IRLF B 3 flSl BOTHY MITH < < , :t::c:o;t. mm :<:<:* :M THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA PRESENTED BY PROF. CHARLES A. KOFOID AND MRS. PRUDENCE W. KOFOID STKTJCTUKAL AND SYSTEMATIC BOTANY: BEING AN ABBANGEMENT OF PLANTS, FORMING A BASIS FOR THE STUDY OP BOTANY, EITHER ON THE LINNJBAN OR NATURAL SYSTEMS. WITH NUMEROUS MICROSCOPICAL AND OTHER ILLUSTRATIONS. EDWARD SMITH, M.D., LL.B., B.A., Late Lecturer on Botany and Anatomy at the Charing- Cross Hospital Medical School, London ; Honorary Secretary of the Medical Society of London ; fyc., fyc. LONDON: CHAELES GKIFFIN AND COMPANY, 10, STATIONERS'-HALL COURT. PREFACE THE following Treatises are devoted to the consideration of the structure of Plants and Animals ; and it has been the aim of the authors to write with scientific accuracy, and with sufficient detail, without introducing discussion upon contested subjects. They trust that the work will be found intelligible to the unlearned, and instructive to those also who have obtained an elementary knowledge of the subjects. Occasional observations will be met with, by which the reader is reminded that Plants and Animals are not only parts of the same great Creation ; but that so closely are some plants associated with the so-called higher kingdom, that no definite line of demarcation can be drawn between them. It is for this reason that the reader is advised to study Botany in connexion with Zoology ; and it is probable that a closci acquaintance with the structure and functions of certain parts of plants will ultimately enable us to trace more correct as well as more striking resemblances between the members of the two kingdoms than have as yet been conceived. For example, no nerves, or analogues of nerves, have as yet been found in plants ; and yet it is quite clear that not only is a low degree of vital sensibility as universal in plants as in animals ; but that in certain instances, as in the sensitive plant, it is developed to a far greater extent than is perceptible in animals taken from the lowest point in the scale of animal life. This mode of investigation will give greater breadth and interest to the study of Natural History than the more simple and yet more difiicult one of studying the parts of plants or of animals as detached points bound together by no universal law ; and it is one, moreover, which tends to train the mind to habits of reflection as well as of observation. The authors have endeavoured to aid the mind in this search by introducing a very large number of microscopic and other illustrative engravings, which have the merit of showing the extreme beauty and elegance of design existing in the composition of plants, and offer many new points for analogical comparison with the exquisitely minute structures of animals. A microscope is now as necessary to tiie naturalist as a telescope to the astronomer. d JfREPACE. in the remarks on Classification, the author of the Treatise on Botany has been drawn, by force of circumstances, to give much prominence to the Linnaean system ; and this is the less to be regretted, since the analysis of the system, and the directions which follow it, may suffice to enable the reader to enter upon the study with facility, and to learn almost without trouble the positions of nearly all the most important plants of native origin. He will also find not only that there is a similarity between plants and animals from the presence of vital functions viz., those of reproduction, respiration, circulation, digestion, growth, and decay but that the very structures which give them bulk and form have in many instances close analogical resemblances. Thus the simple cell, which is the universal basis of animal structures, is, in like manner, and in equal degree, the universal basis of vegetable tissues. The thick- walled cells are very like to bone cells, the milk-bearing vessels to capillary blood- vessels, and their milky juice to the chyle or digested food of animals. Many other parts are analogous to those of. animals in appearance ; whilst others, again, are like them in function. In accordance with the train of reasoning which this close connexion between Plants and Animals suggests, the ordinary method of arranging the animal kingdom haa been reversed ; the arrangement adopted having the obvious advantage of bringing together those plants and animals which so closely resemble each other as to render it sometimes doubtful to which of the kingdoms of Nature they belong. "With these few remarks we conclude the Natural History of PLANTS And INTER- TEBRATED ANIMALS. The remaining portion of Organic Nature, which embraces the nigher forms of animal organization, commencing with the Fishes and terminating with Man, will be concluded in another volume. LONDON, January, 1855. CONTENTS - TREATISE ON BOTANY. PAOB Important objects of BOTANT ... 1 History of the Science, and its distin- guished Promoters 2 Early Classification of PLANTS ... 8 Definition of a Plant 8 Sensitiveness of Plants 4 AXATOMT or STBUCTUBE of Plants . . 6 Elementary Tissues and Formative Fluid 5 Elementary Membrane 6 Elementary Fibre 7 Cellular Tissue, or Parenchyma . . 8 Intercellular Spaces 12 Thick- walled Cells, or Sclerogen . . 12 Fibro-Cellular Tissue 14 Multiplication of Cells 16 Pitted Tissue 17 Woody Tissue 18 Woody Fibre 19 Uses of Woody Fibre 20 The Flax Plant 22 Flax, Cotton, Wool, and Silk ... 23 The Palmyra Palm 24 The Vascular Tissue 25 Spiral Vessels 25 The Ducts 27 Unity of Design pervading the whole Structure of Plants 28 Lacticiferous, or Milk-bearing Vessels 28 The Banyan Tree 80 Caoutchouc and Gutta-Percha ... 81 SECRETIONS or PLANTS ... 81 FAOB Various Plants which secrete pur* Starch 32,83 The Arum Maculatum 83 The Sago Palm, containing a large quantity of Starch 84 Starch Granules 8ft Cellular Character of Starch . . 36 Starch Cells 37 Cells of the Potato 40 Vegetable Secretions Kaphides . . 41 Vegetable Oils 42 Fixed Oils Olive Oil 43 Palm Oil Cocoa-nut Oil Linseed Oil 44 Rape OU Castor Oil Poppy Oil, &c ...,.,..,., 45 Vegetable Butters, Tallow, and Wax . 48 Volatile Oils 47 Gums and Resins 48 Gum Arabic Gum Senegal, &c. . . 48 Reservoirs of Secretion Turpen- tine - ... 48 Tar, Pitch. Resin, Lac, Assafoetida, would clearly establish the existence of vegetables ; but recent microscopic researches have shown that starch is also met with in the lower classes of animals, Fig. 4. Section of a potato, showing the grains of starch inclosed -within cells. Fig. 5. Varieties of DF.SMIDIJE.E, or SKA-WEEDS. A, clusters of Protococcus viridis. B, filament of Schizogonium murale. C, a similar filament, subdividing laterally at D. and in the brain and spinal cord of the higher animals, and even of man himself. Lastly, certain of the Algce, or sea-weeds, as the Desmidiea and Diatomacea (Fig. 5), are still claimed equally by the botanist and the zoologist. Thus simple as at first sight it might seem to state what a plant is as distinguished from an animal, we find it impossible to distinguish the lowest plant from the lowest animal ; and have therefore no alternative than to say that we cannot give an unim- peachable definition of a plant. Definition of the Subject. We shall assume that our readers can recognise a plant, although we cannot define it, and proceed to a description of those various parts of which a plant is composed, and of the arrangement of plants into classes. These two branches of the subject viz., structure and classification have a necessary dependence upon each other ; for the idea of classification implies that certain members have some properties or parts in common such, for instance, as the leaf or flower ; or in other words, that their structure corresponds. Therefore a knowledge of structure is essential to classification ; and before we describe the latter, we must indicate the internal and external parts of which plants are composed. ANATOMY OR STRUCTURE OF PLANTS. Elementary Tissues. In proceeding to a consideration of the anatomy of plants, it will be evident that, as plants in general have external organs, as leaves and flowers, so must they have more minute parts of which these organs are composed. These will correspond with the flesh and bones of the various parts of our body, and are termed " elementary tissues." "We shall take them first in order, since they are formed before the organs can be developed. They will also furnish us with drawings of some of the most exquisitely-minute beauties of nature. Formative Fluid. But as the formation of a leaf, for example, implies the previous existence of elementary tissues, so does the presence of an elementary tissue imply the production of a material fluid, out of which the elementary structure was formed. This latter is called the " formative fluid," or " organic mucus," or " cambium," or " organizable matter" (all of which terms have the same original signification), and is the sole source of production of every tissue foxmd in plants. It is, in this respect, tween the bark and the wood in the early spring. THE ELEMENTARY TISSUES. similar to the blood of animals j for that fluid is the source of all the solid parts of the body. It is semi-transparent and semi-fluid in the internal parts of many plants, and of young plants, and those with thick leaves, more particularly. In this condition it is also found in great abundance between the bark and the wood of all trees in the early spring months ; and then separates those parts (A, Fig. 6), so as to permit the bundles of young wood to pass down from the leaves, and thus enable the tree to grow. It is under these circumstances that the woodman strips the bark from trees which are to be cut down, since then it does not adhere to the wood. The F ig. 6.-Section of the stem of a t- 4-v.' a oi-Hiatirm "WhpTi this tree, the -white line showing fluid is termed cambium in this situation. the colourless cambium, or formative fluid is met with in the external parts of plants, formative fluid, deposited be- it is still semi-transparent ; but it is then solid, as may be observed by scraping the surface of a box-leaf. Elementary Membrane. The first step in the formation of any tissue from this formative fluid is the production of a solid structureless fabric, caUed elementary membrane, and a modification of that fabric termed elementary fibre. It will be ob- served that these elementary parts are structureless, and are produced, apparently, by inspissation or thickening of the formative fluid. The process may be grossly illustrated by a reference to the manufacture of paper, in which the rag-pulp (viz., rags torn into threads and soaked in water) correspond^ to the formative fluid, and the paper, which is subsequently produced, to the elementary membrane. The paper thus obtained is fitted for the manufacture of books, and other articles ; and, in like manner, the ele- mentary membrane is the solid material out of which vegetable tissues are formed. Elementary membrane, then, as in Fig. 7, is structureless; but, theoretically, it is assumed to consist of a layer of rounded particles, which lie side by side, and leave most minute spaces between them. This must be so, when we reflect that all fluids, including the formative fluid, are made up of rounded Fig, 7. Cells of EPIDERMIS, from the seed of the Gourd. drops, with spaces between them ; and that M r hen a fluid is inspissated the drops are brought closer toge- ther. Thus, whilst evident openings are no t naturally met with in membrane, except as shown by Pro- fessor Quekett, in the leaves of a moss called sphag- num (Fig. &), it must be highly though invisibly po- rous, and permit certain fluids to filter through it. It is at first thin and translucent, as may be seen in the membrane covering the seed of the gourd (Fig. 7) ; but in many cases it subsequently becomes thicker and more opaque. In the struc- tures of the ferns (JHices) it assumes a decidedly brown colour ; and in the elaters of Fig. 8. Leaf of the SPHAGNUM, showing at a the natural openings through the tissue. THE ELEMENTARY TISSUES. , a kind of moss (Fig.10), it is of abeautiful red colour; these variations, and especially in thickness, result from the altered duties which it is required to perform. Thus, in the structure of bark and fruits, it is not merely thickened, but is lined by a deposit of hard sedimentary matter, of great power of resistance, in order to increase its strength and to resist decomposition. This hardened tissue is called sclerogen, or hard tissue (Fig. 9). In less extreme cases the deposit is in much smaller quantity, and appears only as minute grains scattered over the surface. Such is the case in the pith of the elder (Sambucus niger Fig. 11). A yet more interesting in- stance of this scattered mode of deposit is found in the hairs of the fornix (a part of the flower) of the Anchu&a italica (Fig. 12). These are covered with a series of tubercles, which are nothing more than isolated masses of a new deposit. In other instances still, the thickening of the membrane appears to have been produced by a deposit of the ordinary transparent organic mucus of which it was originally composed, and still remains transparent, and beyond this differs only from ordinary membrane in that this new matter is laid on unequally, and certain transparent spaces are found where the deposit has not taken place. These spots are oftentimes found arranged Fig. 9. Thick walled cells of the Pinus Web- biana, showing the amount of deposit be- tween the cavity a and the outer cell wall. 10. Fibres of the Junger- mannia crossing each other spi- rally, and, in their natural state, of a red colour. Fig. 11. Pith of the ELDER (Sambucus niger), showing the dotted tissue. Fig. 12. Tuber- cles on the hair of the fornix of the Anchusa Italica. Fig. 13. Section Fig. 14. Elementary of the stem of fibre free from mem- the VINE ( 7i- brane. tis Vinifera], showing the vacant spaces or dotted tissue with great "regularity, and sometimes in a spiral manner ; so that the tissue becomes one of the most beautiful of vegetable microscopic objects. Such tissue is termed " dotted" tissue, and is found in most plants, but more particularly in the common cane (Rattan), and^he vine ( Vitis vinif era-Fig. 13). The use of this tissue is not well known. Elementary Fibre (Fig. 14) is not formed from membrane, as though the latter 8 CELLULAR TISSUE. were cut up or drawn out into threads of almost inconceivable fineness, and therefore a production of membrane ; but both it and the elementary membrane are alike formed out of the formative fluid. Moreover, it is not regarded as a substance separate from membrane, but as a deposit upon one side of a pre-existent mem- brane. Whenever it is found detached from membrane, we must assume that the membrane which supported it has been removed, or that it has detached itself from the membrane. This is admirably shown in Fig. 15, in which the fibre is in process of being denuded by the destruction of the membrane. It is usually, perhaps invariably, solid, and commonly has a rounded figure. It is also transparent, except in a few eases, as in those of the Jungermannia, before referred to, (Fig. 10.) Its use is clearly that of supporting the more extended membrane, and of preventing any folds of it from approximating too closely to each other. Cellular Tissue, or Parenchyma. Having now considered the "raw material" we may proceed to describe the structures which are produced from it. These structures are very varied in appearance, and are ultimately applied to very varied purposes ; but yet, in accordance with the simplicity which marks all the works of God, all this may be reduced to one tissue, a structure which, in addition to its being the fundamental tissue, is, in its own proper form, the most widely dis- tributed of all tissues. This is termed Cellular tissue, to signify that it is made up of Fig. 15 Tube from the RICINUS COM. MUNIS, or castor-oil plant, showing the fibre at a, and the edge of the broken enclosing membrane at b. Magnified 200 diameters.* i 1 Fi ;,, 16 '~ DetachedCens< Fig. 17.-Cells with Fig. 18. SAKCIXA, magnified a, cells of the yeast plant ( Torula cerevisia;) only two attach- 800 diameters, found in the with their granular contents. ments. stomach in states of disease. b, the same cells in process of forming new It is a vegetable of low or- cell8,a 88 eenbythebuging 8 . ganization, and resembles c, similar cells of the sugar plant found in . somewhat the ornament for- the urine in diabetes. mer l y worn on tne breagt of the Jewish high-priest. It consists of a mass of cells. hollow cases or cells. It is, moreover, that tissue which is the first found in all plants. * This and a large portion of the subsequent drawings have been made from original specimens Others have been derived from various sources, and more particularly from the excellent lectures of Professor Quekett, delivered at the Royal College of Surgeons. CELLULAR TISSUE. , 19 ORAXGE. the cell-wall. The cells of which it is composed may be either detached wholly or partially (Fig. 16), or be more or less conjoined in masses, (Figs. 17 and 18). Their characters are of course the best seen when they are detached from each other. The only difficulty, if any, in reference to tissue is in obtaining a correct idea of the simplest of all structures the cell. This may be likened to an orange (Fig. 19), when the rind, a, will correspond to the cell-wall, or boundary of the cell, and the juicy part, b, will represent the contents of the cell. Thus an orange is a cell on a large scale. Or it may be compared to a fowl's egg, when the shell will represent the cell- wall, and the white, with the yolk, the contents of the cell. The egg, therefore, and all similar inclosed bodies, are magnified cells. But the egg has other points of resemblance to the cell. Thus, if the white of the egg be drawn from the shell through a small hole, so that the latter shall remain empty (a process very familiar to school- , . . 5 ' . . iT _ i, n -. boys), we may form a just estimate of the cell-wall as separate b, the contents of the from its contents. A cell in botany, therefore, consists of a cell- cel1 ' wall and contents, although it be so small as to be undiscernible by the unaided sight. "We have already stated that cellular tissue is formed from elementary membrane ; and therefore the cell-wall is nothing more than elementary membrane folded, with the edges adherent together, so as to be able to inclose the contents. The contents of cells are, however, of another nature, and are not produced from elementary membrane. They are of three kinds. 1st, a substance lining the inner side of the cell-wall, as illustrated by the white of egg, and called the primordial utricle of Mohl. It is well shown by the shading in Fig. 20, A. This substance is of ex- ceeding importance in the develop- ment and growth of the cell, and in the production of its other contents. 2nd, a roundish, tolerably - large body, or nucleus, or cytoblast, re- presented in Fig. 21, b, met with in various parts of the cell, but usually near to some part of the cell- wall. This may be likened to the yolk of the egg, and bears the like degree of importance to the other parts of the cell that the yolk bears to the egg. 3rd, cer- tain lesser bodies varying in size, shape, and number, termed nucleoli, formed within the nucleus. It appears that the nucleus is a central point of all actions proceeding within the cell, but that the primordial utricle is the efficient agent. All these parts may be fami- liarly and readily observed in the common strawberry (Fragaria), or the mistletoe berry (Visctim album), or any other juicy fruit. "We assume that our readers have a small microscope of some kind, which may be obtained for a sum varying from 2 to 4 of any respectable optician, with pieces of glass and other apparatus needful for microscopic observation. Take then, with the point of a needle, a piece from the centre of the strawberry, not larger than a pin's head; place it in the glass slide, Fipr. 20. Cell after Unger. The out- lines, C, are intend- ed to represent the boundary of the cell, or the cell-wall. B is the central nu- cleus or cytoblast. A, the lining of the cell-wall or the pri- mordial utricle of Mohl. 21. Cells from the flower- ing stem of the leek (Allittm Porrum), showing at athe cell- wall, and at b the nucleus and the nucleoli. The other contents of the cell are trans- parent. 10 CELLULAR TISSUE. l-'i-. 22. Cells from the Straw- berry, showing their oval shape, loose connexion, large nucleus, and translucent walls. and add a drop of water. Pull it to pieces by the help of two needles, and then cover it with thin glass, and place it under the microscope. It will be found to consist of a mass of large cells (Fig. 22), with transparent walls, and a slightly coloured fluid, in- closing the large rounded nucleus. It is of importance to'obtain clear notions of a cell, since it is the foundation of all other tissues, and since it contains the starch and all other secretions of plants. The figure of the cell is unimportant, and varies very greatly. It is believed to be generally accidental, as the phrase is, the accident being that of pressure : not that by the term " accident" is meant that the figure is a matter of chance ; for in certain parts of plants, as in the pith, for example, the figure, whatever it may be, is always the same. If pressure, therefore, in such cases be the efficient cause, it is exerted in determinate degrees and directions in the various parts of plants. \Vhen the schoolboy blows bubbles of soap-and-water he makes rounded cells, because the walls are of equal weight, and the pressure of the air of an even degree all round. If, however, a drop of water be attached to the bubble it will destroy its rounded form, and elongate it in the direction of the earth, rendering the ceil more or less oval. But if the same soap-and-water be well shaken in a half-filled bottle, the unequal pressure will drive the cells together, and render them distinctly six-sided. This little experiment will convince the reader that the figure of the cell does, in a great degree, depend upon pressure, and that it may be altered as the direction or degree of pressure is changed. So also in plants when each cell is detached from every other, as in decomposing vegetable infusions ; or aa in the yeast plant (Torula Cerevuia-Fig. 16), the form is spherical or ovoid ; when it lies loosely in juicy fruits, as in the strawberry (Fragaria Fig. 22), it is large and nearly round ; when two or more cells are attached end to end, as in the mushroom (Fig. 23), they are ovoid or elongated; and when they are numerous and inclosed in a common skin or bark, they become more or less six-sided, as in the pulp of the orange (Citrus), from mutual and surrounding pressure (Fig. 24). It will then be readily understood that the figures of cells may be innumerable ; but experience has shown that hexa- gonal and octagonal forms are those which most abound. These are the forms observed almost uni- versally in pith, cuticle, leaves, flow- ers, and fruit ; but it should be re- mush attached end membered that regularity of outline, to end. although of common occurrence, is by no means'essential. But, whilst it must be admitted that the figure, in most instances, results from pressure, in other instances it pro- ceeds from a more determinate source ; viz., the direction of the growing process. This is readily understood, if we imagine a spherical cell in which the growing process is not equally carried on all over it, so that it may 'ir\ Fig. 24. Hexagonal cells. Continue to grow spherical ; but whilst the process is arrested at one point it proceeds CELLULAR TISSUE. 11 at an opposite one. Fig. 25. Elongated cells of a mushroom (Boletus) resembling tubes. This will terminate in an elongated cell, such as those observed in the mushrooms (Fungi Fig. 23), and more parti- cularly in a gigantic kind of mushroom termed the Boletus (Fig. 25), in which the length of the cell ex- ceeds the hreadth by many diameters. In this mode it is conceivable that a tube might be formed from a single cell, or from a series of cells, if placed Fig. 26. Diagram showing end to end, and the parti- series of cells which, the breaking up of their tions broken down, al- partition walls, are form- though no satisfactory ing a tube, illustration of this mode of conversion of cells into tubes has yet been discovered (Fig. 26). The terms, oblong, lobed, square (Fig. 27), nmriform (Fig 28 ), prismatical, cylin- drical, compressed, sinuous (Fig. 30), and stellated, have, amongst others, been devised to indicate other forms of cells than those above indicated. The cell varies as greatly in size as its figure ; so that, on the one hand, they may be seen by the naked eye, as in the pulp of orange, lemon, or shad- dock ; on the other they are so minute that it is neces- sary to examine them with a high magnifying power, and ! poo parts of an inch in diameter. I I ' I I , I . I I I.I.I I I Fig. 27. Cubical or Fig. 28. Muri- form cells, or cells resembling the bricks in a wall. square cells. The limits of variation are Some form of cellular tissue constitutes the whole of most of the lower classes of plants, as the Fungi; and in all other plants it is found in the roots, or subterranean (as the potato, radish, and tur- nip) ; in bark, pith, leaves, flowers, seeds, and fruit. The cuticle of leaves, in general, is furnished with cells, having a sinuous or wavy outline, thence termed the sinuous variety (Fig. 29). The most interesting variety of cell is that termed stellate, or star- like, from the radiating form which it assumes. This is well seen in the rush (Fig. 30), in the sweet-burr reed (Sparganium ramosum Fig. *>). * ^ yellow water-lily (Ifu- phar lutea), and in many other water-plants of loose tissue. "We have also met with a beau- tiful illustration of it in the partitions of the cells constituting the thick central parts of the long leaves of the Banana tree (Jtfusa paradisaical}. The construction of this Fig. 29. Very irregular stellate cells from the foot- stalk of a leaf of the sweet- burr reed (Sparganium\ra- mosum). showing the la- Fig. 30. Star -shaped cells of regular character, frdni the stem of a rush, having lacunae at a, bounded by cell-walls, and the union of the cells indicated by the transverse line at the mid- dle of each arm or ray. 12 CELLULAR TISSUE. from of tissue is simple, and results from a puckering inwards of the cell-wall towards the centre. If an orange "be cut through, and the contents partly removed, and the rind be then pressed by two or three fingers and a thumb until the projected portions approach the centre, we may form a correct idea of this form of tissue. Some- thing more, however, is necessary. Inter-cellular Spaces. When a number of cells are pressed closely together, so closely even as to cause them to assume the form of a many (say twelve) sided figure, there will yet be spaces of triangular shape at each corner, at which the walls do not absolutely touch. These are termed inter, cellular spaces, and are the larger by so much as the Fig. 31. The fibrous structure of the -n t c i ose i v applied to each other. When fowl's eo-z-shell, almost exactly simu- UU11& " ., i j -T. lating the cells of the Boletus (Fig. 25). these inter-cellular spaces are placed one over the other for some distance, they constitute inter-cellular passages, and are very abundant in all aquatic plants. The relation which the inter-cellular spaces bear to the stellate cells is this, that when the cell-wall is pressed inwards, in various direc- tions, towards the centre of the cell, the cell seems to be reduced to a series of arms (Fig. 30), whilst the spaces between the cells now appear to be a series of cells themselves (Fig. 32). These enlarged inter-cellular spaces are termed lacunce. The uses of the inter- cellular spaces and pas- sages are of great importance, since, in aqua- of an aquatic tic P lants ("* wnicl1 &ey chiefly abound), they contain the air which imparts buoyancy, and re- tains' it on the surface. This fact may, in some degree, account for the great size of these spaces in many aquatic plants (Fig. 33). In other plants, their use is chiefly that of a depository of secretions. ing the formation of in- ter-cellular spaces in disease. Fig. 33. Air-chambers plant the LIMNOCHAIUS PLUMIERI, ex- kibiting_extreme regularity of form. Before concluding our account of cells we must briefly refer to some modifications. The DOTTED CELL differs from the ordinary cell only in having been constructed from dotted membrane in place of plain. This form is very abundant, and especially in the stem of the vine (Fig. 13) and other fast-growing plants, in the bark of most wooded trees, and in the roots of many plants, as of the common horse-radish. They are usually of large size. Thick-walled Cells, or Sclexogen, are the result of the deposit of the peculiarly hard tissue termed sclerogen, on the inner side of the cell-wall. This substance is usually found deposited in concentric layers (Fig. 34), so that at length CELLULAR TISSUE. 13 g. 34. Beautiful thick wall-cells from the seed of the IlUcium ani- satum, or star-anise, showing the concentric layers, central cavity, and radii. t Fig. 35. A, a mass of thick wall- cells from the PEAK, known as the gritty tissue. B, a cell more highly magnified. the cavity of the cell is nearly filled. There is, however, always a central vacuity, and this is in direct connexion with the cell-wall by a series of canals, which pass through the various layers of hard tissue. This is absolutely necessary, since all actions proceeding in the cell must require the direct communication of the cell- wall. The thick- walled cells constitute the gritty tissue of the pear (Fig.3o) a tissue found in the form of small hard grains near to the centre of the fruit. It is also abundant in the so-called bulbs of many orchids, as the Mirchantia poly- morpha ; on the covering of the seeds of many plants, as of the star - anise (IlUcium anisatum Fig. 34), and the apple (malus Fig. 36) ; in the strong part of many nuts, as of the ivory nut (Figs.37,38),nowso usefully supplying the place of ivory ; in the common haw- thorn ( Cratfeffus") , plum, and our garden Fitr. 36. Sclerogen immediately in- fruits, and in the eiosing the seed of the apple. C ocoa-nutshell(Fig. 39). It is also met with in the bark of almost all trees, as on the beech (Fig. 39). This structure is well seen by cut- ting a thin section, and placing it in a drop of water in the ordinary way ; or. Fig. 37. b, perpendicular section of the bark of the IVORY NCT (Phytelephus macrocarpa} . a, longitudinal section. Both show the lines of communica- tion between the centre and the circumference. Fig. 38. Transverse section of thick n . ,.-,, -, ' , wall-cells of the IVORY NUT. (Phy- better stlll > "7 P lac ~ telephas macrocarpa). ing it in Canada balsam. If the section is too thick it must be ground down on a whetstone, in the Fig. 39. Thick wall-cells from the COCOA NUT shell, with their central cavities and communicating tubes. 14 CELLULAR TISSUE. Fig. 41. Fibre cell from the leaf of the PLECROTHALLIS, having a single fibre. in which sections of tone are prepared for examination, It is impossible to examine these interesting structures, and to observe how admirahly they are adapted to give strength and power of resistance to parts which pre-eminently require it, without being reminded of the great similarity between them and bone cells in the bones of animals. There are, however, several points of dissimilarity; and, amongst others, that the cell- wall, which is retained in thick-walled cells, is lost in bone cells. Fibre Cellular Tissue This form of cell is marked by having one or more fibres wound in a spiral direction on its inner side (Figs 41 & 43). ri 40 . _ Concentric laycr , of Sclero . The fibre may be loose in the cell, as in the Opuntia gen j n ^ ce n s of the bark of tue vulgaris (Fig. 42), where it is flat, or in the elongated BEECH TREE (Fagus). cell of the hairs on the seed of the Cottomia grandiflora, or of the common sage, where 'it is round. We have already re- ferred to elementary fibre (p.7); and have only further to remark that it obtains its spiral direction by the growing process being car- ried on at the free end, hilst the other part of the fibre is attached to the mem- brane. In this mode the resistance is unequal, and a circular or spiral direc- tion is given to the new structure. This form of cell is very abundant, and is probably more or less filled with air, since the inclosed fibre is well fitted to prevent the collapse of the two sides of the cell. It is usual to find the cells not isolated, but in clusters, and oftentimes arranged in masses with much symmetry, as may be seen in the drawing (Fig. 44) of the fibro- cellular tissue lying in situ in the leaf of the Pleurothallis. There is no [structure in animals corresponding with the nbro-eellular tissue in vegetables ; but cellular tissue in the simple form is exceedingly abundant, and, in the form of fat cells (Fig. 45), bears great resemblance to cells of vegetable origin. It is also an interesting fact that the cartilage of the ear of the rat and mouse (Fig. 46), and mere particularly of the rudimentary spinal column of the lamprey, is so modified as almost exactly to simulate a vegetable cell. Fi Fig. 42. Fibre cell from the OPUKTIA VTJLGARIS, show- ing a flattened fibre lying detached from the cell- wall. 43. Fibre cell from the leaf of an ORCHIS (Saccola- bium guttatum), having seve- ral fibres wound in opposite directions. CELLULAR TISSUE. the Pleurothallis ruscifolia. This resemblance between animal and vegetable structures is equally well seen in the tissue of the egg - shell (Fig. 31), when contrasted with the elongated cells of the Bo- letus (Fig. 25). It is an evi- dence of the power and wis- Fig. 44. Cells of fibro-cellular tissue dom'of the De- in situ, A, in the leaf of an ORCHIS, ~* " -"- ity that all the tissues, both in animals and plants, are produced from one simple structure the fundamental cell. The uses of the cellular tissue are : 1st. To contain various important secretions, as that of starch, and the organs of reproduction in all classes of plants. 2nd. To carry on the circulation more or less in all plants, but more particularly in those which con- Fig. 46.-Cartilage from the sist only of this tissue. This is well exemplified in ear of the rat, closely re- fa e i ea f O f the Vattisneria (Fig. 47), in which the sembling loose cellular , ,. , ,, tissue in vegetables. circulation may be seen proceeding under the microscope. 1 Fig. 45. Fat cells in animals. Fig. 47. Leaf of an aquatic plant, the VALLISNERIA SPIRALIS, showing the circulation in plants. 1 represents the leaf after the upper surface has been sliced off, and shows at B the cellular tissue, with small rounded grains, chiefly composed of starch, and a larger detached body the nucleus. The portion at C is a bundle of woody fibre, in which the circulation is also proceeding. The circulation proceeds around each cell separately, and the arrows indicate its direction along the bottom of each cell. 2 has been drawn from the surface of the leaf, and shows a number of starch granules in cells chiefly aggregated together, and which do net circulate. Magnified two hundred diameters. 1Q MULTIPLICATION OF CELLS. n Paper, 3rd. By the tenacity of its structure, and the looseness of its parts, to bind the component parts of the plant together, and to increase its elasticity. 4th. It has for thousands of years been of great use to man for various eco- nomic purposes : First, in the form of papyrus, or the paper derived from the stem of a rush of that name, and employed as such by the ancient Egyptians, Grecians, and Eomans, until long after the birth of Christ. In a similar way it is still used by the Chinese, and by them is derived from the pith of a plant (JEschynomene Fig. 48), which they cut into very thin slices. This material lends a charm to Chinese drawings, since its cellu- lar character enables it to absorb the colour- ing materials in great abundance. Secondly, as a textile fabric. The mummy-eloths of the Peruvians, who existed long before the era of Montczuma and the Spanish invasion, are com- posed of this tissue only. At the present time we ob- tain cotton (Fig. 62 B) chiefly from America, where it is derived from the seeds of the cotton plant (Gos- sypiuin). It is far less resisting and durable than woody fibre or linen ; but its comparative abun- !. Section of the Chinese rice- dance, low price, and easy working have obtained , or JSschymomene, showing large m, -.-, -, cells with a scattered deposit. for it great favour. The present war with Russia will probably induce a determination to use the cotton cell to the still greater exclusion of the woody fibre ; and it has recently been shown in America that ropes made of cotton are far stronger and more durable than has hitherto been believed. Paper is made from the manufactured cotton, and also from the refuse part of the raw material. Multiplication of Cells. It is not within the limits of this essay to enter upon the interesting question of the production of cells ; but we may state that a common mode is that of division of the cell into two or more cells. This is effected in the fol- lowing manner : First, there is an aggregation of the con- tents of the cell around the nucleus, whilst the nucleus manifests a disposition to divide itself into two by a line of construction on either side. Secondly, the cell- wall is bent inwards towards the point of division of the nucleus, and by degrees insinuates itself between the two parts of the nucleus as the division of the latter proceeds, until at length the cell- walls from opposite sides meet at the centre of the nucleus, and the nucleus is divided, and two cells pro- luced. Each of the new cells contains half the original Fig . ^.-various stages of de- Mis, which now constitutes the nucleus of each cell ; velopment of the HJBMATO- and after a period it is prepared to subdivide and to form another cell, and thus progressively, so long as the vital process lasts. In this way it is conceivable that an im- mense multitude of cells may be produced ; and should the d, a divided cell again repeating division be speedily effected, we may form a conception of thc process of subdivision - ^ the astounding fact, that in some of the fast-growing cellular plants as the mushroom -the cells have been produced at the rate of sixty-six millions in a minute. C t Vl ccus , the%%?eparing to divide. PITTED TISSUE. 17 Fig. 50. Section of the root of the ALDER TIIEE (Alnus), sho-sving the large-sized pores, or se- mi-transparent spaces, of its pitted tissue. It is proper to state further, that certain authorities attribute the production of cells to the evolution of bubbles of gas in an azotized fluid, and they are of opinion that only by that mode can we account for the extreme rapidity with which cells are developed. Bothrenchym, or Fitted Tissue; "We now proceed to describe the various modifications of the fundamental cellular tissue, and first, that of Bothrenchym, since it is very nearly allied to cellular tissue. It is so called from two Greek words signify- ing pitted tissue, to indicate that a number of translucent spots are distributed over its surface. We have already described the mode of formation of this tissue when considering dotted cells, p. 7. It differs from dotted cells chiefly in size ; for it may be regarded as a series of very large cells, placed end to end, and separated from each other by obliquely-placed partitions. At a later period of life it puts on the character of a tube by the breaking-up and removal of the partitions. Its ordinary position in plants is in the stems of wooded plants, and more particularly of such as attach themselves to other trees for support, and grow rapidly. Thus it is met with on a thin longitudinal section of almost all trees, but more readily in the alder (Fig. 50), vine, clematis, cane (Rattan}^ and similar fast-growing plants, and wherever a rapid circulation is proceeding. In this respect it differs from mere dotted cellular tissue, since that is more commonly found in the herbaceous than wooded plants. This, in common with other vegetable tissues, retains its^ characters perfectly for thousands of years, as may be observed in the annexed figure of a duct (Fig. 51), taken from a piece of anthracite coal. It is not uncommon to find a spiral fibre associated with the dotted tissue, as in Fig. 52, when the tissue may be regarded as a spiral duct with pores. It is a microscopic object of much interest, and very easily obtained. Take a piece of common cane, and having cut away a por- tion of the outside, take a thin section down the cane, and place it under the microscope in a drop of water. The little pits will be seen with much ease, as also the large size of the tissue as compared with the woody tissue which accompanies it. We have found the best illustration of it in a piece of deeply-coloured rose-wood, for there the dark tint of the secretion gave a peculiar distinctness to the tissue. Its chief use in plants is to carry on the circulation with great rapidity, and is therefore particularly necessary in such plants as grow in southern and eastern climes, and yield refreshing juices, as, for example, the vegetable fountains of India. The importance of this tissue to all plants may be inferred from the large amount of vapour which they throw off by perspiration. Thus an ordinary-sized cabbage, in our climate, was found to perspire to the extent of 1 Ib. 9 oz., and a sun- flower to that of 1 Ib. 14 oz. in a day of twelve hours ; and it is evident that the great heat of southern climes must induce a far greater amount of perspiration, and, by consequence, require a more active circulation. The fluid thus exhaled is supplied chiefly by the bothrenchym, which therefore has a circulation proceeding from the roots towards the leaves of the plant. This function is not Fig. 51 Porous duct, from An- thracite coal. Fig. 52. Pore?, and a spiral fibre, from the ELM TREE ( Ul- mus). ORGANIC NATURE. No. XIII. 18 WOODY TISSUE. seriously if at all impeded by the partitions which lie across the tube, as would at first r h U P pear for even should such partitions be perfect, they readily penmt the proper S to niter through them. The great size of this kind of tissue, and the large quantity of fluid which it contains, render it imperative that it should be supported ^ ct ^ e3 more resisting than its own. For this reason it is always found surrounded by bundles of stem- woody tissue. Another function assigned to it in later life is that of conveying air into the interior of the plant. This occurs when the walls of the cell or tube have become imperfect, and would permit contained fluid to pass out of them ; and then th fluid disappears, and its place is supplied by air. A third, and not less important duty, is that of a depository of the secretions of the plant. This only occurs when the tree is mature, and the central parts of the trunk, which are not then devoted to the rapid conveyance of fluid for the purposes of perspiration. The deep-colouring matter of rose-wood and mahogany, and all similar trees, is chiefly found in this tissue. From the above remarks it will be evident that bothrenchym is a tissue of great interest and importance, and is seen in its integrity only in the early life of a plant. Its large size, thin walls, and active functions, seem to predispose it to injury ; ai therefore such tubes have the duty assigned to them of conveying air, or of storing up secretions which do not circulate. Gridiron Tissue.-Under the term of gridiron tissue, Professor Quekett has described an interesting structure, oftentimes met with at the end of the ducts of pitted tissue. It consists of a series of bars which pass transversely across the tube, and occupy the position of the usual transverse septum. It is probably not a distinct structure, but only the remains of the original septum. We have met with fine examples of it in several trees, but more particularly in the alder and white birch (Betula alba). A similar condition has also been observed in a fossil palm found at St. Vincent's. Pleureiichym, or Woody Tissue. The tissue most closely allied to bothrenchym, and yet widely removed from both it and cellular tissue, is pleurenchym, or woody tissue. This constitutes the mass of the stems of our forest trees, and is thus of the utmost social use to man. It is, also, found in all young and tender shoots, and in bundles in the stems of all, even the most delicate O f a dotted duct in flowering plants. Its peculiar characteristic is that of great tena- the alder ( Alnus )- city and power of resistance, and for this its structure is admirably adapted. As these characters are opposed to those of bothrenchym, we are prepared to find a tissue dif- fering widely from that large and wide structure. The contrary is found in woody tissue, for it consists of bundles of very narrow fibres, with tapering extremities, and so placed end to end that the pointed ends overlap each other. Each fibre is very short, and the partitions which result from the apposition of the fibres, end to end, do not interfere with the circulation through them. Moreover, the tube is not com- posed of simple thin membrane only ; but, in addition, has a deposit within it, which, without filling the tube, adds very greatly to the strength of the fibre. Perhaps we have here as good an illustration of the wisdom and power of the Creator as can readily be produced nz., an arrangement whereby the greatest strength and power of resistance and elasticity shall be obtained, and at the same time the functions of cir- culation uninterruptedly maintained. The strength is mainly due to the shortness of each fibre, the connexion by apposite ends of many fibres almost in one direct line, WOODY FIBRE. 19 from the root upwards ; and, lastly, to the deposit on the inner side of the membrane. This sentiment is irresistible, when we remember the various economic purposes to which man in all ages has applied the wood of forest trees, and also the power of resistance and elasticity which trees are required to offer while supporting large branches at a considerable angle, and to prevent their being uprooted or broken to pieces by violent storms, all of which is mainly due to the tissue now under con- sideration. There are two kinds of woody tissue viz., the plain and the glandular. The plain we have already described. The glandular is that form which more nearly resembles bothrenchym, and indeed may easily be mistaken for it. It consists of a plain fibre or tube, such as that already described ; but, in addition, there is super- imposed, with great regularity, a series of rounded translucent bodies called, or rather their m i sca lled, glands (Fig. 56). These are, for Fig. 54. Bundles of woody fibre of the flax plant fJMnim), considerably mag- mfied - de p 0s it and pointed extremities , -., overlapping each the most part, arranged in single rows, and other< are so large as to occupy the whole face of the fibre. There is great difference of opinion as to the nature of these so-called glands ; some authors regarding them as simple concavities in the nature of a simple pit, whilst others believe that there is a pit, and in that pit is deposited the rounded, flattened body termed the gland, or bordered pore. Professor Quekett adopts the opinion that these bor- dered pores lie in concavities between two adherent fibres (Fig. 57). The bordered pore is hollow, and biconvex, so as to fit into the two cavities. They are best seen in a section of wood, taken parallel to the medullary rays. It is not a little remarkable that this form of woody fibre should be found only in one class of trees viz., the Conifer ce, or fir tribe, with their allied genera ; and in such Fig. 56. Section of common fir plants it is the only form of woody tissue met with. If a very thin section of a piece of fresh fir tree, or of a piece of deal or cedar, be examined with the microscope, as before directed, the glands will be seen very distinctly (Fig. 56) ; and if a piece of rotten fir be selected, it will not be difficult to find a spot at which the gland appears to have fallen out. Such also is the case with the coal shale, a large portion of which is composed of the stems of the fir tribe, which have been buried during thousands of years ; and if care be taken to grind down a thin section, not only may the glands and their remains be seen, but in some instances the pits which once contained the gland. This, however, is chiefly a matter of curiosity, since we do not know anything of wood, or deal; showing the pointed extremities of the woody fibre and the gland, or bordered pores, in a single row on each fibre. 20 USES OF WOODY FIBRE. the especial functions of this kind of woody tissue. The botanist, however, attaches value to it, since it enables him to demonstrate, in recent and fossil woods, the^exist- ence of the Conifora, or fir tribe of plants. It is not uncommon to find a spiral fibre associated with this glandular structure, and sometimes, as in the yew (Taxus baccata, Fig. 60), there are two which are wound Fig. 57. Fig. 58. Fig. 59. Fig. 60. Fig. 57. A lateral view of two adjoining fibres to show the concavity in each, and the space formed by both for the reception of the bordered pore. B, bordered pores from the Salisburia adian- llfolia, which are naturally found in cavities similar to those in A. Fig. 58. Similar arrangement of tubercles and cavities of the Aporum anceps. A, a fibre with the tubercles or glands in situ, and projecting. D, the glands detached. C, the concavities on one fibre whence the glands have been removed. B, the spaces for the lodgment of the glands formed by two adjoining fibres. Fig. 59. Rows of bordered pores on the woody fibre of a fossil member of the fir tribe, which had been long buried in the State of Ohio. Fig. 60. Porous woody fibre in the yew (Taxus baccata), with the spiral fibres wound in opposed directions. in opposite directions, and give the appearance of a net- work. This is presumed to assist in maintaining the patency of the tribe. The uses of woody fibre are very varied, and most important, and may be divided into two categories, 1st, such as benefit the plants ; and 2nd, such as benefit man, 1st. Such as benefit the plant. It is the chief organ of the circulation in all wooded plants, and for this purpose pervades the plant from the root to the branches, and even to the minutest leaves and flowers. The current in this tissue is slow and uninterrupted, and is directed upwards from the shoot through the stems to the leaves, and downwards from the leaves through the bark to the root. Thus its current has a twofold direction ; the ascending and chief one being for the purpose of taking the raw sap from the ground, to be digested in the leaves, and the descending being devoted to the removal from the leaves of the digested sap, to be applied to the purposes of the plant, and also of the refuse matter to be car- ried to the roots, and thence thrown out into the soil as a noxious material. These functions are carried on more vigorously during the spring and summer seasons; but it is probable that even in the depths of winter it does not cease. ^ Another function of woody fibre is to be the store-house of the perfected secretions. It is well known that as trees advance in life, the wood assumes a darker colour, and more particularly that lying near to the centre of the stem. This is due to the deposit of the perfected juices in the woody fibre at that point; and when age has matured the tree, it is probable that the woody fibre so employed is no longer fitted for the circu- lation of the sap ; and also, that the perfected sap, when once deposited, does not again USES OF WOODY FIBRE. join in the general circulation. The dark colour of the heart of oak, as contrasted with oak of very recent growth, is an illustration of this fact, as is also the deep colour which is met with in ebony and rosewood. A third duty under this head is that of giving stability to the tree. It only requires a moment's reflection to enable the mind to appreciate the vast power of resistance which is placed in forest trees. The oaks of an English forest have stood a thousand years, notwithstanding the hurricanes and storms to which they have been yearly sub- jected ; and a familar illustration of the most violent storms, of which we hear and read, is that of the tearing up by the roots of the large forest trees. How mighty must be that power which can withstand influences so terrific as those which each person must have occasionally witnessed ! This power is partly due to the mere mechanical hold which the roots have of the soil ; but the tenacity of that hold is almost entirely due to the woody tissue contained in the roots and stem. Again, it is no uncommon occurrence in our old English parks to find branches of old trees which stretch from the trunk to the distance of fifty feet, and which in circumference are as large as trees of considerable growth. These do not stand perpendicularly from the ground, but pass out of the stem at an angle which is in some instances nearly a right angle, and must therefore be kept from falling directly in opposition to the effects of gravity. The strain exerted by such a branch is enormous ; and yet the branch is maintained in its posi- tion for hundreds of years by the simple cohesive strength and tenacity of a series of woody fibres, each one-sixth smaller than a human hair, and too minute to be appreciated by the naked eye. It is probable that no mechanical agency at present in operation could cifect that_ which is thus so readily effected by nature with the most simple agencies. 2ndly. Such as benefit man. We do not refer to the almost infinite uses to which wood, in boards or masses, is applied by man, and the vast multitudes of beautiful objects which his ingenuity has enabled him to prepare out of the varieties of wood which nature has so bountifully provided. Not less useful is the same woody fibre when reduced to very minute bundles or threads. "When the fibres are obtained in tolerably large bundles, they are used in place of bristles for street brooms, and especially when obtained from the cocoa-nut palm. The flax and hemp which are imported so largely into this country, consist of woody fibre, obtained not from the wood of large trees, but from the stems of slender plants. From this raw material, ropes, sacks, linen, lawn, and other textile fabrics, are now made, as some of them have ever been by all nations. Uncivilized, or partially civilized nations, have been accustomed to use the bark of various trees offering this woody fibre in a very divided condition ; and from this have prepared ropes and other articles of utility. It has long been known that cordage of a very strong kind was used by the ancient Egyptians, anterior, in all probability, to the building of the Pyra- mids ; and Mr. Layard has recently exhumed sculptures which show that the yet more ancient Assyrians removed their gigantic winged bulls and other objects by cables of great size and strength. The bark of the lace-tree (Lagetta lintearia) yields a net-work of woody fibre of exquisite beauty, and of great utility, and is used by* the natives of that clime as a ready prepared fabric. An indisputable proof of the antiquity attaching to the use of this fibre is afforded 22 THE FLAX PLANT. in the fact, that the mummy cloths of the ancient Egyptians, which are nearly five thousand years old, are found to be composed of this material. At the present day, this tissue is abundantly used, and is derived from very various sources. Its relative value depends upon the fineness and evenness of the fibre, and upon its elasticity. It has been found that certain kinds of flax have very great powers of resistance when exerted in a straight line, but readily break when they are bent. This is the case with the Is"ew Zealand flax ; and its brittleness is to be attri- buted only to the nature of the material deposited within the tube. The flax obtained in this country, in Ireland, and India, from the Cannabis, has less resisting characters ; but as it does not break so much in the process of hackling, has a higher marketable value. The pine-apple fibre is very capable of minute subdivision, and is very resisting, and consequently very fitted for the manufacture of fine fabrics. Cocoa-nut-palm fibre is also very strong from the presence of secondary deposits. The cost of flax has induced mercantile men to use woody fibre of less durability, bat at the same time of a less costly kind such as that derived from the China- grass, a species of nettle ( Urtica}; and from it much of the less durable linen cloth and pocket-handkerchiefs are now produced. It is well known that the tissue now under consideration occupies a medium between silk and cotton, as it regards resistance durability, and cost. Silk is the produce of a mem- ber of the animal kingdom (Fig. 62 D), and occupies the highest position in the qualities referred to. Labillardiere ascertained that bundles of fibres of equal size, of silk, flax, and cotton, gave the following unequal powers of resistance, on the application of a weight : Silk supported, -without break- ing, a weight of . . . 341bs. New Zealand flax (Phormiuin tenax} . . . . .23* Hemp (Cannabis) . . . igj Flax (Linum) . . . . 11| , Pita-flax (Agave Americana). 7 The resisting powers of cotton are much below the lowest now in- dicated. In order the better to appre- ciate the characters of these tex- tile materials, single fibres of each have been selected and placed side by side (Fig. 62), and to these have been added hairs, or fibres of wool, and silk. These have not only been used largely for centuries in the manufacture injnummy cloths obtained from 0^^' orl-LAx PLANT. is found woven with FLAX, COTTON, WOOL, AND SILK. 23 The last vise to which we shall now refer, is that of affording saccharine juices to man. This is known familiarly in this country in the wine obtained from the fermented juice of the birch tree (Betula alba] . It is still better known in the Northern and "Western States of America, and in Canada, from the sugar-yielding maple (Acer saccharinum}. This is Fig. 62. Fibre of flax, A ; of cotton, B ; of wool, C; and of silk, D ; placed side by side, so that their relative size and markings may be readily contrasted. The fibre or cells of cotton are manifestly much thinner, and less resistiag, than those of the other substances. still a greatly valued^product in the less accessible parts of the country ; but the introduc- tion of the cane sugar of the Southern States is gradually supplanting it in public esti- mation. The sugar obtained from it is very brown, "but sweetens well, and will probably be one of the treasures of the happy housewife ia the fertile paradise of the " far west" for many years to come. In both of the above instances the juice is collected in a similar way wz., by boring one or more holes into the stem of the tree at the period of the year when the sap has most accumulated ; and, as the sap exudes, collecting it in vessels placed at the foot of the tree. The sugar is thence obtained by mere evaporation and subsidence ; but the wine requires tlie subsequent process of saccharine fermen- tation. The spruce-beer in use in Norway, and i&e refreshing juices of India, are obtained in a similar way, and from the same vessels- viz., woody and pitted tissues. Palm- wine is a delicious beverage, obtained from various species of palm, but espe- cially from the cocoa-nut palm (Cocosnucifero), the gomuto palm (Soguerns saccharifer), and the magnificent Palmyra palm (Borassus flaJbelliformis}. The latter is the most widely distributed of all the palm tribe, since it inhabits all the various regions of the Continent and Islands of India. Mr. Fergusson, in the first illustrated book which proceeded from Ceylon, has given a most valuable account of the palm trees of Ceylon. We counsel our readers to peruse it attentively, and especially that portion which describes the Palmyra palm and its products. The juice is procured by crushing the young inflorescence, and cutting off the upper part. It is then collected in a vessel attached to the cut end, and the daily discharge of the sap is facilitated by cutting a new slice every day. The fresh sap, called taree, or toddy, is very refreshing ; and, if allowed to evaporate, yields a deposit of coarse sugar, or jaggery. "When fer- 24 THE PALMYKA PALM, tnented, it becomes a very excellent wine, and the most intoxicating of all tropical beverages. Fig. 63. The PALMYRA PALM (Borassus flabelliformis) yielding Palm Wine. The size of woody fibre varies from T ^ to ^u part of an inch, and is the larges in hot climates, for the reasons already indicated. THE VASCULAR TISSUE. 25 The position of woody fibre is readily determined, stems of wooded trees, but is found in single bundles in the stems of delicate herbaceous plants, and may be readily seen there when the stem is torn across. In a similar manner it occupies the thin cuticle of herbs, and may be readily observed in the ridges, or veins, which run from the root upwards. It is also met with in the bark of all trees, in the veins of leaves and flowers, and even accompanying the spiral vessels into the fruit of plants. Vascular Tissue or Trachenchym. The tis- sues which we have already described are chiefly de- voted to the circulation of fluids, or to the inclosure of solid substances. Those, under this head, are in great part associated with the transmission of air within the plant. They arc divided into two classes viz., spiral vessels and ducts, and are, perhaps, the most beautiful microscopic objects in plants. It is not at all times easy to distinguish between these two classes of struc- tures, since both consists of thin'membrane in a tubular form, and inclosing a fibre wound in a spiral direc- tion. The theoretical distinction is, that the fibre of the spiral vessel may be unrolled without' breaking, It constitutes not only the A Fig. 64. Spiral Vessels. A, a simple spiral vessel, that is, having but one fibre. The lines bounding tbe pointed extremity represent the inclosing mem- brane. B, a compound spiral, or a vessel composed of many fibres, wound in a spiral manner. C, a compound spiral from the Canna bicolor, with five spiral fibres : more highly magnified. r hilst that of the duct is inseparably connected with the membrane, and cannot be unrolled in its integrity. This general distinction is doubtless correct ; but an unrolled spiral vessel, and a duct, in which the membrane con- necting the spiral fibre has been destroyed, have a very close resemblance to each other. It is highly probable that the distinction is less one of nature than one established by botanists as a matter of convenience. The SPIRAL VESSEL is a cylindrical tube with conical extremities, and having one or more fibres wound as a right or left-handed screw, which may unroll without breaking. It has been disputed whether the fibre is placed within or without the membrane, and whether it is solid or hollow ; but we are of opinion that it is inclosed by the membrane, and that it is always solid. These vessels are not individually of great length, but are con- nected together by their coni- cal extremities; and it is not unusual to find the intervening partition ruptured. When but one fibre is inclosed the vessel is termed a simple spiral vessel (Fig. 64 A) ; but when two or more exist, it receives the appellation of compound (Fig. 64 B & C). In some instances, upwards of twenty fibres have been counted in a compound spiral vessel. The spiral vessels are very numerous in Fig. 65. A bundle of spiral vessels from the veins of the hazel nut (Corylus avellana), showing their great num- ber and very minute size. They are embedded in a mass of hexagonal cellular tissue, as represented at a. Mag- nified 200 diameters. 26 THE \ASCULAR TISSUE. all flowering plants, but more so in certain bulbous plants, as that of a squill growing in the neighbourhood of the Mediterranean. The inhabitants collect them, and tie them in bundles to be used in the lighting of cigars an office for which their smouldering flame renders them well adapted. They are met with in all parts of plants except the roots, but more particularly immediately surrounding the pith, and in all parts emanating from it viz., branches, leaves, flowers, and fruit. They may be readily obtained by cautiously cutting through the cuticle of the footstalk of the strawberry -leaf (Fra- ffctria'), and then gently separating the divided^ portions, when they appear as very fine threads arrange:! in loose spires. They abound in the veins of leaves, and even in the minutest parts of the most delicate flowers. They are also found in the foot-stalks of all fruits, and in the vascular bundles which enter the minutest seeds. This may readily be seen by tearing the seed of the strawberry from the fruit, and placing it in water under the microscope. The spiral vessel is there exceedingly minute and beau- tiful. Perhaps, of all positions in which it Fig- 66> _ A por t ion of a bund i e O f spiral vessels from may be the best inspected, that of the the stem of the potato plant (Solatium tuberosum), ., , embedded in loose cellular tissue, as represented at a. veins running over the brown coat- The tubular character of the tissue is well seen at 6, ing of the common hazel nut ( Corvlus where the separation of the fibres permits the observer 77 I?- ^K\ L J.T- i MI to look within the tube. At that point also the in- MMUfHUjJtlg. bo), alter the shell has closing membrane is well delineated. These are been removed, is the most accessible of lar ^ e size > and > with tQOSe of Fi - 65 ma l wel1 re - mi -, , present the two extremes of development. Magnified Ihe brown membrane should be 200 diameters. soaked in water for a short time, and then the veins carefully torn open with needles, and placed under the microscope. If the light be not passed through them, but be allowed to fall upon them, they appear as bundles of beautifully- white glistening lines, consisting of scores of very minute spires. Such is also the case with other similar fruits, as those of the walnut (Juglans regia] and chestnut (Fagus castanea). They are seen to great advantage also in cer- tain succulent stems, as those of the potato, by cutting the stem across obliquely with a knife in bad condition, and the section placed under the microscope (Fig. 66). They are of very delicate structure, and require other tissues to inclose and protect them. This is chiefly performed by the woody fibre, and thus each vein of a leaf or herbaceous stem has its central bundle of spiral vessels inclosed in a covering of woody fibre. The use of the spiral vessel has been the subject of much investigation, and it appears probable that at some period it conveys air charged with an increased per centage of oxygen, and thus becomes a system of internal respiration, much after the manner of the distribution of the trachea? in insects. At a later period of its existence it is probable that it contains fluid. The spiral fibre is valuable at either of these periods as keeping the tube open, but more particularly when the cavity is filled by air only. THE VASCULAR TISSUE. 27 Ducts are tubes with conical or rounded extremities, and their sides marked by transverse lines or bars. Their size is about twice that of spiral vessels. Their appearance is very various, and depends upon the direction of the spiral fibre which assimilates ducts to spiral vessels, or the presence of other internal deposits, which renders them not unlike pitted tissue. When the spire is so arranged as to differ from that of the spiral vessel only in that it cannot unroll, the vessel is termed a closed duct. When it is broken up at intervals, so that single coils shall be" detached, the term annular is applied (Fig. 67), and properly represents the rings which are so commonly found in ducts. This form is said to be due to the rapidity of the growth, whereby the fibre is carried along more rapidly than the membrane can be produced. The reticulated duct is perhaps the most interesting of the various kinds of ducts, and appears to be formed either by two fibres wound in opposite directions so as to cross each other, or by a single fibre which breaks and anastomoses at intervals. The characteristic feature is that of a net-work. All these various forms of duct, and also other modifica- tions, may be found in the stem of a full grown garden balsam. The succulent stems of herbaceous plants are the more common positions in which ' ducts are found ; but they are abundantly met with in the softer kinds of wood, as of the lime- tree (Tilta), willow (Saliz), or birch (Betula). We cannot omit to refer again to the analogies which exist in the structure of animals and vegetables. Thus, in the animal Fig. 68. The tracheae kingdom, we have a tube which very closely resembles a spiral of & th w C 'er beetle 1 vessel, viz., the tracheas of insects. This is clearly shown in having many of the the accompanying figure of the Dyticus (Fig. 68), which repre- sents a tube made simply of a fibre inclosed by membrane. It is unnecessary to refer to all those forms of duct in which we find a secondary deposit so arranged as to give the appearance of pits^ since we have already considered similar structures under the head of Bothrenchym (pp. 7 and 17). But there is one not described as yet viz., the Scalariform or ladder duct. This is so called from the resemblance which the transverse lines bear to the rounds of a ladder. The scalariform duct is of con- siderable size, and usually six-sided, and has a deposit so arranged, on its inner side, that either its presence or its absence causes certain transparent lines to appear at very regular intervals. In some instances so many as twelve sides have been observed ; but whatever may be the number of sides, they are separated by clearly defined perpendicular lines. The transverse bars do not Fig. 69. Scalariform P ass 9*>ite so far as the boundary line of the side a circumstance vessel, showing the -which gives a greater degree of resemblance to the figure of a transverse oars on . . . nine sides, and the ladder. As there are transverse translucent spaces of about equal open character of the size and at equal distances, there will, of course, be alternate transverse and equal bars separating these spaces. These bars are continued with the] boundary line of the side ; and, upon the whole, it appears probable that the deposit has been placed at these points, and that the translucent THE LACTICIFEROUS VESSELS. lines or pores are the parts at which no deposit has occurred. It is still in dispute if this deposit has taken place in the spiral direction so commonly found in vegetable deposits ; but it is quite certain that in a few instances the scalariform has unrolled like a spiral vessel (Fig- 70). The use of these vessels differs little, if at all, from that of other ducts, viz., that of conveying fluids with rapidity ; but there is this great peculiarity, that they are found only in one class of plants viz., the ferns (Filices), and there supplant all other forms of vascular tissue (Fig. 71). Thus there are two great classes of plants which have distinguishing anatomical characters ; viz., the Conifer a ^ 70 _ \ portion of or fir tribe, distinguished by its glandular woody fibre, and the a * large scalariform fern tribe, known readily by its scalariform tissue. The scala- Jg^gBjSS riform tissue is also enduring in a vessel, and showing remarkable degree, as was stated of ^fJ^SSS^ the glandular woody tissue ; for 'ferns, like firs, are abundantly found in the coal measures, and Professor Quekett discovered it in a funereal urn dug up in the island of Anglesey. This appears a favourable point at" which to request the reader to look back and observe the unity of design which appears to pervade the whole structure of plants. We have just seen that there is not, in truth, any essential Fig. 71.-Bundle7f scalariform distinction to be made between the three classes of vas- yesselsinclosed in cellular tis- cular tissue now described spiral vessels, ducts, and scala- L> riform vessels, all of them being composed of a mem- branous tube, with a secondary deposit assuming the spiral direction. It is also evident that these differ in no essential respect from Bothrenchym or pitted tissue ; and from dotted cells and fibre cells, only in size and figure. Thus we have traced the essential identity of the tube with the cell, and of the highly- figured vascular tissue with the simpler cells with a secondary deposit. The woody tissue is, in like manner, an elongated cell of thickened membrane. The arrangement or classification of these structures is not as yet in a satisfactory condition, and it is yet a desideratum to find out some general feature by which they may be grouped in a less artificial manner. That one which has already been referred to viz., the simple membrane and the membrane with a secondary deposit as the basis of all tissues, is a step in the right direction. It is clearly xmphilosophical to regard mere markings as points of distinction, where there is not real difference in structure and functions. So far as we have now accompanied our readers there can be no difficulty in acknowledging that we have simply passed through modifications of a simple cell. Laticiferous, or Milk-bearing Vessels. There is jet another very inte- resting and somewhat less simple form of tissue to be described viz., the milk-bearing tissue so readily inferred to exist from the white exuding juice of the cut dandelion (Leontodori), and poppy (Papaver], or the yellow juices of the Chelidoniurn. The essential characteristics of this tissue is its branched distribution, and the intermitting or pul- satory motion of its contents. In both these respects it differs from other vegetable tissues, and corresponds very closely with the blood-vessels of animals. It is well THE LACTICIFEROUS VESSELS. 29 known that nature never progresses by bounds, but by gentle ascents, and that, not only does one fundamental structure run through the whole of vital_existences (whilst the anatomical characters of widely - separated classes are yet very distinct) ; yet that there are certain similarities which become, as it were, the larger links which unite them together. The structure now under consideration is the large link which binds vegetables and animals together. No other vegetable vascular tissue uniformly branches, and none has a pulsatory motion of its contents ; but both these conditions are universal in the animal kingdom. There is yet another similarity : The Lacticiferous or milk-bearing tissue (Fig. 72), is devoted to the maintenance of the vitality of the other vegetable structures, and not to any extraneous object whatever. If a stem be Figl : 7 l'~ M - iIk V 7 ess ^ ls from tbe . stipules J J of the Jftcus elastica, or India-rubber in great part cut through, the effect is to kill the fig-tree, showing the branched and plant-not so much by destroying its functions as S^S^SS^ofthd? Stints^ by pouring out the milky juice, which should maintain the life of all the structures in fact, by bleeding it to death. This is not the 4. Fig. 73. The smallest vessels or capillaries of the frog's foot, as seen by the microscope, -whilst the circulation is proceeding, a indicates a vessel of a larger sixe, which subdivides at b into c'iie capillaries. The vessels anastomose with each other, and branch in every direction, and con- tain the oval bodies, or blood globules, which correspond to the granules in Fig. 74. Fig. 74. Milk-vessels of a water-plant the| Limnocharis Hiimboldtii, showing their granular con- tents ; and the walls apparently made up of a series of oblong cells of cellular tissue, aud the whole inclosed in hexagonal cells, as shown at b. The arrows indicate the direction of the current. case with the woody tissue ; for if that were nearly drained of its contents the plant would not necessarily perish ; but if the milky juice be withdrawn too -abundantly 30 THE BANYAN TREK. -as from the cow-tree (Palo de Vacca] of Ceylon, or the hya-hya tree, of British Guiana, which yields refreshing juices-the plant droops and dies. The similarity between this structure and the blood-vessels of animals is weU seen in diagrams, Figs. 73 and 74, which represent, side by side, the capillaries or smaller blood-vessels in the frog's foot, with the contained blood highly magnified, and the lacticiferous tissue, with its contents. The undulatory or pulsatory motion of the contents of the tissue may be well seen in the Limnocharis Hamboldtii, a water-plant found in hot-houses (Fig. 74), if a portion be cut off, and exposed to the sun for a short time, and subsequently placed in water. The exposure to the sun causes so much evaporation as to greatly lessen the quantity of fluid in the vessels ; and the subsequent immersion in water enables the plant Fig. 75. The BANYAN TREE (Ficus rdigiosa), showing its original trunks, and the branches which have passed down to the ground and taken root, and have become new centres of growth and nourishment. This troe is so large that a regiment of soldiers may take refuge in its shade. to supply its wants, and to pump, so to speak, vigorously. This diagram is also illustra- tive of the opinion formed by certain authors as to the relations of this tissue viz., that it is very analogous to mere inter-cellular passages. In this view, it is not a distinct tissue, although it may have special functions. The latex, or milky fluid, is of immense service .to man, in two ways more parti- cularly : First As already intimated, it constitutes refreshing beverages, readily obtained, and in large quantities, to travellers in the sunny climes of Asia. Such are the cow- tree of South America, the kiriaghuma (Gymneuralactiferum), and hya-hya (Jabernce- mantana utilvi] before-mentioned, and also the Euphorbia balsamifera, of the Canary CAOUTCHOUC AND GUTTA-PERCHA. 31 Islands, the juice of which, as a sweet milk, or evaporated to a jelly, is taken as a great delicacy, and the Banyan tree (Ficus reUgiosa Fig. 75). Many of these juices also contain medicinal properties of great value. Secondly In the production of caoutchouc, or India-rubber. This invaluable sub- stance is found in all plants, but more particularly in the Fig, Euphorbia, and Cactus trees of the East Indies, South America, and Africa within the torrid zone. Of all these, the fig, known as the Ficus, or Siphonia elastica, is the most valuable ; but in the countries where the manufacture of India-rubber is a daily occupation, it is not exclusively selected. This increased quantity of caoutchouc in the latex of hot cli- mates is believed to be due to the powerfully elaborating property of the sun's rays in those climates. The following is the mode in which the India-rubber is prepared from the milky juice : The natives having selected a fine specimen of the Siphonia elastica, sixty feet in height, make deep incisions into its smooth, brownish-gray bark; after which the white juice flaws forth in considerable abundance. Before it dries upon the trunk, or in a hole at the foot of the tree, it is spread over bottles of unburnt clay, and dried over a smoking fire ; care being taken to prevent the flame burning it. When it is dried, another coating of the juice is placed upon it, and that again is he^d over the fire ; and the process is thus repeated, until the required thickness has been attained. When the process is completed the bottle of clay is broken and the pieces extracted ; after which the Indian-rubber is ready for the market. It is met with in commerce of various colours, terminating in a deep black ; but the juice is originally colourless, and the colour is produced by the smoke in which it is immersed in the process of drying. This tissue is found in all parts of a plant ; but, from its ramifications amongst other tissues, cannot be readily separated. It is most readily seen in the fresh stipules of the Ficus elastica. Gutta-percha is another invaluable substance, recently obtained from the latex of certain plants, and especially of the class called Sapotacea, abounding in the Indian Archipelago. The trees whence it is obtained are large, but not otherwise valuable. The gutta-percha is obtained by incising the bark and collecting the milky juice, which speedily coagulates. Each tree yields from twenty to fifty Ibs., so that the destruction of a large number of trees is required in order to meet the present enormous demand for this article of commerce. It appears that the proper term is Gutta-Pulo-Percha gutta signifying gum in the Malay language, and Pulo-Percha the island whence it is obtained. When translated into English words, it is " gum of the ragged island." The Secretions of Plants. We now proceed to describe the chief secretions of plants, some of which are of the utmost value to man. They are Starch, Eaphidcs, Silica, Oils, and Fats, and the colouring principles of plants. Starch. This alimentary substance was, until recently, believed to be peculiar to vegetables ; and, although it is not strictly, it is almost exclusively confined to them. It is, moreover, the chief element in vegetables, which renders them fit to be the food of animals, and enjoys, therefore, a position of the utmost importance. Starch is not to be understood as directly represented by the article of commerce which bears its name ; for, although that is starch, it has been so prepared as to lose the anatomical charac- teristics which starch in its'natural state possesses. All plants, probably, possess this substance, but in very unequal degrees ; and it is only when it" exists in quantities much greater than the plant requires for its own purposes that it is sought after by 32 THE SECRETIONS OF PLANTS STARCH. man. As a rule, a vegetable, if nutritious at all, is so in proportion to the amount of starch which it contains ; but there are many plants which yield starch in tole- rable abundance, but which are inedible from the presence of acid or poisonous fluids. In selecting articles of food, it is needful to bear both these facts in mind. It is most abundantly found in the seeds of plants, and especially in the cereals, or wheat tribe ; and thence this article of diet is accounted to be very nutritious. It is also met with in the cellular tissue of plants, and especially in the cellular matrix of such underground stems as the potato, turnip, and radish, and the stems of such plants as the sago-palm-fig, whence it is obtained in large quantities. Green vegetables contain a considerable proportion of starch at the period of their maturity ; but they are nutritive beyond the quantity of starch contained by them, since the vegetable structure itself has a very similar chemical composition to that of starch. Starch is also found in the bark of trees ; and, during periods of famine, the bark of certain trees in this country has been made into bread. This practice ,was more common in the northern countries, where Nature has less bountifully distributed her treasures. Mr. Laing, in his interesting " Journal of a Eesidence in Norway," states 'that he observed many trees which had been thus dila- pidated; and, after referring to the country mode of grinding meal, remarks " This mode of grinding and baking makes intelligible the use of bread of the bark of the fir-tree in years of scarcity. Its inner rind (liber], kiln-dried, may undoubtedly be ground along with the husks and grain, and add to the quantity of meal it may even be nutritious. I had previously been rather disposed to doubt the fact, and to laugh at the idea of a traveller dining on sawdust pudding and timber^bread. In years of scarcity, however, this use of fir-bark is more extensive than is generally supposed. The present dilapidated state of the forests is ascribed to the great destruction of young trees, for this purpose, in the year 1812." But, notwithstanding its universal distribution, it is to be found in quantities only in the storehouses provided by nature viz., the seeds and fruit of plants ; the potato (Solanum tubcrosum), carrot (Daucus carota), turnip (Brassica rapa), and similar underground stems, as they arc termed ; and, lastly, the stems of palms, and similar cndbffenotu plants. Amongst plants Avhich yield an acrid juice with the starch, we may first mention the tapioca plant, or Yucca duke, the sap of which is used to poison the arrows ; but the starch is fitted for food after the roots have been beaten, dried, heated, washed, and pressed. The common arum of this country was formerly collected on account of the starch or arrowroot contained in its corm or underground stem ; but the aridity of the juice was so great as to cause the hands of the operator to inflame. The horse-chestnut is not edible for the like reason, although it contains much starch, and is excellent food for some inferior animals. It is also known that whilst the tubers of the potato are so wholesome, the berries are poisonous. The horse- chestnut was tried in this country as an article of diet in 1846, but its acidity arrested its use. Those plants which offer the starch unmixed with deleterious matters are : 1st. All the grasses, including, wheat, oats, barley, rye, and all trinclar seed-bearing plants. 2. Many leguminous and cruciferae, or pod-bearing plants, such as the pea, bear., and lentil, cabbage, and turnips. STARCH. 33 3. The Marantn arundinacea, or arrow-root plant. 4. The sago palm. 5. Several bulbs and tubers, as the onion and potato. 6. A species of plantain, which offers it so abundantly and in small masses that it was introduced and sold in this country as flour. The most interesting illustration of the admixture of deleterious and edible substances is that of the preparation of the Cassava meal, a kind of arrow-root, from the Mandiocca farinha, a tree pos- sessing excellent starch, and, at the same time, the most poisonous juices. Its preparation is thus graphically de- scribed by M. Schleiden : " In a dense forest of Guiana the Indian chief has stretched his sleeping mat, between two high stems of the magnolia; he rests indolently smoking beneath the shade of the broad-leaved banana, gazing at the doings of his family around. His wife pounds the gathered mandive roots, with a wooden club, in the hollowed trunk of a tree, and wraps the thick pulp in a com- pact net, made from the tough leaves Fig> 76 The AR MACULATUM, with its cormus, or , ,., , root, containing starch. of the great lily plants. The long bundle is hung upon a stick which rests on two forks, and a heavy stone is fastened to the bottom, the weight of which causes the juice to be pressed out. This runs into a shell of the calabash gourd (Crescentia Cujete) placed beneath. Close by squats a little boy, and dips his father's arrows in the deadly milk, while the wife lights a fire to dry the pressed roots, and by heat to drive off more completely the votalilo poison- ous matter. Next, it is powdered between two stones, and the cassava meal is ready. Meanwhile, the boy has completed his evil task ; the sap, after standing some con- siderable time, has deposited a delicate, white starch, from which the poisonous fluid is poured off. The meal is then well washed with water, and is their fine white tapioca, resembling in every respect arrow-root." Let not our readers be alarmed when they eat their next tapioca pudding; but yet it may be well to remember how closely life and death are associated. Starch is met with in two forms : First, amorphous; that is in Bne powder, without any distinct form or marking, as in the Salep, commonly sold in this country. Secondly, and almost universally in the form of variously-figured cells. We have nothing tc add in reference to the former, except that, in common with the other form, it is found inclosed in the large cells of vegetables, as may be seen in the section of the potato (Fig. 83), and that the presence of both alike mar be chemi- TOL. ii. 'D 34: THE SAGO PALM. cally demonstrated, if a drop of a solution of iodine be added to the smallest quantity of starch and water, and placed under the microscope. The chemical effect of the iodine is to colour the starch of a beautiful deep violet shade. We may also add, that as starch has the property of polarizing light, its presence may be readily shown by placing it in the microscope with the polarizing apparatus. Fig. 77. The SAGO PALM (Cycas revoluta), contain 1 ! g a large quantity of starch in its stem. Further attention is, however, necessary to the consideration of the second kind of starch, or that consisting of cells ; and chiefly on the ground, that it is possible to dis- tinguish the starch grains or cells of one plant from those of another, and thus to detect the adulterations which are practised in reference to flour, bread, arrow-root, and other articles of farinaceous food. Much attention has been given to this mattei during the past ten years, and with the result, it is believed, of having lessened, at Least, the frequency with which fraud has been perpetrated. Starch grains are distinguished from each other by their size, figure, and markings. STARCH GRAINS. 35 In reference to their size it will suffice to glance at Fig. 78, to show that it varies very greatly, and that it is very small in the rice (Fig. 78 a), and very large in the Tous les Mois (Fig. 78 b] ; whilst wheat (Fig. 78 c) and potato (Fig. 78 d] starch occupies a medium position. The ordinary figure is rounded or oval, sometimes much flattened, as in the Curcuma leucorrhiza, or East Indian arrow-root ; less flattened, as in the wheat and barley ; oval and roundish, as in the potato and the pea (Fig. 78 t). The figure, however, although permanent in each variety is. its general charac- acteristics, varies considerably. In every specimen a multitude of smaller or imperfectly-developed granules will be observed; and they do not assume the form which is obtained by the perfect granule. The consideration of the markings and their nature is the most interesting and impor- tant part of the subject, inasmuch as they are most permanent, and imply an acquaintance with the structure of the cell. "We shall therefore say a few words in re- ference to the composition of the starch grain before we describe the markings which distinguish the various kinds of starch. A reference to Fig. 78 will show that in almost all instances there is a central spot (Fig. 78, 1), called the hole or hilum, and that a series of lines arrange themselves around it. This will be better seen in Fig. 78 c, which represents the cell much more Fig. 78. The more common forms of the starch cell, highly magnified. The nature of f ** TSS^SSlgSft^,. c, wheat, do., do., faintly marked with concentric lines. d, potato ; medium size, flattened, and with well-inarked lines. e, the same, more highly magnified, so as to show the nucleus, 1, and the markings, 2. /, Tout les Hois, the largest kind of starch, of oval shape, well-developed markings, and sometimes with a double hilum, 1. g, the same, ruptured by the application of heat, so that the membrane at h is retracted and corrugated, and the contents exposed. t, the starch of the common pea (Pisum), with its deep central folding or cavity. The precise figure of thui cavity or folding differs in various grains. both of these is the point in dispute. There is a cell-wall, as may be seen in Fig. 78 y, in which, on the application of heat, it has rup- tured, and is a little reflected. But is there no central cavity, and do the lines observed on the gra- nules correspond with layers within the cell-wall ? There have been two leading views on these points. 1st. That the starch granule is really a vesicle or cell, having an inclosing wall differing in consistence, and perhaps in chemical characters, from the starch-itsel 36 STARCH GRAINS. 2nd. That it is a solid body, constituted by layers one upon the other, beginning either -within (centripetal), or without (centrifugal). On the first of these theories the markings upon the surface are produced by the folding of the cell-wall ; and on the second, by the successive layers of the solid starch. Leeuwenhoeck, a celebrated microscopist, published certain investigations made by him nearly a century and a-half ago, in which he showed the cellular character of starch. Since his era many eminent observers have adopted his views, with certain modifications ; and very recently two, whose experiments we shall describe, viz , M. Martin, the librarian of the Imperial Polytechnic Institute at Yienna, and Mr, Busk, a distinguished naval surgeon and microscopist. Both these gen- tlemen agree in the theory of the constitution of the starch granule m., that it is a cell, having a cell-wall much larger than the contents of the cell in the dried state, and, therefore, puckered and plaited, as indicated by the lines upon the surface. M. Martin says, that "the primary form of the starch grain is a spherical or ovate cell. If this be considered as empty, and so contracted that one-half lies in the other half, a watch-glassrshaped basin is formed, which, after boiling and pressure between two glasses, appears, in consequence of the delicacy and elasticity of the membrane, as a flat, round^edged disc." Thus, in his opinion, the ovate cell is inrolled upon itself. Mr. Busk has not satisfied himself in reference to this unfolding of the membrane, but thinks that the swelling up of the cell by the addition of strong sulphuric acid rather indicates the distinction of plaits or folds, and more particularly in such varieties of starch as have, when dried, a puckered centre, as is exhibited in Figs. 78 /, and 80. As this is a most interesting and undetermined question, and one, more- over, which our intelligent readers who have microscopes may be desirous to investi- gate, we subjoin the methods adopted by the observers just mentioned. In any examination of starch it is only necessary to take a pin's point of flour of wheat, or of some other grain, or to scrape a very little morsel from the cut surface of a potato, and in both cases the starch will be found partly in free grains and partly inclosed as masses of grain within the cellular tissue of the plant. The grains of Tous Us Mois (Fig. 78 /) are the largest, and therefore, in many re- spects, the most convenient for examination ; as also those of the horse-chestnut (Fig. 79), and pea (Fig. 78 ), when it is desired to notice the unfolding of the central puckerings. M. Martin's method was as follows : " Between two very thin glasses, of the same size as the stage of the microscope, a little starch, with a sufficient quantity of water, is to be put, and the former well spread out with the finger, to prevent, as much as possible, the formation of bubbles, The number of starch grains in the field of view should not exceed ten or fifteen. The glasses should He freely on the spring-piece, which must be raised by means of two pieces of cork, introduced below it, so that while the two glasses are lying right upon the object-bearer, a current of cold air will ascend from below, and permit the little flame to continue burning in the hole of or below the stage. As the glasses are wide they protect the microscope from too great a heat or other danger. The small flame is to be obtained from a common thread, doubled and slightly waxed. This, when ignited, gives a flame quite sufficient to boil the starch." The object of this experiment is to cauee the distension of the cell-wall by the introduction within the cell of hot water, and thereby to notice what changes take place in the markings upon the surface. Mr. Busk seeks the same end by applying the most powerful of acids m., concen- THE STARCH CELL. 37 trated sulphuric acid, or oil of vitriol. Our readers, whilst repeating this experiment, must exercise the greatest caution lest they burn their fingers and clothes. The fol- lowing is Mr. Busk's method : "A small quantity of the starch is placed upon a slip of glass, and covered with five or six drops of water, in which it is well stirred about ; and with the point of a slender rod of glass the smallest quantity of solution of iodine is applied, which is to be quickly and well mixed with the starch and water. Any excess of water must be allowed to drain off, leaving the moistened starch between, and a portion of it is then to be covered with a piece of thin glass. It must then be placed on the microscope, and a quarter or one-fifth object glass brought to a focus close to the upper edge of the piece of thin glass. With a slen- der glass rod a small drop of sulphuric acid is to be care- fully placed imme- diately upon, or rather above, the edge of the cover, care being taken that it does not run over it. The acid, of course, quickly insinuates itself be- tween the glasses, and its course may be traced by the rapid change in the appearance of the starch grains with which it comes in contact. The course of the acid is to be followed by moving the object up wards ; and when, from its diffusion, the re- agent begins to act more slowly, the peculiar changes in the starch granules, now also less rapid, may be readily witnessed." M. Martin thus describes the changes observed by him : " First the starch grain Fig. 79. 38 THE STARCH CELL. sinks in that place where the nucleus is situated. On the surface minute fissures appear, two of which almost regularly diverge towards the thicker end of the grain. The grain continues to be depressed inwards until a cavity is formed, which is sur- rounded by an elevated edge. In proportion as the grain swells up, this ridge increases in circumference, and decreases in breadth ; that is, continues to get flatter, until fissures, mostly of a star-like form, appear in the hitherto little altered thicker part of the grain. The process is not very rapidly developed, and it is very difficult for the eye to follow it. Suddenly something is torn off, the grain is extended lengthways, and in the next moment a wrinkled skin of a rounded, generally oval shape, lies on the glass." Fur- ther examination shows that they are collapsed bodies, consisting of an extremely fine, but strong and elastic, membrane. Mr. Busk obtained a different impression from his experiment. He considered that the line upon the surface were simply plaits or foldings, and that the whole process consisted of unfolding these plaits, and, by distending the cell, to render the cell- wall perfectly plain and free from any markings. In Fig. 79 A, we have the starch of the horse-chestnut in its unaltered state, and at B is i epresented a stage of the unfolding which results from the use of the sulphuric acid. Fig. 79 c, D, and E, represent other views of this process, showing that the cell becomes gradually larger, until it reaches the great size figured at F. The fringe around the figures c, D, and E he regards as plaits in the process of being unfolded. Figs. 80 a b, have been copied from Schlieden's work, and represent the starch from the cormus or roots of the Arum maculatum, of our hedges, and of the Colchicum autumnale, in which the star-like centre is presumed by Mr. Busk to indicate the central folding of the mem- brane referred to by him. On a review of the whole evidence now offered, we may infer that the starch granule consists of a cell- wall, contracted and plaited when dry, and smooth and distended when heated with mois- ture, and also of contents in insufficient quan- tity to fill it, and thereby leaving a central cavity. On this principle, it is difficult to conceive that the plaits can retain the same characters in the same plants under all atmospheric condi- tions ; and it is proper that we should state that Dr. Allman of Dublin has, during the present year, published an article in the Quarterly Fig. SO.-Starch cells copied from Journal of Microscopic Science, in which, by a fhnflp ft . Schlieden. .-L, - ,, ' * i those of the Colchicum autumnale. the same processes as those above indicated, he *, those of the Arum maculatum, both has come to totally opposite conclusions. In his foldTn^o^cavfr 611 * degrees the central opinion the statement of Fritzsche is correct c, the centra? clvi^y well developed in the viz. , that the starch cell is in fact a series of cells, 8tarch f the Ia18 - placed within each other, as exhibited in Fig. 80 . He sums up his opinions in the following words : 1st. That the starch granule consists of a series of lamella, in the form of closed hollow cells, included one within the other, the most internal inclosing a minute cavity THE STARCH CELL. 39 filled with, amorphous (?) starch ; that the concentric striae visible in the granule indi- cate the surfaces of contact of these lamellae ; and that the so-called nucleus of Fritzsche corresponds to the central cavity. 2nd. That while the lamellae appear to be all identical in chemical constitution, yet the internal differ from the external in consistency or other conditions of inte- gration. 3rd. That the order of deposition of the lamellae is centripetal. 4th. That while the starch granule is thus a lamellated vesicle, it cannot be included in the category of the true vegetable cell, from which it dffers, not only in the absence of a propei nucleus, but in presenting no chemical differentiation between membrane and contents. So widely do equally eminent observers disagree in their description of the same object as seen by the same means ! Rice (Fig. 78 a) is known by the small size of its grains, by their angularity, and the absence of evident markings. Sago starch (Fig. 78 b] is very much larger than that of rice, but still less than that of wheat ; it is rounded, and its surface is rather granular than plaited. Wheat starch (Fig. 78 c) occupies a medium position in point of size, and is more regularly round than any grain of similar size. Its markings are not so distinct as those of the potato. Potato starch (Fig. 78 d) is distinguished from wheat starch by its large size irregularity of outline, and flattened lenticular figure. The plaitings on its surface are very distinct, as is also the hilum around which they are gathered. Pea starch (Fig. 78 i) is in size about equal to that of wheat; but it differs remarkably in its flattened figure and the star-like plaits which invariably occupy its centre. Tous Us mots (Fig. 78 g] is the largest of all known forms of starch, and from its size, void figure, and concentric rings, is not unlike a cocoon. It has occasionally two hilums or holes, and its markings are usually very regular. This article enters largely into the commerce of the day. The starch grains, found in the Euphorbias (Fig. 82 a) are very characteristic, and are readily distinguished by their dumb-bell form from those of any other plant. The same grains are seen in Fig. 82 A, floating in the milky juice of the laticiferous tissue. Wheaten flour, when adulterated with inferior starch, is usually mixed with potato, pea, or rice starch, each of which may be distinguished under the microscope. So also with wheaten bread, if the smallest crumb be broken up in water, and examined in the ordinary way. It is not known if the varieties of starch possess any variation in the degree of their nutri- tive properties. It is therefore the quantity of pure starch which any substance can yield, conjoined with the abundance and ease with which the sub- stance may be obtained, that gives the market- able value. It is also of importance to determine the state of perfection of any Fig. 82. Starch cells in the EUPHORBIAS. 6, floating in the milk vessels. a, greatly magnified, so as to show their dumb-bell figure. 40 THE STARCH CELL. starch-yielding plant, since, in reference to fresh vegetables, the quantity of starch differs with the season of the year. Thus in the potato the least proportion of starch is found at an early and a later period, and consequently the full-developed potato is the most valuable. Moreover, the state of health of a plant is of moment ; for in disease the secretion of starch diminishes. This has been painfully investigated in connexion with the potato blight ; and it has been shown that not only does the quantity of starch diminish with the advent of the disease, but cells of another and an injurious nature appear. These new cells are of the lowest order of growth, such as the mushroom, and received the name of the " potato fungus." The diagrams, 83, 84, and 85, represent this con- dition ; Fig. 83 showing the potato in a healthy and vigorous condition, with the cellular meshwork filled with starch granules ; Fig. 84 shows the same cells nearly emptied of their contents ; and Fig. 85 the diseased cells occupied by the fungus growth. The inference to be derived from these facts is, that old potatoes are not valuable, and that the diseased parts should be carefully removed. Fig. 83. Potato in its healthy and mature condition. Fig. 84.- A slice of a potato, as it appears after germination, when it is thoroughly withered ; or as produced by disease, at the commencement of the "potato dis- ease." The cell-wall remains, but nearly the whole of the starch has been removed. A few grains remain, as shown at a. Fig. 85. Diseased potato, showing the pre- sence of a fungus at b, and the isolated grain of starch at a. The ordinary starch of laundresses is oftentimes prepared from potatoes which are not fit for the food of man ; but the purest kinds are obtained from rice. It is prepared by Bimply breaking up the pulp so as to disengage the starch from the cellular meshes ; then, by maceration, heat, and motion, to rupture the cell- wall of the granule, and to effect the escape of its contents. Lastly, it is filtered, in order to obtain the starch separate from the membranous cell- wall. VEGETABLE SECRETIONS. 41 Raphides. Another secretion found very abundantly in plants is certain crystal- line bodies termed Raphides, from the resemblance of some of them to a needle (raphis). The term, however, is not a happy one ; since many varieties of these crystals exist which have no resemblance to a needle. They are not secreted in the form in which we see them, but are deposited from the secretions. They occupy both the cavities of the tissues and the passages which lie between the tissues, but are the most abundant in the cells of succulent plants. They may be observed with great ease in the stem of the common garden rhubarb (Rheum), or of the balsam, and in the bulbs of the onion, and all bulbous garden plants. In the former case they have a square outline, and are isolated (Fig. 87), or they are aggregated into separate star-like bodies (Fig. 88) ; whilst in the latter they are usually needle- form, and lie in dense bundles (Fig. 86) . Their number is so great as to impart a grittiness to rhubarb-root when bitten ; and the most so in the finest specimens of Turkey rhubarb. Their chemical composition is that of oxalate, phosphate, tartrate, malate, or citrate of lime, and in size they differ from one-fortieth to one-thousandth of an inch. Phosphate of lime is found abundantly in the bones of the animal body, but not in the precise form in which we observe it in Raphides. "We have no instance of oxalate of lime crystals in the body ; but they are not unfre- Fig. 86. Rhapides ; acicular quently met with in the urine of persons, both in apparent LXn^VebS tKquili health and in disease ; so that it has been inferred that (Scilla mauritanica). ft^y have b een introduced with the food. We do not know the uses of these substances in the vegetable economy; but although they render certain plants brittle, it is not ascertained that they are the result of any diseased action. This brittleness is the best seen in some of the large Cactus plants (Fig. 89). One which was re- moved, after a lapse of a thousand years, from the woods of South America to the Fig. 88. Royal Gardens at Kew, was wrapped in Fig. 87. Raphides found in the common onion (Allium). A, octohedral. B, prismatic. C, a stellate or star-like cotton, and packed as mass of crystals found in though it were the rhubarb root. most fragile of sub- stances. They are readily seen on microscopic examination, if a thin section of an onion be placed in water in the usual way ; but as they are found in all parts of a plant, from the rough bark (Fig. 90) to the delicate spiral vessels and the pollen, they will be observed in almost every investigation. They have beea produced artificially, and, so far as may be seen, in a state as perfect as those deposited from the vegetable juices. The late eminent botanist, the brother of Professor Quekett, produced the stellate and rhomboihedral forms artificially VEGETABLE SECRETIONS. in cells, but could not produce tlie needle-shaped crystals. He took a portion of rice- paper, and placed it in lime-water under an air-pump, in order to fill the cells with the fluid. The paper was then removed and dried, and the process repeated until the cells were filled. After this the paper was immersed in weak solutions of oxalic and phos- phoric acids, and the crystals appeared at the end of three days (Fig. 91). This, however, is a mere chemical experiment, and has no relation to vegetable tissue, Fig. 89. Fig. 90. Fig. 91. Fig. 89. Raphides. A mass of crystals from the cuticle of a Cactus. Fig. 90. Raphides from the bark of the LIME TREE (Tilia Europva), of considerable breadth and prismatic figure. Fig. 91. Crystals of oxalate of lime raphides, produced artificially in the cells of rice-paper. except in so far that a detached morsel of vegetable structure was used as the containing vessel. Oils and Fats. The most widely distributed of all vegetable secretions, next to that of starch, is essential and fatty oil, of various degrees of consistence ; and, with the exception just referred to, none has so high a value for economic purposes. There are probably few, if any, plants from which some portion of oil cannot be obtained by distillation ; but it is more particularly in the hot climates of India, China, New Holland, Africa, South of Europe, and South America, that they attain their highest degree of perfection, and are found in the greatest abundance. The mustard- seed, for example, which is grown in our climate, yields oil only in a non-remunerative degree ; but in the continent of India, with its burning sun, the produce is of great value. So also with the otto or atar of roses an exquisite volatile oil, obtained from the rose-leaf growing in Persia, but scarcely perceptible in our northern climate. This is doubtless due to the chemical influence of the sun's rays, by which all vegetable secretions become highly elaborated. The oil is most commonly found in the seeds, as in the linseed and rape-seed, of our climate ; for as the seed is the product of the plant in its most mature condition, it is the most fitted to be a depository of the most mature secretions. It is, however, found to a great extent in the leaves of plants, as the rose and the peppermint, and in the wood of a comparatively few trees for example, the Sassafras and the Sandal- wood. The bark is not an unfrequent depository of oil secretions. A recent discovery made by Mr. Young, of Scotland, has demonstrated the wonder- ful length of time during which vegetable oils retain their distinctive characters. He has obtained by distillation, at a low red heat, no less than 20 per cent, in weight of VEGETABLE OILS. 43 oil from cannel coal. When was that oil first formed ? Thousands of years ago : and yet its quality remains so good that it is now compared with sperm oil. Its non-oxi- dizing property renders it peculiarly fitted for the lubrication of machinery. As respects the varied social purposes to which it is applied, we may refer to the perfumes of Eau de Cologne and Lavender ; the immense quantities of candles and soap which are manufactured in great part from vegetable fats ; the oiling of machinery, which is carried to so great an extent, that the London and North "Western Railway Company alone use about 50,000 gallons of oil per year ; the support of artificial light by lamps ; the exhibition of oil for medicinal purposes as the castor and cocoa-nut oils ; and the employment of oil as an article of diet by the inhabitants of all extreme climates. Thus but few articles of commerce can more materially influence the well- being of the community than that under consideration. It is also worthy of remark how closely the production of oil links together the animal and vegetable kingdoms, not merely in the general chemical and economic characters of the substance, but in its minuter details. Thus we have the fluid oils, as the olive oil, and the semi-fluid, or such as require a higher temperature than that of the air in order to render them fluid, and which closely resemble the fat of animals. There is also vegetable butter, which is largely used in India to adulterate the ghee, or animal butter ; and vegetable wax and tallow may, in some sense, rival the like produc- tions from the animal kingdom. There is, however, this remarkable difference viz., that the fat of animals and of vegetables, each abound in climates the most opposed to each other. The vegetable oils and butters are chiefly derived from the Palm trees of the hottest climates ; but the animal oils and fats are met with in greatest abundance where the rigours of a polar clime call for the internal use of such articles of food in order to maintain the animal heat. Thus the fat of animals is, for the most part, smployed by the Laplander as food ; whilst that of vegetables is chiefly used by the Asiatic and African for external inunction, as a defence from the action of the sun's rays, and as a perfume, which is more than a luxury in the stifling atmosphere of the sunny south. Nature has thus bountifully provided for the wants of man, and in g?-eat wisdom has selected, as her depositories, that division of vital existences which is the most abundant in their respective climates. The inhabitants of temperate regions, ts of England, find within their own territories only feeble representatives of the products of the two classes ; and in order to enjoy them they require to collect the animal oils from the Polar Seas, northern forests, and the banks of Newfoundland, and the vegetable oils from the neighbourhood of the tropics. Commerce, therefore, is to them a necessity. This branch of trade is as yet in its very infancy, for {he Great Exhibition of 1851 has shown that a very large proportion of vegetable oils is unknown to the commerce of the world ; and the great effort which has been of late put forth to increase it, has led us to infer that multitudes of vegetable sources yet remain untouched. "We cannot enter largely into this question, but shall now proceed to indicate some of the more ordinary and useful sources of this substance. Fixed Oils, Olive Oil is produced from the Olea Europcea, a shrubby tree, culti- vated with great sare in Spain and Italy, Syria, and other shores of the Mediterranean Sea. It thrives hest in stony ground, and requires a southern clime, in order to perfect the oil contained in the olive berry. The virgin oil is produced by simple pressure of the olives ; but that of the inferior qualities is such as is drawn off after the virgin oil has been removed, and which requires heat and water in order to obtain the full quantity remaining. It is mentioned as an article of food in the Sacred writings j and 44 VEGETABLE OILS. in eastern, and southern climes is almost indispensable to the inhabitants, both as food and for inunction. It is less commonly used in this country than is desirable, since it is highly conducive to health. Its chemical composition, per cent., is, carbon, 69*38 ; hydrogen, 13*47 ; nitrogen, 058 ; oxygen, 17'092. Palm Oil is an article but recently introduced into commerce, and has the great commendation of offering the most effectual means for the suppression of the slave trade. It is obtained from the seeds of various palms, and more particularly from those growing in barbarous states on the western shores of Africa. It is far more con- sistent than other oils, and approaches to the condition of ordinary fat; so that it is well fitted for the manufacture of candles, and when mixed with sulphur is the most valuable grease for railway carriage wheels. In the countries in which it grows, it constitutes an important article of food ; and, from its golden colour and consist- ence, may be said to be a substitute for butter. Cocoa-Nut Oil has a re- lationship to palm oil, in- asmuch as it, too, is pro- duced from the palm tree. Fig. 93. Globules of con- crete oil, filling the hexa- gonal cells of the cocoa- nut. Fig. 92. COCOA-NUT PALM (Cocos Nucifera). It is a concrete oil, and is found in the cells of the seed of the cocoa-nut before germi- nation. It is likewise obtained by pressure ; and is of great value in the production of artificial light. Colonel Rowcrofthas shown to us some very excellent candles, prepared in India, from an admixture of wax and cocoa-nut fat. It is also used not unfrequently as an article of food, in the form of butter in India, and of cocoa and chocolate in this country, and has recently been introduced as a medicinal agent in the treatment of consumption. Its chemical constitution is carbon, 69'62 ; hydrogen, 12*49 ; nitrogen, '060 ; oxygen, 17*850 per cent. Linseed Oil is obtained by pressure, with and without heat, from the seeds of VEGETABLE OILS. 45 the flax plant (Linum), grown in the British Islands, America, and the Continents of Europe, and of India. It is a common article of food to the serfs of Eussia, and is regarded as the highest luxury by the Greenlanders and other inhabitants of polar climes ; but it is chiefly used in the arts. It is prepared by distillation for drying, and then is fitted for the preparation of paint. A large proportion of this seed is grown in England and Ireland; but it is chiefly imported from Russia: no less than 482,813 quarters out of a total importation of 626,495 quarters of the seed having been received from that country in the year 1850. It is considered a profitable crop, and is now much cultivated in Ireland. The pressed seeds from which the oil has been partly extracted, constitute the oil-cake, much used in the fattening of cattle. Rape Oil is in like manner extracted from the rape-seed, which is the product of the Brassica Napus, and other species of the cabbage genus of plants. It is considered to be better adapted, when purified, for the lubrication of machinery than any other oil ; so much so, that 90 to 100 gallons of it are yearly expended upon each locomotive railway engine. It is also inferior to few, if any, oils in the production of artificial light in lamps. Mr. Brotherton affirms that the English grown seed is to be preferred to that imported from the Continents of Europe and India ; and so profitable is the crop, that an acre of land will yield five quarters at 50s. per quarter, or 12 10s. yearly. It is, however, probable that the foreign seed is equally good with the English production, and that the inferior quality of the oil may be attributed to its careless and unskilful preparation. The importation of rape-seed in 1850 was 29,490 quarters. Turnip-seed Oil (Brassica rapa) is very nearly allied to the rape-seed oil, and is much employed in Egypt. Castor Oil is obtained from the seeds of the Ricinus commttnzs, which grows chiefly in the East Indies and the United States of America. It is much used in medicine, but more particularly in the arts, and the manufacture of pomatum. When intended to be used medicinally, it is obtained by pressure without heat, and is then colourless and tasteless, and will so remain for a lengthened period ; but that which is employed for other purposes is obtained by heat and pressure, after the first or virgin oil has been removed. This is slightly coloured, and has a rancid odour and taste, and conse- quently realises but a very inferior price. The seeds do not grow to perfection in our climate. The importation of the oil, in 1849, was 9,681 cwts., of which 9,315 cwts. were obtained from our Indian possessions alone. Ootton Seed (Gossypium) yields a large quantity of oil on pressure ; but, on account of the difficulty of removing its colouring and other impure matters it has been hitherto but little used. The seeds are very abundant, and as large as orange seeds, and are either wasted or iised as manure and for the fattening of pigs. It is believed that the oil would be of great value if purified ; and it could be obtained in any quantity. The seed is chiefly produced in America, Egypt, and India. "W s have seen immense quan- tities of it rotting around ^every cotton plantation we have visited in the Southern States of America. The Indian corn (Zea Mays'), or maize, in the State of New York, has been found to contain a valuable oil. Ground-Nut Oil, obtained from the seed of the Arachis hypogcea, is used largely in India, Malacca, and Java, both as food and fuel for lamps. It is a clear, pale yel- low oil, and constitutes fully one-half the entire weight of the seed. Poppy Oil is produced from the seeds of the Opium Poppy, or Papaver somniferum, whether grown in this or other countries. It is, however, chiefly produced in India, 46 VEGETABLE BUTTEKS, TALLOW, AND WAX. since there the plant is scientifically and extensively cultivated by the Honourable East India Company for the opium which it yields. It has many valuable properties, and is a very good substitute for salad oil. Mustard Oil is expressed from the seeds of the common mustard plant (Sinapis), and chiefly in the various parts of India. That our English mustard yields oil, is familiar to the eyes of every housewife who has kept it in paper, or has mixed it with warm water in its preparations for the table. Croton Oil possesses powerful medicinal properties, and is procured by pressure from the seeds of the Narpaula, and other species of croton. It is prepared in India and other eastern countries. Sesamum Oil, derived from the seeds of the Sesamum orientals, and the Eam-til oil, from the seed of the Guizotia oleifera, are well known, and greatly valued in India. The seed yields from thirty-four to forty-five per cent, of oil. Vegetable Butters. The plants which yield vegetable butters, are (besides the palm oil to which we have referred) chiefly the various species of Bassia, all indigenous to India and "Western Africa. These oils consist of saccharine matter, spirit, and oil, and therefore are as well adapted for food as for fuel. The Epie Oil is obtained from the seeds of the Bassia latifolia, and is common in the Bengal Presidency. It begins to melt at about 70. The Ilpa oil is expressed from the seed of the Bassia longifolia in the Madras Presi- dency. It is white and solid at ordinary temperatures, and until a heat of 70 or 80 has been produced. It is therefore well fitted for the preparation of both candles and soap. The Bassia butyracea is the plant which yields the purest vegetable butter, and is common on the hill districts in the eastern part of Kemaon, and in the Province of Dotee. It is white and solid at a temperature under 120, and is so abundant and agreeable that the butter from milk is largely adulterated with it. Shea butter is obtained from another species of Bassia viz., the Bassia Parkii, in Bambara (Western Africa), and at Egga, on the banks of the Niger. It melts at 97. Kokum butter is obtained from the seeds of a Mangosteen (Garcinia purpurea], and is not only used largely to adulterate butter, but is forwarded to this country to serve the like purpose with genuine bear's grease. Cacao butter is solid up to 120, and is the produce of the Theobroma Cacao, growing in Trinidad. Crab, or Carapa oil, from British Guiana, is also another kind of butter derived from the Carapa guianensis, but of inferior quality. The natives, in its preparation, boil the kernels, leave them in a heap for a few days, then skim them, and at length beat them into a paste in a wooden mortar. This paste is then spread on an inclined board, and ex- posed to the heat of the sun, until the butter has trickled into a vessel placed to receive it. Vegetable Tallow is procured from the tallow tree of Java, known as the Minyak kawon, and from trees, probably of the genus Bassia, growing in the western countries of the Archipelago. Piny tallow is another variety produced by the Vateria indica, a fast growing plant, common in Malabar and Canara. It is white and solid, and melts at about 97. Vegetable tallow differs from oil chiefly in the higher temperature required to render it liquid, and its solidity at the ordinary heat. Wax is obtained from a variety of trees growing in similarly Outta Podah is a wax of a bright-green colour, obtained from Biliton. VOLATILE OILS. 47 Myrtle or Candle-berry wax, has been made, without admixture, into candles in New Brunswick. Wax of very good quality has been obtained from trees growing at Shanghae, in China, in Japan, and in St. Domingo ; and in connexion with this it may be mentioned that a fungoid growth, found in decayed branches of our English trees, has recently been shown by Professor Quekett to so far resemble wax, that it is not possible to distinguish it by the microscope from the waxy comb of the wasp's nest. Volatile Oils. The aromatic and volatile variety of oil is exceedingly extensive, and is largely employed in medicine and perfumery. Amongst the English specimens we may mention the peppermint (Mentha piperita), and spear-mint (Mentha viridis), lavender (Lavandula\ rosemary (Rosmarinus), fennel (Meum fceniculatum], thyme (Thymus), from the leaves of all of which essential aromatic oils are procured. The seeds of the carraway (Carum carui], aniseed (Pimpinella Aniswn), dill (Anethum graveolens), coriander (Coriandrum sativwn), are well known to yield medicinal aromatic oils on distillation. It is, however, to hotter climes that we turn for the spices and perfumes which we covet, and especially to the inter-tropical regions. The atar of roses is at the head of this series, and is produced in its highest perfection in Persia, Turkey, the Raapootana States, and other parts of the great Continent of India. The quantity of rose-leaves required to obtain a tea-spoonful of this princely perfume is almost fabulous, and more than accounts for the high price which the oil obtains. It is much adulterated, and chiefly with the oil of geranium, 'or Andropogon. The atar of Ecova, derived from the fragrant flowers of the screw-pine (Pandanus odoratissimus), and the jasmine atar, from the Jasmimim grandiflorum, and Sambac, aro favourite perfumes in India. So also with oil of aloes wood, of saffron, and of sandal wood (Santalum album). Orange flowers (Citrus) also yield a most exquisitely scented oil, as maybe familiarly observed by walking through the orangeries of this country and of France, when Che orange tree is in blossom. It is obtained chiefly from Turkey. Oil of cloves is obtained from the Caryophyllum aromaticus, in India and the Archi- pelago ; and oil of lemons from the rind of the fruit of Citrus Limonum ; and oil of cin- namon from the Cinnamomum zeylanicum. Oil of bitter almonds (Amygdalus amard) is obtained from the seed, and is highly poisonous. It is produced in Asia. Cajeputi oil (Melaleuca), from India, with oil derived from the Leptospermum and the Eucalyptus piperata, of Western Australia, in addition to the medical properties of the first, have the power of dissolving India rubber and various resins, and might therefore be used in the manufacture of varnishes. There are two other vegetable volatile oils, to which we will refer, on account of the favour with which they have long been regarded in India, and are now being viewed in this country. The grass oil is a stimulating aromatic oil, obtained from the seed of the Andropogon tckcenanthus, or Calamus aromaticus ; and the lemon grass oil, from other species of the same genus. Both are used to the skin medicinally, and as valued perfumes. The peculiar odour and great durability of Russian leather is attributed to the employment, during the process of tanning, of a volatile oil obtained by the distillation of birch bark (Setula}. The oil has a brown or black colour, and after it is dried up, it leaves upon paper the odour peculiar to Russian leather 48 GUMS AND RESINS. Camphor is a substance fitly associated with oils, since it is a volatile oil in a solid Btate. It is derived from various sources, but the best is the Barus camphor, from Borneo, the product of the Dryobalanope CampJiora, growing in Sumatra. It is chiefly exported to China, where it realises a price one hundred times greater than that of ordinary camphor. Its flavour is exceedingly fine. The Dutch camphor, or that obtained by the Dutch from Japan, is prepared by boiling chips of the root ai)d stem with water in an iron vessel, to which an earthen head containing straw is adapted. The camphor is volatilized by the heat, and con- denses on the straw. The process is varied somewhat in the preparation of China camphor. The chopped branches are steeped in water, and boiled until the camphor begins to adhere to the stick used in stirring the fluid. The liquid is then strained, and by standing the camphor concretes. It is then sublimed by placing alternate layers of finely-powdered dry earth and camphor in a copper basin, with a similar one inverted luted upon it, and heat applied, until the camphor passes off, and condenses upon the upper vessel. Gums and Resins. These two classes of secretions are distinguished from each other by the solubility of gums and insolubility of resins in water, and the solubility of resins and insolubility of gums in alcohol. In some instances the substance is partially soluble in both menstruums ; in which case it is called a gum-resin. Each of the classes is used abundantly in the arts, and in medicine ; and almost every member of them is obtained from Asia, Africa, and islands of the Southern Sea. The cheapest gum is that obtained from roasted starch, and is used largely in calico- printing. Gum-arabic, obtained from many species of Acacia and other genera, is carefully collected in Turkey, Egypt, Tripoli, and India. It stands at the head of this series in the quantity imported ; and amounted to 33,136 cwts. in 1849, from the following sources : India, 13,687 cwts. ; Egypt, 6,232 cwts. ; America, 6,OG4 cwts. ; South Africa, 4,876 cwts. ; Italy, 664 cwts. ; Gibraltar, 460 cwts. ; Aden, 397 cwts. ; Australia, 372 cwts. ; France, 212 cwts. ; miscellaneous, 172 cwts. It varies very greatly in quality ; and it appears that no very great care is exercised by the collectors in separating the inferior from the better specimens. Of gum-senegal and the cherry-gum, or Tragacantha (Astragalus gwninif era), &c., from Syria, there was an importation of 6,577 cwts. and 314 cwts. respectively, in the same year. Of the resins and oleo-resins, the most abundant are turpentine and lac, both of which are of essential value in the arts. Turpentine is obtained from the fir tribe of plants, and chiefly from the Pinus palustris, by making incisions into it, and subsequently distilling the exuded secretion. It is found in special vessels in the plant, which were dis- covered so early as the seventeenth century by the great vegetable anatomist Green, and also in blisters under- neath the bark (Fig. 94). It is of the utmost value in its power of dissolving resins, and in mixing and drying paints. The quantity imported in 1849 was 412,042 cwts., Fig. 94.-Ite8ervoir8 of secre- nearl y tte whole of ^ hich was from fa Q United g tates of America. The distillation of impure turpentine, or turpentine as it is obtained from the tree. THE RESINS. U effected through the medium of water, by which the volatile oil passes over and is collected, and the resin with which it is naturally associated is left behind. Tar and pitch are also produced from the fir tribe of plants at the same time that the turpentine is collected. The wood is cut into billets, and piled up in a hole made in the ground. It is then covered with turf, or some similar covering, and set on fire. During the slow combustion, the tar runs down the wood, and is collected in the dam prepared in the ground for its reception. This tar contains a portion of turpentine, but may be made from trees which have ceased to emit turpentine on incision. Pitch is obtained when the tar is distilled ; so that an inferior kind of turpentine passes over, and the pitch remains, Resin results from the distillation of turpentine, or from the drying of the secretion as it exudes from the tree. It is brought to this country in large quantities from the United States, Asia Minor, and other parts of Turkey. It is produced from various species of. Abies and Pinm. Burgundy pitch and frankincense are obtained from another pine, the Abies excdsa of the north of Europe, and Canada balsam from the Abies balsamea. Lac is furnished to this country almost ex- clusively by India, and amounted to 14,786 cwts. in 1849. It is obtained from a great many sources, but chiefly from the Coccus lacca, and some of the firs, as the Ficus Indica and Ficm religiosa, or Banyan tree (Fig. 75). Its varieties are known by the designations of stick lac, seed lac, orange and ruby shell lac, lump and buton lac, lac dye, and white or bleached lac. It is produced by the injuries inflicted upon the young shoots of various trees by an insect, the coccus lacca, which feeds upon them. It is employed in the manufacture of varnishes. It is not possible to name even the great mul- titude of members of this class, and it must suffice to mention the sources of the following well- known substances : Assafcetida is the product of the Narthax assa- foetida, in India ; benzoin of the Styrax benzoin, in Singapore ; copal from the Hyrnencea of Western Africa, Dammara aiistralis of New Zealand, and Trachylobium martinianum of South America; dragon's blood from the Dracaena Draco of India; (Fig. 95) ; gamboge, from Siam ; myrrh, from the talamodendron myrrha of Persia, and yellow gum from the Zanthorhcea hastilis of New Holland. It is highly probable that the magnificent gum trees of the continent of Australia, which have hitherto been a great inconvenience to the settler in the clearing of his land, will ere long yield gums and resins which will convert them into sources of great wealth, 95. A younpr plant of the DRAC.ENA DRACO. A specimen in the island of Teneriffe is to be very ancient in the year 1406. 50 VEGETABLE ACIDS TANNIN. Acids. Various acids are yielded by vegetables, chiefly from their fruit, but very abundantly from the distillation of their -wood. Of the former are citric acid, from the lemon Citrus, the acid juices of the apple (malic acid), pear, gooseberry, and other fruits of our own climate, and the oxalic acid from the leaves of the sorrel, or Oxalis Acetosella. All these acids appear to have distinct chemical characters, and to require distinct names. Pyroligneous acid, or wood vinegar, is obtained from the distillation of almost all kinds of wood, and is capable of perfect purification. It is colourless, abundant, and cheap, and has therefore greatly lessened the demand for the coloured vinegar derived from the fermentation of beer or wine, and more particularly in the preparation of such pickles and other substances as would be deteriorated by immersion in coloured fluids. The process is simple viz., the burning of billets of fast-growing wood, as poplar, in closed iron tubes or kilns, and the separation of the empyreumatic oils, and other impure substances, from the acid. This acid can be obtained in a highly-concentrated state, a'nd is usually sold so that one part is equal in strength to eight of wine vinegar. It is thus a convenient as well as necessary article for the use of persons on ship-board, or for residents in new countries, where vinegar has not hitherto been made. Gallic acid is obtained from gall-nuts, and tannic acid from all sources supplying tannin. Tannin. This is the chemical principle which is employed in the tanning of leather, and produces its effect by acting upon the gelatine contained in the skin. It is obtained from a great variety of sources, and not only from the oak bark, as is usually supposed ; although it is probable that the excellence of good oak bark, and the ready supply of it aiforded by our own country, will ever give it a preference in the estima- tion of the manufacturer. Notwithstanding the supply of oak bark from our own forests, so large a quantity as 1,200,000 cwts. of tanning materials were imported in 1849 ; but it must be understood that the tanning principle forms but a small portion of the barks and other materials thus imported. The following are the commercial substances which contain tannin in quantity sufficiently large to render them efficient in the tanning of leather : Oak bark, from various species of Quercus, but particularly the Quereus pedunculate* , growing in England and the north of Europe. Cork-tree bark, from the Quereus Stiber, imported from Laruche and Rabat. Valonia, from another oak, the Quereus JEgilops, flourishing in the Morea, and the south of Europe, and Asia. No less than 333,420 cwts. of this substance was imported in 1849. Oak-galls, from the Qncrcus infcetoria of India and Turkey. Terra Japonica, Kutch, and Catechu, extracts from the Acacia Catechu, growing in the East Indies. These substances contain a very large quantity of tannin. Sumach, in powder and in leaves, from Sicily and the south of Europe. It is the product of the Rhus Coriaria. Besides the above principal sources may be mentioned Kino, the extract of the Buchanania latifolia, of India; Divi-divi, of the Ccesalpinia coriaria, from South America ; mimosa bark, and bark of the black wattle tree, Acacia mollisima ; hemlock barf:, from the fir, Abies Canadensis, of the United States of America ; the bark of several trees growing in New Zealand ; and the larch bark, Pinus larix, of Scotland. Opium. This highly important medicinal substance is procured from the Con- tinent of India, and chiefly from the provinces of Behar, Benares, and other parts of OPIUM AND THE POPPY-SPIED. 51 the Bengal and Agra Presidencies, in our East Indian possessions, and the Independent States of Malawa, and others in the south of India. It is the produce of the white poppy (Papaver somniferuir), almost exclusively, in our Indian territories ; hut in the Independant States it is also obtained from the dark-red and other varieties of poppy. The poppy-seed is sown in the months of October and November, in shallow beds of about seven feet square, and the plant is thence regularly irrigated throughout the season. The capsules (ovaries) are ready for bleeding, or patching, as it termed, about the end of January, when this process commences, and proceeds during the whole of the month of February. It is effected by making incisions into the poppy-head at about four o'clock P.M. daily, and allowing the milky juice to exude and thicken by evapora- tion upon the capsule during the night. The next day it is scraped off, placed in porous earthen vessels, and allowed to inspissate further. In this crude state, it is carried to the factory, where the drying process is carried on until the opium has attained a cer- tain standard of spissitude, when it then retains from 25 to 30 per cent, of water. It is then made into large round balls, technically termed cakes, each ball being enveloped in a case composed of the petals of the poppy, cemented together by means of thin crude opium in lieu of paste. When the balls have become hard they are ready for the market ; forty of them constitute a chest of opium, and weigh about 160 Ibs. The produce of one agency, that of Patna, in 1853, was 35,000 chests, or about five and a-half millions of pounds. The East Indian Company exercise no control whatever over the growth and pro- duction of opium in the Independent States, but impose a tax upon it on its exporta- tion to Bombay. In the territories of the Company, however, the government not only watches over its production, but are, in fact, the sole growers of the drug. Any indivi- dual growing opium is bound to deliver it to the government agent at a fixed sum per pound ; and upon his undertaking to do so, the government makes advances of money from time to time to enable him to prepare the ground, and to plant, irrigate, and gather the crop. In this mode a great many thousands of persons become the servants of the Company, not by compulsion, but from the greater profit attending upon this, than upon other agricultural produce. The opium thus delivered to the Com- pany is in a crude state, and still requires much attention before it is fitted for the market. No fewer than 1,200 persons are engaged in the Company's factory at Patna alone. The opium, when packed in chests, is offered to public sale by auction for exporta- tion, and is purchased by dealers of all nations, but chiefly with a view to the supply of the Chinese market. The profit made upon this one Indian production is the most important element in the income of the East Indian Company. [We are indebted for the above account to Colonel Rowcroft and Dr. James Corbet, both distinguished officers of the E. I. C. Dr. Corbet for some years held an appoint- ment at the Patna opium factory, in the province of Bekar]. Sugar. Sugar is not exclusively a vegetable production, since it is found abun- dantly in honey and in milk, both of which are natural animal products, and in the blood and excretions in certain instances of disease. It is, however, chiefly obtained from vegetables, and always so when it is separated from all other substances and made marketable. Vegetables yield it largely in their fruits, as those of the grape and apple ; and many in their sap ; but as an article of commerce it is obtained from three sources : 52 THE the wgar-cane (Saccharinum offlcinale), beet-root (Beta vulgaris), and the sugar-maple (Acer saccharinum], Beet-root alone can he grown in our climate, hut not as a remunerative crop tor tle production of sugar. It is, however, largely cultivated in France, Belgium, Austria, and Prussia ; since those coun* tries have no colonies whence they can derive cane sugar. The sitgar*maple is also a tree of somewhat northern latitudes, and one of great value to the new settler in Canada and the United States, since it not only yields the sugar which he so much needs, and which -in his distant and solitary habitation he could scarcely otherwise ohtain, hut is valuable as wood also. The sugar is readily obtained by boring holes in the tree, so as to permit the juice to exude, and then causing evaporation of the latter by exposure to the air or by heat. The quality of sugar derived from the fruits of plants, and also from the beet and the sugar-maple, is much infe- rior in sweetening powers to that ob- tained from the next source the sugar- cane. The sugar-cane is a member of a family which abounds in sugar, and grows readily in low alluvial lands of all southern climes, and especially in the countries bordering upon, or lying within, the tropics. Such are the states bounding the Lower Mississippi, up to about 33 of N. latitude; the West Indian Islands; the East Indies; fte **' 96 - THE SUGAR-CAKE (Saccharinum Mauritius, and parts of China. The cultivation requires a large capital and the employment of a great number of hands ; so that, with the exception of the Indian crop, it is the product of slave labour, The plants are set at regular intervals, and grow luxuriantly with a single stalk and large waving leaves (Fig. 96), to the height of ten or twelve feet; so that a sugar plantation, with its wellrcultivated .fields, large red boiling-house, planter's mansion, and village of negro huts, is a picturesque scene. It is also a busy scene during the period of cultivation, but more particularly at that of boiling, when the process is not stayed night or day until it is finished. "We have inspected many, and have been struck with the air of richness and wealth which usually pervades them, When the plant is mature it is cut down near to the root, and carried in wagon loads to the boiling-house, where it is crushed between powerful rollers, impelled by steaia, THK COLOURING PRINCIPLES OF PLANtS. 53 until the juice has been thoroughly extracted. The juice, mixed with quicklime, in then transferred to large boilers, where it is evaporated, and afterwards set aside to crystallize. The larger portion of the sugar is thus separated from the fluids in which it was secreted; but a considerable quantity remains uncrystallized in the mother- liquor, and constitutes the molasses so abundantly used in those climates as food, and for the distillation of rum. The colour of the sugar is more or less brown, and is purified either in this country or in the country of its production, by filtration through animal charcoal. Bullock's blood was formerly used for this purpose. The coloured uncrystallized liquor which then remains is the treacle of commerce. We may mention that, as a curiosity, some cane sugar was made from sugar-cane grown in this country, and exhibited at the Great Exhibition of 1851. Good specimens of giape sugar were forwarded to the Great Exhibition from Tunis and the Zollverein States. Palm sugars have hitherto been mere curiosities, but they have been made from the date palm of the Deccan, the Gomutus palm (Arenga sacchari- fera] of Java, the Nipa palm stem, and the flower of the Bassia latifolia, and might, doubtles, be procured from all palms yielding refreshing and fermenting juices. Colouring Principles. The colours presented by plants are exceedingly varied, and all alike depend upon the presence of colouring principles in the cells of colourless tissue. There are eight principal colours recognised in vegetables viz., white, gray, brown, yellow, green, blue, red, and black; and each of these has many distinct shades. Of these shades of colour, nine have been associated with white : pure, snow, ivory, chalk, and milk white ; with silvery, whitish, turning white, and whitened. A similar number is also attributed to gray, and are designated ash, lead, slate, and pearl gray ; smoky, hoary, and rather hoary, and mouse-coloured. Twelve have been computed in connexion with brown ; viz., brown, chestnut, deep and bright brown, rusty, red, brown, rufous and cinnamon-coloured, with lurid, sooty, and liver-coloured. Yellow has twenty shades ; thus, lemon, yellow, golden, pale, leather, waxy, and Isabella yellow ; sulphur, straw, ocre, orange, apricot and saffron-coloured ; testaceous, tawny, and livid. There are seven varieties of green, of the shades of olive, grass, sea, yellowish, apple, meadow, and leek. Bed has seventeen shades : carmine, rosy, purple, sanguine, scarlet, eumaba, vermil- lion, coppery, brick, flame-coloured, &c. ; whilst its compound blue has but seven viz., pmssian, blue, indigo, lavender, violet, lilac, and sky blue"; and black has four: pure, coal, raven, and pitch black. Thus as many as eighty-six different shades of colour have been determined to exist in plants; but only two chemical colouring principles have been discovered viz., chlorophyl and chromule. Chlorophyl is so called from its imparting a green colour to plants ; that is, that kind of green which is universally met with in all plants growing in the light. It is distributed to the tissues themselves, but more particularly to the surface of the starch cells, which are abundant in all green plants. Chromule is the general term for the colouring principle of all other colours, although they may be so closely approximated that adjoining cells may have totally different colours. Dyes. Another highly important series of vegetable secretions are such colouring 54 VEGETABLE DYES. matters as are capable of being used as dyes of textile fabrics. These are very varied, and are also chiefly found in southern countries. This series comprehends nearly all the known dyes, since but few (as the cochineal insect) belong either to the animal or mineral kingdom. The chief substances are Indigo, of which no less a quantity than 70,482 cwts. were imported in 1850. It is the product of the leaves of the Indigofera tinctoria, and I. anil, growing in the low districts of India and South America. It is a fast dye, if in the process of dyeing it be first deoxidized, but otherwise it is not permanent. It yields the Indigo colour, and also a green when mixed with yellow. Madder is one of the most useful and common dyes, and is derived from the root of the Rub-la tinctori-i. Its home is Naples, France, and the North of Europe. 2,985 tons were imported for this purpose in 1850. It forms one of the most permanent dyes, and constitutes the Turkey red dye, so celebrated for its brilliancy. Garancine is the red principle of madder, obtained by the action of sulphuric acid. 2,985 tons of this sub- stance were imported from France in 1850. Logwood is the wood of the Hcematoxylon campechianwn, found in the Bays of Cam- peachy, and Honduras, in Central America. Its value is sufficiently great to cause the right cutting it to be the subject of a treaty between this country and the States in which it grows. Its colour is red, but black when precipitated with iron, purple with tin and alum, and brown with copper. 3,500 tons were imported in 1850. Brazil wood, from the Ccesalpina braziliensis, is one of the largest importations of dye woods, 3,120 tons were imported in 1850. Amongst the remaining dyes are alkanet root, from the Anchusa tinctoria, grown in Asia and the North of Europe ; Nut-galls, an excrescence on an oak, the Quercus infectoria, in Turkey ; Saffloiver, produced in Southern Asia, Egypt, and the Levant, from the dried flowers of the Carthamus tinctoria ; Annatto, a South American orange-colouring matter, from the seed of the Bixa orellana ; Turmeric, from the root of a cucumber, the Circuma, longa of India ; Peach wood, or Nicaragua wood, of the Ccesalpina, from South America ; Fustic, the wood of the Rhus cotinus of Cuba ; Camwood, from the Baphil nitida of Sierra Leone ; Quercitron bark of South America, from another oak, the Quercus tinctoria ; the alder bark of this country, from the Alnus glutinosa ; Catechu, an extract of the wood of the Indian Acacia Catechu ; red sanders, from the Pterocarpus santalinus of India ; the Persian berries, from the Rhamnus infectoria of the Levant ; and many others of less note. It is worthy of remark, that the lowly- organised Cryptogamic cellular plants, or lichens, afford colouring matters in great abundance, under the designations of Orchall and Cudbear. The following are the chief : Ramdnia furfuracea, from Angola ; Rncccllafuciformis, from Mauritius, Madagascar, Lima, and Valparaiso ; Roccella tinctoria, from the Cape de Verd Islands ; Parmelia perlata, from the Canaries ; with the Parmelia tartarca, Umbilicaria pustulata, and Gyrophora murina, of Sweden. We have purposely avoided the chemical questions which naturally arise when considering the interesting and important vegetable products which have been passed in review ; but we cannot omit to state here, that, although the widely-distributed substances starch, sugar, and gum are apparently so very diverse in their external characters and general properties, they have very close chemical relation. Indeed, so closely are they associated that they are daily and hourly converted in the living plants, the one into the other, in the order in which we have placed them viz., starch THE VEGETABLE SECRETION OF SILICA. 55 sugar, gum. In the early stages of development, the major product is starch; but, as maturity approaches, this is gradually changed to sugar ; and to gum when the period of decay ensues, or the starch at once passes into the state of gum. So in the malting of barley : the object there is to convert the starch into sugar ; but if the process of germination be carried a little too far, the sugar begins to disappear, and is supplanted by gum. The prolonged cookery of any farinaceous substance has always this ten- dency ; so that biscuits not unfrequently contain a portion of gum, difficult of digestion, with the starch which is capable of ready conversion into the material of the blood. Silica. The last secretion to which we shall now refer, is one of peculiar interest vis., silica, or flint. This is a mineral substance ; and, apart from vegetable structures, is so indestructible that the strongest chemical acid is required for its solution, and yet it has structures so delicate that a stem of wheat can dissolve it with facility. It is not pretended that vegetables have the power of producing flint, but only that they are enabled to dissolve it in their juices, when water and other fluids alone cannot dissolve it. This power seems to reside at the extremities of the rootlets, for it is impossible that flint could be taken into their delicate tissues until it has been dissolved. The sources of silica or flint, are 1. The sand which is so largely met with in almost all kinds of soil, and which has the further valuable property of permitting the rain to percolate to the roots of the plant. Its composition, is chiefly that of silica, as may be familiarly inferred from its essential presence in the manufacture of glass. 2. From the flint nodules which are found in the chalk formations, and which themselves are the productions of long-buried sponges, mosses, and minute animalcules. 3. From the skeletons of animalcules which still remain in the soil. These skeletons are com- posed of flint, as may be proved from their non- solubility in boiling nitric acid (Fig. 97). So numerous are they that Richmond, in Virginia, United States, is built upon a stratum eighteen feet deep, and upwards of thirty miles in length ; a stratum representing an innumerable number of animalcules, when it is borne in mind that each animalcule is almost too small to be seen by the naked eye. Similar deposits also exist in the old world. These skeletons are also found in other posi- tions. Thus guano, a substance consisting of the excrements of birds, contains vast numbers, chiefly of three genera, Actinocyclus, Gallionella (Fig. 97), and Coscinodiscus. A powdery sub- stance is known in Germany as Berg Mehl, or mountain meal, which is chiefly composed of Fig:. 9 7 - SilHous pkeletons of the Diato- them. This is the produce of the strata through ^UT^^^^t^S- which the mountain torrents run, and is brought lodtscus ch/peus, both found in guano. down by the waters. From its resemblance to flour, it is used in certain localities as an article of diet. 4. From the remains of plants in the form of manure or otherwise, which contain silica ; as, for example, the wheat straw. fr m THE VEGETABLE SECRETION OF SILICA. i?. 98. Silicious cuticle from the husk of the wheat (Triticum), showing cups for the insertion of hairs, and also spiral vessels. The parts of plants in which the silica is chiefly found, are the external layers of the cuticle, as in the shining straws of our corn fields-, and the canes and bamboos of hotter climates ; and certain rough straws*, as that of the Equisetum hyemale, which is so rough as to be used in the polishing of metals. It is also found in the interior of the joints of certain bamboos, and then is termed tabasheer, and from its rarity com- mands a high price. It is also found in the hard grains themselves, as- cf wheat and oats, and more particularly of the rice; from which cause the Caribs, the Malays, the South Australians, and other savage nations have their teeth ground down by the trituration of the uncooked grain. The layer is exceedingly thin, but yet it is- one of pure flint, as may be proved by its non- solubility in boiling nitric acid. It o-verlays the vegetable tissue, and assumes its form, and therefore varies greatly in appear- ance, according to the object examined. In Fig. 98 we have an illustration of its appearance in the common wheat. From this silex the flinty haira of the oat arc formed ; and it is well known that animals living much on oats are liable to intestinal accumu- lations of these indigestible hairs ; and in a lesser degree men eating oatmeal are liable to a like inconvenience. The common meadow grass (Fe-stuca pratensis, Fig. 100), presents a silicious coating of considerable beauty. The most beautiful examples are the Eqwsetum ffyemale, the Pharus Cristatus (Fig. 101), the common rice (Oryza sativa), and the stellate hairs of the Deutzia seabra (Fig. 102). It must be clearly understood that this substance constitutes no part of vegetable structure, neither does it assume any form of organization, its sole and most important duty being to give strength to the slender stem, and to protect the delicate tissues from atmospheric in- fluences. That the quantity 101. Silica in square and star- required to supply the wants of a field of corn Fip. 102 Sinous cells and stellate is .cry considerable, %%. ^ k * "' * may be proved from the following table ; and tbe more Fig. 100. Cups of Silica on the chaff or palese of the common meadow grass (Festucu pra- ten&is.) THE ORGANS OF PLANTS. 57 so, when it is remembered that the layer is so thin that it cannot be removed without detaching also a portion of the vegetable tissue. Proportion of Silica, or flint, in 1000 parts of the ashes left after burning the following vegetable substances. Oat straw . . . . .45- Barley ...... 38-5 Wheat ...... 287 Indian corn . . . . .27* Oak leaves . . . . .15' Ferns ...... 10'4 Pea straw . . . . .10' Potato tops . . . . 8' Heath . . . . . 5'S Beans ...... 2'2 Bean straw . . . . .2* Cabbage . . . . .2*1 Buckwheat . . . . .1-0 This subject has an important bearing upon the rotation of crops, for it is manifest that if successive crops of corn, and especially of oats, be obtained from the same land, there must be an enormous expenditure of this necessary article ; but that a much less quantity suffices, if potatoes, pease, beans, or cabbage be given as intermediate crops. So, also, with regard to manures. It is clear that a manure must not only contain the carbon which forms the straw, and the salts which are always found with it, but there must be a constant and abundant supply of silica. This is effected by using corn, and especially oat straw, as manure, and also by the use of guano, which contains a large per centage of silicious skeletons. THE ORGANS OP PLANTS. Having now considered, in such detail as our space has permitted, the various ele- mentary tissues which have been discovered in vegetables, and the juices and secretions which they contain, we proceed to describe the parts or organs which are formed by their combination. Such are the leaves, flowers, and fruit, and the structures which support them. The modes in which we might proceed are numerous, and partly arbitrary, varying with the fancy of each author ; for no one arrangement of the organs of plants is found in Nature which is acknowledged by all investigators to be more natural than any other. The nearest approach to Nature will be found in proceeding either centripetally or centrifugally : that is, either first to describe the seed, and thence pass to the centre of the stem, through the fruit, flowers, leaves, and other appendages to the stem : or to commence at the stem and roots, and then clothe these organs with leaves, flowers, and fruit, in the order which nature has selected. Of these two we prefer the latter course, and shall proceed to describe the stem, with its root, and the various organs supported by them. 58 THE ORGANS OF PLAOTS. The Stem. In all flowering plants the stem proceeds from the seed and that part of it termed the plumule ; whilst, at the same time, the root is developed from another part of the same seed viz., the radicle. These two newly- formed organs thence assume diverse directions, the root passing downwards to fix the plant firmly to the earth, and to abstract nutriment from the ground ; whilst the stem usually emerges from the soil, and grows in a perpendicular direction, so as to bear the leaves and other organs of growth and reproduction from the ground, and expose them freely to the action of the light, air, and moisture. The point in the seed whence the stem and root diverge is known as the collum or neck (Fig. 100 i), and even in trees which attain to a consider- able size this line remains more or less distinct. When the seed has begun to germinate, and the growing points just referred to have lengthened, the other parts of the seed viz., the cotyledons, or seed-leaves, enlarge, and take on the function of nutrition by converting the starch contained within them into sugar. At length, by their elongation, they emerge from the soil, and appear as two opposite roundish leaves, which are capable of absorbing oxygen from the air, and fixing carbon within the tissues which are then in process of formation. At this stage, then, we find a root, stem, collum, and seed-leaves, all of which are represented in'Fig. 103. The current of sap having been set in motion by the action of the cotyledons, or seed-leaves, the latter disappears, and the plumule, or young stem, continues to elongate rapidly, and until it arrives at the point whence its first leaf is to issue, is technically termed a node. At this point the stem swells, and the structures of which it is composed are bent out of their former direction, and, in part, enter within the structure of the newly-developed leaf. The stem may now fairly take on the term of ascending axis, which is usually given to it, since it has begun to develop the organs which are subsequently to be arranged around it as their centre. It has also received a variety of other names, which it may be useful to mention viz., the cau- dex intermedius and ascendens, truncus or truncus as- cendens, with culmus and stipes. All these have a similar signification. The growth is not arrested by the development of a node and leaf, but proceeds for a certain period, until ano- leaves7wh7clTave' appeared ther leaf and node are formed ; and so on progressively point of the stem, elongated then a scries of nodes and spaces between them, which Det ^thVcollumf s e e ( p a 1 I : ating (or s P aces are termed internodes. A stem may thus be said to rather connecting-) the part of consist of a number of nodes, with their internodes. KS^^^rtbTm Nodes.-These are well seen, in all grasses, as the it, the descending axis. ordinary grass of this country; with wheat, oats, and other grasses ; and more particularly in the bamboos and canes of southern climes. It is there found as a distinct bulging around the stem, of a hard and rounded character, and oftentimes bending the stem from the perpendicular direction. Ifi wooded plants, or trees, in general, it is less per- Fig. 103. Exhibiting the parts of a plant soon after the com- mencement of germination. c, the cotyledons, or geed- d, the radicle, with the root- lets proceeding from it. VEGETABLE ceptible, since the small swelling at tlie base of the single leaf which is there developed, bears but little proportion to the size of the trunk of the tree. The essential difference in structure between a node and an internode is, that the bundles of wood are com- pressed and turned aside in the former, so as to enter the leaf, and thus a slight interruption to the course of the general circulation ensues ; whilst, in the internode, the bundles of woody fibre pass perpendicularly, and lie parallel to each other. In some instances, as in the grasses with hollow stems above mentioned, this compression or con- traction of parts is so great, that a septum is formed across the stem, dividing it into two or more cavities. This may readily be seen on malting a perpendicular sec- tion of a stalk of wheat, or of the bamboo, and with the septum of the latter may sometimes be found the flinty deposit before men- tioned, under the term of tabasshcer. They are then said to be closed, in opposi- tion to the pervious or open condition, found when the pith passes through it. When the node surrounds the stem, as in the grasses and the hemlock, it is desig- nated as entire; and when otherwise, as in trees, it 18 termed divided. As the essential element of a node is a new disposition of the woody and other tissues, to meet the require- ments of a leaf, it is manifest that wherever a node exists there must be, or have been, a leaf, perfectly or incompletely developed. In many instances the grow- ing process ends after the formation of a node and before the entire development of a leaf; and then will be formed a leaf-bud, immediately above the base of a leaf. "When such leaf-bud is evident, the node is termed compound ; and when otherwise it is called simple. So far this account may suffice for both herbaceous and woody stems, but it is need- ful here to interrupt our description, and consider herbaceous and woody stems sepa- rately. This results from the great difference which is observed in the structure, as well as in the degree of delicacy of organization of the two kinds of stems. Steins of Herbaceous Plants. Herbaceous plants are, for the most part, annuals that is, such as are produced and die in the same season. It is, therefore, not a a the nodes, will woody fibre passm;. 1 : from their parallel course in the stem to enter the leaf bud or the foot stalk of a leaf. Figr. 104. A stem of the family of grasses, showing at o theenlargeme ts indicating the existence of nodes. The interval between the two nodes is termed an inter- node. 60 THE CUTICLE OF HERBS. necessary that they should possess the rudeness and strength of texture which appro- priately belong to plants that have to combat the power of the elements through a long series of years. The stem, for the most part, is small, seldom attaining to a greater diameter than one and a-half inch ; and, with the exception of twining plants, and such grasses as the bamboo, do not exceed six feet in height.- The structure is delicate, being composed of cellular tissue of a somewhat loose kind, with bundles of woody fibre running at intervals from the root upwards. They are thus but ill-fitted to resist the influence of strong winds, or the destructive propensities of animals. There are, however, some circumstances which tend to increase their strength. Such are firsty the cylindrical form of the stem ; secondly, the hollowness of the stem ; and, thirdly, the inclosure of the stem by a tough cuticle or bark, and, in sqrne instances, a further layer of silica or flint. That the cylindrical form is stronger than any other is well known ; but it may not be so commonly understood that a hollow cylinder, with moderately thick walls, is stronger than a solid rod of the same material. Thus that vacuity, which at first sight is indicative of weakness, is really fitted to impart increased strength. The cause of the hollowness is the more rapid development of the perpendicular than the horizontal layers of the stein. The stem of an herbaceous plant thus consists of three parts : a central pith, which is frequently wanting ; an external envelope or skin ; and an internal mass of cellular tissue and woody fibre. The pith is composed of cellular tissue, of the hexagonal or octagonal form. The woody fibre of the stem is not found in even layers, but in bun- dles lying detached from each other, as may be readily seen by tearing a stem across, when the bundles of tough fibres will be stretched, and project somewhat from the broken surface. It may also be seen through the cuticle of the common parsley, in ribs passing in parallel lines from the root upwards into the leaves. Each bundle is usually inclosed in a mass of cellular tissue, to which it gives firmness. Cuticle. The cuticle of herbs is an interesting structure, and the seat of a large part of the respiration and digestion which proceeds in those plants. It consists of two layers an epidermis or scarf-skin, and a true skin, with certain appendages viz., stomata, hairs, prickles, warts, and reservoirs of secretions. The Epidermis is a layer of inspissated organic mucus, which sometimes may be readily detached from the cuticle, as in the common box-leaf, but at others requires maceration in water for some time before its exist- ence can be demonstrated. It covers all the external surface of the plant, except the stomata and the free end of the stigma, and it even forms a covering for the hairs. Mohl considers it to be a secretion poured out from the external sur- , 6> outer layer of the cuticle, composed of compressed cells, face of the cells, the walls of the d > a subjacent layer of larger cells, with vacuities, or pareii- cells themselves being at the same c , S?S5&g%^S& the cutide to the air time thickened by internal depo- cavities above. Bits. It is not a cellular structure, although, when removed from the surface of the cuticle, it has a cellular outline ; but is a simple layer, with markings corresponding to THE STOMATA OF PLANTS. Cl Pig. 107. Exhibiting a front vie\v of four stomata at , im- bedded in hexagonal cellular tissue. the cell-walls over which it is placed, Hartig has divided it into three layers an internal, an external, and an intermediate layer ; but such is not the experience of other observers. Its use is to protect the delicate structures lying beneath it, and is analogous to the scarf-skin which protects the skin of man. The True Cuticle is composed of one or more layers of cells, the outer one being much flattened (Fig, 106 a). The cells are mostly of hexagonal figure and wavy out- line. Some anatomists have denied the cellular nature of this structure, on the grounds that the cells are not demonstrable, and that the skin may readily be peeled from the subjacent tissue ; but this theory is not usually admitted. Moreover, in the cactuses and orchids, and also in the Ne- rium Oleander, there are several layers of cuticular cells, the whole of which may be demonstrated (Figs. 106 d, and 1 10). Whenever any shred of cutis is removed from the stem of a herb, some portions of woody fibre are removed with it, so that it may be questioned if woody tissue is not a .component of the skin ; but it is perhaps more correct to associate the wood with the structures immediately be- neath the skin rather than with the cellular skin itself. Stomata (Fig. 107) are mouths by which respiration and exhalation are carried on in vegetables. They con- stitute openings into and channels through the epidermis, and lead into cavities beneath (Fig, 108, A). Their structure is somewhat complicated, since, for the most part, there are a series of rounded cells bounding the opening, with two larger kidney- sb.aped cells in the centre, pressing A < closely against each other when the a stomate is closed, and cemented to the surrounding cells by something in the nature of a hinge, which permits toem to rise and fall with consider- able force (Fig. 108, C a). In the centre of the stomate there is a raised line when it is closed, and a slit when it is open (Fig. 108, C c) ; and through this opening an entrance is effected to the cavity beneath (Fig. 108, A c). This cavity varies in figure and form ; but it is always surrounded by cells, which communicate freely with other cells of the epidermis (Fig. 108, A). It is thus that air and moisture, having entered by the stomata, act not only in the cavity beneath that organ, but in the surrounding open cellular net- work of the leaves or cuticle. Such is a general description of the stomata; and before entering further into detail we will request our readers to verify the above account by an examination of these structures. Take a very thin slice from the under surface of a leaf or flower of any plant, as of the lily (Fig. 109, A), the Zea Mays (Fig. 109, B), or the common geranium ; or strip a thin piece of the cuticle of a herb, as of the parsley, and place it in water between two pieces of glass, and examine it with the microscope. First examine tho outer surface, on which may be seen the cells and slit referred to, and then turn over Fig. 108. A, stomata of the IRIS, a a, green cells bounding: the orifice, b b, cells of the parenchyma, c, air chamber. B, the same as seen from above, a a, cells of the stoma. c, opening between them. C, stoma of the apple leaf, a, cells of the stomate. bb, cells of the cuticle, c, opening of the stoma. 62 THE STOMATA OF PLANTS. the object, and carefully notice the cavity into which the slit is directed. The minute and regular arrangement of the various parts of each stomate, and of all the stomata on Fig. 109. View of ordinary stomata, as seen between the veins of the leaf of the LILY, A, or, ZEA MAYS, B, both endogenous plants, and of an exogenous plant at C. Their regularity in figure and position, and the uniformly oval outline, will be observed. the cuticle, will excite admiration ; and the more so when, on examining a variety of plants, the little organ is found very variously figured. The general outline of the stomate is commonly circular or oval ; hut in the flax plant, the Agave Americana (Fig. 61), and a somewhat similar one, the Yucca gloriosa, it is quadrangular. In Marchantia they resemhle funnels, and are composed of several cells arranged in tiers, and forming tubes, which perforate the epidermis, and terminate in the cavity beneath. In the oleander (Nerium Oleander] the cells have disappeared, and the cavity is simply protected by hairs. This may readily be seen, if a portion of the leaf be placed under the microscope, as above directed. The Myrodendron, punctulatum, growing on trees in the antarctic regions, has a remarkable modification of the stomata. Dr. Hooker states that the stomate expands on both sides into a kind of cup a condition which results from the hour-glass construction which is met with at the aperture. But whatever may be the figure of the organ it is so uniform in the same species that certain botanists, as Brown, are of opinion that they might be made a basis of clas- sification. This, however, would be very difficult, on account cf their minute size and the necessity for the constant use of the microscope ; and further, from the fact that a few plants present more than one form of stomate. Thus, in the Nepenthes or pitcher plant, there are two forms of stomata, one being semi-transparent and nearly colourless, of an oblong figure, and with pellucid globules within the cells whilst the other is roundish, red, and more opaque, and rests not over a cavity, but upon a gland. It is proper to state that certain observers of eminence have denied the accuracy of the above statement, as to the construction of stomata, and have affirmed that they do not lead into a subjacent cavity, and consequently have no opening at the slit. Some German anatomists have affirmed that the supposed opening is simply a thinner translucent portion of the membrane, and that the slit is the thickened border of this space. Brown believed them to be usually imperforate, and to be formed by an opaque and sometimes coloured membrane. Such, however, is not the opinion commonly entertained ; and we may confidently appeal to the investigations of our readers to refute it. Stomata are not found upon all plants, the exceptions being such as are submersed THE STOMATA OF PLANTS. 63 in water, or grow in darkness, and also the lowest classes of plants, as mushrooms, sea- weeds, and lichens, except mosses. Neither are they found upon all parts of any plant, but are absent from the roots and ribs of leaves. They are most abundantly found on Fit,'. 110. Fig. ill. Fig. 110. A side view of the modified stomata of the NKRIUM OI.TSANDER, and of a BANKSIA, in which they are seen clustered together at the bottom of a pit, a, the entrance of which is defended by hairs, b. Fig. 111. A front view of the same organ. the under surface of such leaves as present one surface to the soil (Fig. 106), hut on both surfaces equally, if the edges only be directed vertically. They are also met with on the cuticle of stems, on flowers, and even on the seeds of a few plants, and on their cotyledons. The number of stomata found upon a moderate-sized leaf is sometimes prodigious, amounting in some instances to 160,000 on each square inch of surface. Thomson gives the following enumeration, which shows not only the total number but the relative quantity on the two surfaces of the leaf: On each square inch of upper side, and of under sicJe. 12,000 none. 38,500 Alisma Plantago (Water plantain) ..... Coboea scandens Dianthus Caryophyllus (Pink) Daphne Mezcreum (Mezercum) none. Jlypericum Grandiflorum (St. John's Wort) . . . none. Ilex (Holly) none. Iris Germaniea (Iris) 11,572 Olea Europoea (Olive) none. Pseonia (Pseony) none. Pvrus (Pear) none. "Rurnex Acetosa (common Sorrel) 11,088 Tussilago Farfara (Coltsfoot) 1,200 Vitis vinifera (Vine) none. Viscum album (Mistletoe) 200 Syringa vulgaris none. 6,000 20,000 38,500 4,000 47,800 63,600 11,572 57,600 13,790 24,000 2*0,000 12,500 13,600 200 160,000 Of 28 plants in this table which had been examined, 15, or more than- half, had no 64 THE STOMATA OF PLANTS. stomata on the upper surface ; 6 had fewer stomata on the upper than en the under surface ; and 5 had an equal number on both surfaces, leaving only two instances in which the number was greater on the upper than on the under surface of the leaf. The number and position of the stomata must have an immediate reference to their function. It is commonly understood, as has already been intimated, that the function is that of admitting air and moisture to promote the digestion of the crude sap which had been brought to the leaves, and that for this purpose they are endowed with the faculty of opening and closing according to the momentary requirements of the plant. This will explain the necessity for their conformation. As to their position, that seems to be due to several causes. First, that by being placed on the under surface they are shaded from the direct action of the sun's rays, and are thus permitted to carry on their functions without being impeded by too great a degree of evaporation. Secondly, they are also more sheltered from the injurious deposition of dust. Thirdly, the exhalation of moisture from the ground is in the form of vapour, which, from its specific gravity, rises, and thus reaches and enters the under surface more certainly than the upper surface. It is not presunied that in any case water enters the stomates as such, but only in the state of vapour ; for although plants are refreshed after a shower, it does not follow that the rain was bodily introduced within them ; and it seems inconceivable that bodies of so minute a size should at the same time be fitted for the admission of gases, and of fluids of such density as water. There are those, however, who maintain that such is not the function of the stomata, but that they arc in the nature of glands. Link says that he cannot 2nd a distinct connexion between the stomata and the subjacent cavities in the cellular tissue of the leaves. Moreover, he cannot understand how organs of so distinct a structure should only lead to mere cavities in the cellular structure; and the obstructing and covering matters which they produce have always led him to consider them as organs of secretion. Brown also affirms that they are rather of the nature of glands ; but there cannot be a doubt that in the vast majority of instances this view is incorrccv,. It is true that in a few instances the stomata are modified both in figure and in function to perform the office of glands. Such is the case in the Dionsea Muscipula, or Venus' fly-trap (Fig. 1), in which the stomata are reduced each to a pair of parallel green cells, which are placed upon the surface of the leaf, and secrete a tenacious mucus ; but such are exceptional cases. It would be interesting if we could determine with certainty the precise mode in which these beautiful organs are formed; but such seems hitherto to have been a hopeless task. Mohl sought to determine it by examining the different parts of a growing hyacinth, in the expectation that the parts of the leaf, which are successively developed from above downwards, would have stomata of various degrees of perfection. He noticed that in the lower part of the leaves, or that most recently developed, small quadrangular cells, with a slit of about equal diameter either way, were placed between the layers of the epidermis. These sometimes contained a granular substance, which, higher up in the leaf, became a compact mass. At the same period a partition waa formed in the middle of the cell, at first slightly, but subsequently more strongly marked, and at length unfolded, so that the simple cell became divided, and a stomate was formed. After this the surrounding cells enlarged, and the central slit increased at a still greater rate. All this and the subsequent completion of the stomate may be observed by any of our readers who may have a tolerable microscope, and will obtain, by practice a certain delicacy in cutting minute structures. THE HAIRS OF PLANTS. 65 Hairs are minute, semi-transparent, transparent, or opaque thread-like processes, attached to the cuticle by one extremity, and remaining free at the other (Fig. 112). They are always of a cellular charac- ter, the cells, if more than one, being larger and more numer- ous at the bottom, and then piled one upon the other, and laid in one or more rows, until the apex is attained, with its single elongated, rounded, or pointed cell. The figure and minute anatomical characters vary considerably, so that the above general description may require modification when ap- a a hair. mity. hair. d a, a gland, surmounted by b, a hair with an enlarged and secreting free extre- >, e, simple hairs with pointed extremities, d, branched plied to individual instances. Thus the hairs of certain plants are attached by their middle, and have both ends free. Such are those of Indigofera, Cap- sella, and Astragalus asper ; but in order to bring these within the definition above-mentioned, it is customary to assert that it is not one single hair attached by its middle, but two hairs springing from the opposite sides of an elevated cell. Such, doubtless, is the correct explanation of hairs which assume a stellate or star-like form, and which are really clusters of hairs attached each by one extremity. This variety is met with readily on the leaves of the MaUows, in which, with the assistance of a small hand magnifier, the stars may be perceived. The most beautiful illustration, however, is that of the hairs of the Deutzia scabra and corymbosa (Fig. 102), and the Elceagnus, which, as has already been demonstrated, are coated with a layer of silica or flint. They are very resplendent when viewed with the light thrown upon, and not through them that is, as opaque objects, and may aptly be compared to the jewelled star of the Most Noble Order of the Garter. Certain hairs are bent at the points of articulation of the cells, whilst others have their points only thus distorted. This latter variety is seen familiarly in the common teasel (Dipsacus), and has been used with much sagacity by cloth-workers, for the purpose of Fig. 113.-A prickle raising the nap of the cloth. The extremity is hooked, and by that f^/ Sd^S" means adheres to an object with great pertinacity, as any one may * fuUomtm)', prove by placing the fruit of the teasel in his hair (Fig. 113). f sistin s ? m eih a a t Another and very interesting modification is that in which the bent hair consists of a single ceU, but having an elastic spiral fibre coiled up within it cell, thick- by layers, embraced at Such hairs are almost imperceptible, so long as they the base by amass sometimea with a crackling THE HAIKS OF PLANTS. Bound, on their immersion in -water. They are found in the common mustard (Sinapis], which any one may examine after immersion for three hours, and hare the form of an elongated cell, terminated by a bell-shaped expansion. In the seed-covering of the Collomia grandiflora and common sage (Salvid), each hair is simply an elongated cell of even diameter, terminated by a rounded obtuse end, and with a single coiled elastic fibre proceeding from the base to the apex. This is an interesting object, but requires considerable dexterity and quickness to see it with advantage. Slice the smallest portion of the outside of the common sage, and place it dry between two glasses tinder the micro- scope. No hairs will then be perceived ; but if, whilst it is so placed, and the eye is upon it, a drop of water be insinuated between the glasses, until it touch the seed, there will instantly start out scores of long fibro-cellular hairs ; and as the complete development occupies a perceptible interval of time, the eye may readily trace the process of elonga- tion. "When the change has been entirely effected, the object has no longer a defined smooth border, but is bounded all round by thread-like projecting points. A similar structure has been discovered in the hairs of the seed of Acanthodium, but with this difference, that two or three spiral fibres have been traced in one cell ; and in some instances the fibres are broken up into numerous rings. This is doubtless a beautiful object. All the foregoing varieties of hairs may be termsd single, but there are others which may fitly be designated as compound. Such are toothed hairs, in which there are short cellular projections on both sides of the hair ; and branched hairs when the teeth are greatly elongated (Fig. 112 rf). In a few instances this development is carried yet fur- ther, and the branches themselves are toothed, and the hair is said to be plumose. In others, the branches are restricted to one side of the hair, when the latter is termed one-sided. But perhaps the most interesting cir- cumstance in connexion with the anatomy of hairs, is, that in some plants, as the Sago-palm (Cycas revolutaFig. 114), the cuticle of the hair can be unrolled spirally. Professor Quekett has described this upon the fruit of that plant, and has delineated Fig> nJf^tions of hair from the fruit of the t in Fig. 114. Sago-palm (Cycas revoluta), exhibiting a spiral The foregoing remarks have exclusive dis P sition of the membrane, reference to one great division of hairs r/z., the Lymphatic, or such as bear innocuous fluids ; but there is another large division which have a different conformation, and contain juices of highly acrid and poisonous properties. The sting of the nettle (Urtica) is a familiar and painful illustration, but the hairs of the leaves of certain tropical plants are yet better examples. These contain juices so poisonous, that if the hand grasp a leaf, it speedily inflames and swells, and so disturbs the whole system, that life is endangered. Such is the Jatropha when growing in our hot-houses even, and is handled only with the protection of a pair of thick leathern gloves. Moreover, if any part of the body be placed under this tree during a shower of rain, the poison which is washed from the- plant by the water would, in like manner, cause very serious ease. The anatomical difference between the lymphatic and secretive variety of hairs is, that THE HAIKS OF PLANTS. C7 in the latter there is a bulging at the free end (Fig. 112,3), or immediately beloir the hard sharp-pointed apex (Fig. 112, e), which co mmuni<;ates with ^ the other cells of the hair, or at the base of the hair, and contains a poisonous juice. "Whenever such a hair is seized the sharp point enters the skin, and the end breaks off immediately below the point, and the contained fluid is emitted with a great impetus into the wound produced by the puncture. The juice in the perfect hair is maintained at a high state of tension, so that it may be emitted with violence, after the fashion of the poison in the poison-fangs of the serpent. It will be inferred, from these remarks, that there must be a circu- lation of the sap in all kinds of hairs. Such is the case ; and the circulation proceeds in currents from the base to the apex of the leaf and back again (Fig. 115, B). It may be seen proceeding under the microscope in the Tradescantia virginica, and appears to proceed between an internal and an external wall of tissue. At a certain period, a cytoblast (page 9) may be detected, and then the current appears to proceed from and return to it. "When the hair has emitted its contents it shrivels, and in some instances (Fig. 116) retracts like the parts of a pocket-telescope. Hairs are not found upon roots, nor upon any part of the plant which is buried in the ground or covered by water ; and whenever they appear on one side of a leaf only, it is, with few exceptions, on the under side. When a portion only of any surface is covered by them, it is uniformly the ribs or veins. They are sometimes found within the cells of water plants, as of the white and yellow water-lilies, Nymphcea alba and Nuphar luteum. Their functions appear to be that of promoting perspiration and of absorbing moisture, inde- pendently of that of secreting fluids. Hairy surfaces have received various names, according to the nature of the hairs which cover them, as rough, silky, arachnoid (resembing a cobweb), stellate, bearded. The hairs themselves are also variously desig- nated ; thus, stings when they emit an acrid juice, and glandular hairs when the end is tipped with a fluid exudation (Fig. 112 b}. Hooks, barbs, bristles, and velvet are terms which explain themselves. Cilia are long and sparse hairs, arranged in a row on the margin, as in the horse-leek, Sempervivum tectorum. Hairiness expresses a form of hair f a rather long and soft character, as seen in the common hemp nettle (Galeojpsit tetrahii) ; pilosity, when the hairs are longer and more erect, as in the carrot (Daucus carffta) ; and villous, when very long, straight, erect, and soft, as in the JSpilobium. The term tomentum expresses a mass of hairs entangled and closely pressed to the skin, as in the Geranium rotundifol'ium. The longest hairs are probably those which envelop the cotton seed (Gossypium, Fig. 62, B), and constitute the cotton of commerce. They are also very long on seeds of the ccitton tree^, Fig. 115. Stinging Hairs. A, 1, club-shaped hair, filled with the poison- ous .secretions of the Stinking Hellebore (Helleborus fastidus). 2, a pimilar hair, which has discharged its contents, ai'd then collapsed. B, pointed one-celled hair of the WIOANDIA URKNS, filled with poison. The dotted lines show the current of the circulation, and the arrows its direction. 68 THE PRICKLES OF PLANTS. and in the willows of our own country. On ferns they are scattered, long, brown, and entangled. Fig. 116. Fig. 117. Fig. 116. Two hairs from the style of a CAMPANULA, showing in a the circulation proceeding, and in b emptied of its contents. The latter is not only collapsed, but retracted within itself. Fi?. 117. Representing the mode of growth of hairs from a single epidermal cell ; a, club-shaped; 6, pointed. Both from the Evening Primrose (^NOTHERA). The development of hairs appears to be usually a very simple process, being none other than the inordinate growth of a cell of the cuticle on its free surface. Such is figured by Schleiden (Fig. 11 7). Prickles are hard unyielding processes, with an acute and usually slightly curved extremity, well fitted to hold and tear any object which may be carried against them. They are very common in the rose (Rosa), and bramble (Rubus), in which plants they are the growth of a single year. In other plants, as the Xanthoxylum juglandifolium, they are the result of two or three years' growth. They are essentially allied to hairs, since they are cellular prolongations of the cuticle, but differ greatly from them in their far greater development, the rudeness of their texture, and the functions which they perform. They have also a less real but a greater apparent resemblance to spines, as of the sloe tree (Prunus spinosa), inasmuch as both are large and rude, and sharply pointed ; but there is this essential dissimilarity viz., that the spine is a prolongation of the wood of the tree (in other words, an abortive branch), whilst the latter is simply connected with the cuticle or the epiphloeum of the bark of herbaceous shrubs. Their use is not well known ; but they are not depositories or secretions, neither have they any independent circulation. They are well adapted to enable the long and slender branch to support itself by attachment to stronger plants, and also (if we may apply such an expression to a mere vegetable), to enable it to defend itself from the attacks of animals. They may be detached from the cutis by the force of the thumb and finger. Scurf has been regarded as a production analogous to hairs, inasmuch as it is a cellular structure and is a process from the cutis There, however, the analogy ends, and it fails in the most essential point viz., a similarity in function. It consists of scales of various forms and sizes, adhering to the cutis by the whole or only a part of THE RAMENTA AND GLANDS OF PLANTS. 69 the surface ; and when hy a part only, it is the central portion ; and the edges become irregular in outline and crenate. This latter peculiarity has induced a belief in the mind of an acute observer, Dr. "VYillshire, that the crenate scale in the Adelia and the Eleceagnus marks a transition from the simple scale to* the beautiful stellate hairs of which we have just spoken, p. 65. Scurf is commonly met with in plants, and gives a spotted or leprous appearance to the cutis, as may be seen in the pine apple. H amenta are thin, scales abundantly found on the backs of the leaves of ferns (Alices), and on the young shoots of many plants. They are slightly foliaceous in their appearance, and not unlike the leaves of some mosses ; but they want the structure, the position, and the leaf-buds of true leaves. Their function, as well as that of scurf, is unknown. Glands. We have now to consider a series of organs about which there has been much controversy one party regarding them as reservoirs of secretions and true secreting organs ; and another (represented by M. Schleiden), doubting if such organs can be found in vegetables. M. Schleiden writes : " I have already remarked that I can connect no precise and definite idea with the term gland, as referred to a plant. No attentive observer can avoid seeing how different is life in different cells, whether they are found in different plants or in the same plant, or near each other. It appears to me quite foolish to denominate that cell or that group of cells which contains different matter from its neighbours a gland or organ for secretions; for there are many plants and parts of plants which would then consist only of glands. It is ridiculous to call a cell containing volatile oil a gland, and to refuse the name to one that contains red or yellow colouring matter ; and should we call the last glands, then almost all petals would consist only of glands. The epidermis would be sometimes an epidermis, but sometimes a glandular surface, and with many single cells we should have to admit they are partially glands and partially not so." The force of this reasoning will be perceived when we remember that all cells have contents, and that these contents have been secreted or produced within the same cell. Each cell is therefore both a secreting and a containing organ. Again, there is no anatomical structure in vegetables which is peculiar to these organs called glands, as distinct from mere ordinary cells of cellular tissue. In animals, on the contrary, there is in most instances a special glandular structure, and beyond this there is a series of cells called epithelium, to which is confided the duty of producing the larger part of the secretions of the body. These latter offer the nearest points of analogy to the glandular structures of vegetables, But whilst admitting that there is a difficulty in defining a gland, there cannot be a doubt as to the existence of certain small hardened masses of cells, which perform the office of glands. Thus the nectarium, on the claw of the petal of the common Ranunculus, secretes a sweet honey-like substance, and is a true gland. So, also, with the glands situate beneath the cuticle, also the base of the pitchers of the Nepenthes and other pitcher plants. These pitchers contain a considerable quantity of water, not from having col- lected it from the air, but from the action of the glands referred to. In the latter instance there is a broad line of distinction between such bodies or glands and that of an ordinary secreting cell ; for whilst in the latter case the secreted matter is retained within the cell, and the quantity corresponds with the size of the cell, in the former the secretion is altogether emitted from the gland, and its quantity is infinitely greater than the size of the organ which produced it. The subject is, however, involved in great obscurity, and it is probable that ere long it will be necessary to exclude such 70 THE STEMS OF PLANTS. cellular organs as the lenticular glands of the willow, and to include such reservoirs aa the vittse or receptacles of the volatile oils of plants. Glands are sessile or sitting when resting immediately upon the cutis, aa may be teen near the base of the ovary or seed-vessel of such pod-bearing plants as the Cruci- ferae. They are also found upon the calyx of some campanulas, and upon the petiole or foot-stalk of the leaves of the peach, the cassias, and the passion flower. Their forms, colour, and appearance are very various, and of many it may be doubted if they are true glands. Stalked glands (Fig. 118), are such as are elevated from the cuticle by something in the nature of a hair, and are simple if they consist of one or perhaps more cells and have a stalk of but one conduit, and compound where there are several cells and several conduits. This division of glands has been termed indifferently stalked glands or glandular hairs. They are common in the rose and brambles, the Hypericums, the Rue, the Tatropha, the Snapdragon (Antirrhinum!) , the Lysimachis, the Drosera or sun-dew, and many other plants. In the sun-dew the hair of the leaf has an internal fibre, and is therefore a fibre cell ; and the gland head consists of several layers of cells, the outer ones being small and cuticular, whilst the inner ones are long and columnar, and some- times contain a spinal fibre. Before proceeding to a consideration of the stems of wooded plants we will direct attention to two modifications which are met with, not exclusively, but chiefly, in herbaceous plants viz., first an enlargement of that part which is under ground, and which lies between the roots or rootlets below, and the true stem above ; and secondly, such stems as take a horizontal rather than a perpendicular course above ground. These are termed respectively subterranean and aerial stems. Subterranean stems, as the potato, onion, and turnip, include almost all the recep- tacles of starch, except seeds, provided for the use of man. There can be no doubt as to their analogies, seeing that they do not possess the anatomical and physio- logical properties of roots, and do, notwithstanding their deformity, resemble stems. They are commonly arranged under four heads the bulb, conn, tuber, and creeping fltem. The creeping stem (soboles), unlike the others is unimportant as an article of food, but yet is of great value from the property which it has of insinuating itself rapidly amongst the sandy particles of loose soils, and binding them together. It may thus lay the foundation of hills of sand which shall suffice to resist the encroachments of the sea. It is represented by the couch grass (Triticum repcns), the bane of farmers, not only from the property above mentioned, but from the rapidity with which it multiplies itself whenever the stem is broken Fi*. 118.-The underground stem of the ^ the farmers> efforts to clear the land ' potato (Solanum tuberosum), -with its The tuber or potato is an irregularly ovoid S b o^ pS Sct^to^the? enlargement of the stem, having upon its surface by small bundles of fibre, 6. a number of growing points, familiarly termed eyes. The tubers of the same plant are all con- nected together and to the parent stem by single bands of small diameter, consisting chiefly of woody fibre for the purposes of the THE CORM AND THE BULB OF PLANTS. 71 circulation of the plant. The precise mode in which the tuber enlarges is unknown but it is quite clear that it must be freely supplied with circulating juices from the stem. This is effected by the woody fibre, and bundles of it ramify within, the tuber, and pass to each growing point. The structure of the tuber is very simple, being only a large mass of cells containing starch, inclosed in a layer of condensed cells or cuticle. The woody fibre and other structures bear no proportion whatever to the cellular tissue, and are not readily de- tached. The cellular character is at once evident by placing a very thin slice of it under the microscope, when a number of straight lines will be observed forming cells of much regularity, and inclosing a large number of starch cells (Fig. 83). The starch may be demonstrated by the addition of a watery solution of iodine whilst the section is uader examination, when a beautiful violet colour will be instantly produced. This form of stem is also found in arrow-root, and has a more regular figure in the asparagus potato. The Corm, as in the crocus, colchicum, and arum (Fig. 119), is a rounded, flattened, solid organ, bearing a bud upon its point or at its side, and leaves from its upper part. It is a compressed stem, and is restricted to monocotyledonous plants, and intervenes between the true roots and the reproductive buds. It usually contains much starch, accompanied by an acrid poisonous secretion, which militates against its employment as an article of food. The bulb, as of the onion and lily, is also an underground stem, or a stem in the rudimentary state of a leaf-bud. It is a fleshy, conical body, with scales surrounding Fifr. 119. The Cor- mus of the ARUM MACCLA.TUM, con- taining starch. Fi. 120. A tuni- cated bulb. with, tern and roots. Fig. 121. A, naked bulb of LILY, showing its lateral stem and foliaceous covering. B, section of a bulb, showing its growing point at a. AERIAL STEMS. a growing point, and emitting roots from its base, and thus theoretically resembles the leaf-bud of an aerial stem. It reproduces itself by developing buds, or cloves, at the base of its leaves or scales, which buds grow at the ex- pense of the parent plant, and at length destroy it. There are two kinds, according to the arrangement of the leave? First, the tunicated (Fig. 120), when they more or less sur- round the whole organ, and cohere in a membranous sheet of tissue. Such is the case in the onion (alliutri). Secondly, the naked, when the scales are Fig. 122. The RUNNER, emitting roots and leaves at intervals, smaller and more fleshy, and are imbricated in rows one above another, as in the tulip. Both of these forms contain much starch (Fig. 121) and also many raphides (Fig. 87). They are not so exclusively com- posed of cellular tissue as was noticed in the structure of the tuber ; but also contain vascular and woody structures. Aerial Stems are of five kinds, the Sucker, the Vine, the Eoot- stock, the Runner, the Offset, and the Pseudo-bulbs of orchidaceous plants. The Sucker is common in mo- nocotyledonous plants, as the pine-apple, and consists of a branch proceeding from the col- lum of a plant underground, which becomes erect and bears leaves, and subsequently emits roots from its base. In other instances it proceeds from the stem downwards to the earth, and there takes root. The Vine, as in the Vine (Vi- tis vinifera) and Cucumber (Cucumis), is a slender twining stem, which situates itself amongst and adheres to other plants for Fig. 123. The GINGER plant (Zingiber officinale), with support*,.. It does not give off lts rhlzome from whi CQ the leaves and flowers spring. foots along its course. The Runner^ on the other hand, is also a creeping stem ; but it emits a bundle of WOODED STEMS. 73 Fig. 124. The tubers, or pseudo-bulbs, of the SPIDER orchis. roots and leaves at intervals, and, in fact, forms new plants (Fig. 122). Such is the Strawberry (Fragaria). The Offset, as in the House-leek (Sempervivum tectorutri), is a short branch terminated by a cluster of leaves, and capable of independent existence after separation from the parent plant. The Hootstock, or rhizome, is a thickened root- ing stein, as in the Ginger (Fig. 123), and Iris, which produce young branches or plants yearly. The Pseudo -bulbs of orchadaceous plants (Fig. 124) very closely resemble tubers, except that they retain the marks of leaves which they once bore. They exist above ground, and contain amorphous starch. Wooded Steins. Having now offered such remarks on herbaceous stems (dis- tinguished from woody stems) as seemed to be required by their greater delicacy, we proceed to describe woody stems and their appendages. When treating of the mo- difications of herbaceous stems (page 59), we inti- mated that such changes also affected woody stems, but in a lesser degree, and shall therefore not again re- fer to them under this head. There are, however, a few preliminary remarks which are necessary as to the general conformation of the tree before we enter upon an examination of the in- ternal structure. The general divisions of a stem are called branches (nwm), and the arrangement *i&r?5&~~^ f '-~f3&s&&&a&mx nmrsrti ia^s^^eg?^ ^ them as a whole is termed corona, a head, as that of a forest tree. (Figs. 125, 126.) "When they pro- ceed from either side of the stem, and then pass from the base to the apex of the tree, it is called a caulis excurrens, but when the stems break Fig. 125. The BEECH TREK (Fagus), showing the corona, or head, of forest trees. up into a mass of branches, it is known as a caulis deliquescens. Incompletely grown Bhoots are termed innovations, and ramuli, or twigs, when very young. If the shoot is long and flexible, it is called a vimen ; and when it proceeds from the stem at nearly a WOODED STEMS. right angle, it is called Irachiate. This arrangement of the branches is further used to distinguish trees, shrubs, and herbs. A tree (arbor) is composed of a trunk supporting perennial branches ; and, when small, it is called arbusculus. A shrub differs from a tree in there being no central stem or trunk, but the branches proceed directly from the earth. This is called frutex, fruticulus when small, and dumosus when low. The undershrub (suffrutex) has the same arrangement of branches ; but it approaches nearer to the herb, since it wholly or partially dies annually. It has, however, wooded branches, and not merely, or chiefly, cellular ones. The stem of a forest tree, and of any other which has not its growth terminated by a flower-bud, or any other organic cause, is said to be indeterminate, and determinate when otherwise. 126. Representing a variety of trees, all of exogenous growth. Th j science of Botany is rich in descriptive terms ; and although they may be disagreeable to a student, are very welcome to the botanist who would intelligibly describe a plant. We must therefore counsel our readers not to pass them hastily by, but to read them attentively, and, if possible, commit them to memory. Wooded Stems are divided into two great and well-defined classes, according to their internal conformation viz., such as grow from without (exogenous), and such as enlarge from within (endogenous). The former are more common in cold, and the latter in hot climates. There are, however, the following points of resemblance : Each has & EXOGENOUS STEMS. 75 cellular basis through which the bundles of wood pass, and each is inclosed by a cuticle or bark (endogens are said to have no bark). The cellular system is horizontal, and constitutes the woof of the structure ; whilst the vascular and woody system is longi- tudinal, and corresponds to the warp. Exogenous Stems. On examining a section of the stem of an oak, or any other of our forest trees (Fig. 127), we observe the following parts first, the pith, , or its remains, in the centre ; secondly, the B bark, rf, on the outside ; thirdly, a mass of wood, b, between the two, broken up into portions by the concentric deposition of its layers, and by a series of lines or rays, c, which pass from the centre to the circumference. Thus there are always pith, bark, wood, and medullary rays (Fig. 127). It has already been mentioned that Fig. 127 A, transverse, and B perpendicular section of an exo- genous stein, showing parts of which it is composed. a, the central pith ; b, four layers of woody fibre ; c, the cambium in the spring ; d, the bark ; e, the medullary rays. each stem has two systems, the cellu- lar and the vascular ; and the parts just mentioned must belong to one or other of those systems. Thus the pith, medullary rays, and bark belong to the horizontal or cellular system, and the wood, with its associated ducts, constitutes the longitudinal or vascular system. This division of stems comprehends nearly every wooded plant of our climate. The Pith occupies the centre of the stem (Fig. 128, a), and remains throughout the period of growth of some trees, as of the elder (Sambucus nigra), or is absorbed after a few years, as in the oak and almost all large trees. In the latter class of plants there are some remains of the pith for many years after the process of ab- sorption has commenced ; but at length no vestige can be detected, and its position is known only by the central spot around which the wood is placed in circles. It is, however, at this period found in young shoots just as it was at the earliest mo- ment of the formation of the plant (Fig. 129). When it exists, it passes Fig. 128.- -A scheme of the parts of an exogenous stem. a, the pith ; ft, the bark ; c, medullary rays uniting the pith and the bark (greatly exaggerated) ; d, woody fi bre. uninterruptedly from the ri ?- 129.-*ection of young *_ shoot of the MAPLE TREK root to tne end ot each branch and leaf-bud ; but is sometimes thickened, and rendered more dense, as in the ash, at the nodes the place, indeed, where all the structures are somewhat compressed. Its structure is at all times cellular ; and, for the most part, the cells are hexagonal in form, as shown in Fig. 11. The cells are commonly (Acer campestre), show- ing the large size of the pith, a; the bundles of wood of one year's growth, and the bark with its hairs. 76 THE PITH THE MEDULLARY SHEATH. of large size, and may be well examined in the pith of the elder. Their colour is green whilst they freely perform their function ; but subsequently the tissue is nearly colourless. In the old age of the plant the pith often assumes a colour which it has obtained from the juices which have been deposited within it. In a majority of instances the pith forms a solid cylindrical mass ; but in certain fast-growing plants, as in the hollow stems of the Umbelli- ferce, it is torn, and vacuities are left. Fig. 130. Chambered pith in the WALNUT TREE. I n a f ew plants the ruptured pith assumes a very regular form, and is thence termed chambered pith, since it is divided into a series of compartments which pass across the column in small stems. Such is the case in the walnut (Fig. 1 30), as may be readily seen by selecting a very young shoot and slicing away a portion of one or both sides. According to the researches of Professor Morrison this change depends upon the lateral elongation of the cells, and the conse- quent disappearance of the contents of the cells, and is induced immediately by the absorbing action of the leaf 'bud. The connexions of the pith are highly important, and demand special enumeration. It has already been intimated that it does not exist in the root, at least, of tolerably grown plants, and therefore its functions are confined to the stem. First. It is in direct and unbroken connexion with every branch, leaf, bud, and flower, and is the structure which first conveys fluids to, and receives fluids from, the newly-developed leaf. It thence becomes the main organ of nutriment ; and, at the same time, the chief depository of the secretions. Secondly. It is in equally direct and unbroken connex- ion with the bark, through the medium of the medullary rays ; and thus becomes the centre of all the movements of sap which proceed in the horizontal system ; it is that system which more especially presides over the life of the plant. The mode in which its ultimate disappearance occurs has been a matter of doubt and speculation. It seems quite clear that it is not converted into wood, as was asserted by Mirbel, and there are certain facts which militate against the opinion that it is gradually compressed by the wood ; but since it is known that in the growth of the plant much compression of the previously formed wood must occur, and since this compression is a reasonable theory by which to account for the disappearance of the less resisting pith, it is now pretty generally admitted to be at least one of the causes of this occurrence. As a general rule, the pith, so long as it exists, is not mingled with other than cellular structures ; but, in a few instances, woody fibre has been found with it ; and in others, as Nepenthes, spiral vessels have been detected. The economic uses of pith have not been numerous, but amongst them must be mentioned the rice-paper used in China, and prepared by cutting the pith of the -ZEschynomene (Fig. 48), and the Aralia papyrifera, in a circular manner, so as to obtain large, thin, and evenly cut sheets. It is used for drawing and for writing. The cellular pith-like stems of the JEschynomene aspera, called "shola," have been forwarded to this country from India, and have been made into various ornaments, models of buildings, hats, boxes, and life-buoys. Its lightness, and non-conducting property of heat, render it very fitted for the manufacture of hats. Medullary Sheath. Immediately surrounding the pith of all exogenous plants there is a layer of vascular tissue, which has received the name of medullaiy sheath MEDULLARY RAYS THE BARK. 77 b 6 Fig. 131. Vertical (Fig. 128). This sheath has no special walls, but is simply bounded by the pith on the inner, and by the wood (when it exists) on the outer side. It is in this situation that we may find ducts of various kinds, and spiral vessels ; and in all cases it conveys the vascular structure from the root direct to each leaf and flower. The integrity of this structure is therefore highly necessary to the life of the plant. It is said to retain its green colour to the latest period of the existence of the plant; thus showing the impor- tance of the functions assigned to it. Medullary Rays. These structures come next in order ; and, as has been already intimated, belong to the horizontal cellular system of the stem. They constitute the channels of communication between the bark and pith, and are composed of a series of walls, of single muriform cells resting upon the root, and pro- ceeding to the apex of the tree, and radiating from the centre. They lie between the wedge-like blocks of wood, and, as they have a lighter colour than the wood, they are evident on a section of any stem, and are called the silver grain (Fig. 131). Their colour and number suffice to enable us to distinguish various kinds of wood, and greatly increases their beauty. They cannot, of course, exist before the wood is of an egenou formed, and are therefore not met with in the earliest condi- across the medullary tion of the plant. They begin to exist with the first deposited ravs, showing their open /. -, ^ -n character and their rela- Ia 7 er of wood, and continue to grow outwardly, or nearest to tive position to the wood, the bark, so long as the wood continues to be deposited. a. Dotted duct. , i -, i -n -, i . b. Woody fibre. The Bark. As the medullary rays terminate in the bark e. End of medullary rays. on their outer s {^ we are naturally next led to a considera- tion of that structure. It forms the outer covering a sheath of the tree, and, in some form or other is present in all plants. "When discussing the constitution of the cuticle of herbaceous plants we explained the points of difference between the two varieties of the same structure, and showed that the rudeness of the bark of wooded trees had destroyed many of the characters of the cutis, such as stomata and hairs. We have now to regard it as a dense cellular organ, well fitted to endure the influences of sea- sons through a long series of years. It may anatomically be divided into two structures viz., an outer one, which is cellular, and an inner one, which is vascular or woody. The former is sub-divisible into three parts, whilst the latter is composed of several layers of the same material, and forms a link between the wood and the bark. The three divisions of the cellular part are the Epidermis, the Epiphlaoum, and the Mesophlaeum. The Epidermis is the most external layer, and is continuous with that upon the leaves. Its cells are flattened and lengthened, and but very rarely possess stomata. The Epiphleeum has acquired much importance from the fact of its being the part of the bark in which the cork is deposited. It cracks and peels off at intervals in almost all trees. In the birch and cherry it may at all times be seen hanging from the stem in silvery shreds, and in other trees as rough broken patches. In the cork tree (Qnercus suber] it remains firm until the tree has attained a certain age, after which it exfoliates in the large masses in which it is brought to this country. It is probable that the deposition of cork proceeds in all trees ; but in the cork tree it attains so great a thick* ness as to become a highly important article of commerce. The removal of the cork from the cork tree is not left to natural exfoliation ; but, when 78 THE BARK OF TREES. the tree is sufficiently mature, incisions are made from the top to the bottom of the stem, so that the cork may be more quickly removed. The sheets are then placed upon the ground to flatten, and are at length cut up into convenient lengths for packing. The tree will permit this process to be renewed during seven or eight successive years. The cause of the exfoliation has not well been determined. It certainly does not depend upon the growth of the tree, as though the increased size of the stem caused the bark to rupture and thence to fall off; but it is said that a layer of tabular cells are formed within it which cuts off its communication with the internal structure of the stem, and thence it dies. No doubt can exist as to the fact of the constant destruc- tion of the old bark and the formation of new structures, and it appears to arise either from the death of the external layers only, or from the formation of cork on the inner- most layer of the bark, which causes an arrest of the circulation, and at length the death of the more external parts. It is said that the bark of exogens is much more extensible than that of endogens ; and that, as a consequence, the stems of the former exceed in diameter those of the latter. But the fact just mentioned seems to prove that in fact the cellular part of the bark of exogens possesses but little extensibility ; for, when the enlargement of the trunk has proceeded but even to a moderate extent, the bark cracks off from a lack of this power of extension. It is far more probable that the increasing size of the zone of bark is less due to the extensibility of the old bark than to the formation of new cells year by year as the stem enlarges, and in a layer at all times proportioned to the increasing size of the stem in fact, that the old coat becomes too small, and rends, and a new one is supplied of larger dimensions. It is quite clear that the external layers, after rupture, either peel off, or the width of the rents increases as the tree grows larger. The Epiphlceum consists of several layers of thin flattened cells, usually without colour. Thirdly, the Mesophlaum is a thin layer of green cells lining the epiphlseum, and, in the cork tree, exfoliating with it. Its cells lie in a direction different from that of the cells of the epiphlaeum, and sometimes contain cellular secretions. The vascular part of the bark is called the liber, from its offering a smooth enduring structure, which was formerly used as paper (liber a book). It consists of several layers of small interlaced bundles of woody fibre, connected together by loose cellular tissue. In some trees, as the lace bark tree (Lagetta lintearia, Fig. 132), it resembles a textile fabric, and may be ob- tained from the tree in sheets of large size. The woody fibre of the liber has always the peculiarity of being very strong, and of lying in small bundles, and has been used as cordage by most nations. It is still employed in Russia in the manufacture of mats, and in many parts of the world for whip- lashes. It is not equally smooth on both aspects ; since, on its outer side, it has cellular connexion with the mesophlaeuin, but on its inner surface it is opposed to the smooth wood, or is covered by the semi-fluid cambium. Its mesh-work character Fig. 132. Bark of the Lace Tree of Jamaica, composed of fine and loosely arranged bundles of woody fibre. Natural size. permits the medullary rays to pass through it, and to keep up a circulation with the cellular part of the bark. It is not subsequently converted into the wood of the tree, THE WOOD. Fig. 133. The branching vessels of the bark along which the fluids are con- veyed. as some have supposed, but is formed in the Spring season from the leares -with the wood, and lies in successive layers -within the mesophlaeum. The more immediate use of the hark is that of giving protection to the wood. If bark did not exist there would be no cambium, and without cambium there could not be any deposition of woody fibre ; and thus the presence of bark is necessary to tbe growth of the tree. It is also essential to the life of the tree, from its connexion with the cellular system, and with the undeveloped leaf-buds. The bark contains a large number of air vessels and vasa propria, and not only conveys refuse matter from the leaves to the soil, but is in almost all cases a depository of elaborated secretions. This is well seen in the oak bark, yielding tan- nin ; the cinchona bark, producing quinine ; and the fir-tree, emitting turpentine. There are also many milk vessels ; but, with the exception of the Nepenthes, there are no spiral vessels. We have oftentimes found thick wall-cells, as in Fig. 40, arranged in columns with great regularity. Wood. We now proceed to the most important division of the parts formed in exogenous stems viz., the Wood a substance not merely giving stability and beauty to the tree, but offering the greatest service to man. We find it occupying nearly the whole body of the trunk, and arranged, as a rule, in a very regular manner in this class of trees. On taking up any piece of wood, but more particularly the entire section of a stem, we first notice a series of circles, which incraase in diameter, and are separated by wider intervals as we approach the bark. In this manner the trunk is composed of numerous zones inclosed within each other. Again, in almost all trees, we observe the medullary rays before-mentioned passing in straight lines from the centre to the circumference ; and as the circle of the stem at the bark is much larger than any circle near to the centre, it follows that the medullary rays will be wider apart at the bark than at the pith. On this view of the subject we may state that the stem is composed of a series of wedge-shaped blocks, which have their edges meeting at the centre. The combination of these two views gives the correct idea of the arrange- ment of the wood viz., a series of wedges, each divided into segments of unequal width by circular lines passing across them. From this description it must not be supposed that these various portions are detached, or may be readily detached, from each other ; for, although the medullary rays and the circular mode of deposition both tend to a less difficult cleavage of the wood, they yet bind the parts very closely and firmly to each other. The explanation of the occurrence of distinct zones of wood is that each zone is the produce of one year, and that in our climate, more so than in tropical countries, the period of growth of wood ceases for many months between the seasons, and thus induces a distinction in appearance between the last wood of a former and the first wood of the succeeding year. This distinction is maintained throughout each year, and throughout a long series of years. The inclosure of zone within zone is owing to the mode in which the wood is pro- duced, and the position in which it is deposited. Wood is formed by the leaves during the growing season, and passes down towards the root between the bark and the wood of the previous year (if any}, or in the position in which cambium is effused ; and, as th 80 THE WOOD. leaves more or less surround the whole stem, the new layer at length completes a zone, and perfectly encloses the -wood of all former years. This is the explanation of the term exogenous, which is derived from two words signifying to grow outwardly, for the stem increases in thickness by successive layers on the outer side of the previously- formed wood. That this is the mode of growth has been abundantly proved by experi- ment, and demonstrated by accidental discoveries. Thus, if a plate of metal be inserted between the bark and wood, it will in progress of time become inclosed by the new wood which has overlaid them. So in like manner, if letters be cut deeply through the bark and into the wood, the spaces will not be filled up from the bottom, but may be seen in subsequent years overlaid by new wood. A statement appeared in a daily paper, during the past year, to the effect that in cutting down a tree a cat had been discovered inclosed in the wood of the trunk. These facts prove that the wood is applied from without. Again, if a branch be stripped of its leaves down to a certain point, it will not grow above that point ; and so, in like manner, if branches be stripped from one side of a tree, the tree will not grow on that side. If a circle of bark be removed from a branch above and also below a leaf, it will be found that increase of size will occur below, but not above that bud ; and so, likewise, whenever a ring of bark is removed from a tree, the new woody fibre will not proceed from the lower but from the upper free edge. Further, if a scion be engrafted upon a stock having wood of a different colour from that of the scion, it will be found that the wood produced from the scion overlays that of the stock. This may actually be seen in operation in the spring season, if a leaf be exposed immediately below its base ; for then bundles will be seen to shoot below the ring of bark or cuticle, and to divide into two sets, one of which proceeds to the liber, and the other to the wood of the trunk. These facts are undoubted, and the inferences seem to be indisputable ; but yet various men of eminence have held contrary opinions. Thus, Linnaeus believed it to be the produce of the pith, and Malpighi, that of the last year's wood ; whilst Du Hamel affirmed that it was produced by neither, but solely from the cambium, which, according to him, was secreted by the bark. It cannot be denied that the bark exercises an influence in the formation of wood ; for if a zone of red bark be made to grow upon a tree having white bark, all the wood appearing below this new bark will be red. But this is not the result of any power in the bark to form wood, but simply that the wood, as a part of the horizontal cellular system of a plant, has a controlling influence over its secretions. These experiments, and others of a similar character, may be most readily performed by any one of ordinary ingenuity. And what amusement could be more instructive to our young friends of both sexes, and possibly through them to the world at at large ? If our readers will cursorily glance at the cut surface of any stem, they will at once perceive another fact in relation to the zones of wood, viz., that whatever may be the thickness of the zone for the year, it is rarely equal around the whole circumference of the stem. This is no matter for wonder ; but, on the contrary, it is surprising that there is any approach to regularity, seeing that the position of leaves upin the branches seems to be an accidental rather than a circular or spiral one. The occurrence is readily accounted for on the theory above propounded, and is due to the lesser abun- dance of leaves on the branches of one side than on the other, or to the prevalence of winds, or some other physical cause, acting in that direction in opposition to the growing process. SECTIONS OP EXOGENOUS STEMS. 81 Figs. 134, 135, 136, 137, 138 exhibit horizontal and perpendicular sections of an exogenous stem, from the end of the first to the end of the fifth year. In each figure Fig. 134. End of first year's growth III" ! I , ' Fig. 135. End of second year's growth. Ill Fig. 136. End of third year's growth. Fig. 137. End of fourth year's growth. . , ii ! Fig. 138. End of fifth year's growth. the pith occupies the centre, and is the largest at the end of the second year; after which it pro- gressively diminishes. Immediately around it is the medullary sheath. The bark is on the outer boundary ; and the woody and pitted tissues occupy the intervening spaces, and increase at the rate of one layer or zone per year. The medullary rays pass from the pith to the bark. From the preceding remarks it will at once be inferred that a plant of one year's growth has but one layer of wood ; and that that, therefon-, does not inclose wood, but pith only. When the tree has reached the end of the seccnd season it will have two layers ; and so on, successively, through any number of years. The above Figures represent each a horizontal and vertical section of a steni at various periods ; and in Fig. 138 it will be seen that the stem of a plant five years old exhibits a centra] pith, five zones of wood, and the bark, besides the cambi/im in the spring season and the medullary rays. The age of trees has been inferred, when a section of the whole stem could be examined, by counting the number of rings of wood whit, h have been deposited around the pith. When only a part of the stem remained, and yet its original diameter was known, the same end has been s ught by multiplying the width of one zone by one half the diameter, or by counting; the number of zones from the pith to the bark, should so 82 IMMENSE GROWTH OF TREES. much of the stem be found. In a large proportion of cases these modes will evoke tolerably accurate results ; but there are several sources of fallacy to which we must refer. First, it is highly probable that in tropical climates the wood of more than one year may produce but one zone ; for as there is but a short if any period of cessation of growth, but very slight evidences of any line of demarcation can be detected. The real age of trees may thus be underrated. Secondly. It is highly probable that in some plants more than one zone of wood is formed in the year; for such is evidently the case in the root of the Beta Vulgaris. This would unduly increase the age of the tree. Thirdly. When examining a fragment of a tree the observer should remember that the zones are not of equal thickness throughout, and that it is quite possible that in some years no wood whatever was formed in the fragment under examination. The varying width of zones results from the age of the tree ;, so that it is less as the tree advances in life, as also from the interruption to growth, which not unfrequently continues on one side of a plant throughout a greater part of the growing season. This may be readily observed by noticing a section of almost any stem; for then it will be evident that the pith does not occupy the geometric centre of the plant. Dr. Lindley gives the measurements of two sides of four stems, which he selected from East Indian trees, which exemplify this fact clearly : Real age or No. of zones. Total diameter. Diam Smaller side. eter of Larger side. 1st stem . .. 40 45 lines. 9 lines. 36 lines. 2d . . . 36 30 8 22 3d ... 17 31 11 20 4th . . . 8 34 11 23 ,, " Suppose that a portion of the smaller side in the first example were examined, the observer would find that each zone is 0*225 of a line deep, and as the whole diameter of the stem is 45 lines, he would estimate the side he examined to be 22 '5 lines deep, consequently he would arrive by calculation at the conclusion that as his plant was one year growing 0'225 of a line, it would be a hundred years in growing 22*5 lines, while in fact it has been only forty years." Thus, whilst it is difficult to ascertain with great certainty the age of any tree when a whole section can be obtained, the difficulty is vastly greater when only a fragment can be examined. The great size of the trunk of a tree is prima facie evidence of its antiquity ; and judging from that fact alone we should be disposed to admit that the following remark- able trees must be very aged : The Chesnut pf Mount Etna (Castanea de Centi Cavalli) is 180 feet in circum- ference. A Plane tree in Turkey, 150 feet in circumference. Some of the Brazilian Hymenaeas, 84 feet in circumference. In respect of height, it is known that the Araucarias sometimes attain to the height of more than 200 feet. The Pinus Darglariana of Oregon is 193 feet high ; and the Pinus Lambertiana is 226 feet in height. LONGEVITY OF TREES. 83 The real value of these enormous dimensions will be best felt if our readers would make a circle in a field of 180 feet in circumference, and then measure a distance oi 70 yards to indicate the width and height of a tree. There are several ancient oaks in England, through the remains of whose hollow trunks coaches have been driven ; and in New Zealand it is said to be a common txjcurrence to use decayed trees as stables. The following list of ancient trees may be found in a French work, the " Teratologie Vegetale," and their ages have been computed upon the principles now laid down. List of old trees, according to Maguire and Tandon. There are known : Palms of 200, 300 years. Cereus 300 Chirodendron 327 Ulmus (Elm) 355 Cupressus (Cypress) 388 Hedera (Ivy) 448 Acer (Maple) 516 Larix (Larch) 263, 576 Castanea (Chesnut) 360, 626 Citrus (Orange) 400, 509, 640 Plantanus (Plane) 720 Cedrus (Cedar) 200, 800 Juglans (Walnut) 900 Tilia (Lime) 364, 530, 800, 825, 1076 Abies (Spruce) . 1200 Quercus (Oak) .... 600, 800, 860, 1000, 1600 Olea (Olive) 700, 1000, 2000 Taxus (Yew) .... 1214,1466,2588,2888 Schubertia 3000, 4000 Leguminosae 2052, 4104 ,, Adansonia (Baobab) of Senegal 6000 Dracaena (Dragon' s Blood Tree) of Teneriffe . . 6000 When we remember that the two latter periods carry us back to the days of Adam, and contrast them with the ordinary destructibility of vegetable growths, they appear to be incredible, and we cannot but suspect that some elementary error has crept into the computation. Since the quantity of woody fibre produced depends mainly upon the number of leaves upon the tree, and the number of leaves must bear some proportion to the size of the tree, it might be inferred that the quantity of wood deposited would increase with much regularity as the age of the tree advanced. This increase might be mani- fested in two, or one of two ways viz., the increasing length of the zone and its increasing width. It is very probable that an increase does take place in the annual deposit, until the tree has attained its maximum of growth ; and it is quite clear that so long as the tree enlarges, the circumference of each zone must increase likewise ; but there is no evidence that the zone at the same time increases in thickness. This militates against the oft-repeated attempt to determine the age of a tree from its diameter ; and if there were no- other source of fallacy, it would suffice to remind our readers that the growth of trees must depend upon the varying nature of the soil, the CELLULAR STRUCTURE OF TREES. changing seasons, and the prevalence of winds ; and that all these act with tenfold greater effect upon a fidl grown than upon a very immature tree. It may therefore be affirmed, that the zones of wood increase in length, and decrease in thickness, as the age of the tree advances, and that both proceed from determinate causes, but that the increase and decrease alike do not follow any rule of universal application. Moreover the width of the zones of wood, in the same species of tree growing in different positions, is not the same. Thus the Scotch Fir (Pinus sylvestris), growing at various altitudes, produces rings of wood varying from 0'39 lines, to 10 times that amount. That such must be the case we may readily infer from the fact, that in any plantation trees of the same species, and planted at the same time, attain, within a few years, to very different dimensions. This dissimilarity is far greater when we compare trees of various species ; but yet, in reference to all wooded plants, it may be stated that there is a general resemblance in the size, both in height and thickness, which plants of the same species attain in the course of years. Numerous efforts have been made to discover a relation between the height and the thickness of trees ; but whilst there may be an approach to similarity in trees of the same species, there is not a shadow of resemblance in wooded plants as a whole. Thus it has been found, that of two species of Pine the difference was so great, that whilst the relation was as 1 to 5 in one instance, it was as 1 to 120 in another. Such speculations may tend to increase a spirit of inquiry, but hitherto they have had no other good effect. The foregoing description may suffice for exogenous stems which follow this usual course of development, and therefore for the great majority of trees ; but it is readily conceivable that a difference in figure may exist to a great extent, as in the cells of cellular structure, considered at page 11. Fig. 139. Fig. 140. Fig. 141. Fig. 139, representing the section of a tree in which, from the irregular development of the stem, there are no concentric zones of wood. Figs. 140 and 140*, showing, in the section of a stem of a Bignonia, four internal deposits of bark, a, by which the wood is divided into four wedges. The lines crossing the centre are well developed medullary rays. Fig. 141. The stem of a Clematis, in which the medullary rays are greatly thickened, a, the pith ; b, the smaller ; and d, the larger wood bundles ; c, the large medullary rays ; e, the bark. Thus, whenever the process of growth is so disturbed that it proceeds on one side, whilst it is nearly arrested on the other, it is evident that the figure of the stem will CELLULAR STRUCTURE OF TREES. 85 not be cylindrical, and that the layers of wood will not be in perfect zones. So also when this disturbance is restricted to a portion only of one side, fhere will be no growth at that part, and in process of time a depression in the stem will result, giving it a furrowed appearance. At a still later period, assuming that the like causes exist, this furrow will become deeper, but at the same time it will be narrower; for the woody fibre, as it passes down on either side, will find little resistance in that direction, and will push into the furrow and lessen its size. At the same time the bark will also increase in thickness, and in process of time the original furrow will have disappeared. A section of such a stem would show a triangular interval in the circumference of the trunk, which would either be vacant or filled up with layers of bark. If, whilst these changes are proceeding, others of a similar character were met with in other parts of the circumference, the section, instead of exhibiting a circular outline, would greatly resemble the figure of the stellate cell (page 11). These are the expla- nations of a great variety of twining stems growing in hot climates, and which are angular, or present a cruciate appearance on section. An interesting modification, and one very nearly allied to the above, is that in which the medullary rays increase in thickness so greatly as not only to be mere lines, giving a grain to the wood, but large wedge-shaped blocks between alternate masses of wood. This is not remarkable, when we remember that at every moment of growth there are two processes going on, one the cellular or horizontal, and the other the woody or vertical ; and it is no more a matter of surprise that nature should occasionally increase the one at the expense of the other, than that she should rigidly adhere to the rule which she has laid down ; for both the rule and the exception are alike wonderful and inexplicable. Such exceptions, greatly varied, but yet for the most part originating in the " Wood," or cellular structure of the stem, are by no me ins uncommon. The general configuration of exo- genous stems is conical, the circum- ference being, for the most part, cir- cular, and the base much larger than the apex, or the free terminal part of the stem. This necessarily results from the remarks which we have made on the production of wood ; for it is manifest, that if the wood be a product of the leaves, and the number of leaves on the tree increases from above downwards, the quantity of wood deposited will be greater below than above. The apparent exceptions to this rule are in such fast-growing trees as grow in the midst of a dense wood, where the light reaches them e d c d cd Fig. 142, showing the component parts of a stem in the fourth year of growth, only at the top. bucn trees run up ot A, a part of a transverse section. B, a perpendicular nearly even diameter, and without Bother h6 PartS f GaCh arranged accuratel y over a branch, until more than two-thirds a, the pith; b, the surrounding medullary sheath; c and d layers of wood and bothrenchym intermin- gled. The open-work in A shows the position and the extent of bothrenchym more clearly ; e, the bark of their entire height has been at- tained ; but from the point where branches arise, the conical figure may readily be traced. The common asparagus 86 ENDOGENOUS STEMS. plant is also said to be an exception to this rule. The circular figure of the stem is due to the somewhat even distribution of the leaves around the trunk ; and this will be the most perfect when the tree has grown apart from others, and where it is freely exposed on all sides to the influence of light. The wood of plants is not composed exclusively of woody tissue, but with that structure is bothrenchym, or dotted tissue and ducts, in greater or less abundance. This, as before mentioned at page 17, is more particularly the case in fast-growing plants. The diagram on page 85, of an exogenous stem, shows how largely pitted tissue is intermingled with the wood. Fig. 143, representing a Palm forest, and some of the leading characters of endogenous growth. Endogenous Stems. We now proceed to a description of stems which will be less familiar to our readers, and which can usually be examined in museums, or as dried plants only. These are almost peculiar to tropical regions, and are exclusively so if we refer to wooded plants of considerable size. The giant representative of this class is the Palm tree, with its wonderful utility and beauty. The class is represented in this country, and in almost all cold climates, by plants of lesser growth, and more particularly by the grasses ; yet, with the exception of the direction of the veins of leaves, they afford but unsatisfactory indications of the peculiar structure of the plant. The most ready illustration will be found in the common Cane and Bamboo ; and these will suffice for a sufficient inquiry into this subject. The term "endogenous" signifies to grow inwardly, and is explained by stating that the bundles of wood sent down from the leaves do not range themselves in layers THE CUTICLE OF ENDOGENOUS STEMS. > on the outer side of the previously-formed wood, but pass down in irregular masses near to the centre of the stem. Such stems, like exogenous stems, are composed of a woof and warp, each of which holds the same relation to the other in both great divisions of trees, and they differ only in their relative proportions and mode of arrangement. Thus the cellular or horizontal warp is proportionally in- creased in endogenous rather than in exogenous stems; and this, together with the arrangement of the woody fibre into bundles, gives a more open character to the section of the stem. A section of an endogenous stem (Fig. 144) exhibits the following struc- tures: First, an external inclosing layer or bark, x ; secondly, a series of circular lines, which represent the cut surfaces of vascular tissue, y; and thirdly, the mesh- work intervening be- tween the bundles, which is the cellu- lar tissue or pith, z. "We shall consider each of these separately, Cuticle. The epidermis, cuticle, or bark, of endogenous stems, differs materially from the analogous structure in exogenous plants. It cannot, in any lormal instances, be separated from the stem, as may be readily seen by attempting to peel a cane. It does not naturally crack and separate as does the bark of our forest trees; but is hard, dense, smooth (usually), non-corrugated, inelastic, but slightly extensible, and is a permanent unchanging structure. Thus, the diameter of such stems is necessarily greatly restricted ; and it is in length only that endogenous plants can be greatly developed. It does not consist of a series of layers, which may be detached from each other, and distinguished by various names, but is simply formed of one or two layers a mass of flattened cells, with bundles of woody fibre intermixed, and connecting it with the internal parts of the stem. The non-extensibility of these layers is not evident until the tree has attained to somewhat of its natural diameter ; for the bamboo may appear at first as large as the finger only, and subsequently exceed in circumference a man's thigh. Moreover, a few plants, as the Dracaena or dragon's blood tree, referred to at page 1, has attained to a circumference of forty feet. Thus, whilst it is true that the width of endogenous stems, as compared with their height, is much less than in exogenous trees, we must admit that the cuticle is extensible, and must infer that its further development is prevented by a degree of expansibility which does not proceed beyond a certain point ; or that its further non-development is simply a part of the general law which governs the growth of these plants. It is difficult to agree with the common opinion, that the limited power of expansion, which the cuticle is said to possess, is the cause of the limited diameter of the stem ; and it seems more philosophical to assume, that it is only a part of these occurrences which accompany the normal development of these structures. That the size of the stem remains the same at all periods after its full development d t fc * Fig. 144, showing, by a horizontal and perpendicular section, the structure of endogenous stems, a, 2, cellular woof of the stem. b d, bundles of vascular tissue, y, their cut ends. x, the so-called cuticle or bark. 88 ON VASCULAR STRUCTURE. is quite evident from the fact that twining plants may encircle it for many years without compressing it ; but this is begging the question ; for if the stem be fully developed, as at first referred to, no further increase of the tree is expected. The truth seems to be, that endogons cease to grow at their lower part, whilst growth proceeds above ; and thereby the cuticle may have attained to a maximum of extension near to the base, whilst it may be comparatively undeveloped above. Schkiden explains the peculiarities of the cuticle of endogenous stems, as distin- guished from that of exogenous ones, by employing the term " limited growth" to the former, and "unlimited growth" to the latter; and explains them by stating, that in the former, after a certain period, the production of the fast-growing thin walled- cells of the cuticle ceases, and the partitions become thicker ; whilst in the latter, the cells are continually reproduced throughout the whole period of growth of the plant. This seems to be rather a statement of the facts than an explanation of them. It is the fashion to state that endogens have no bark, since none is separable from the wood, and that the cuticle is simply the hardened exposed cells of the stem, with the ends of bundles of woody fibre intermixed. If analogies are truly founded upon function, and not upon structure, we must admit that there is a cuticle or external protective covering to endogenous stems. Vascular Structure. This is a mixture of woody fibre and bothrenchym, with the addition of spiral ducts or spiral vessels. If we examine a transverse section of a cane, we do not find a central pith, with wood arranged in layers around it, but a surface marked by fourteen cut ends of round bundles of vascular tissue, set in a cellular matrix. f-oi// "K ] I >C V ; N' ^ a ^ so on ma ki n g a perpendicular section, we notice that v^-. li/T^ /( /vxvfi fO *ke surface of the section presents a number of perpendicu- lar defined lines, which may be torn out, and a series of intervening connecting substances. The distinguishing peculiarity of endogens is the arrangement of the woody fibre. The general direction of the woody fibre is clearly from above downwards ; but it is highly probable that it does not descend in straight lines, and that when the tree has attained a tolerable height the wood does not descend directly to the root. As the structure is not indigenous 145, showing the arciform to climes where scientific men abound, the observers have arrangement of the bundles been few ; and as the subject is an intricate one, it has not. of woody fibre m endogens . ,. ,.-,, - r i i -, i t (as the Palm), as they pass as yet, been fully elucidated. Mohl is the best authority, from the series of interfoliar and he affirms that $& bundles of fibres descend from the organs at the head of the stem, and their parallel leaves in arcs, which direct then- convexities towards the sM^of The hark n tlie inner centre of the stem. Thus the fibre, in its descent, first a ft, fully developed part of passes towards the centre, and thence towards the circum- to d, 8t Strices of leaves, with ferer ice, until it reaches the bark, or nearly so, when it their vascular bundles. passes down . in a more direct manner towards the root. the'biS dl6S Pr C