); but it scarcely accords with Linnseus's 
 definition of that appendage* ; and may rather be 
 considered as a protection to the embryon leaf, 
 until it has attained sufficient vigour to bear the 
 stimulus of light, and to admit of that degree of 
 perspiration, which its exposure to the atmo- 
 sphere occasions. The gem of the Tulip tree, Li- 
 riodendron Tulipifera, affords a very beautiful ex- 
 ample of this form of foliation. The leaf before 
 expanding is conduplicate and arched, or bent 
 
 * " Stipula est squama, quae basi petiolorum aut pedimculo- 
 " rum enaseentium utrinque adstat." Phil. Bot. 84. 
 
474 
 
 CONSERVATIVE ORGANS. 
 
 [LECT. ix. 
 
 down as represented at a. in 
 the marginal cut ; and the sti- 
 pules, as they are termed, which 
 are flat foliaceous plates (see b. 
 which is one of them separated 
 to show its form and vessels), 
 form a bivalve case for it, con- 
 taining at the same time all 
 the younger leaves, each arched 
 and enclosed in a similar man- 
 ner. As soon as the leaf is capable of bearing the 
 exposure, the two plates of the case separate, 
 bending down as at c. c. and in a short time drop 
 off; meanwhile the footstalk of the leaf becomes 
 
 straight and the disk is 
 spread out to the light 
 and air. In some in- 
 stances this covering is 
 univalvular and sepa- 
 rates at the base, at the 
 same time that it opens 
 laterally, as exemplified 
 in the Magnolias; and 
 I very elegantly in the 
 Elastic-gum tree, Fie us 
 elastica; the sheath of 
 which (see fig. 1. a. in 
 the marginal cut) is of 
 a deep red colour, 
 
LECT. IX.] HYBERNACULA GEMS. 475 
 
 thick, opaque, and covering the whole of the 
 terminal shoot above the insertion d. of the 
 last evolved leaf, the footstalk of which b. is pur- 
 posely left in the figure : in fig. 2, the sheath is re- 
 moved to display the leaf a. seated on its footstalk 
 e. and wrapped round the sheath of the next ex- 
 pected leaf. In other instances this sheath is thin, 
 semi-transparent, and filled with a gelatinous 
 matter, which involves the young leaf; as exem- 
 plified in the Dock tribe, Riimex. These sheaths or 
 utricular coverings cannot be regarded as hyber- 
 nacula, as they are present in every season of the 
 year; but, inasmuch as they preserve the young leaf 
 from the stimulus of light and the effects of mois- 
 ture, they bear a close analogy to the hybernacu- 
 lar scales. Their chief use, however, is to re- 
 strain the perspiration of the young leaf, till such 
 time as its vessels are sufficiently perfect to supply 
 by absorption the exhaustion of moisture which 
 that function necessarily occasions. 
 
 The origin of the gem has been already suffi- 
 ciently investigated (p. 383-406). It is evidently 
 nourished during the summer by the leaf, which 
 is, perhaps, to the embryo in the gem, what the 
 flower is to the fruit * ; but when the leaf falls, the 
 gem is left to its own resources; and scarcely any 
 visible change occurs in its aspect or its magnitude 
 
 * " La feuille est au bourgeon ce que la fleur est au fruit 
 " et a la graine. " Essais sur la Veg. par A. Aubert du Petit- 
 Thouars, p. 14-5. 
 
476 CONSERVATIVE ORGANS. [LECT. IX. 
 
 until the following spring. During this torpidity, 
 which is maintained throughout the winter, the 
 scales are supposed to preserve the enclosed em- 
 bryo from the effect of cold ; but if we reflect 
 on the insufficiency of so feeble a guard, and 
 further consider the great degree of cold which a 
 seed can withstand without losing its vitality, we 
 shall be able to appreciate justly the value of this 
 opinion. The fact is, the vitality possessed by the 
 embryo in the gem, like that it enjoys in the seed, 
 is not susceptible of the stimulus of heat under a 
 certain degree of temperature; and until it re- 
 ceives this, in combination with circumstances 
 otherwise favourable for vegetation, no change of 
 organization is produced in it, and the vital prin- 
 ciple remains unaffected, even in very low tem- 
 peratures. Nor is this wonderful when we con- 
 sider that a caterpillar may be frozen, and yet 
 live after it has been thawed. But if the gems 
 remained uncovered duiing the long period which 
 intervenes between their formation and evolution, 
 they would run great hazards from the effect of 
 moisture, and from the depredations of insects, 
 against which the scales and the varnishes which 
 cover them are excellent safeguards. We, besides, 
 know that light is unfavourable to the evolution of 
 the embryo in the seed, and may we not conclude 
 from analogy, that this is the case also to the 
 young branch in the gem? 
 
 When the spring returns, and the temperature 
 
LECT. IX.] HYBEKNACULA GEMS. 4.77 
 
 of the atmosphere has arrived at that point which 
 the excitability of the gem demands for arousing 
 its vital energy into activity, the outer scales 
 being no longer useful, drop off; but the inner 
 ones remain and assume the functions of leaves, 
 until the real leaves are fully expanded. All the 
 gems on a tree, however, do not open at the same 
 time, for the current of fluid in the sap vessels 
 communicating with the terminal gems being more 
 direct than that which supplies the lateral gems, 
 the former always open sooner than the latter. 
 Flower gems almost always open before leaf gems 
 on the same tree; but flower gems which are 
 at a distance from leaf gems, generally fall with- 
 out producing fruit ; and perhaps they possess al- 
 together less individuality than leaf gems, yet 
 flower gems live and flourish when they are de- 
 tached and then budded near a leaf gem on the 
 same or on another stock. We are now treating, 
 however, of the conservative organs only of plants ; 
 I shall, therefore, at present, not enter upon the 
 examination of the flower gem; but pass on to 
 treat the contents of the leaf gem ; or leaves and 
 their appendages. 
 
 LEAVES are organs of essential importance to 
 the vegetable. They are, also, objects of great de- 
 light and interest, whether we examine them indi- 
 vidually as the clothing of a single plant, or col- 
 lectively as producing the lively freshness of the 
 
478 CONSERVATIVE ORGANS. [t,ECT. IX. 
 
 verdant vale, and the massive luxuriance of the 
 darkened forest. The most beautiful flower loses 
 half its charms when it is displayed on a naked 
 stem; the miserable hovel becomes picturesque 
 when spread over with the foliage of the Vine ; 
 the ruins of former magnificence acquire more 
 reverence, and command a double share of our 
 respect, when seen through the tracery of the 
 Ivy; and the horrors of the frowning rock are 
 softened into beauty when mantled with pendent 
 creepers or with Alpine shrubs. Leaves are still 
 more important when we regard them as af- 
 fording food to man and the rest of the animal 
 creation; and supplying medicinal agents to re- 
 lieve their sufferings in disease. Notwithstanding, 
 however, the interest which they thus excite ; and 
 our familiarity with leaves, as objects of sight, from 
 our earliest years, it is impossible to form an un- 
 exceptionable definition of the leaf. This difficulty 
 arises from the great diversity of figure, substance, 
 surface, and colour which it assumes in different 
 plants. If we cannot, therefore, define it accu- 
 rately from its external characters, we must have 
 recourse to its functions; and perhaps the following 
 is the least exceptionable definition we can offer : 
 The leaf is, a temporary organ of plants., which 
 performs nearly the same function in the economy 
 of vegetable life as the lungs perform in that of 
 animal life : or, in fewer words, leaves are the 
 
LECT. IX.] LEAVES. 479 
 
 respiratory organs of plants*. It may be ob- 
 jected to this definition, that some plants, as for 
 example the Dodder, Cuscuta Europea, 'the Sta- 
 pelias, and many of the Cactus tribe, are devoid of 
 leaves ; but in these instances, and in all aphyl- 
 lous plants, the surface of the stem performs the 
 function of the leaves. 
 
 The diversity of character which leaves dis- 
 play is taken advantage of by systematic Botanists 
 for determining species, and consequently every 
 circumstance connected with that diversity, as 
 form, substance, position, attachment., and direction 
 should be made familiar to the student ; as well 
 as the more intimate or internal structure of the 
 leaf itself. In our examination, therefore, as in 
 the case of stems, I shall first demonstrate the 
 external characters of leaves, and then investigate 
 their anatomy or internal structure. 
 
 Let us take any leaf from among those now 
 scattered before us ; this for instance of the Lilac. 
 
 * " Folia transplant et adtrahunt (uti pulmones in anima- 
 " libus) umbramque praebent." Phil. Bot. 81. 
 
480 CONSERVATIVE ORGANS. [liECT. IX. 
 
 We find that it consists of two parts ; the one, a. 
 (see the figure) thin and expanded, and which in 
 common language is named the leaf (folium); the' 
 other b. long, equally thick as broad, and stalk- . 
 like, which is denominated the footstalk or petiole 
 (petiolus). The footstalk and the expansion, 
 however, constitute but one organ or proper leaf, 
 the footstalk being merely a prolongation of the 
 mid-rib c. c. which in this leaf divides the expansion 
 into two equal portions. This is further proved by 
 the fact, that the expansion cannot i>e separated 
 from the footstalk without tearing or cutting ; and 
 that in autumn, when a leaf withers, both parts 
 fall together, the whole leaf separating, on the 
 slightest touch, at the point where the foot- 
 stalk is attached to the branch*. But many of 
 the leaves before us have no prolongation of the 
 mid-rib, thence we conclude that the petiole is not 
 universal. Continuing our examination, we observe 
 that the two surfaces of this leaf are not alike; 
 that one is of a deep green colour and smooth ; 
 the other is a pale green and marked by a num- 
 ber of elevated ridges (costulce), branching off 
 from the mid-rib : the deeper green and smoother 
 surface is always turned upwards or towards 
 the light, and is named the upper disk (pa- 
 
 * The error of Linnaeus's definition of the footstalk is very 
 apparent: " Petiolus, trunci species, adnectens folium, nee 
 " fructificationem.'' PhlL Bol. SI. F. 
 
LECT. IX.] LEAVES. 481 
 
 gina superior), or face of the leaf; the latter, 
 which has of course the opposite direction, is 
 termed the under disk (pagina inferior)) or back 
 of the leaf: but, as I remarked with respect to 
 the footstalk, these distinctions of surface are not 
 universal, for we meet with some leaves which 
 stand vertically on the branches and have both 
 surfaces alike*. That part of the leaf d. d., which is 
 next to the footstalk or to the point of attachment, 
 is always considered as the base ; and the part e., 
 which is directly opposite, the apex ; whatever may 
 be the shape of the leaf. The line e.f. d. d.f. e. 
 forming the contour of the leaf, is named the 
 margin. The angle which the leaf or its footstalk 
 forms at its point of attachment with the stem, 
 or the branch, is termed its axilla. 
 
 Leaves are either Simple, consisting of one 
 expansion only, with or without a footstalk, 
 as those of the Lilac, the Apple tree, the Nettle, 
 Urtica dioica, and many other plants; or Com- 
 pound, consisting of several distinct expansions, 
 with or without distinct footstalks united to- 
 gether on one common footstalk, as those of 
 
 * Mirbel considers these as transformed footstalks. He re- 
 marks, speaking of the Acacia of New Holland, " A mesure 
 " que les folioles disparaisserit, les petioles changent visible- 
 " ment de forme et de structure. La plupart s'elargissent vers 
 " les deux bouts, a la maniere d'un fer de lance." Element de 
 Phys.veg. 1. 149. 
 
 VOL. I. I I 
 
482 
 
 CONSERVATIVE ORGANS. 
 
 [LECT. ix. 
 
 Buck-bean, Menyanthes trifoliata, of Horse Ches- 
 nut, <#sculus, the Vetch tribe, Vicia, &c. 
 
 A. SIMPLE LEAVES (Folia simplicia) differ in 
 respect of general Jigure ; form or solid configu- 
 ration ; apex; base; margin; surf ace ; and sub- 
 stance. 
 
 a. The general Jigure or superficial aspect of 
 a leaf is derived from the line which circumscribes 
 its flat surface, or which is described by its mar- 
 gin. In demonstrating the diversities which it 
 displays, I shall begin with the simplest and pass 
 progressively to the more complex. A leaf is termed 
 Capillary (folium capillare), a. } when it is long, 
 fine, and flexible, resembling a hair. Linear 
 ( linear e), b., when it is long, about a geome- 
 
 trical line in breadth, and the sides parallel, or 
 is the same breadth near the apex as at the 
 base. Gramineous or riband-like (fasciarium), c. y 
 when it resembles the linear, with which it is 
 sometimes confounded, but from which it differs in 
 being broader and not parallel towards the apex. 
 Needle-shaped (acerosum *), d., when, resembling 
 
 * " Acerosum est lineare persistens : ut in Pino, Abiete, 
 " Junipero, Taxo.'* Phil. Bot. Notwithstanding this high au- 
 
LECT. IX.] GENERAL FIGURE OP LEAVES. 483 
 
 the linear, it is rigid and acute. Awl-shaped 
 (subulatum), e. } when it is thick at the base and 
 gradually attenuated to a sharp point. Lanceolate 
 (lanceolaturn) , f., when it is four or five times 
 longer than it is broad, and tapers towards 
 both the base and apex. Sword-shaped (ensi- 
 forme), *., when it is long, tapering to a point; very 
 thin on both edges, and slightly curved. Spatu- 
 late (spathulatum), h., when round at the apex 
 it gradually tapers towards the base. Wedge- 
 shaped (cuneiforme vel cuneatum), i., when broad 
 
 and abrupt at the apex it tapers towards the 
 base. Fan-shaped (flabelliforme) , A:., when it re- 
 sembles the wedge-shaped leaf in the base, but 
 is more dilated and rounded at the apex. Ob- 
 
 thority, neither the leaves of the Yew nor of Juniper can be re- 
 garded as needle-shaped. Linnaeus adds another circumstance 
 connected with the needle-shaped leaf, more correct, " ple- 
 " rumque basi articulatione ramo inserta." Phil. Bot. 277. 
 
484 CONSERVATIVE ORGANS. [LECT. IX' 
 
 long (oblongum), when the length exceeds the 
 breadth at least more than three times, with the 
 ends generally rounded: but the base and apex 
 may be variously defined ; " and this term," as Sir 
 J. E. Smith justly remarks, " is used with great 
 " latitude." Oval or elliptical (ovale vel ellip- 
 ticum), /., when it is twice as long as it is broad, 
 and is nearly equally rounded at both extremities. 
 Ovate (ovatum), m., when the length is greater 
 than the breadth, with both extremities rounded, 
 but the base much broader than the apex. Obovate 
 (obovatum),n. } when it has the ovate shape reversed ; 
 
 and is consequently attached by the narrower ex- 
 tremity. Roundish (subrotundum) , o., when it ap- 
 proaches to the circular figure. Circular (orbicu- 
 lare),p., when its length and breadth are equal and 
 the circumference is a circular line. Crescent- 
 shaped (lunulatum s. semilunatum), q., when it is 
 curved, as the name implies, like a crescent: whe- 
 ther the footstalk be inserted into the concave or 
 the convex edge of the crescent. Angled (angu- 
 
LECT. IX.] GENERAL FIGURE OF LEAVES. 485 
 
 
 
 mmm 
 fi 
 
 latum), when the circumference has considerable 
 projections, which are not lobular: and the leaf 
 is termed three-angled (triangulatum), r., four- 
 angled (quadrangulatum) , and five-angled (quin- 
 quangulatum), s., as the angles are either three, 
 or four, or five. If the angles be obscure, the leaf is 
 said to be repand (repandum). It is trowel-shaped 
 (deltoides*), t., when it has three angles, or 
 
 * " Deltoides, rhombeum est ex quatuor angulis, e quibus 
 " laterales minus a basi distant quam reliqui." Phil. Bot. Sir 
 J. E. Smith states that " a wrong figure is quoted for this in 
 " Philosophia Botanica, which has caused much confusion." 
 Introduc. p. 155. He might have added, that the whole de- 
 scription is erroneous. 
 
 n3 
 
486 CONSERVATIVE ORGANS. [LECT. IX. 
 
 resembles the Greek A, one of the angles forming 
 the apex of the leaf: and diamond-shaped (rhom- 
 boideum), u., when the lines describing the edges 
 of the leaf, instead of being curved, form obtuse 
 angles pointing outwards on each side. A leaf 
 is fiddle-shaped (pandurceforme) , v., when it is 
 oblong and has a curvilinear indentation in both 
 its sides : and lyre-shaped (lyratum), *, when there 
 
 is one large circular or elliptical lobe towards the 
 apex, and several small lateral lobes towards the 
 base. It is termed lobed (lobatum), when it is 
 deeply divided into rounded segments ; and is, 
 therefore, said to be two-lobed (bilobum), w. ; 
 three-lobed (trilobum), x. ; four-lobed (quadrilo- 
 
 bum), &e. according to the number of the lobes, 
 
LECT. IX.] GENERAL FIGURE OF LEAVES. 487 
 
 It is arrow-shaped (sagittatum), y., when the disk 
 is triangular, and the sides are produced down- 
 wards into two pointed lobes, like a barbed ar- 
 row: and halberd-shaped (hastatum), z. 1., when 
 the sides are produced into two lateral spread- 
 ing points or lobes near the base. Sometimes the 
 lateral lobes are distinct, as represented at z. 2, 
 
 A leaf is heart-shaped (cordatum), a., when 
 it is hollowed at the base into two lobes and 
 pointed at the apex, so that the leaf has some- 
 what the appearance of the heart on a card. 
 When the apex 5 instead of being directly oppo- 
 site to the base, is thrown off at one side, the leaf 
 is said to be oblique cordatum, , as beautifully 
 illustrated in Begonia. Kidney-shaped (reni- 
 
 n4 
 
488 CONSERVATIVE ORGANS. [LECT. IX. 
 
 forme), i/., when the apex is broad and rounded, 
 and the base deeply hollowed out. A leaf is 
 termed palmated (palmatum), , when it is cleft 
 into oblong or finger-like lobes, not, however, ex- 
 tending to the base; but leaving an entire flat 
 space, which has been likened to the palm of the 
 hand. Laciniated or incised (laciniatum sen sec- 
 turn) , s, when it is cut into numerous irregular 
 
 divisions, which are termed segments. Parted 
 (partitum), i., when the clefts reach nearly to 
 the base : and according to the number of these, 
 the leaf is said to be bipartitum, tripartitwn, qua- 
 dripartitum, qmnquepartitum, multipartitum. It 
 is said to be cloven (fissum), when the margins of 
 the segments are nearly straight lines : and accord- 
 ing to the number of the clefts the leaf is termed 
 bifidum, trifidum, multifidam^ x. (page 491), &c. 
 Runcinate (runcinatum) , A, signifies that the ex- 
 pansion is deeply cut into many transverse acute- 
 angled segments, the points of which tend to- 
 wards the base of the leaf. When the segments 
 are deeper, and more regular and distant from 
 
LECT. IX.] GENERAL FIGURE OF LEAVES. 489 
 
 each other, the figure of the leaf is termed pin- 
 natifid (pinnatifidum) , ^; and pectinate (pectina- 
 tum), v, when the segments are very narrow, 
 linear, and parallel like the teeth of a comb. 
 
 These terms are frequently combined to ex- 
 press modifications of two or more of the forms 
 they imply conjoined in one leaf. Thus you will 
 find in the descriptions of leaves, in systematic 
 works, such terms as ovato-lanceolatum, cordato- 
 lanceolatum, kastato-lanceolatum, cordato-ovatum, 
 lineari-lanceolatum, cordato-sagittatum, sagittate - 
 ovatum, lanceolato-ellipticum, mbrotundo-corda- 
 tum, &c. the meaning of which can be accurately 
 acquired by practice only in the examination of 
 plants. The three last-mentioned terms, I ought 
 to notice, involve a contradiction; or, at least, 
 are too nice for practical purposes ; and con- 
 sequently we find, that several of the best sys- 
 tematic Botanists have confounded and misap- 
 plied them. The terms incisum and dissectum 
 are merely modifications of lacmiatum. I may 
 take this opportunity of remarking that the 
 
490 CONSERVATIVE ORGANS. JJLECT. IX. 
 
 terms angled and lobed are, also, not unfre- 
 quently misapplied, although the distinction is 
 perfectly obvious: thus, each segment of an 
 angled leaf has the margins, which meet to form 
 the angle, straight or nearly so; whereas in a 
 lobed leaf the margins are always curved, so as to 
 give the lobes a rounded appearance, whether 
 their apexes be obtuse or pointed. The import- 
 ance of accuracy in the application of terms sig- 
 nificant of the forms of leaves, will be fully seen 
 when I come to treat of the classification of plants. 
 b. The solid configuration of a leaf is taken 
 from its real form, including length, breadth, and 
 thickness; determined by transverse and longi- 
 tudinal sections. It is termed Cylindrical (teres, 
 cylindrica), 1, when a transverse section, made 
 any where throughout the greater part of the 
 length of the leaf, is circular. If the diameter 
 be very small, so that the leaf is as fine as a 
 hair, the configuration is termed capillacea, the 
 distinction of which from capillary, consists in 
 the form of the capillaceous leaf being exactly 
 that of a hair, whereas the capillary is only 
 as small as a hair : Semicylindrical (semicy- 
 lindracea), 2, when one side of a leaf is flat 
 and the other convex: Tubular (tubulosa), 3, 
 when the greater portion of the leaf is cylindri- 
 cal, or nearly so, tapering to a point, and hollow 
 within. Sometimes the hollow appears as if it 
 
LECT. IX. j SOLID CONFIGURATION OF LEAVES. 491 
 
 were formed by the two sides of the leaf being 
 compressed together, but separated near the 
 midrib, so that one part of the leaf is flat 
 and another tubular, as beautifully exemplified 
 in the genus Sarracenea, 4. The configuration 
 is four-edged (tetragona}, when there are four 
 longitudinal sides, and consequently four corners: 
 but if there be three sides only, as in Mesem- 
 bryanthemum aureum, the configuration is termed 
 
 trigona, 4 (see page 492) ; Linnaeus uses trique- 
 trum to express an awl-shaped leaf, which has 
 three flat sides; but the term is superfluous. 
 Tongue-shaped (UngulataJ, 5, implies that the 
 leaf is thick, oblong, and blunt. This form of 
 leaf is often cartilaginous at the edges, as in 
 some of the Aloe tribe. The configuration is 
 gibbous (gibbaj, 6, when it is thick and swells 
 out, or is humped on one or both sides. Symitar- 
 shaped (acinaciformis) , 7) when one edge is 
 thick, flat, and nearly straight, and the other 
 thin, sharp, and curved like a symitar. Hatchet- 
 shaped (dpfabriformis), 8, when it resembles the 
 
492 CONSERVATIVE ORGANS. [LECT. IX. 
 
 former, but has the keel or compressed part more 
 abruptly prominent, and the base nearly cylin- 
 drical. Sir J. E. Smith remarks, that " these two 
 " last terms might well be spared, as they seem con- 
 " trived only for two plants," but this is supposing 
 that the whole vegetable world is already known, 
 which is very far from being the case. The same 
 leaves are examples, also, of the two next terms of 
 configuration: the Compressed (compressa), which 
 is used when a thick leaf is flattened laterally, 
 so as to make it thicker than it is broad ; and 
 the flat (plana), when both surfaces of a thick 
 leaf are flat and parallel to each other. A two- 
 edged leaf (folium anceps), JO, displays both the 
 edges, in a transverse section, produced to a very 
 acute angle. The configuration is spherical 
 (sphceroidea) , when it approaches to the globular 
 form : Ovoide (ovoideaj, 1 1 , when it some- 
 what resembles that of an egg: Coccoon-shaped 
 (fusina), 12, when it is cylindrical in the middle 
 
 and tapers to a point at each end : Club-shaped 
 (clavata), when it is round and stem-like, with a 
 
LECT. ix.] APEXES OF LEAVES. 493 
 
 thick, blunt apex : Hooked (uncinata), 1 3, when 
 it is curved so as to resemble, in some degree, a 
 hook : Lenticular (lenticularis) , when it is flat, 
 roundish, and convex on both surfaces, and a 
 transverse section of the leaf has the appearance 
 represented at 14, in the cut. 
 
 c. The apex of a leaf, as has already been de- 
 scribed, is that part which is opposed to the 
 base or the footstalk ; or to the point of attach- 
 ment when it has no footstalk. It differs very 
 considerably in shape in different leaves. The 
 apex is termed acute (acutus), 15, when the 
 conjunction of the two lines of the edges forms an 
 acute angle : acutiusculus, 1 6, when there is a 
 slighter degree of this kind of termination : acu- 
 minate ( acuminatus) , 17, when it is long and very 
 tapering : spine-pointed (cuspidatus), 1 8, when it 
 runs out gradually into a small, awl-shaped, rigid 
 spine; and mucronate (mucronatus) , ]Q, when 
 it is rounded with an herbaceous spine standing 
 on it. The apex is awned (aristatus) ,* , when it is 
 
494 CONSERVATIVE ORGANS. [LECT. IX. 
 
 terminated by a long rigid spine, which does not 
 appear as a continuation of the leaf: cirrose (cir- 
 rosw, circinatus), 20, when it is produced into a 
 kind of tendril ; and this is in a few instances " fur- 
 " nished with an additional organ for some par- 
 " ticular purpose not essential to a leaf J." Thus, 
 in one species of the genus Nepenthes-}-, 21, the 
 
 J Smith's Introduction, p. 173. 
 
 f This singular family of plants was first noticed by Hiero- 
 nymus Benzoni, an Italian, who visited India about the middle 
 of the sixteenth century (1542 1556); and was described by 
 him in a work entitled, " Nova novi Orbis Historia," Genevae, 
 1578. One species of it, the Phyllamphora (Lin.) 9 was af- 
 terwards fully described and figured in the Herbarium Amboi- 
 nense of Rumphius, who was appointed Governor of Amboyna 
 in 1706. Rumphius regards the fluid found in the pitcher as a 
 secretion of the plant itself, and says it increases during the 
 night ; that it has a sweetish taste and attracts worms and other 
 insects into the pitcher; who, however, all die, except a 
 species of squilla, " squilla gibba/' that seems to prey upon the 
 carcasses of the others. He describes the pitcher itself as being 
 beautifully coloured in the inside with purple streaks and spots ; 
 and the lid opening and shutting. This species is found in 
 
LECT. IX.] APEXES OF LEAVES. 495 
 
 apex of each leaf terminates in a long rigid thread, 
 a continuation of the midrib, bearing a small 
 covered pitcher, which is generally found nearly 
 full of water : in another species this pitcher is 
 sessile/* 1 ; and, in Dionsea muscipula, the ap- 
 pendage is composed of a pair of toothed lobes, 
 22, which are irritable; and which close together 
 and imprison insects that alight upon them-f~. 
 The apex is obtuse (obtmus), 23, (p. 493), when it 
 forms the segment of a circle or is rounded. The 
 rounded apex of a solid leaf, when a little thick- 
 
 Amboyna growing in dry waste places; and also in Ceylon; 
 but I suspect that the Ceylon plant is a variety, if not a distinct 
 species, for the pitcher is not contracted at the neck, as in Rum- 
 phius's figure, and it is found growing only in moist valleys and 
 on the banks of rivers. At this time (August 1821), there are 
 several plants of Nepenthes distttlatoria vegetating in pots, in the 
 magnificent hothouse of Messrs. Loddiges, at Hackney. The 
 pitcher in this species is attached to the apex of the leaf, without 
 the medium of the twisted wire, which is found in Phyllam- 
 phora ; and there are, also, two leafy appendages running the 
 whole length of the pitcher, on that side of it which is next to the 
 plant. The lid exactly resembles that of Phyllamphora. A more 
 beautiful vegetable pitcher is found in the Cephalotus^/^ttfo- 
 ris, a New Holland marsh plant, which was discovered and de- 
 scribed by Mr. Robert Brown, to whose exertions and talents 
 Botanical science is most extensively indebted ; and is figured 
 in the atlas of Capt. Flinders's voyage ; but, as it is not ap- 
 pended to the leaf, I shall describe it among the general ap- 
 
 f The cause of this vegetable phenomenon shall be after- 
 wards investigated. 
 
496 CONSERVATIVE ORGANS. [LECT. IX. 
 
 ened, but not sufficiently so as to render it 
 clubbed, is termed incrassatus. If a small point 
 project from the middle of the obtuse apex, the 
 leaf is said to be obtusum cum acumine, 24 (p. 
 493). The apex is termed retuse (retusus), 25, 
 when it is obtuse, with a broad shallow notch 
 in the middle: emarginate (emarginatus), 26, 
 when the notch is sharper, or nearly triangular : 
 truncated (truncatus), 27, when it appears as if 
 cut across in a straight line; as beautifully exem- 
 plified in the leaf of Liriodendrum tulipifera. It 
 is jagged (prcemorsus) , 28, when it appears as if 
 gnawed off, and the cross lines describe several ir- 
 regular points. Ex. Caryota urens (28) ; and tri- 
 dentate (trident atus) , 29, when it forms three 
 teeth. 
 
 25" 
 
 d. The differences in the bases of leaves depend 
 on the general superficial configuration ; I must, 
 therefore, refer you to what has been said on that 
 subject, and notice here one circumstance only, 
 
LECT. IX.] LEAVES. 497 
 
 connected with the base, which has not already 
 been described. When the two halves of the ex- 
 pansion are of different lengths, this is observable 
 chiefly at the base, and the leaf is said to be un- 
 equal or oblique (basidncequale), 3O, (page 496). 
 
 e. The Margin of a leaf may be either entire, 
 indented, bordered, or rolled. 
 
 * Entire. 
 
 An entire leaf (folium integerrimum) has the 
 line of the margin uninterrupted, or free from 
 every kind of incision or indentation. Sir J. E. 
 Smith properly remarks that this term refers 
 solely to "the margin of a leaf; whereas in- 
 " tegrum respects its whole shape, and has no- 
 " thing to do with the margin-^-." I may add, it 
 is used in contradistinction to compositum. 
 
 ** Indented. 
 
 A leaf is termed sinuated (smuatum), 31, (page 
 498), when the margin is cut into roundish scollops, 
 as in the Oak, Quercus robur; but when the notches 
 or scollops are very irregular, as if formed by the 
 gnawing of some insects, the margin is then said to 
 be gnawed (erosus), 32. It is termed toothed (den- 
 tatus), 33, when it displays pointed marginal pro- 
 jections of the expansion, with interstices between 
 them ; and the following terms are employed to 
 express the character of the margin as far as re- 
 
 f Introd. to Phys. and Syst. Bot. p. 161. 
 VOL. I. K K 
 
498 CONSERVATIVE ORGANS. [LECT. IX. 
 
 gards its denticulations: equally toothed (cequaliter 
 dentatus), 34 ; unequally toothed (incequaliter den- 
 tatus), 35 ; deeply toothed (profunde dentatus) ; 
 obscurely toothed (obsolete dentatus), 36. If the 
 denticulations themselves be again dentated, then 
 the margin is termed doubly dentate (duplicato- 
 dentatusj, 37. 
 
 The margin is denominated serrated (serratus), 
 38, when the teeth are sharp, and lie as it were 
 upon each other, as in a saw, all pointing towards 
 the apex of the leaf. The nature of the serratures 
 is distinguished by the following terms applied to 
 the margin : equally serrated (cequaliter serratus); 
 unequally serrated (incequaliter serratus); sharply 
 serrated (argute serratus) ; deeply serrated (pro- 
 funde serratus), 3Q; and doubly serrated (du- 
 pUcato-serratus), 40. When the serratures are 
 minute, or not distinct, the margin is termed 
 serrulatus, 41. 
 
LECT. IX.] LEAVES. 499 
 
 Crenated (crenatus), 42, implies that the in- 
 dentations of the margin are blunt and rounded, 
 and do not incline to either extremity of the leaf. 
 The crenatures themselves may be crenated, in 
 which case the margin is termed doubly crenated 
 (duplicato-crenatus); or they may be of a doubt- 
 ful form, being neither completely rounded nor 
 yet pointed, in which case it is termed dent at o- 
 crenatus, 43 ; and crenulated (crenulatus), 44, if 
 they are very shallow and at the same time perfect. 
 
 When the marginal denticulations, whatever 
 form they assume, are terminated with sharp, rigid 
 spines, the margin is termed spinous (spinosus), 
 45; and as a comparative term, a leaf is said to 
 be unarmed (inerme), when it occurs in a species 
 or a variety belonging to a tribe of plants, which 
 has for the most part spinous-leaved species. 
 
 Bordered. 
 
 When the substance of the margin of a leaf 
 differs from that of the expansion, the leaf is con- 
 sidered as bordered ; and according to the charac- 
 
 KK2 
 
500 CONSERVATIVE ORGANS. [LECT. IX. 
 
 ter of the border, the margin receives different ap- 
 pellations. Thus it is termed cartilaginous (carti- 
 lagineus), when it is firmer than the disk and 
 somewhat elastic. This cartilage is generally 
 whitish, yellowish, pinkish, or some other colour, 
 but is seldom green. It is termed horny (cor- 
 neusj, when it resembles the cartilaginous, but is 
 harder and less elastic: ciliated (ciliatm), 46, 
 when beset with soft parallel hairs, not closely set 
 together ; but if the hairs be stiff and like bristles, 
 it is then said to be aculeato-ciliatus. (See fig. 1 . 
 Plate 4). 
 
 If the margin be studded with small granular, 
 either opaque or semitransparent bodies, exuding 
 some kind of fluid, it is termed glandular (glan- 
 dulosus) ; but, if these glands be supported on 
 hairs, glanduloso-ciliatus, 48. 
 **** Rolled. 
 
 When the margin is rolled backwards, or upon 
 the under surface of the leaf, it is said to be re- 
 volute (revolutus), 49; when forwards, involute (in- 
 volutus). In some instances the margin, compre- 
 hending a portion of the disk of the leaf, is so much 
 more expanded than the rest of the disk, that it 
 assumes a waved character, or is undulated (un- 
 dulatus), 5O ; and when it is still more expanded, 
 so that the margin is variously curled and twisted, 
 it is termed curled (crispus). These appearances 
 occur in leaves, which have very different kinds of 
 margins in other respects. 
 
LECT. IX.] LEAVES. 501 
 
 f. The surface of a leaf comprehends both the 
 upper and the under disks. In general, the upper 
 disk is smoother than the under disk ; for, although 
 the vascular fasciculi can be traced in the form 
 of white or coloured lines on the upper, yet, they 
 very rarely produce those elevated ridges which 
 mark their course on the under disk. In treating 
 of the different characters that distinguish the 
 surfaces of leaves, the upper disk only is alluded to. 
 It is necessary to state that the greater number of 
 the following terms are equally applicable to the 
 surface of the stem as to that of the leaf, when the 
 contrary is not expressed. 
 
 The surface of a leaf which exhibits no in- 
 equalities is said to be flat (plana vel lasvis) ; if 
 there be no hairs nor spines, it is smooth (glabra, 
 nuda); and if no fasciculi of vessels be apparent on 
 it, veinless (aveniaj. If it be smooth and shined, 
 it is termed polished (nitida); and lucid (lucidaj, 
 if it be so considerable as to present the appearance 
 of being varnished. If the upper surface be con- 
 vex and the under concave, the leaf is termed 
 convex (convexum); and the opposite of this 
 state, concave (concavum) . Both these states are 
 the consequence of a tightness of the margin. 
 When an oblong or a linear leaf is longitudinally 
 hollowed, and a transverse section of it is a se- 
 micircle, the surface is said to be channelled (ca- 
 naliculata) , 52, (p. 503); but when the transverse 
 
 KK3 
 
502 CONSERVATIVE ORGANS. [LECT. IX. 
 
 section is angular, and the midrib on the under 
 surface resembles the keel of a boat, it is keeled 
 (carinata), 53. When, instead of one longitudinal 
 hollow, there are several linear depressions, the 
 surface is said to be furrowed (sulcata), 54 ; and 
 streaked (striata), if the depressions be super- 
 ficial, very narrow, and in parallel lines. If the 
 surface be depressed in the centre, and the leaf is 
 peltate, it is said to be navel-like (umbillcata) , 
 55: but if it rises and sinks alternately, in straight 
 angular furrows, like the folds of a fan, it is termed 
 folded (plicata) ; and waved (undulata) if in un- 
 dulations commencing from the midrib. When 
 the inequalities proceed from the portions of the 
 expansion between the network of the vascular 
 fasciculi being fuller than is requisite to fill the 
 vacant spaces of the meshes, and rising upwards, 
 the surface is wrinkled (rugosa), 56; and blis- 
 tered (bullata), when these elevations are still 
 more considerable; but when, on the contrary, the 
 fulness between the vascular fasciculi produces der 
 pressions, the surface is said to be pitted (lacu- 
 nosa velfavosa). 
 
 When a leaf is covered with small hard tuber- 
 cles, which are more easily distinguished by the 
 finger than the eye, the surface is said to be sca- 
 brous (s cobra) : it is rough (asp era) when these 
 are more visible ; warty (verrucosa), 57, when 
 they are still larger and more solid ; and pustular, 
 
LECT. IX.] LEAVES. 503 
 
 or vesicular (papillosa), when they are evidently 
 elevations of the cuticle filled with aqueous fluid, as 
 in the Ice plant, Mesembryanthemumtr^frz/Kmtm. 
 If the surface of a leaf be studded with short her- 
 baceous spines, it is termed muricated (muri- 
 cata); when these have stiff points, it is prickly 
 (echinata) ; and aculeated (aculeate), when., in- 
 stead of being herbaceous, the spines are hard 
 and pungent. The surface is termed hispid (his- 
 pidajy when it is beset with short stiff hairs ; when 
 these are longer, and consequently less rigid, it is 
 hirsute (hlrsuta) ; bristly (setosa), 59, if they stand 
 
 2. 
 
 singly and resemble bristles ; strigose (strigosa), if 
 they are firm, and stand upon small prominences, 
 or papillae* : and bearded (barbata), when they 
 are rather long and crowded together. Soft hairs 
 are generally termed pubescence, and the surface 
 of the leaf receives various appellations from the 
 
 * " Strigae arcent setis rigidis animalcula et linguas. Cae- 
 " tus, Malpighia, Hibiscus, Rubus." Phil. Bot. 163. 
 
 K K 4 
 
504 CONSERVATIVE ORGANS. JJLECT. IX. 
 
 character of this description of covering. Thus it is 
 hairy (pilosa), when the hairs are soft, distinct, 
 somewhat long, and bent ; shaggy or velvety (vil- 
 losa), when they are soft, nearly erect, and paral- 
 lel; silky (sericea), when they are soft, and 'lie 
 thick and flat on the surface, giving it a satin-like 
 lustre; downy (tomentosa*), when they are very 
 soft and matted together, so that the individual 
 hairs are not distinguishable; woolly (lanata^-), 60, 
 (page 503), when they are also matted together, but 
 yet individually distinguishable ; tufted (floccosa), 
 when they are soft and matted, and can be easily 
 detached in small tufts; and starred (stellata), 
 when the hairs or the spines are radiated like 
 stars. In some instances the stellated appearance 
 proceeds from pedicillated tufts ; which under 
 the microscope appear like branched shrubs de- 
 void of foliage. It is necessary to remark that 
 differences of age, climate, soil, dryness and hu- 
 midity, alter very considerably the pubescence of 
 plants ; some which are tomentose when young, 
 become hispid, or smooth, when old; others which 
 are naturally hairy, become quite smooth when cul- 
 tivated ; and others, which in their native climate 
 are smooth, become hairy when removed. Sir J. 
 E. Smith, nevertheless, in opposition to the 
 
 * " Tomentum servat plantas aventis; gaudet saepius co- 
 " lore incano." Phil. Bot. 163. 
 
 f " Lana servat plantas ab sestu nimio." PhiL Bot. 163. 
 
LECT. IX.] LEAVES. 505 
 
 maxim of Linnaeus, " pubescentia ludicra est dif- 
 " ferentia, cum cultura ssepius deponantur *," 
 remarks that " the direction of the hairs or 
 " bristles proves a very sure means of distinguish- 
 " ing species, especially in the genus Mentha, the 
 " hairs about whose calyx and flower-stalk point 
 " differently in different species; and/' he adds, 
 " I have found it the only infallible distinction 
 " between one Mint and another ^." 
 
 The surface of a leaf may be furnished with 
 visible glands. When these are elevated, or on 
 pedicils, the surface is said to be glandular (glan- 
 dulosa) ; but, when they are not raised, they ap- 
 pear like punctures, which either penetrate the 
 substance of the leaf, or are merely superficial and 
 visible on one disk only. In either case the surface 
 is said to be dotted (punctata), 58, (page 503). Any 
 glandular exudation, if considerable on a surface, 
 gives a character and denomination to it: thus, if 
 it be moist and tenacious, the surface is termed 
 viscid (vlscida vel glutinosa) ; it is hoary (pruinata 
 vel incana), if the secretion be a dry, very fine, 
 waxy powder of a bluish colour, devoid of gloss, 
 and easily wiped off; and mealy (farinosa), i it 
 resemble a mealy powder. 
 
 The majority of leaves is green ; and, as has 
 bqen already mentioned, this colour is of a deeper 
 
 * Phil. Bot. 272. f Introd. p. 228. 
 
506 CONSERVATIVE ORGANS. [LECT. IX. 
 
 tone on the upper than on the under disk: 
 but the green colour, from its being nearly uni- 
 versal, is not noticed in the description of a leaf, 
 except as regards its depth or tone ; thence, the 
 comparative terms dirty (sordidus) ; intense ( tn- 
 tensus) ; full (saturatus) ; pale (pallldus) ; and 
 diluted (dilutus). The colour is denominated olive 
 (olivaceus) when it is green with a shade of brown ; 
 and sea-green (glaucus), when it appears bluish, 
 or as if formed from a mixture of blue and green. 
 When other colours mingle with the green, the 
 leaf is termed coloured (coloratum) ; and the 
 differences of the colouring receive a determinate 
 designation : thus, when the coloured portions 
 afford the semblance of decay or disease, the leaf 
 is termed variegated (variegatum) ; spotted or 
 maculated (maculatum), when the colour is dark 
 and in spots or blotches; and zoned (zonatum), 
 when the colours are displayed in one or more 
 curved lines. The term discolor is employed to 
 denote that a leaf displays one colour on one sur- 
 face, and another on the opposite surface, as in 
 purple-leaved Spiderwort, Tradescantia discolor,. 
 two-coloured Begonia, Begonia Evansiana, &c. 
 
 The vessels of every leaf enter it by the 
 petiole, or by the point of attachment, in fasciculi ; 
 which afterwards separate, and are spread in 
 various ways through the substance of the leaf. 
 These, when visible, form lines, which are very 
 
LECT. IX.] LEAVES. 507 
 
 prominent on the back or under surface of the 
 leaf, and have been very improperly denominated 
 nerves and veins-, for nothing has yet been dis- 
 covered in vegetables bearing any analogy to 
 nerves ; and as the fasciculi ' contain both con- 
 ducting and returning vessels, they may be 
 termed arteries with as much propriety as veins. 
 But the terms, notwithstanding their absurdity, 
 being in general use, require to be explained. 
 The larger fasciculi are denominated nervi and 
 costas, and the smaller vence, in whatever man- 
 ner they are disposed throughout the leaf; but 
 the terms nervosum, costatum, and venomm, imply 
 distinct dispositions of the fasciculi. 
 
 A leaf is said to be nerved (nervosum) when 
 the larger fasciculi run, in simple, slightly curved 
 lines, from the base to the apex ; and the leaf is 
 named according to their number, among which 
 the midrib is reckoned as one. Thus three-nerved 
 (trinervis), 6i, (page 509), means that the leaf has 
 one longitudinal fasciculus of vessels on each side 
 of the midrib, taking its origin from the base ; and 
 five-nerved (quinquenervu), that it has two lon- 
 gitudinal fasciculi on each side of the midrib, un- 
 der the same circumstances. It is seven-nerved 
 (septemnervis), 62, when there are three fasciculi 
 on each side; nine-nerved (novemnervis), when 
 there are four ; and many-nerved (multinervis}, 
 when the number on each side exceeds four. The 
 
508 CONSERVATIVE ORGANS. [JLECT. IX. 
 
 nervation is in some instances not regular ; but one 
 large fasciculus is given cff on each side of the 
 midrib, at the very base of the expansion, dividing 
 and subdividing as it proceeds, as in the annual 
 Sunflower, Helianthus annuus; in which case the 
 leaf is said to be basi-trinerve, 63. The same leaf 
 is also an example of the term venoso-nervosum, 
 which is used by some authors to imply that the 
 nerves pass into veins. If the lateral longitudinal 
 fasciculi do not spring directly from the base, but 
 so far above it, that part of the expansion of the 
 leaf is below them, as in the leaf of the Cinnamon 
 tree, Laurus Cinnamomum, 64, the terms em- 
 ployed are triplinerve, quintuplinerve, multipli- 
 nerve. In one example of the multiplinerved leaf, 
 Hydrogetoufenestralis*, 65, the longitudinal fas- 
 ciculi are united by transverse bands, forming 
 square meshes, which are perfectly void, like 
 wire-work, giving that character which Botanists 
 have termed fenestrated, or open ( fenestratum) . 
 But when the longitudinal fasciculi, forming ex- 
 current nerves, are united by transverse fasciculi, 
 however elevated or strongly marked these may 
 be, if the intermediate spaces be filled with the 
 expansion, as in 66, the leaf receives no particular 
 appellation. 
 
 Ribbed (costatum), is sometimes employed as 
 
 * This singular plant is an aquatic, a native of Madagascar. 
 
LECT. IX.] LEAVES. 509 
 
 the synonime of nerved, and is certainly the more 
 proper term of the two ; but it is, also, specifically 
 used to imply that the veins proceed from the mid- 
 rib in lines nearly straight towards the margin, 
 and parallel t6 each other. In some instances the 
 costae are close together and scarcely elevated, as 
 in the Banana, Musa sapientium; but in others 
 they approach to the character of nerves, except 
 that the angle they form with the midrib is less 
 acute, 67, and they do not appear to be split off 
 from the midrib as in the multiplinerved leaf. 
 
 61 
 
510 CONSERVATIVE ORGANS. [LECT. IX. 
 
 Veined (venosum), expresses merely that 'the 
 fasciculi of vessels are so elevated or marked in 
 their branching and sub-branching, as to form a 
 kind of network over one or both surfaces of the 
 leaf. When the 'surface is altogether free from 
 any appearances of the vascular fasciculi, the 
 leaves are said to be nerveless, or veinless (enervia, 
 aveniaj, 70. 
 
 In speaking of the substance of a leaf, as far 
 as that can be determined from its external cha- 
 racters, we refer to the expansion only ; for, al- 
 though the substance of the petiole is often the 
 same as the expansion, yet this state is neither con- 
 stant nor essential. All leaves may be regarded as 
 herbaceous; but the term is occasionally employed 
 in a determinate sense to denote a soft, green, 
 pliable leaf, the vascular fasciculi of which 
 are as succulent, and scarcely firmer than the 
 rest of the leaf; as exemplified in Spinage, Spi- 
 nacia dleracea, the different species of Goose-foot, 
 Chenopodeum, &c. A leaf is termed membra- 
 nous (membranaceum) , when it is thin and pliable, 
 the quantity of parenchymatous matter being so 
 small that the cuticle of the one surface appears 
 almost closely applied to the other; as in Broad- 
 leaved Birthwort, Aristolochia sipho; Scented 
 Bramble, Rubus odoratus ; and most trees and 
 shrubs : but this term does not imply that uni- 
 formity of substance which the ^ appellation herba- 
 
LECT. IX.] LEAVES. 511 
 
 ceous denotes. The terms scariose (scariosum), and 
 chartaceous (chartaceum, papyraceum) r are given 
 to varieties of the membranous leaf; the first im- 
 plying that it is dry, or apparently sapless, and 
 somewhat translucent ; the second, that it re- 
 sembles paper, as in Draco terminalu. Leathery 
 (coriaceum) implies that the leaf is thick, tough, 
 and elastic; as in the Mistletoe, Viscum album, 
 Changeable Hydrangea, Hydrangea hortensis, &c. : 
 and rigid (rigidum), that it is hard, with little elas- 
 ticity, as in Butcher's broom, Ruscus aculeatus, 
 Scotch fir, Pinus sylvestris, &c. Fleshy (carnosum) 
 denotes that the leaf is thick, and consists chiefly 
 of a juicy but firm cellular parenchyma, as in 
 Houseleek, Sempervivum tectorum ; and succulent 
 (succulentum), that the pulp is laxer and more 
 juicy, as in Mesembryanthemum echinatum, &c. 
 Mirbel says the consistence of the fleshy leaf is 
 that of the Apple ; of the succulent that of the 
 Plum *. 
 
 As all the characteristics of leaves, which I 
 have yet described, relate to the expansion, they 
 are consequently peculiar to simple leaves only, or 
 to the individual leaflets of compound leaves. Be- 
 fore detailing those common to both descriptions 
 of leaves, it is requisite to understand the pecu- 
 
 * Elemens de Phys. veg. iii. p. 642. 
 
512 CONSERVATIVE ORGANS. [LECT. IX. 
 
 liarities connected with the petiole or footstalk ; 
 and, as naturally arising out of these, the circum- 
 stances which constitute the compound leaf, with 
 its species and varieties. The description of these, 
 therefore, shall form part of the subject of our next 
 Lecture. 
 
 Before closing this Lecture, however, I may 
 remark that, although the study of the terms 
 which denote the peculiarities of formation in 
 the vegetable body, be apparently the least amus- 
 ing part of our subject, yet, it is not altogether 
 devoid of interest, from the great variety which 
 Nature displays in this part of the creation ; 
 and I can assure those who may think it tedi- 
 ous, tKat the readiness with which it enables us to 
 describe plants in proper Botanical language, 
 and to understand the descriptions of others, fully 
 repays the labour of the acquirement. Like learn- 
 ing a language of any kind, its utility becomes 
 evident only after its acquisition; but then the 
 stores of knowledge to which it serves as the key, 
 are opened with a facility which is not less gratify- 
 ing, than their magnitude and richness are asto- 
 nishing and their possession delightful. 
 
 3 
 
513 
 
 LECTURE x. 
 
 i 
 
 OP THE PETIOLE * COMPOUND LEAVES. THE SITUA- 
 TION, POSITION, INSERTION, DIRECTION, MAGNI- 
 TUDE, AND EXTENSION OF LEAVES. ANATOMY OP 
 THE LEAP. 
 
 THE FOOTSTALK (petiolus) in every instance in 
 which it is present, constitutes a part of the leaf. 
 It is simple, in some instances, consisting of one 
 piece only, as in all simple leaves; or it is com- 
 pound (composites), consisting of one common 
 stalk divided into several distinct parts. The com- 
 mon petiole is generally termed primary (pri- 
 marius) ; the immediate divisions of this se- 
 condary ( secundarii) ; the divisions of these ter- 
 nary (ternarii), and those which support the leaf- 
 lets partial (partiales seu proprii). The petiole 
 further differs in form, in the nature of its ap- 
 pendages, its mode of insertion into the leaf, and 
 its articulations. 
 
 In respect of form, some of the terms em- 
 ployed in the description of the stem are applicable 
 to the petiole. Thus it is said to be round (teres) ; 
 half-round (semiteres); compressed (compressus), 
 &c. according to the figure of its trans verse section. 
 The compressed petiole occasionally assumes the 
 
 VOL. I. L L 
 
514 CONSERVATIVE ORGANS. [LECT. X. 
 
 aspect and functions of a leaf, in leaves which 
 suffer that change which is termed alienated 
 (alienatum) ; that is, when the compound leaves 
 which are the first leaves of the plant, and na- 
 tural to the tribe, afterwards give place to 
 simple leaves, which are merely dilated petioles ; 
 as exemplified in several of the Mimosas from 
 Botany Bay. De Candolle has named these in- 
 termediate forms phyllodia. The transition might 
 be supposed to depend on the energy of the 
 plant diminishing with its growth; for, when a 
 plant of this kind is topped, the new leaves which 
 are put forth display the same characters as the 
 original foliage * ; but, that this is not the case is 
 evident, from the transition occurring constantly 
 in New Holland, where the genus has every op- 
 portunity of following its natural habits. The ma- 
 jority of petioles are slightly furrowed on the up- 
 per side ; but, when this is deep, it is particularly 
 denoted by the term channelled (canaliculatus), 
 and when much dilated the petiole is said to be 
 concave (concavus). In the last-mentioned in- 
 stance it sometimes partially embraces the stem 
 
 * I saw an illustration of this fact yesterday (25th September 
 1821), in the garden of Comtesse de Vandes, near Bayswater. 
 An old plant of Acacia falcata, on which no pinnated leaves 
 had been seen for several years, had been cut down and had 
 put forth pinnated leaves, resembling in every respect, except 
 in size, the first leaves of the plant. The second series of shoots, 
 however, displayed falcated leaves only without any pinnae. 
 
LECT. X.] LEAVES THE PETIOLE. 515 
 
 (amplexans), 7^; or wraps completely around it, 
 and then is termed sheathing (vaginans), as in the 
 Grasses. In some cases the petiole is inflated (in- 
 flatus), and the plants in which this occurs being 
 aquatic, it serves to float the leaf, as in Trapa 
 natans, 73, &c. 
 
 The appendages of the petiole are not nume- 
 rous. A footstalk is said to be winged (alatus), 
 when it has on each side of it a portion of the 
 expansion, isolated from the rest, as in the Orange 
 tribe, Citrus, 74. But there are leafy appen- 
 dages of a distinct character, denominated sti- 
 pules, which are yet to be described, in many in- 
 stances attached to the petiole; as in the Rose 
 tribe, Rosa, 75, in which case the petiole is 
 termed stipuliferous (stipuliferus). It is termed 
 glanduliferus, 76, when one or more glands are 
 
 seated on it, as in the genus Passiflora ; in the 
 Castor-oil plant, Ricinus communis, &c.: and 
 floriferus when it bears the flower, as in Elm- 
 leaved Turnera, Turnera ulmifolia. 
 
 In respect to insertion, in the majority of in- 
 
 LL*2 
 
516 CONSERVATIVE ORGANS. [LECT. X. 
 
 stances the petiole and the expansion are in the 
 same plane; the insertion of the footstalk being at 
 that portion of the margin of the expansion, which 
 is regarded as the base of the leaf; but in some 
 instances it is in the centre of the disk, and then 
 the leaf is termed shieldlike (peltatum), 77. The 
 consideration of terms denoting the other inser- 
 tions of the petiole is deferred until we examine 
 the various insertions of the leaf, of which the 
 footstalk is merely a part. 
 
 The term articulation, as applied to the petiole, 
 is intended to denote that it consists of more than 
 one piece, the pieces being generally united by a 
 small intermediate portion, thicker and more 
 spongy than the parts it unites, commonly of a 
 different colour and capable of motion. The pe- 
 tiole of the simple leaf is rarely, although some- 
 times, articulated, as in Citrus aurantium, 74, a. ; 
 and, also, in the majority of Grasses, at that point 
 which separates the real leaf from its sheathing 
 petiole, and which is generally marked on the 
 inner side by a small membranous appendage, 
 which the elder Botanists termed ligula and mem- 
 brana foliorum, but which is now properly con- 
 sidered a stipule. Articulation is very common 
 in compound leaves. It occurs generally at the 
 attachment of the partial to the common pe- 
 tiole, in such leaves as fold together their leaflets 
 during the night; but, in some instances, there is 
 an articulation, also, near the point where the 
 
LECT. X.] LEAVES THE PETIOLE. 517 
 
 primary petiole springs from the branch, particu- 
 larly in those plants which have irritable leaves, as 
 Mimosa sensitiva, &c. At these secondary arti- 
 culations the leaflets separate, and fall in autumn; 
 sometimes before the common petiole falls, par- 
 ticularly when it is not articulated near its in- 
 sertion. The term inarticulatus is employed com- 
 paratively, when leaves belonging to a tribe of 
 plants, in which articulation is common, are de- 
 ficient in this peculiarity. 
 
 The composition of the petiole necessarily im- 
 plies that of the leaf; but a compound leaf does 
 not necessarily imply the existence of either se- 
 condary, ternary, or partial petioles. The COM- 
 POUND leaf may be thus defined: a leaf which 
 consists of seveal distinct expansions or leaflets, 
 connected by articulations either directly or in- 
 directly, and a common footstalk. This defini- 
 tion differs from that of the majority of Botanical 
 writers, in regarding the connexion of the leaflets 
 by articulations as the chief charasteristic of the 
 compound leaf * ; but I cannot consider any leaf 
 
 * Mr. Keith seems to be fully aware of this characteristic of 
 compound leaves (see Syst. of Phys. Bot. vol. i. p. 54) ; and 
 Bulliard thus defines the compound leaf: " La feuille composee 
 " a une ou plusieurs folioles attachees au petiole commun par 
 " une articulation, au moyen delaquelle chacune d'elles peut se 
 " mouvoir dans certaines circonstances, et 6tre detachee sans 
 " lesion, soit spontanement, soit artificiellement." Diet, ele- 
 ment, de Bolanique, p. 59. 
 
 L L 3 
 
518 CONSERVATIVE ORGANS. [LECT. X. 
 
 as compounded, or consisting of distinct parts, in 
 which the divisions of the expansion, however 
 multitudinous they may be, are still parts of the 
 same expansion, inasmuch as they are con- 
 nected by the direct and immediate prolongations 
 of the same petiolei That the leaflets in a true 
 compound leaf are distinct organs, is confirmed 
 by the articulations being conspicuous by anato- 
 my, and by the natural habits of the leaf. The 
 articulations in many leaves are rendered conspi- 
 cuous by a cartilaginous structure ; and in others 
 by a swelling of the partial petiole, at its point of 
 union with the common footstalk, which almost 
 impresses the idea of an artificial attachment: in 
 some instances, however, this is so obscure, that 
 it is by dissection only that the fact can be deter- 
 mined. In a longitudinal section of the petiole of a 
 simple leaf and its ramifications, the vascular 
 bundles distributed to the latter appear merely 
 slips from those of the common petiole; but in a 
 compound leaf we find a peculiar vascular arrange- 
 ment, closely resembling that which occurs in the 
 knotted culm and other articulated stems (see 
 p. 312), marking the place where the vessels of 
 the common petiole apparently terminate, and 
 those of the leaflets commence ; thus demonstrat- 
 ing the individuality of the leaflet. At this point, 
 also, as has been already stated, the leaflets spon- 
 taneously detach themselves from the common 
 
LECT. X.] COMPOUND LEAVES. 519 
 
 footstalk in autumn, in the same manner as the 
 leaf detaches itself from the tree. Every ex- 
 pansion, therefore, in a compound leaf, is an in- 
 dividual leaf; and it assumes different forms on 
 different plants, in the same manner as the simple 
 leaf. All compound leaves may be arranged under 
 the three following divisions : simply compound 
 (composita) ; doubly compound (decomposita) ; 
 more than doubly compound (supradecomposita). 
 
 1. The simply compound leaf consists of a 
 common petiole only, supporting two or more 
 leaflets. 
 
 When the leaflets are sessile, attached to the 
 apex of the petiole, and three in number, the 
 leaf is termed trifoliate or ternate (trifoliolatum, 
 ternatum), 82 ; as in the genus Clover, Trifolium, 
 
520 CONSERVATIVE ORGANS. [LECT. X 
 
 &c. It is quadrinate (quadrinatum), when there 
 are four leaflets, as in Marsilea quadrifolia, 83, 
 and some of the Hedysarums: quinate (quinatum), 
 when there are five, as in ^Esculus Pavia, 84; 
 digitate or fingered (digitatum), 85, when there 
 are seven, as in several of the Potentillas ; and 
 multifoliolatum when the number exceeds seven; 
 or umbellatum, 86, when being numerous they 
 are so arranged as to form the figure of a parasol, 
 as exemplified in many of the Lupine tribe. 
 
 When the leaflets, instead of being supported 
 on the very apex of the petiole, are attached on 
 its sides, the leaf is termed yoked and pinnate. It 
 is termed simply yoked (conjugatum}, when one 
 pair only of opposite leaflets is supported on a 
 common footstalk, as in the genus Zygophyllum, 
 87, (p. 521), which is named from this character of 
 the leaves : and bijugum, when there are two pairs. 
 But the terms bijugum, trijugum, quadrijugum, 
 quinquejugum, and multijugum, are not employed, 
 except to denote the particular number of opposite 
 leaflets on a common footstalk, when such an 
 enumeration is requisite for establishing specific 
 characters; otherwise all compound leaves having 
 more than one pair of opposite leaflets attached 
 along the side of a common petiole, are, usually, 
 regarded as pinnate (plnnata). The individual 
 leaflets are termed pinncc; and according to the 
 
COMPOUND LEAVES. 
 
 521 
 
 LECT. X.] 
 
 arrangement of these on the petiole, pinnate 
 leaves receive different appellations. 
 
 When all the leaflets are in pairs, and the com- 
 mon petiole, or rachis, is not terminated either by 
 a leaflet or a tendril, the leaf is termed abruptly 
 pinnate (pari-pinnatum, sen abrupti-pinnatum) , 
 88 ; but it is pinnate with a terminal or solitary 
 leaflet (impari-pinnatum, pmnatum cum impari), 
 when, there is a single leaflet at the apex of the 
 petiole, 8p, .; and the expression, with a tendril 
 (cirroswn), is added, if, instead of a leaflet, the 
 termination be a tendril, as in the Vetch tribe, 
 Vida *, 90, a. If the terminal leaflet be much 
 
 * There is no specific term to designate a leaf, which has one 
 pair of leaflets only, on a common petiole which, extending 
 beyond them, is terminated by a solitary leaflet, as in the Kidney 
 Bean, Phaseolus vulgaris; for, although the term ternate is 
 usually applied to it, yet it cannot be regarded as ternate on ac- 
 
522 CONSERVATIVE ORGANS. [LECT. X. 
 
 larger than the other leaflets, the leaf is said to be 
 lyrato-pinnatum ; but this is a term of very rare 
 application in compound leaves ; those so deno- 
 minated being, for the most part., truly simple 
 lyrate leaves, altogether devoid of articulations, 
 or that modification of vessels at the union of the 
 lateral divisions, which is the requisite charac- 
 teristic of the leaflet, and consequently of the 
 compound leaf. If the leaflets be in opposite 
 pairs, and it be not essential to enumerate them, 
 the leaf is said to be oppositely pinnate (opposite 
 pinnatum) y 88 ; b.b. b. b. (page 521 ), and alternately 
 pinnate (alternatim pinnatum), when they are al- 
 ternate, QO, b. c. It is interruptedly pinnate (inter- 
 rupte pinnatum), when the leaflets are alternately 
 large and small on both sides of the petiole, 89, 
 b. c.b.c. ; jointedly pinnate (articulate pinnatum) , 
 when the common petiole is jointed betwixt each 
 pair of leaflets, .91 ; and decreasingly pinnate 
 (pinnatum foliolis decrescentibus), when the 
 leaflets gradually diminish in size from the base to 
 the apex of the leaf, as in Vicia sepium. In al- 
 most every writer on elementary Botany, the term 
 decurrently pinnate (decursive pinnatum) is de- 
 scribed as denoting that the leaflets are decurrent, 
 or united by a foliaceous membrane, extending 
 
 count of the lateral leaflets, this term implying that all the 
 leaflets are on the apex of the petiole; I would, therefore, 
 propose the term impart '-conjugatum, for the above-mentioned 
 form of leaf. See cut, fig. 97, page 523, which is the leaf of 
 Hedysarum gyrans. 
 
LECT. X.] COMPOUND LEAVES. 523 
 
 from one leaflet to another, down the common 
 petiole; but this is the description of the pin- 
 natifid leaf; for the real decurrently pinnate is a 
 modification of the jointedly pinnate, each joint 
 consisting of one pair of pinnae supported on a 
 winged petiole (see fig. 91, page 521, a. a. a.). In 
 some instances the leaflets, instead of being ar- 
 ranged in the same plane on each side of the com- 
 mon petiole, are placed around it; and the leaf 
 is consequently termed verticillato-pinnatum. 
 
 2. The second division of compounded leaves, 
 the doubly compound, comprehends those leaves in 
 which the common petiole is divided into, or sup- 
 ports secondary petioles. 
 
 When near the apex of the common petiole, 
 there is a single pair of secondary petioles, each 
 of which supports a pair of opposite leaflets, as in 
 Mimosa unguis cati, the leaf is termed twice 
 paired (bigeminatum, seu biconjugatumj , Q2: it is 
 
 92 
 
524 CONSERVATIVE ORGANS. [LECT. X. 
 
 thrice paired (tergeminatum), when the leaf re- 
 sembles the twice paired in its petiolar divisions, 
 and has besides a third pair of leaflets at the point 
 where the secondary petioles originate, as in Mi- 
 mosa tergemina, Q3; but if the common foot- 
 stalk supports three secondary petioles on its apex, 
 and each of these support three leaflets, then the 
 leaf is termed doubly tern ate (biternatum, dupli- 
 cato-ternatum) , Q4. 
 
 A leaf is termed doubly pinnate (bipinnatum), 
 when the secondary petioles are arranged in pairs 
 on the common petiole, and each secondary petiole 
 is pinnate, or displays the characters of the simply 
 pinnate leaf, Q5 ; it is conjugated and pinnate 
 (conjugatum-pinnatum), when a common petiole 
 supports a single pair of secondary petioles, each 
 of which is pinnate, as in Mimosa purpurea, 96; 
 ternated and pinnate (ternatum-pinnatum) , when 
 the common petiole supports on its apex three pin- 
 nate leaflets, as in HofFmannsegia: and digitated 
 and pinnate (digitatum-pinnatum) , when the num- 
 ber of these exceed three, as in Mimosa pudica. 
 
 The pedate leaf (folium pedatum) is general- 
 ly described as a decompound leaf, composed of 
 a common petiole divided at its summit into 
 two diverging branches, with an intermediate 
 leaflet, and each branch supporting two or 
 more lateral leaflets on their anterior edge; as 
 
LECT. X.] COMPOUND LEAVES. 525 
 
 in Helleborus niger, Q8; but according to the 
 
 definition of the compound leaf which we have 
 adopted, the pedate is merely a deeply divided 
 simple leaf, having a close affinity to the palmate, 
 or rather, as Sir J. E. Smith observes, who never- 
 theless regards it as a compound leaf, to " those 
 " simple leaves which are three-ribbed at the base." 
 
 3. The third division of compounded leaves, 
 the more than doubly compound, comprehends 
 those in which the common petiole supports se- 
 condary petioles, which in their turn support ter- 
 nary petioles. 
 
 When the common petiole supports, on its 
 apex, three secondary petioles, which each sup- 
 ports three ternary petioles, and every one of these 
 three leaflets, the leaf is termed thrice ternate 
 (tritematum s. triplicato-ternatum), 99, (p. 526) ; 
 and when along the sides of the common petiole, 
 
526 CONSERVATIVE ORGANS. [LECT. X. 
 
 there are secondary petioles, supporting ternary, 
 which are pinnate, it is triply pinnate (tripinna- 
 tum s. triplicato-pinnatum) , as in the Carrot 
 genus, Daucus, &c. 100, (p. 525). These are the 
 only species of the decompound leaf; but the term 
 is occasionally applied to leaves which are very 
 much and irregularly divided. 
 
 There is, however, one species of the compound 
 leaf, which we have not yet examined, because it 
 cannot properly be classed in any of the foregoing 
 divisions. It is sometimes termed vertebrated (ver- 
 tebratum), and sometimes jointed ( articulatum) . 
 It consists of several leaflets, which appear to 
 grow out of each other, or are attached one 
 upon the summit of another, with an evident 
 
LECT. X.] COMPOUND LEAVES. 527 
 
 joint at the point of attachment, as in prickly- 
 leaved Fagara, Fagara tragodes *, 1 00. 
 
 f02 
 
 In the majority of plants the form of the 
 leaf, whatever that may be, is the same over 
 the whole of the plant; but there are exceptions 
 to this rule ; and when the diversity in the form 
 of the leaves is constant, the term heterophyl- 
 lus is occasionally adopted as the specific naine 
 of the plant. Thus various-leaved Spurge, Eu- 
 phorbia heterophylla, is named from having the 
 lower leaves short, wedge-shaped, emarginate 
 and mucronate, while the upper are long linear- 
 lanceolate, acute, and entire, 101. Heterophyllous 
 plants, however, must not be confounded with 
 
 * Mirbel (Elem. de Phys. veg. Zde Partie, p. 655) quotes 
 the leaf of spike-flowered Cussonia, a curious Cape plant, as an 
 example of the vertebrated leaf; but this Cussonia presents an 
 instance only of a digitated leaf, with articulated, winged, se- 
 condary petioles. 
 
528 CONSERVATIVE ORGANS. [LECT. X. 
 
 those which have alienated leaves, as exempli- 
 fied in Mimosa verticillata (see 102, p. 527 ; a. the 
 forn^of the earlier leaves, b. those which succeed 
 them) ; for, in these, the leaves, which are alien- 
 ated or different from those which first appeared 
 on the plant, and from those peculiar to the 
 genus, are ultimately the only leaves of the plant. 
 
 Besides those characteristics of leaves which 
 have been described, there are others common both 
 to simple and to compound leaves, whatever may 
 be their form and structure. These refer to the 
 situation of the leaves ; to their disposition on the 
 stem and branches ; to the mode of their attach- 
 ment or insertion ; and to the direction of their 
 surfaces with respect to the stem and the branches 
 as well as to the plane of the horizon. 
 
 In point of SITUATION the majority of leaves 
 may be regarded as aerial; being suspended on 
 the stem or the branches, in such a manner that 
 the air is applied to both surfaces of every leaf. 
 The position of such leaves in relation to the hori- 
 zon, is determinate, or always the same in the 
 same description of plants, but varies in different 
 kinds of plants ; and this constitutes, in Botanical 
 language, their direction: in ascertaining which, 
 the plant must be in a healthy state, for an un- 
 healthy state of the plant and the natural decay 
 of the leaf in autumn, alter the ordinary direction 
 of this organ. The following are the determinate 
 
LECT. X.) 
 
 COMPOUND LEAVES. 
 
 529 
 
 directions of leaves which are 
 employed in forming the spe- 
 cific characters of plants. 
 
 When the direction of a 
 leaf is nearly perpendicular, it 
 is said to be erect (erecta)*; 
 in which case it forms an acute 
 angle with the stem (see the 
 diagram, a. a.) : but if the angle 
 be so acute that the upper 
 disk of the leaf is closely pressed 
 to the surface of the stem or 
 the branch, it is then termed 
 adpressa. When the angle is 
 moderately acute only, or about 
 forty-five degrees (.), and the 
 surface of , the leaf, consequently, approaches the 
 line of the horizon, the direction is termed spread- 
 ing (patens sen patula); and horizontal (hori- 
 zontalis sen palentissima), when it spreads still 
 more, approximating to a right angle with the 
 stem or the branch when these are erect (c.), or 
 to ninety degrees in relation to the horizon. When 
 the feaf is spreading with a drooping apex (d.) 9 the 
 direction is termed nodding or inclined (cernua seu 
 inclinata): it is reflex (reflexa seu recurva), when 
 
 * The term vertical is also employed by some writers, but 
 it is superfluous, the position of the most vertical leaf being 
 sufficiently described by the word erect. 
 
 VOL. I. MM 
 
530 CONSERVATIVE ORGANS. [LECT. X. 
 
 the leaf forms a curve, the convexity of which 
 (e.) is upwards; inflex (incurva seu inflexa), 
 when the convexity is downwards (/!); and 
 pendulous (dependens, pendula, seu demissa), 
 when the whole leaf droops (g. g.). When the 
 leaf is so twisted that one part of it is vertical 
 and' another horizontal, it is termed twisted 
 (oUiquum, deviatum), as exemplified in oblique- 
 leaved Garlic, Allium obliquum; and reversed 
 (resupinatum) , when the surface which is com- 
 monly undermost *is found uppermost, as in 
 spotted-flowered Alstraemeria, Alstrseineria pele- 
 grina. If $1 the leaves lean or point to the 
 same side, as in Polygonatum mitltiftora (see 
 fig. c. p. 246), the direction is termed unilateral 
 (secunda seu unilateralis) . Some leaves, instead 
 of being 1 suspended in the air, lie on the surface of 
 the ground, as for instance in several species of 
 the genus Plantago, and the common Daisy, 
 Bellis perennis ; in which case the direction is 
 termed procumbent (procumbens seu humifusaj. 
 
 In aquatic plants, the direction of the leaves is 
 determined by their relation to the surface of the 
 water. When the leaf is raised upon its pe- 
 tiole, above that surface, and is, therefore, an 
 aerial leaf although growing in water, it is said 
 to be emerging (emersa), as exemplified in the 
 greater Water Plantain, Alisma Plantago: if 
 it lie on the surface of the water, and the up- 
 
LECT. X.] DIRECTION OF THE LEAVES. 531 
 
 per disk of it only be exposed to the light and 
 air, it is termed floating- (natans), as in the 
 White Water Lily, Nymphaea alba, floating Wa- 
 ter Plantain, Alisma natans, &c. : and when it is 
 surrounded on every side by the water, as the 
 majority of leaves are by the air, its direction is 
 denoted by the term sunk or immersed (submersa, 
 immersa, demersa), as in perfoliate Pond-weed, 
 Potarnogeton perfoliatum. Some aquatics have 
 leaves which are immersed and also leaves which 
 float, as, for instance, Various-leaved Crow-foot, 
 Ranunculus aquatilu, the beautiful white flow- 
 ers of which decorate our ponds in the spring 
 and summer months: others, as verticillate 
 Water-milfoil, have both immersed and emerging 
 leaves. In these and similar plants, it is curious 
 to remark the manner in which the form of the 
 leaf is modified by the medium in which it 
 is naturally placed: the leaves, for instance, of 
 Ranunculus aguatUis, which grow under the 
 water, are divided into capillary segments (a. a. 
 fig. 1, page 532), while those which float on the 
 surface are merely lobed and notched (b.J. In 
 plants even which are not aquatics, but which may 
 happen to be planted in water, we perceive the me- 
 tamorphose from the flat to the capillary leaves 
 taking place in the fresh shoots before they gain 
 the surface of the water, after which they assume 
 
 M M 2 
 
532 CONSERVATIVE ORGANS. [LECT. X. 
 
 the form consonant to the natural habitat of the 
 plant: a, fig. 2, is the natural form of the leaf of 
 Horehound, Ballota nigra ; when it grows on 
 
 dry land; b. h. fig. 3, display the change which 
 takes place when it grows under water. 
 
 Regarding the situation of leaves in relation to 
 the part of the plant on which they are seated, 
 they may be referred to the root, the stem, and 
 the branches, or they are radical, caulinar, and 
 rameal. A radical leaf (folium radicals) is seated 
 upon or springs directly from the root, as exem- 
 plified in the Primrose, Primula vulgaris, the 
 Dandelion, Leontodon taraxacum, &c. ; but ra- 
 dical leaves must not be confounded with seminal 
 leaves, which are the first leaves of the majority 
 
LECT. X.] SITUATION OF LEAVES. 533 
 
 of plants proceeding from seeds that have more 
 than one seed-lobe. The seminal leaf (/'. semi- 
 note) is, in fact, a transformation of a seed-lobe 
 to a leaf of a very temporary duration, and which 
 performs the functions of a leaf until the real 
 leaves appear, after which it drops off. 
 
 Although it may be anticipating the remarks 
 we have afterwards to make on the nature and 
 functions of the cotyledon, yet it is proper to state 
 here, that the cotyledon is a nutritive organ, con- 
 taining in its cells a large portion of farinaceous 
 matter, which becomes saccharine during the 
 germination of the seed, and is admirably adapted 
 for the nourishment of the embryon plant. In 
 those seeds, the cotyledons of which rise above 
 the ground when they vegetate, as, for instance, 
 the Lupine, the cotyledons acquire a green colour 
 as soon as they are exposed to the light; and then, 
 besides continuing to supply nutriment to the 
 young plant, the root of which is still incapable of 
 taking up any thing from the soil, perform all the 
 functions of the real leaf. If the seminal leaves 
 be destroyed before the other leaves appear, the 
 plant dies ; and, therefore, as the saccharine qua- 
 lities of the seminal or cotyledon leaves in the 
 Turnip attract a species of small beetle, which 
 does not attack the proper leaves of the plant, whole 
 crops of this useful vegetable are often destroyed. 
 Farmers, indeed, do not consider the crop of tur- 
 
 MM3 
 
534 CONSERVATIVE ORGANS. [LECT. X. 
 
 nips safe until the second leaf appears, or, in the 
 language of agriculture, until the plants come into 
 rough leaf'. 
 
 The seminal leaves, in almost every instance, 
 are readily distinguished by their form, which al- 
 ways varies more or less from that of the proper 
 leaves; thus, in fig. 4 (page 532), a. shows the co- 
 tyledons changed into seminal leaves, b. b. are 
 the first proper leaves of the plant. A stem leaf 
 (f. caulinare), as the term implies, grows upon 
 the stem, and is attached to it either mediately, 
 or immediately by means of a petiole. A branch 
 leaf (f. rameum) is described as such only 
 when it differs from the leaves on the main stem 
 of the same plant, in which case it is requisite to 
 distinguish it from them ; as exemplified in purple 
 Cow-wheat, Melampyrum arvense. When stem 
 or branch leaves are seated on joints, they are 
 designated by the term articular (articulares) , 
 
 Fig. 5. 
 
 Fig. a ; and when situated close to or between the 
 
LECT. X.] SITUATION OF LEAVES. 535 
 
 flowers, they are termed floral (folia floralia), 
 Fig. 6. 
 
 Elementary writers usually distinguish these 
 floral leaves, which are green and resemble the 
 other leaves of the plant, from those which are of 
 a different shape and colour, giving to the latter 
 the name of bractes (bractece), and place them 
 among those organs which I have yet to describe 
 under the term appendages. Both varieties, how- 
 ever, are real leaves, having the same anatomical 
 structure, and differing in shape not more from one 
 another, and from the other leaves of the plant, 
 than these last differ among themselves. That 
 colour is a bad cause of distinction is evident, for 
 many plants have all their leaves coloured; and 
 in purple-topped Clary, Salvia Horminum, and 
 .many other plants, the transition from common 
 leaves to green floral leaves (a. a. a. a. fig. 6), and 
 from these to coloured (b. b. b. fig. 6), is so gra- 
 dual as clearly to display their close affinity; and 
 to prove that all the three kinds are merely modifi- 
 cations of the same organ. The early Honeysuckle, 
 Lonicera Caprifolium; Green Hellebore, Helle- 
 borus viridis; and several of the Orchis tribe, af- 
 ford examples of green floral leaves: the Laven- 
 ders, Lavandulce ; crested Cow-wheat, Melampy- 
 rum cristatum ; Purple bracted Monarda, Monar- 
 da media, &c. display specimens of those that 
 are coloured ; and several of the Sages, Salvise, 
 
 M M 4 
 
536 
 
 CONSERVATIVE ORGANS. 
 
 X. 
 
 exhibit both kinds. The floral leaves form a 
 tuft above the flowers in the Crown Imperial, 
 Fritillaria Imperialism above those of the Pine 
 Apple, Bromelia Ananas, and of several other 
 plants; and under the flowers of Anemone, they re- 
 semble and have received the name of an involucre 
 (involucrum) . All these, and such-like, are there- 
 fore true leaves; but as some are more inti- 
 mately connected with the flower, and in con- 
 formity with the custom of other elementary wri- 
 ters, I shall revert to the consideration of these 
 as bractes, when we examine the floral ap- 
 pendages *. 
 
 Leaves, besides differing in situation, are also 
 variously distributed on the stem and branches. 
 
 * Linnaeus remarks, that no bractes have been observed in 
 *ny plant belonging to the class Tetradynamia. 
 
LECT. X.] POSITION OF LEAVES. 537 
 
 The position is termed opposite (opposita),(6.) when 
 they appear directly on opposite sides of the stem, 
 in pairs; and when these alternately cross each 
 other they are said to be decussated (decussa- 
 ta), (7.)- The position is ternate (terna), when the 
 leaves stand by threes around the stem, on 
 the same plane of the horizon ; and quaternate 
 (quaterna) when in fours ; which, however, is not 
 applicable when the four leaves, lying in the plane 
 of the horizon, point towards four opposite di- 
 rections, the term cruciate (cruciata seu crwa*- 
 formis), 8, being employed to denote this posi- 
 tion. When the number of leaves grounding 
 the stem or branch exceed four, and point to 
 different directions, forming a starlike figure, 
 the position is termed whorled (verticillata seu 
 stellata), (.). In the majority of instances the 
 term whorled is used without any reference to the 
 number of rays; but in large natural genera, as, 
 for instance, Galium (Bed-straw), it is necessary 
 to designate these, and for this purpose the terms 
 quina, sena, octona, &c. are employed. When, in- 
 stead of being in pairs, leaves stand solitarily on the 
 stem or branches, spreading in various directions, 
 the position is termed alternate (alterna), (10, 
 page 538); and in this state they form either a 
 spiral line around the common axis (spiralia), as 
 in the Norway spruce fir, Pin us Abies , or are 
 irregularly scattered (sparsa); or they are two- 
 
538 CONSERVATIVE ORGANS. [LECT. X. 
 
 ranked (disticha), (1 l), which implies that they 
 spread " in two directions, and yet are not re- 
 gularly opposite at their insertion," as in the 
 
 Yew, Taxus baccata, &c. When several leaves 
 spring from the same point they are said to be 
 tufted (fasciculata) ; and the numerical terms 
 bina (a. b.) applied when there are two leaves, 
 terna when there are three, and quiriu when 
 there are five, are used to denote the number of 
 leaves in each fascicle. 
 
 With respect to proximity, in the distribution 
 of leaves, the term Crowded (conferta) implies that 
 their points of attachment are comparatively very 
 
LECT. X.] POSITION OF LEAVES. 539 
 
 close; and imbricated (imbricata), (12, and also 
 fig. l . Plate 4), that they partly cover each other, 
 like the tiles upon a house-top : but if they do not 
 overlap very closely, and the leaves regularly di- 
 verge, producing a figure somewhat resembling 
 that of a rose, the position is termed roselata (13), 
 and crowning (coronantia) , when they terminate 
 the stem or its divisions like a plume of feathers, as 
 in the Palm tribe. Remote (remota) is employed 
 solely as a term of comparison, and implies that 
 the leaves are at greater distances from one an- 
 other than is usual in the majority of plants. 
 
 In whatever manner leaves are disposed on 
 the stem or branches, the mode in which they are 
 connected with these parts is termed their in- 
 sertion; and the diversities of this are taken ad- 
 vantage of in forming specific characters. The 
 majority of leaves are supported on footstalks ; 
 and those thus furnished, whether the foot- 
 stalk be long or short, siinple or compound, 
 are said to be petiolate (folia petiolata) ; but if 
 there be no footstalk, they are termed sessile 
 (sessilia). There are several varieties of sessile 
 leaves : thus, if the leaves clasp the stem with 
 their bases, they are termed embracing, or clasp- 
 ing (amplexicauliaj, (14, page 540); if the em- 
 bracing leaves be opposite and united at their 
 bases, they are said to be connate (connata), (15, 
 page 540) ; and connato-perfoliata, ( \ 6, and fig. 6. 
 
540 CONSERVATIVE ORGANS. [LECT. X. 
 
 Plate 4), if the union be in the whole, or nearly 
 the whole breadth of the leaves, so as to give the 
 two leaves the appearance of being united into but 
 one leaf. Connate leaves are .in some instances 
 united by a membrane, which stretching from the 
 margins of the opposed leaves, near the base, 
 forms a kind of pitcher around the stem ( 1 6 *) in 
 which the rain-water is retained ; as exempli- 
 fied in Fuller's Teasel, Dipsacusfullonum, which 
 has received its generic name SAJ/axof, or thirsty, 
 from this circumstance. A perfoliate leaf (fo- 
 lium perfoliatum) , (17), is itself perforated by 
 the stem. When leaves embrace the stem with 
 their bases, so as to enclose it as with a sheath, 
 
 they are termed sheathing (vaginantia), ( 1 8, a 
 
LECT. X.] POSITION OF LEAVES. 541 
 
 the stem, b. b. the sheathing leaves) ; they are 
 equitant (equitantia), when being opposite they 
 clasp each other, as in the Iris tribe ; and de- 
 current (decurrentia), when the lamellar part of 
 the leaf runs down on each side of the stem (19. 
 in ^ which a. a. mark the leaves, and b. b. their de- 
 current portions). Some succulent leaves ap- 
 pear as if they were unconnected with the stem, 
 and merely resting upon it ; on which account they 
 are termed loose (soluta). 
 
 Leaves which produce spines in the same man- 
 ner as the stem, are termed spiniferous (spini- 
 fera), (21, page 542): when they give birth to 
 other leaves, they are said to be foliferous (folii- 
 fera), as exemplified in Duckweed, Lemna tri- 
 sulca; and floriferous (florifera), if they bear 
 flowers, as, for instance, on the petiole in Tur- 
 nera cuneiformis, (22, page 542), on the upper 
 disk of the leaf in Butcher-broom, Ruscus acule- 
 atus, (23, page 542): and from the serratures of its 
 margin, in Xylophylla (24, page 542). When they 
 
542 CONSERVATIVE ORGANS. [LECT. X. 
 
 throw out roots, and produce plants in every 
 
 respect resembling the plant to which they belong, 
 they are termed proliferous (prolifera). The 
 plant which displays the most beautiful example of 
 the proliferous leaf is the Cotyledon calydnum; 
 see fig. 1. Plate 10, in which the letters a. a. a. 
 a. a. a. mark the young plants springing from the 
 serratures of the leaf, some of them sufficiently 
 advanced to admit of their being separated from 
 the leaf, and sustained by their own vegetative 
 powers. The attachment of the young plants is 
 extremely slight., and evidently effected by a cord 
 of umbilical vessels, originating in the proper 
 vessels of the leaf. Leaves of this description 
 have the closest affinity with those bulb scales 
 which, as I demonstrated to you in treating of 
 bulbs, produce new bulbs when they are separated 
 
LECT. X.] LEAVES. 543 
 
 from the stem which bears them, and are planted. 
 The young plants produced on such leaves are the 
 lateral progeny of the adult plant, by which its 
 existence is renewed, without the aid of the sexual 
 stimulus; in the same manner as buds are formed 
 on stems and branches, offsets on bulbs, and 
 gems on tubers, to the last of which, indeed, such 
 leaves are closely allied. They possess the same 
 distinct vitality as tubers; for the leaves of Co- 
 tyledon calydnum will produce perfect plants from 
 their serratures, if even worn in the pocket, 
 wrapped in a piece of paper; and, holding, as 
 they do, an intermediate place between tubers 
 and leaves, they might be almost regarded as 
 foliaceous tubers. It may be asked, are the 
 germs of the plants, which rise on the margins 
 of such leaves, coexistent with the origin of the 
 leaves, as is the case with the germs in the eye or 
 gem of the tuber? To answer this question we 
 must have recourse to the microscope ; and on 
 examining with it the margins of those leaves of 
 Cotyledon calycinum, which have not yet become 
 proliferous, we perceive in each serrature a small 
 rough papilla, projecting on the under disk of the 
 leaf; and in a transverse section the cellular 
 matter at this place is seen to be differently ar- 
 ranged from that in the rest of the leaf; and 
 displaying in its centre a small opaque point, 
 from which a vessel extends to the surface of the 
 
544 CONSERVATIVE ORGANS. [LECT. X. 
 
 papilla, while another enters the surrounding cel- 
 lular matter. This point is the germ of the new 
 plant ; and the vessel, or rather fascicle of vessels, 
 entering the cellular matter is its umbilical cord. 
 As soon, therefore, as circumstances favourable to 
 its evolution are present, the same vital actions 
 commence in it to promote its growth, and for the 
 formation of new parts, as occur in gems situated 
 on tubers; the leaf, like the tuber, supplying 
 the necessary nutriment, until the roots of the 
 young plants are capable of taking up the nu- 
 tritious fluids of the soil; after which it decays, 
 its assistance being no longer required. In 
 tracing the progress of the germ, we perceive 
 that the radicles shoot out from the surface of the 
 rough papilla ; while the two first leaves of the 
 young plant, imperfectly developed and applied 
 face to face, push out from the edge of the ser- 
 rature on the same plane as that of the surface of 
 the leaf; but the young plant afterwards turns up- 
 wards, so as to rise and stand erect on that surface. 
 These two primordial leaves are always developed, 
 and sometimes expanded, before the radicles make 
 their appearance. But the real proliferous leaf, 
 such as that of Cotyledon calycinum, must not 
 be confounded with leaves which became pro- 
 liferous only when separated from the tree and 
 planted in the ground, under favourable circum- 
 stances; as, for example, those of the Lemon tree ; 
 
 2 
 
LECT. X.] ANATOMY OF LEAVES. 545 
 
 which are never productive while they remain 
 attached to the parent. These leaves, however, 
 closely resemble the scales of the scaly bulbs; 
 each scale of which produces a young bulb when it 
 is separated from the others on the same caudex, 
 and planted, although one new bulb only is the 
 result of the united functions of all the scales, when 
 they are allowed to remain as aggregated parts of 
 the adult bulb: and the explanation which has 
 been already given (see pages 176-177) of this 
 circumstance, as it occurs in bulbs, is appli- 
 cable to its occurrence in this description of 
 leaves *. 
 
 * It is rather extraordinary, that although the inhabitants 
 of the Radick islands, lately discovered in the Pacific Ocean 
 (see Kotzebue's Voyage J, are aware of this fact, and constantly 
 raise their Taro, Arum esculentum, by planting the leaves ; 
 yet, it was unknown in Europe until the middle of the seven- 
 teenth century ; when Agostino Mandirola, an Italian minorite 
 of the Franciscan order, first described the art in a small 
 work entitled, Manuale de Giardinieri, published at Venice, in 
 the year 1684?. The leaves he planted were those of the Cedar 
 and the Lemon, and the mode of conducting the operation, 
 which he thus describes, is, I believe, still followed : " Ho 
 " preso un vaso pieno di buonnissima terra sottile e grassa, poi 
 " intorno all orificio vi ho posto le foglie con il gambo sotto terra 
 " tanto che resti meza la folia sopra; posciaho fatto un' orcio- 
 " letto d' acqua che a stilla inaffiasse esse foglie, almo do detto di 
 " sopra, aggiongendovi sempre terra nel scavo dell acqua, ed in 
 " tal modo hanno fatto presa, e gettato fuora le vergelette 
 " in breve tempo." For other particulars on this subject see 
 Beckmans Hist, of Inventions, vol. iii. p. 426. Trans. 
 
 VOL. I. N N 
 
54(5 CONSERVATIVE ORGANS. [LECT. X. 
 
 The size of leaves differs very considerably in 
 different species of plants ; but, as has been cor- 
 rectly remarked, " it is not always the largest 
 " plant that has the largest leaf*." The Burdock, 
 Arctium lappa, produces larger leaves than any 
 other British plant ; but these seldom exceed 
 three feet in length, and two and a half in breadth ; 
 whereas the leaves of the Banana, Musa sapien- 
 tium, are sometimes found ten feet in length by 
 two in breadth ; and those of the Talipot Palm, 
 Licuala spinosa, have been known to exceed 
 thirty feet in circumference -^. 
 
 Having now concluded our examination of the 
 
 external or physiognomical characters of leaves, 
 
 we have next to investigate their internal structure 
 
 or anatomy. To pursue this inquiry, however,. 
 
 with advantage, some mode of classifying leaves, 
 
 in reference to their structure, should be adopted. 
 
 As all leaves have more or less affinity, in point of 
 
 structure, to the stems on which they are produced, 
 
 we might adopt the same arrangement that we 
 
 followed in our inquiries into the nature of stems, 
 
 and examine them as they belong to acotyledonous, 
 
 monocotyledonous, and dicotyledonous plants ; but 
 
 the varieties of structure which each of these 
 
 * Keith's Syst. of physiological Bot. i. p. 37. 
 
 t These leaves, which are fan -shaped, when propped up on 
 one side with a pole, serve as a temporary hut or shade to the 
 natives of Ceylon, who sell their merchandise under them. 
 
LECT. X.] ANATOMY OF LEAVES. 547 
 
 classes present, and the difficulty of pointing 
 out the general features which should be re- 
 garded as the fixed characteristics of each class, 
 present too many difficulties to permit the adop- 
 tion of this arrangement. Equal difficulties occur 
 to render objectionable any classification founded 
 on the form, or the substance, or the arrangement 
 of the parts of leaves. The only plan, therefore, 
 that we can adopt to render our investigation me- 
 thodical, is to discover in what circumstances all 
 leaves agree; and to examine the nature of these, 
 with their modifications in the three great divisions 
 of plants which we have just noticed. 
 
 In the most cursory examination of the ma- 
 jority of leaves, we perceive that these organs are 
 composed of three distinct parts : one part, firm 
 and apparently ligneous, constitutes the framework 
 or skeleton of the leaf; another, succulent and 
 pulpy, fills up the intermediate spaces of this 
 framework; and a third, thin and expanded, 
 incloses the other two, or forms the covering for 
 both surfaces of the leaf. On a closer examina- 
 tion we find that the first of these parts is vascular, 
 the second cellular, and the third a transparent 
 cuticular pellicle. Admitting, therefore, that 
 these parts are present in every leaf, although we 
 may not be able to discover all of them distinctly, 
 owing to the imperfection of our instruments; 
 we may conduct our inquiries into the structure of 
 
 NN 2 
 
548 CONSERVATIVE ORGANS. [LECT. X. 
 
 leaves in reference to their vascular, their cellular, 
 and their cuticular systems. 
 
 a. Of the vascular system of leaves. 
 
 Among fallen leaves which have been exposed 
 to the action of the atmosphere in a damp place, 
 or which have dropped into a pond, we generally 
 find some in which the cuticle and pulp are com- 
 pletely destroyed; whereas the ribs or veins, as 
 they are commonly but erroneously termed, being 
 less susceptible of decomposition, remain almost 
 entire, and display the appearance of a beautiful 
 tissue of network, more or less complicated. This 
 is the vascular system of the organ, and the leaf 
 in this state is termed a skeleton leaf. Leaves are 
 frequently artificially made into skeletons by ma- 
 cerating them in water until they begin to putrefy, 
 when the cuticle is easily separated by gently 
 rubbing and pressing them ; and the pulp washed 
 out from between the meshes of the vascular net- 
 work by rinsing in water : and if the operation 
 be carefully performed, the most minute cords of 
 vessels may be preserved * (see fig. 2, Plate 10). 
 
 * Although skeleton leaves produced by spontaneous de- 
 composition must have been very early observed, yet they were 
 not artificially prepared until 164?5, when Marcus Aurelius 
 Severinus published a figure, with a description of a leaf of 
 Cactus Opuntia reduced to a skeleton. The art, however, was 
 little attended to, until it was revived by Ruysch, in the com- 
 mencement of the eighteenth century. This naturalist at first 
 prepared them, by covering the leaves with insects, which ate 
 away the pulpy part ; but as these anatomists, or satellites, to 
 
LKCT. X.] ANATOMY OF LEAVES. 549 
 
 These preparations enable us to trace more readily 
 than in the natural leaf, the divisions, subdivisions, 
 and various ramifications of the vascular fasciculi; 
 but beyond this they afford us no information, and 
 we must have recourse to the microscope to obtain 
 a satisfactory knowledge of the vascular structure 
 of leaves. 
 
 If we commence our investigation with the 
 simplest description of plants, the Lichens and the 
 Mushroom tribe (Fungi) for instance, we perceive, 
 even by the assistance of the best glasses, scarcely 
 any trace of a vascular structure, the whole plants 
 appearing to be little more than an aggregation of 
 cellular substance enclosed in a cuticle. This ap- 
 pearance, however, arises in some degree from the 
 transparency of the vessels preventing them from 
 being distinguished from the cells, and in some de- 
 gree from the simplicity of their structure ; for, as 
 the fluid they convey is not required to be raised to 
 
 use his own expression, sometimes made sad havoc with the 
 solid parts also, he soon dismissed them from his service, and 
 employed the method I have described in the text (see his 
 Adversariorum Decas tertia, Amst. 1723-40). Fruits were also 
 prepared by the same method ; and the description of the in- 
 terior structure of a pear, by Du Hamel, illustrated with 
 engravings, may be seen in the Memoires de V Academic des 
 Sciences, An. 1730-32. In the Philosophical Trans. 1730, No. 
 ccccxiv. p. 371, Francis Nicholls gives an account of the ske- 
 leton of a Pear leaf, the network of which he split into two 
 equal layers. 
 
 N N'3 
 
550 
 
 CONSERVATIVE ORGANS. [LECT. X. 
 
 considerable heights, as in the more perfect 
 plants, the conducting tube is consequently more 
 simple. If, however, we take a plant in which 
 the vessels convey a colourless fluid through a 
 coloured cellular structure, as, for example, Mar- 
 chantia polymorpha, we find that the surface of the 
 lobes of the leaf-like frond, when examined by an 
 ordinary lens, is reticulated by depressed lines, 
 within each of which a small nipple-like body rises. 
 When a thin slice (1. c.) of a lobe is placed under 
 the microscope, these lines are discovered to be 
 occasioned by vessels which run immediately 
 under the cuticle, anastomosing with one another, 
 as represented at 1. d. d. d. d.; and the papillary 
 
 bodies are seen to be cuticular pores surrounded 
 by a slight elevation of the cuticle (1. b. b.) 
 modified as shall be afterwards described. This 
 vascular network is formed by a single porous 
 tube, branching and anastomosing so as to form 
 irregular, lozenge-shaped meshes, which are 
 filled with a dark-green cellular parenchyma. 
 
LECT. X.] ANATOMY OF LEAVES. 551 
 
 The vessel itself is closely connected with the 
 cellular matter, and when separated (see 2, a 
 highly magnified representation), bears the marks 
 of the cells on its sides. We find nearly the same 
 vascular structure in the Mosses. Thus, if we 
 take a leaf of broad-leaved Bog-Moss, Sphagnum 
 obtusifolium. as a specimen, we find it, when 
 magnified as at 3 (b. shows the natural size of the 
 leaf), consisting of a midrib (a.), on each side of 
 which are many oblong cells, arranged apparently 
 in straight lines : but, under the microscope, these 
 oblong cells are seen to consist of elevated cuticle 
 (as at 4. b. b. b. b. b.) in the meshes of a reticulated 
 vascular system (4. a. a. a. a.) 3 too minute to al- 
 low of the nature of the vessel to be made out by 
 the aid of the highest magnifying powers. It 
 is probably the same as that of the vessels of 
 Marchantia. The leaves of all the Mosses are 
 sessile, although many of them are sheathing; 
 and most of them are furnished with a midrib; 
 but their minuteness prevents any certain informa- 
 tion being obtained as to the manner in which the 
 leaves receive their vessels from the stem, or 
 whether there be a distinct set of returning 
 vessels : they appear to be merely a continuation 
 of the vessels of the cortex of the stem. Sprengel 
 asserts that in the Sphagnum before us, both the 
 cells of the leaf and those on the surface of the 
 
 N N 4 
 
552 CONSERVATIVE ORGANS. [LECT. X. 
 
 stem contain a fine spiral fibre; which, however, 
 I have not been able to discover. 
 
 Proceeding to the next division of plants, those 
 produced from monocotyledonous seeds, we ob- 
 serve the costae or vascular fasciculi distinguishable 
 by the naked eye; of different sizes, and running 
 in gently curved or nearly straight lines, either 
 from the base to the apex, or transversely from the 
 midrib to the margin of the leaf. The former is 
 found chiefly in those leaves which have no de- 
 cided petiole, but spring directly from a bulb or a 
 tuber; the latter in those which are petiolated. 
 We shall examine each kind separately. 
 
 A bulb leaf of the White Lily, Lilium candi- 
 dum, may be taken as an example of the general 
 distribution and character of the vascular system 
 in the first description, the sessile leaves of mono- 
 cotyledonous plants. On examining it, we find that 
 the vascular framework consists of a distinct 
 midrib, which forms the keel of the leaf, and of 
 less elevated ribs (costce), that extend on each 
 side of the midrib in longitudinal lines, which 
 form a gentle curve, following the shape of the 
 leaf. In the smoother and more succulent leaves 
 of this division, however, these costae are scarcely 
 visible externally, or at least appear merely as 
 striae on the surface of the leaf: and this is the 
 case, also, as far as regards many of the smaller 
 vascular fasciculi, even in those leaves, which have 
 
LECT. X.] ANATOMY OF LEAVES. 553 
 
 prominent costse. If we now make transverse and 
 longitudinal sections of the Lily leaf, we perceive 
 that the costae are composed of fasciculi of spiral 
 vessels closely accompanied with corresponding 
 fasciculi of proper vessels, and embedded in cel- 
 lular substance; or, that the leaf has a double 
 system of vessels, one for conducting forwards 
 the sap, and the other for returning the proper 
 juice into which the sap has been changed by the 
 functions of this organ. In the transverse sec- 
 tion, these vascular bundles appear like dots upon 
 the divided surface ; and, when magnified in trans- 
 mitted light, display their twofold nature by dif- 
 ference of transparency; the part of each fasci- 
 culus composed of spiral vessels being particularly 
 distinguished by a greater degree of opacity, owing 
 to the spiral thread which composes the coats 
 of these vessels being firmer and more opaque 
 than the coats of the proper vessels. Thus, in 
 the midrib (5. a.), we perceive that the three spots 
 
554 CONSERVATIVE ORGANS. [LECT. X. 
 
 formed by the vascular fasciculi, which it en- 
 closes, have each one half darker than the other, 
 and the darker half is turned towards the upper 
 disk of the leaf. The same circumstance cha- 
 racterizes the fasciculi enclosed in the costse 
 (5. b. b. b. b.) ; and also those of the intermediate 
 or secondary ribs, which form no prominence on 
 either surface of the leaf. By the aid of more 
 powerful glasses, the distinct character and dis- 
 position of both kinds of vessels are perfectly per- 
 ceptible: and in placing the principal fasciculus 
 of the midrib, detached from the others, under the 
 microscope, this is not only satisfactorily demon- 
 strated, but we become acquainted, also, with the 
 fact, that the spiral vessels (6. a. page 553) of the 
 leaf as well as those of the stem, are found ge- 
 nerally empty, like the arteries of animals; while 
 the proper or returning vessels (6. b.) are always 
 full. I may here remark, that the closer proxi- 
 mity of the spiral vessels to the upper disk of the 
 leaf is common to the majority of leaves ; for, in- 
 dependent of the fact, that the chief function of 
 these organs, namely, the exposure of the sap to the 
 light and air, would lead us, a priori, to conclude 
 that the vessels carrying forwards the sap must, 
 necessarily, be on that side of the leaf most exposed 
 to these agents; the sap- vessels receiving their 
 origin in the stem from the vessels of the albur- 
 num, and the returning vessels terminating in 
 
LECT. X.] ANATOMY OF LEAVES. 555 
 
 those of the bark, the disposition could not well 
 be otherwise, seeing that the relative position of 
 the upper and under disk of every leaf, to the 
 centre of the stem, is exactly that of the albur- 
 num and the bark. In leaves, however, which 
 stand vertically, or have no distinction of sur- 
 faces, the situation of the spiral vessels is either 
 the reverse, or in the centre of the entire vessels : 
 anatomy thus confirming the idea of the close 
 affinity of such leaves to stems. 
 
 I have already stated that the bundles and 
 threads of vessels, in leaves belonging to this di- 
 vision of the class of leaves under consideration, 
 run in longitudinal lines. These are not exactly 
 parallel, but approach both at the base and the 
 apex of the leaf; and, also, communicate la- 
 terally in their course by small threads, given off 
 at irregular intervals. This structure is easily de- 
 monstrated by placing a small slice of the Lily 
 leaf (7, page 553), cut immediately withhi the cu- 
 ticle of the upper disk, under the microscope. 
 We perceive that the longitudinal bundles (a. a.) 
 are united by transverse threads (b. b.) ; and this 
 is the case at irregular intervals throughout the 
 whole extent of the leaf. 
 
 These transverse fasciculi, however, are not 
 threads simply detached from one longitudinal 
 layer, and coming into contact with another, as 
 was supposed by Dr. Grew to be the case in all 
 
556 CONSERVATIVE ORGANS. [LECT. X. 
 
 leaves*; but are distinct vessels, uniting with 
 the longitudinal bundles in a singular manner, as 
 is apparent (8. a. page 553) in a very highly mag- 
 nified view of one of the angles formed by a 
 transverse fasciculus and a longitudinal vascular 
 cord. One of the vessels appears to belong 
 to the longitudinal fascicle ; but the other termi- 
 nates there, and has its extremity applied to the 
 side of one of the vessels forming a part of the 
 longitudinal fascicle. Whether there is any open- 
 ing directly into the longitudinal vessel on which 
 the extremity of the transverse vessel is applied I 
 have not been able to determine. From these 
 demonstrations we may conclude that the vas- 
 cular system of the sessile leaves of monocoty- 
 ledons, consists of fasciculi composed of spiral 
 vessels accompanied with proper vessels which 
 are not spiral, arranged in longitudinal lines, and 
 connected by smaller transverse threads; the 
 whole forming a reticulated texture with irregular 
 rhomboidal meshes. The longitudinal vessels are a 
 continuation of those which are nearest to the 
 surface, in the root caudex, or the stem from 
 which the leaves immediately spring; and thus 
 
 * It is bold to dissent from such authority on the subject of 
 vegetable anatomy ; but the improvement of microscopes since 
 Dr. Grew's time, has enabled many Phytologists of very in- 
 ferior abilities to that great man, to point out some errors into 
 which he had been led by the imperfection of his instruments. 
 
LECT. X.] ANATOMY OP LEAVES. 557 
 
 the greater number of the circles of the distinct 
 fasciculi, which compose the stems of monocoty- 
 ledons, terminate in leaves until the plant attains 
 its ultimate growth. 
 
 In order to examine properly the vascular 
 framework or skeleton of the petiolated leaves of 
 monocotyledonous plants, we must arrange them 
 under two subdivisions. 1. Those in which the 
 ribs run longitudinally, or in a direction from the 
 base to the apex of the leaf: and, 2. those in which 
 they run nearly transversely, or in a direction 
 from the midrib to the margin. 
 
 1. In this subdivision we perceive that, in the 
 Grasses, the vascular fasciculi resemble, very 
 closely, those of the former division: the ribs 
 being in longitudinal, nearly parallel lines, con- 
 verging towards the apex of the leaf; and united 
 at irregular distances by obliquely transverse 
 threads. If we take a stem leaf of Indian Corn, 
 Zea Mays, as a specimen, we perceive the petiole, 
 which is broad, expanded, and sheathing, deriving 
 its origin from the whole circumference of the 
 knot of the articulation which produces it; dilat- 
 ing gradually as it rises upwards, until its edges 
 become a thin fimbriated membrane, and again 
 contracting, but less gradually, at its upper part, 
 or where it is united to the expansion of the leaf. 
 The vascular bundles, which can be readily traced 
 by the naked eye, are composed of the two distinct 
 
558 CONSERVATIVE ORGANS. [LECT. X. 
 
 kinds of vessels described in the former division, 
 which appear as dots in a transverse section of the 
 petiole situated almost close to its external sur- 
 face; or as represented at a. a. a. a. (g.), a highly 
 magnified view of the section. The number of the 
 spiral vessels in each fascicle is generally six, three 
 large and three smaller, symmetrically arranged, as 
 may be seen in a transverse section of one of the 
 fasciculi (10. a.) viewed under the microscope ; and 
 the whole surrounded by a mass of much denser 
 cellular matter than the rest of the substance of 
 the petiole. The returning or proper vessels 
 (10. ft.) are much smaller and more numerous than 
 the spiral; and are congregated into a bundle which 
 occupies a space close to the former, between it 
 and the cuticle, and is bounded by a mass of the 
 same dense cellular matter (10. c.) as that which 
 
LRCT. X.J ANATOMY OF LEAVES. 559 
 
 surrounds the spiral vessels : the object of which 
 is, probably, to give such a degree of firmness to 
 the petiole, as will enable it to sustain, in the erect 
 position, the expansion of the leaf. If we now 
 make a vertical section of the petiole, so as to 
 divide one of the fasciculi longitudinally, in the 
 thickness of the petiole we perceive that the 
 larger vessels are regular spirals (1 1. e.), furnished 
 with diaphragms (h.) at certain distances, the struc- 
 ture of which, however, we shall perhaps never 
 be able to ascertain, owing to the minuteness of 
 the parts ; the diameter of these vessels, although 
 comparatively large, not exceeding ^-^ of an 
 inch. In this section, also, we perceive that the 
 proper vessels (l 1 .f.) are membranous and porous: 
 and that the cells in immediate contact with both 
 sets of vessels are oblong ( u . d.) ; whereas those 
 (g.) which are between the proper vessels and the 
 cuticle of the outer surface of the leaf, and which 
 form the elevated portion of the costa, although 
 they are not oblong, yet, differ both in size and 
 in regularity of structure from those (n. c.) that 
 form the inner substance of the petiole. Close to 
 the cuticle of the upper disk ( 1 1 . a.) is a mass of 
 oblong cells (b.) resembling those in contact with 
 the vessels. 
 
 Ascending to the expansion of the leaf, which 
 is separated from the petiole by a semitranspa- 
 rent white, condensed, membranous space (see cut 
 
560 
 
 CONSERVATIVE ORGANS. 
 
 [LECT. x. 
 
 12. c.), from which the expansion of the leaf 
 spreads out like a shoulder on each side ; we per- 
 ceive that the midrib (12. b.), which is not distin- 
 guishable in the lower part of the petiole (12. a.), 
 becomes very conspicuous on the under disk at this 
 point; forming almost a knob, which passes into 
 a striated ridge, and extends, gradually dimi- 
 nishing in size, to the apex of the leaf. From 
 ten to twelve parallel costae are visible on each 
 
 side of the midrib, 
 22 t> .Jill JL:9L which when magni- 
 fied appear like white 
 parallel lines (13. a. 
 a. a.) , running through 
 the green smooth sub- 
 stance of the expan- 
 sion, and taking the 
 curve of its shoulders 
 as if originating in the 
 white semitransparent 
 space (12. c. c.) al- 
 ready described. But 
 between these costse 
 there are several smaller vascular cords, which are 
 scarcely visible on the surface, neither producing 
 elevation nor difference of colour ; and which can 
 be demonstrated only on the dissection of the leaf. 
 One of the more obvious distinctions, therefore, 
 in the structure of the petiole and the expansion 
 
 2 
 
LECT. X.] ANATOMY OF LEAVES. 561 
 
 in the leaves of the gramineous tribe of plants is, 
 that, in the petiole, the vessels run in distinct fas- 
 ciculi, which are all nearly equal in point of 
 size (14.) ; whereas in the expansion the fasciculi 
 differ considerably in size ( 13.), the larger only 
 being very visible on the surface. In both, there 
 are transverse threads which connect the longitu- 
 dinal bundles, and these are conspicuous even to 
 the naked eye in the more succulent leaves, par- 
 ticularly in those which involve the fructification 
 of the Mays (15.), when viewed by transmitted 
 light. 
 
 In examining a transverse section of a portion 
 of the expansion, of the leaf of Indian Corn, con- 
 taining one of the visible costae and the interval 
 between it and the next costa; we immediately 
 perceive the difference of structure in the two kinds 
 of fasciculi. The visible costa consists of two 
 large spiral vessels on the same line, and a com- 
 pact fasciculus of proper vessels on each side of 
 the line of spirals, towards both surfaces of the 
 leaf (c. c. fig. 13, Plate 10); while, in the interval, 
 each fasciculus is composed of one small spiral ves- 
 sel only, surrounded with a circle of proper ves- 
 sels, and placed in the heart of the substance 
 of the leaf (d. d. d. fig. 13, Plate 10). But, be- 
 sides these, there is another kind of fasciculi, 
 two of which are generally observed in each space 
 between the visible costse, connected with a pe- 
 
 VOL. I. 00 
 
562 CONSERVATIVE ORGANS. [LECT. X. 
 
 culiar cellular apparatus to be afterwards de- 
 scribed. These appear to be modifications of the 
 two vascular fasciculi already noticed ; having the 
 same structure as the obscure or invisible fascicu- 
 lus, and the accompanying compact bundle of pro- 
 per vessels of the visible costa (see e. e. fig. 13, 
 Plate 10). In a section obtained by slicing the 
 leaf, we find all these fasciculi united by trans- 
 verse threads, forming rhomboidal meshes, si- 
 milar to those which have been already described. 
 
 But although the arrangement of the vascular 
 system of the leaf of Indian Corn, just described, 
 may be taken as a specimen of that peculiar to the 
 leaves of all the Grasses; and to those leaves of 
 monocotyledonous plants which are petiolated, and 
 furnished with longitudinal costse, yet, there must 
 necessarily be many modifications of this arrange- 
 ment. I shall, however, particularly notice one 
 only, that which characterizes very thick and 
 fleshy leaves; such, for instance, as those of the 
 Aloe tribe. 
 
 On the exterior surface of the leaf of the Aloe, 
 and other leaves of a similar character, we per- 
 ceive no appearance of a vascular system ; but on 
 attempting to tear the leaf across, considerable 
 resistance is opposed to the effort, by a number of 
 tough, longitudinal fibres. These constitute the 
 vascular fasciculi ; and in a transverse section of 
 the leaf, we find that they run through its sub- 
 
LECT. X.] ANATOMY OF LEAVES. 563 
 
 stance, nearly in the same manner as the fasciculi 
 in solid monocotyledonous stems. Viewing the sec- 
 tion (16.) through a magnifying lens, we perceive 
 that the fascicles are of different sizes, the largest 
 being in the centre: and, in a portion of it (17.) 
 placed under the microscope, we perceive that the 
 central fasciculi (a.) differ from the others (&.), 
 in their structure as well as size, being composed 
 of a dense cord of spiral vessels, accompanied by a 
 very large bundle of proper vessels, which is sepa- 
 rated from it by a thin layer of cellular substance ; 
 
 whereas the smaller or marginal fascicles appear 
 to be entirely composed of proper vessels. This 
 structure of the central bundles is still more deci- 
 dedly observed, in a very thin longitudinal slice, 
 
 o o 2 
 
564 CONSERVATIVE ORGANS. [LECT. X. 
 
 (18.) cut in the thickness of the leaf, and viewed 
 in the microscope by transmitted light. The cord 
 of spiral vessels (a.) is a few proper vessels sur- 
 rounded by , and a layer of cellular matter in- 
 terposed between it and the large fascicle (c.) 
 of proper vessels. In splitting the leaf, we per- 
 ceive that these vascular fasciculi run in parallel 
 lines (19.), and take the same curves as the mar- 
 gin ; but do not enter into the spines (a. a.), which 
 are of a hard ligneous consistence, and supplied 
 by small threads of vessels given off from the 
 fasciculi nearest to them. The vascular cords do not 
 anastomose in any part of the leaf; and very few 
 transverse threads are perceptible, compared with 
 those which occur in the membranous leaves of this 
 natural order. But besides the vascular fasciculi 
 we find, in this leaf, and other monocotyledonous 
 fleshy leaves, a system of tubular cells, which might 
 be mistaken for vessels, situated immediately un- 
 der the cuticle (17. d.) 9 from which they extend in 
 straight contiguous lines to the cellular parenchy- 
 ma, the chief substance of the leaf. These resemble 
 beaded or moniliform vessels (les vaisseaux en 
 chapelet of Mirbel), and appear to be composed of 
 transparent membranous oblong vesicles, united 
 at their extremities; and are either perforated, 
 or contain small granules sparsely spread over 
 their inner surface ( 1 9. a.). It is probable that 
 these cells are part of the absorbing system by 
 which fleshy plants, such as the Aloe, which grow 
 
LECT. X.] ANATOMY OF LEAVES. 565 
 
 in sandy, arid soils, chiefly derive their nou- 
 rishment : for, as very little moisture is taken up 
 by the roots, these plants are supported, almost 
 entirely, by cuticular absorption. The natural func- 
 tions of these tubular cells, also, being to absorb 
 and to carry fluids towards the centre of the leaf, 
 enable us to understand why the leaves of an 
 Aloe, when separated from the stem, are very 
 long in drying and losing their plumpness ; where- 
 as, if thrown into water, when they are very 
 much shrivelled, they almost immediately regain 
 their original size. The absorbing mouths by 
 which they are supplied will be demonstrated, 
 when we examine the cuticular system of leaves. 
 
 In the leaves of those monocotyledonous plants 
 the costae of which, instead of being longitudinal, 
 run in transverse parallel lines, forming acute an- 
 gles with the midrib, we find that the arrangement 
 of the vascular framework resembles that of the 
 Grasses in some circumstances ; but differs from it 
 in other respects. Thus the costae are parallel to 
 one another, and communicate by small transverse 
 cords of vessels, so as to form meshes which are 
 rhomboidal or square according to the angles at 
 which these transverse cords are given off from the 
 costae, as in the Grasses. The petioles are., also, in 
 general sheathing, and many of them are furnished 
 with ligulse. But, in almost all of them, the peculiar 
 cartilaginous articulation, which divides the petiole 
 
 oo3 
 
566 CONSERVATIVE ORGANS. [LECT. X. 
 
 from the expansion in the Grasses, is not present ; 
 and the petiole assumes a stalk-like aspect before 
 it reaches the expansion. 
 
 Taking this leaf of Canna Indica (21.), as a 
 
 specimen of the vascular system in this description 
 of leaves, we perceive, looking at the under disk, 
 that the midrib is much elevated near the base, 
 and gradually diminishes in size, until it appears 
 little more than a mere line at the apex of the 
 leaf. The more elevated costse (a. a. a. a. a.) are 
 the primary vascular fasciculi ; and between these 
 are secondary fasciculi, which are less elevated. 
 To the unassisted eye they all appear to go off from 
 the midrib ; but viewed by a magnifying lens, and 
 with transmitted light, we perceive that all of 
 them do not proceed directly from the fasciculi of 
 the midrib (22. b. b. see page 567), but that some 
 of them (22. a. a.) are branches of the others*. At 
 
 * In figure 22, the cuticle, except at the space c. d. is taken 
 off, and the midrib pared down, to show the transverse vascular 
 threads, which unite the parallel fascicles ; and which are ren- 
 dered very conspicuous when viewed by transmitted light, 
 
ANATOMY OP LEAVES. 
 
 567 
 
 LECT. X.] 
 
 the margin they all inosculate, and form, as it 
 were, one fasciculus which, extending from the base 
 to the apex, is the real living boundary of the leaf. 
 Pursuing our examination more closely ; and 
 placing a slice (23.) of the petiole cut transversely 
 near the base of the expansion, under the micro- 
 scope with a glass of a moderate power, we per- 
 ceive that the vessels are arranged in distinct fas- 
 ciculi, which are nearly of the same size in the cen- 
 tre of the section ; alternately larger and smaller 
 (23. a. b. a. b.) near the circumference on the con- 
 vex surface, or that part of the petiole which is 
 towards the under disk of the leaf; and all small 
 
 
 (c. c. c. c. c. c.) on the concave surface. The costae 
 (22. e. e. e.) are continuations of those on the con- 
 owing to the dark green colour of the parenchyma in the meshes 
 formed by these threads. 
 
 * o o 4 
 
568 CONSERVATIVE ORGANS. [LECT. X. 
 
 cave surface of the midrib, which are curved out- 
 wards in opposite pairs, at different distances be- 
 tween the basis and the apex of the leaf; but the 
 central fasciculi pass on its apex. These vascular 
 fasciculi are embedded in a cellular tissue; besides 
 which the petiole and midrib of this description of 
 leaves contain peculiar pneumatic or air cells (23. 
 d.d. d.) closely resembling those which I shall after- 
 wards demonstrate to you, constitute a great part 
 of the substance of aquatic plants. In a transverse 
 section of a small part of the expansion of the leaf 
 (24. see page 567), we perceive that the vascular 
 cords (a. a. a) run nearly in the centre between 
 the two plates of cuticle, embedded in an opaque 
 green parenchyma; and that, instead of the 
 pneumatic apparatus of the petiole and midrib, 
 there is a transparent layer of large cells (24. b.) 
 immediately under the cuticle of the upper disk. 
 I should, however, inform you that these pneumatic 
 cells are not present in the petiole and midrib of 
 all leaves with transverse costse, belonging to mo- 
 nocotyledonous plants; but the same general ar- 
 rangement of the vascular cords, and, conse- 
 quently, the same structure of the framework, 
 are seen in all of them. 
 
 With regard to the composition of the fasci- 
 culi; these, as in the other leaves we have ex- 
 amined, consist of spiral and proper vessels; dif- 
 fering, however, in the relative position of the 
 spiral vessels, which in each fasciculus, in these 
 
LECT. X.] ANATOMY OF LEAVES. 569 
 
 leaves, are placed between two bundles of proper 
 vessels. If we cut a superficial slice from the under 
 disk of the leaf, where any of the fasciculi ra- 
 mify (25. see page 567); and examine it by a 
 powerful microscope, we may rationally conclude 
 from what we perceive, that, although some of 
 the costse are merely continuations of the vas- 
 cular fasciculi of the midrib, separated like threads 
 from a skein of silk, yet that others which also 
 branch from these, and the smaller transverse 
 vascular threads, are actually united by that 
 kind of connexion which, in the vessels of animals, 
 is termed anastomosis. Thus, in the slice under 
 examination, we find that both the fasciculi (a. a.) 
 contain the same number of vessels, which would 
 not be the case, were the one parcel separated from 
 the other ; and although the transverse thread (b.) 
 contains one spiral vessel only, yet this vessel does 
 not appear to be split from the larger fasciculus ; 
 but to be simply united to it, the end of b. being 
 evidently applied to the side of a. if it do not ac- 
 tually open into the cavity of that vessel. 
 
 Examining, by the same power of the micro- 
 scope, a transverse section of one of the larger 
 fasciculi of the midrib of the leaf of Canna In- 
 dica, we find it to consist of one large, and 
 from three to six smaller spiral vessels, arranged 
 and relatively connected with the proper vessels 
 in a manner closely resembling the arrangement of 
 those in the fasciculi which are found in the 
 
570 CONSERVATIVE ORGANS. [LECT. X. 
 
 stems of White Bryony (see fig. 4, A. Plate 8). 
 The arrangement of the vessels, however, in the 
 fasciculi of the expansion differ, in some de- 
 gree, from those of the midrib. Placing a trans- 
 verse section (26.) of one of these fasciculi under 
 the microscope, we find that it is composed of 
 two large tangent spiral vessels (a.) surrounded by 
 firm cellular matter ; and of two small isolated 
 vessels (b.), which are spirals also, situated nearer 
 to the upper disk of the leaf; the one before the 
 other, and, in like manner, surrounded by firm cel- 
 
 lular substance. The proper vessels are collected 
 into two distinct fasciculi ; the largest of which 
 (d.) is on the under disk or back of the leaf, 
 and covered by the cuticle only, while the 
 smallest (c.), which is towards the upper disk, 
 is covered by one layer of cellular substance. 
 In the longitudinal section (27.) made through 
 the centre of the fasciculus, in the thickness of 
 
LECT. X.] ANATOMY OP LEAVES. 571 
 
 the leaf, e. being the upper and f. the under 
 disk, the relative situation of the vessels is still 
 more clearly demonstrated. 
 
 We may pause here a few moments to re- 
 mark, that the colour of the juice in the cells of 
 the leaf, is more intense towards the surfaces, 
 while in the centre it is scarcely deeper than that 
 which is contained in the cells of the cutis (e.f.). 
 Is not this probably owing to the sap which is 
 current in the spiral vessels, and which is co- 
 lourless, being given out laterally, and diffusing 
 itself through the cells, in which the change 
 effected by the air and light, that causes the co- 
 lour is produced ? The manner in which the co- 
 lour is diluted as it approaches the limits of 
 the spiral vessels, would authorize such a suppo- 
 sition ; but, wherefore it may be demanded, are 
 the cells immediately under the cutis free from 
 colour ? It is probable, we may reply, that these 
 cells are filled by pure water only, absorbed from 
 the atmosphere; and, consequently, their con- 
 tents are unfitted to undergo those chymical 
 changes to which the sap is subjected in the leaf. 
 But this discussion is premature. 
 
 From this demonstration of the vascular sys- 
 tem in the leaves of monocotyledonous plants, 
 it is evident that a general character, however 
 variously modified in many instances, pervades 
 the whole. The fasciculi of vessels are distinct; 
 they run in directions parallel to one another; 
 
572 CONSERVATIVE ORGANS. [LECT. X. 
 
 and the principal bundles are united by smaller 
 transverse cords or fasciculi; which form meshes 
 of a rhomboidal figure, all nearly of the same 
 size in the same leaf. 
 
 Passing on to the leaves of Dicotyledons, we 
 find the reticulated structure of the vascular 
 framework more complex and varied, than we 
 have found it in the leaves of the two natural di- 
 visions^ which we have already examined. This is 
 made evident to the unassisted eye by holding up 
 between it and the light any newly expanded leaf ; 
 but it is more beautifully demonstrated in the ske- 
 leton of a full-grown leaf, carefully prepared. In 
 a leaf of the Indian Fig, Ficus religiosus, thus pre- 
 pared (fig. 2, Plate 10), we perceive seven princi- 
 pal costae, springing from each side of the midrib 
 (a.), and extending to the margin of the leaf, where 
 they bend towards its apex, and are enarched or 
 inosculate with one another (b. b. b. b.). From each 
 side of these costae, a series of secondary fasciculi 
 spring, which, inosculating, also, with their oppo- 
 nents, form a secondary set of arches (c. c. c. c.) be- 
 tween each pair of the principal costae ; and inclose 
 a tissue of minute and exquisitely beautiful reticu- 
 lations, the result of the numerous ramifications of 
 the vascular threads, as they divide and subdivide 
 as it were out of a greater into a less. But besides 
 this distribution of these vascular fasciculi, we 
 observe a fascicle (d. d.), proceeding from each 
 
LECT. X.] ANATOMY OF LEAVfiS. 573 
 
 side of the midrib, at the very base of the ex- 
 pansion, and bounding the margin of the leaf. 
 This receives supplies from the arches of the costse, 
 as it passes onwards, until it unites with its fel- 
 low at the apex of the leaf. Such is the general 
 distribution of the vascular fasciculi in the leaves 
 of dicotyledonous plants. It would be incon- 
 sistent with any elementary plan of instruction, to 
 enter largely upon the consideration of the various 
 circumstances which modify the distribution of 
 these fasciculi ; and, therefore, I shall examine the 
 modifications depending upon two states only of 
 dicotyledonous leaves : 1. When the leaf or its ex- 
 pansion is thin or membranaceous ; and, 2. when it 
 is thick QY fleshy. 
 
 1. The general distribution of the vascular 
 fasciculi, in thin leaves of dicotyledonous plants, 
 in the majority of instances, resembles that which 
 we find in the skeleton of the leaf of the Indian Fig 
 tree. The vessels of the costse proceed from the 
 principal fasciculus of the midrib, and run between 
 the laminse of cuticle, embedded in the cellular mat- 
 ter, in cords which form visible elevations on the 
 back of the leaf, and corresponding furrows on its 
 face. Each fascicle consists of spiral and proper 
 vessels throughout all its ramifications; and, in 
 whatever manner these vessels are arranged in the 
 fasciculi, the spiral and proper vessels are always 
 associated and, in general, tangent. This arrange- 
 ment is common both to sessile and to petiolated, to 
 
574 CONSERVATIVE ORGANS. [LECT. X. 
 
 simple and to compound leaves, as far, at least, as 
 respects the expansion. In sessile leaves, how- 
 ever, all the fasciculi do not proceed from the 
 midrib, but some are given off directly from the 
 stem or the branch, and enter the expansion of the 
 leaf at its base, on each side of the midrib. In 
 petiolated leaves, also, the petiole is generally 
 dilated at its point of union with the branch, and 
 at this point the vessels enter the petiole in distinct 
 bundles ; the remains of which are visible in the 
 eschar produced by the falling of the leaves in 
 autumn. 
 
 Thus in the Apple, the Pear, the Peach, and 
 many other trees, the leaf is attached to the 
 wood by three fasciculi, one of which enters the 
 middle of the petiole, and the others on each side 
 of it. In the Lilac, the attachment is also by 
 three distinct fasciculi ; but there is besides a line 
 of coalesced fasciculi which forms a kind of open 
 crescent; and in the Laurustine the whole of the 
 vessels pass from the wood into the petiole in one 
 fascicle, the transverse section of which is nearly 
 a complete semicircle. In compound leaves, the 
 number of fasciculi passing into the petiole from 
 the wood, is in some instances regulated by the 
 number of the leaflets; in the Elder, we find 
 generally five ; and in the Horse Chesnut, from 
 five to seven or eight. It is, however, the inner 
 part only of these fasciculi, or that which con- 
 
 2 
 
LECT. X.] ANATOMY OF LEAVES. 575 
 
 veys the sap to the leaf, that is given off from the 
 wood, or rather from the medullary sheath ; for 
 the outer part, which consists of the proper or re- 
 turning vessels, enters the bark, but not the 
 wood. This fact is beautifully illustrated by 
 placing young leafy twigs in coloured fluids. The 
 colour is seen passing tip from the stem into the 
 leaf through the upper portion of each fascicle; 
 while that part which consists of the returning 
 vessels remains perfectly free from colour. 
 
 Such is the general arrangement of the vascu- 
 lar framework in the thin leaves of dicotyledonous 
 plants ; to examine the intimate structure of the 
 fasciculi, we must have recourse to the same me- 
 thod that we adopted in our examination of them 
 in the leaves of the two natural divisions we have 
 already investigated. Taking the leaf of the 
 Lilac, Syringa vulgaris, as an example of the 
 simple petiolated leaf; and placing a thin transverse 
 slice of the petiole under the microscope, we find 
 that the vessels are arranged in the following man- 
 ner. Close to the upper or channelled surface of 
 the petiole, we find three small distinct fasciculi 
 of spiral vessels (c. c. c. fig. 10, Plate 8), one im- 
 mediately within the cutis, in the hollow of the 
 channel, and one at each side ; but the principal 
 vessels constitute one large compound fasciculus, 
 in the centre of the petiole, which appears of a 
 horseshoe shape, in the transverse section ; and 
 
576 CONSERVATIVE ORGANS. [LECT. X. 
 
 consists of one fasciculus of spiral vessels, and 
 two fasciculi of proper vessels. The spiral vessels, 
 which form the central fasciculus (d.), are arranged 
 in rays, which are sometimes tangent, at other 
 times separate ; whereas the proper vessels con- 
 stituting the two fasciculi (e. e.), one of which is 
 situated within, and the other without the fasci- 
 culus of spirals, are irregularly embedded in a 
 pulpy parenchyma, and are readily distinguished 
 by their greater transparency. The bark, or true 
 cutis (a.) of the petiole, seems, also, to consist 
 chiefly of several series of the same kind of proper 
 or returning vessels. In the various modifications 
 of this structure of the vascular system, in the 
 petioles of dicotyledonous leaves, the radiated ar- 
 rangement of the spiral vessels is found in all: 
 the petiole in this respect, as well as in the other 
 parts of its structure, closely resembling the 
 stem or the branch from which it springs. In 
 simple leaves, with a few exceptions, although 
 the vascular part forms at first several fasciculi, at 
 the base of the petiole, yet these soon coalesce into 
 one compound fasciculus ; but in compound leaves 
 they remain distinct. 
 
 If we take a leaf of the Elder, Sambucus 
 nigra, and place a transverse section of the com- 
 mon petiole under the microscope, we perceive 
 ten distinct fasciculi of vessels. Five of these 
 (b. b. b. b. b. fig. 11, Plate 8) are compound fas- 
 
LECT. X.] ANATOMY OF LEAVES. 577 
 
 cieles, embedded in the cellular substance of the 
 petiole; and five (a. a. a. a. a.) fasciculi of proper 
 vessels occupying the angles of the footstalk, and 
 situated in the bark, or at least exterior to the 
 former and immediately within the cuticle. The 
 compound fasciculi consist, each, of a band of 
 spiral vessels, arranged in rays, and two fasciculi 
 of proper vessels ; one interior, and the other ex- 
 terior to the band of spirals, but both tangent 
 upon it. One of these compound fascicles passes 
 into each leaflet ; and consequently their num- 
 ber, in the common petiole of compound leaves, 
 generally corresponds to that of the leaflets. In 
 compound leaves, however, which have moveable 
 articulations, we perceive that all the separate fas- 
 ciculi are collected into one fasciculus in the arti- 
 culations. Thus, in the common Kidney-bean, Pha- 
 seolus vulgaris, the petiole of which is channelled, 
 with an articulation at the base of the common pe- 
 tiole and, also, at that of each partial petiole, we 
 find that the vascular fasciculi (a.a.b. b. fig. 8, Plate 
 10) are distinct, and form a circle situated immedi- 
 ately under the bark in the channelled parts of the 
 petiole ; with a considerable portion of lax cellular 
 substance or medulla (c.), enclosed within the circle 
 which they form : whereas, in the articulated parts, 
 there is one central fasciculus only (a. fig. 7, Plate 
 10), surrounded by a large mass (b.) of very firm 
 cellular matter. The advantage of this change of 
 VOL. u p P 
 
578 CONSERVATIVE ORGANS. [LECT. X. 
 
 disposition of the vascular bundles, in the articu- 
 lations, is very obvious: for, had the fascicles 
 remained distinct, and surrounding the pith, in 
 the articulations, those on the outside of the 
 flexure, in every considerable motion of the joint, 
 must have described so large a circle, as would 
 have endangered the organization of the vessels by 
 the extension; while those on the inner side 
 would have suffered, equally, by the compression 
 to which they must necessarily have been subjected. 
 But> by the whole of the vessels being situated in 
 the centre of the petiole, the extension and com- 
 pression produced by the flexure, on every part of 
 the fascicle, is not more than can be borne by any 
 individual vessel, whether spiral or entire ; and, 
 thence, the freest and most varied motion of the 
 joint can be exercised with impunity. The neces- 
 sity of such a modification of structure, in the 
 petioles of compound leaves, susceptible of mo- 
 tion, may indeed be inferred from the fact, that 
 articulations are present in all those which per- 
 form certain movements; as, for example, those 
 which fold together their leaflets at night ; those 
 which are endowed with the power of spon- 
 taneously moving their leaflets, as Hedysarum 
 gyrans; and those which fold their leaflets together 
 when touched, as Mimosa sensitiva and pudica. 
 
 Some simple leaves, those for instance of 
 the Holly Hock, of the Geranium tribe, &c. 
 which have several principal costse diverging from 
 
LKCT. X.] ANATOMY OF LEAVKS. 579 
 
 the summit of the petiole, and in this respect 
 have an affinity to digitate leaves, present 
 nearly the same vascular structure of the petiole 
 as the compound leaves. The fasciculi are dis- 
 tinct ; and correspond in number to the princi- 
 pal costse of the leaf; each of which may be thus 
 regarded as a kind of midrib, and the leaf as com- 
 posed of a number of conjoined leaflets: so that 
 these leaves, although they are necessarily classed 
 as simple leaves from their external appearance, 
 yet, bear in anatomical structure the same affinity 
 to digitate compound leaves, which the webbed 
 foot of a bird bears to one which is not webbed. 
 A similar structure, also, is found in the petioles 
 of those leaves which are longitudinally ribbed, or 
 nerved as the common expression is, from the 
 base of the expansion, as for instance those of the 
 genus Melastoma; but, when the ribs do not origin- 
 ate from the base, although they are very conspicu- 
 ous, as, for example, in the leaf of the Cinnamon 
 tree, the structure of the vascular system of the 
 petiole is exactly the same as in simple dicotyledo- 
 nous leaves, which are not longitudinally ribbed. 
 
 If, instead of a transverse section, we place a 
 longitudinal section of any of these leaves under 
 the microscope, we perceive that each fasciculus is 
 composed of spiral and proper vessels, the same as 
 we have already seen constitute the ribs in the 
 leaves of monocotyledons. 
 
 pp2 
 
580 CONSERVATIVE ORGANS. [LECT. X. 
 
 Tracing the vascular fasciculi from the petiole 
 into the expansion, in the thin, simple leaves of 
 dicotyledons, we find their divisions, subdivisions, 
 and ultimate ramifications much more diversified 
 and minute than in the leaves of monocotyledons. 
 Whatever may be the origin of these divisions 
 and subdivisions, whether they proceed from one 
 central fasciculus, or from several longitudinal 
 costae, the ramifications become smaller and 
 smaller, owing to a diminution of the number 
 of the vessels which they contain ; but not owing 
 to any diminution of the diameter of the vessels 
 themselves: for, although a principal fasciculus 
 may contain larger and smaller spiral vessels, 
 yet the general comparative magnitude of the 
 vessels, in the smallest fasciculus, is the same as 
 in the largest. This question, therefore, again 
 presents itself: Do the vessels of the leaf inoscu- 
 late and anastomose, or are the smaller fasciculi 
 merely separations from the larger? 
 
 Dr. Grew, as I have already stated, denied 
 that they ever inosculate or anastomose until they 
 arrive at their final distribution. In appealing to 
 nature for a solution of this disputed point, we find 
 Grew's opinion so far correct, that the vascular 
 fasciculi of the costse, which are given off from the 
 midrib, are separations from the petiolar fasciculi 
 in their progress towards the apex of the leaf; and 
 that the fasciculi forming some of the secondary 
 
LECT. X.] ANATOMY OF LEAVES. 581 
 
 costae, also, are separated in a similar manner. 
 But in the smaller ramifications, we perceive that 
 many of the fasciculi are connected with each 
 other at nearly right angles; and in these in- 
 stances the vessels are not separations from the 
 larger fasciculi, but are distinct and merely applied 
 in a peculiar manner to the sides of those from 
 which they seem to arise ; as can be readily demon- 
 strated by dissection, with the aid of the micro- 
 scope. In this minute portion of a leaf of the Lilac, 
 sliced from between the cuticles, and examined, 
 by transmitted light, under a very high magni- 
 fying power, we observe that, in the smaller fasci- 
 culus (g. 28.), which is composed of seven spiral 
 
 vessels, and united nearly at a right angle with 
 the larger fasciculus (h.), three of the vessels 
 (a.) form a curve upwards, and three (b.) a 
 curve downwards, before they unite with the 
 
 p P 3 
 
582 CONSERVATIVE ORGANS. [LECT. X. 
 
 larger fasciculus ; while the central vessel (c.) 
 seems to terminate in a straight line on the side 
 of the vessel 3, which is one of those composing 
 the larger fasciculus. In this case it is evident that 
 the smaller fasciculus is not a separation from the 
 larger ; but is joined to it by a species of anasto- 
 mosis ; which; in the central vessel, is effected in 
 a direct manner by the application of its extremity 
 to the side of the vessel on which it terminates; 
 and, in the other six vessels, in a less direct man- 
 ner by the lateral application of a portion near the 
 extremity of each vessel, before it curves outwards 
 to the particular vessel on which it terminates. In 
 other leaves, as in those of the garde'n Lettuce for 
 instance, in which single vessels are often united to 
 large fasciculi (a. b. c. 29. page 581) and to other 
 single vessels (a. b. c. 30. page 581), the nature of 
 the first species of anastomosis, just described, is 
 still more perceptible. One of these examples 
 (28.) demonstrates, also, that the proper or re- 
 turning vessels (d. e.f.f.) unite in the same man- 
 ner as the spiral. 
 
 Whether the communication of the cavities of 
 these united vessels be direct, as in the vessels of 
 animals, so as to allow the fluids they convey to 
 flow in a uninterrupted stream from the one to 
 the other, I have not been able to determine. It 
 is, however, evident that in the leaves of dicotyle- 
 dons, as in those of monocotyledons, all the vascu- 
 
LECT. X;] ANATOMY OF LEAVES. 583 
 
 lar ramifications of the foliar expansion are not pro- 
 longations of the vessels forming the petiolar fas- 
 ciculi ; but that many of them are distinct vessels 
 anastomosing with others, although in a different 
 manner from this kind of union as it occurs in ves- 
 sels in animal bodies. It is probable that the in- 
 osculation which occurs in the proper or return- 
 ing vessels, more nearly resembles that which we 
 find in vessels of animals ; for, as the proper ves- 
 sels are simple membranous tubes, any commu- 
 nication between them must be by direct openings, 
 such as are found to exist in the vessels of Mar- 
 chantia (see page 550). 
 
 2. The thick and fleshy leaves of dicotyle- 
 donous plants are seldom petiolated ; but when 
 they are so, the arrangement of the vascular 
 fasciculi, both in the petiole and in the expansion, 
 closely resembles that of the thin membranaceous 
 leaves. The sessile leaves of this division are ge- 
 nerally thicker and more succulent than the pe- 
 tiolated. If we take the genus Mesembryan- 
 themum, as affording specimens illustrative of the 
 character of these sessile leaves, we find that the 
 vessels pass from the stem into the leaf in one or 
 more fasciculi, according to the figures of the 
 leaves. Thus in the Hatchet-leaved Mesembryan- 
 themum (M. Dolabriforme) , the leaves of which 
 are connate, the sap- vessels enter the leaf in one 
 bundle, which extends in the direction of its 
 
 p p 4 
 
584 CONSERVATIVE ORGANS. . [LECT. X. 
 
 axis, the whole length of the leaf, giving off in its 
 course a few thread-like branches only at consi- 
 derable intervals; and as this vascular fasciculus 
 and its ramifications are situated in what may be 
 termed the pith of the leaf, and are, consequently, 
 imperceptible on its surface; this description of 
 leaves appears to the unassisted eye destitute of 
 vessels. These organs are, indeed, comparatively 
 few in succulent leaves ; and are less necessary 
 than in membranaceous leaves ; for, as succulent 
 leaves either exhale very little moisture, or absorb 
 a considerable quantity from the atmosphere by 
 their surfaces, the nutriment of the plant, in the 
 first case, is sufficient although the fluids taken up 
 by the roots be comparatively scanty ; and, in the 
 second, it is supplied, independent of that which 
 may be furnished by the roots, by cutaneous ab- 
 sorption. In the leaves of the broad-leaved species 
 of Mesembryanthemum, and in similar succulent 
 leaves, the vessels enter the leaf in several distinct 
 fasciculi; which diverging, pass on in nearly 
 straight lines, giving off a few bundles only in their 
 course ; but as they approach the apex of the leaf, 
 whatever its form may be, they divide, subdi- 
 vide, and inosculate as in thin leaves ; and the 
 proper or returning vessels accompany and sur- 
 round the spirals in all their divisions. In the suc- 
 culent leaves of dicotyledonous plants, also, we 
 find the same system of tubular cells, between the 
 
LECT. X.] ANATOMY OP LEAVES. 585 
 
 pulp and the cuticle, which we described in the 
 Aloe (page 564) ; and in the leaf of the Mesem- 
 bryanthemum, under examination, we perceive 
 these tubes commencing immediately under the 
 cutis, and terminating generally in the cells of 
 the central pulp ; but sometimes in follicles, which 
 are both very irregular in form, and of very dif- 
 ferent dimensions. It is probable that part of the 
 fluid taken up from the atmosphere passes at once 
 into the central cells, the contents of which are 
 colourless, while another part remains in the tu- 
 bular cells, and undergoes that change, which is 
 the usual result of the agency of light on the 
 juices of all leaves exposed to its influence. The 
 green colour of the fluids contained in these cells, 
 marks out their limits, in a transverse section of 
 the leaf, even to the naked eye. 
 
 The structure of the vessels in succulent dico- 
 tyledonous leaves is the same as in all other leaves. 
 The conducting vessels are spiral tubes, of the 
 same diameter at the apex as at the base of the 
 leaf; and the proper or returning vessels are mem- 
 branous, and apparently perforated, although their 
 transparency renders it difficult to determine their 
 real character. The ramifications are all given off 
 at acute angles ; and appear to be merely separa- 
 tions from the caulinar or petiolar cluster, as Dr. 
 Grew supposed was the case in all leaves ; at least 
 
586 CONSERVATIVE ORGANS. [LECT. X. 
 
 they do not anastomose until, as I have already 
 stated, they approach the apex of the leaf. 
 
 In this view of the arrangement and struc- 
 ture of the vascular system of the leaf, I have 
 not noticed those cutaneous vessels which Hed- 
 wig has described as lymphatics; but the exist- 
 ence of which has been denied by Mirbel and 
 others. If we admit their existence, these ves- 
 sels must undoubtedly be regarded as forming 
 a part of the vascular system of the leaf, and 
 ought now to be described; but as this involves 
 a knowledge of the entire cuticular system, the 
 consideration of this point must be deferred until 
 we examine that system. 
 
 II. Cellular system of the leaf. On cutting a 
 thick, succulent leaf transversely, we immediately 
 perceive that it consists chiefly of a pulp ; which, 
 when placed under the microscope, or examined 
 by a good magnifying glass, is evidently com- 
 posed of cellular tissue. Extending our inquiries, 
 we find that this substance forms a large part of 
 the structure of leaves; filling up the meshes of the 
 network formed by the vessels in the thin and very 
 vascular leaves ; and, in all, occupying that space 
 which separates the two cuticular layers, which 
 constitute the upper and the under disks of the 
 leaf. 
 
 The cellular substance of leaves differs very 
 
LECT. X.] ANATOMY OF LEAVES. 587 
 
 considerably in density ; but this diversity depends 
 more on the quantity and quality of the juices the 
 cells contain, than on any diversity of structure 
 in the cells. To the same causes, also, may be 
 attributed, in a great degree, the variety of figure 
 which these cells exhibit: for, although they are 
 in some instances globular, or nearly so; and in 
 others triangular ; or more or less regularly hex- 
 agonal ; yet, it is probable, that the majority are 
 originally spheroidal vesicles; and that the va- 
 riations frqm this figure depend on the turgescence 
 of the vesicles, and the consequent compression 
 which must necessarily result from their conti- 
 guity. The hexagonal figure being that which 
 spheroidal vesicles, mutually comprising one an- 
 other, are naturally disposed to assume, we find 
 that a more or less regular hexagon is the most 
 common form of these cells; and this figure is 
 generally more regular in the cells forming the 
 centre of the substance of the leaf, owing to these 
 being there more distended with fluid, than in 
 those towards either of the cuticles. 
 
 But that the diversity of figure in the cells 
 of leaves does not, altogether, depend on me- 
 chanical compression, is evident from the fact, 
 that those towards the upper disk of the leaf 
 often differ in form from those towards the un- 
 der disk; and yet in both these situations we 
 may suppose the compression to be nearly equal. 
 
588 CONSERVATIVE ORGANS. [LECT. X. 
 
 This difference, as shall afterwards be explained, is 
 probably necessary for the distinct functions of 
 these two surfaces ; and thence, in every attempt 
 to theorize on the structure of parts, the pro- 
 priety of keeping in view the fact, that plants as 
 well as animals are living beings, and consequently 
 not regulated by those laws which control the 
 configuration of inanimate matter. No plant is 
 better adapted than the Christmas Rose, Helle- 
 borus niger, to demonstrate this diversity of cel- 
 lular structure in the same leaf. If we examine 
 a thin transverse slice of a leaf of this species 
 of Hellebore, with a good magnifying glass, we 
 perceive that, immediately under the cells of the 
 cutis (31. a.), which are large and oval, there is a 
 range of tubular cells (b.) terminating in the true 
 pulp or parenchyma of the leaf (c.) ; which con- 
 sists of irregular hexagonal cells, and occupies the 
 whole of the space between the tubular cells and 
 the cuticle (d.) of the under disk of the leaf. Under 
 the highest power of the microscope, we find that 
 these tubular cells (32. b.) have apparently a di- 
 rect communication with the cells (a.) of the 
 cutis ; and also with the range of cells (c.) im- 
 mediately beneath them: but in neither are 
 the mouths open, for, a membrane bounds the 
 oblong cell in every direction. In the trans- 
 verse section of some leaves, as for instance those 
 of Calla j&thiopica (33.), which is an aquatic 
 
LKCT. X.] ANATOMY OF LEAVES. 589 
 
 plant, we find several ranges of tubular cells 
 (b.) commencing under the cutis (a.) of the su- 
 
 perior disk. Some of these terminate in the hex- 
 agonal cells (d.), and others in empty cavities 
 (f*f.) y such as are present in the leaves and the 
 petioles of all aquatic plants, and which, being filled 
 with air, seem intended for enabling them to rise 
 above or to float on the surface of the water. 
 Under the microscope these tubular cells (34. b.) 
 in the leaves of Calla, resemble a chain of short 
 vessels, with valvular partitions; and were, in- 
 deed, erroneously regarded as such by Malpighi 
 and Leuwenhoek, who observed them in the 
 stem. But these cells are not furnished with open 
 mouths, nor with valves, neither where they 
 originate in the cuticular cells (34. a.), nor at their 
 union with each other, nor where they termi- 
 nate (d.) in the common pulp of the leaf; and 
 this is the case, also, in all leaves furnished with 
 tubular cells. When the tubular cells are cut 
 transversely, they appear to be of an hexagonal 
 
590 CONSERVATIVE ORGANS. [LECT. X. 
 
 figure (35.), and not round 3 as might be sus- 
 pected from their longitudinal aspect. Sprengel 
 and some others have stated that the cells in all 
 , leaves are elongated near the upper surface ; but 
 the simple inspection of many leaves is sufficient 
 to refute this statement. Among the succulent 
 leaves, even, in which the tubular cells are more 
 frequently met with than in membranaceous 
 leaves, they are not always present ; as, for in- 
 stance, in the leaf of Hoya carnosa, the only dif- 
 ference between the upper and under disk of which 
 is in the structure of the cutis, which on the su- 
 perior surface (a. fig. 16, Plate 10) is a simple 
 transparent pellicle, while on the inferior (b. ibid.) 
 it is cellular ; and in the cells near the upper 
 disk being filled with a greener and more opaque 
 juice than those near the under disk. 
 
 With regard to the individual structure of the 
 cells constituting the parenchyma of leaves, we 
 find it is the same as that of the cells in the other 
 parts of the plant. Each cell appears to be a dis- 
 tinct, transparent, membranous vesicle, formed 
 into the figure it displays by the pressure of the 
 contiguous cells, and thence, the partition sepa- 
 rating each cell, must be a double membrane. 
 This is more evident in the microscopic examina- 
 tion of the cellular substance of some leaves than 
 of others; thus, in this minute portion (36. page 
 2 
 
LECT. X.J ANATOMY OF LEAVES. 591 
 
 589), taken from the leaf of Iris Germanica, 
 we perceive that not only the cut edges (c.) of 
 the cells appear double; but that where some 
 of the cells deviate from the hexagonal figure, 
 there are evident interstitial spaces (a. d.) be- 
 tween them, which if the cells were not distinct- 
 vesicles would not occur. These interstices have 
 been noticed by Leuwenhoek, Treviranus, Com- 
 paretti, and M. Kieser; the last of whom sup- 
 poses them to exist at every angle of every cell, 
 and by their conjunction to form canals which 
 surround it ; and to be the only passages by which 
 the fluids are conveyed through the cellular sub- 
 stance*. It is unnecessary to point out the im- 
 probability of this opinion ; and it is sufficient foi 
 our purpose to demonstrate the existence of these 
 interstices, to prove the double nature of the in- 
 tercellular partitions. This is very evident in the 
 elongated cells, which we have seen exist near 
 the upper disk of many leaves ; and in the spaces 
 formed by the conjunction of these only, have I 
 been able to perceive any resemblance to the in- 
 tercellular canals of M. Kieser. 
 
 A question arises in consequence of the sup- 
 position that each vesicle is a distinct sac: in 
 what manner do the cells communicate with each 
 other, and with the vessels which they surround ? 
 
 * Mem. sur I* Organisation des Plantes, p. 20. 
 
592 
 
 CONSERVATIVE ORGANS. 
 
 [LECT. x. 
 
 Malpighi, aware of the necessity of an explanation 
 of this point, maintains that a small tubular pro- 
 duction (a. a. 37.) issues from each cell or vesicle, 
 by which it communicates with the contiguous 
 cells (b. b.), and with the vascular system of the 
 leaf (c. c.); and has given a microscopic repre- 
 sentation of this cellular structure in the Cactus 
 (37.) to illustrate his position. A similar idea 
 was entertained, also, by M. de Saussure, who 
 describes the cellular part of the leaf as a con- 
 geries of minute transparent vessels, which are so 
 dilated between their junctions as to assume the 
 appearance of cells or vesicles. But, notwith- 
 standing the high authority advancing this opi- 
 nion, my observations prevent me from according 
 with it: since in no leaf, which I have examined, 
 have I been able to detect these communications. 
 In the Cactus, if we select a small portion of a 
 vessel with some cellular matter adhering to it, as 
 in the minute morsel (38.), under the microscope, 
 before us, we perceive that the cells (b. b. b.) are 
 
LKCT. X.] ANATOMY OF LEAVES. 593 
 
 in close contact with the vessel (a. .), but neither 
 spring out of it, nor appear to have any direct 
 communication with it; and that neither the elon- 
 gated cells (b.b.b.b.b.), nor the spheroidal (d.d. d.), 
 appear to communicate with one another by any 
 tubular production. The transparency of the cellu- 
 lar membrane produces an appearance (c. c. e.e.e ) 
 at the points of contact of the cells, which might 
 be mistaken for small tubes, but which arises from 
 the impression of the contiguous cells upon one 
 another. Even in that peculiar modification of the 
 cellular structure, which is found immediately with- 
 in the cutis of the inferior disk of some leaves; and 
 in which the cells assume the appearance of ana- 
 stomosing tubes (3Q.), none of the tubular connect- 
 ing processes, described by Malpighi, are perceived; 
 nor do these cells appear to communicate directly 
 with the vessels which they surround. As this is the 
 most curious modification of the cellular structure 
 of leaves, I shall demonstrate it to you as it 
 appears in the floral leaf of Helleborus viridis, 
 which I select for this purpose, from its being 
 almost devoid of colour. In the minute portion 
 before us, as it appears under the microscope, we 
 perceive the range of cells e. e. (39) closely ap- 
 plied to the proper vessels d. d. but not communi- 
 . eating with it: the cells c. c. c. c. assume various 
 forms, but all are apparently tubular ; and, where 
 they are more transparent than common, we dis- 
 VOL. i. Q Q 
 
594 CONSERVATIVE ORGANS. [LECT. X. 
 
 tiuctly perceive the nature of their conjunction 
 (b.b.); but no projecting tubular processes. The 
 spaces, such as a. a. are filled with air in the same 
 manner as the vacuities in the leaves of aquatic 
 plants. In what manner then do the cells commu- 
 nicate? To answer this question properly, we ought 
 to understand the structure of the intercellular 
 membrane. But here our instruments fail, if 
 they do not mislead us ; and, under glass.es of the 
 highest power, this membrane appears different 
 under different circumstances : by transmitted light, 
 it seems a simple, unorganized, transparent pel- 
 licle ; but, by reflected light, is evidently porous. 
 I have already stated my belief that the cells of 
 the stem communicate by pores, and I see no 
 reason for altering this opinion with regard to 
 those of the leaf: although I do not concur in 
 opinion with M. Mirbel and Sprengel, that the 
 form, position, magnitude, and number of these 
 pores can be determined. An opinion has been 
 advanced, that the fluids may be transmitted 
 from cell to cell, " consistently with the integrity 
 of the cellular structure," by the exercise of the 
 alternate functions of secretion and absorp- 
 tion;" but these functions imply the existence of 
 either glands or vessels connected with the absorb- 
 ing and secreting surface, which are, however, 
 even less demonstrable than the pores. Upon the 
 whole, the question is still unanswered; and all 
 
LECT. X.] ANATOMY OF LEAVES. 595 
 
 that we certainly know of the subject is, that the 
 fluids are transmitted from cell to cell, through 
 every part of the vegetable system, although the 
 structure by which this is accomplished remains 
 undiscovered. 
 
 Whatever may be the mode in which the cells 
 communicate with one another, their contents are 
 more or less fluid or solid, according to their situ- 
 ation in the thickness of the leaf. Thus, in thin 
 leaves the cells near the inferior disk are more trans- 
 parent, owing to their contents being more fluid 
 than those near the upper disk ; but in both we per- 
 ceive a number of granules, which are more opaque 
 and of a deeper green, as the cells containing them 
 approach the upper disk. In succulent leaves, and 
 those which maintain a vertical position, the 
 opacity and green colour of the granules, are the 
 same towards every face of the leaf; but they are 
 generally colourless in its centre. In the cells, 
 also, of some leaves, regular crystallized salts are 
 found; and in others the fluids are tinged of dif- 
 ferent hues besides green; in which cases the 
 leaves themselves display the same hues on one 
 or both surfaces. 
 
 The size of the cells varies in different leaves ; 
 in some, even when examined under the most 
 powerful glasses, they appear like the smallest 
 vesicles ; while, in others, they are so large as to 
 be perceptible to the unassisted eye. 
 
 QQ2 
 
596 CONSERVATIVE ORGANS. [LECT. X. 
 
 I have already demonstrated to you the exist- 
 ence of large vacuities in the foliar parenchyma of 
 the leaves of aquatic plants. Mirbel regards these 
 as accidental productions, rents or defects in the 
 cellular texture; an opinion, however,, which is 
 instantly refuted on a minute examination of these 
 parts. If we place a portion of the petiole, or any 
 of the larger costse of an aquatic, this thin trans- 
 verse slice, for example, of the petiole of Trapa 
 natans (fig. 12, Plate 10), under the microscope, 
 we perceive that the vacuities have a symme- 
 trical arrangement around the centre (c.), which 
 is vascular and consequently more opaque than 
 the rest of the slice; and that some of the va- 
 cuities are open (a. a.), while others (b. b.) are 
 closed. The membrane which covers some of the 
 vacuities as they appear in the slice (fig. 12.) 
 before us, is a diaphragm, which, as it forms the 
 roof of one cavity, is also the floor of another ; and 
 it is owing to these diaphragms not being all on the 
 same plane that some of the vacuities appear de- 
 void of them, in the transverse slice of the petiole 
 of the leaf of any aquatic plant. The intimate 
 structure of these diaphragms is seen in a highly 
 magnified view of one of them, as represented at 
 fig. 13, Plate 10 ; in which b. shows that the dia- 
 phragm consists of regular hexagonal framework, 
 with the intervening membrane either perforated 
 or studded with small transparent, amylaceous gra- 
 
LECT. X.] ANATOMY OF LEAVES. 597 
 
 miles; and a. that the lateral partitions between 
 the cavities, apparently consist of square cells, 
 when transversely divided, as in the figure before 
 us, although they are hexagonal, when viewed 
 laterally, as in the diaphragm. Each cavity is 
 lined on every side with a thin pellucid pellicle, 
 closely resembling the external cuticle ; and 
 frequently hairs, knobs, and similar cuticular 
 productions are found projecting into these cavi- 
 ties. Kieser, who is the only author who has no- 
 ticed these bodies, remarks that he had sometimes 
 observed, in the cavities of Calla -^Ethiopica, small 
 globular, pedunculated bodies ; which, springing 
 from the sides, project towards the centre of the 
 cavities ; but, according to my observations, they 
 are more common in those of Typha, Equisetum, 
 and Nymphcea, in the latter of which they closely 
 resemble the branched hairs (see Plate 9, fig. 14.), 
 which form the tufted pubescence on the under 
 disks of some leaves. 
 
 In closing this view of the anatomy of the 
 cellular system of leaves, I have to remark, that 
 although it embraces the more common varieties 
 that are met with, yet it is probable that, in the 
 vast range of the vegetable kingdom, many other 
 diversities of structure of the cellular matter exist. 
 
 From these inquiries into the structure of the 
 vascular and cellular systems of leaves, the affinity 
 which exists between the stem and the leaf is very 
 
598 CONSERVATIVE ORGANS. [LECT. X. 
 
 obvious. In the stems of monocotyledons, the 
 vessels run nearly in straight lines in distinct fas- 
 ciculi, embedded in a cellular pulp; and a simi- 
 lar vascular arrangement presents itself in the 
 leaves of this tribe of plants. In dicotyledons, on 
 the other hand, the vascular fasciculi of the stem 
 are not distinct, but form a reticular tissue which 
 covers the whole circle of the stem ; and., in like 
 manner, in the leaves, the vessels ramify in every 
 direction, forming a most complicated and beau- 
 tiful network, the interstices of which are filled 
 with the cellular pulp. The leaf, therefore, may 
 be regarded., in some respects, as a mere expansion 
 of the stem; and, consequently, in aphyllous plants, 
 we perceive that the stem is adapted to perform all 
 the functions of the leaf. The internal structure 
 of the floral leaves or bractece, and of those more 
 temporary foliar appendages, which are termed 
 stipulce, is nearly the same as that of the real 
 leaf; even the scales that envelop buds, and which 
 are always described as deriving their origin from 
 the cortical part only of the stem, and consisting 
 chiefly of cellular matter, have in every respect 
 the same structure as leaves, as far, at least, as 
 relates to their vascular and cellular systems. 
 
LECT. XI.] ANATOMY OF LKAVES. 599 
 
 LECTURE XL 
 
 OF THE CUTICULAR SYSTEM OF LEAVES! USE OF 
 
 THE CUTICULAR APERTURES. OF THE APPEND- 
 AGES OF THE STEM AND LEAVES PUBESCENCE 
 
 THORNS PRICKLES GLANDS PROPS: USES 
 
 OF THESE APPENDAGES. 
 
 EVERY leaf is covered with a real skin or epi- 
 dermis, which not only guards the vascular and 
 the cellular matter from external injury; but 
 is the medium by which it performs the important 
 functions of absorption and exhalation. In the 
 majority of leaves, the epidermis can be separated 
 from the parts it covers: and appears to be a 
 compound organ, or to consist of two distinct 
 layers; the exterior of which is a fine, transparent, 
 apparently unorganized pellicle, and the interior 
 vascular and cellular. But the opinions and de- 
 scriptions of phytologists are at variance on this 
 subject. Grew*, Malpighi "f~, Du Hamel J, Des- 
 fontaines, Mr. Keith ||, M. Kieser f , M. Mirbel **, 
 
 * Anal, of Plants, p. 62. 
 
 t Anat. Plantarum, p. 212. 
 
 J Phys.des Arbres, i. 8. 
 
 Mem. de Tlnst. Nat. i.4-81. 
 
 || Syst. of Phys. Bot. i. p. 313. 
 
 5f Mem. sur F Organ, des Plantes t p. 141. 
 
 ** Elcm. de Phys. veg. i. 36.' 
 
600 CONSERVATIVE ORGANS. [LECT. XI. 
 
 and some others, have described the cuticular co- 
 vering of leaves as a simple body ; while M. de 
 Saussure*, Mr. Francis Bauer -}-, and M. De- 
 eandolle;}:, concur in the opinion which I main- 
 tain of its compound nature. Let us examine 
 the proofs upon which this is founded. 
 
 The true epidermis, or the delicate pellicle 
 which forms the outermost covering of the leaf, 
 can be readily demonstrated in any small portion of 
 the cuticular covering carefully raised by the point 
 of a lancet, and placed in a drop of water under a 
 powerful microscope. In this small portion, taken 
 from a leaf of Dianthus Caryophyllus,\t isseen (a.40. 
 page 602) extending beyond the area of the meshes 
 (b. b.) of the interior cuticular layer, which are 
 seen through it, and is evidently a simple pellicle. 
 But Mr. Keith , who admits that it may be seen 
 in this manner, supposes that its individuality is 
 not proved by such a demonstration, as the meshes, 
 the intervals of which it might originally have filled 
 up, may be accidentally obliterated ; but, although 
 there is some plausibility in this objection, yet, 
 when we take this appearance in conjunction 
 with the double character observed in the trans- 
 verse section of the cuticular covering of every 
 
 * Encyclop. Method, i. 67. 
 
 f Tracts relative to Botany. 
 
 I Mem. de I'Inst. Nat. i. 351. 
 
 Syst. of Physiol Bot. vol. i. p. 313. 
 
LECT. XI.] ANATOMY OF LEAyES. 601 
 
 leaf which we have examined, there is sufficient 
 reason for believing that it is as much a distinct 
 layer as the cuticle in the human body, although, 
 in the leaf, it cannot be readily detached from the 
 interior layer of cutis. It is described by Saussure 
 as being perforated by the slits or pores which, I 
 shall soon demonstrate to you, are found on one or 
 both of the surfaces of every leaf; but we shall 
 find, on minutely examining these, that it is not 
 perforated by them, but enters into them, as well 
 as into every gland opening on the surface of a 
 leaf, as a lining membrane ; and is, in fact, the 
 covering of every part of the vegetable texture, 
 which would otherwise come in contact with the 
 air. If, however, it cover every part of the sur- 
 face of the leaf, and is an imperforated mem- 
 brane, by what means, it may be asked, does the 
 fluid which exhales so freely from the leaves es- 
 cape? It is certainly not easy to answer this ques- 
 tion ; but as we can scarcely form an idea of a 
 membrane perfectly free from pores, even in a 
 living body, transmitting fluids ; we may conclude 
 that, although no pores are visible in this mem- 
 brane, even when it is examined under the mi- 
 croscope, yet, it does not follow that no pores 
 exist ; and, in accounting for the transudation of 
 the fluids, which the leaf throws off, we must 
 always bear in mind, that the functions of living 
 bodies are influenced by different powers from 
 
602 CONSERVATIVE ORGANS. [LECT. XI. 
 
 those which regulate the operations connected 
 with inert matter. 
 
 The second or interior cuticular layer is seen 
 through the epidermis, and consists of a vascular 
 network resting upon a layer or layers * of cells. 
 
 Taking the same portion of the cutis of Dian- 
 thus Caryophyllus (40.) to demonstrate the super- 
 ficial structure of this layer; we find that, except 
 within the boundary of the detached epidermis 
 (a. a.), the whole is spread with a network of ir- 
 regular hexagons formed by lines which appear 
 double, and terminate in a ring surrounding a 
 slit or oblong pore (c. ,*.), which occupies the centre 
 of one of the longest bounding lines of almost 
 every alternate hexagon. The same appearance of 
 the interior layer of cutis is seen on both surfaces 
 of the leaf of Dianthus ; but, as I shall afterwards 
 demonstrate, this is not the case in the majority of 
 leaves-}-. If we now place a very thin transverse 
 
 * Mr. F. Bauer describes the cuticle of a species of Hae- 
 manthus as composed of several layers of cells. See Tracts 
 relative to Botany. Lond. 1805. 
 
 I In Plate 10, figure 3 represents a portion of cuticle 
 
LECT. XI.] ANATOMY OF LEAVES. 603 
 
 slice of the leaf of Dianthus under the micro- 
 scope, to examine this layer in its thickness, we 
 can readily distinguish it (b. 4 1 .), by the form of 
 its cells (c.) from the parenchyma (d. d.) upon 
 which it rests; and, also, from the epidermis 
 (a.) which covers it; for, in this leaf, the cells of 
 the parenchyma assume an oblong form im- 
 mediately under the cutis, whereas the cells of 
 the cutis are irregular spheroids, and the simple 
 layer of epidermis is remarkably distinct. 
 
 Whether these cuticular cells have any direct 
 communication with the oblong cells beneath 
 them, I have not been able to determine; but in 
 separating the cutis, by tearing, some of the ob- 
 long cells always adhere to it; and, when viewed 
 through it, by transmitted light, appear like a 
 smaller cuticular network (d. d. 40.), filling up 
 the larger meshes. These might be mistaken for 
 the cuticular cells; but the transparency of the 
 cutis prevents its cells (e. 4 1 .) from being visible 
 in a superficial view of the organ. In this trans- 
 verse section of the leaf of Dianthus (41.) the dis- 
 tinct nature of the epidermis (a.) is perfectly evi- 
 dent, both as a covering to the true cutis (b.) and 
 as lining the slits (e.), one of which is here di- 
 vided lengthways. 
 
 taken from the under disk of the leaf of Hoya carnosa; and 
 figure 4-, a portion from the upper disk of the same leaf. Both 
 are magnified about 300 times. 
 
604 CONSERVATIVE ORGANS. [LECT. XI. 
 
 The lines forming the meshes which thus cha- 
 racterize the cutis of leaves, were first described 
 by Hedwig as vessels, originating in the circum- 
 ference of the pores; an opinion which is sup- 
 ported by the elder M. De Saussure and M. 
 Kieser ; and which is confirmed by the microsco- 
 pical examination of a portion of the cutis of any 
 leaf. Remarking the facility with which this part 
 of the cuticular structure can be demonstrated, our 
 surprise is excited that Sprengel, Link, Mirbel, 
 Jurine, Krocker, and others, should have ad- 
 vanced the opinion, that these reticulations form 
 no part of the real structure of the cutis, but 
 are merely the adherent fragments of the sides of 
 the subjacent cells : for, as I have already demon- 
 strated, the parenchymal cells are much smaller 
 than the cuticular meshes ; and, when the cutis 
 is sufficiently transparent, they are seen through 
 it very distinctly (4O. b. .), but not at all coin- 
 ciding with the sides of these meshes. Admit- 
 ting, therefore, that these lines are lymphatic 
 vessels, it is not improbable, as M. Kieser has 
 asserted, that they terminate by one extremity 
 in the larger vascular fasciculi ; but on this point 
 I have not been able to satisfy myself. The 
 meshes, which they form, differ very much, both 
 in form and size, in different leaves*. In al- 
 
 * Mirbel, reasoning from the false opinion which he had 
 formed of the structure of the cutis, observes, " les differences 
 
 2 
 
LECT. XI.] ANATOMY OF LEAVES. 605 
 
 most all the monocotyledons, in the Grasses, and 
 in every plant the leaves of which have parallel 
 costae, the meshes are nearly irregular parallelo- 
 grams ; but, in forming these, the vessels some- 
 times run in straight lines, as in common Meadow 
 grass, Poa trivialis (45.) ; sometimes in slightly un- 
 dulated lines, as in the White Lily, Liliurn candi- 
 dum (44.); and sometimes zig-zag, as in Indian 
 Corn, Zea Mays (fig. 14, Plate 10). In some of the 
 fleshy leaves they are nearly regular hexagons, 
 as on the upper disk of Hoya carnosa (fig. 4, 
 Plate 10), and on both surfaces of the leaves of 
 Aloe verrucosa (43.) : but, in the majority of di- 
 cotyledons, they assume very irregular figures -j~. 
 
 WK 
 
 " qu'elle presente viennent de la forme des cellules dont elle 
 ** faisait partie." " Les parois cellulaires restant attachees a 
 " l'piderme, y dessinent de petits compartimens dont la forme 
 " indique celle du tissu cellulaire lui-meme. Tantot ce sont des 
 " parallelogrammes plus ou moins reguliers, tantot des hex- 
 " agones, tantot des polygones divers, dont les cotes sont on- 
 dules.' 1 Elem. de Phys. veg. 1 partie, p. 36. 
 
 f This irregularity is well exemplified in common Sorrel, 
 Rumex acetosa. In Plate 10, fig. 9 represents a minute portion 
 
606 CONSERVATIVE ORGANS. [LECT. XI. 
 
 Whatever may be the figures which they pre- 
 sent in the cutis covering the spaces between 
 the vascular ramifications of the leaf, they in- 
 variably appear as irregular parallelograms (<i6. 
 a. a.) * in that which covers the vascular fas- 
 ciculi; a fact which gives some support to the 
 opinion of M. Kieser, that the vessels forming the 
 meshes terminate in these fasciculi. The differ- 
 ence in the size of the meshes, in different leaves, is 
 still more striking than in their forms; but in all 
 they are very minute. On a portion of the cutis 
 of Aloe verrucosa, -^fa of a square inch in size, I 
 counted ninety-six meshes, or 55,296 to the square 
 inch ! 
 
 The form of the cuticular cells (41. 4 2. c. page 
 602), owing to the cutis being more transparent 
 
 of the cutis taken from the upper disk of a leaf of that plant ; 
 and fig. 10, a portion from the under disk. 
 
 * This represents a very minute portion of cutis taken from 
 the under disk of a leaf of Gardenia latifolia, magnified 300 
 times, and viewed by transmitted light. 
 
LECT. XI.] ANATOMY OF LEAVES. 607 
 
 than the epidermis which covers it, can be demon- 
 strated only as they appear in a vertical section. 
 They are either spheroidal or oval ; and are found 
 generally empty, or filled with a colourless fluid. 
 I have not been able to detect any immediate com- 
 munication between them and the cells of the pa- 
 renchyma, or even between one and another. In 
 the greater number of leaves the cutis contains one 
 layer only of cells ; but it may contain several 
 layers, as Mr. Francis Bauer * has demonstrated 
 is the case in the genus Hsemanthus; and I have 
 found that this is the case, also, in the leaf of 
 commpn Oleander, Neriurn Oleander. 
 
 The slits or apertures which have been already 
 noticed as existing on one or both surfaces of all 
 leaves, were first described by Grew as orifices; but 
 afterwards regarded by the elder M. De Saussure 
 as glands, and by M. Von Gleichen, who ex- 
 amined them in the leaves of Polypody, as the 
 anthers of the Fern tribe. The more correct ob- 
 servations of Hedwig and of Decandolle, however, 
 have confirmed the opinion of Grew; and, indeed, 
 it is only necessary to examine them, under a good 
 microscope, to be satisfied that they are real 
 pores -f-. In the leaves of trees and of some other 
 
 * Tracts relative to Botany, Lond. 1805. 
 
 f It is extraordinary that Senebier, who searched for these 
 apertures in the leaves of a great variety of plants, never could 
 detect them. Vide Phys. veg. i. p. 4-56. 
 
608 CONSERVAT1VK ORGANS. [ LECT - XI - 
 
 plants, they are observed on the inferior disk only ; 
 but in others, particularly in the Grasses, the Coro- 
 nariae, and the Palms, they occupy both surfaces. 
 Some Phytologists have asserted that the lower 
 tribes of plants are destitute of pores; but this 
 statement is incorrect, as they are easily demon- 
 strated in Marchantia and a few of the Mosses. 
 Plants which have no leaves, such as the Cactus 
 tribe and many of the Rushes, and some of 
 those, also, which have leaves, as the Grasses, 
 have pores on the stem ; but in general they are 
 confined to the leaves. Those leaves, however, of 
 aquatic plants which are constantly under water 
 are destitute of pores ; the upper disk only of 
 leaves which float on the surface of water possess 
 them ; and when a land plant is made to grow 
 under water, the new leaves, which are evolved 
 under the water, have no pores, although those 
 which they have succeeded, or the aerial leaves, 
 were furnished with them. Even in plants which 
 are partly emersed and partly submersed, as for 
 instance Ranunculus aquaticus, the leaves that 
 grow under the water are destitute of pores, while 
 those which float, or are above that fluid, are pro- 
 vided with them. It has, also, been asserted that 
 etiolated leaves, or such as are excluded from 
 the light, are destitute of pores ; but there is some 
 inaccuracy in this remark, as I have found them 
 as numerous on the interior etiolated, as on 
 
LECT. XI.] ANATOMY OF LEAVES. 609 
 
 the exterior green leaves of the common Cabbage 
 and the Lettuce. 
 
 These foliar apertures vary very considerably 
 in form, size, number, and position, in different 
 leaves. They are commonly oblong (46.), but in 
 some instances circular (47-)> an d in the Agave 
 tribe (59- p. 6li), and a few other families of 
 plants, they are quadrilateral. In almost all 
 leaves they are surrounded by a border, in which 
 the vessels forming the cuticular meshes appear 
 to terminate. Placing minute portions of the cu- 
 ticle of different leaves under the microscope, 
 we can readily ascertain the superficial form of 
 these pores : the following are the principal diver- 
 sities of form which I have observed *. 1. A simple 
 slit, more open in the middle than at either 
 end, bisecting an oval shield ; which may, there- 
 fore, be termed the oval scutiform aperture, oscu- 
 lum scutiforme ovatum, as exemplified on the lower 
 disk of the leaves of Sage (48. p. 610), of Lactuca 
 quercina (4Q.), Dandelion, Leontodon Taraxacum, 
 Sweet-scented Coltsfoot, Tussilagofragrans, many 
 of the Grasses, the common Bean, Vicia Faba, &c. 
 2. A simple slit, bisecting an oval shield enclosed 
 
 * In naming the different kinds of pores, I have assumed the 
 fact, that they are respiratory organs, or apertures resembling 
 in their functions the spiracula of insects ; but, on account of 
 the simplicity of their structure, I have preferred the term 
 osculum to that of spiraculum. 
 
 VOL. 1. R R 
 
610 CONSERVATIVE ORGANS. [LECT. XI. 
 
 within a ring, which I name the annulated scu- 
 tiform aperture, osculum scutiforme annulare, as 
 seen on the inferior disk of the leaves of Helle- 
 borus fcetidus (51.), the Violet tribe (52.), the 
 
 Coffee plant, Coffea Arabica (53.), the White 
 Lily, Lilium candidum (44. p. 605), Gardenia la- 
 tifblia (46. p. 606) ; the common Cabbage, Bras- 
 sica oleracea ; the outside of the tubular leaf of 
 Saracenia (54.), &c. 3, An open slit, or an oblong- 
 pore, enclosed by a simple oval ring, which may 
 thence be termed the annulated aperture, osculum 
 annulare; as on the inferior disk of the leaf of 
 Hibbertia scandens (50.), Ivy, Hedera Helix (55.), 
 Jacquinia ruscifolia (56.), Dianthus Caryophyllus 
 (40. p. 602), Laurus Canarlensis, Wolfsbane, 
 Aconitum neomontanum, Privet, Ligustrum vul- 
 gare, &c. 4. A circular pore in the centre of a 
 circular shield, which we may name the circular 
 aperture, osculum circular e ; as on the inferior 
 
LKCT. XI.] ANATOMY OF LEAVES. 611 
 
 disk of the leaf of common Sorrel, Rumex acetosa 
 (a. b. fig. 10. Plate 10), of the Primrose, Primula 
 (57.), and, very beautiful, on both surfaces of 
 Cactus opuntia (38.). 5. A quadrilateral pore, 
 osculum quadrilaterale, surrounded by an ele- 
 vated margin, as on both surfaces of the leaves 
 of Agave Americana (59-), and of all the other 
 species of the succulent tribe to which it belongs. 
 I cannot avoid remarking, in this place, the na- 
 tural separation, which may be traced by the 
 form of these apertures, between the Aloes and 
 the Agaves. In the former the pores are always 
 circular (60.), and in the latter they are inva- 
 riably quadrilateral (59.) 
 
 61 
 
 It is impossible to notice all the modifications 
 of these different species of the cuticular aper- 
 ture; I shall, therefore, only remark, that among 
 the varieties of the annulated aperture, we some- 
 times find the space between the pore, or the shield 
 and the enclosing ring, divided into distinct por- 
 
 R R 2 
 
612 CONSERVATIVE ORGANS. [LECT. XI. 
 
 tions ; and occasionally a double ring, with the in- 
 tervening space, also, divided into four or more 
 equal parts: examples of the first variety are found 
 on the lower disk of the leaves of Lilac (61. p. 
 611), of Acuba Japonica (6^.), Cussonia thyrsi- 
 flora (63.), Hoya carnosa (fig. 3, Plate 10) ; and 
 on the upper disk of the leaf of Rumex ace- 
 tosa (fig. 9, Plate 10). The upper disk of the 
 leaves of Viola odorata affords an excellent illus- 
 tration of the double ring (64.). But the most re- 
 markable form of the cuticular pore, which I have 
 yet observed, is found on the back of the leaves 
 of common Oleander, Nerium Oleander. It ap- 
 pears, on a superficial view, a simple oval aper- 
 ture without any shield, but guarded by hairs 
 which cross it in different directions (65. a. .); 
 
 and is comparatively much larger than any of the 
 other kinds of pores. 
 
 Some writers have ventured to assert, that no 
 apertures are found in those plants which are 
 generally regarded as composed almost entirely 
 of cellular matter, among which Marchantia is 
 usually reckoned ; but the incorrectness of this 
 opinion can be easily proved, by placing a small 
 
LECT. XI.] ANATOMY OF LEAVES. 613 
 
 slice of the cutis of Marchantia 
 under the microscope. The aper- 
 tures are oval, and placed in the 
 centre of a slight elevation, as re- 
 presented in the marginal cut (*). 
 
 In respect of size, pores differ 
 considerably in different plants ; 
 but on the leaves of the same plant their size is 
 nearly uniform. The largest, as far as rny obser- 
 vations extend, are those found on the leaves of 
 Oleander; and the smallest on those of the genus 
 Myrteae. Sprengel says, that in the Coronariae 
 " their longitudinal diameter is from -rV to ^ 
 " part of a geometrical line, and their diameter, 
 " in the cross direction, is from -^V to ^V part;" 
 but in " the Myrteae, Rosaceae, Leguminosae, 
 " and Caryophylleae, two hundred of them, at 
 " least, might lie upon a geometrical line-f~." 
 
 In number the foliar apertures vary, also, in dif- 
 ferent plants. The more minute they are, the more 
 numerous. On the lower surface of the leaf of 
 Gardenia latifolia, we find an aperture in almost 
 every mesh ; but in the Aloe tribe scarcely one pore 
 for twenty meshes, and on the leaf of Oleander, one 
 among sixty. With regard to position, these aper- 
 tures are in some instances arranged in lines from 
 the base to the apex of the leaf, and have the same 
 
 t Elements of the Phil, of Plants, fyc. by A. P. DecandoUe 
 and K. Sprengel, 310. 
 
 RR3 
 
614 CONSERVATIVE ORGANS. [LECT. XI. 
 
 direction throughout; but in the majority of 
 leaves they have no regular arrangement, and as- 
 sume different directions. In herbaceous plants 
 we generally find them on both surfaces of the 
 leaves; but in ligneous plants they are scarcely 
 ever seen on the upper surface. They are never 
 situated on the costae, nor on the edges of the leaf. 
 But these demonstrations make us acquainted 
 with the superficial aspect only of the foliar aper- 
 tures, beyond which it is surprising that no Phy- 
 tologist has yet attempted to push his investiga- 
 tions; although it is by no means difficult to 
 determine their structure by the aid of the micro- 
 scope. Placing a very thin vertical slice of a 
 leaf of the Clove Pink, Dianthus Caryophyllus, 
 cut in the direction of the axis of the leaf, under 
 the microscope, we find that the aperture (e. 41. 
 p. 602) which is thus divided in its longitudinal 
 diameter, is a short cylindrical tube penetrating 
 completely through the cutis, and terminating in 
 a cul de sac, which is impressed into a vesicle 
 (f.) that appears to communicate with the oblong 
 cells (d.) immediately beneath the cutis. But al- 
 though the aperture penetrates the cutis, there is 
 no opening through the epidermis (.), which, on 
 the contrary, enters into the tubular part of the 
 pore and lines it throughout. In another slice of 
 the same leaf, cut so as to divide one of the aper- 
 tures in its cross diameter (42. p. 602), we per- 
 
LECT. XI.] ANATOMY OF LEAVES. 615 
 
 ceive that the vesicle (/*.) appears to be double ; 
 from which it is probable that it is this vesicle, 
 seen through the transparent substance of the 
 cutis, which gives the appearance of the shield 
 in the superficial view of the aperture. As we 
 find that, in the superficial view of these apertures, 
 the character varies considerably in different 
 plants, so this form of the tube and the vesicle is 
 also variously modified ; but the general charac- 
 ter is nearly the same, with a very few exceptions, 
 throughout the vegetable kingdom, as far, at 
 least, as my observations extend. Thus in the 
 Agave (59- p. 611), the superficial form of the 
 aperture is very different from that in Dianthus 
 (40. p. 602) ; but if we examine it in a transverse 
 section of the leaf, although we find the general 
 structure of both agreeing, inasmuch as the aper- 
 tures of both are lined with the epidermis, pene- 
 trate the cutis, and have at their bottom the vesi- 
 cular ring ; yet we perceive that that of the Agave 
 differs from that of Dianthus, in terminating in a 
 large dilated cell (66. f.), which is found always 
 
 R R 4 
 
616 CONSERVATIVE ORGANS. [LECT. XI. 
 
 filled with air, although it is closely surrounded 
 by the oblong cells (e.) of the parenchyma, turgid 
 with green juice. In the oblong section, also, of 
 this aperture (67.) the vesicular ring (f.) does 
 not appear to be simple as in Dianthus, but is 
 divided by a duct, in which the aperture (a.) 
 seems to terminate, and which apparently opens 
 into the air cell (f. 66.) ; which is cut away in 
 this section (6?.)- 
 
 In the leaf of Oleander the aperture (d. 68. p. 
 615) expands into a kind of sac where it pene- 
 trates into the substance of the parenchyma (c.) ; 
 and it is throughout lined with the same kind of 
 hairs which guard its orifice ; but I have not been 
 able to determine whether its lining membrane, 
 which is a production of the epidermis (a.), be 
 porous ; although I have examined it by glasses of 
 the highest powers. I may here remark that the 
 section of this leaf displays an example of a cutis 
 consisting of four layers of cells (b.). Decandolle 
 considers that the cuticular apertures are con- 
 nected with the ultimate ramifications of the ves- 
 sels of the leaf* ; and, if it be true, that the cu- 
 ticular meshes are formed by lymphatic vessels, 
 which terminate on one hand in the larger vessels 
 of the leaf, and on the other, in the vesicular 
 circles surrounding the fundus of the aperture, 
 this opinion must be correct. 
 
 * Journ. de Phys. iii. p. 130. 
 
LECT. XI.] ANATOMY OF LEAVES. 617 
 
 The information we have thus obtained of the 
 structure of these pores, -induces me to believe 
 that they are the respiratory organs of plants. But 
 Phytologists have considered them intended for 
 the functions of absorption and exhalation*; and 
 even Sprengel, who hints something regarding 
 their analogy to the breathing spiracula of insects, 
 rejects the idea of their being respiratory organs, 
 because "they are not in immediate contact with 
 the spiral vessels-f~." If, however, it be admitted, 
 as I have endeavoured to prove, that the spiral 
 vessels are not air-tubes, but sap-vessels, this ob- 
 jection must fall to the ground. The idea that they 
 are absorbing organs, is supposed to gain support 
 from the circumstance, first ascertained by Bon- 
 net J, that leaves absorb more powerfully with 
 their lower than with their upper surface; and 
 Sprengel remarks that " the slits are more nume- 
 " rous in juicy plants, which are nourished more 
 " by the surface of the leaves than by the roots**." 
 But 1 reply, that although leaves absorb chiefly 
 iby their inferior surface, yet, this does not prove 
 that these apertures are the absorbing organs ; for 
 we find none of them on the lower side of the 
 leaves of Nymphsea and other aquatics, which 
 
 * Among those holding this opinion are MM. Bonnet, 
 Decandolle, Sprengel, Mirbel, Mr. Ellis, and Mr. Keith. 
 
 f Elements of the Phil, of Plants, j 31 1 . ** Ibid. I. c. 
 
 t Recherches sur I' Usage des Feuilles, p. 20. 
 
618 CONSERVATIVE ORGANS. [LECT. XI. 
 
 have floating leaves ; although these leaves ab- 
 sorb powerfully by their lower surface, and exhale 
 by their upper, which is covered with these aper- 
 tures. Decandolle and Sprengel's remarks regard- 
 ing succulent and fleshy leaves, are also incor- 
 rect ; for, in the genus Aloe, which is supported 
 chiefly by absorption, the apertures are compara- 
 tively few ; and the function of absorption in these 
 plants seems to be connected with a small papilla, 
 which rises in the centre of every mesh ; and pro- 
 bably acts in the same manner as radicles on roots. 
 It is still more difficult to accord with the opinion 
 that the same foliar apertures perform such oppo- 
 site functions as those of absorption and exhalation ; 
 although there is nothing incongruous in supposing 
 that they are both exhalant and respiratory organs. 
 That they exhale, was first rendered probable by the 
 experiments of Treviranus, who found that plates 
 of glass applied to the lower disks of leaves were 
 soon covered with drops of water, while they were 
 not at all bedewed when they were affixed to the 
 upper disks ; and Decandolle afterwards proved 
 that the aqueous transpiration is greatest in those 
 plants which are supplied with the greatest num- 
 ber of apertures. The opinion, however, still 
 prevailed, that leaves exhale also by the upper 
 disk, although the majority of leaves have no 
 apertures on that disk; but before yielding im- 
 plicit credence to the assertion, that these aper- 
 
LECT. XI.] ANATOMY OF LEAVES. 619 
 
 tures are the foliar exhalants, it was necessary to 
 prove that no exhalation takes place when they 
 are obstructed; and to determine this point I 
 made the following experiment: Two twigs of 
 Laurustine, each having four leaves nearly of the 
 same size, were cut from the plant, and brought to 
 the same weight by being placed in opposite scales. 
 The lower disks of all the leaves on one twig were 
 next brushed over with a composition of mucilage 
 of gum arable and a small proportion of Traga- 
 canth; and when this was dry, each twig was placed 
 under a cylindrical glass jar containing air, and 
 immersed in a saucer of water. In a short time the 
 sides of the jar containing the twig in its natural 
 state, were covered with drops of water ; but, at the 
 end of two days, not the smallest quantity of mois- 
 ture appeared on the sides of the jar containing the 
 twig, the apertures of the leaves of which had been 
 obstructed by the mucilage. The conclusion to be 
 drawn from this experiment is, that that surface 
 only on which apertures exist exhales, and conse- 
 quently that these apertures are the exhaling or- 
 gans. This experiment leads us, also, to draw a 
 conclusion from the experiments of M. Bonnet, dif- 
 ferent from that drawn from them by that author. 
 He concluded that, because the leaves of trees 
 which were laid with their lower disk upon water 
 remained longer green and fresh than those which 
 had the upper disk applied to the water, this fluid 
 
620 CONSERVATIVE ORGANS. [LECT. XI, 
 
 was absorbed by the under surface; but if, by 
 thus placing such leaves, we obstruct the exhaling 
 pores, we can readily see why the leaves will be 
 longer withering, since no exhalation takes place ; 
 while in those placed on the opposite disk, the ex- 
 halants are free to perform their functions, and 
 thus empty the foliar cells of their aqueous con- 
 tents more quickly than the absorbents of the 
 upper disk can supply them. In stating this ar- 
 gument, I do not feel bound to point out by what 
 media leaves absorb : although I have already 
 hinted my opinion, that this function in the suc- 
 culent plants of arid soils is performed by a dis- 
 tinct set of organs. A further proof of the truth 
 of this conclusion is, that the leaves of herbs, as 
 Bonnet himself observed, remain fresh nearly the 
 same length of time when placed on either sur- 
 face; for these apertures are present on both 
 surfaces; and, besides, these leaves sooner wither, 
 whichever surface is in contact with the water, 
 than the leaves of trees which are laid with 
 their inferior surface upon that fluid. 
 
 Were I now to enter fully into the proofs, that 
 the foliar apertures are, also, respiratory organs, I 
 should be anticipating the arguments which must 
 be again detailed, when we come to the consider- 
 ation of the general functions of the leaves ; and, 
 therefore, I shall at this time, as briefly as possible, 
 examine those proofs only which are connected 
 with the structure of these organs. 
 
LKCT. XI.] ANATOMY OF LEAVES. 621 
 
 All animals that require the presence of air 
 for their existence, have some peculiar apparatus 
 for producing that change in the blood which has 
 been termed its oxygenizement ; and the change, 
 so termed, is said to be the result of respiration, 
 whether it be performed by lungs or by spira- 
 cula. Plants, also, require the presence of air; 
 vitiating it, under certain circumstances, in the 
 same manner as animals, but, under others, in- 
 creasing the proportion of its oxygen : hence 
 plants may properly be said to respire, and the 
 question arises, by what organs is this function 
 performed? Phytologists have generally agreed, 
 that the leaves are the lungs of plants ; but still it 
 may be inquired, does the whole of the leaf act, 
 or in what part of it are the respiratory organs si^ 
 tuated ? My answer is, that the foliar apertures 
 are the actual breathing organs of the plant. In 
 support of this position I refer to the situation of 
 these apertures, which are never seen on leaves that 
 are not exposed to the air ; for the leaves of sub- 
 mersed aquatics are devoid of them; even the 
 leaves of plants which are not naturally aquatics, 
 if they be submersed, soon lose them ; and al- 
 though some plants of the higher classes, which 
 grow in the air, have no leaves, yet, these have 
 apertures on the stem, which, in such instances, 
 perform the respiratory function. But the most 
 perfect plants are furnished with leaves which, 
 
622 CONSERVATIVE ORGANS. [LECT. XI. 
 
 from being membranous and from the nature 
 of their attachments, are moveable in the air, and 
 thence have constantly a fresh atmosphere of that 
 fluid applied to their breathing apertures; this 
 mobility of the leaf supplying, in some degree, 
 the motion of the thorax and the diaphragm in the 
 more perfect animals. The plants which have very 
 thick and immoveable leaves, on the contrary, or 
 which are devoid, of leaves, as they resemble the 
 cold-blooded and slow-moving animals in their 
 tenacity of life, like them, also, require a smaller 
 supply of air, and consequently, as we have al- 
 ready seen, are less amply supplied with breathing 
 apertures. I have not been able to ascertain whe- 
 ther the apertures themselves have the power of 
 opening and shutting; but from the appearance 
 of the orifices of these organs, as they are seen on 
 the leaf of Indian Corn, when very highly magnified 
 (see Plate 10, fig. 15), it is not improbable that 
 some degree of dilatation and" contraction takes 
 place, although we cannot determine the fact. In 
 structure these organs seem well adapted for the 
 purposes of vegetable respiration, when we con- 
 sider that the changes effected by this function in 
 the sap of vegetables in the leaf are not required 
 to be so quickly produced as those in the blood of 
 animals ; even of insects of the lowest description. 
 The air is admitted through the funnel-shaped 
 pore, whiqh perforates the cutis, into a vesicle si- 
 
LECT. XI.] ANATOMY OF LEAVES. 623 
 
 tuated under it ; and which probably communi- 
 cates with the cuticular cells, as these are in ge- 
 neral found filled with air. The aqueous contents 
 of the cells that form the parenchyma of the leaf, 
 are thus brought into immediate contact with 
 the atmosphere. It is not easy to assign a rea- 
 son why these apertures are found on the under 
 disk only of the leaves of trees, while they ap- 
 pear on both disks of herbaceous leaves; there 
 being lymphatics on both disks of the former 
 as well as of the latter description of leaves. If 
 any connexion could be traced between the re- 
 turning vessels and the apertures, the difficulty 
 would be diminished, the situation of these vessels 
 being on the lower disk of the leaves of trees. 
 
 With regard to the origin of these apertures, 
 M. De Saussure's and M. Kieser's observations 
 would lead us to believe, that they are merely the 
 terminations of numerous vascular processes 
 from the larger fasciculi, which, gradually pene- 
 trating the cuticle, are thus enabled to discharge 
 their fluids. This opinion, however, is altogether 
 hypothetical. They are so far essential that they 
 are found on every leaf in contact with the at- 
 mosphere; their structural characters, position, 
 and situation, are the same on the leaves of every 
 plant of the same species ; and their existence 
 seems to be influenced by no conditional circum- 
 stance except the presence of air; for I have al- 
 
624 CONSERVATIVE ORGANS, [LECT. XI. 
 
 ready demonstrated the incorrectness of the as- 
 sertion, that etiolated leaves are devoid of aper- 
 tures, or at least the remark is not universally 
 applicable. With regard to the fact, that they 
 are not found on submersed leaves, even of land 
 plants which are made to grow in the water, I may 
 merely observe, that the leaves produced on such 
 plants differ from those which are natural to them, 
 not in the absence of apertures only, but in form, 
 structure, and functions. 
 
 The knowledge of the structure of leaves en- 
 ables us to form a correct idea of the importance 
 of these organs in the economy of the plants. 
 We find the vessels which convey the sap from the 
 roots terminating in the leaf, and spreading out 
 their contents through its cells, to undergo certain 
 chemical changes which are essentially influenced 
 by the action of the air and light : we find, also, 
 a new system of vessels commencing here, which 
 take up again the sap thus converted into proper 
 juice and conduct it downwards, depositing in their 
 course the various secretions formed from it, either 
 in the stem or in the roots, as the nature of the 
 plant requires; and, in aid of these operations, a 
 cuticular system admirably adapted by its trans- 
 parency to transmit the rays of light into the foliar 
 cells, and by its organic apertures to admit the 
 air, and at the same time favour the exhalation of 
 the superabundant water, which the ascending 
 
 2 
 
LECT. XI.] ANATOMY OF LEAVES. 625 
 
 sap necessarily contains. But, besides fitting the 
 sap for yielding the secretions found in the bark, 
 wood, and roots of plants, the leaf itself is a 
 secerning organ, and contains in its cells and fol- 
 licles many secretions useful, undoubtedly, to the 
 plant itself; but, independent of that, of the first 
 importance in medicine and the arts; and in 
 supplying food for the support of animal life. Thus 
 the leaves of Henbane, Hyosciamus niger; Deadly 
 Nightshade, Atropa Belladonna; Wolfsbane, Aco- 
 riitum napellus and neomontanum; Hemlock. Co- 
 nium maculatum ; Fox-glove, Digitalis purpurea ; 
 the whole genus Tobacco, Nicotiana ; Wild and 
 Garden Lettuce, Lactuca virosa and saiiva; the 
 genus Thorn Apple, Datura ; Yellow-flowered 
 Rhododendron, R. Chrysanthum; the Poison Oak, 
 Rhus Toxicodendron, and many other plants, con- 
 tain alkaline principles, which produce very 
 powerful sedative and narcotic effects on the ani- 
 mal economy ; and the Prussic acid, a still more 
 direct sedative, is present as a secretion in the 
 leaves of the Laurel Cherry, Prunus Lauro-Cera- 
 sus. Bitter and tonic principles are found in 
 the leaves of the genus Wormwood, Artemisia; 
 Centaury, Chironia Centaurium ; Horehound, 
 Marrubium vulgare; Marsh Trefoil, Menyanthus 
 trifoliata; Garden Angelica, A. Archangelica ; 
 Hyssop, Hyssopus officinalis, &c. : astringent in 
 those of the Oak genus, Quercus; Bears Whortle 
 VOL. i. s s 
 
626 CONSERVATIVE ORGANS. [LECT. XI. 
 
 Berry, Arbutus uvce Ursi; almost the whole of 
 the genus Sumach, Rhus; the Tea, Thea; and 
 many other genera: and emetic in Asarabacca, 
 Asarum Europceum, &c. The purgative proper- 
 ties of the leaves of Senna, Cassia senna, and 
 of Hedge Hyssop, Gratiola officinalis ; and the 
 diaphoretic of Sage, Salvia officinalis, are well 
 known. The secretions of some leaves are so acrid 
 as to inflame and blister the skin when applied 
 to it; as those of many of the species of the 
 genus Ranunculus*; and of Savine, Juniperus 
 Sabina: on the other hand, some leaves, as those 
 of Marsh Mallow, Althea officinalis, and of Com- 
 mon Mallow, Malva sylvesiris, afford bland mu- 
 cilages; others, as those of Sorrel, Rumex acetosa, 
 and of Wood-Sorrel, Oxalis acetosella, contain 
 cooling acids: and some again, as those of the 
 Mints, Menthce; Balm, Melissa officinalis; Rue, 
 Ruta graveolens; the Cajuputi tree, Melaleuca 
 Leucadendron, &c. secrete essential oils, which 
 rouse and stimulate the animal system when taken 
 into the stomach, or even when applied to the 
 skin. As food, men employ a great variety of 
 leaves, which yield a bland fecula and saccharine 
 
 * The leaves of R.jlammula are used for raising a blister 
 in the Hebrides. They are chopped and rubbed between hot 
 stones immediately before being applied ; and generally raise a 
 blister in an hour and a half. The leaves of R. sceleratus have 
 the same effect ; but often occasion an irritable sore, which 
 cannot readily be healed. 
 
LECT. XI.] ANATOMY OF LEAVES. 627 
 
 matter, or in which the acrid secretions can be 
 easily destroyed by cooking; and the number of 
 those which might be used for this purpose, but 
 are still neglected, is very considerable*. 
 
 No distinct secerning organs have yet been dis- 
 covered in leaves, except as relates to some sac- 
 charine and resinous exudations and to the essen- 
 tial oils; and the organs producing these have been 
 termed glands. The exudations give various cha- 
 racters to the surfaces of leaves; but the oils are 
 preserved in distinct follicles; which, in many in- 
 stances, open by excretory pores, that are rea- 
 dily distinguished from the common foliar aper- 
 tures ; and through these they are exhaled, pro- 
 ducing the odours for which many leaves are 
 distinguished. I should now endeavour to de- 
 monstrate the forms and structure of these glan- 
 dular organs; but as they are found sometimes 
 on the stem as well as on the leaf, I shall not con- 
 fine myself to the examination of them as con- 
 nected with the leaf only; but as part of the ge- 
 neral vegetable appendages. 
 
 The term appendage is applied to certain or- 
 
 * The leaves of the common Dock, Rumex patientia, were 
 eaten by the ancients under the name of Lapathum; and are 
 still eaten in some places of Germany under the name of Eng- 
 lish Spinage. The leaves of R. scutatus and of many species 
 of the genus Atriplex, were also formerly used as pot-herbs, 
 and, indeed, afford very palatable and nutritious food. 
 
 ss2 
 
628 CONSERVATIVE ORGANS. [LECT. XI. 
 
 gans which are occasionally, but not invariably, 
 found connected with the universal vegetable 
 organs. They are never all present on the same 
 species of plant ; but which of them soever is 
 found on any individual is general to the species, 
 and invariably present. All of them are import- 
 ant to the plants on which they are found ; and 
 a knowledge of them, besides throwing great 
 light on vegetable physiology, is of utility to the 
 practical Botanist, in affording characters for 
 specific distinctions. The caullnar and foliar ap- 
 pendages, or those connected with the stem, 
 branches, and leaves, to which we have now to 
 direct our attention, may be classed under the 
 six following heads : Glands, Pubescence, Spines, 
 Prickles, Props, Foliaceous appendages, and ano- 
 malies *. 
 
 1. GLANDS, Glandulce. Linnaeus has defined the 
 vegetable gland to be " a little tumour excreting 
 " an humour -f^;" but this definition comprehends 
 those glands only which are external and elevated 
 above the cutis ; and, as we find many minute or- 
 gans of a structure distinct from the common tex- 
 ture of the part on which they are situated, and se- 
 
 * I have adopted this term from Mr. Keith, because I can 
 suggest no better for the classification of the objects intended 
 to be described under it. 
 
 f " Glandula est papilla humorem excernens." Phil. Bol, 
 
 *.*, 
 
LECT. XI.] CAULINAR AND FOLIAR APPENDAGES. 629 
 
 parating a peculiar fluid, embedded in the cellular 
 substance, or half sunk in the cutis, and, if elevated 
 above its surface, displaying great diversities of 
 form, its exceptionable character is evident. In 
 rejecting, however, this definition, the difficulty 
 of forming an appropriate one must be acknow- 
 ledged. A definition formed altogether on the 
 existence of the secretory function, would occasion 
 us erroneously to regard as glandular any part 
 where the presence of a fluid, distinct from the 
 common juices of the plant, might lead us to sus- 
 pect the operation of that function, although the 
 part should display no organic peculiarity sufficient 
 to authorize the application of the term gland to it. 
 On the other hand, a definition founded on struc- 
 ture alone, or on figure or position, would lead us 
 as far astray. Perhaps we shall arrive nearer the 
 truth if we take into consideration both structure 
 and function, and say that a vegetable gland is a 
 minute organ, differing in structure from the com- 
 mon texture of the part where it is situated, and 
 separating some peculiar matter from the ordinary 
 v eg eta b le fluids. 
 
 Guided by this definition, we find glands on the 
 stem and leaves, situated both under the cutis and 
 on its surface. In describing these organs some 
 arrangement is necessary ; and in looking into 
 books to know what has been done in this way, 
 we find that the arrangement proposed by Guet- 
 
 ss3 
 
630 CONSERVATIVE ORGANS. [LECT. XI. 
 
 tard, a French Phytologist, who first attempted 
 the subject, has been adopted by almost every 
 succeeding writer. He describes seven species of 
 vegetable glands : the miliary, the vesicular, the 
 scaly, the globular, the lenticular, the utricular, 
 and the cup-shaped; but as the cuticular aper- 
 tures, which he mistook for glands, constitute 
 his first species ; and the thin scales which cover 
 the fructification of the Ferns his third, there is 
 sufficient reason for rejecting this arrangement. 
 In attempting another, we must first take into 
 consideration the situation of these minute organs 
 as far as relates to their being under the cutis, 
 or exterior to it; and, consequently, I propose to 
 divide them into two classes, internal and external, 
 and to subdivide these into genera and species. 
 
 A. The INTERNAL caulinar and foliar glands 
 are probably of various kinds, but one only, the 
 follicular, has yet been detected. 
 
 1. The follicular gland, glandulafollicularis, 
 is in the form of a small sac or follicle. It is ge- 
 nerally found in the substance of leaves, and is 
 furnished with an excretory duct which opens upon 
 the under disk of the leaf. It is readily disco- 
 vered by its transparency, which gives the leaf a 
 punctured appearance when it is held up between 
 the eye and the light ; as exemplified in the leaves 
 of Perforated Saint John's Wort, Hypericum per- 
 foratum ; All Spice, Myrtus Pimenta ; the genus 
 
LECT. XI.] CAULINAR AND FOLIAR APPENDAGES. 631 
 
 Citrus, &c. A beautiful variety of this gland 
 is observed on the leaf of Coffea AraUca, si- 
 tuated in the angles formed by the parting of the 
 larger costse from the midrib : its follicle, which 
 occupies a space rather greater than the thick- 
 ness of the leaf, forms a small elevation on the 
 upper disk, and opens on the lower by a large ex- 
 cretory pore, guarded by stiff hairs inclining over it. 
 
 The real glandular part of the follicular gland 
 is cellular, and forms the parietes of the fol- 
 licle, which is the receptacle only of the secre- 
 tion; and this, in general, is an essential oil. As 
 the odours of leaves depend chiefly on the exhala- 
 tion of their essential oil, they are often regu- 
 lated by circumstances affecting the excretory 
 ducts of these follicles. Thus the duct being closed 
 by the pressure of the cells turgid with sap, in the 
 fresh stem and leaf of Sweet-scented Vernal 
 Grass, Anthoxanthum odoratum, no odour is per- 
 ceived ; but it opens, when these cells shrink, as 
 the grass dries, and, then, the agreeable perfume 
 which is peculiar to new hay is exhaled. The 
 odour is permanent in some plants, as Mint, Sage, 
 &c. but very evanescent in others, as, for example, 
 in the leaves of Gaultheria odorata, which yield a 
 very agreeable odour when fresh, but become 
 scentless a few hours after their separation from 
 the tree. 
 
 B. The EXTERNAL caulinar and foliar glands 
 
 S 8 4 
 
632 CONSERVATIVE ORGANS. [LECT. XI. 
 
 are more easily detected than the internal, and 
 appear to be more numerous. They may be ar- 
 ranged under two genera, the sessile and the pe- 
 diculated; and each of these subdivided into 
 species. 
 
 a. The sessile gland lies on the surface of 
 the stem, or of the leaf, or is slightly depressed in 
 the cutis. It comprehends three species : the 
 simple papillary, the compound papillary, and the 
 scaly glands. 
 
 1. The simple papillary gland, glandula pa- 
 pillaris simplex, is usually situated on the lower 
 disk of leaves; and, in many instances, it appears, 
 to the unassisted eye, a mere pore, exuding a drop 
 of viscous or oily fluid ; but is, in fact, a small 
 tubercular elevation. Thus on the back of the leaf 
 of Crescent-leaved Passion-flower, Passiflora la- 
 nata, the dark spots seen by the naked eye on each 
 side of the midrib, are found to be slightly elevated, 
 circular, papillary glands, with an apparent pore in 
 the centre (Plate 9, fig. 27. a.) when viewed with a 
 good glass ; but when the gland is placed under 
 the microscope, the pore is discovered to be a de- 
 pression only, covered with a very thin transparent 
 epidermis, which extends over the whole surface 
 of the gland. In general, however, the papillary 
 glands are more conspicuous ; and appear, even 
 to the unassisted eye, small elevated bodies, with 
 a broad base, placed, in some instances, as it were, 
 in a socket. Their structure is cellular; but the 
 
LECT. XT.] CAULINAR AND FOLIAR APPENDAGES. 633 
 
 cells are smaller, more regular than those of the 
 substance of the leaf, and arranged in circles. I 
 have not been able to detect any vessels passing 
 into these glands, nor to discover their excretory 
 pores ; except in the sting of the nettle, which is 
 the excretory duct of a papillary gland. A va- 
 riety of this gland, generally described as a dis- 
 tinct species, under the name lenticular, glandula 
 lenticular is, is found on the surface of the stems 
 of Stripe-flowered Psoralea, P. glandulosa, and 
 of many other dicotyledons. It is a small follicle, 
 which generally contains an oily or a resinous 
 fluid ; and differs from the internal follicular gland 
 only in its situation on the surface. 
 
 2. The compound papillary gland, glandula 
 papillarum composita, is best exemplified as it is 
 found on the leaf of the Stone Pine, Pinus pinea. 
 If we examine the surface of this leaf, with a 
 good magnifying glass, we find that it is streaked 
 with whitish lines, on which are seen small black 
 spots arranged in a regular series (Plate 9, fig. 
 28. A.). Under the microscope each of these spots 
 is discovered to be the excretory pore of a com- 
 pound gland, composed of six distinct glandules, 
 forming a ring or collar (fig. 28. B. a.) around 
 the pore (&.), which generally appears obstructed 
 by minute, dark-coloured, terebinthinous par- 
 ticles ; and is seen to be really a pore, only when 
 the cutis is very carefully raised. The glandules 
 
634 CONSERVATIVE ORGANS. [LECT. XI. 
 
 resemble the papillary glands in some degree, each 
 being a slight elevation with a depression in the 
 centre; and it is probable that these are the secret- 
 ing organs, and, severally, communicating with 
 the excretory pore, pour the fluid they secrete 
 into it; whence it is exuded: and acquires its 
 dark colour by exposure to the atmosphere. 
 
 3. The scaly gland, glandula squamom*, re- 
 sembles a minute scale attached to the surfaces of 
 the leaves on which it is found, as, for instance, 
 on that of Rhododendron punctatum. The under 
 surface of this leaf is covered with glands of this 
 species, which appear, when viewed with a good 
 glass, like small brilliant detachable scales, white 
 and shining round the edge and dark in the centre 
 (Plate 9, fig. 29. A. a.). When one of these scales is 
 placed under the microscope, the white border is 
 found to be beautifully fluted (fig. 29. B. b. c.), and 
 lying flat upon, but not attached to the surface of 
 the leaf ; and to be the loose margin of the scale 
 covering the gland, which appears to be a slightly 
 elevated papilla, discharging its secretion by se- 
 veral excretory pores which open upon the surface. 
 The real shape of the gland, however, is that of 
 an inverted cone, of which the scale is the base. 
 
 * I am surprised that the error of Guettard, who gave 
 this name to the thin scale which covers the fructification of 
 Ferns, has been copied by Mr. Keith in his System of Physio- 
 logical Botany. See vol. .i. p. 69. 
 
LECT. XI.] CAULINAR AND FOLIAR APPENDAGES. 635 
 
 It is seated in a depression of the cutis, and com- 
 municates with the interior of the leaf by means 
 of a duct, which passing through the apex to the 
 base of the cone penetrates the cutis. The texture 
 of this gland is cellular ; and its secretion is an 
 essential oil. The leaves of the Sea-side Balsam, 
 Croton Eluteria, furnish examples, also, of the 
 scaly gland *. 
 
 b. The pediculated gland is elevated from the 
 surfaces on which it is found, by an interposed 
 pedicle or stalk. It comprehends four species, the 
 cup-shaped, the knob-like, the stipitate, and the 
 branched glands. 
 
 1. The cup-shaped gland, glandula cyathifor- 
 mis 9 as its name imports, resembles a shallow cup 
 or saucer, supported on a thick, short, footstalk 
 (Plate 9, fig. 30). It is found on the petioles of 
 some leaves, as, for instance, those of the Nec- 
 tarine, Amygdalus Persica, and the Passion- 
 flower ; and in the serratures of others, as those of 
 the Bay-leaved Willow, Salix pentandra, &c. The 
 secretion is generally of a resinous character, and 
 exudes from the hollow part of the gland, which is 
 devoid of epidermis. This species of gland, like 
 the majority of the external glands, is cellular, 
 and we can distinctly trace into it a cord of both 
 
 * Sprengel has figured these in his Elements of the Phi- 
 losophy of Plants (P.-vi. fig. 8); but regards them merely a* 
 scales. 
 
636 CONSERVATIVE ORGANS. [LECT. XI. 
 
 spiral and proper vessels, which, apparently, ter- 
 minates in the substance of the gland. 
 
 2. The knob-shaped gland, glandula clavifor- 
 mis, resembles a knob or a small nail, which, in 
 the language of the artisan, has not been driven 
 home. The head, which is the glandular part, is 
 slightly convex on the upper surface; and displays 
 a rough striated border, encircling a round flat 
 spot devoid of epidermis (Plate 9, fig. 31), from 
 which the secreted fluid is discharged. The in- 
 ternal structure of this gland closely resembles 
 that of the cup-shaped gland. It is generally 
 found either on the stem or the petiole of the leaf, 
 or on both in the same plant, as for instance in the 
 Castor-oil plant, Ricinus communis. 
 
 3. The stipitate gland, glandula stipitata, is 
 so named from being supported on a long slender 
 stalk (Plate 9, fig. 15), and is, in fact, a stalked 
 variety of the cyathiform gland. It is the smallest 
 of the external glands, and is situated either on the 
 margin of leaves, as in Croton penicillatum ; or 
 on the disk, as in Sun-dew, Drosera rotundifolia. 
 
 4. The branched pediculated gland, glandula 
 pediculata ramosa, is a small hemispherical gland 
 supported on a branched stalk (Plate 9, fig. 32). 
 The appearance of moss on the stem of the Moss 
 Rose is produced by glands of this description. 
 The individual glands are cellular, devoid of epi- 
 dermis, and each is furnished with vessels, which 
 are branches of a fasciculus, which enters the 
 
LECT. XJ.] CAULINAR AND FOLIAR APPENDAGES. 637 
 
 gland-bearing stalk at its base. These glands ge- 
 nerally secrete a viscous resinous matter, which 
 is also sometimes odorous. 
 
 The minuteness of the vegetable glands pre- 
 vents me from attempting to offer you any anato- 
 mical demonstration of their structure. They 
 have, indeed, been arranged into cellular and vas- 
 cular glands by writers who have endeavoured to 
 trace their structure, and who have stated some of 
 them to be entirely cellular, and others chiefly 
 vascular ; but as we can scarcely suppose that any 
 part, completely devoid of vessels, possesses the 
 function of secretion, we must receive these state- 
 ments with caution. With regard to the use of 
 glands to the plant, at least as far as relates to 
 the conservative organs, we know nothing. They, 
 probably, do not play so important a part in the 
 vegetable as in the animal economy ; but we can 
 hazard nothing more than conjecture on the sub- 
 ject. 
 
 ii. PUBESCENCE, Pubescentia. Under this term 
 are included all the kinds of down, hairs, and 
 bristle-like bodies, found on the surfaces of the 
 conservative organs. They differ very considerably 
 in form and texture, and on these differences I 
 shall attempt such an arrangement of them as 
 may facilitate your knowledge of the subject. 
 
 All vegetable pubescence consists of small, 
 slender bodies, which are either soft and yielding 
 to the slightest impression, or *rigid and compa- 
 
638 CONSERVATIVE ORGANS. [LECT. XI. 
 
 ratively unyielding; the former are, properly 
 speaking, hairs (pili), the latter bristles (setce) ; 
 and, therefore, under these two heads every kind 
 of pubescence may be arranged. 
 
 A. HAIRS, Pili, are fine, slender, cylindrical, 
 flexible bodies found on the surfaces of the herba- 
 ceous parts of plants. Some of them are the excre- 
 tory ducts of glands, a fact which was first de- 
 tected by Guettard ; and on which Linnaeus too 
 hastily formed his definition of the hair, which 
 he describes generally to be <f a bristle-like ex- 
 " cretory duct of the plant*;" but many of them 
 are not excretory ducts, and it is not easy to con- 
 ceive any satisfactory opinion of their use to the 
 plant. In some instances indeed they serve one of 
 the purposes which Linnaeus ascribes to them ; 
 that of defending the plant from external injuries*^, 
 as we find downy and hairy leaves are not so fre- 
 quently attacked by insects as smooth ones; but 
 they can be very imperfect safeguards against 
 heat, cold, or wind ^. 
 
 When placed under the microscope, vegetable 
 hairs appear to be membranous tubes, articulated 
 in the majority of instances, often punctured, and 
 
 * " Pilus est ductus excretorius plantae setaceus." Phil. 
 Bot. 84. 
 
 f " Pubescentia est armatura plantae, qua ab ex'ternis in- 
 " juriis defenditur." Phil. Bot. 163. viii. 
 
 t " Lana servat plantas ab cestu nimio. Toraentum servat 
 " plantas a ventis." Phil. Bot. 1. c. 
 
LECT. XI.] CAULINAR AND FOLIAR APPENDAGES. 639 
 
 in some plants, as Borago laxiflora, covered 
 with warts. They are either simple or undivided, 
 or compound or branched. 
 
 1. Simple hairs (Pili simplices). The com- 
 monest form of the simple hair is that of a jointed 
 thread generally too flexible to support itself; there- 
 fore it is more commonly found variously bent and 
 waved (Plate 9, fig. 10. a. b.)*. According to its 
 degree of fineness, its quantity and the mode of its 
 application to the surfaces of stems and leaves, it 
 constitutes the characteristics of surfaces : thus the 
 surface is termed hairy (pilosus) when the hairs are' 
 few and scattered, but conspicuous, as in Mouse- 
 ear Hawkweed, Hieracium Pilosella; woolly (lana- 
 tus), when they are complicated, but, nevertheless, 
 the single hairs are distinguishable, as in Mullein, 
 Verbascum; shaggy (tomentosus) , when they are so 
 thickly matted that the individual hairs cannot be 
 distinguished ; and when the position of the hair is 
 nearly parallel to the disk, being at the same 
 time straight or very slightly curved (Plate 9, fig. 
 10. c.), and thick although unmatted, it consti- 
 tutes the silky surface, as in the leaves of Wild 
 Tansey, Potentilla anserina; Silvery Ladies' mantle, 
 Alchemilla alpina, &c. In some instances the 
 simple hair is firm enough to support itself erect; 
 
 * In all the figures of hairs and bristles in Plate 9, the size of 
 the appendage, when viewed with a common lens, is placed 
 beside its highly magnified representation. 
 
640 CONSERVATIVE ORGANS. [LECT. XI. 
 
 in which case it is usually awl-shaped, and the 
 articulations are shorter towards the base, as in 
 White Bryony, Bryonia alba (Plate 9, fig." 11): 
 it does not always, however, terminate in a point, 
 but sometimes in a small knob, as on the newly 
 evolved, succulent shoots of ligneous plants, on 
 Belladonna, &c. (ib. fig. 12). In some instances^ 
 also, as on the under disk of the leaves of Com- 
 frey, Symphytum officinale, and Agrimony, Agri- 
 monia Eupatoria, the simple hair is hooked 
 towards its apex (ib. fig. 13, 14) ; which occa- 
 sions the velvety feeling when the finger is passed 
 over the surface of these leaves, the convex part 
 of the curve of the hair being that only which 
 comes in contact with the finger. Another va- 
 riety of the simple hair, necessary to be no- 
 ticed, is that which has given rise to the term 
 glanduloso-ciliata. It is a slender hollow thread 
 supporting a small, cup-shaped, glandular body; 
 and is rather to be regarded as a stipitate gland, 
 under which name I have already noticed it, than 
 as a hair. 
 
 2. The compound hair (Pilus compositus) is 
 either feathery (plumosus), which is a simple hair 
 with other hairs attached to it laterally, as in 
 wave-leaved Hawkweed, Hieracium undulatum ; or 
 it is branched (ramosus), that is, lateral hairs are 
 given off from common stalks, as on the petiole of 
 the Gooseberry leaf; or it consists of an erect, 
 
 2 
 
LECT. XI.] CAULINAR AND FOLIAR APPENDAGES. 641 
 
 rather firm stem, from the summit of which smaller 
 hairs diverge in every direction (Plate 9, fig. 16), as 
 in Marrubium peregrinum, Melhania Erythroxy- 
 lon, &c. ; or it is starlike (stellatus), being com- 
 posed of a number of simple diverging awl-shaped 
 hairs, springing from a common centre, which is a 
 small knob sunk in the cutis (ib. fig. 17), as on the 
 leaves of Marsh Mallow, Althaea officinalis. Some 
 authors have applied the term ramenta to small, 
 flat, or strap-like hairs, which are found on the 
 leaves of some of the genus Begonias ; but I agree 
 with Sir E. J. Smith *, that they "do not merit 
 " to be particularly distinguished," and form 
 merely a variety of the simple hair. 
 
 B. Bristles, setae. These are, also, hollow 
 tubes, which are often of a different texture from 
 that of the cutis of the leaf; being rigid, sharp- 
 pointed, and either wounding the finger when it is 
 pressed upon them, or giving a very harsh, sca- 
 brous, or prickly character to the surface of the 
 stem, or of the leaves when the finger is rubbed 
 over them. They are often arranged with prickles 
 (aculei), in elementary works; but they have more 
 affinity to hairs; and, therefore, I have placed 
 them under the head of pubescence. They are 
 simple and compound. 
 
 a. Simple bristles (setae simplices) are of two 
 kinds, the awl-shaped and the spindle-shaped. 
 
 * Smith's Introduction^ p. 227. 
 VOL. 1. T T 
 
642 CONSERVATIVE ORGANS, [LECT. XI. 
 
 1. The awl-shaped bristle (seta subulata) is the 
 most common of the simple bristles : it is slightly 
 curved, and gradually tapering from the base to 
 the apex (Plate 9, fig. 18), which is rigid and very 
 sharp. These bristles, when they all incline in 
 the same direction, produce the scabrous charac- 
 ter of some leaves, which is perceived when the 
 hand is passed lightly over their surface, from the 
 apex towards the base; as exemplified in those 
 of Symphytum orientate, and many other plants. 
 A variety of the subulate bristle, found on the 
 stem and branches of the Sensitive Plant, Mimosa 
 sensitiva, is barbed on its sides (Plate 9, fig. 19) ; 
 and another variety, as exemplified on the leaves 
 of Borage, Borago officinalis, is seated on a ve- 
 sicular tubercle (ib. fig. 20), containing a fluid, 
 which is ejected through the bristle when it is 
 compressed so as to wound the finger; and which, 
 being left in the wound, excites a slight degree of 
 inflammation in the part. But the sting of the 
 Nettle is the best example of this form of bristle, 
 when it is an excretory duct of a gland ; and it 
 has, not inaptly, been compared to the fang of 
 a serpent. Its structure has been known since 
 the time of Hook, who first described it *. It con- 
 sists of two distinct parts: one, to employ Hook's 
 language, "like a bodkin, very hard and stiff, 
 
 * Micographia, p. 142. 
 
LECT. XI.] CAULINAR AND FOLIAR APPENDAGES. 643 
 
 " exceedingly transparent, and hollow from top 
 " to bottom ; the other, a little bag more pliable 
 " than the bodkin, and within it a cellular struc- 
 " ture, which contains a thin transparent liquid." 
 In figure 21, Plate 9, a. represents the hollow 
 bristle, with a drop of fluid hanging upon its 
 point; b. the cellular bag or sponge which con- 
 tains the poison, and in which, also, it is pro- 
 bably secreted. When the bristle penetrates the 
 skin of the finger, or any other part of the 
 body, it is pressed down upon the sponge, from 
 which a quantity of the liquid is thus squeezed, 
 and rising in the tube, is ejected and depo- 
 sited beneath the skin, causing the inflammation 
 and painful irritation which succeed. 
 
 2. The spindle-shaped bristle ( seta fusiformis) 
 is, as its name implies, thickest in the centre and 
 acuminated at each end. It lies parallel to the 
 surface of the leaf, to which it is fixed by a very 
 short footstalk (Plate 9, fig. 22) ; is hollow, and 
 contains a coloured liquid, which apparently 
 enters it through the footstalk : but I have not 
 been able to discover any opening in the bristle, 
 through which it could be ejected, as in the sting 
 of the Nettle. This form of bristle is peculiar 
 to the genus Malpighia, at least I have never 
 met with it on any other plants. 
 
 b. Compound bristles (setce composites) are 
 
 TT2 
 
644 CONSERVATIVE ORGANS. [t,ECT. XI. 
 
 almost always solid. The term comprehends two 
 species of bristles: the forked and the fasciculated. 
 
 1. Forked bristles (setcefurcatce) are, in some 
 instances, merely rigid, hairlike bodies terminating 
 in two or three diverging points (Plate 9, fig. 23, 
 24), as in Thrincia hispida; but in other cases, as, 
 for instance, on the stems and leaves of the Hop 
 plant, Humulus lupulus, the stalk of the bristle, 
 which is supported on a firm cellular tubercle, is 
 very short, and its forking extremities resemble 
 two flattish, awl-shaped bristles (Plate 9, fig. 25) 
 pointing in opposite directions. 
 
 2. Fasciculated bristles (setce fasciculatce) con- 
 sist of a number of simple straight bristles diverg- 
 ing from a papillary knob, as in Cactus flageUi- 
 
 formis (Plate 9, fig. 26). 
 
 There is still another species of pubescence 
 that cannot properly be arranged with any of those 
 which have been described; it is found on a spe- 
 cies of Houseleek, Sempervivum arachnoideum, 
 extending like a very fine thread, stretching from 
 the tip of one leaf to that of another, and resem- 
 bling so exactly a spider's web, that the plant 
 has been named arachnoideum. 
 
 The pubescence of plants is liable to be af- 
 fected by climate, soil, culture, and other circum- 
 stances: thus, to mention a few only of these 
 changes, Sweet-scented Woodruff, Asperula odo- 
 rafa, is villous, or covered with shaggy hairs, when 
 it grows in the shade, and scabrous when in ex- 
 
LECT. Xi.] CAUIINAR AND FOLIAR APPENDAGES. 645 
 
 posed places: the Turk's-cap Lily, Lilium Mar- 
 tagon, is found covered with rough hairs, or 
 hirsute, in the woods, and yet is smooth when 
 cultivated in gardens ; and some of the Mint tribe, 
 as for instance Mentha hirsuta^ naturally hairy, 
 are occasionally found smooth; and yet, "if 
 " transplanted soon resume their former habits*." 
 Notwithstanding these changes, and although Lin- 
 nseus regards distinctions founded on pubescence 
 as ridiculous-}-, yet systematic Botanists have suc- 
 cessfully founded specific distinctions on the di- 
 rection of the pubescence; for, as it has been 
 justly remarked, although " the degree of pubes- 
 " cence varies from culture, and even its struc- 
 " ture be changeable," yet " its direction is as 
 " little liable to exception as any character that 
 "vegetables present^:" and, consequently, in 
 treating of the hairs and bristles on plants, their 
 direction is necessary to be noticed. When the hairs 
 are placed in a line on two sides only of a stem, 
 the pubescence is said to be bifarious (brfariam 
 pilosus) ; as in Germander, Veronica Chcemcedrys; 
 its direction is horizontal (horizontalis) on the 
 flower-cup in Corn Mint, Mentha arvensis; and 
 on the stems of the common Red Poppy, Papaver 
 Rhdeas ; and patent or spreading (patens) on the 
 
 * Smith's Introduction, p 228. J Ibid. p. 229. 
 
 f *' Pubescentia ludicra est differentia, cum cultura saepius 
 deponantur." Phil. Bot. 272. 
 
 TT3 
 
646 CONSERVATIVE ORGANS. [LECT. XI. 
 
 pedicles of fragrant sharp-leaved Mint, Mentha 
 acutifblia. In these and similar instances the 
 direction forms essential distinctions in the spe- 
 cific characters of the plants. Indeed, Sir E. 
 J. Smith, speaking of the direction of the hairs 
 about the calyx and flower-stalk in the Mint tribe, 
 says, " I have found it the only infallible distinc- 
 " tion between one Mint and another." Hairs are 
 said to be ascending (ascendentes) when they are 
 directed towards the summit of the part on which 
 they are seated ; descending ( dependent es) when 
 towards the base; and appressed (adpressi) when 
 they are closely applied lengthways to the part, as 
 on the peduncle of long smooth-headed Poppy, 
 Papaver dubium, which is distinguished from the 
 common red Poppy chiefly by this character. A 
 very curious effect of the direction of hairs is per- 
 ceived in the pitchers or ascidia of Sarracenia, 
 and in some tubular flowers. The stiff hairs, in 
 these instances, by pointing inwards and towards 
 the bottom of the cavities in which they are found, 
 perform a service similar to the wires which point 
 inwards at the mouth of a mouse-trap, preventing 
 insects which enter these cavities from escaping 
 out of them. 
 
 With regard to the uses of the hairs, some 
 Phytologists have considered them to be trans- 
 spiring and absorbing organs. I have already de- 
 monstrated that the cnticular pores are the trans- 
 
LECT. XI.] CAULINAR AND FOLIAR APPENDAGES. 647 
 
 piratory organs of plants ; and, independent of 
 other reasons that might be advanced against the 
 opinion that they are absorbents, we have only 
 to notice the fact, that the succulent plants of arid 
 soils, which live almost entirely by cuticular ab- 
 sorption, are often nearly devoid of hairs: besides, 
 they are observed in the interior of plants, as in 
 the vacuities within the stems of aquatics, where 
 their absorbent function, did they possess it, is 
 not required. Whether their presence can modify 
 the action of light, air, and temperature upon 
 plants, has not yet been determined ; and we must 
 confess that we are still ignorant of the use of these 
 minute organs in the vegetable economy. 
 
 iii. THORNS, Spince. These are rigid, sharp- 
 pointed processes firmly connected with the tex- 
 ture of the parts on which they appear*. They 
 are either simple or compound. The simple spine 
 (spina simplex) is a slender tapering body ter- 
 minating in a sharp point, and covered with a 
 bark and cuticle the same as those of the stem or 
 the branch: it is, also, generally solitary, as in the 
 common Hawthorn (see cut 1, p. 268) and the 
 Cockspur-thorn, Mespilus oxycantha, and Crus 
 galli; Box-leaved Staff Tree, Celastrus buxifolius, 
 &c. The compound spine (spina composita) com- 
 prehends several kinds, which are named accord- 
 
 * Linnaeus defines the thorn thus : " Spina est mucro plantae 
 " e Hgno plantae protrusus." Phil. Bot. 84. 3. 
 
 TT4 
 
648 CONSERVATIVE ORGANS. [LECT. XI. 
 
 ing to the number or division of their parts: thus 
 it is termed forked (bipartita) when it is divided 
 into two points, or appears like two simple spines, 
 united near the base; as in two-spined Arduina, 
 Arduina bispinosa: three-pronged (tripartita), 
 when there are three points, as in three-t horned 
 Gleditchia, Gleditchia triacanthes ; and branched 
 (ramosa), when it is divided into many lateral 
 points. 
 
 In respect of situation, thorns are caulinar, 
 petiolar, or foliar. They are said to be terminal 
 (terminates) when they are situated at the termi- 
 nation of a branch or shoot, as in Buckthorn, 
 Rhamnus catharticus ; axillary (axillares), when 
 seated in the upper angle formed by the petiole 
 of the leaf and the branch, as in the Lemon tree, 
 Citrus medico; superaxillary ( super axillares), 
 when a little above that angle, as in Gleditchia 
 triacanthes; and subaxillary (infer axttUxrcs) , when 
 in the opposite situation. 
 
 The anatomical structure of the thorn is, with 
 a few exceptions, the same as that of the branch 
 on which it remains as a part, after the bark is re- 
 moved; and in many instances it appears to be 
 merely an abortive shoot, arising, as Malpighi 
 suggested, from defective nutriment; but this 
 cause can be regarded as occasional only, for, 
 were it general, every description of thorn would 
 entirely disappear under culture, which is not the 
 
LECT. XI.] CAULINAR AND FOLIAR APPENDAGES. 649 
 
 case. In some instances, however, as in the Pear 
 tree, Pyrus sativa, and in some other fruit-trees 
 which have thorns in their wild state, they dis- 
 appear by culture. The petioles of several pin- 
 nate leaves, as those of Astragalus Tragacantha, 
 which are persistent, become acuminated, and 
 change into thorns, after the leaflets fall ; the 
 peduncles, also, of some flowers, as those of 
 Pisonia, undergo a similar transformation: and 
 in the genus Mimosa and a few other tribes of 
 plants, we find that the stipules* sometimes be- 
 come ligneous, and pass into thorns. The struc- 
 ture of the foliar thorn, which appears either 
 on the margin of the leaf or on the costee, does 
 not so closely resemble that of the part on which 
 it is seated. It generally consists of a cord of 
 vessels derived from the nearest fasciculus of the 
 leaf, enclosed in a firm cellular tissue, and co- 
 vered with a horny cuticle. 
 
 iv. PRICKLES, Aculei, may be defined rigid 
 sharp-pointed processes that do not adhere firmly, 
 but come off with the bark of the parts on which 
 they are seated (see cut 2 p. 268) -f~. They are, in 
 general, laterally compressed, and either straight 
 
 * As these organs have not yet been described, it is ne- 
 cessary to state here, that they are small foliaceous appendages, 
 generally situated on each side of the base of many petioles. 
 
 j " Aculeus est mucro plantae, ejusdem cortici tantum af- 
 " fixus." Phil. Got. 8-1-. 4. 
 
650 CONSERVATIVE ORGANS. [LECT. XI. 
 
 (rectij, that is, free from any curvature, and di- 
 minishing gradually from the base to the apex, as 
 on the Scotch Rose, Rosa spinosissima ; or curved 
 (curvi), as on the Bramble, Rubusfruticosus. If 
 the curved prickle have its point directed up- 
 wards, it is said to be incurved (incurvus vel in- 
 Jlexus), and if in the opposite direction, recurved 
 (recurvus vel reflexus). It is, also, in some 
 instances spiral (circinnatus) , with the apex 
 turned inwards, as in the genus Hugonia. Like 
 the thorn, the prickle is simple or compound, ac- 
 cording as it has one or more points ; and it is 
 termed caulinar, petiolar, or foliar, from its si- 
 tuation being on the stem, or on the branch, the 
 petiole or the leaf. It is in general solitary ; but 
 in some plants prickles are always found in pairs 
 (geminati) ; and on others, as for example the 
 Barberry, Berberis vulgaris, several stand together 
 on the same plane, and are said to be palmated 
 (palmati). Prickles consist of condensed cellular 
 matter covered with an epidermis, which becomes 
 dry, hardj, and coloured with age. They originate 
 immediately under the cuticle; and when picked 
 off leave no impression deeper than the exterior 
 layer of the bark. Indeed in the majority of in- 
 stances they appear to be productions of that layer, 
 and consist altogether of a mass of oblong cells, 
 which become more condensed and tubular as 
 they approach the point, and over which the 
 
LECT. XI.] CAULINAR AND FOLIAR APPENDAGES. 651 
 
 common cutis of the part on which they are si- 
 tuated is reflected. Willdenow states the prickle 
 to be vascular ; but I have not been able to detect 
 any vessels in it, unless we regard the tubular 
 cells as vessels *. They are a more permanent ap- 
 pendage than thorns ; not at all liable to disap- 
 pear by culture ; and, consequently, are better 
 fitted for forming specific distinctions. 
 
 Linnaeus regarded thorns, prickles, and bristles 
 as the armour of plants ; and the poetical ima- 
 gination of Darwin has led him to suppose, that 
 the great Author of all things has impressed on 
 organized bodies " a power of producing armour 
 " to prevent those more violent injuries which 
 "would otherwise destroy them -f- ;" and, conse- 
 quently, that plants, now unprotected, may ob- 
 tain bristles and other defensive organs in the pro- 
 gression of time. But although the depredations 
 of animals upon the tender foliage of plants are 
 occasionally checked by these organs, yet, such 
 fanciful notions as those I have just quoted, and 
 indeed most of those which our reasonings upon 
 final causes lead to, are neither philosophical nor 
 accordant with correct observation; and we must 
 
 * Willdenow, in his Principles of Botany, 270, says, 
 " This (the prickle) consists of reticular, more or less ex- 
 " panded, adducent vessels, and a few air vessels, and is co- 
 " vered with the vascular cutis. 1 ' Translation. 
 
 f Phytologia, Sect. xiv. 3. 2. 
 
65 % 2 CONSERVATIVE ORGANS. [LECT. XJ. 
 
 confess our ignorance of the utility of this de- 
 scription of armature in the vegetable economy. 
 Man, however, has ingeniously taken advantage 
 of its existence for his peculiar benefit; and 
 many of those spiny and prickly shrubs, which 
 originally opposed his progress in penetrating to 
 the depths of the primeval forests, are now trained 
 as useful and ornamental fences around those 
 portions of the soil which the arm of Cultiva- 
 tion has wrested from the dominion of Nature. 
 
 v. PROPS, Fulcra. Under this term, Linnaeus 
 and several other phytological writers have com- 
 prehended a variety of vegetable appendages, 
 which afford no prop or support to the plant *. I 
 confine its application to those organs by which 
 climbing and weak flexible stems attach them- 
 selves to one another, to firmer plants, and to 
 other objects in their vicinity, for support. By 
 these means many plants, which would remain 
 prostrate upon the earth, elevate themselves to the 
 summits of the highest trees; and, in tropical 
 countries, where vegetation revels in all the lux- 
 uriance of its powers, the Lianas, as these plants 
 are termed, hanging down in festoons adorned 
 with blossoms, form the richest garniture of the 
 forests. There are four kinds of vegetable props, 
 the tendril, the claw, the hook, and the bladder. 
 
 * " Fulcra adminicula plantae sunt, pro commodiore sus- 
 44 tentatione ; numerantur hodie vii. Stipula, Bractea, Spina, 
 Aculeus, Cirrhus, Glandula, Pilus." Phil. Bet. 84. 
 
LKCT. XI.] CAULINAR AND FOLIAR APPENDAGES. 653 
 
 a. The tendril, Cirrhus*, is a long, cylindrical, 
 slender, spiral body issuing from various parts of 
 plants. The tendril is either simple (simplex), 
 consisting of one undivided piece, as in Bryony, 
 Bryonia dioica, and square-stalked Passion-flower, 
 Passiflora quadrangular is (Plate 4, fig. 8. a. a.) ; 
 or compound (compositus), consisting of a stalk va- 
 riously branched or divided. When there are two 
 divisions, the compound tendril is termed bifid 
 (bifidus), as in Marsh Lathy rus, L. palustris, 
 Smooth Tare, Ervum tetraspermum, &c. ; trifid 
 (trifidus), when there are three, as in rough-pod- 
 ded Lathyrus, L. hirsutus, and in the Garden Pea ; 
 and branched (ramosus vel multifidus), when the 
 divisions are more numerous, as in Everlasting Pea, 
 Lathyrus latifolius (Plate 4. fig. 7) ; climbing Cobea, 
 C. scandens, &c. Tendrils rising from the stem, or 
 the branches, in the axillae of the leaves, are named 
 axillary (axillares), as exemplified in the Passion- 
 flower (Plate 4, fig. 8) ; subaxillary (subaxillares), 
 when they originate below the leaf; lateral ( late- 
 rales), when at one side of it, as in Bryony; and 
 opposite (oppositifolii), when they are directly op- 
 posite to the insertion of the leaf, as in the Vine, 
 Vitis. They are said to be petiolar (petiolares), 
 when terminating the common petiole of a com- 
 pound leaf, as in Everlasting Pea (Plate 4, fig. 7) ; 
 
 * " Cirrhus est vinculum filiforme spirale, quo planta alio 
 " corpori alligatur." Phil. Bot. 84-. 5. 
 
654 CONSERVATIVE ORGANS. [LECT. XI. 
 
 and foliar (foliares), when they are a continuation 
 of the midrib of a simple leaf, as that of superb 
 Gloriosa, G. superba. The petiolar tendril is 
 sometimes distinguished by the number of leaf- 
 lets which grow under it; thence we find in sys- 
 tematic authors the terms Cirrhi diphylli, tetra- 
 phylli, and polyphylli. The flower-stalks even of 
 some plants, as those of smooth-leaved Heart- 
 seed, Cardiospermum Halicacabum, bear tendrils. 
 Tendrils closely resemble petioles in their struc- 
 ture ; but not so intimately as to lead us to adopt 
 the opinion of Willdenow, that they are merely 
 petioles, which not having exhausted their sap in 
 forming the leafy expansion, become too feeble to 
 keep their straight direction, and have thence ac- 
 quired their twisted shape*. If we examine a 
 transverse slice of a tendril of Bryony, under the 
 microscope, and compare it with a slice of the 
 petiole which rises at its side, we shall find that 
 although they agree in some particulars, yet, they 
 differ in others. The cortex of both closely re- 
 sembles that of the stem (see p. 415) ; and the 
 internal structure in both, also, consists of fas- 
 ciculi of spiral and proper vessels embedded in a 
 cellular parenchyma. But the number of these 
 fascicles in the petiole is always nine, and in the 
 tendril four or five only: in the former, also, the 
 
 * Principles of Botany, 271. 
 
LfiCT. XI.] CAULINAR AND FOLIAR APPENDAGES. 655 
 
 fascicles are of different sizes, and arranged in a 
 regular series according to their sizes, the largest 
 being towards the convex side of the petiole, and 
 the two smallest, which are more distant from one 
 another than the others, at each angle of the con- 
 cave side ; whereas all are of the same size and 
 equidistant in the tendril. The structure of the 
 fascicles themselves also differs, for, in. the ten- 
 dril, we find three spiral vessels only in each fas- 
 cicle, arranged in one line extending inwards; 
 while in the petiole each fascicle contains from five 
 to nine of these vessels arranged in two or three 
 lines. From these remarks, although we find 
 that the structure of the tendril closely resembles 
 that of the stem and the petiole, yet, it is evident 
 that this organ cannot be regarded as an abortive 
 leaf. The resemblance of the tendril to the stem 
 is even still closer, as far as regards the cutis, for 
 in both we find pneumatic pores, in that portion 
 of it which covers the green streaks ; a fact which 
 suggests the idea that these streaks perform, in 
 both, the functions of the foliar expansion. But 
 the most satisfactory proof of the affinity of all 
 these parts is the fact, that a ypung shoot, which 
 Mr. Knight grafted upon the tendrils of the Vine, 
 succeeded nearly as well as if the operation had 
 been performed on the stem or the branch. This 
 similarity of structure occasionally produces the 
 transmutation of one part into another : I noticed 
 
 
656 CONSERVATIVE ORGANS. [LECT. XI. 
 
 to you that of petioles and other organs into 
 spines ; and I have now to state that a similar 
 change into tendrils is occasionally observed : as 
 exemplified in the stipules in Smilax. 
 
 The tendril is at first tender, green, and put 
 forth in a straight direction ; but it gradually be- 
 comes firmer in its texture, occasionally acquires 
 colour, and always assumes the spiral character. 
 When all the gyrations are regular in the same 
 direction, the tendril is said to be convolute ( con- 
 volutus); and revolute (revolutus), when it winds 
 itself irregularly, sometimes on one side, some- 
 times on the other. Phytologists have endea- 
 voured to explain the cause of the spirality of 
 tendrils: their opinions, which are by no means 
 conclusive, shall be noticed when we treat of the 
 movements of plants. 
 
 b. The claw (clavicula) is a small thread-like 
 body which is protruded from the stems of some 
 plants ; and adheres so firmly to the surfaces of 
 other bodies, as to enable the plants producing it 
 to elevate themselves from the ground. By means 
 of this description of prop, the Ivy and the 
 Cissus climb not only to the summits of the highest 
 trees, but up the face of the smoothest perpendi- 
 cular rocks, and to the battlements of the loftiest 
 towers; thus rendering picturesque the monotony 
 of the naked cliff, and, by the richness of their 
 living tracery, adding a new interest to the moul- 
 dering pile of antiquity. 
 
LECT. XI.] CAULINAR AND FOLIAR APPENDAGES. 657 
 
 There are two varieties of vegetable claws, the 
 cirrhal and the radicular. 
 
 1. The cirrhal claw (clavicula cirri for mis ) 
 resembles the branched tendril, except that each 
 of the branches is terminated by a small fleshy 
 knob ; which spreading out in the shape of an 
 oval disk, adheres strongly to a wall or any flat 
 surface with which it comes in contact. In the 
 Virginian creeper, Cissus hederacea, the claw, 
 which is of this description, is opposite to the 
 leaf, like the tendril of the Vine, and is spiral in 
 its branches, so that it performs a double office, 
 acting sometimes as a tendril by twining round 
 slender cylindrical bodies, but more frequently as 
 a claw. The internal or anatomical structure of 
 this species of claw, as far as regards its stalk and 
 branches, is exactly the same as that of the ten- 
 dril, and, like it, originates from the alburnum of 
 the stem : the claw itself consists chiefly of cel- 
 lular matter, which, being a continuation of the 
 pith of the other parts of the organ, is here 
 checked in its extension and swells out laterally. 
 The under part of the claw is covered with 
 scarcely any cutis. 
 
 Three theories exist with regard to the mode 
 by which this organ adheres to smooth surfaces : 
 some writers adopting the opinion of Malpighi, 
 that it is produced by a viscous fluid, which is fur- 
 nished by small papillae on the under surface of 
 VOL. i. u u 
 
658 CONSERVATIVE ORGANS. [LECT..XI. 
 
 the disk or flattened knob : others contending 
 that the adhesion is produced by the disk acting 
 like a piece of thick moistened leather at the end 
 of a cord, such as boys employ for lifting stones, 
 which adheres by the external air pressing it 
 closely to the surface on which it is applied : and a 
 third set imagining that it operates by exhausting 
 the air in the same manner as is done by the 
 foot of the fly, and of one species of lizard, 
 which can run up smooth perpendicular walls, 
 and along the ceilings of rooms*. I am dis- 
 posed to set aside all these opinions, and to regard 
 the attachment as the effect of a real radication; 
 having found that the inferior surface or sole of 
 the knob, which terminates each branch of the 
 claw, is studded with minute stellated fibrils ; 
 which entering into the almost invisible pores of 
 stone, bricks, &c. swell, and maintain the claw 
 firmly attached. I am confirmed in this opi- 
 nion, by the fact, that these claws will not ad- 
 here to glass, to Parker's cement, and other very 
 close grained bodies; and that they adhere strongly 
 to stones and other bodies long after the death of 
 the plant. 
 
 Like tendrils these claws turn always from the 
 light ; and, from the experiments of Mr. Knight, 
 
 * For a description of the apparatus necessary for producing 
 this effect in the foot of the lizard, see a paper by Sir Everard 
 Home, Phil. Trans, 
 
LECT. XI.] CAULINAR AND FOLIAR APPENDAGES. 659 
 
 this property is so strong, that a piece of dark-co- 
 loured paper placed at the distance of a few inches 
 from them, and changed to different sides of the 
 plant, has the power of altering their direction. 
 The cause of these movements shall be afterwards 
 investigated. 
 
 2. The radicular claw (clavicula radiciformis) 
 is a small cylindrical body, resembling a radicle, 
 which is protruded from the stem ; as exemplified 
 in the Ivy and the Ash-leaved Trumpet-flower, 
 Bignonia radicals. The claws of the Ivy are pro- 
 truded in lines, generally on the side of the stem 
 which is next to the wall on which the plant is 
 supported (fig. 1. p. 250). This is probably owing 
 to the greater moisture and shade on that side 
 being favourable to their formation, as in the case 
 of the real roots *, which appear on a stem by sur- 
 rounding a portion of it with a ball of moist 
 earth ; or of those which protrude spontaneously 
 under peculiar circumstances, as in the case of the 
 Laurel, mentioned in page 197: nor is this opi- 
 nion rendered more problematical by the fact, that 
 the radicular claws are put forth on every side of 
 the old^r stems of the Ivy, giving them a bristled 
 aspect ; for, as in the case of branches and roots, 
 the rudiments of these claws may exist in the 
 stem, although they are not protruded, until cir- 
 
 * I have already noticed (p. 280) the fact, that these claws 
 become perfect roots under certain circumstances. 
 
 uu2 
 
660 CONSERVATIVE ORGANS. [LKCT. XI 
 
 cumstances favouring their development occur: 
 and the stem having ceased to throw out claws 
 on the side next the wall where they origin- 
 ally appeared, a smaller degree of shade and 
 moisture is now sufficient for the development of 
 those which remain unprotruded. In plants of 
 Bignonia radicans, which are not trained upon a 
 wall, but supported by sticks in pots in the 
 greenhouse, the claws are put forth in clusters at 
 four opposite points around the stem near the base 
 of each pair of leaves; for here, circumstances being 
 equal on all sides, the power of the stem to pro- 
 trude ciaspers is not diminished in one part by 
 being increased on another, and, consequently, 
 the natural effort takes place on all sides, in the 
 same degree. 
 
 In structure, the radicular claw closely re- 
 sembles both the petiole and the radicle. In the 
 Ivy it consists of a cortex inclosing a cellular 
 mass in which the vessels are embedded, and ar- 
 ranged in five distinct fasciculi, which evidently 
 proceed from those of the ligneous, or rather al- 
 burnous part of the stem, although Mr. Knight 
 has remarked (Phil. Trans. 1812) that the claw of 
 the Ivy " appears to be a cortical production only. v 
 The vascular fasciculi are given off nearly at 
 right angles with those of the stem; and are 
 placed at equal distances from one another, in a 
 circle nearer to the centre than to the cortex of 
 
LECT. XI.] CAULINAR AND FOLIAR APPENDAGES. 661 
 
 the organ. In Bignonia the vessels appear more 
 condensed, forming one large central fascicle. 
 The epidermis in both is studded with minute 
 fibrils like the radicle ; and these are the real ad- 
 hering organs when the claw is applied to any 
 solid body ; for the adhesion is not confined, as in 
 Cissus, to a knob at the point of the organ, but 
 extends over as much of its surface as is in contact 
 with the body to which it adheres. 
 
 Some writers have classed with this descrip- 
 tion of prop the small tubercles, or absorbing warts 
 (haustoria), by which a few parasitic plants, for 
 instance the Dodder, Guscuta, fix themselves on 
 other plants. But these warts are of a mixed 
 character, performing, under all circumstances, 
 at the same time, the functions both of an attach- 
 ing prop and of a nutrient absorbing organ. 
 
 c. The bladder (ampulla*). This is a small 
 membranaceous bag attached to the roots and the 
 immersed leaves of some aquatic plants, render- 
 ing them buoyant: on which account I have placed 
 it among the props. In shape, the bladder is ge- 
 nerally globular ; but in common Hooded Milfoil, 
 Utricularia vulgaris, it is pear-shaped. It con- 
 tains a watery fluid and a small bubble of air, 
 which enables it to give buoyancy to the parts to 
 which it is attached ; and which must be either 
 
 * Linnaeus terms it a follicle. " Folliculi sunt vasa acre 
 " distenta." Phil. Dot. 163. ix. 2. 
 
 tJU 3 
 
662 CONSERVATIVE ORGANS. [LECT. XI. 
 
 separated from the water, and absorbed through 
 the substance of the sac, or is a secretion of the 
 plant. All the species of Utricularia, which are 
 not uncommon in our ponds and ditches, have 
 these bladders attached to the roots ; but in Al- 
 drovanda vesiculosa, an inhabitant of the Italian 
 marshes, they are present as foliar appendages. 
 
 d. The hook (hamus) is generally described 
 among the bristles, and in point of structure, in 
 the majority of instances, it certainly belongs to 
 these bodies ; but I prefer placing it here, as it is 
 in every sense of the word a real fulcrum. It is 
 well illustrated in Cleavers, Galium Aparine, the 
 angles of the stalk and the margin and midrib of 
 the leaves of which are furnished with hooks, 
 which enable the plant to climb to the tops of the 
 hedges near which it is generally found. The 
 most beautiful specimen, however, of the ve- 
 getable hook is found on the pitcher of Nepenthes 
 (see p. 672), in which it serves the purpose of sup- 
 porting that curious appendage, when it is over- 
 loaded with fluid. 
 
 vi. Foliaceous appendages. These, as their 
 name implies, resemble leaves in several particu- 
 lars ; and this similitude extends even to their 
 anatomical structure. There are three kinds of 
 foliaceous appendages ; the stipule, the bracte or 
 floral leaf, and the pitcher. 
 
 a. The stipule (stipula) is a foliaceous organ, 
 
LECT. XI.] CAULINAH AND FOLIAR APPENDAGES. 663 
 
 which in some instances accompanies the proper 
 leaf, yet is distinct from it : and, in others, is at- 
 tached to the petiole, appearing as a part of the 
 leaf itself*. It is not a universal and not always 
 a permanent organ. In some instances it is fuga- 
 cious (fugax, caduca), accompanying the leaves in 
 the bud only, and falling at the moment of their 
 evolution, or before they are fully expanded ; as 
 is the case in the Lime tree, Tilia Europcea, and 
 the Tulip tree, Liriodendron tulipifera: in others 
 it is deciduous (decidua), or falls with the leaf, 
 which is the most common occurrence ; but in 
 this case it occasionally appears withered (mar- 
 clda) before the leaf falls, although it remains at- 
 tached: and in others again, it remains after the 
 natural fall of the leaf, or is persistent (persist ens), 
 as in Downy Sea-side Grape, Cocoloba pubescens. 
 Stipules vary in size, number, form, substance, 
 and situation, in different plants; and these diversi- 
 ties constitute, occasionally, excellent specific dis- 
 tinctions. The presence or the absence of stipules 
 has, also, been regarded as an indication "that 
 " plants belong to the same natural order and even 
 " genus ;" but Sir E. J. Smith has justly remarked 
 this is not invariably the case. " Some species of 
 " Cistus have stipulas, others none, which is nearly 
 
 * " Stipula est squama, quae basi petiolorum aut peduncu- 
 ** lorum enascentium utrinque adstat." Phil. Bot. 84. 1 . 
 
 U U 4 
 
664 CONSERVATIVE ORGANS. [LECT. XL 
 
 " the case with the Grasses *." The diversity of 
 size of stipules in different plants is very consider- 
 able; but this circumstance is seldom noticed by 
 Botanical writers. In respect of number, they are 
 most commonly twin (gemince), one being si- 
 tuated at each side of the insertion of the leaf; 
 but in some instances, as the Sun-Rose, Hell- 
 anthemum, they are in fours; and in the Bar- 
 berry, Berber is ; in some species of the Honey- 
 flower, Melianthus, and in many other plants, they 
 are single (solitarice). The form of the stipule is 
 nearly as diversified as that of the leaf, and it re- 
 ceives the same appellations; thence we find the 
 terms stipulce subrotundce, ovales, lunatce, sagit- 
 tatce, semisagittatas, &c. &c. in systematic works, 
 and, consequently, the terms which have been ex- 
 plained, descriptive of the margin, apex, base, sur- 
 face, as well as those designating the distinct, con- 
 joined, sessile, and petiolated characters of leaves, 
 are applicable to this organ. In point of substance, 
 the stipule is termed foliaceous (foliacea), when it 
 resembles the leaf in colour and consistence, which 
 is most usual : membranous (membranacea), when 
 it is thin, nearly semitransparent, and in some de- 
 gree coloured, as in Amphibious Persicaria, Poly- 
 gonum amphibium; the Magnolia, and Fig tribe, 
 &c.; and chaff-like (scariosa), when it is dry and 
 
 * Smith's Introduction, p. 220. 
 
LECT. XI.] CAULINAK AND FOLIAR APPENDAGES. 665 
 
 sernitransparent, as in many species of the Fir tribe, 
 Pin-us; Knot-grass, Polygon um aviculare; Shrubby 
 Cinquefoil, Potentilla/r?^/cosa, &c. With respect 
 to situation, or attachment, stipules are most com- 
 monly lateral (laterales), which implies that they 
 stand at the base of the petiole, on each side of it, 
 as in Passiflora, Lathy rus, &c. ; but the term in- 
 termediate (intermedice) is used when their situa- 
 tion is on each side of the stem, between opposite 
 leaves, as in many of the Geranium tribe, and in 
 the Coffee plant, Coffea arabica. They are said 
 to be embracing (amplexantes vel amplexicaules), 
 when their base surrounds the stem, as in the Mul- 
 berry, Moras ; the Fig, &c. ; and sheathing ( va- 
 ginantes), when they inclose a portion of the stem 
 like a sheath, as in the natural families of Poly- 
 gonece and Rubiacece ; in which case they are appa- 
 rently a mere dilatation of the internal part of the 
 petiole. When the sheathing stipule separates at 
 the top from the stem, and forms a projecting bor- 
 der, it is termed salver- shaped (hypocraterifor- 
 mis), as in the Oriental Plane (see d. d. cut p. 460); 
 Persicaria, Polygonum orientate, &c. When the 
 attachment is upon the petiole itself, it is either 
 marginal (marginalis petiolo adnata), resembling 
 a membranous border extended along the sides of 
 the petiole, as in the Rose tribe (75. p. 515), the 
 Cinquefoils, the Pepper Plant, Piper nigrum, &c. ; 
 or intrafoliaceous (infrafoliacea vel intrapetiolaris), 
 
666 CONSERVATIVE ORGANS. [LKCT. XI. 
 
 which implies that it is situated between the stem 
 and the petiole, with which it is united at the 
 lower part only, as in common Clover, Trifolium 
 prat ens e ; or extrafoliaceous (extrqfbliacea}, when 
 it is the reverse of the former. When stipules are 
 situated at the basis of the secondary footstalks 
 in compound leaves, as in Chinese Dolichos, D. 
 sinensis, and Hedysarum gyrans (97. p. 523), they 
 have been termed stipellae by M. Decandolle ; but 
 the distinction is superfluous. The ramenta of 
 some authors; the ochrea of Rottball*; the ligula 
 or membranafoliorum of the old writers, which is 
 a white membranous fringe, that crowns the 
 sheathing part of the leaf, encircling- the culm in 
 many grasses; and the sheath, which covers 
 each leaf before it is evolved, in some plants, as 
 exemplified in the genus Liriodendron, and the 
 Magnolia tribe (see cuts p. 474), are stipules. 
 I have already described the peculiar function of 
 this sheath (p. 475) : with regard to the functions 
 of stipules in general, little is known, although in 
 some instances they supply the place of the leaves : 
 thus the Yellow Vetchling, Lathyrus Aphaca, has 
 one or two pairs of real leaves only on the seedling 
 plants, which soon disappear, and their place is 
 afterwards supplied entirely by the stipules -}~. 
 Like some other parts of the vegetable body, the 
 
 * Willdenow *s Principles of Botany, 51. 
 t Smith's Introduction, p. 221. 
 
LECT. XI.] CAULINAR AND FOLIAR APPENDAGES. 607 
 
 stipule is also liable to undergo transformations : 
 it becomes a tendril in Smilax, and a prickle in the 
 Acacia. 
 
 b. The braete, or floral leaf (bractea), is a 
 foliaceous appendage, which appears in the vici- 
 nity of the flower ; distinct from the perianth,, and 
 in some instances exactly resembling the proper 
 leaves, but in others differing from them both in 
 form and in colour *. The spathe, a membranous 
 sheath which encloses the flowers of the Irises 
 and some other plants before they blow ; and the 
 involucre, a foliaceous appendage situated at the 
 base of the umbel in umbelliferous plants, are 
 modifications of the bracte ; but as they shall be 
 described amongst the proper appendages of the 
 flower, I shall at present confine my remarks to 
 those bractes which have more of the foliar cha- 
 racter. Bractes, in this limited sense of the term, 
 differ in form, colour, situation, and duration. 
 
 The form and aspect of the bracte, as I have 
 already stated, is frequently that of the proper 
 leaf; and its diversities, therefore, are designated 
 by the same terms which are employed to distin- 
 guish those of the leaf. In some instances there 
 is a gradation scarcely perceptible from the proper 
 leaves to bractes, as in Purple-topped Clary, 
 Salvia Horminum, Alpine Bartsia, Bartsia alpina, 
 
 * " Bractea dicitur folium florale cum colore et figura recc- 
 " dit a ceteris." Phil Hot, 84/2. 
 
668 CONSERVATIVE ORGANS. [LECT. XI. 
 
 Purple and Common Yellow Cow-wheat, Melam- 
 pyrum arvense, and M. pratense, &c.; but the 
 braete may be truly foliaceous, and yet differ 
 considerably in figure from the leaves of the plant 
 to which it belongs. The Lime tree, Tilia Eu- 
 ropcea, affords a striking example of the difference 
 
 in figure and in 
 aspect of the 
 real leaf (a. a. a.) 
 and the braete 
 (b. b.) 9 which, in 
 this instance, is 
 attached to the 
 peduncle of the 
 flower. In Black- 
 berried Honey- 
 suckle, Lonicera 
 nigra, the braete 
 is a scale; and in 
 Atractylis can- 
 
 ^ ., cellata it is spi- 
 
 Nj nous. The co- 
 
 lour of the braete is often merely a differ- 
 ent shade of green from that of the leaves; but 
 in many instances bractes are very beautifully 
 coloured: purple, for example, in Cow-wheat, 
 Melampyrum arveme, Dwarf Orchis, O. ustulata, 
 Purple-topped Clary, Sal via Horminum; blue 
 in Milk Vetch, Polygala vulgaris; and bright 
 
LECT. XI.] CAULINAR AND FOLIAR APPENDAGES. 669 
 
 scarlet in Bartsia coccinea. The situation of 
 bractes, in the majority of instances, is on the 
 peduncle or flower-stalk, as in the Lime tree, &c. ; 
 but in others, on the stem, either beneath the 
 flower, as in Anemone, in which they are re- 
 garded as an involucre (involucrum) ; or forming a 
 tuft above the flowers, when they are termed 
 coronant ( coronantes) , as in the Crown Imperial, 
 Fritillaria imperialis ; tongue-leaved Eucomis, E. 
 regia, and the Pine Apple, Bromelia Ananas, &c. ; 
 and, in several species of Mussaenda, they arise 
 from one of the teeth of the calyx. In point of dura- 
 tion these organs are either caducous, deciduous, 
 or persistent. The use of the bractes, in the ve- 
 getable economy, is very little understood. When 
 they have the aspect and colour of leaves, their 
 functions are probably the same as those of leaves ; 
 and, when they are coloured, they may resemble, 
 in some degree, those of the petals of the flower ; 
 for, in plants which have the bractes beautifully 
 coloured, there is either no distinct evolution of 
 the corolla, as in Buginvillea, or the uppermost 
 flowers do not expand, as in Melampyrum nemo- 
 rosum and cristatum. Their use to the systematic 
 Botanist, in furnishing characters for the distinc- 
 tion of species, is very important. 
 
 c. The pitcher (ascidium*) is a hollow foli- 
 
 * Willdenow introduced this term from the Greek 
 a small bottle. 
 
670 CONSERVATIVE ORGANS. [LECT. XI. 
 
 aceous appendage, resembling, as its name im- 
 ports, a small pitcher. It is of rare occurrence; 
 but has been found as a caulinar 9 a foliar , and a 
 peduncular or floral appendage. 
 
 1. The only caulinar ascidium that is yet 
 known, belongs to an Australasian plant, the Ce- 
 phalotus follicularis, discovered by M. Labillar- 
 diere, and afterwards found near the shores of 
 Princess Royal Harbour, in the neighbourhood of 
 King George's Sound, in Terra Australis, by Mr. 
 Robert Brown, who has described it in the ap- 
 pendix to Flinders's Voyage (vol. ii. p. 600). 
 This singular vegetable production grows in- 
 termingled with the leaves of the plant, form- 
 ing a circle round the base of each flower- 
 stalk. It is pendent by a curved projecting 
 petiole; but, supported in such a manner, that 
 its cavity is upright. The pitcher itself (1.2.3. 
 page 671.) is nearly egg-shaped, an inch in 
 length, and furnished with a lid. It is, exteriorly, 
 ornamented with three double costae (fig. 1. 2.) 
 proceeding from a crested lip (fig. 3. a.). These 
 costee are projecting with acute pilose margins (.), 
 and extend downwards below the bottom of the 
 pitcher (c.). The mouth consists of a ring (d.) 9 
 which gives origin to a number of parallel rib- 
 like processes (e.), which are curved inwards 
 over it by their upper extremities. The greater 
 
 3 
 
LECT. XI.] CAULINAR AND FOLIAR APPENDAGES. 671 
 
 part of the inside is shining, and of a beautiful 
 dark purple colour. The lid (/*.), which is pro- 
 duced from the petiole (g.), and attached to the 
 edge of the pitcher by a broad base, is slightly pu- 
 bescent on the outside, smooth within, and of a 
 green colour, painted with broad, branching, dark 
 purple veins (2.). The structure of this organ is 
 said closely to resemble that of the leaf. " The as- 
 " cidia, or pitchers of Cephalotus," Mr. Brown re- 
 marks, ce were observed to be in general half filled 
 " with a watery fluid, in which great numbers of 
 " a small species of ant were frequently found 
 " drowned. This fluid, which had a slightly 
 " sweetish taste, may possibly be in part a sec re- 
 " tion of the pitcher itself, but more probably con- 
 
672 CONSERVATIVE ORGANS. [LECT. XI. 
 
 " sists of rain-water received and preserved in it. 
 " The lid of the pitcher in the full-grown state 
 " was found either accurately closing its mouth (see 
 " cut, fig. 2), or having an erect position, and, 
 " therefore, leaving it entirely open (fig. l .) ; and 
 " it is not unlikely that the position of the lid is 
 " determined by the state of the atmosphere, or 
 " even by other external causes*." The sweet 
 taste of the water proves the existence of a 
 secerning power in some part of the interior of 
 the pitcher; and it is this saccharine quality 
 of the secretion which entices insects to enter 
 it ; but whether the plant derive any advantage 
 from the decomposing animal matter, that re- 
 sults from their destruction, has not yet been as- 
 certained; although, from the result of some ex- 
 periments, which I shall presently have occasion 
 to notice in reference to another plant, the putre- 
 factive process may prove very beneficial to the 
 economy of this plant. 
 
 2. The foliar ascidium is peculiar to the genus 
 Nepenthes. In all the species, the pitcher is at- 
 tached by a cirrhose extension of the midrib at the 
 apex of the leaf, the sessile pitcher, as Mr. Brown 
 suggests, being peculiar to the young plant. In the 
 specimen figured in the margin, which is half the 
 
 * Flinders' 's Voy. vol. ii. p. 602. 
 
LKCT. XI.] CAULINAR AND FOLIAR APPENDAGES. 673 
 
 size of the original, 
 the cirrhose wire (fig. l 
 c.) is elastic, and suffi- 
 ciently firm to sup- 
 port the pitcher, when 
 full of water, in an 
 upright position. It 
 gradually enlarges as 
 it approaches the 
 pitcher, becoming in- 
 flated on the upper 
 surface (</.), but re- 
 maining flat and firm 
 
 on the lower; the angles of which gradually ter- 
 minate in two costae (e. e.), that run up the 
 fore part of the pitcher, and give out branches 
 which pass obliquely across the pitcher, and ter- 
 minate in the vessels supplying the lid (a.). The 
 structure of the cirrhose support is the same as 
 that of the petiole ; the proper or returning vessels 
 are very numerous, the spirals are large, and 
 constructed of four flattened threads. The pitcher 
 exactly resembles the leaf in its structure, the 
 whole of the vascular fascicles being prolonga- 
 tions of the petiolar bundles, or branches from the 
 two costae already described. The coalescence of 
 the fascicles at the back of the pitcher, near the 
 ring of the mouth, forms a third large costa, 
 which is, as it were, inverted, and branches down- 
 VOL. L xx 
 
674 CONSERVATIVE ORGANS. [LECT. Xf. 
 
 wards. The trunk, also, if it may be so termed, 
 of this costa, which is close to the hinge of the 
 lid, supports a beautiful hook (2. a. p. 673), armed 
 with a cartilaginous, acute point ; and as this pro- 
 jects backwards, it may afford further support 
 to the full pitcher, by hooking it upon any firm 
 object in its immediate neighbourhood. The lid 
 (I. a.) exactly resembles a flat, orbicular, sessile 
 leaf; moveable at its insertion, being furnished 
 with an articulation, or hinge, immediately be- 
 hind which the hook is situated. But the most 
 curious part of the pitcher is the ring, which 
 distends its mouth. This is apparently a firm, 
 transversely ribbed, thick wire; but is really 
 formed of the lip of the pitcher, which is cartila- 
 ginous and transversely striated, rolled outwards 
 like a scroll. It terminates very abruptly at the 
 hinge of the lid, and is larger there than in the 
 fore part of the pitcher. 
 
 The pitcher, in the early stage of its growth, 
 is of the same colour as the leaf; but, as it ad- 
 vances in age, it becomes beautifully coloured 
 with dark, purplish red streaks and blotches. 
 Its form in two of the species resembles that of the 
 finger of a glove; but in the third, the phyllam- 
 phora, it is contracted a little under the mouth 
 and again bulges out below, acquiring thus more 
 of the pitcher shape than the specimen before 
 us displays. It varies greatly in size, and some- 
 
LECT. XI.] CAULINAR AND FOLIAR APPENDAGES. 675 
 
 times is capable of holding- more than a pint of 
 fluid. 
 
 The fluid found in the pitcher of Nepenthes is 
 sweet and limpid; and, according to Rumphius, 
 is the production of the plant. The same author, 
 also, remarks that the waste of it during the day, 
 which is generally about one half, is fully repaired 
 during the night * ; but when the lid is completely 
 open the pitcher becomes dry. The pitchers ap- 
 pear dry and withered when they are half full only 
 of water; and, when the dry season sets fairly in, 
 and the seed is nearly ripened, they completely 
 decay. In Amboyna and Java the plant is found 
 on dry, stony, elevated spots only; although in 
 Ceylon it is said to grow in the valleys on the 
 banks of streams. 
 
 Phytologists have differed in opinion regarding 
 the cause which produces the opening and the 
 shutting of the lid of this vegetable pitcher. 
 The rising of the lid has been ascribed, by some, 
 to a sudden afflux of fluid rendering the vessels 
 connected with the hinge of the lid turgid; and: 
 the shutting to the receding of the fluid. By one 
 
 * " Aqua refertus est limpida et dulci, operculo autem 
 " operto, haec sensim minuitur usque ad dimidiurn partem, ita 
 ** tamen ut per noctem iterum adcrescat tanta copia, quanta 
 " per diem fuit exsiccata, quum vero operculum totura sit 
 " contractual aqua haec sensim minuitur fere tota." Rumph. 
 Amboin. lib. vii. c. 61. 
 
 xx2 
 
676 CONSERVATIVE ORGANS. f^LECT. XI. 
 
 writer*, however, the rising is ascribed to the 
 contraction of the " fibre," or costa connected 
 with the hinge, u by the hot and dry atmo- 
 sphere," and the shutting, to its expansion when 
 the air is saturated with moisture ; while by others 
 again, these movements are regarded as spon- 
 taneous or dynamical, like some other of the 
 movements of plants. In reviewing these opi- 
 nions the first might be considered probable, as 
 far as concerns the immediate or mechanical 
 cause of the change in the position of the lid, 
 but it does not satisfy the mind; and we na- 
 turally inquire, what occasions the afflux and 
 receding of the fluids to this particular set of 
 vessels ? for, without an answer to this query, 
 we have gained little by the information afforded 
 us, admitting it to be correct, respecting the state 
 of the vessels. The second opinion is less pro- 
 bable, because we cannot conceive how the costa 
 in question can contract, without producing a cor- 
 responding contraction of the whole back part of 
 the pitcher, the consequence of which would, ne- 
 cessarily, be to raise the lip of that vessel to the 
 same elevation as the lid, and thence to place it 
 in the same relative position to that part as it pre- 
 viously maintained. Lastly, the idea of explain- 
 ing the phenomenon, by saying, that it is a spon- 
 
 * Mr. Barrow. 
 
LECT. XI.] CAULINAR AND FOLIAR APPENDAGES. 677 
 
 taneous movement, either asserts too much, or has 
 no meaning: for if, by spontaneous motion, we 
 do not imply a power of volition in the moving 
 agent, a power I am certainly not prepared to ad- 
 mit as an attribute of plants, we must use some 
 other term to express our meaning. 
 
 The deficiency of correct observations on the 
 habits of the plant is, probably, the chief reason 
 why no satisfactory theory of this phenomenon 
 has yet been advanced. Thus, if it had been 
 observed, that the lid opened every morning and 
 closed every night, its elevation might be reason- 
 ably ascribed to the stimulus of light, acting on 
 its irritability, and exciting such an increased 
 action of the vessels as would produce that af- 
 flux of fluid which has been supposed to oc- 
 casion its erect position; and its depression, to 
 the withdrawing of this exciting cause: for, as 
 the lid is really a leaf, and its hinge an arti- 
 culation closely resembling that which connects, 
 with the common petiole, the leaflets of those 
 pinnated leaves which fold together their leaflets 
 at night, we might regard its movements as the 
 result of the same cause which produces the 
 diurnal motions of these leaflets. But we have no 
 evidence that this daily change of position of the 
 lid occurs: we are informed that it opens when 
 the weather is showery and damp as well as at 
 night ; and I am disposed to think that the heavy 
 
 xx 3 
 
678 CONSERVATIVE ORGANS. [LECT. XI. 
 
 evening dews, which fall in the climates where the 
 plant is indigenous, are the remote cause of the 
 lid opening at night. 
 
 These facts, and a careful examination of the 
 structure of the organ, have led me to imagine 
 that the movements of the lid are entirely me- 
 chanical, and depend on a hydroscopic action of 
 the ring forming the lip of the pitcher. We find 
 that this ring (d. d. 3. 4.), as I have already stated, 
 is a scroll formed of the lip of the pitcher, rolled 
 outwards : it ends abruptly (3. a. b.) close to the 
 hinge of the lid; and is there much thicker, owing 
 to the convolution of the scroll being larger at 
 that part, than in the front of the pitcher. At the 
 
 hinge, also, the lid 
 has a small auricle 
 or projection (a. 
 4.) on each side*. 
 Now I suppose that 
 the natural position 
 of the lid is that in 
 which it covers the 
 mouth of the pitcher ; and, i n a dry state of the 
 atmosphere, it lies close upon the mouth, be- 
 cause the scroll is contracted or closely rolled 
 up, like any other hydroscopic body : but, when 
 
 * These cuts show also that the lid is cmarginatc in front 
 (c. c. 3. 4.) ; and in 4-. ?>> we have a view of the costa which 
 terminates in the hinge. 
 
LECT. XI.J CAULINAR AND FOLIAR APPENDAGES. 679 
 
 the air is charged with moisture, the scroll swells, 
 and by unrolling itself enlarges the thickness of 
 the ring, and thus produces a pressure upwards 
 and backwards, by which the lid is forced open. 
 I have found, from experiment, that the en- 
 largement of the ring one sixteenth of an 
 inch, would bring the lid nearly into the erect 
 position ; and it is evident that the opening of 
 the lid must follow such an enlargement of the 
 ring, unless we suppose that the hinge length- 
 ens synchronously with the unrolling of the scroll, 
 which is not probable. In advancing this explana- 
 tion, I must allow that it is purely hypothetical, 
 and requires to be confirmed by observations on 
 the habits of the plant in its living state. 
 
 With regard to the fluid found in these vege- 
 table pitchers, the most probable opinion is, that 
 it is obtained from the atmosphere, and is intended 
 for the nourishment of the plant; for we can 
 scarcely suppose that so large a quantity of mois- 
 ture can be thrown out as a excretion, in a plant 
 growing in the dry, sterile situations where Ne- 
 penthes is found, and for the sole purpose of drown- 
 ing a few insects*. Rumphius indeed observes, that 
 the insects which crawl into the pitcher all die, 
 
 * Sir E. J. Smith supposes these pitchers to be merely fly- 
 traps; and, speaking of the source of the fluid, says it is 
 " certainly secreted through the footstalk of the leaf." Introd. 
 to Phys. and Syst. Bot, p. 197. 
 
 x x 4 
 
680 CONSERVATIVE ORGANS. [LECT. XI. 
 
 " except a small squilla or shrimp, with a gibbous 
 " back, sometimes met with, which lives there;" 
 but it does not appear that putrefaction goes on 
 in these pitchers, and the constant renewal of 
 the water is, certainly, not favourable to this 
 process. . 
 
 Another pitcher is the tubular leaf of Sarrace- 
 nia, for it can scarcely be termed an appendage, 
 seeing that it does not issue from a leaf, but 
 originates, directly, from the collar (collet) of the 
 plant, which is stemless. In the species before us, 
 S. purpurea, the hollow part of the leaf (see 4, 
 page 491) is an infundibuliform, ventricose cavity, 
 almost tubular below, and having a wide open 
 mouth, bounded in the fore part by a revolute 
 lip, and backwards by a broad dilated margin, 
 auricled on each side, and somewhat resembling 
 the spout of an ewer. In two of the species, 
 however, S.jlava and S. adunca, this expanded 
 part of the lip projects forwards over the mouth 
 of the cavity, and constitutes a kind of lid, al- 
 though not moveable. The lower part of the 
 tube terminates in a thick spongy cord, that ul- 
 timately expands to form the part which attaches 
 it to the plant ; and the remainder of the leaf is a 
 thin expansion, extending along the whole front of 
 the tubular part. Dividing the funnel or pitcher 
 longitudinally, we perceive that its narrower or 
 lower half is devoid of any proper cutis, and lined 
 
LKCT. XI.J CAUL1NAR AND FOLIAR APPENDAGES. 681 
 
 with a reticulated epidermis only, which is studded 
 with long hairs all pointing downwards, and co- 
 vers a number of glands, the excretory pores of 
 which open upon its surface. The ventricose part of 
 the funnel is smooth, shining, and lined with a 
 cutis closely resembling that of the outside of the 
 leaf; this terminates, however, by a well-defined 
 line a little below the lip ; and at the faux, if it can 
 be so termed/ of the funnel, we again find a band 
 of the same reticulated, glandular epidermis as at 
 its bottom, except that it is devoid of hairs, and 
 exudes a sweet, viscid secretion. The whole of the 
 interior surface of the dilated lip or hood, is co- 
 vered with short stiff hairs, all pointing down- 
 wards. The pitchers of Sarracenia vary consi- 
 derably in size; some, particularly those of S. 
 flava, being often more than three feet in height. 
 All of them contain some fluid. The intimate 
 structure of the whole is the same as that of the 
 leaf. 
 
 If the use of the pitchers in Cephalotus and 
 Nepenthes be problematical, there is sufficient evi- 
 dence for asserting, that those of Sarracenia are 
 chiefly intended for fly-traps; and it is very pro- 
 bable that the gases, and the other results of the 
 putrefactive process, produced by the bodies of 
 the insects which enter them and die there, may 
 be essential to the healthy economy of the plant. 
 
 According to some observations on the power 
 
 of Sarracenia to entrap insects, made by Dr. J 
 
 * 
 
682 CONSERVATIVE ORGANS. [LECT. XI. 
 
 Macbride, of South Carolina, it appears that the 
 flies, which are attracted to these leaves, first alight 
 upon the faux of the pitcher, and appear to sip, 
 with eagerness, the sweet secretion exuded from 
 the glandular band, which you have seen is situ- 
 ated just below the margin. " In this position they 
 " linger ; but at length, allured as it would seem 
 " by the pleasure of taste, they enter the tubes. 
 " The fly which has thus changed its situation, will 
 " be seen to stand unsteadily, it totters for a few 
 " seconds, slips, and falls to the bottom of the tube, 
 " where it is either drowned, or attempts in vain to 
 " escape against the points of the hairs*." Dr. 
 Macbride attributes the fall of the fly to the down- 
 ward or inverted position of the short attenuated 
 hairs at the faux, on which the fly is unable to take 
 a hold sufficiently strong to support itself; but 
 I am inclined to think that a kind of intoxication 
 is produced in the insect, either by the secretion 
 it sips, or by some exhalation within the pitcher ; 
 for I have seen flies, which had fallen, take wing 
 within some of the large pitchers, and again drop 
 before they had reached the faux : and we may 
 infer that this frequently occurs from the humming 
 noise within the pitcher, which is never heard, but 
 when a fly is using the wings. That this seldom 
 occurs in S. adunca, the species on which Dr. 
 Macbride made his observations, is probable, be- 
 
 * Linnean Transactions, vol. xii. p. 4-8. 
 
LECT. XI.] CAUL1NAR AND FOLIAR APPENDAGES. (583 
 
 cause the faux in this species is covered by the 
 hood, and the light excluded. If the fly attempts 
 to crawl up, the inverted position of the hairs is a 
 sufficient obstacle to its escape. Spiders, a small 
 species of Phalaena, and some other insects which 
 enter these tlibes, appear, however, to ascend 
 without difficulty. 
 
 I have, already, stated my accordance in the 
 opinion that these putrefying masses may be be- 
 neficial to the growth of the plant ; but this 
 conjecture, Mr. Keith observes *, " cannot be re- 
 " garded as quite satisfactory till such time as it 
 " shall be shown that the health of the plant is 
 " injured when insects are prevented from ap- 
 " proaching it." It is curious to observe, that 
 these fly-traps become serviceable to some indi- 
 viduals belonging to the very division of the 
 animal creation which they serve to destroy. 
 Dr. Macbride says, " in the putrid masses of 
 " insects thus collected, are always to be seen 
 " one or two maggots in a very active state." He 
 was unable, for some time, to ascertain the in- 
 sect to which these belonged ; " but while watch- 
 " ing attentively some tall tubes of Sarracenia 
 " flava growing in their natural situation, a large 
 V' he remarks, " caught my attention: it 
 
 * Syst. of Physiol. Bot. vol. ii. p. 286. 
 
 f This viviparous musca was more than double the size of 
 the common house-fly, had a reddish head, and the body hairy, 
 and streaked greyish. Lin. Trans. I. c 
 
684 CONSERVATIVE ORGANS. [LECT. XI. 
 
 " passed rapidly from one tube to another, delay- 
 " ing scarcely a moment at the faux of each, 
 " until it found, as it should seem, one suitable 
 " to its purpose; then, hanging its posterior ex- 
 " tremity over the margin, it ejected, on the in- 
 " ternal surface of the tube, a larva with a black 
 " head, which immediately proceeded downwards 
 " with a brisk vermicular motion." Sir J.E. Smith, 
 also, notices an observation made at the Botanic 
 Garden at Liverpool, which shows that, even in this 
 country, the Ichneumon fly employs the pitchers 
 of these plants for a similar purpose. An Ichneu- 
 mon was, one day, observed by one of the gar- 
 deners forcing large flies into the tubular cavity of 
 a leaf of Sarracenia adunca; and it is probable, 
 that it had previously deposited its eggs in their 
 carcasses, the eggs of the Ichneumon being often 
 deposited, and the larvae hatched, in the carcasses 
 of other flies or their larvae*. 
 
 c. Peduncular ascidium. This description of 
 organ is rarely found on the peduncle. On 
 Surubea Guianemis -f~, however, we find a small 
 hollow body, connected with a singular forked 
 projection, which rides as it were across the 
 flower-stalk: and a similar body, but without 
 the fork, is observed on the peduncle of Ruyschia 
 
 * Some Ichneumons deposit their eggs in the aurelia of 
 moths and butterflies. 
 
 t Aubl. Boyl. Meyer, Fl. Essequtb. p. 120. 
 
LECT. XI.] CAULINAR AND FOLIAR APPENDAGES. 685 
 
 clusicefolia *, and that of Marcgrafia. In these 
 instances, however, the name ascidium can apply 
 to the form only of these organs, as they do 
 not appear intended to hold fluids ; and perhaps 
 they may rather be regarded as ascidiform bracteae 
 than asascidia-f~. 
 
 vii. Anomalies. The only appendage which 
 I shall notice under this head > belongs to a North 
 American plant, Venus' Fly-trap, Dionoea musci- 
 pula ; and it is certainly the most extraordinary 
 production of the vegetable kingdom. The leaf of 
 this plant is radical, sessile, and nearly spa- 
 tulate in figure (Plate 10, fig. 5. c.) : the midrib, 
 however, is produced beyond the apex of the leaf, 
 and supports ^an appendage which has some re- 
 semblance to a steel trap. It consists of two 
 lobes, almost elliptical (fig. 5. b.), connected to- 
 gether by a whitish, cartilaginous costa, which is, 
 apparently, a production of the midrib of the leaf. 
 The lobes resemble the leaf in colour and con- 
 sistence, but their margin is somewhat cartilagi- 
 nous, and furnished with long setaceous teeth, 
 placed at the distance of the tenth of an inch from 
 one another. The superior disk of each lobe is 
 studded with minute glands, and furnished with 
 erect little spines (fig. 5. a.), placed so as to form 
 an equilateral triangle, with the apex pointing 
 
 * Jacq. Amer. Tab. 51. fig. 2. 
 
 f They have been termed Anthocerynium. 
 
686 CONSERVATIVE ORGANS. [LECT. XI. 
 
 towards the midrib which unites the lobes. To the 
 naked eye, these spines appear like simple Tmstles ; 
 but when they are examined under the microscope, 
 each spine is found to consist of two distinct parts ; 
 the one (fig. 6. a.), a small cellular papilla; and the 
 other (&.), which is supported on its apex, a firm 
 tapering pointed body, resembling a small, in- 
 verted bodkin. 
 
 This appendage is endowed with so much ir- 
 ritability, that as soon as a fly or other insect 
 alights upon the upper disk of either of the lobes, 
 so as to touch any of the spines, the lobes, if the 
 plant be in a healthy condition., immediately 
 close upon it; and the spines either empale the 
 little animal, or the teeth on the edges of the 
 lobes, crossing one another, prevent its escape, 
 and detain it until it dies. 
 
 The anatomical examination of these lobes does 
 not elucidate the phenomenon connected with 
 their functions. They resemble a leaf in their 
 cellular and vascular structure: the vessels being 
 given off from the midrib in arching fascicles, 
 which anastomose, towards the outer margin of 
 each lobe. The epidermis is glandular, and is 
 probably the seat of the irritability of the ap- 
 pendage; but, I have not had an opportunity of 
 examining it with sufficient care, to enable me to 
 determine in what particulars it differs from that 
 of the leaf. 
 
LECT. XI.] CAULINAR AND FOLIAR APPENDAGES. 687 
 
 Mr. Ellis, who first described this curious 
 appendage*, imagined that the glands were the ir- 
 ritable parts; and that, as soon as an insect 
 touched any of these, the motion of the lobes was 
 produced. Every other succeeding writer has 
 stated, generally, that it is merely necessary to 
 touch the upper surface of the lobes to excite their 
 action. From a variety of experiments, however, 
 I am convinced that no motion is produced until 
 one or other of the spines be touched; and, from 
 the manner in which these are affixed to the pa- 
 pillae, and the connexion of the latter with the 
 cuticle of the lobes, I am induced to suppose, that 
 the touching the spines communicates a thrill or 
 tremor to every part of the surface on which they 
 are situated, which excites into action the irri- 
 tability on which their motion depends. It may 
 be stated as an objection to this opinion, that it is 
 altogether hypothetical ; but no hint that can 
 tend to explain so interesting a phenomenon 
 should be withheld. 
 
 As the intention of this appendage is evidently 
 
 * " The Dionoea was first brought to this country, in the 
 " summer of 1768, by Mr. Young, gardener to the Queen; 
 " and Mr. Ellis described it, and had a drawing and a plate 
 " engraved from a plant which flowered in his chambers in the 
 " following August. It was from this plate and his characters of 
 " the plant, that Linnaeus's description was drawn up for his 
 " Mantissa. '* Vide Smith's Selection of the Correspondence of 
 Linn&us, vol. i. p. 235, and vol. ii. p. 72. 
 
688 CONSERVATIVE ORGANS. [LKCT. Xf. 
 
 to intrap flies and other insects; this question 
 presents itself what benefit can result to the 
 plant from such a function? We may reply, 
 that there is reason for supposing that the plant 
 derives some advantage either from the putrefac- 
 tion of the dead insects, or from something which 
 can be obtained from animal matter; a suppo- 
 sition, the probability of which is much strength- 
 ened by an experiment made by a Mr. Knight *. 
 Having laid fine filaments of raw beef upon 
 the appendages of a plant of Dioncea, he found 
 that this plant was more luxuriant than any other 
 in the same place, although they were all treated 
 alike, with the exception of the supply of beef. 
 That some principle, therefore, is evolved during 
 the decomposition of animal matter, peculiarly 
 favourable to the growth of this plant, is pro- 
 bable, and to secure this, may be the intention of 
 its singular appendages. 
 
 An appendage resembling that of the Dionoea, 
 in miniature, is found upon the glume of another 
 North American plant, the Leersia lenticularis. 
 
 * Mr. Knight was, at the time of making the experiment, 
 gardener to George Hibbert, Esq. and is now a respectable 
 nursery-man in the King's Road, Chelsea. 
 
INDEX FIRST; 
 
 CONSERVATIVE ORGANS METHODICALLY ARRANGED. 
 
 The Numbers indicate the Page. 
 
 THE CONSERVATIVE ORGANS 
 comprehend, 
 
 A. The root; 
 
 B. The stein and branches ; 
 
 C. The leaves; 
 
 D. Appendages, 
 
 A. THE ROOT, Radix, consists of 
 
 Caudex, caudex, 128; 
 
 Rootlets, radiculee, 129; 
 
 fibrils, fibrillce, 129. 
 
 In situation, roots are 
 
 subterraneous, subterraneee, 189: 
 
 aerial, aerece, 190: 
 
 floating, natantes, 191 : 
 
 parasitical, parasiticts, 189. 
 In direction, 
 
 perpendicular, perpendicular ~es, 
 192 : 
 
 horizontal, horizontales, 192 : 
 
 oblique, obliques, 195. 
 In duration, 
 
 annual, annute, 208: 
 
 biennial, biennes, 208 : 
 
 perennial, pcrennes, 208. 
 In substance, 
 
 woody, lignosee, 199: 
 
 fleshy, carnosce, 190. 
 Inform and composition, 
 
 simple, simplices, 130: 
 
 branched, ramosee, 1 39 : 
 
 articulated, articulate*, 140. 
 The simple root is 
 Sp. 1. conical, conica, 130; 
 
 var. a. spindle-shaped, fusi- 
 
 formis, 131 : 
 b. truncated, preemorsa, 
 132: 
 
 VOL. r. 
 
 Sp. 2. subglobular, subrotuitda, 134. 
 var. a. turnip-shaped, rapifor- 
 
 mis, 134. 
 6. flattened, placentifor- 
 
 mis, 134. 
 3. fibrous, fibrosa, 136. 
 
 var. a. filiform, > /?/(/brmtJ, 138. 
 6. capillary, capillarif,}38. 
 c. cord-like, funiliformis, 
 
 139. 
 
 The branched is 
 Sp. 1. branched, ramota, 140 : 
 
 2. toothed, dentata, 140. 
 The articulated is 
 Sp. 1. jointed, articulata, 141 : 
 2. kneed, geniculata, 141: 
 var. a. contorted, contoi'ta, 
 
 142: 
 i. necklace-like, monilifm- 
 
 mis, 1 42. 
 
 The appendages of the roots are 
 scales, squamee, 144: 
 suckers, stolones, 145: 
 tubers, tubera, 146 : 
 bulbs, 6u/6t, 164. 
 The fier is 
 
 /i. closely attached, conjunctum ; 
 
 comprehending, 
 
 Sp. 1. the conjoined ovate, conju- 
 gatum ovatum, 149. 
 
 2. conjoined club-shaped, 
 
 clavceforme conjttnctum, 
 150. 
 
 3. fingered, digit atum, 151. 
 
 4. palmated, palmatum, 151. 
 
 5. 
 
 prehending, 
 
INDEX FIRST. 
 
 Sp. 1. the solitary, solitarium, 153. 
 S. congregated, congrega- 
 
 tum t 154. 
 The bulb is 
 
 a. solid, solidus ; comprehending 
 Sp. 1. the superincumbent, soli- 
 dus superpositus, 1 66 : 
 
 2. lateral, laterally, 169: 
 
 3. inclosing, includens, 171. 
 6. scaly, squamosus, 
 
 Sp. 1. the squamous, squamnsus, 
 
 172: 
 2. granulated, granulatus, 
 
 178. 
 c. Laminated, tunicosus, 
 
 Sp. 1 . Concentric, concentricus, 179: 
 2. nestling, nidulans, 186. 
 
 B. THE STEM comprehends 
 The trunk, truncus, 279. 
 stalk, caulis, 280. 
 straw, culmus t 281. 
 scape, scapus, 281. 
 stipe, stipes, 282. 
 In composition, the stem is 
 simple, simplex, 254. 
 divided, ramosus, 255. 
 In direction, 
 1. Erect, erectus, 244. 
 
 var. a. straight, strictus, 245. 
 4. fiexuose, flexuosus, 245. 
 c. tortuous, toi'tuosus, 245. 
 <f. nodding, nutans, cernuus, 
 
 246. 
 . Oblique, obliquns, 246. 
 
 var. . ascending, adscendens, 246. 
 6. declined, declinatus, 247. 
 c. incurved, incurvus, 247. 
 8. Supported, fulcratus, 247. 
 
 4. Climbing, scandens, 248. 
 
 var. a. twining, volubilis, 248. 
 6. radicating, radicans, 249. 
 c. climbing, scandens, '251. 
 
 5. Decumbent, decumbent, 252. 
 
 6. Procumbent, prociimbens, 252 s . 
 var. a. creeping, repens, 252. 
 
 6. floating, nutans, 252. 
 In duration, 
 
 Annual, anmtus. 
 Biennial, biennis. 
 Perennial, perenni*. 
 In substance, 
 
 A. Woody, lignosus, 285. 
 Sp. 1. solid, solidus, 286. 
 2. fibrous, fibrosus, 286. 
 
 B. Herbaceous, herbacevs, 286. 
 Sp. 1. fleshy, carnosus, 287. 
 
 2. spongy, spongiosus, 287. 
 
 3. hollow, fistulosus, 287. 
 
 var. . uninterrupted, Jtnt 
 septis transversis, 287. 
 
 6. interrupted, je>^/t 
 transversis intertinctus, 
 287. 
 In/orw, 
 Sp. 1. round, teres, cylindricus, 272. 
 
 2. half round, semiteres, 273. 
 
 3. compressed, compressus, 273. 
 var. a. two-edged, anceps, 273. 
 
 5. niembranaceous, ^Ay/- 
 loidcus, 273. 
 
 4. angled, engulatus, 273. 
 
 var. a. obtuse, obtuse angula- 
 
 tus, 273. 
 
 ub-var. a. three-corner- 
 ed, trig-onus, 274. 
 
 sub-var. 3 four-corner- 
 ed, tetragonus, 274. 
 
 sub-var. <y. five-cornered, 
 pentagonus, 274. 
 
 sub-var. 8. six-cornered, 
 hexagonus, 274. 
 
 sub-var. t. many-cor- 
 nered, polygonus, 274. 
 ft. acute, acute angulatus, 
 274. 
 
 sub-var. . triangular, 
 triangular is, 275. 
 
 sub-var. 0. four-angled, 
 quadrangularis, 275. 
 
 sub-var. y. five-angled, 
 quinquangularis, 275. 
 
 sub-var. 5. six-angled, 
 sexangularis, 275. 
 
 sub-var. i. much- angled, 
 
 multangularis, 275. 
 c. Three-sided, triqueter, 
 
 275. 
 rf. angular, angulosus^lb. 
 
 sub-var. a. furrowed, 
 sulcatus, 275. 
 
 sub-var. 0. striated, .tfn- 
 atej, 276. 
 
 5. knotted, nodosus, 276. 
 
 6. jointed, articulatus, 276. 
 
 7. kneed, geniculatus, 276. 
 Branches, raws'. 
 
 In the morfe o/" branching, a stem is 
 forked or dichotomous, dichotomus, 
 257. 
 
INDEX FIRST. 
 
 266. 
 2. Covered, vestiti, 267. 
 
 var. o. leafy, foliosi, 267. 
 
 b. winged, alati, 267. 
 
 c. sheathed, vaginati, 
 267. 
 
 </. stipulated, stipulati, 
 
 267- 
 *. tendril-bearing, ctVrt- 
 
 feri, 267. 
 /. bulb-bearing, bulbiferi, 
 
 268. 
 
 tricliotomous, trichotomus, 257. 
 slightly-branched, subramosus, 256. 
 much-branched, ramosissimus, 256. 
 abruptly-branched, determinate ra- 
 
 mosus, 257. 
 
 * In situation, branches are 
 opposite, oppositi, 258. 
 
 var. a. verticillated,rerte'ci//aft,258. 
 
 b. two-ranked, distichi, 259. 
 alternate, alterni, 259. 
 scattered, spars i, 259. 
 ** In direction. 
 erect, erect i, 259. 
 
 var. a. approximated, adpressi, \ 
 260. 
 
 b. inflected, introflexi, 260. \ 
 
 c. f&$t\g\a,te,fastigiati, 260. | 
 spreading, patent es, 260. 
 
 var. a. open, patuli, diffuti, 26'0. i 
 6. very open, patentusimi, 
 
 260. 
 c. diverging, divergentea, 
 
 261. 
 rf. four-banked, brachiati, 
 
 261. 
 e. divaricated, divaricati t 
 
 261. 
 
 /. close, confer ti, 261. 
 #. supported, fulcrati, 262. 
 deflected, dejflexi, 264. 
 pendent, reflexi, 264. 
 pendulous, penduli, 264. 
 With regard to surface, stems and 
 
 branches are 
 Sp. 1. Bare, maft, 265. 
 
 var. a. shining, lucidi, 265. 
 6. smooth, glabri, 265. 
 c. even, tev^, 265. 
 rf. dotted, punctati, 265. 
 e. blotched,nactt/a/t, 266. 
 /. leafless, aphylli, 266. 
 ^. unarmed, inermes,<266. 
 
 var. g. spiny, spinosi, 268. 
 A. prickly, nculeati, 268. 
 . bristly, setaceosi, 268. 
 A. scaly, squaniosi, 269. 
 sub-var. ramentaceoui, 
 
 foment acei, 269. 
 /. pubescent, pubescentet, 
 
 69. 
 sub-var. . hairy, pilosi, 
 
 269. 
 sub-var. 3. hispid, Aw- 
 
 ^trft, 270. 
 sub-var. y. downy, /o- 
 
 mentosii 270. 
 sub-var. J. shaggy, vil- 
 
 losi, 270. 
 sub-var. e. woolly, /- 
 
 na^t, 270. 
 sub-var. i. silky, tericei, 
 
 270. 
 m. powdery, pulverulen- 
 
 tes, 271- 
 sub-var. . hoary, incani, 
 
 271. 
 sub-var. 0. mealy, /im- 
 
 o, 271. 
 sub-var. y. glaucous, 
 
 glauciy 271. 
 n. clammy, viscosi, 271. 
 sub-var. a. viscid, ww- 
 
 cirft, 271. 
 sub-var. 0. glutinous, 
 
 glutinosi, 271. 
 3. Rough, asperiy 272. 
 
 vur. a. scabrous, scabri, 272. 
 6. warty, verrucosi, 272. 
 ?', 272. 
 
 C. LEAVES, /o/ia, are in 
 
 A, the unexpanded state, contained in 
 
 HYBERNACULA, 
 
 * spontaneously separating. 
 
 Sp. 1. the propago, propago, 450. 
 
 2. gongylus, gongylus, 451. 
 
 3. bulb, bulbus, 452. 
 
 var. caulinar, caulinus, 452. 
 ** remaining attached. 
 
 4. gems, gemmae, 459. 
 
 var. . leaf-gems, foliiferte, 
 
 466. 
 
 A. flower ,fioriferte y 467. 
 c. mixed, mLvtcr, 467. 
 ,In situation the gem is, 
 
 terminal, terminalis, 460. 
 axillary, aril/arts, 461. 
 
 Y y t 
 
INDEX FIRST, 
 
 var. a. opposite, opposita, 46*1. 
 
 b. alternate, alternans, 461. 
 
 c. spiral, spiralis, 461. 
 In number, 
 
 solitary, soli t aria, 461. 
 aggregate, aggregata, 461. 
 In attachment, 
 
 sessile, scssilis, 462. 
 stalked, pedicillata, 463. 
 In gems the leaves are 
 Folded, 
 
 var. a. doubled, conduplicata, 
 
 463. 
 
 b. plaited, plicata, 470. 
 Overlapping. 
 
 var. . imbricate, imbricata, 470. 
 
 b. equitant, equitantia, 470. 
 
 c. ob volute, obvoluta, 471. 
 Rolled. 
 
 var. . convolute, ctnvohtta, 471. 
 6. involute, involuta, 472. 
 c. revolute, revoluta, 472. 
 rf. circinal, circittata, 472. 
 c. turned down, reclinata, 
 
 473. 
 jB. I'M Me expanded state leaves 
 
 consist of 
 the footstalk, petiolus, 513. 
 
 expansion, pagina, 513. 
 
 In situation the leaf is 
 radical, radicate, 533. 
 caulinar, caulinum, 533. 
 rameal, rameum, 533. 
 seminal, seminale, 534. 
 floral, florale, 535. 
 In distribution leaves are 
 opposite, opposita, 537. 
 decussated, decussata, 537. 
 ternate, tcrnata, 537. 
 quaternate, quaterna, 537. 
 cruciate, cruciata, 537. 
 whorled, verticillata, 537. 
 alternate, alterna, 537. 
 spiral, spiralia, 537. 
 scattered, sparsa, 537. 
 two-ranked, disticha, 538. 
 tufted, fasciculata, 538. 
 
 var. fcVia, terna, quina, 538. 
 crowded, conferta, 538. 
 imbricated, imbricata, 539. 
 rose-like, roselata, 539. 
 crowning, coronantia, 539. 
 remote, remota, 539. 
 In direction, 
 
 erect, frect a, 529. 
 
 closely applied, adpressa, 529. 
 
 spreading, patentia, 529. 
 
 horizontal, horisontalia, 529. 
 
 nodding, cernua, 529. 
 
 reflex, reftexa, 529. 
 
 inflex, inflexa, 530. 
 
 pendulous, dependentia, 530. 
 
 twisted, obliqua, 530. 
 
 reverse, resupinata, 530. 
 
 unilateral, secunda, 530. 
 
 procumbent, procumbentia, 530. 
 var. a. floating, natantia, 531. 
 
 emerging, emersa, 530. 
 
 sunk, submersa, 531. 
 In duration a leaf is 
 
 caducous, caducum. 
 
 deciduous, deciduum. 
 
 withering, marcidum. 
 
 persistent, persistens, 
 In insertion, 
 
 sessile, sessile, 539. 
 
 var. a. embracing, amplexicaule, 
 
 539. 
 
 6. connate, connatum, 539. 
 e. sheathing, vaginans, 540. 
 rf. equitant, equitans, 541. 
 
 decurrent, decurrens, 541. 
 
 perfoliate, perfoliatum, 540. 
 var. connato-perfoliatum, 539. 
 
 petiolate, petiolatum, 539. 
 var. . loose, solutmn, 641. 
 
 5. peltate, peltatiim, 516. 
 The footstalk is 
 
 simple, simplex, 513. 
 
 compound, compositus, 513. 
 The simple is 
 
 round, feres, 513. 
 
 half-round, semiteres, 513. 
 
 compressed, compressus, 513. 
 
 alienated, alienatus, 514. 
 
 channelled, canaliculatus, 514. 
 
 concave, concavus, 514. 
 
 embracing, amplexans, 515. 
 
 sheathing, vaginans, 515. 
 
 inflated, iiiflatus, 515. 
 The compound is the same, and, also, 
 
 jointed, articulatus, 516. 
 
 jointless, in articulatus, 517. 
 In relative position the -footstalk is 
 
 primary, primarius, 513. 
 
 secondary, secundarius, 513. 
 
 ternary, ternarius, 513. 
 
 partial, partialis, 518. 
 /w respect to appendages it is 
 
 winged, alatns, 515. 
 
INDEX FIRST. 
 
 stipuliferous, stipulifcrus, 515. 
 
 glanduliferous, glanduliferus, 515. 
 In respect of expansion leaves vary, 
 a. The simple leaf in superficial figure 
 is 
 
 capillary, capillare, 482. 
 
 linear, lineare, 482. 
 
 gramineous, fasciarium, 482. 
 
 "needle-shaped, acerosum, 482. 
 
 awl-shaped, subulatum, 483. 
 
 lanceolate, lauceolatum, 483. 
 
 sword-shaped, ensiforme, 483. 
 
 spatulate, spathidatum, 483. 
 
 wedge-shaped, cuneiforme, 483. 
 
 fan-shaped, fiabelliforme, 483. 
 
 oblong, oblongum, 483. 
 
 oval, owa/e, 484. 
 
 ovate, ovatum, 484. 
 
 obovate, obovatum, 484. 
 
 roundish, subrotundum, 484. 
 
 circular, orbiculare, 484. 
 
 crescent-shaped, lurntlatum, 484. 
 
 angled, angulatum, 485. 
 var. . triangulatuniy 485. 
 6. quadrangulatuni, 485. 
 
 0. pentangulatum, 485. 
 rep and, repandum, 485. 
 trowel-shaped, deltoideum, 485. 
 diamond-shaped, rhomboideum, 486'. 
 fiddle-shaped, jtandurceforme, 486. 
 lyie-shaped, lyratum, 486. 
 lobed, lobatum, 486'. 
 
 var. . bilobum, 486. 
 
 1. trilobum, 486. 
 
 4. yuadrilobiem, 486. 
 af row-shaped, sagittatitm, 487. 
 halberd-shaped, kastatum, 487. 
 heart-shaped, cortlatum, 487. 
 
 var. a. oblique coi'datum, 487. 
 kidney-shaped, reniforme, 487- 
 pal mated, palmatum, 488. 
 incised, laciniatum, 488. 
 var. a. bilaciniatum t 488. 
 
 6. trilaciniatuniy 488. 
 
 c. quadrilaciniatum, 488. 
 
 rf. quinquclaciniatum, 488. 
 much parted, multipartitum, 488. 
 rnncinate, runcinatwm, 488. 
 pinnatifid, pimiatifidurn, 489. 
 pectinate, pectination, 489. 
 pedate, pedatum, 524. 
 In *o/trf configuration leaves are 
 cylindrical, cylindracea, 490. 
 var. hair-like, capillacea, 490^ 
 
 semicyluidrical, tanicylir.Jracta, 
 490. 
 
 tubular, tubulosa, 490. 
 
 four-cornered, tetragona, 491. 
 
 three-cornered, trigona, 491. 
 
 tongue-shaped, lingulata, 491. 
 
 gibbous, gibba, 491. 
 
 symitar-shaped, acinaciformia, 491. 
 
 hatchet-shaped, dolabriformia y 491. 
 
 compressed, compressa } 492. 
 
 flat, ;>/"> 492. 
 
 two-edged, adcipitcs, 492. 
 
 spherical, spfueroidea, 492. 
 
 ovoid, ovoidea, 492. 
 
 coccoon-shaped, fusina, 492. 
 
 club-shaped, clavata, 492. 
 
 hooked, nncinata, 493. 
 
 lenticular, lenticularia, 493. 
 The opej; of the leaf is 
 
 acute, acutusy 493. 
 
 sharpish, acutiusculus, 493. 
 
 spine-pointed, cuspidatus t 493. 
 
 muc ron ate, mucronatus, 493. 
 
 awned, aristatus, 493. 
 
 cirrhose, 'cirrosus, 494. 
 
 obtuse, obtusiis, 494. 
 
 var. obtusus cum acumine, 496. 
 
 thickened, incrassatus, 496. 
 
 retuse, retusus, 496. 
 
 emarginate, emarginatus, 496. 
 
 truncated, truncatus, 496. 
 , jagged, prasmorsus, 49S. 
 
 tridentate, tridentatus y 496'. 
 In respect to 6awe, the general figure 
 
 gives its character; but a leaf is 
 
 also 
 
 unequal, iiuequale, 497. 
 The margin of the leaf is 
 * entire ; 
 
 ** indented; 
 *** bordered; 
 **** rolled. 
 
 * 
 
 entire, integerrima y 497. 
 
 # 
 
 sinuatcd sinuata, 497. 
 gnawed, erosa, 497. 
 toothed, dentatay 497. 
 
 var. a. equally, tequaliter, 498, 
 6. unequally, ineequalitery 
 
 498. 
 
 c. deeply, profundcy 498. 
 </. obscurely, obsolete, 498. 
 c. doubly, duplicate, 498. 
 sawed, serrata, 498. 
 
 TVS 
 
INDEX FIRST. 
 
 var. a. equally, eequaliter, 498. 
 
 b. unequally, intequalitfr, 
 498. 
 
 c. sharply, argute, 498. 
 
 d. deeply, profunde, 498. 
 
 e. doubly, duplicate, 498. 
 lightly sawed, serrulata, 498. 
 cvenated, crenata, 499. 
 
 var. a. doubly, duplicate, 499- 
 6. toothed, dentato-irena- 
 
 ta, 493. 
 
 crenulated, crenulata, 499. 
 spinous, spinosa, 499. 
 unarmed, inermis, 499. 
 
 ### 
 
 cartilaginous, cartilnginea, 500. 
 horny, cornea, 500. 
 ciliated, ciliata, 500. 
 
 var. aculeato-ciliata, 500. 
 glandular, glandulosa, 600. 
 
 var. glanduloso-ciliata, 500. 
 
 #.*** 
 
 revolute, revoluta, 500. 
 involute, involuta, 500. 
 undulated, undulata, 500. 
 curled, crispa, 500. 
 In respect of surface a leaf is 
 flat, planum, 501. 
 smooth, glabrutn, ib. 
 shining, nitidwn, ib. 
 lucid, lucidum, ib. 
 convex, convexum, ib. 
 concave, concavwn, ib. 
 
 channelled, canaliculatum, ib. 
 
 keeled, carinatum, 502. 
 
 furrowed, sulcatum, ib. 
 
 streaked, striatum, ib. 
 
 navel-like, umbilicatttm, ib. 
 
 folded, plicatum, ib. 
 
 waved, undulatum, ib. 
 
 wrinkled, rugosum, ib. 
 
 blistered, bullatum, ib. 
 
 scabrous, scabrum, ib. 
 
 rough, asperum, ib. 
 
 warty, vemtcosum, ib. 
 
 pustular, papiflosum, 508. 
 
 muricated, muricatum t ib. 
 
 prickly, eckinatum, ib. 
 
 aculeated, aculeatum, ib. 
 
 hispid, hispidum, ib. 
 
 hirsute, hirsutum, ib. 
 
 bristly, setosum, ib. 
 
 strigose, strigosum, ib. 
 
 bearded, barbatum, ib. 
 In respect of pubescence, 
 
 hairy, pilosum, 604. 
 baggy, villosum, ib. 
 silky, tericeum, ib. 
 downy, tomentosum, ib. 
 woolly, lanatum, ib. 
 flocculent, floccvsum, ib. 
 starred, stelfatum, ib. 
 From glandulation, 
 
 glandular, glandulosum, 505. 
 dotted, puHCtatum, ib. 
 viscid, viscidum, ib. 
 hoary, incanum, ib. 
 mealy, farinosum, ib. 
 In respect of colour, 
 
 coloured, coloratum, 506. 
 variegated, variegatum, ib. 
 blotched, maculatum, ib. 
 zoned, zonatum, ib. 
 * In depth, the colour is 
 sordid, sordidus, 506. 
 intense, intensvs, ib. 
 full, saturatits, ib. 
 pale, pallidus, ib. 
 diluted, dilutus, ib. 
 ** In Surfeit is 
 
 olive, olivacetts, 506. 
 sea-green, glaucus, ib. 
 J5. Compound leaves are 
 
 simply compounded, composite*, 5 1 9. 
 doubly compounded, decompotita, 
 
 ib. 
 much compounded, /pra decom- 
 
 posita, ib. 
 
 The simply compound leaves are 
 ternate, tcrnata, 519. 
 quadrinate, guadrinata, 520. 
 quinate, quitutta f ib. 
 fingered, digitattr, ib. 
 
 var. multifoliolata, ib. 
 umbellate, umbcllata, ib. 
 yoked, conjugata, ib. 
 
 var. bijuga, ib. 
 pinnate, pinnata, ib. 
 
 var. a. pari-pinnata t 521. 
 i. impari-pinnata, ib. 
 c. cirroso-pinnata, ib. 
 rf. lyrato-pinnata, 522. 
 e. ojtpositi-pinnata, ib. 
 /". alternatim-pinnata, ib. 
 ^r. interrupte-pinnata, ib. 
 A. articulate-pinnatay ib. 
 t. pinnata, foliolis decre- 
 
 acentibus, 522. 
 >J. verticillato-pinnnta, 523. 
 vertcbrated, vertebrata, 596. 
 
INDEX FIRST. 
 
 The doubly compounded are 
 
 twice paired, bigeminata, 523. 
 
 thrice paired, tergeminata, 524. 
 
 twice ternate, biter nata, 524. 
 
 doubly pinnate, bipinnata, 524. 
 
 conjugated and pinnate, conjugata- 
 pinnata, 524. 
 
 ternate and pinnate, ternata-pin- 
 nata, 524. 
 
 digitated and pinnate, digitata-pin- 
 
 nata, ib. 
 The much compounded are 
 
 thrice ternate, triternata, 525. 
 
 triply pinnate, tripinnata, 526'. 
 In substance the leaf is 
 
 membranous, membranaceum> 510. 
 
 chaff-like, scariosum, 511. 
 
 chartaceous, chartaceum, 511. 
 
 leathery, coriaceum, 511. 
 
 rigid, rigidum, 511. 
 
 fleshy, carnosum, 511. 
 
 succulent, succulentum, 511. 
 In productions it is 
 
 spiue-bearing, spiniferum, 541. 
 
 leaf-bearing, foliifcrum, 541. 
 
 flower-bearing, fl&riferum, 541. 
 
 plant-bearing, proliferum, 541. 
 
 D. GENERAL APPENDAGES: these 
 
 comprehend, 
 
 i. Glands, glandules, 628. 
 ii. Pubescence, pubescentia, 637. 
 iii. Thorns, spince, 647. 
 iv. Prickles, aew/a, 649. 
 v. Props, fulcra, 652. 
 vi. Foliaceous appendages, appendi- 
 
 culifoliacei. 
 
 vii. Anomalies, anomnli. 
 i. Glands, glandula, are 
 internal, 
 external. 
 Internal glands are, 
 
 Sp. 1. the follicular gland, g-. /b//t'-' 
 
 cularis, 630. 
 External glands are 
 sessile, 
 pediculated. 
 
 * The sessile^ comprehend 
 Sp. 1. the simple papillary gland, #. 
 papillaris simplex, 632. 
 var. glandula lenticular is, 633. 
 
 2. compound papillary, papilla- 
 rum composita, 633. 
 
 3. scaly, squamosa, 634. 
 ** The pediculated. 
 
 Sp. 1. the cup-shaped, cyathiformis, 
 635. 
 
 2. knob-shaped, clavifurmis, 
 636. 
 
 3. stipitate, stipitata, 636. 
 
 4. branched, ramosa, 636. 
 
 ii. Pubescence, pubescentia, com- 
 prehends 
 hairs, />i7t, 638. 
 bristles, jeftp, 638. 
 A hair is, 
 
 Sp. 1. Simple, pilus simplex, 639. 
 var. a. awl-shaped, subulatus, 640. 
 6. hooked, hamosus, ib. 
 c. gland-bearing, glandulosu*, 
 
 ib. 
 
 2 . compoun d , /w7e/,y compositus, 640. 
 var. a. feathery, plumosus, ib. 
 6. branched, ramosuy, ib. 
 c. starlike, stellatus, ib. 
 The bristle is, 
 Sp. 1. Simple, simplex, C41. 
 
 var. a. awl-shaped, subulata, 
 
 642. 
 i. spindle-shaped, fusifor- 
 
 mis, 643. 
 
 2. compound, *e/ composita, 643. 
 var. . forked, furcata, 644. 
 6. fasciculated, fascicu- 
 
 lata, ib. 
 
 iii. Thorns, spinee, are, 
 Sp. 1. Simple, spina simplex, 647. 
 
 var. solitary, solitaria, ib. 
 2. compound, spina composita, ib. 
 var. a. forked, bipartita, 648. 
 6. three-pronged, tripar- 
 
 tita, ib. 
 
 c. branched, ramosa, ib. 
 In situation thorns are 
 
 terminal, terminales, 648. 
 axillary, axillares, ib. 
 superaxillary, super axillares, ib. 
 subaxillary, infer axillares, ib. 
 iv. Prickles, aculei, 649. 
 Sp. 1. straight, ratft', 660. 
 
 2. curved, eww, ib. 
 var. a. incurvi, ib. 
 
 6. recurvi, ib. 
 
 3. spiral, circinnati, ib. 
 In composition they are 
 
 in pairs, geminati, 650. 
 palmated, palmati, ib. 
 v. Props, fulcra, comprehend 
 
 * tendrils, cirrhi, 653. 
 ** claws, claviculi, 656. 
 
 Y Y 4 
 
INDEX FIRST, 
 
 *** bladders, ampulla, 661. 
 **** hooks, hamiy 662. 
 The tendril is, 
 
 Sp. 1. Simple, cirrhus simplex, 653. 
 2. compound, compositus, ib. 
 var. a. bifid, bifidus, ib. 
 i. trifid, trifidus, ib. 
 c. branched, ramosus, ib. 
 In situation the tendril is 
 axillary, axillaris, 653. 
 subaxillary, subaxillaris, ib. 
 lateral, laterally, tb. 
 opposite, oppositifolius, ib. 
 petiolar, petiolaris, ib. 
 foliar, foliar is, ib. 
 In direction : 
 
 convolute, convolutus, 656. 
 revolute, revolutus, ib. 
 ** The c/rtw is, 
 Sp. 1. cirrhal, cirriformis, 656. 
 
 2. radicular, radiciformis, ib. 
 *** the bladder, ampulla, 661. 
 **** the hook, hamus, 662. 
 vi. Foliaceotts appendages are, 
 Sp. 1. the stipule, stiptila, 662. 
 In duration it is 
 
 fugacious, fugaz, 663. 
 
 deciduous, decidua, 663. 
 
 persistent, persistens, ib. 
 In number : 
 
 solitary, solitaria, 664. 
 
 twin, gemina, ib. 
 In substance : 
 
 leafy, foliacea, 664. 
 
 membranous, membranacea, ib. 
 
 chaff-like, scariosa, ib. 
 In situation : 
 
 lateral, lateralis, 665. 
 
 intermediate, intermedia, ib. 
 
 embracing, amplexans, ib. 
 
 sheathing, vaginosa, ib. 
 var. hypocrateriformis, ib. 
 
 marginal, marginalia, ib. 
 
 interfoliaceous, intrafoleacea, ib. 
 
 extrafoliaceous, extrafoliacea, ib. 
 
 2. The bracte, bractea, 667. 
 var. a. spathe, spatha, ib. 
 
 A. involucre, involucrum, ib. 
 
 3. The pitcher, ascidium, 669. 
 Sp. 1. caulinar, caulinum, ib. 
 
 2. foliar, epiphyllum, 672. 
 
 3. peduncular, pedunculare, 
 684. 
 
 vii. anomalous, anormcs, 685. 
 
INDEX SECOND. 
 
 A. 
 
 AERIAL, application of the term to leaves, 628. 
 u?Esculus Hippocastaminiy structure of its gems, 463. 
 Agave Americana, its foliar apertures, 611, 615. 
 Agostino Ma7idirola, extract from his treatise, 545. 
 Air, a component of soils, 218. 
 
 vitiated by vegetating roots, 219. 
 
 kind of, contained in hollow stems, 424 . 
 
 Alburnurft, its character, 336. 
 
 changes into hard wood, 337. 
 
 " hardens when a tree is barked, 337. 
 
 simple hardening of, does not constitute wood, 338, 
 
 formation of the, 340. 
 
 dies when exposed to the air, 354. 
 
 is a reservoir of proper juice in winter, 355. 
 
 ^ loses its irritability on becoming- wood, 856. 
 Algae are propagated by the propago, 450. 
 Alienated leaves, their character, 528. 
 
 Aloje, its leaf has few pneumatic apertures, 618. 
 
 soccotrina, its proper juice affords a dye, 118. 
 
 mode of its growth, 205. 
 
 structure of its leaf, 562. 
 
 verrucosa, form of its cuticular meshes, 605. 
 
 Althaea officinalix t structure of its root, 439. 
 Annual herbaceous roots, structure of, 431. 
 
 i zones of wood, origin of, 338. 
 
 Annular vessels, their characters, 82. 
 
 Anthoxanthum odoratum is odorous only when dried, 631. 
 
 Apertures, foliar, 608. 
 
 their varieties, 6o9. 
 
 their size and number, 613. 
 
 are the exhaling organs of leaves, 610, 619. 
 
 are the respiratory organs, 62 1 . 
 
 Aphis, its lateral propagation, 457. 
 Appendages, enumeration of, 628. 
 Aquatic plants, structure- of their foliar parenchyma, 596. 
 
 . the leaves have no pneumatic slits, 608. 
 
 Arctium lappa, structure of its root, 433. 
 
 - has the largest leaf of any British plant, 546. 
 
 Argillaceous earth, its effects in soils, 214. 
 
 Ascidium of Cephalotus/oWicM/ara, 670. 
 
 Nepenthes Distillaloria, 672. 
 
 Atropa Btlladonna, structure of its root, 439. 
 2 
 
INDEX SECOND. 
 
 B. 
 
 Banyan tree, a remarkable one, 198. 
 
 Barclay, Dr. his opinion respecting the cells of honeycomb, 373, 
 Bark, structure of the, 317. 
 
 reproduction of the, 848. 
 
 Barley indicates a poor soil, when it has long roots, 224. 
 
 Bauer, Mr. Francis, his opinion of the cuticle, 600. 
 
 Bauhin, Casper, first described the potatoe, 27. 
 
 Beauvois, M. de, his opinion respecting the medullary tube, 867. 
 
 Biennial herbaceous roots, structure of, 343. 
 
 Boerhaave, his definition of a plant, 42. 
 
 Bonnet, his remarks on absorption by leaves, 617. 
 
 Botany, derivation of the term, 2. 
 
 its antiquity, 6. 
 
 its utility to medicine, 19. 
 
 its utility to agriculture, 28. 
 
 its importance as a branch of general education, 29. 
 
 Bradley, Mr. his theory of grafting, 397. 
 Branch, origin of the, 384. 
 
 organization of its germ in the bud, 386. 
 
 is fully formed when protruded from the bud, 388. 
 
 . origin of the adventitious, 391. 
 
 buds, when formed, 395. 
 
 remain latent, 395. 
 
 * progress of its germ, when it is not evolved, 403. 
 
 Branching, its theory illustrated by a diagram, 404. 
 
 . new theory of, 391 405. 
 
 Brunfels, the restorer of the science of Botany in Europe, 10. 
 
 Bryonia alba, structure of its stem, 414. 
 
 its stem contains three kinds of vessels, 419. 
 
 Buds, supposed by Darwin to have a sensorium, 376. 
 
 origin of, 485 395. 
 
 contain the germs of future branches, 386. 
 
 theory of their formation, 391. 
 
 do not proceed from the alburnous vessels, 393. 
 
 branch, when formed, 395. 
 
 are distinct individuals, 395. 
 
 stem, when formed, 395. 
 
 effects of temperature on, 399. 
 
 Bulbs, how to distinguish from tubers, 165. 
 
 -- - are reservoirs of nutriment, ib, 
 . .. are hybernacula, 165. 
 
 are the lateral progeny of the plant, 165. 
 
 are exhausted in producing the stem and leave*, 169. 
 
 are subterraneous buds, 1 87. 
 
 scales of, can produce new bulbs, 170. 
 
 flowering, the last of the natural series, 187. 
 
 their vessels may be injected, 181. 
 
 their spiral vessels are easily detected, 184. 
 
 new leaf, are the lateral progeny of the old bulbs, 185. 
 
 new, sometimes formed within the old, 181. 
 
 cauliriar, structure of, 453. 
 
 erroneously regarded as gems by Linnaeus, 453. 
 
 . produce leaves only, 455. 
 
 Bulliard detected the seeds of fungi, 452. 
 
INDEX SECOND. 
 
 C. 
 
 Cactus, structure of its foliar cells, 592. 
 Ceesalpinus first classed plants, 1 1 . 
 Calcareous earth, its use in soils, 213. 
 
 too much, injurious in soils, 214. 
 
 Calla jtEthiopica, structure of its leaf, 588. 
 Caloric, a part in soils, 221. 
 Cambium, 341. 
 
 Camcrarius first proved the sexuality of plants, 1 2. 
 Canna Indica, structure of its leaf, 566. 
 Carbonic acid gas, present in soils, 220. 
 Carbonated hydrogen gas, formed in soils, 220. 
 Carex arenaria, utility of, 1.93. 
 Caterpillar, its tenacity of life, 62. 
 
 frozen, lives after it is thawed, 476. 
 
 Caudex, a reservoir of nutriment, 129. 
 
 structure of, in dicotyledons, 406. 
 
 Cells, how those of the pith are formed, 372. 
 
 symmetrical arrangement of, in some annual roots, 432. 
 
 some have transverse slits in their sides, 432. 
 
 longitudinal, in some roots, are valvular, 433. 
 
 lateral communication of, 595. 
 
 their sides are double, 324. 
 
 Cellular integument, its character, 321. 
 
 is the seat of colour, 322. 
 
 texture, its nature, 71. 
 
 - pores, their existence doubtful, 826. 
 Cephalotus/o//tctt/<m,y, its ascidium, 670. 
 Chaptal, his experiments on the proper juice, 120. 
 Cherry tree, method of obtaining a clean stem of a, 394. 
 Chicorium endivia, structure of its stem, 421, 
 
 Cissus hederacea, structure of its claw, 657. 
 
 mode by which it adheres to walls, ib. 
 
 Coffea Arabica, peculiarity of its foliar glands, 63 1 . 
 Collet, part so named by the French Botanists, 408. 
 Comparetti noticed the interstitial cellular spaces, 591. 
 Components, general, of the vegetable body, 69- ' 
 Concentric layers, their character, 83 1 . 
 
 . their numbers declare the age of a tree, 386. 
 
 Conium maculatum, structure of its stem, 424. 
 
 Corona, part so named by Hill, 358. 
 
 Cortex, of solid monocotyledonous stems, 301. 
 
 of dicotyledonous stems, 317. 
 
 Cotyledon calycinum, structure of its leaf, .543. 
 Cubber Burr, account of, 198. 
 Culm, anatomy of its knots, 312. 
 
 use of the cellular matter of its knots, 314. 
 
 Cuticle, structure of that of the stem, 318. 
 : is annually renewed, 321. 
 
 structure of that of the leaf, 600. 
 
 is not renewed on the leaf, 98. 
 
 structure of its inner layer, 602. 
 
 Cuticnlar meshes are formed by lymphatics, 604. 
 . diversities of their forms, 605. 
 their sizes, 606. 
 
 " always parallelograms over costs-, 606. 
 
INDEX SECOND. 
 
 Cribriform vessels, their character, 81. 
 Cyclamen Europeeum, peculiarity of its root, 135. 
 
 D. 
 
 Darwin, Dr. taught that plants are sentient beings, 44. 
 
 supposes each joint of the culm an individual, 310. 
 
 taught that the spiral vessels carry fluids, 36*6 
 
 1 considered the spiral vessels absorbents, ib. 
 
 - supposes each bud possesses a sensorium, 376. 
 
 his opinions of the use of the pith erroneous, 375. 
 
 his poetical theory regarding armature, 651. 
 
 Daucus carota, structure of its root, 435. 
 
 Davy, Sir H. his remarks on the heat of soils, 32 1 . 
 
 on the fertility of a soil in East Lothian, 222. 
 
 Decanclolle considers the cuticle a compound body, 660. 
 
 noticed the cuticular apertures, 607. 
 
 his remarks on foliar transpirations, 618. 
 Declivity, effects of, on trees, 263. 
 Desfontaines, his arrangement of stems, 289. 
 
 considered the cuticle a compound body, 599. 
 
 Devil, his malignity demonstrated, 132. 
 Dicotyledons, structure of their leaves, 572. 
 
 structure of their stems, 315. 
 
 Dioncea muscipula t its singular appendage, 685. 
 Dioscorides, his knowledge of plants, 8. 
 Direction of roots, 192. 
 
 ' deviations from the natural, 204. 
 Disks of the leaf, 481. 
 Divergent layers, 303. 
 
 are not processes of the pith, 335. 
 
 Dracena, its mode of growth, 305. 
 
 has apitnctum vitale in the axilla of every leaf, 306. 
 
 Du Hamel, his opinion regarding fibrils, 129. 
 
 believed the liber changed to alburnum, 328. 
 
 his opinion regarding the formation of wood, 339. 
 
 first noticed the reproduction of bark, 347. 
 
 his opinion regarding branches, 390. 
 considered the cuticle a simple body, 559. 
 
 E. 
 Earth, general components of, 213. 
 
 vegetable, 206. 
 
 Ellis, Mr. his opinion respecting the communication of cells, 373. 
 
 supposed that the glands in Dionoea were the seat of its irritability, 
 
 686. 
 
 Entire vessels, their character, 80. 
 Epidermis, its character, 93. 
 
 is destitute of vessels, 96. 
 
 the old, is pushed outwards, 98. 
 
 uses of the, 99. 
 
 is a distinct organ, 101. 
 
 F. 
 
 Ferruginous, in soils, 215. 
 Fibrils are annual productions, 130, 207, 412. 
 
 are the absorbing mouths of the root, 136, 206. 
 
 structure of the, 4 1 0. 
 
 Fieus clnstica, beautiful foliation of, 470. 
 
INDEX SECOND. 
 
 Ficus Indica, a remarkable tree, 198. 
 
 Final causes, conclusions drawn from, 6'5). 
 
 Foliation, 469. 
 
 Fontana supposed he saw globules in the proper juice, 119. 
 
 Footstalk, a part of the leaf, 480. 
 
 Forest trees, suggestions regarding their stems, 394. 
 
 Fungi, structure of their stems, 292. 
 
 are erroneously supposed to be propagated by gongyli, 451 . 
 
 G. 
 
 Geertner, his definition of the propago, 450. 
 
 - his definition of the gongylus, 451. 
 
 Gardeners, their method of obtaining a clean Cherry tree .stem, 394. 
 Gaultheria odorata is odorous only in its recent state, 631. 
 Gay Lussac, his experiments on vegetable secretions, 123. 
 Gems are found on tubers, 163. 
 their structure, 463. 
 
 a knowledge of them is useful to the gardener, 468. 
 
 contain the rudiments of the branch, 385. 
 
 - origin of, 384. 
 
 - are distinct individuals, 386. 
 
 Gerarde, his account of the truncated root, 132. 
 
 Germ, is at first an isolated speck, 397. 
 
 how it is evolved, 397. 
 
 Glands, definition of, 629. 
 
 i classification of, 635. 
 
 Glandular texture, its character, 88. 
 
 Gleichen, Von, supposed the cuticular apertures were glands, 607. 
 
 Gramineous plants, the vascular system of their leaves, 561. 
 
 Grew, Dr. first described the root of the Primrose, 1 33. 
 
 believed that the liber changed into alburnum, 328. 
 
 supposed that the spiral vessels exist in perfect wood, 360. 
 
 first suggested that the spiral vessels convey sap, 365. 
 
 his opinion regarding the pith, 376. 
 
 denied the inosculation of vessels in plants, 581. 
 
 considered the cuticle a simple body, 599. 
 
 noticed the cuticular apertures, 607. 
 
 Guettard, M. bis classification of glands objectionable, 630. 
 Gum, its components, 123. 
 
 H. 
 
 Hairs are not absorbing organs, 64 1. 
 
 some of them are excretory ducts, 688. 
 
 Halts, Dr. his hypothesis of the formation of wood, 338. 
 
 his opinion of the use of the pith, 375. 
 
 Holler, Baron, his extraordinary acquirements, 18. 
 Hcdwig maintained that spiral vessels exist in wood, 360. 
 "detected sap in the spiral vessels, 365. 
 
 his opinion of the cuticular meshes, 694. 
 
 had seen the cuticular apertures, 607- 
 
 Helleborus niger, peculiarity of its foliar cells, 588. 
 
 - viridis, character of its foliar cells, 593. 
 Heterophyllous plants, their characters, 527. 
 Hill, Mr. Daniel, his experiments on roots, 220. 
 Hilt, Dr. first noticed the medullary sheath, 358. 
 his examination of buds partial, 400. 
 
INDEX SECOND. 
 
 Hill, Dr. his opinion of the origin of the branch, 401. 
 
 Hippuris vulgaris, structure of its stem, 298. 
 
 Hope, Dr. supposed that the liber changes into alburnum, 33.9. 
 
 his experiments to prove the transmutation of the liber, 339. 
 
 Hoya carnostty structure of its leaf, 590. 
 
 its cuticulai- meshes, 605. 
 
 Humboldt, Baron, made galvanic experiments on plants, 45. 
 Hybernacula, definition of, 448. 
 four kinds of, 450. 
 
 are lateral progeny, 449. 
 
 I. 
 
 Injecting plants, method of, 72. 
 Inner bark, its relative situation, 326. 
 
 its structure, 327- 
 
 Inorganic bodies form a division of nature, 40. 
 Iris Germanica, its foliar cells, 591. 
 JungiuSy his merits, 11. 
 
 his definition of a plant, 4 1 . 
 
 Jurine, M. his opinion of the cuticular meshes, 604. 
 Jussieu, opinion of his works, 37. 
 
 K. 
 
 Keithy the Rev. Mr. his anatomical arrangement of stems, 290. 
 his opinion regarding the cellular integument objection- 
 able, 322. 
 his opinion regarding the divergent layers, 335. 
 
 his opinion regarding the proper juice, 350. 
 
 supposes the spiral vessels convey both air and sap, 366. 
 
 his theory of the use of the pith, 376. 
 
 considers the cuticle a simple body, 599. 
 
 Kieser, M. supports the double character of the cellular partitions, 373. 
 his observations on the sap vessels of the Gourd, 427. 
 
 supposes there is a transmutation of vessels, 435. 
 
 notices the interstitial cellular spaces, 591. 
 
 considers that the cuticle is a simple body, 599. 
 
 Knight, Mr. his opinions regarding fibrils, 1 29. 
 his experiments on tuberiferous roots, 158. 
 
 his experiments on the direction of roots, 204. 
 doubts whether fibrils be annual productions, 208. 
 
 his opinions regarding green manure objectionable, 236. 
 
 his theory of the formation of wood, 342. 
 
 proves that alburnum is not transmuted liber, 342. 
 
 some points in his theory objectionable, 350. 
 
 his experiments on the pith, 375. 
 
 his theory of the origin of buds erroneous, 393. 
 
 grafted successfully on the tendril of a Vine, 655. 
 
 Knobs, formation of those found on the root, 442. 
 Krocker, M. his opinion of the cuticular meshes, 604. 
 
 L. 
 
 Lactuca sativa, structure of its stem, 421. 
 
 Lathraea squamaria, its scales, 145. 
 
 Lathyrus odoratus, knobs are sometimes found on its roots, 442. 
 
 Layers, concentric, of the wood, 331. 
 
INDEX SECOND. 
 
 Leaves, essential for the increase of the diameter of stems, 346. 
 
 their state in the bud, 448. 
 
 their evolution from the bud, 469. 
 
 are to gems what flowers are to fruit, 475. 
 
 characters of, when growing under water, 581. 
 
 division of their parts, 481. 
 
 proliferous, their structure, 543. 
 
 vascular system of, 548. 
 
 1 skeleton, how formed, 548. 
 
 - cellular system of, 586. 
 
 Leontodon Taraxacum, structure of its root, 437. 
 Leuwenhoek had noticed the interstitial cellular spaces, 691. 
 Liber, its structure, 327. 
 
 is the seat of vitality, 328. 
 
 its importance in grafting, 328. 
 
 Lichens are said to be propagated by the propago, 450. 
 
 Licuala spinosa, size of its leaf, 546. 
 
 Ligneous fibre, components of, 124. 
 
 - stems are not all perennial, 422. 
 
 Lilies resemble the Palms in their growth, 306. 
 
 Lilium super bztm, the attachment of its young bulb, 174. 
 
 candidum, structure of its leaf, 552. 
 
 its cuticular meshes, 605. 
 
 Lime, its use as a manure, 233. 
 
 Lindsay, Mr. his supposition regarding the irritability of Mimosa sensitive* 
 
 375. 
 Link, M. his opinion regarding the structure of cells, 326. 
 
 denies the existence of the cuticular pores, 373. 
 
 his theory of the cuticular meshes objectionable, 604. 
 
 biographical sketch of, 14. 
 
 his definition of a plant, 43. 
 
 fell into an error regarding soils, 211. 
 
 his theory of the formation of wood erroneous, 338. 
 
 his theory of the use of the pith, 375. 
 
 his definition of a gland objected to, 628. 
 
 objections to his definition of the hair, 638. 
 Liriodendron Tulipifera, its beautiful foliation, 473. 
 Ludwtg, his definition of a plant, 42. 
 
 M. 
 
 Magnesian earth, its effect in soils, 215. 
 
 when calcined is hurtful to plants, 234. 
 
 Malpighiy believed in the transmutation of liber, 329. 
 
 his opinion regarding the use of the pith, 376. 
 
 considered the cuticle a simple body, 599. 
 
 his theory of the origin of thorns, 648. 
 
 Malpigbia, peculiar bristle on the leaves of, 643. 
 Manures, in what manner their effects are produced, 23. 
 Marchantia polymorpha, structure of its leaf, 650. 
 
 ^ its cuticular apertures, 607. 
 Medicine, Botany useful in, 19. 
 Medulla, its characters, 366. 
 
 its form regulated by circumstances, 367. 
 
 varies in diameter in the same stem, 368. 
 
 - .. peculiarity of, in the Walnut tree, 868. 
 

 INDEX SECOND. 
 
 Medulla, peculiarity of, in Magnolias, 368. 
 
 - varies in colour in different plants, 870. 
 
 - character of its cells, 370. 
 
 - - distinctions of the, stated by M. Aubert du Petit Thouar*, 37 1 . 
 
 the membrane forming its cells is double, 372. 
 
 - its- cells communicate by pores, 373. 
 
 - its use to the plant, 374. 
 
 - Mr. Knight's experiments on the, 375. 
 
 new theory of its use, 377. 
 -- its functions soon cease, 378. 
 
 -- is never obliterated in the sound stem, 380. 
 
 - is never converted into wood, 381. 
 Medullary sheath, its character, 357. 
 --- vessels of the, 358. 
 -- cells of the, 359. 
 
 - the arrangement of its vessels is regulated by circumstances, 
 361. 
 
 Membranous texture, 70. 
 
 Mesembryanthemum dolalriforme, structure of its leaf, 583. 
 
 Michelius detected the seeds of Fungi, 451. 
 
 Midrib of the leaf, 480. 
 
 Mirbel, his opinion of vegetable life, 45. 
 
 -- his remarks on fibrils, 207. 
 
 - considers the cellular integument glandular, 323. 
 
 - believes in the transmutation of liber, 329. 
 
 - considers the cuticle a simple body, 599. 
 
 - his opinion of the cuticular meshes, 604. 
 Monocotyledons, structure of their leaves, 559. 
 Mosses are very tenacious of life, 57. 
 
 Musa sapientum, size of its leaf, 596. 
 
 N. 
 Nerium oleander, structure of its foliar cuticle, 607. 
 
 '. its foliar apertures, 612, 616. 
 
 Nettle, structure of its sting, 643. 
 Nicholls, Francis, prepared skeleton leaves, 549. 
 
 O. 
 
 CEder began the Flora Danica, 18. 
 Olive oil, its components, 123. 
 Organic bodies, 4 1 . 
 Osculum scutiforme ovatum, 609. 
 -- annulare, 610. 
 
 - annulare, 610. 
 -- quadrilaterale, 611. 
 
 Oxygene gas, a healthy stimulus to roots, 220. 
 Oxygenous portion of the air is vitiated by roots, 219. 
 
 P. 
 
 Palms, structure of their stems, 294. 
 
 - their mode of growth, 803. 
 
 Papaver somniferum, structure of its root, 432. 
 
 Parenchyma of leaves, its cellular structure, 590. 
 
 Perennial herbaceous plants, structure of their roots, 437. 
 
 Perforated vessels, their characters, 81. 
 
 Petiole is a part of the leaf, 480. 
 
 Petit 77iotfars, his observations on Dracena, 805. 
 
INDEX SECOND. 
 
 Petit Thouarsy his theory of the origin of wood, 352. 
 
 of the divergent layers, 353. 
 
 Phaseolus vulgaris, structure of its petiole, 577. 
 Physiognomy of plants, importance of attendingto it, 255. 
 Phytology, definition of, 2. 
 Pith, its characters, 366'. 
 
 causes which form its cells into hexagons, 372. 
 
 its use to the plant, 374. 
 
 is not the vegetable brain, 374. 
 
 Mr. Knight's experiments on it, 375. 
 
 new theory of its use, 377. 
 
 is never obliterated in a sound stem, 380. 
 
 - is never converted into wood, 381. 
 Plant, definition of, 2. 
 
 Plants, bulbiferous, seldom ripen their seeds, 458. 
 
 tubei iferous, change their place in the ground, 152. 
 
 i vital functions of, 50. 
 
 1- consequences of propagating those from warm climates by slips, 450. 
 
 Platanus oriental, its gems are latent during summer, 460. 
 
 Pliny, his limited knowledge of plants, 8. 
 
 Poa trivialis, its cuticular meshes, 6'05. 
 
 Polypi, how they are nourished, 48. 
 
 Potatoe, when brought to Europe, 27. 
 
 Prickle, its structure, 651. 
 
 Progeny, lateral, is merely an extension of the parent. 449. 
 
 Proper juice, the vegetable blood, 116. 
 
 is sometimes coloured, 117. 
 
 effects of the air on, 118. 
 
 ' cannot be procured quite pure, 119. 
 
 . supposed to contain globules, 119. 
 
 elementary principles of, 121. 
 
 Pubescence is changed by climate and soil, 504, 645. 
 kinds of, 638, 647. 
 
 - affords specific distinctions, 645. 
 
 Pyrites, iron, in large quantity is injurious in soils, 215. 
 
 R. 
 
 Radicles have no medulla, 408. 
 
 in the root originate from the medullary sheath, 409. 
 
 in a branch laid down, spring from the alburnum, 409. 
 
 always form a right angle with the part whence they issue, 4 1 0. 
 
 Radishes, how to produce them early and large, 135. 
 
 Radix filipendula, mistake regarding it, 143. 
 
 Rafn imagined he had detected globules in the proper juice, 119. 
 
 Raleigh, Sir Walter, did not bring the Potatoe to Europe, 27. 
 
 Ranunculus aquatilis has two kinds of leaves, 608. 
 
 Ray, John, his character as a Botanist, 1 1 . 
 
 Resin, its components, 123. 
 
 Rhododendron punctatum, structure of its foliar glands, 634. 
 
 Roots are not nutritious organs in all plants, 127. 
 
 filipendulous, not to be confounded with tuberiferous, 143. 
 
 appendages of, 144. 
 
 in some instances absorb nutriment from the air, 190. 
 
 .. some change their place, 193. 
 
 their direction always opposite to that of rootlets, 195. 
 
 may be produced on the stem and branches, 198. 
 
 VOL. I. Z Z 
 
INDEX SECOND. 
 
 Roots are not elongations of the radicle, 204. 
 
 1 causes of their tapering form, 202. 
 
 circumstances change their natural character, 205. 
 
 animal, may become perennial, 208. 
 
 are the most vital parts of the plant, 209. 
 
 convert oxygen gas into carbonic acid gas, 219. 
 
 - economical uses of, 237. 
 
 yield medicinal agents and dye stuffs, 237. 
 
 - structure of, in dicotyledonous plants, 406. 
 cease to elongate when the apex is destroyed, 408. 
 
 herbaceous, structure of, 431. 
 
 annual, which secrete a milky juice, their structure, 432. 
 
 some have no proper vessels, 433. 
 
 Rubia tinctorum, structure of its stem, 419. 
 Rumphius, a celebrated Botanist, 18. 
 Rush, structure of its stem, 296. 
 
 i. structure of its medullary cells, 297. 
 
 Ruysch, his mode of preparing skeleton leaves, 548. 
 
 S. 
 
 Sambucus nigra, anatomy of its leaf, 576. 
 Sap, is the vegetable chyle, 104. 
 
 its sensible qualities when newly drawn, 107. 
 
 ^ ferments when kept, 108. 
 
 sugar extracted from it, 108. 
 
 - experiments on it, 109. 
 
 - chemical constituents of, 115. 
 
 is found in the ascending vessels only, 115. 
 
 Feburier erroneously thought it was found in two states, 1 1 5. 
 
 elementary principles of, 121. 
 
 vessels through which it is raised in trees, 362. 
 
 Sap-vessels vary in number and size in the same stem, 427. 
 
 are all punctured in annual roots, 431. 
 
 Sarment, its character, 253. 
 
 Saussure, M.-de, considers the cuticle a compound body, 600. 
 
 considers the cuticular apertures glands, 607. 
 
 Scales of bulbs possess a distinct vitality, 176. 
 
 can produce new bulbs, 170. 
 
 of gems differ from leaves, 465. 
 
 resemble seed lobes, 465. 
 
 Schubler, Professor, his experiments on calcareous soils, 214. 
 Secretions, enumeration of, 122. 
 
 ' principles of, 123. 
 
 Senebier, M. his opinion regarding the structure of cells, 324. 
 
 - detected sap in the spiral vessels, 365. 
 
 Severinus, M.A. 6rst taught the art of making skeleton leaves, 548. 
 
 Silicious earths, their effects in soils, 214. 
 
 Smithy Sir E. J. thinks plants are sentient beings, 43. 
 
 his opinions regarding fibrils, 129- 
 
 i accords with the opinion of the ancients respecting the pith, 
 
 374. 
 
 Soils, general remarks on, 210. 
 general components of, 213. 
 
 are hot and cold, 221. 
 
 fertility of, 222. 
 
INDEX SECOND. 
 
 Soils, effects of much manure on them, 223. 
 
 their character known by the plants growing on them, 224. 
 
 a correct knowledge of them difficult to be obtained, 225. 
 
 method of analysing them, 226. 
 
 Sphagnum obtttsifoliuw, structure of its leaf, 551. 
 Spiral vessels are not found in old wood, 360. 
 
 their characters, 83. 
 
 contract and dilate, 361. 
 
 have been considered bronchiae, 363. 
 
 Mr. Knight's opinions respecting them, 864. 
 
 Sprengel, his remarks on the leaf of Sphagnum, 551. 
 Stems, not present in all plants, 242. 
 
 woody, their characters, 285. 
 
 herbaceous, 286. 
 
 structure of those which consist of a homogeneous mass, 291 
 
 monocotyledonous, general structure of, 293. 
 
 have no medullary rays, 302. 
 
 solid, their structure, 294. 
 
 - hollow, their structure, 300. 
 dicotyledonous, general structure of, 315. 
 
 woody, structure of, 316. 
 
 herbaceous, structure of, 413. 
 
 ligneous, not all perennial, 422. 
 
 hollow herbaceous, structure of, 423. 
 
 Stem buds, when they are formed, 395. 
 
 Stipe, structure of the, 304. 
 
 Sucker, analogy to the leaf gem and the branch, 145. 
 
 Syringa vulgaris, anatomy of its leaf, 575. 
 
 Systematic Botany, definition of, 2. 
 
 T. 
 
 Temperature, effects of, on plants, 62. 
 Tendrils, structure of, 654. 
 
 varieties of, 653. 
 
 Thenardy bis experiments on the vegetable secretions, 1 2GV 
 
 Theophrastus, his knowledge of Botany, 7. 
 
 Thutmnigt his theory of the use of the pith, 396. 
 
 Toothwort, scales of, 145. 
 
 Tournefort, his character as a Botanist, 12. 
 
 Tradescantia virginica, structure of its stem, 299. 
 
 . its lateral shoots, 309. 
 
 Trees, increase very little in cold summers, 337. 
 
 how to ascertain their age, 336. 
 
 - are generally barked before they are felled, 337- 
 
 German foresters object to barking them, 337. 
 
 Treviramus noticed the interstitial cellular spaces, 591. 
 
 his remarks on foliar transpiration, 618. 
 
 Tubers belong to the stem rather than to the root, 148. 
 
 are reservoirs of nutriment, 154. 
 
 . formation of, 155. 
 
 anatomy of, 159. 
 
 their connexion with their offsets, 161. 
 
 organization of, 162. 
 
 gems on, how formed, 163. 
 
 are hybernacula, 164. 
 
INDEX SECOND. 
 
 V. 
 
 a celebrated Botanist, 1 2. 
 Vascular texture, 75. 
 '-' layer of the bark, S25. 
 
 Vegetable, definition of the, 49- 
 i torpidity of, in winter, 65. 
 
 gland, definition of the, 627. 
 
 - " earth, components of, 215. 
 Vegetables, they possess vitality, 33. 
 
 - resemble animals in many respects, 33. 
 are not sentient beings, 34. 
 Venus' fly-trap, its singular appendage, 685. 
 Veronica Chamcedrys, its pubescence is bifarious, 645. 
 Vessels, varieties of, in the vegetable, 79. 
 entire, their character, 80. 
 perforated, 81. 
 
 annular, 82. 
 
 spiral, 83. 
 
 ringed membranous, 417. 
 
 Vine, peculiarity in the origin of its branches, 389. 
 
 i- structure of its rootlets, 409. 
 
 Virginian creeper, its power of adhering to upright bodies, 656*. 
 
 Vitality, functions of plants that depend on it, 53. 
 
 W. 
 
 Water a component of soils, 216. 
 
 '. too much of it is injurious to plants, 2 1 6. 
 Wheat, structure of its stem, 300. 
 
 y his opinion regarding fibrils, 129. 
 states the prickle to be vascular, 65 1 . 
 his opinion regarding tendrils, 654. 
 Wood, relative situation of it in stems, 329. 
 .. exists in a hard and a soft state, 330. 
 
 concentric layers of the, 331. 
 origin of the annual zones of, 338. 
 
 use of it to the plant, 354. 
 
 ... period at which it is completely indurated, 357. 
 
 X. 
 
 Xylophylla bears flowers in the serratures of its leaves, 54 1 . 
 
 Y. 
 
 Yucca differs from Palms in growth, 305. 
 
 Z. 
 
 Zea Mays, structure of its leaf, 557- 
 .. its cuticular meshes, 605. 
 
 THE END. 
 
 Printed by S. Gosnell, Little Queen Street, London. 
 

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