/ THE 
 
 PLANT WORLD 
 
 G. MASSEE. 
 
THE LIBRARY 
 
 OF 
 
 THE UNIVERSITY 
 OF CALIFORNIA 
 
 PRESENTED BY 
 
 PROF. CHARLES A. KOFOID AND 
 MRS. PRUDENCE W. KOFOID 
 
X 
 
LIBRARY OF POPULAR SCIENCE. 
 
 BOTANY. 
 
WHITTAKEE'S LIBEAEY OF POPULAE 
 SCIENCE. 
 
 Illustrated. Square Crown Svo. Cloth. 
 
 PICTORIAL ASTRONOMY. By G. F. CHAMBERS, F.R.A.S. 
 
 134 Illustrations. 48. 
 
 LIGHT. By SIB H. TRUEMAN WOOD. 86 Illustrations. 28. 6d. 
 THE PLANT WORLD. By G. MASSEE. 56 Illustrations. 3 s. 6d. 
 GEOLOGY. By A. J. JUKES-BROWNE, F.G.S. In the press. 
 MINERALOGY. By DR. F. H. HATCH. 
 CHEMISTRY. By T. BOLAS, F.C.S. : F.I.C. 
 ELECTRICITY AND MAGNETISM. By S. R. BOTTONE. 
 ANIMAL PHYSIOLOGY. By W. SNODGRASS, M.D. 
 
THE PLANT WORLD. 
 
 ITS PAST, PRESENT, AND FUTURE. 
 
 AN INTRODUCTION TO THE 
 
 STUDY OF BOTANY. 
 
 BY GEORGE MASSES, 
 
 LECTURER ON BOTANY TO THE LONDON SOCIETY FOR THE EXTENSION 
 OF UNIVERSITY TEACHING. 
 
 WITH FIFTY-SIX ILLUSTRATIONS. 
 
 LONDON: 
 WHITTAKER & CO., 2, WHITE HART STREET, 
 
 PATERNOSTER SQUARE. 
 
 GEORGE BELL & SONS, YORK STREET, COVENT GARDEN. 
 1891. 
 
CHISWICK PRESS : C. WHITTINGHAM AND CO., TOOKS COURT, 
 CHANCERY LANE. 
 
PREFACE. 
 
 THE idea of this little book is to furnish an intro- 
 duction to the study of Botany from the standpoint 
 of considering plants as living organisms, subject to all 
 the varied vicissitudes that are more generally recognized 
 as influencing animal life. From this point of view, 
 the changes in structure and function that plants have 
 undergone from time to time become intelligible, a 
 point of primary importance, as a preliminary to a clear 
 comprehension of the meaning of relationship amongst 
 the members constituting the Vegetable Kingdom. 
 
 GEORGE MASSEE. 
 
 KEW, 1891. 
 
 M358403 
 
TABLE OF CONTENTS. 
 
 CHAPTER I. 
 PLANT ARCHITECTURE. 
 
 The Vegetable Kingdom. Leading characters of Plants 
 contrasted with those of Animals. Origin of " Division of 
 Labour." Uses of the various Organs of Plants. Modifica- 
 tions of Structure caused by external agencies. Microscopic 
 Structures ........ pp. I 53 
 
 CHAPTER II. 
 CHEMISTRY AND PHYSICS OF PLANT LIFE. 
 
 Nature of Plant Food and how it is obtained. Influence 
 of Light on Plant Life. Influence of the Vegetable Kingdom 
 on surroundings. Origin of Carnivorous Plants. Sapro- 
 phytes. Parasites. Retrogression . . . .pp. 54 89 
 
 CHAPTER III. * 
 PROTECTIVE ARRANGEMENTS. 
 
 Origin of the Vegetable Kingdom. The struggle for 
 existence. Protection against climate. Protection against 
 living enemies. Saving of energy and expenditure of material 
 exhibited in modern modes of protection . . pp. 90 115 
 
 CHAPTER IV. 
 REPRODUCTION OF PLANTS. 
 
 Vegetative or asexual method. Sexual method. Gradual 
 evolution and advantages of the latter method. Alternation 
 of generations. Cross-fertilization. Protection of reproduc- 
 tive portions of Plants ..... pp. 116 157 
 
TABLE OF CONTENTS. 
 
 CHAPTER V. 
 RELATIONSHIP AMONGST PLANTS. 
 
 Characters of importance in proving relationship. Primary 
 Divisions of the Vegetable Kingdom. Natural Orders of 
 Plants. What is a Species ? .... pp. 158 185 
 
 CHAPTER VI. 
 
 FOSSIL PLANTS. 
 
 Vegetation of early Geological Periods. Disappearance of 
 groups of Plants. The Evolution of Plants corroborated by 
 Geological evidence ..... pp. 186 192 
 
 CHAPTER VII. 
 GEOGRAPHICAL DISTRIBUTION OF PLANTS. 
 
 Principal factors influencing the Distribution of Plants. 
 British Flora, past and present. Distribution of Cryptogams. 
 Distribution of Phanerogams . . . . pp. 193 206 
 
 INDEX 
 
 207 
 
LIST OF ILLUSTRATIONS. 
 
 FIG. PAGE 
 
 1. Pleurococcus vulgaris , . . 12 
 
 2. Facus vesiculosus ........ 95 
 
 3. Maize (Zea mays) . 19 
 
 4. Hazel ( Corylus avellana) . . . . . . .128 
 
 5. Melon leaf .......... 101 
 
 6. Honeysuckle (Lonicera glauca) 29 
 
 7. Diagram of typical flower . 31 
 
 8. Cell of celandine . . ... . . . -33 
 
 9. Cells of beet * -36 
 
 10. Cactus (E cliinocactus decaisneanus) 37 
 
 11. Epidermis showing stomata ...... 39 
 
 12. Epidermis of Oycas revoluta ...... 40 
 
 13. Palm stem, diagram of 43 
 
 14. SeqfortJiia elegans ........ 46 
 
 15. Section of melon stem ....... 47 
 
 1 6. Section of maple stem 49 
 
 17. Section of spiderwort stem 50 
 
 1 8. Section of stem of Bcehmeria argentea . . . 52 
 
 19. Cell of Vallisneria spiralis ....... 63 
 
 20. Starch of potato (i) ; of tapioca (2) 64 
 
 21. Venus's fly-trap (Dioncea muscipula) 73 
 
 22. Pitcher-plant (Geplialotus follicularis) .... 75 
 
 23. Pitcher-plant (Nepenthes gracilis) . . . . 77 
 
 24. Pucciftia graminis . 85 
 
 25. Lepidodendron trunk 190 
 
LIST OF ILLUSTRATIONS. 
 
 FIG. 
 
 PAGE 
 
 26. Cycas circinalis ........ 
 
 . 94 
 
 27. Fucus vesiculosus ....... 
 
 95 
 
 28. Melon leaf 
 
 . 101 
 
 29. Horse-chestnut leaf ....... 
 
 . 103 
 
 30. Orchid ( Oncidium papilio) 
 
 12 
 
 31. Screw-pine (Pandanus) 
 
 . 107 
 
 32. Passion-flower (Passlflora coerulea) .... 
 
 . Ill 
 
 33. Lords and ladies (Arum maculatum) .... 
 
 US 
 
 
 126 
 
 
 
 36. Wheat, portion of inflorescence 
 
 . 129 
 
 37. Daffodil (Narcissus) . . . . 
 
 131 
 
 38. Lime, inflorescence of 
 
 134 
 
 39. Oxlip (Primula elatior) ...... 
 
 136 
 
 40. Oncidium papilio ....... 
 
 12 
 
 41. Pollen-masses of an orchid 
 
 . 141 
 
 42. Sage (Salvia scalarea) 
 
 143 
 
 43. Fruit of dandelion 
 
 153 
 
 
 lie 
 
 45. Tornelia fragrans 
 
 . I 5 6 
 
 46. Christmas rose, fruit of 
 
 I6 3 
 
 47. Primrose, fruit of 
 
 I6 3 
 
 48. Ked corn-poppy, fruit of 
 
 . 164 
 
 49. Fuchsia globosa ...... 
 
 . 126 
 
 50. Pod of garden pea 
 
 . I6 7 
 
 5 1. Fruit of peach 
 
 . I6 9 
 
 52. Fruit of maple 
 
 . 171 
 
 53. Cycas circinalis ........ 
 
 . 94 
 
 54. Livistonia australis 
 
 179 
 
 55. Lonicera glauca 
 
 . 29 
 
 56. Fossil fern (Neuropteris) 
 
 . 189 
 
BOTANY. 
 
 CHAPTER I. 
 
 PLANT ARCHITECTURE. 
 
 The Vegetable Kingdom. Leading characters of plants con- 
 trasted with those of animals. Origin of " Division of Labour." 
 Uses of the various organs of plants. Modifications of structure 
 caused by external agencies. Microscopic structures. 
 
 TO those whose schooldays terminated a quarter of a 
 century ago, the word Botany, as a rule, recalls to 
 memory long strings of Greek or Latin names, or dry 
 and uninteresting definitions of the various parts of 
 plants ; hence it is not difficult to understand the in- 
 difference manifested by such victims towards the study 
 of a science which yields to none in the varied beauty of 
 its members, neither in the manifestation of those peculiar 
 features characteristic of life. 
 
 The popular conception of life is as a rule associated 
 more intimately with the members of the Animal King- 
 dom, and more especially with the most highly developed 
 forms with which we are most familiar, where movement 
 and a more or less perfect development of the special 
 senses, as seeing, hearing, etc., are present. As a matter of 
 course, it is generally known that plants are living bodies ; 
 but there are not unfrequently indications of an inward 
 
 B 
 
BOTANY. [CHAP. i. 
 
 feeling that the life of a plant must be of a very different 
 nature to that of an animal, say a human being. Such 
 an idea is, from the present standpoint of knowledge, a 
 mistake ; in the broader sense there is but one kind of 
 life, and although a perfect definition of life is at present 
 impossible, yet the important characters which separate 
 it from every other known force are clearly understood 
 and fall under the two headings, growth and reproduction. 
 Growth means increase in size, along with replacement 
 of worn out substance composing the individual, brought 
 about in a special manner due to a combination of 
 chemical and physical processes as follows. It is well 
 known that both plants and animals, when quite young, 
 are very small in bulk compared to the size assumed 
 when full grown, and it is further generally known that 
 growth or increase in size depends on a regular and 
 continuous supply of food. The peculiarity of all forms 
 of life is that the food when first taken into the body 
 differs in chemical composition from the living body, 
 and the latter possesses the property of chemically break- 
 ing up its food, retaining those portions that it requires 
 for the building up of its own body, getting rid of the 
 surplus useless matter. As illustrations of the above, a 
 human being can convert a dinner of bread and beef 
 into human flesh ; in the same way a plant that feeds on 
 carbonic dioxide and water containing certain substances 
 in solution can convert these substances into what may 
 be termed plant flesh. The food taken as a matter of 
 course must contain all the chemical elements required 
 for the formation of animal or plant substances respec- 
 tively, but combined in different proportions and often 
 mixed with other elements not required ; and the pecu- 
 
CHAP. T.] PLANT ARCHITECTURE. 3 
 
 liarity of living bodies, whether plant or animal, is the 
 power of chemically decomposing these food substances, 
 re-arranging the constituents into the required chemical 
 compounds, and rejecting the useless surplus. As already 
 stated, one use of food is to enable the individual to grow 
 or increase in size, a second use is that of replacing 
 worn out portions of the body, the result of work done ; 
 and after the full growth has been attained, the latter 
 function of food is the most important one. In addition 
 to the above important uses of food, it is known that 
 during the physical and chemical changes undergone by 
 the food material previous to its assimilation or conver- 
 sion into the substance of the body, various forces are 
 generated, as heat, electricity, etc., which may be con- 
 sidered as forms of energy that are factors in the complex 
 force called life. 
 
 An illustration of change produced chemically on 
 carbonic dioxide (C0 2 ) and water ('H 2 0) by plants in 
 the formation of starch (C 6 H I0 5 ), will give some idea 
 of the manner in which the raw food material is mani- 
 pulated and re-arranged, and also how bye- products are 
 formed. 
 
 6 CO, X 5 H,0 = C 6 H I0 5 + 60 2 . 
 
 (Carbonic dioxide.) (Water.) (Starch.) (Oxygen.) 
 
 The above chemical equation means that the raw food 
 materials, carbonic dioxide and water, are taken into the 
 plant in the proportion of six of the former to five of the 
 latter, and under favourable conditions become chemically 
 re-arranged into one part of starch, the substance re- 
 quired by the plant for its own use in building up its 
 tissues, and there remains as a surplus a certain amount 
 of oxygen which is restored as such to the atmosphere. 
 
BOTANY. [< 
 
 It must be clearly understood that the above equation 
 does not profess to show all the various changes under- 
 gone by the crude material during its transformation 
 into starch; all that is intended is to show the propor- 
 tions of the various chemical elements before and after 
 the change. 
 
 Carbonic dioxide and water are both inorganic sub- 
 stances ; that is, their chemical composition is not 
 necessarily the result of life ; on the other hand, starch 
 is an organic substance, because its chemical constitution 
 is determined by a living body, or by life. 
 
 From the above it will be seen that the material 
 composing the bodies of animals and plants is not of a 
 kind peculiar to themselves, but consists of the most 
 abundant of chemical elements forming inorganic matter, 
 so that organic matter only means the re-arrangement 
 of the elements or constituents of inorganic matter in 
 new proportions, and this is true of every organic 
 product, whether animal or vegetable. 
 
 It will have been observed that food is indispensable 
 to the well-being of the individual; but in spite of an un- 
 diminished food supply, individuals do not continue to 
 live on for ever, but in every form of life there is a limit 
 to the existence of the individual terminating in death, 
 and which is shadowed in under normal conditions by 
 the lessened physical and chemical activity of the entire 
 organism, resulting in the liberation of less energy, which 
 to a great extent constitutes the flow of life manifested 
 during the earlier period of the existence of an indi- 
 vidual. 
 
 The comparatively short period of time constituting 
 the life of an individual may be divided into distinct 
 
CHAP, i.] PLANT ARCHITECTURE. 5 
 
 phases, the vegetative, and the reproductive. All the 
 various functions performed for the well-being of the 
 individual, as the assimilation of food, respiration, pro- 
 tection, etc., belong to the vegetative phase, whereas the 
 reproductive phase is concerned with the formation of 
 specialized portions of the individual which, under 
 favourable conditions, possesses the power of growing 
 into an organism resembling the parent. In the plant 
 world several modes of reproduction are known which 
 will be described at a later stage. 
 
 Other peculiarities less pronounced might also be 
 given as distinguishing living bodies from all forms of 
 inorganic matter, but growth or increase in size by the 
 method defined above, and reproduction, have no parallel 
 in inorganic nature. 
 
 A statement to the effect that plants and animals are 
 so closely related to each other that in numerous instances 
 it is difficult if not impossible to say with certainty to 
 which of the two groups a given organism belongs, would 
 doubtless be considered as a romance of science, and not 
 intended to be literally accepted ; nevertheless, such is the 
 actual condition of things. The cause for doubting such 
 a statement depends on the fact that those plants and 
 animals most familiar to the unscientific person represent 
 respectively the most perfectly developed forms belong- 
 ing to each group, that is, they have the plant or animal 
 peculiarities strongly pronounced, and consequently are 
 in reality very dissimilar both in general structure and 
 appearance, and if such highly developed plants and 
 animals were alone known to us, in all probability no 
 one would ever have suspected the close affinity between 
 the two groups; but if we trace animals and plants 
 
BOTANY. [CHAP. i. 
 
 backwards from the most highly developed forms of each, 
 we come in the end to a series of living organisms in 
 which those peculiarities that give individuality to plants 
 and animals respectively are absent ; such organisms 
 are included in a group known as the Protozoa, the 
 simplest representatives of which are amongst the most 
 primitive of living bodies, and at the point where the 
 plant and animal kingdoms appear to converge, consist- 
 ing of exceedingly minute portions of protoplasm without 
 any external protecting cell- wall, and furnished with one 
 or more exceedingly slender prolongations or cilia for 
 purposes of locomotion; such infinitesimal organisms are 
 spoken of as the Flagellate Protozoa, from the presence 
 of the cilia or flagellae alluded to above. 
 
 The Protozoa, in common with all primitive types, are 
 aquatic in habitat, feed on organic food, and are generally 
 considered by zoologists as representing the starting 
 point of the Animal Kingdom, and certainly as one of 
 the radiating branches from this primordial group be- 
 comes more and more differentiated, we observe the 
 characteristics that become slowly evolved in each suc- 
 ceeding group to constitute collectively those structures 
 and functions which give individuality to the Animal 
 Kingdom, and may be briefly enumerated as follows. 
 
 From a comparatively neutral starting point in the 
 sense of presenting the minimum known amount of dif- 
 ferentiation and division of labour, the most important 
 feature evolved by the members of the Animal Kingdom 
 is the specialization of structures that enables them to feed 
 on organic matter taken into the body in the solid form. A 
 second feature is the gradual evolution of the nervous 
 system, which culminates in the higher groups in the 
 
CHAP, i.] PLANT ARCHITECTURE. 1 
 
 development of the special senses ; but it must be re- 
 membered that many of the lower groups of organisms 
 universally admitted to belong to the Animal Kingdom 
 are entirely destitute of every structural trace of a nervous 
 system. A third character of a negative nature is the 
 absence of differentiated cell- walls. 
 
 The primitive types of the Vegetable Kingdom, if not 
 actually derived by modification from certain members 
 usually included in the Protozoa, are certainly most 
 nearly allied and often almost indistinguishable from the 
 latter, and the first indication of a break away from such 
 primordial types consisted in the development of a green 
 colouring substance called chlorophyll, which enabled 
 the organism to feed on inorganic matter ; and the 
 power of feeding on inorganic food taken into the body of 
 the plant in a gaseous form or in solution is the most 
 important characteristic of plant life, and it will be shown 
 that the adoption of this new method of obtaining food 
 has been the direct or indirect cause of the very great 
 variety of form and structure presented by the vegeta- 
 tive parts of plants. A second important character is 
 the presence of highly differentiated permanent cell-walls. 
 No trace of nerve tissue is present in any member of 
 the Vegetable Kingdom, nevertheless it will be shown 
 that certain movements and responsions to external 
 agencies manifested by some plants agree in important 
 points with similar movements manifested by members 
 of the Animal Kingdom, and which in the latter are con- 
 sidered as being the outcome of nervous excitation. 
 
 The conception as to the origin of plants and animals 
 entertained at the present day differs from the older idea 
 of so-called " special creation " in the belief, which on 
 
BOTANY. [CHAP. i. 
 
 broad lines has passed beyond the theory stage and is 
 proved by facts, that from a primordial type of life of 
 an exceedingly low order of development, animals and 
 plants have become gradually evolved, and that the line 
 of departure characterized by the formation of chloro- 
 phyll which enabled its respective members to feed on 
 inorganic matter, constitute collectively the Vegetable 
 Kingdom, whereas the branch that varied from the 
 primordial type in developing an internal cavity or 
 stomach for the reception of solid organic food consti- 
 tuted the starting point of departure of the Animal 
 Kingdom. 
 
 As would be expected, the earliest groups of plants 
 and animals were but little removed structurally from 
 the parent stock, but as additional new features were 
 evolved, the differences became more marked, while in 
 the highest members the differences are so great that if 
 only the primordial type and the highest members of 
 plants and animals existed, the origin of the latter 
 from the former would probably never have been sus- 
 pected. 
 
 For a similar reason it can be readily understood that 
 the earliest departures from the primitive types possess- 
 ing respectively plant and animal characteristics would 
 yet possess many points. in common, in fact so many 
 that even at the present day the best authorities differ 
 as to the exact plant or animal nature of numerous 
 organisms hovering round the primordial group, and in 
 which more or less visionary characters of plant and 
 animal overlap. As plant and animal characteristics 
 become more sharply pronounced and stereotyped, the 
 two divisions recede from each other to the extent of 
 
CHAP, i.] PLANT ARCHITECTURE. 9 
 
 the differences exhibited between a forest tree on the 
 one hand and a human being on the other. 
 
 In addition to the animal and plant lines of departure 
 from the primitive stock, several other types of departure 
 are known to scientists, which for some reason or other 
 never made much progress, that is, did not by constant 
 modifications or emendations of the idea they started 
 out with, keep improving their position in the struggle 
 for life, and never gave origin to higher developments, 
 and consequently either disappeared or still remain as so- 
 called terminal groups. For example, on the plant side 
 we have at least three such departures, one including 
 the minute plants called diatoms, remarkable for having 
 the cell-wall rendered rigid by a deposit of silica or 
 flint, and in having the green chlorophyll the central 
 idea of plant-life masked by the presence of a brown 
 colouring matter. 
 
 In the simplest known plants belonging to the Algce 
 or Seaweed family, such structures as root, stem, leaf, 
 flower, etc., are entirely absent, the various kinds of 
 work performed in the higher plants by the organs 
 above enumerated, being in the simplest plants fre- 
 quently performed by a single microscopic cell, which 
 in numerous instances constitutes an individual. Such 
 one-celled plants are generally called in botanical lan- 
 guage, unicellular. As an illustration of the mode of 
 life of such simple organisms we may select the well- 
 known Pleurococcus viridis, a minute plant belonging to 
 the AlgaB, that forms green stains on the trunks of trees, 
 old palings, stones, etc., in fact on everything that has 
 been exposed for any length of time to the air. If a 
 very small portion of the green substance is placed in 
 
10 BOTANY. [CHAP. i. 
 
 water and examined under the microscope with a suffi- 
 ciently high magnifying power, numerous minute green 
 balls will be seen of various sizes and presenting different 
 appearances. If we select one of medium size that is 
 perfectly spherical and without any lines on its surface, 
 it will at first resemble a minute green ball, and appear 
 devoid of structure. If a small quantity of hydrate of 
 potash is now mixed with the water, in a very short time 
 a thin colourless ring will appear encircling the green 
 ball ; the colourless ring is the cell-wall or protective 
 portion of the plant that has been rendered visible by 
 the hydrate of potash, and forms a continuous outer 
 pellicle or skin inclosing and protecting the living por- 
 tion of the plant the protoplasm along with the green 
 colouring matter or chlorophyll. A plant presenting the 
 appearance described above is in the vegetative condi- 
 tion, that is, simply doing the work requisite for its own 
 individual well-being, taking into its substance carbonic 
 dioxide and water, which its chlorophyll, under the influ- 
 ence of light, converts chemically into its own substance ; 
 and at the same time breathing for the same purpose 
 that animals do, the removal of carbon from the body in 
 the form of carbonic dioxide. After passing some time 
 in the vegetative phase, the second or reproductive 
 phase, for the object of continuing the same kind of 
 plant, or species, in time is entered upon. Amongst 
 the specimens under the microscope it will not be diffi- 
 cult to select an individual yet perfectly spherical but 
 with a dark line across the surface ; such an individual 
 illustrates the first condition of the second or reproduc- 
 tive phase, the dark line corresponds to a thin wall that 
 has grown completely across the protoplasm, thus 
 
CHAP, i.] PLANT ARCHITECTURE. 11 
 
 dividing the cell into two equal parts; after the dividing 
 wall is formed it begins at the circumference to split 
 into two parts which will show under the microscope a3 
 a minute notch at each end of the dark line in the cir- 
 cumference of the cell; this splitting becomes deeper 
 and deeper, and finally the two halves completely sepa- 
 rate from each other and form two new individuals. 
 Each young Pleurococcus is at first hemispherical, but 
 within a very short time becomes spherical and enters 
 the vegetative phase until it reaches the full size, when 
 it divides in a similar manner to its parent, producing 
 in turn two young plants. Reproduction by the splitting 
 up of an entire individual into two young plants is a 
 purely vegetative method, that is, not the result of ferti- 
 lization, and is termed, reproduction by fission or cell- 
 division, and is the most usual method amongst the 
 lower forms of life, both plant and animal. When the 
 Pleurococcus is placed under favourable circumstances, 
 reproduction often takes place so rapidly that when the 
 plant has formed the first wall for division into two 
 individuals, each half commences to divide again by a 
 wall at right angles to the first ; such individuals show 
 two lines crossing each other at right angles, and with 
 constrictions at the margin corresponding to the amount 
 of separation of the four individuals that has taken place. 
 The Pleurococcus can only obtain food and live actively 
 when a certain amount of moisture is present, conse- 
 quently during very dry weather it becomes dormant 
 and forms a dry, crumbling powder that is blown about 
 as dust. In this dry, powdery condition, the plant pos- 
 sesses the power of retaining life for a long time, even 
 many years, and when placed in a damp situation, at 
 
12 BOTANY. [CHAP. i. 
 
 once expands and proceeds with its life work. As a 
 general rule, the simpler the structure of a living 
 organism, the greater its power of remaining alive under 
 extreme conditions, whereas organisms presenting a great 
 complexity of structure are limited to, comparatively 
 speaking, one set of conditions as regards temperature, 
 moisture, etc., and if removed from that sphere usually 
 perish. 
 
 i. ii. ui. iv. v. 
 
 Fig. i. Diagrammatic outline of Pleurococcus in various stages of 
 development. I. Vegetative stage. II. First indication of reproduc- 
 tive stage. III. Same, further advanced. IV. A plant dividing into 
 four individuals. V. The four portions completely separated and 
 rounded off. (Highly magnified.) 
 
 There are thousands of minute Algae that agree with 
 Pleurococcus in being unicellular and showing quite as 
 little division of labour or differentiation of structure, 
 the one cell having in turn to perform both vegetative 
 and reproductive functions. 
 
 From this primitive condition of things we pass to 
 slightly higher types of structure where the individual 
 consists of a number of cells joined together, forming 
 either very slender simple or branched threads composed 
 of a single row of cells placed end to end, as in many 
 species of fresh-water Algae common in our ponds and 
 streams, and forming the bright green floating masses 
 so general during the summer; or the cells are arranged 
 to form a thin continuous sheet often of considerable 
 dimensions, as illustrated by many of the common red 
 
CHAP, i.] PLANT ARCHITECTURE. 13 
 
 and green seaweeds. Plants that consist of more than 
 one cell are called multicellular. To the multicellular 
 type belong all flowering plants, ferns, mosses, also 
 many of the funguses and seaweeds. Unicellular plants 
 only occur in the seaweeds (Algce), and the funguses 
 (Fungi}. The multicellular type of structure is not entirely 
 new and independent of the more primitive unicellular 
 type of plant structure, but is in reality only a modifica- 
 tion of the latter type. It will be remembered that in 
 the unicellular organism, the single cell could only be 
 considered as an individual during the vegetative phase, 
 as on entering the second or reproductive condition its- 
 own individuality was lost by becoming divided into two 
 parts quite independent of each other and constituting 
 two distinct individuals. This sacrifice of the individual 
 at the termination of the vegetative phase is due to the 
 primitive mode of reproduction by fission. 
 
 Every living body, both plant and animal, consists in 
 the earliest condition of a single cell, and further, the 
 single cell constituting the starting point of the multi- 
 cellular plant divides by fission, forming two cells as in 
 the unicellular type; these two cells do not separate 
 from each other, but remain in organic contact, that is > 
 the separating wall does not split; each cell thus formed 
 again divides, exactly as in Pleurococcus, and thus by the 
 repeated fission of cells that remain in contact, a tissue 
 is formed that takes the form of slender filaments or 
 thin, broadly extending sheets, as already stated in the 
 simpler forms of multicellular plants, and by exactly the 
 same process of cell-division the entire substance of the 
 largest forest tree is built up. 
 
 An early indication of division of labour amongst the 
 
14 
 
 BOTANY. 
 
 [CHAP. i. 
 
 simplest of multicellular plants belonging to the Algae is 
 the restriction of the reproductive function to certain 
 cells or portions of the individual, the remaining por- 
 tion, usually constituting the greater part of the plant, 
 doing vegetative work only, and frequently living for 
 several years, giving origin each season to a number of 
 
 Fig. 2. A portion of one of the olive-brown seaweeds (Fucus vesicu- 
 losus) showing division of labour or differentiation of the individual. 
 F, thallus or vegetative portion ; T, fructification, confined to the tips 
 of the thallus ; L, air-bladders formed on the thallus for the purpose of 
 buoying up the plant on or near the surface of the water. (Natural 
 size.) 
 
 reproductive bodies capable of developing into new in- 
 dividuals. It will be noticed that the above indicated 
 division of labour into localized vegetative and reproduc- 
 tive portions is contemporaneous with the formation of 
 all the larger perennial forms of plant life, which in many 
 instances require half a century or even more to attain 
 
CHAP, i.] PLANT ARCHITECTURE. 15 
 
 their full development, a condition of things impossible 
 so long as the act of reproduction necessitated the loss 
 of the parent form as in the Pleurococcus type. 
 
 Closely following the division of multicellular plants 
 into vegetative and reproductive portions, we meet with a 
 corresponding differentiation in each part ; for example, 
 the vegetative portion of many seaweeds consists of parts 
 resembling in appearance the root, stem, and leaves of 
 the higher flowering plants, and although the specializa- 
 tion of these parts is nob so complete in the seaweed as 
 in the flowering plant, yet we have indicated in the lower 
 forms those types of structure that by degrees become the 
 most prominent characteristics of plant life. 
 
 In seaweeds the root-like portion, which is frequently 
 a discoid body, only performs the mechanical function of 
 fixing the plant to one particular spot, and is in no way 
 concerned with the absorption of food as in the higher 
 plants; the flattened out portion of the seaweed again, 
 although not the exact equivalent of the leaf of a flower- 
 ing plant, is nevertheless expanded into a thin sheet for 
 the same purpose, that of exposing a large area in con- 
 nection with the assimilation of food ; thus we have 
 shadowed in amongst the simplest of plants all the most 
 important structural features of the Vegetable Kingdom. 
 
 There is no evidence of any preconceived scheme in 
 connection with the gradual extension or evolution of the 
 plant world from primitive types. Keeping in view the 
 fact that protoplasm is the only vital portion of a plant, 
 it follows that the possibility of a given plant to live 
 under varying conditions of environment depends on the 
 limits under which its protoplasm can perform the various 
 functions collectively constituting life. As illustrating 
 
16 BOTANY. [CHAP. i. 
 
 the wide range under which protoplasm retains its indi- 
 viduality and performs its functions with regard to 
 temperature, certain minute Algae flourish in hot springs, 
 whereas other species find their home replete with every 
 comfort on the surface of snow or ice in high latitudes 
 or elevated regions, thus existing under a range of tem- 
 perature varying from freezing-point to within a few 
 degrees of the boiling-point of water. The above illus- 
 tration shows the possible range of protoplasm under 
 certain conditions, but the protoplasm of any given 
 species that has become differentiated and stereotyped 
 in one groove is always confined within much narrower 
 limits with regard to all surrounding forces, as tempera- 
 ture, pressure, amount of moisture, etc., and, as already 
 stated, the range becomes more restricted in proportion 
 to the amount of differentiation and division of labour 
 presented by an individual; consequently, while many 
 of the lower forms of Algas are met with living under 
 very varying external conditions, the higher types of 
 plant life are divided into groups that are confined, more 
 especially by temperature and amount of moisture, to 
 certain portions of the earth's surface. 
 
 The pioneers of plant life Algae were aquatic, and 
 the gradual extension of these forms to the dry land neces- 
 sitated an unforeseen amount of division of labour not 
 anticipated by the earliest members attempting this change 
 of habitat ; eventually, however, after many false starts, a 
 proper method was hit upon, that is, the living organism, 
 by a certain amount of modification of its already exist- 
 ing unit of structure, the cell, was enabled by degrees 
 to establish itself on dry land, and from these primitive 
 microscopic forms of algal life the whole of the Vegetable 
 
CHAP, i.] PLANT ARCHITECTURE. 17 
 
 Kingdom at present living on dry land has been directly 
 derived. The division of the latter into numerous groups 
 depending, and the endless variation in the properties of 
 protoplasm within certain limits as illustrated by the not 
 unfrequent occurrence of an unusual development popu- 
 larly known as a " sport/' meaning a departure from the 
 ordinary type in some minor feature, such as the colour 
 of the flower or the form of the leaf. At this stage it is 
 necessary to state that the great variety of form, colour, 
 and size presented by the various parts of plants are 
 those best suited to their requirements, and not mere 
 fanciful developments produced with no special object in 
 view, and in many instances, as the fertilization of flowers 
 by insects, not only is colour and form of importance, 
 but the various parts of the flower are so constructed 
 that certain movements take place at the proper moment 
 with machine-like accuracy. Now if the modification of 
 structure presented by a " sport " enables either the 
 vegetative or reproductive portions to do their work 
 better than by the old method, other things being equal, 
 it is not difficult to understand that the descendants of 
 the "sport," inheriting its peculiarity, will spread at a 
 greater rate than the old and superseded parent stock ; 
 thus we get the foundation for a new form or variety 
 depending on the amount of difference existing between 
 the parent form and its aberrant offspring. As the 
 above mentioned element of variation, due to unexplained 
 causes, but for that reason none the less conformable to 
 natural laws, is constantly at work, a second <( sport " 
 originating from the first will result in the production 
 of a plant still further removed from the original type in 
 structure, thus by repeated variations in vegetative 
 
 c 
 
18 BOTANY. [CHAP. i. 
 
 and reproductive portions a group of plants eventually 
 evolve, which if not traced through all the sequence of 
 changes to the parent form, would very probably never 
 be suspected of having evolved from the latter. It is 
 not to be inferred from the above that all existing 
 groups, as at present understood, have originated by 
 variation ; another factor of equal importance degenera- 
 tion or the arrest and cutting down of structures 
 already highly evolved, has in all probability produced 
 as many or even more groups, distinct as such at the 
 present day, than the one previously explained. The 
 results of degeneration are as a rule more obvious in the 
 reproductive than in the vegetative portions of plants, 
 and illustrated by the cutting down or arrest of the corolla 
 or showy portion of the flower that was of functional value 
 when the flower was fertilized by insect agency, but has 
 disappeared as the plant adopted the method of self- 
 fertilization, or became so modified that the pollen or 
 fertilizing substance is conveyed by wind. The grasses 
 afford an illustration of a group of plants that are wind- 
 fertilized at the present day. 
 
 Returning for a moment to the division of labour 
 necessitated by the change from an aquatic to an aerial 
 habitat, it was soon realized that desiccation or loss of 
 water, an indispensable substance in connection with 
 active life, should be guarded against ; various primitive 
 methods, each more or less successful in its way, were 
 tried by different groups, more especially the massing 
 together of a large number of individuals, whereby the 
 required amount of moisture was better retained than in 
 the case of the same number of isolated individuals ; but 
 notwithstanding the various efforts on the part of uni- 
 
CHAP. I.] 
 
 PLANT ARCHITECTURE. 
 
 19 
 
 Fig. 3. Maize, or Indian corn (Zea mays). One of the grasses 
 having a cluster of male or staminate flowers terminating the stem, 
 lower down is a cluster of female or pistillate flowers having every 
 part except the long tassel of stigmas protected by sheathing leaves 
 or bracts. The pollen is blown from the male to the female flower by 
 the wind. 
 
 cellular individuals, or those consisting of a few cells 
 only, no great progress was made, and such forms, as a 
 rule, still remain inhabitants of water ; yet if, as in the 
 
20 BOTANY. [CHAP. i. 
 
 case of Pleurococcus and its allies that have established 
 themselves on dry land, active life can only proceed 
 when the cells are supplied with the requisite amount of 
 water, under other conditions the plant passes into a 
 dormant or resting state. Certain members of the 
 Hepaticce, small moss-like plants, were amongst the first 
 to solve the problem as to the method of preventing 
 desiccation by introducing the idea of division of labour, 
 brought about as follows : In the species of Marchantia, 
 popularly known as liverworts, the vegetative portion is 
 prostrate and in contact with the damp ground by the 
 whole of its under surface, the outer layer of cells of the 
 upper surface undergoing a change by which they are ren- 
 dered waterproof, and thus form a protective layer that 
 prevents evaporation of water from the tissues of the 
 plant into the surrounding dry air. This superficial 
 layer of modified cells constitutes the epidermis, and 
 proved so effectual that the idea has never been super- 
 seded, and is still the means of preventing undue loss of 
 moisture employed by the most highly differentiated 
 flowering plants. The epidermis is furnished with minute 
 apertures called stomata which admit of an interchange 
 between the gaseous contents of the plant and those of the 
 atmosphere, details of which will be given at a later stage. 
 A second important modification of plant structure 
 necessitated by the previous development of an epidermis 
 was the formation of fibro-vascular bundles, or modified 
 portions of the original cells of aquatic plants into elon- 
 gated, thick- walled cells pointed at the tips, or elongated 
 cells of large diameter having the walls strengthened by 
 internal ribs arranged in various ways; these modified 
 cells are usually arranged in groups, and in the higher 
 
CHAP, i.] PLANT ARCHITECTURE. 21 
 
 plant constitute the portion called wood. To under- 
 stand the value of fibro-vascular bundles to the plant, it 
 must be remembered that Algae, growing in water, are 
 not furnished with an epidermis, consequently every por- 
 tion of the plant's surface is capable of absorbing water 
 containing in solution the gases required for food and 
 respiration, also certain other elements of plant food held 
 in solution, hence no special structures for the conduc- 
 tion of water from one portion of the plant to another 
 are required. In land plants, on the other hand, the 
 leaves and other green parts developing in the air are 
 completely surrounded by a waterproof epidermis, that 
 prevents the cells from taking water from the air, and 
 no water enters the plant through the stomata, conse- 
 quently the quantity of water required by the above- 
 ground portions of the plant is in the first instance 
 obtained from the soil by the underground portion or 
 root, and thence passed up into the leaves. The primi- 
 tive unmodified tissue, known as fundamental tissue, of 
 which seaweeds are composed, does not possess the power 
 of transmitting large quantities of water from one part 
 of the plant to another, hence the necessity of a portion 
 of this tissue becoming modified into fibro-vascular 
 bundles in land plants, as these structures, especially the 
 thick-walled portion called wylem, are good conductors 
 of water, and thus serve as channels of communication 
 between the source of water in the roots and the above- 
 ground parts. The larger cells of the bundles, called 
 vessels, usually contain air. 
 
 Finally a third modification induced by the change 
 from an aquatic to a terrestrial habitat, although some- 
 what later in its appearance than that of epidermis or 
 
22 BOTANY. [CHAP. i. 
 
 fibro-vascular bundles, was the evolution of the structure 
 popularly known as the flower. The only mode of plant 
 reproduction hitherto mentioned fission or cell-division 
 is termed the asexual or vegetative mode, but even in 
 the Algae a second and much more highly evolved method 
 is known called the sexual mode of reproduction, which 
 fundamentally consists in the amalgamation of the proto- 
 plasm of two distinct bodies, presumably male and 
 female, to form a single reproductive organ called an 
 oospore } but which would popularly be called a seed. Now 
 in all seaweeds the male or fertilizing element consists of 
 a very minute portion of protoplasm that becomes free 
 from the plant, and possesses the peculiarity of exhibiting 
 spontaneous movement, swimming about in the water 
 by means of very fine hair-like appendages or cilia. The 
 object of this animal-like movement of the fertilizing 
 body or antherozoid is to enable it to come in contact 
 with the female element with which its substance blends 
 the act of fertilization and a minute body results 
 that eventually becomes liberated from the parent plant, 
 and under favourable conditions germinates or sprouts 
 and produces in turn a plant resembling the one to which 
 it owed its origin. This mode of sexual reproduction by 
 means of motile antherozoids that reached the female by 
 swimming in water is still kept up by several groups 
 of plants that had firmly established themselves on dry 
 land, as the Liverworts (Hepaticce), Mosses (Musci), 
 Ferns (Filices], and Club-mosses (Lycopodiacece) , conse- 
 quently in all the above groups there is as a rule a 
 tendency to grow in damp districts, and the sexual mode 
 of reproduction takes place during the winter in tem- 
 perate regions, or during the rainy season in the tropics, 
 
CHAP, i.] PLANT ARCHITECTURE. 23 
 
 when the presence of water enables the motile anthero- 
 zoids or fertilizing bodies to find their way to the female 
 element. It is impossible to enter into details in con- 
 nection with this subject of fertilization, but it may 
 be stated that the portion of the plant producing the 
 sexual organs is usually very small, and could be covered 
 by a dewdrop, which would afford a superabundance of 
 water for the purpose of enabling the antherozoid to 
 swim about and come in contact with the passive female 
 element. All plants having the male element of the 
 sexual generation possessed of spontaneous movement 
 belong to the class of plants called Cryptogams, which 
 constitutes one of the two primary subdivisions of the 
 Vegetable Kingdom. As plants receded more and more 
 from their primitive aquatic habitat, and became differen- 
 tiated so as to carry on their entire existence on dry land, 
 the sexual mode of fertilization by motile antherozoids 
 that reached the female by swimming, became untenable, 
 and by degrees a radical change took place in the struc- 
 ture of the male or fertilizing body. Instead of the 
 naked, spontaneously moving antherozoid, the fertilizing 
 bodies took the form of minute cells inclosed in a cell- 
 wall and entirely devoid of spontaneous movement ; 
 these cells or pollen-grains were produced in considerable 
 numbers in the immediate neighbourhood of the female 
 organs, on to which they were shed when mature, thus 
 the agency of water as the medium by which the male 
 element reached the female was dispensed with. By the 
 above arrangement it will be observed that both male 
 and female elements were produced by the same plants, 
 consequently self-fertilization resulted. Owing to the 
 great advantages of cross-fertilization (when the male and 
 
24 BOTANY. [CHAP. i. 
 
 female elements are produced on different individuals of 
 the same kind) over self-fertilization, a further differen- 
 tiation took place, and the two sexes were either pro- 
 duced on distinct individuals of the same species, respec- 
 tively male and female, as in the willows and poplars, or 
 on different parts of the same plant as in the hazel, and 
 under such circumstances, the pollen being devoid of 
 spontaneous movement had to be transported to the 
 female by some outside agent, which in the above and 
 numerous other examples consisted of the wind, the 
 pollen being blown when mature from the male to the 
 female plant. Plants that utilize the wind as the agent 
 for bringing the pollen in contact with the ovules, or 
 female bodies requiring fertilization, are termed anemo- 
 philous. 
 
 Anemophilous plants are often characterized by having 
 the flowers developed before the leaves, as the latter 
 would interfere with the pollen being blown on to the 
 stigma or special structure of the female part for receiv- 
 ing the pollen. The anemophilous method, although as 
 a rule securing the desired cross-fertilization, was a very 
 extravagant way of effecting that object, enormous quan- 
 tities of pollen having to be produced for the purpose of 
 securing fertilization by what may be termed a chance 
 method, and has been to a great extent superseded by 
 utilizing insects as the agents for conveying the pollen 
 from one plant to the stigma of another and thus securing 
 cross- fertilization . 
 
 Having traced the origin of the highly differentiated 
 group of flowering plants from the lowly aquatic sea- 
 weed, it is necessary in the next instance to indicate 
 briefly the work done by the various specialized parts 
 
CHAP. I.] 
 
 PLANT ARCHITECTURE. 
 
 25 
 
 common to flowering plants in general. As already 
 explained, the work done by an individual that com- 
 pletes the full cycle of life may be conveniently divided 
 into two phases : first, vegetative ; second, re- 
 productive. In many of the lower types of 
 plant life, as already illustrated by the species of 
 Pleurococcus, these phases follow each other, the 
 first being completed before the second is en- 
 tered upon ; this condition also holds good in 
 numerous flowering plants in fact, in all 
 annual species, or those that last for one season 
 only, and also in biennial species, 
 or those that live for two years 
 before completing the life-cycle. 
 The annual species develop the 
 vegetative portion first, this is 
 followed by the reproductive 
 during the same season, the last 
 phase producing' seed that pro- 
 duces new individuals the fol- 
 lowing year. In biennials, the 
 first year is devoted entirely to 
 the vegetative phase, which 
 often concentrates a considerable 
 amount of reserve material or 
 
 surplus food in the root, as The upper flowers are pis- 
 illustrated by turnips and car- tillate or female, the lower 
 rots ; during the second season 
 this reserve material serves to 
 build up the reproductive structure, consisting of a 
 stem bearing flowers, that in due course produce seed, 
 thus completing the life-cycle of the individual. A 
 
 Fig. 4. A flower-bear- 
 ing branch of the common 
 hazel (Corylus avellana), 
 a wind-fertilized flower. 
 
 large catkins staminate or 
 male. 
 
26 BOTANY. [CHAP. i. 
 
 third type, comprising all trees and shrubs, and the 
 great majority of the larger forms of vegetable life, is 
 characterized by the vegetative portion of the individual 
 enduring for more than two years ; such are collectively 
 known as perennial plants, many of which endure for a 
 century or even longer. Under ordinary circumstances, 
 such perennials produce a new reproductive part every 
 season. The above sequence of the life- cycle is not 
 absolutely stereotyped, but can under certain conditions 
 be made to depart from the usual course of development. 
 As an illustration, the common sweet-scented Migno- 
 nette is an annual, but if the flower buds are pinched off 
 as they appear, the vegetative portion persists through 
 the winter and produces an abundance of flowers the 
 following year. 
 
 In the great majority of flowering plants the vegeta- 
 tive portion consists of the three following differentiated 
 parts, each doing a specific kind of work not capable of 
 being done by any other part. 
 
 (r) Root. A true root, as understood botanically, 
 serves to fix the plant in one particular place, a mecha- 
 nical and comparatively unimportant function, the more 
 important and in fact indispensable function being that of 
 supplying the plant with the required amount of water con- 
 taining in solution certain indispensable elements of plant 
 food ; in fact the entire substance of every plant, with the 
 exception of carbon, taken in from the atmosphere in the 
 form of carbonic dioxide by the leaves, is absorbed in a 
 soluble condition by the root. A marked difference be- 
 tween the members of the animal and vegetable kingdoms 
 respectively consists in the power of locomotion or free- 
 dom to move from place to place by the former, whereas 
 
CHAP, i.] PLANT ARCHITECTURE. 27 
 
 the latter are, as stated above, permanently fixed to one 
 place by the root. This marked difference depends on 
 the nature of the food. Plant food consists of carbonic 
 dioxide obtained from the atmosphere along with certain 
 soluble substances present in the ground that are taken 
 in by the roots in solution in water; now the composition 
 of the atmosphere is practically the same everywhere, 
 and the substances derived from the ground are very 
 widely diffused, hence it may be stated in broad terms 
 that wherever a plant grows, it is certain to be surrounded 
 by its food, consequently the power of locomotion is 
 unnecessary, the only fluctuating factor in determining 
 the presence or absence of plant life being water, and 
 in proportion to the relative scarcity of the latter we 
 observe a corresponding scarcity of plant life, which is 
 altogether absent from the dryest parts of the earth's 
 surface, not on account of the absence of plant food, but 
 the absence of water for dissolving the food which can- 
 not be absorbed by the plant in the solid form. All 
 plant food is absorbed in the gaseous or liquid condi- 
 tion, never as a solid. Animals, on the other hand, feed 
 on organic food that is never so universally diffused as 
 the inorganic food of plants, consequently the power of 
 moving from place to place for the purpose of obtaining 
 the requisite amount of food. 
 
 (2) Leaves. The green, flattened portions of a plant 
 known as leaves perform several functions, the most 
 important and universal being the following: Nutrition, 
 in the sense of taking in food ; carbonic dioxide, as pre- 
 viously stated, being absorbed from the atmosphere by 
 the green parts of plants. Transpiration, or the escape 
 of water into the atmosphere in the form of vapour 
 
28 
 
 BOTANY. 
 
 [CHAP. i. 
 
 through the stomata of the epidermis. Respiration. 
 Oxygen is inhaled from the atmosphere through the 
 stomata, and carbonic dioxide is returned through the 
 same channels to the atmosphere. 
 
 Assimilation. The water taken in by the roots passes 
 up the xylem portion of the vascular bundles of the 
 
 Fig. 5. Melon leaf. A typical leaf showing the stalk or petiole, and 
 blade or lamina traversed by numerous anastomosing fibro-vascular 
 bundles or veins. 
 
 stem, and from thence into the leaves by their veins ; 
 there it unites with the carbonic dioxide taken in from 
 the atmosphere, and the two are chemically changed 
 into starch by the action of the chlorophyll, or green 
 portion of the cell-contents under the influence of light. 
 The formation of starch as above is termed assimilation. 
 
CHAP, i.] PLANT ARCHITECTUEE. 29 
 
 The solid starch that has been formed in the leaf during 
 the day becomes dissolved during the night, and passes 
 
 Fig. 6. One of the Honeysuckles (Lonicera glauca), showing the 
 large irregular corolla furnished with scent and honey for attracting 
 insects. 
 
 along the veins of the leaf into the substance of the 
 plant, where it is either used at once as a building tissue, 
 
30 BOTANY. [CHAP. i. 
 
 forming the cell-walls, or is re-solidified and stored up 
 for future use. 
 
 The reproductive portion of the plant, i.e., the flower, 
 with all its various accompaniments, is developed for the 
 sole purpose of producing seeds that, under suitable con- 
 ditions, develop into a plant similar to the parent form. 
 The parts of a typical flower, commencing from the out- 
 side, are as follows : 
 
 (1) The calyx. Function, protective ; usually consists 
 of a ring or whorl of green leaf-like structures called 
 sepals. The use of the calyx being to protect the inner 
 parts of the flower during the bud stage, it usually either 
 falls away or bends back and becomes inconspicuous 
 after the expansion of the flower. 
 
 (2) Corolla. The second whorl of leaves, situated 
 within the calyx or higher up on the axis of the flower. 
 Function, usually attractive to insects in connection with 
 the act of pollination or fertilization. The component 
 parts of the corolla are called petals, and are usually 
 large, coloured, and frequently in addition secrete a 
 semi-liquid saccharine substance that serves as food for 
 insects. The corolla varies much in size, form, and 
 brilliancy of colouring, and is most highly developed in 
 entomophilous or insect fertilized species. 
 
 (3) Stamens. Within the corolla, and consequently 
 situated higher on the floral axis, are to be found a vary- 
 ing number of slender yellow stalks, each terminating 
 in a thickened portion or knob-like head ; these are the 
 stamens, collectively constituting the male element of the 
 flower ; the stalk of the stamen is called the filament, and 
 the knob-like apex, the most important part, is called the 
 anther, which contains the pollen, or fertilizing substance. 
 
CHAP, i.] PLANT ARCHITECTURE. 31 
 
 (4) The pistil, or female organ of the flower, is again 
 situated within the ring of stamens, and occupies the 
 apex of the floral axis. It consists of one or more 
 structures called carpels, that in the majority of flower- 
 ing plants form closed cavities, the ovaries, that contain 
 the ovules, or young unfertilized reproductive bodies. 
 After fertilization the ovules undergo great structural 
 changes the result of fertilization and are called seeds, 
 the ovary or protective portion then also undergoes 
 
 Fig. 7. Diagrammatic section of a typical flower showing the 
 various parts in their relative positions. I., calyx; II., corolla; 
 III., stamen, consisting of filament and anther ; IV., pistil, consisting 
 of a lower swollen portion, the ovary, and a terminal knob-like part, 
 the stigma, supported on a stalk, the style. 
 
 certain changes and becomes the fruit. There are two 
 primary divisions of flowering plants or Phanerogams 
 
 (1) Oymnosperms, including the pines, firs, cedars, 
 yews, etc., characterized by having the ovules naked, 
 that is, not contained within an ovary. In the members 
 of this group fertilization is direct, the pollen coming di- 
 rectly in contact with ovule. 
 
 (2) Angiosperms. The majority of flowering plants 
 are included in the present division, characterized by 
 
32 BOTANY. [CHAP. i. 
 
 having the ovules concealed in an ovary, hence fertiliza- 
 tion is indirect ; the ovary terminates in a structure of 
 variable form, called the stigma, the function of which 
 is to receive the pollen, which then germinates and finds 
 its way indirectly to the ovules for effecting fertilization. 
 
 The cells, or ultimate structures of plants, have been 
 incidentally alluded to, but being of primary importance 
 and indispensable to a clear comprehension of the work- 
 ings of plant life, a more detailed account of the most 
 prominent features of the cell and its modifications is 
 necessary. 
 
 The cells of plants are, as a rule, very minute and 
 invisible to the unaided eye, and when fully developed 
 present the following structures, proceeding from with- 
 out : 
 
 (1) An external continuous pellicle or protective 
 layer, known as the cell-wall, which although showing 
 no visible perforations is pervious to liquids and gases. 
 The cell- wall is composed of a substance called cellulose. 
 
 (2) Closely applied to the inner surface of the cell- 
 wall is a somewhat irregular layer of protoplasm the 
 living portion of the cell. 
 
 (3) The nucleus, a small, differentiated portion of the 
 protoplasm in which it is embedded. 
 
 (4) The sap-cavity or central cavity bounded by the 
 layer of protoplasm. 
 
 The cell- wall is at first very thin, and of equal thick- 
 ness throughout, but this condition rarely continues 
 throughout the entire existence of the cell ; in many 
 pollen grains, also the spores of many cryptogams, the 
 outside of the cell- wall becomes ornamented with warts, 
 spines, or ridges that often anastomose to form a net- 
 
CHAP. I.] 
 
 PLANT ARCHITECTURE. 
 
 33 
 
 work. The cells in the central part of the stem of 
 some of our common rushes (Juncus) have a stellate 
 form ; from a cell originally spherical several ray-like 
 prolongations are formed due to local growth of certain 
 portions of the cell- wall ; the tips of these rays are 
 joined to similar arms from adjoining cells, the whole 
 
 Fig. 8. A single cell of the celandine 
 (Chelidonium majiis) showing the cell- 
 wall lined inside by an irregular layer 
 of protoplasm from which strands, p, 
 pass into the large central sap -cavity ; 
 k, the nucleus, with a nucleolus. The 
 arrows indicate the direction of circu- 
 lation of the strands of protoplasm. 
 (Highly magnified.) 
 
 forming a light and porous tissue. The original very 
 thin wall is almost invariably thickened and strengthened 
 by the deposition of cellulose on its inner surface, but 
 this thickening matter is not uniformly deposited over 
 the entire surface, certain portions of the original thin 
 cell-wall remaining unthickened. The cells are said to 
 
34 BOTANY. [CHAP. i. 
 
 be pitted when the unthickened portions are small and 
 circular; scalariform when elongated and arranged in 
 parallel series. When the internal thickening takes the 
 form of a thread-like band arranged in a spiral manner 
 we have spiral cells, and annular when the band takes 
 the form of detached rings. 
 
 The object of all forms of secondary thickening of 
 the cell-wall is that of giving additional strength ; the 
 unthickened portions that are opposite to each other in 
 adjoining cells are left for the purpose of allowing liquids 
 and gases to pass from cell to cell, which could not take 
 place, or at all events very slowly, if the entire surface 
 of the wall was thickened. The hardness and durability 
 of wood is due to the much thickened walls of its com- 
 ponent cells, the substance of which changes its compo- 
 sition with age, and at the same time usually becomes 
 coloured. 
 
 Protoplasm is of a semi-liquid consistency, colourless, 
 and is either homogeneous and transparent or, more 
 frequently, turbid, owing to the presence of minute 
 drops of oil, starch, etc. In young cells the protoplasm 
 with the nucleus almost completely fills the cell, and the 
 water which saturates it collects into minute drops called 
 " vacuoles." These ' ( vacuoles" eventually run together 
 and form the central sap-cavity. The power of spon- 
 taneous movement exhibited by protoplasm is often very 
 marked, especially in the lower groups of plants, as sea- 
 weeds, fungi, mosses, etc., where the male or fertilizing 
 element, called the antherozoid, consists of a very minute 
 primordial or naked cell, i.e. } not furnished with a cell- 
 wall, and provided with one or more exceedingly slender 
 hair-like continuations of its protoplasm that serve as 
 
CHAP, i.] PLANT ARCHITECTURE. 35 
 
 organs of locomotion and enable the antherozoid to swim 
 in water. Even when inclosed within a rigid cell-wall, 
 the protoplasm not unfrequently exhibits well-marked 
 movements, the whole of the peripheral layer of proto- 
 plasm moving round the cell (rotation), or currents that 
 carry along minute granules and move in its substance. 
 
 Cell- contents. In addition to the protoplasm, which 
 itself constitutes the cell, a considerable number of sub- 
 stances are met with in cells, the presence of these sub- 
 stances being determined by the position occupied by a 
 given cell in the general structure of the plant. The 
 following are the most important of cell-contents : 
 
 (1) Chlorophyll, or the green colouring matter pre- 
 sent in the superficial cells of plants. Light, being an 
 indispensable factor in the formation of chlorophyll, it 
 is consequently absent from the internal parts of plants, 
 and also from underground portions, but in the latter 
 case it can be shown that the absence of light is the 
 cause of the absence of chlorophyll, as when the under- 
 ground portion is exposed to light it often becomes 
 green, as seen in potatoes that have been exposed to 
 light during growth. In the majority of plants the 
 chlorophyll consists of minute particles called chlorophyll- 
 grains that are imbedded in the protoplasm, but in some 
 of the simpler Algae the chlorophyll is diffused as a 
 liquid throughout the protoplasm. The almost universal 
 green colour of the vegetable kingdom is due to the 
 presence of chlorophyll in the superficial cells. Its 
 important functions will be dealt with at a later stage. 
 
 (2) Starch first makes its appearance as a solid organic 
 product within the chlorophyll grains, and continues to 
 accumulate so long as the chlorophyll is exposed to 
 
BOTANY. [CHAP. i. 
 
 light. During the night the starch that has been formed 
 during the day, in the cells of the leaves more especially, 
 is dissolved, and passes along the veins of the leaf into 
 the branches, and becomes diffused over every portion of 
 the plant, a certain portion being used up at once in the 
 formation of new cell- walls, the remainder being stored 
 away for future use in certain internal tissues, or very 
 frequently in underground parts, as bulbs, tubers, etc., 
 that become much swollen owing to the formation of 
 thin- walled tissue containing starch. Such swollen 
 underground parts usually serve as vegetative repro- 
 ductive bodies. 
 
 Fig. 9. Cells of beet (Beta 
 maritima), containing agglome- 
 rations of crystals. (Highly mag- 
 nified. ) 
 
 (3) Crystals are of very common occurrence in the 
 cells of plants, and almost invariably consist of oxalate 
 of lime. When the crystals are very long and slender 
 they are often called r aphides, and occur in enormous 
 quantities in the cells of some plants. If the flower- 
 stalk of the common hyacinth is crushed, and a minute 
 quantity of the juice examined under the microscope, 
 numerous very slender, needle-shaped crystals will be 
 seen floating in the liquid. Crystals are present in 
 enormous quantities in the stems of old cactus plants, 
 rendering them quite brittle. 
 
 The material forming crystals is not absorbed by the 
 plant as oxalate of lime from the soil, but is formed by 
 
CHAP. I.] 
 
 PLANT ARCHITECTURE. 
 
 37 
 
 the plant itself; oxalic acid is one of the most general of 
 organic acids produced by plants, and the lime finds its 
 way into the plant as a carbonate or phosphate of lime ; 
 these eventually combine to form oxalate of lime, which 
 
 Fig. 10. A characteristic cactus plant (Echinocactus Decaisneanus) , 
 having the cells of the trunk rilled with crystals when old. (Reduced. ) 
 
 may be considered as a by-product, the result of certain 
 chemical changes taking place in the contents of the 
 cell- sap. As a rule, crystals are deposited in those parts 
 of plants that fall away annually, more especially the 
 
38 BOTANY. [CHAP. i. 
 
 leaves, which in the spring contain a very small trace of 
 ash or mineral matter, whereas at maturity most of the 
 cells contain quantities of crystals. 
 
 (4) Cell-sap. This substance saturates the cell-wall 
 and protoplasm, and also fills the central sap-cavity in 
 the fully-developed cell. It is a watery solution of 
 various substances, amongst which certain salts derived 
 in solution from the soil are never absent ; in certain 
 cells of some plants, as sugar-cane, beet, maple, etc, 
 large quantities of cane-sugar are present ; in certain 
 cells of the grape, and many other fruits, grape-sugar 
 occurs -, in addition, tannin and many vegetable acids 
 are present, as also many of the blue and red colouring- 
 matters of flowers and fruits. 
 
 The epidermis or protective covering formed on the 
 surface of those parts of plants growing surrounded 
 by air, usually consists of a single layer of cells that 
 become differentiated in the following manner. The 
 cells touch each other at every part, intercellular spaces 
 being entirely absent; the outermost, or free surfaces 
 of the epidermal cells become much thickened and con- 
 verted into a substance impervious to water ; the proto- 
 plasm and chlorophyll usually disappear at an early stage, 
 their place being taken by air or water, the epidermis 
 serving as a reservoir for the latter in many plants. At 
 a very early stage of the development of the epidermis 
 the stomata, or openings through its substance, are 
 formed. Their mode of formation varies, to a certain 
 extent depending on the particular species examined. 
 If the tip of a very young leaf that is just showing at 
 the crown of a growing hyacinth bulb is removed, and 
 a minute portion of its epidermis removed with a pair of 
 
CHAP, i.] PLANT ARCHITECTURE. 39 
 
 forceps and examined in water under the microscope, 
 the origin and development of the stomata may be easily 
 followed. 
 
 The cells of the epidermis as seen from the surface 
 are brick- shaped, their long diameter being arranged in 
 the direction of the length of the leaf. The stomata 
 originate as follows. A certain epidermal cell is divided 
 
 Fig. ii. A fragment of epidermis from the under surface of a leaf 
 of Euonymus japonica, showing four stomata; sp, guard-cells of the 
 stoma. (Highly magnified.) 
 
 into two parts by a wall that is always formed at right 
 angles to the length of the leaf. One of the small, or 
 daughter-cells thus formed, undergoes no further de- 
 velopment, but loses its protoplasm, becomes cuticularized, 
 and forms an ordinary epidermal cell ; the other daughter- 
 cell, that is, the other half of the epidermal cell, now 
 called the mother-cell of the stoma, retains its protoplasm 
 
40 
 
 BOTANY. 
 
 [CHAP. i. 
 
 and chlorophyll, and becomes divided by a wall formed 
 at right angles to the one previously formed, or parallel 
 to the long axis of the leaf; the two small cells thus 
 formed from the stoma mother-cell are called the guard- 
 cells of the stoma. The common- wall separating the two 
 guard-cells splits, and the guard-cells becoming concave 
 on the side facing each other thus form a small opening 
 
 >Fig. 12. Transverse section through the epidermis of the leaf of 
 Cycas revoluta, one of the Cycads ; n, the elevated epidermis ; e, 
 epidermal cells ; sp, stoma ; c, air cavity below the stoma ; p, paren- 
 chymatous cells of the leaf. (Highly magnified.) 
 
 through the split wall of the epidermis into the substance 
 of the leaf. 
 
 Stomata are most numerous and perfectly developed 
 on leaves, and are either scattered, the most general 
 method, arranged in groups, or, as in the fir-trees, in 
 lines. Their number varies from 200 to 160,000 or even 
 more in a square inch of surface. In the white garden 
 lily there are about 60,000 in a square inch on the under 
 
CHAP, i.] PLANT ARCHITECTURE. 41 
 
 surface of the leaf, and about 3,000 on the upper ; in 
 the cherry laurel, about 90,000 in a square inch of the 
 under surface of the leaf, and none on the upper surface. 
 When leaves grow erect, stomata are usually about 
 equally abundant on the upper and under surface ; but 
 when growing horizontally, with one surface to the 
 earth the lower and the other to the sky the upper 
 stomata are usually much more numerous on the under 
 surface. Owing to the disappearance of the greater 
 portion of the protoplasm from epidermal cells at an 
 early period, no secondary growth or cell- division can 
 take place ; hence, as already stated, typical epidermis is 
 met with as the permanent covering of leaves, for the 
 full development of a leaf takes place rapidly and is 
 contemporaneous with that of the epidermis which is 
 formed from its superficial layer of cells, and however 
 long a leaf may continue to live, there is no secondary 
 growth or increase in size. Young twigs and shoots are 
 protected with epidermis during the first year, but at 
 the commencement of the second year's growth, when 
 the twig begins to increase in thickness, the epidermis, 
 unable to grow and keep pace with the expansion of the 
 twig, is ruptured and thrown off, its protective function 
 being superseded by the formation of a waterproof 
 structure called periderm, which is formed from the 
 superficial cells of the twig, but differs from epidermis in 
 not being composed of one layer of cells only, the absence 
 of stomata, and more especially by a provision for the 
 increase in the number of cells by means of which the 
 periderm keeps pace with the increase in thickness of 
 the twig. 
 
 When cells by repeated bipartition produce other 
 
42 BOTANY. [CHAP. i. 
 
 similar cells that remain organically connected, the result 
 is a tissue ; and when these cells are morphologically 
 (structurally) and physiologically (functionally) of com- 
 paratively equal value, being furnished with comparatively 
 thin walls, and not much longer than broad, the tissue is 
 called cellular or fundamental tissue. Some groups of 
 plants, as Algae and Fungi, are composed entirely of 
 fundamental tissue, and have consequently been called 
 cellular plants, whereas all other groups of plants, on 
 account of the presence of other tissues in addition to 
 fundamental tissue, have been called vascular plants. 
 Fundamental tissue constitutes the starting point of 
 every plant, however highly differentiated it may become, 
 and is also indispensable at every stage of its existence, 
 inasmuch as it is the only tissue possessing the power of 
 growth or of adding to the bulk of the individual by 
 cell-division, consequently where growth is taking place 
 is a certain sign of the presence of fundamental tissue, 
 as the tips of stems, roots, etc., such portions are called 
 growing-points. 
 
 The trunks of all forest trees in the earliest condition 
 consist of fundamental tissue, the outer layer having 
 become differentiated into an epidermis. The fibro- 
 vascular bundles present in the stem originate in the 
 young leaves that appear at first as very minute papillae 
 or outgrowths arranged round the growing-point or 
 apex of the stem which they protect by being arched 
 over it during the bud stage. In the bud state the 
 youngest leaves are so near the apex of the stein that 
 they might probably be considered, on a superficial 
 examination, to originate from the actual apex of the 
 stem. Such, however, is not the case ; there is no such 
 
CHAP. I.] 
 
 PLANT ARCHITECTURE. 
 
 43 
 
 thing known as a terminal leaf, and a thin vertical slice 
 of a young bud examined under the microscope will show 
 the youngest leaves to be truly lateral in origin, the 
 centre or actual apex of the stem being composed of 
 undifferentiated fundamental tissue. 
 
 From these young leaves the rudimentary fibro-vascular 
 
 Fig. 13. Diagrammatic re- 
 presentation of a section of a 
 palm stem, showing the ar- 
 rangement and direction 
 taken by the fibro-vascular 
 bundles that originate in the 
 leaves and pass down the 
 stem. 
 
 bundles pass downwards into the stem, where they usually 
 join on to older bundles and become arranged in various 
 ways depending on the group to which the specimen 
 under examination belongs. Fibro-vascular bundles that 
 originate as above from leaves are usually called foliar 
 vascular bundles, or leaf-traces. From the above state- 
 ment it will be seen that the increase in size of the trunk 
 and branches, in other words, the formation of the fibro- 
 vascular element, which constitutes that portion of the 
 trunk popularly known as " wood," is entirely dependent 
 on the presence of leaves ; consequently, if during any 
 given season the leaves of a tree are destroyed by insects 
 or prevented by any means from attaining their full 
 
44 BOTANY. [CHAP. i. 
 
 development, and doing the usual amount of work, so 
 in proportion will the formation of wood be arrested. 
 
 In rare instances a few fibro- vascular bundles originate 
 in stems quite independent of the leaves ; these are 
 differentiated from the fundamental tissue of the growing- 
 point at a higher level than the origin of the youngest 
 leaves, and are known as cauline bundles. 
 
 In Phanerogams, or flowering plants, a typical fibro- 
 vascular bundle consists of two kinds of permanent tissue, 
 that is, tissue which, once formed, undergoes no further 
 differentiation ; the two kinds, as previously stated, are 
 respectively called phloem or bast, and xylem or wood, 
 and these are arranged collaterally or side by side, the 
 phloem being outermost or nearest the periphery, the 
 xylem innermost or nearest the centre of the trunk. In 
 many of the Vascular Cryptogams, the arrangement of the 
 two parts of a bundle is concentric, the phloem completely 
 surrounding the xylem. 
 
 Depending on the further mode of development, and 
 on the manner of arrangement of the fibro-vascular 
 bundles in the stein, along with other characters derived 
 from the seed, flower, and leaf, Phanerogams are arranged 
 under two subdivisions, Monocotyledons and Dicotyledons. 
 
 (i) Monocotyledons. The fibro-vascular bundles con- 
 sist of the elements phloem and xylem only, and no 
 secondary growth, that is, no additions to the elements 
 existing in the bundle as originally formed, takes place ; 
 such bundles are said to be closed, meaning, as stated 
 above, that no additions in the way of new cells are 
 added at a later stage, hence the bundles remain small, 
 and for the greater part of their length isolated, coalescing 
 by their tapering tips only with other bundles lower 
 
CHAP, i.] PLANT ARCHITECTURE. 45 
 
 down the stem. Grasses, sedges, lilies, and palms are 
 typical Monocotyledons, and in the palms the mono- 
 cotyledonous stem structure reaches its maximum of de- 
 velopment, the bundles on entering the stem from the 
 leaves at first curve towards the centre, then grow down- 
 wards for some distance, eventually curving back towards 
 the periphery and anastomosing by their tapering ends 
 with lower and older bundles, as shown in fig. 13. In 
 palms the stem is cylindrical and terminated by a bud, 
 the only one possessed by the tree ; at a very early age 
 the stem acquires its full diameter, and henceforth the 
 terminal bud gives origin annually to about the same 
 number of leaves, which consequently supply an equal 
 number of fibro-vascular bundles that only proceed for 
 a short distance down the stem, the lower portion, as 
 it is left behind by the apical bud, being unable to 
 increase in diameter on account of its bundles being 
 closed. 
 
 (2) Dicotyledons. In the dicotyledonous stem a ring 
 of detached vascular bundles, each consisting of an ex- 
 ternal phloem and an internal xylem portion, appears 
 in the fundamental tissue about midway between the 
 centre and the circumference of the stem ; that portion 
 of fundamental tissue lying outside the ring of vascular 
 bundles, and bounded externally by the epidermis, is 
 called the primary cortex, the central portion surrounded 
 by the vascular ring is the medulla or pith, while those 
 portions of fundamental tissue that pass between the ring 
 of isolated vascular bundles and connect the pith with the 
 primary cortex are called medullary rays. The xylem 
 and phloem elements of the fibro-vascular bundles do 
 not lie in contact with each other as in Monocotyledons, 
 
Fig. 14. A palm (Seaforthia elegans), showing the erect, semi- 
 cylindrical stem crowned by a rosette of large leaves that were formed 
 by the single apical bud. 
 
CHAP. I.] 
 
 PLANT ARCHITECTURE. 
 
 47 
 
 but are separated by a thin zone of fundamental tissue 
 that has received the name of cambium, and which by 
 rapid cell-formation adds periodically to the xylem and 
 phloem elements of the bundle, which thus increases in 
 size from year to year. Bundles furnished with cambium, 
 and thus capable of adding to their substance periodically, 
 are said to be open. 
 
 In perennial plants increase in thickness of the stem 
 commences with the activity of the cambium situated 
 
 M 
 
 Fig. 15. Horizontal section through 
 stem of a Dicotyledon, the melon, in- 
 cluding one fibre-vascular bundle, 
 \vhich is completely surrounded by fun- 
 damental tissue composing the follow- 
 ing parts : M, pith ; RM, medullary 
 rays ; PC, primary cortex ; the wedge- 
 shaped bundle consists of L, the phloem, 
 followed internally by the xylem, the 
 two being separated by a thin band of 
 cambium. The large circles in the 
 xylem correspond to the sections of 
 vessels. E, the epidermis. (Magnified. ) 
 
 between the phloem and xylem of each vascular bundle, 
 by repeated bipartition of the cells of the cambium a 
 mass of tissue is formed that becomes differentiated into 
 the elements of phloem and xylem respectively. Owing 
 to the position of the cambium, it will be observed that 
 the new elements of the xylem or wood will be added to 
 the outside of the already existing portion, whereas the 
 additions to the phloem will be on its inner surface, but 
 very much more material is periodically added to the 
 xylem than to the phloem, so that while the former may 
 
48 BOTANY. [CHAP. i. 
 
 have increased to a yard in diameter, the latter may not 
 be half an inch thick. 
 
 All European forest trees are Dicotyledons, and the 
 ringed appearance seen in a trunk that has been sawn 
 across is due to the periodical additions made by the 
 cambium to the xylem or wood. In temperate regions, 
 where there is only one season of growth during the 
 year, a single ring is formed annually, hence the term 
 annual rings, as applied to these markings, which may 
 be used in determining the age of the tree with approxi- 
 mate accuracy ; such rings give at least the minimum 
 age of the plant. In the tropics, where there is more 
 than one growing season during the year, two or more 
 rings are formed by some species in one year. 
 
 The popular expression " rising of the sap }> corre- 
 sponds to the renewed growth of the cambium in the 
 spring ; the tender mass of thin-walled tissue thus 
 formed readily admits of the removal of the outer 
 portion, or " bark." 
 
 The distinct appearance of the annual rings of wood 
 originates as follows : The first additions to the wood 
 made by the cambium during the spring, consists for 
 the most part of vessels of large diameter and with com- 
 paratively thin, pitted walls ; the formation of these 
 vessels is favoured in the spring by the slight amount of 
 pressure exerted by the bark, that has been kept moist 
 during the winter season, but as the summer advances 
 the bark becomes dry and rigid, and the pressure on 
 the newly-formed wood becomes greater, consequently 
 the formation of vessels in the xylem is superseded by 
 that of wood cells with very small cavities and thick 
 walls, the result being that the porous spring wood, 
 
CHAP. I.] 
 
 PLANT ARCHITECTURE. 
 
 49 
 
 composed of vessels with very large cavities, gradually 
 changes towards the autumn into very dense wood, with 
 thick cell- walls and very minute cavities. Each season 
 the porous spring wood following abruptly on the dense 
 wood of the preceding autumn causes the rings known 
 as annual rings. The following are the most important 
 types of cell structure forming xylem and phloem respec- 
 tively : 
 
 Xylem. There are two distinct types of cell structure; 
 
 P. L. P. I. P .L.MC. C . F . V . F , V.F.V ,T.M, 
 
 Fig. 16. Horizontal section of a Dicotyledon, the maple, showing 
 three years' growth ; S, cortex ; M, pith ; C, cambium ; the figures 
 i, 2, 3, indicate the three annual rings of wood, including the cam- 
 bium ; the dark portion between the cambium and the cortex is the 
 bast or phloem. (Magnified. ) 
 
 wood cells or tracheides, consisting of long, thick-walled 
 cells with tapering, pointed ends that overlap, the walls 
 become hard and rigid, and form the great bulk of 
 durable wood. Water passes from the roots to the 
 leaves through the substance of the cell- walls of the 
 youngest and last-formed wood-cells. Tracheides are 
 formed in most instances directly from single cambium 
 cells ; vessels are recognized by their large diameter 
 
Fig. 17. Part of a transverse section through the stem of a Spider- 
 wort (Tradescantia Sellei), illustrating the arrangement of the fibro- 
 vascular bundles in a monocotyledonous stem ; e, epidermis, with a 
 stoma, sp ; R, cortex ; v, thickening ring, with the outer vascular 
 bundles, g l ; g l \ inner vascular bundles. (Magnified.) 
 
CHAP, i.] PLANT ARCHITECTURE. 51 
 
 and by the ends being only slightly oblique and not 
 tapering ; they originate from superposed rows of cells, 
 some of the transverse septa being absorbed ; hence the 
 structure called a vessel consists of two or three cells 
 thrown into one by the disappearance of their transverse 
 walls. Vessels formed in the primary wood, or wood of 
 the first year, frequently have their walls thickened 
 internally by the deposition of strengthening material 
 arranged in the form of a loose spiral, and are known 
 as spiral vessels, while vessels that are formed in the 
 secondary wood that is, all wood or xylem formed after 
 the first year, usually, have pitted walls. Ducts are only 
 vessels of extra large diameter, and furnished with 
 pitted walls. Vessels usually contain air, but when the 
 ascent of sap is very rapid, as in the spring, they some- 
 times contain water. 
 
 Phloem or bast, like the xylem, consists of two distinct 
 elements; sieve-tubes, with thin side walls, but having 
 the transverse septa much thickened and perforated with 
 numerous minute holes ; these thickened and perforated 
 septa are called sieve-plates. Sieve- tubes, or soft bast> 
 correspond to the vessels present in the xylem, and 
 contain albuminous substances; bast-fibres, constituting 
 the hard bast, consist of very much elongated, thick- 
 walled cells with tapering extremities, and correspond 
 to the tracheides of the xylem, but differ from the latter 
 in their walls, although usually very much thickened, not 
 becoming rigid, but remaining pliant. The hard bast is 
 the part used in most textile fabrics, as " linen/' "jute/' 
 " hemp/ 3 " Russia matting," etc., " cotton " is an 
 exception to the above, and consists of long, thin- walled 
 cells of cellular tissue that spring from the testa or 
 
Fig 1 8. Transverse section through a young stem of Bcehmeria 
 argentea, a Dicotyledon ; 0, epidermis ; Co, outer cortex (collenchyma) ; 
 B, inner cortex ; S, intercellular space ; 6', cambium ; B, bast ; H, 
 xylem portion of vascular bundle ; Z, medullary ray ; M, pith. 
 (Magnified 120 times.) 
 
CHAP, i.] PLANT ARCHITECTURE. 53 
 
 skin of the cotton seed, and collectively serve as a 
 dispersive organ for floating away the seeds in a similar 
 manner to the pappus or " clock " of dandelion and 
 thistle fruits. 
 
CHAPTER II. 
 
 CHEMISTRY AND PHYSICS OF PLANT LIFE. 
 
 Nature of Plant Food and how it is obtained. Influence of Light 
 on Plant Life. Influence of the Vegetable Kingdom on surroundings. 
 Origin of Carnivorous Plants. Saprophytes. Parasites. Retro- 
 gression. 
 
 /CHARACTERISTIC plants furnished with the green 
 ^.s colouring matter called chlorophyll, as previously 
 stated, feed on inorganic food obtained partly from the 
 atmosphere, partly from the soil or substance in which 
 the roots are fixed. The only food material obtained from 
 the atmosphere is carbonic- dioxide (C0 2 ) ; the remainder 
 is taken in by the roots dissolved in water, and although 
 different food substances are required by different plants, 
 yet the following may be considered as being indispen- 
 sable to the majority of plants : 
 
 Carbon (C), Hydrogen (H), Oxygen (0), Nitrogen 
 (N), Sulphur (S) ; these form the organic compounds 
 of the plant, that is to say, combinations of carbon with 
 other elements which, on exposure of the plant to great 
 heat, are for the most part resolved into volatile pro- 
 ducts, as water (H 2 0), carbonic dioxide (C0 2 ), ammonia 
 (NH 3 ), etc. 
 
 Phosphorus (p), Potassium (K), Iron (Fe), Calcium, 
 (Ca) , Magnesium (Mg) ; these go to form the inorganic 
 
CHAP, ii.] CHEMISTRY, ETC., OF PLANT LIFE. 55 
 
 non-volatile compounds of the plant that remain as a 
 white ash after the plant has been burnt. 
 
 In addition to the above, various other elements occur 
 in certain plants, but their connection with nutrition has 
 not yet been proved ; amongst these are, Manganese 
 (Mn), Sodium (Na), Lithium (Li), Iodine (I), Bromine 
 (Br) , Silicon ( Si) , and in rarer cases some of the metals, 
 as Aluminium (Al), Copper (Cu), Cobalt (Co), Barium 
 (Ba), Zinc (Zn), Nickel (Ni), Strontium (Sr). 
 
 Chlorine (Cl) has so far been proved by experiment 
 to be an indispensable food element in the case of one 
 plant only, the Buckwheat. 
 
 Direct experimental cultures with plants have proved 
 that they can be grown and perfectly nourished if sup- 
 plied with the requisite elements in compounds suitable 
 for absorption ; the same experiments have also proved 
 that certain substances often met with in their ash are 
 not necessary for their growth, inasmuch as equally 
 healthy plants can be produced when such elements are 
 intentionally kept away from their food supply. Such 
 substances, which usually occur in very small quantities 
 in plants, may be considered as having been absorbed 
 by the plant along with the necessary food. 
 
 The above food constituents are not taken into the 
 plant as elements, but as compounds ; carbon, for 
 example, is obtained from carbonic dioxide ; nitrogen, 
 although so abundant an element in the atmosphere, is 
 never assimilated in the free form, but as nitrates or 
 compounds of ammonia that are soluble in water ; hydro- 
 gen is obtained from the decomposition of water ; the 
 remaining substances are taken by the plant in the form 
 of compounds soluble in water ; thus sulphur is obtained 
 
56 BOTANY. [CHAP. n. 
 
 from the sulphates of the soil, such as calcic sulphate 
 (Ca SOJ ; phosphorus from phosphates, etc. 
 
 The elements mentioned as forming the organic 
 matters of the plant, as protoplasm, starch, cellulose, 
 etc., actually build up the substance of the plant, 
 whereas those forming the inorganic parts, or ash, do 
 not necessarily enter into the composition of the tissues, 
 nevertheless in many instances their presence has been 
 proved to be indispensable in connection with certain 
 chemical changes resulting in the formation of certain 
 substances upon which the life of the plant depends. 
 Thus, iron obtained in the form of a chloride or sulphide 
 is necessary for the chemical production of the green 
 colour of chlorophyll, if iron is intentionally withheld 
 from plant food used in experimental culture, the parts 
 that would be normally green become yellowish only, 
 even if exposed to light, whereas if very minute traces 
 of iron are added to the food of such a plant, the chloro- 
 phyll is very soon formed. Iron does not enter into 
 the composition of chlorophyll, but its presence in very 
 small proportions is necessary to set up the chemical 
 changes that result in the formation of this substance. 
 The very general occurrence of chlorophyll-bearing 
 plants on all parts of the earth shows the wide range of 
 iron in a soluble form present in the soil. The formation 
 of starch depends on the presence of potassium. It 
 must be understood that potassium is not the only 
 factor necessary for the formation of starch ; but if this 
 substance is absent, even if all other conditions are 
 favourable, as in the case of iron and chlorophyll so also 
 with starch which contains no potassium, the latter 
 being necessary for promoting the chemical changes 
 
CHAP, ii.] CHEMISTRY, ETC., OF PLANT LIFE. 57 
 
 resulting in the formation of starch. Phosphorus in 
 like manner bears a similar relation to the albuminoids, 
 as these are only formed when phosphates are present in 
 the cells. 
 
 The plant obtains its food from surroundings in a 
 purely physical manner. In the case of submerged 
 aquatics, both carbonic dioxide and all salts are intro- 
 duced in solution in water which is absorbed by the 
 plant. In the case of terrestrial plants, the carbonic 
 dioxide of the atmosphere is taken in by those parts 
 containing chlorophyll, more especially the leaves, accord- 
 ing to the well-known law of gaseous diffusion, which 
 may be briefly expressed as follows : When two or 
 more gases that do not act chemically on each other 
 are liberated in contact with each other, they gradually 
 diffuse or mix until every portion consists of an equal 
 admixture of all the gases, and when they have thus 
 diffused themselves uniformly through one another, they 
 never separate again in the order of their specific 
 gravities. 
 
 The green parts of plants decompose carbonic dioxide 
 during the day, that is, so long as the chlorophyll is 
 exposed to light; hence the gas that passes from the 
 atmosphere through the stomata into the interior at 
 once loses its individuality. Consequently, obeying 
 the law of diffusion, the gas is constantly passing into 
 the leaf in the attempt to restore equilibrium, and by 
 this purely physical process the plant obtains its carbonic 
 dioxide. During the night, when the chlorophyll can no 
 longer perform its functions, the inflow of carbonic 
 dioxide ceases when the equilibrium between the outer 
 air and the gaseous contents of the leaf is effected. In 
 
58 BOTANY. [CHAP. n. 
 
 many of the lower plants, where stomata are absent, 
 diffusion takes place through the cell- wall ; this takes 
 place to some extent in the higher plants also. 
 
 The roots of plants growing in damp soil, and not 
 exposed to desiccation, are not furnished with an epi- 
 dermis, and in many plants certain of the external cells 
 of the youngest rootlets grow out into very delicate, 
 one-celled hairs known as roof-hairs; these are for the 
 purpose of absorbing water from the surrounding soil 
 that contain food substances in solution. In some plants 
 root-hairs are not developed, when the superficial cells 
 of the root perform their function. 
 
 The mode by which water is taken up by the root- 
 hairs or cells of the root from the soil is due to the working 
 of a physical law called osmosis, which may be stated as 
 follows. When two liquids of different densities are 
 separated by a pervious membrane, the denser liquid 
 will attract a large proportion of the rarer liquid to itself 
 through the membrane the act of endosmose a very 
 small proportion of the denser liquid will at the same 
 time pass through the membrane and mingle with the 
 rarer liquid the act of exosmose. The above law can 
 be demonstrated by a simple experiment. If the bladder 
 of a sheep that has been well washed in a weak solution 
 of potassic hydrate, to remove the fat, be half filled with 
 a fairly strong solution of salt and water, and then com- 
 pletely submerged in a bucket of pure water, it will be 
 found after a while to be quite full of liquid, the dense 
 salt and water having drawn through the membrane a 
 large quantity of the rarer water. The cell-walls of 
 root-hairs are permeable to liquids, and the contained 
 cell-sap is normally much denser than the water in the 
 
CHAP, ii.] CHEMISTRY, ETC., OF PLANT LIFE. 59 
 
 soil, that rarely contains more than three per cent, of 
 substances in solution, consequently the latter passes 
 into the substance of the plant by end osmose. 
 
 It is a well-known fact that the ash of different kinds 
 of plants growing close together in the same soil or water, 
 may and does differ considerably in composition ; this 
 at first sight suggests a certain selective power possessed 
 by plants, absorbing certain substances and rejecting 
 others ; when all the facts are analyzed, however, there 
 is no evidence of any selection due to the presence or 
 influence of the life of the organism, and the entire 
 selective process can be fully explained by the laws of 
 diffusion as previously explained. A given substance 
 held in solution by the water in contact with the root of 
 the plant will continue to diffuse into the plant until 
 equilibrium is restored; if the substance is not consumed 
 and chemically changed by the plant, the equilibrium 
 once established remains permanent, and no more of the 
 substance enters the plant, whereas if the substance is 
 at once chemically changed on entering the plant, as in 
 the case of carbonic dioxide already explained, a constant 
 inflow is maintained in the endeavour to restore equi- 
 librium. Since the chemical work done by different 
 plants is varied in its nature, the difference in composi- 
 tion of the ash of different plants can be readily under- 
 stood. 
 
 The above explanation will illustrate the object of the 
 rotation of crops as practised by the farmer. The various 
 food substances derived from the soil by plants are as a 
 rule only soluble in very small proportions in rain water, 
 the efficacy of which to promote this condition depends 
 in many instances on the presence of small proportions 
 
60 BOTANY. [CHAP. n. 
 
 of certain gases in solution, consequently if the same crop 
 was grown for several years in succession on the sauie 
 portion of ground, and the produce removed, as is usual 
 in the case of cultivated crops, the supply of special food 
 required by the particular plant would be exhausted ; 
 whereas, other substances that have been slowly dis- 
 solved, but of no value to the particular plant grown, 
 would be wasted, the principle of rotation of crops over- 
 comes this difficulty, and supplies each particular kind 
 of plant sown with its own special kind of food. As 
 an illustration of the above : 
 
 Wheat, barley, and oats always contain a considerable 
 amount of silica or flint in their ash, and this substance 
 may be considered as the predominant inorganic food 
 required by the above plants; peas, beans, and clover 
 require lime, whereas potatoes and turnips require potash 
 as their speciality. Now if any one of the above crops 
 was sown for many years in succession on the same land, 
 and the entire crop removed, it can be readily under- 
 stood that the special food required would become scarce, 
 whereas if wheat is sown one season and turnips the next, 
 the latter crop not requiring silica, this substance would 
 slowly dissolve and accumulate, and thus be present in 
 sufficient quantity when the turn for sowing wheat came 
 round. 
 
 In some virgin soils, rich in the various food con- 
 stituents required by special plants, the same crop may 
 be grown many years in succession, but eventually 
 exhaustion takes place and the crop becomes deficient. 
 The fact of forests and tracts of heath, etc., occupying 
 the same position for centuries appears to contradict the 
 above statement respecting the rotation of crops, but it 
 
CHAP, ii.] CHEMISTRY, ETC., OF PLANT LIFE. 61 
 
 must be remembered that in the case of forests all the 
 inorganic materials removed from the soil are being 
 constantly returned in the form of dead leaves and 
 wood, so that practically the supply remains the same in 
 quantity, and is used up over and over again by different 
 generations of plants or even by the same plant. The 
 object of manure is to artificially replace plant food in 
 the soil when crops are grown and the produce removed. 
 
 The influence of light on plant life is exercised in a 
 variety of ways, the following being amongst the most 
 important : 
 
 Assimilation. This term is generally used to express 
 the decomposition of carbonic dioxide and water by 
 chlorophyll under the influence of light, and thus differs 
 considerably from the function expressed by the same 
 term by the animal physiologist. As already explained, 
 assimilation takes place only in those superficial cells 
 containing chlorophyll, and further the chlorophyll can 
 only exercise its function when exposed to light. The 
 superficial cells of most young parts of plants growing 
 in the air contain chlorophyll, and consequently assist in 
 assimilation; but leaves are the most important organs 
 in this connection, their general structure and flattening 
 out into a thin sheet being for the purpose of exposing 
 the greatest amount of surface from a given amount 
 of material. Other important functions performed 
 by leaves, as respiration, transpiration, etc., will be 
 explained at a later stage. 
 
 The general structure of a typical leaf growing in a 
 more or less horizontal direction is as follows. Every 
 part is covered with the epidermis, and as a general 
 rule the stomata or openings through the epidermis are 
 
BOTANY. [CHAP. n. 
 
 most numerous on the under surface the surface point- 
 ing to the earth. A single row of cells lying just below 
 the epidermis of the upper surface of the leaf the surface 
 pointing to the sky are closely packed together side 
 by side, and arranged like a palisade with their ends 
 pointing to the epidermis. This layer constitutes the 
 palisade tissue of the leaf, so named on account of the 
 arrangement of the cells already mentioned. The cells 
 of this tissue are richly supplied with chlorophyll and 
 give the deep green colour to the upper surface of the 
 leaf, and their most important function is that of assimi- 
 lation. The cells of the lower half of the thickness of 
 the leaf form a loose spongy tissue with numerous large 
 intercellular spaces, and contain less chlorophyll than the 
 palisade cells, hence the paler colour of the under surface 
 of the leaf. The intercellular spaces contain gases taken 
 in for assimilation by the upper surface of the leaf, and 
 also water vapour that escapes by transpiration from the 
 leaf into the air, hence we observe that there is a division 
 of labour in the work done by a leaf, the upper surface 
 performing chemical work assimilation the under 
 surface physical. The fibro- vascular bundles or " veins " 
 of the leaf are in continuity with those of the branch 
 from which the leaf originates, and form a network in 
 the spongy, lower part of the leaf, and in many plants 
 project from the under surface. The veins consist of 
 phloem and xylem, the latter lies nearest the upper 
 surface of the leaf which it supplies with water that has 
 passed up from the root. The phloem forms the under 
 side of the veins, and conducts from the leaf into the 
 plant during darkness the assimilated material made by 
 the leaf when exposed to light. 
 
CHAP, ii.] CHEMISTRY, ETC., OF PLANT LIFE. 
 
 63 
 
 Chlorophyll grains are always imbedded in the proto- 
 plasm from which indeed they are formed, their forma- 
 tion commences while the cells are still in darkness, for 
 example in young leaves before the expansion of the leaf- 
 bud, and continues until they assume the sickly yellow 
 colour presented by plants that have developed in the 
 dark, as under logs or stones ; for their further develop- 
 ment, that is, the formation of the bright green colour, 
 two conditions are necessary, exposure to light, and the 
 
 Fig. 19. Cell from the leaf 
 of Vallisneria spiralis. The 
 nucleus, k, and chlorophyll- 
 grains, cl, are seen imbedded 
 in the parietal layer of proto- 
 plasm. The arrows indicate 
 the direction of the currents 
 of protoplasm. (Highly mag- 
 nified. ) 
 
 presence of iron in solution in the cell-sap. The chloro- 
 phyll-grains do not fill the cell, but are arranged 
 in the protoplasm just under the cell-wall, the central 
 portion of the cell being filled with sap or the raw 
 material ready for undergoing assimilation. 
 
 The first observable product of assimilation is starch, 
 which makes its appearance as small colourless grains in 
 the chlorophyll- grains. Examined under the micro- 
 scope, starch-grains present a characteristic appearance > 
 
64 BOTANY. [CHAP. n. 
 
 being composed of alternating dark and light bands that 
 are arranged, depending on the particular kind of starch 
 examined, either concentrically or eccentrically round a 
 hilum or starting point. This layered appearance is due 
 to the alternation of dense layers with more watery layers, 
 the hilum being the most watery portion of the whole 
 grain. Starch is readily recognized by becoming blue 
 when mixed with a weak, cold, watery solution of iodine. 
 If the mixture is heated, the blue colour disappears but 
 returns on cooling. The great majority of edible pro- 
 ducts furnished by the vegetable kingdom consist of 
 
 Fig. 20. I, Potato starch, 
 with an eccentric hilum ; 
 //, Tapioca starch, with a 
 central hilum. (Highly 
 magnified. ) 
 
 starch which is obtained from those parts where it has 
 been stored up by the plant for its own future use, as in 
 seeds or fruits, as wheat, barley, rice, indian corn, sago, 
 etc., the meal consisting of starch along with the cells in 
 which it was contained ; starch is sometimes replaced by 
 sugar, as in ripe fruits, sugar-cane, beet, etc. 
 
 The above process of assimilation or conversion of 
 carbonic dioxide into an organic compound is the only 
 one known, hence all carbon present in the tissues of 
 either plants or animals is in the first instance derived 
 from the carbonic dioxide decomposed in the chlorophyll- 
 grains. 
 
CHAP. TI.] CHEMISTRY, ETC., OF PLANT LIFE. 65 
 
 Having shown the importance of light in connection 
 with the very existence of plant life, it is necessary to 
 enter a little more in detail respecting the influence 
 exercised by this agent. It is generally known that 
 what is termed solar light or popularly speaking sun- 
 light, although apparently a white or colourless light, 
 consists in reality of a mixture of several rays of light of 
 different colours. These colours can be separated from 
 each other by proper means, and constitute the solar 
 spectrum, the colours being arranged in the following 
 order : red, orange, yellow, green, blue, indigo, violet. 
 Each colour possesses an individuality of its own, and 
 so far as plant life is concerned it has been proved by 
 experiment that the red end of the spectrum that is, 
 from the red to the green ray inclusive is alone of value 
 in enabling plants to effect certain chemical changes. 
 As an example : if a plant showing the yellow colour due 
 to being grown in darkness is exposed to the rays of 
 the red end of the spectrum, the bright green chlorophyll 
 will soon become visible, whereas if exposed to the violet 
 end of the spectrum blue to violet no change in colour 
 or formation of chlorophyll takes place. In like manner 
 assimilation, or the formation of starch within the chloro- 
 phyll-grains depends entirely on the rays of the red end 
 of the spectrum, no starch being formed when exposed 
 to the violet end of the spectrum. The yellow ray is 
 most powerful in promoting the formation of both chloro- 
 phyll and starch. 
 
 On the other hand all physical work promoted by 
 light, as mechanical movements, are entirely due to 
 the rays of the violet end of the spectrum. If seed- 
 lings of any twining plant be taken and exposed to 
 
66 BOTANY. [CHAP. n. 
 
 the rays of the red end of the spectrum, no attempt 
 at twining will take place, but the plant, if previously 
 yellow, will soon become green, and thus continue to 
 grow, as its chlorophyll will enable it to assimilate. If 
 a similar seedling be exposed to the rays of the violet 
 end it will commence to twine round its support, but 
 not being able to develop chlorophyll will soon perish, 
 thus proving that although all the rays of light are of 
 service to plants, yet special kinds of work depend 
 entirely on the influence exerted by particular rays. 
 
 Heliotropism. Paradoxical as it may appear in face 
 of the above statements, it is nevertheless a fact that 
 light retards the growth of plants, or in other words, 
 when plants are unequally exposed to light the side with 
 least light grows fastest. This is clearly shown in the 
 case of plants grown in a window, which always bend 
 towards the light, not because, as usually believed, they 
 like the light and are bending towards it, but, on the 
 contrary, because the shaded side of the stem grows 
 much faster than the one exposed to the bright light, 
 and consequently becomes longer and convex, the 
 shorter side becoming concave. If a mirror, or even a 
 sheet of white paper is placed behind a plant growing in 
 a window so that the light is reflected on to its dark 
 side it continues to grow erect, whereas another plant 
 of the same kind not so provided will bend towards the 
 light. Plants that are influenced in this particular way 
 by light are said to be lieliotropic, and when the bending is 
 towards the light, positively heliotropic. A few plants, 
 as the common ivy, when unequally lighted, bend away 
 from the light, owing to the side exposed to most light 
 growing fastest. This habit is of value to the ivy, as 
 
CHAP, ii.] CHEMISTRY, ETC., OF PLANT LIFE. 67 
 
 its young shoots are thus pressed close to the wall or 
 tree up which it is growing, and kept in this position 
 until they have become plainly anchored by means of 
 the numerous root-like organs of attachment that enter 
 the crevices of the supporting body. Plants that bend 
 away from the light are said to be negatively heliotropic. 
 
 Light also acts in a marked manner on many of the 
 lower forms of plant life, some moving towards the light, 
 others away from it. 
 
 Water, as already stated, is indispensable to all plants 
 during active growth. Growing points require much 
 water for the purpose' of conveying the formative mate- 
 rials required for the building up of new tissues, and a 
 certain amount of water is also used up in such forma- 
 tions. A cell containing protoplasm saturated with a 
 large amount of water will give up water to a cell con- 
 taining a smaller proportion of this substance, and as 
 the young cells are almost entirely filled with dense proto- 
 plasm, there is a constant slow movement of water towards 
 growing points induced by osmotic action and by the 
 water being used up as it reaches these points. A 
 second rapid movement of water is distinct from the slow 
 movement, and supplies the water that plants exhale in 
 the form of watery vapour through the stomata of the 
 leaves into the air. The water is taken up by the root 
 and is conveyed along the walls of the youngest portion 
 of the xylem to the leaves. In darkness the stomata 
 are almost or quite closed, so that little or no transpira- 
 tion takes place. As light and heat are increased the 
 stomata open, being specially influenced by bright light, 
 and under these conditions the amount of watery vapour 
 given off increases. The rigidity of leaves and young 
 
68 BOTANY. [CHAP. n. 
 
 shoots depends on the presence of a proper amount of 
 water in the cells ; consequently, when the leaves exhale 
 more moisture than is taken up by the roots the plant 
 withers or droops. The drooping of plants on a very 
 hot day is due to the above cause. During the night, 
 when darkness and a lower temperature retard transpi- 
 ration, the plants revive, as the root continues to 
 take in water, which enters the cells and restores 
 their turgidity. 
 
 Gravitation exercises a powerful influence on the 
 growing parts of plants, the upward direction of the 
 stem and the downward direction of the root being 
 influenced by this force. The action of gravitation on 
 growing parts of plants is called Geotropism. If a 
 seedling plant be placed horizontally the stem curves 
 upwards, and the root downwards ; the former is nega- 
 tively geotropic, the latter positively geotropic. The 
 branches and leaves of plants are also affected by geo- 
 tropism. The cause of geotropism is the unequal 
 growth of the cells on opposite sides of the stem or root, 
 as in the case of heliotropism ; hence we get similar 
 results brought about by distinct forces, and in a state 
 of nature the habit of every plant ia the result of the 
 influence of the various forces to which it is exposed; 
 but as there is a distinct individuality in the life of each 
 kind of plant, so we find that the various forces act in 
 different proportions on different species, the result 
 being a difference of habit as illustrated by the erect 
 branches of the poplar and the spreading branches of the 
 oak. That the above explanation as to habit being the 
 result of the balance set up between the life of a given 
 species and surrounding forces is in the main correct, is 
 
CHAP, ii.] CHEMISTRY, ETC., OF PLANT LIFE. 69 
 
 shown by the variation of habit that can be induced in a 
 plant when intentionally placed under unusual conditions 
 relative to the forces that under normal conditions collec- 
 tively determine its habit. When seeds are caused to 
 germinate on a horizontally-placed rotating plate, the 
 plantlets are placed under the influence of centrifugal 
 force, a factor that exerts no influence on them in a 
 state of nature ; but under these artificial conditions 
 this force at once disturbs the previous balance arrived 
 at between the plant and its surrounding potent forces, 
 and we find that the 'rootlets follow the centrifugal force 
 and grow outwards, also downwards, due to the influence 
 of geotropism ; the stem, on the contrary, grows towards 
 the centre of the plate and also upwards. When a 
 number of plates are used that rotate at different speeds 
 different directions can be given to the root and stem 
 depending on the predominance given to centrifugal 
 force or gravitation, the two dominant external forces in 
 the experiment. Other external influences also possess 
 the power of neutralizing the influence of geotropism as 
 exercised under normal conditions. Thus, when seeds, 
 as those of the bean, are grown in a wire sieve filled 
 with damp sawdust, the main roots are at first positively 
 geotropic and consequently grow downwards, but after 
 passing through the bottom of the sieve into dry air 
 they bend upwards again and enter the sawdust, being 
 drawn by the water, which, under these exceptional 
 conditions, completely neutralizes the action of geo- 
 tropism. This attracting influence of water is termed 
 Hydrotropism. 
 
 The influence exercised by the vegetable kingdom on 
 surroundings in performing those functions necessary for 
 
70 BOTANY. [CHAP. ii. 
 
 the welfare of its own members is very varied and 
 important from the point of view of animal life. The 
 exhalation of watery vapour into the air has already been 
 alluded to, and it has been proved that this function 
 influences to a very great extent the climate of a country. 
 Where forests have been cut down on a large scale, as 
 is frequently the case in newly occupied regions, the 
 springs have become less abundant or completely dried 
 up. On the other hand, where the rains are excessive 
 the climate has been rendered drier by the cutting down 
 of the forests. This was especially marked in the neigh- 
 bourhood of Rio Janeiro, where the climate was rendered 
 dry by the removal of the dense forest surrounding the 
 city, and eventually the rain had so much diminished 
 that the Brazilian Government were compelled to pass 
 a law prohibiting the further cutting down of trees. 
 Experiments have shown that a sunflower 3^ feet high, 
 weighing 3 Ibs., and with a leaf area of about 5,616 
 square inches, exhaled 20 ounces of liquid in the course 
 of a day ; a cabbage plant, with a leaf area of about 
 2,736 square inches, exhaled on an average about 
 19 ounces of water in a day. 
 
 It is usually stated that green plants purify the atmo- 
 sphere from the point of view of animal life by removing 
 carbonic dioxide and restoring oxygen, and this is per- 
 fectly true ; but it is equally true that every plant also 
 gives off carbonic dioxide into the atmosphere and 
 removes oxygen, exactly as all animals do, and in con- 
 nection with the same function, that of respiration } or 
 breathing. A little attention to the fact that the 
 removal and restoration of carbonic dioxide to the 
 atmosphere is respectively the outcome of two distinct 
 
CHAP, ii.] CHEMISTRY, ETC., OF PLANT LIFE. 71 
 
 functions will make clear what at first might be con- 
 sidered as a contradictory statement. 
 
 In the act of nutrition, as already explained, carbonic 
 dioxide is removed from the atmosphere in considerable 
 quantities and used by the plant as food. This function 
 can only be exercised when the plant is exposed to light, 
 and ceases when the plant is placed in darkness ; conse- 
 quently, in a state of nature, plants only remove carbonic 
 dioxide from the atmosphere during the day. This act 
 is accompanied by the restoration of a considerable 
 amount of free oxygen to the atmosphere, in fact, an 
 equal amount to that taken in chemical combination 
 with the carbon as carbonic dioxide. The function of 
 respiration, which is common to all forms of life, both 
 animal and vegetable, is a purifying process, exercised 
 for the purpose of removing certain worn-out material, 
 especially carbon, from the body ; this substance is re- 
 moved in the gaseous form as carbonic dioxide. Oxygen 
 is inhaled from the atmosphere, and, chemically com- 
 bining in the tissues with the waste carbon, is exhaled 
 or returned to the atmosphere as carbonic dioxide. 
 This exchange of gases in the plant world is mainly 
 due to diffusion, the mechanical auxiliaries present in 
 connection with respiration in the higher animals being 
 absent from plants. The function of respiration, in 
 plants as in animals, is unaffected by the presence or 
 absence of light, and is exercised uninterruptedly during 
 the life of the individual ; hence in the performance of 
 this function plants are always removing oxygen from 
 and adding carbonic dioxide to the atmosphere ; but 
 the respiration of plants is a comparatively slow process, 
 and as very much more carbonic dioxide is removed 
 
72 BOTANY. [CHAP. n. 
 
 from the atmosphere and oxygen restored to it during 
 the presence of light, in the act of nutrition than is the 
 converse in the function of respiration even during the 
 whole day, consequently the statement that plants purify 
 the atmosphere is perfectly true, yet it is necessary to 
 remember clearly the manner in which this function is 
 effected. 
 
 If the above explanation has been understood, it will 
 be seen that living plants tend to purify the atmosphere 
 of an apartment during the day by removing much more 
 carbonic dioxide from the atmosphere than they give off, 
 and also by adding oxygen to the air, whereas during 
 the night oxygen only is removed from the atmosphere 
 and carbonic acid alone liberated, thus rendering the 
 atmosphere impure for animal life. The above are the 
 results that would be obtained by experimenting with 
 plants in a closed volume of air under the two given 
 conditions, but in a well-ventilated room, unless the 
 amount of plant life is excessive, on account of the 
 slow process of respiration, no inconvenience would be 
 experienced. 
 
 The element nitrogen, being one of the constituents of 
 protoplasm, is required by all plants, and, although 
 abundant in the atmosphere, is never taken in direct in 
 this form, but is obtained from salts of ammonia and 
 nitrates present in the soil. Some plants, however, do 
 not obtain the whole of their nitrogen in this manner, 
 but, according to the extent of differentiation they have 
 undergone in connection with this function, obtain a 
 greater or less amount from members of the Animal 
 Kingdom, and for this reason are known as carnivorous 
 plants, or the term insectivorous plants is sometimes 
 
Fig. 21. Venus's Fly-trap (Dioncea muscipula), a carnivorous 
 plant. The leaves are sensitive to contact, and in the undisturbed 
 condition are expanded. When either of the three small hairs 
 situated on each half of the upper surface of the leaf are irritated 
 by contact with a small insect, the two halves of the leaf close 
 together and remain closed until the irritation has ceased. (Natural 
 size. ) 
 
74 BOTANY. [CHAP. 11. 
 
 used, because the members of the animal kingdom 
 captured by plants are usually insects. 
 
 This peculiar carnivorous propensity exhibited by 
 certain plants does not appear to have been possessed 
 by such for all time, but must rather be looked upon 
 as an acquired character. The evidence in favour of 
 this idea is the fact that carnivorous plants occur belong- 
 ing to widely separated families of plants, and, further, 
 that every phase of differentiation in the development 
 of those characters that enable a plant to benefit by a 
 carnivorous habit is met with in the various members 
 included under this heading. 
 
 Carnivorous plants are generally inhabitants of swamps 
 or marshy places as the sundews (Drosera), butterworts 
 (Pinguicula) , pitcher plants (Nepenthes), etc., others, as 
 the bladderwort ( Utricularia) , are aquatic. Most agree 
 in having imperfectly developed roots or in being en- 
 tirely rootless. The leaves of carnivorous plants, either 
 entirely or in part, are the portions modified for the 
 purpose of capturing insects. In some kinds, as the 
 sundews, the leaves are sensitive and close round the 
 insect alighting on the upper surface which is furnished 
 with glands that secrete an acid and a substance closely 
 resembling pepsine ; these secretions, which closely re- 
 semble in composition and function gastric juice, act on 
 the body of the insect, and a true process of diges- 
 tion, similar to what occurs in the stomach of an animal, 
 takes pi ace, in fact, the leaf when curled up and digesting 
 an insect may be compared to an extemporized stomach. 
 The leaves of our common sundews are bright red on the 
 upper surface, possibly for the purpose of attracting 
 insects, and are furnished round the margin with a row 
 
Fig. 22. Cephalotus follicularis, a carnivorous plant met with in 
 Australian swamps, showing some of the leaves modified into pitchers 
 or ascidia that are furnished with a movable lid. 
 
76 BOTANY. [CHAP. n. 
 
 of glandular hairs, each of which secretes at its swollen 
 tip a sparkling drop of viscid fluid which increases in size 
 as the sun's heat increases, hence the popular name of 
 sundew. If an insect comes in contact with a single 
 gland, more fluid is secreted, and as the victim struggles 
 its movements only hurry on its own destruction, other 
 glands bend over to the place where the struggle is 
 going on, until finally the insect is surrounded by the 
 leaf and eventually digested, after which the leaf slowly 
 expands, the remains of the insect being removed by 
 wind or rain. Nepenthes agrees with the sundew in 
 digesting its prey, the digested matter being then ab- 
 sorbed. In Utricularia and Sarracenia the insects are 
 not digested but become putrescent on the surface of the 
 leaf or in the pitchers, the putrescent matter being then 
 absorbed. In the butterwort, not uncommon in some 
 parts of England, the leaves form a rosette lying on the 
 ground, are of a pale yellow-green colour, and covered 
 on the upper surface with a viscid exudation which acts 
 like birdlime to any insect alighting on its surface. 
 When irritated by the struggles of the insect the leaf 
 curls slowly inwards and enfolds its victim, expanding 
 again when the irritation has ceased and the nitrogenous 
 portions of the insect have been absorbed. The butter- 
 wort digests its food after the fashion of the sundew, 
 but on the whole it does not appear to be specially 
 adapted for the capture of living insects, and depends 
 more on dead nitrogenous matter being deposited on the 
 leaf. The popular name of butterwort is derived from 
 the fact that the leaves were at one time used for the 
 purpose of curdling or giving consistency to milk, due to 
 the presence of the digestive fluid in the leaves. It is 
 
Fig. 23. Nepenthes gracilis, a pitcher-plant inhabiting swamps in 
 the East Indies. Some of the leaves are normal, others have the 
 midrib continued as a long, slender, tendril-like stalk that becomes 
 expanded at the apex into a hollow pitcher -like body furnished with 
 a lateral opening near the apex, and constructed for the purpose of 
 capturing and digesting insects. 
 
78 BOTANY. [CHAP. n. 
 
 interesting to note that a substance called rennet, con- 
 sisting of portions of calves' stomachs, is still used for a 
 similar purpose, its efficacy being also due to the presence 
 of gastric juice. In Utricularia or bladder wort, the 
 plants are aquatic and rootless, and the much cut leaves 
 bear several little bladders that act as traps to water- 
 fleas and other minute aquatic animals. Finally, in 
 many exotic species, popularly known as pitcher plants, 
 certain of the leaves are modified into hollow pitcher- 
 like receptacles specially arranged for the capture of 
 insects, or, in some species where the pitchers are large, 
 of humming birds or small animals. In the species of 
 Sarracenia, inhabiting the turfy, spongy bogs of America, 
 the pitcher- shaped leaves are very effective fly-traps. A 
 sugary juice is secreted round the mouth of the pitcher 
 that attracts insects, which descend lower in the tube, 
 and are precipitated into a watery secretion filling the 
 bottom of the pitcher, their egress being prevented by a 
 ring of reflexed hairs. The walls of the lower portion of 
 the inside of the pitcher are lined with glands that 
 secrete a digestive fluid that mixes with the water in the 
 pitcher. 
 
 Parasites and Saprophytes. The foregoing remarks 
 respecting the nutrition of plants and their influence on 
 surroundings, applied solely to what may be termed 
 typical plants ; that is, plants developing chlorophyll, 
 which embraces the great bulk of the members of the 
 vegetable kingdom. There are, however, a very large 
 number of true plants that never develop chlorophyll, 
 and consequently cannot assimilate inorganic matter as 
 food, but, like numbers of the animal kingdom, require 
 organic food. Such plants fall naturally under two 
 
CHAP, ii.] CHEMISTRY, ETC., OF PLANT LIFE. 79 
 
 sections. (1) Parasites, plants that obtain their food 
 from the bodies of living plants or animals ; as examples 
 may be mentioned the various species of broomrape 
 (Orobanche), the dodders (Cuscuta}, and numerous spe- 
 cies of fungi, as the mildews causing the potato disease, 
 also that of the hop, vine, etc., to which may be added 
 those fungi popularly known as "rust," " mildew," and 
 " bunt/' that are so very destructive to many of our 
 important cultivated plants, more especially the cereals. 
 Several species of fungi grow on the bodies of living 
 insects ; the disease known as " muscardine," that com- 
 mits such havoc with the caterpillar of the silkworm 
 moth, is caused by a fungus. The plant or animal to 
 which the parasite is attached, and from which it derives 
 its food, is termed the hostj a term which, if plants could 
 express their feelings, would probably be considered as 
 sarcastic, inasmuch as the hospitality is altogether invo- 
 luntary, and greatly to the detriment of the host. 
 Parasitism is an acquired function. Parasites occur in 
 natural orders of plants that are widely separated from 
 each other, proving that this function has originated 
 independently at many points, and, judging from the rela- 
 tive amount of modification presented by different plants 
 for the purpose of enabling them to hold their own 
 under the new conditions imposed by becoming para- 
 sites, it would appear that this retrogression or falling 
 back from the characteristic mode of plant nutrition had 
 occurred at widely- separated periods of time; but this 
 need not necessarily be so, as it is well known that 
 plants, like animals, vary to a very marked extent in 
 their power of adaptation to changed conditions, some 
 that possess what may be termed an elastic constitution, 
 
80 BOTANY. [CHAP. n. 
 
 readily accommodating themselves to very marked 
 changes, others being rigid, either entirely disappear or 
 retire into the background when placed under similar 
 conditions. A second reason in support of the idea that 
 parasitism is an acquired function that has been gra- 
 dually evolved, and is still going on at the present day, 
 is the transitional forms from chlorophyll-producing 
 plants to others entirely destitute of chlorophyll. The 
 well-known mistletoe (Viscum album) is an example of 
 such a transitional species, being a parasite to the extent 
 of obtaining from the host upon which it grows all the 
 food and water taken from the soil by the roots of the 
 host plant; but the leaves of the mistletoe contain 
 chlorophyll, hence it still retains and exercises the pro- 
 perty of taking in carbonic dioxide from the air, and of 
 producing starch in the normal manner. The stage of 
 parasitism reached by this plant is that of taxing a host 
 plant to supply the required amount of water with food 
 substances in solution, instead of taking them directly 
 from the soil for itself. In the figwort order (Scrophu- 
 lariacece), as understood in the broader sense, we have 
 even in British species an interesting sequence in the 
 evolution of parasitism; the species of eyebright 
 (Euphrasia) , yellow rattle (EhinantTius) , lousewort 
 (Pedicularis) , and Bartsia, all common plants of our 
 meadows and moorlands, have leaves furnished with the 
 normal amount of chlorophyll, and, so far as general 
 appearance goes, appear to obtain the whole of their food 
 in the manner normal to ordinary plants ; but in reality 
 all are to a certain extent parasites, or, as one might say, 
 have broken away from the normal plant-mode of ob- 
 taining food, and resorted to a device for obtaining a 
 
CHAP, ii.] CHEMISTRY, ETC., OF PLANT LIFE. 81 
 
 certain portion by a means which, if secured at a less 
 cost in the first instance, leads eventually to a compara- 
 tive loss of freedom and individuality. All the species 
 enumerated only grow and flourish when in close contact 
 with other plants. In every instance the seeds on ger- 
 mination give origin to a root that in the first instance 
 derives food by absorbing water from the soil, but this 
 first-formed root soon perishes, and the later-formed or 
 secondary roots become attached to the roots of other 
 plants, from which they draw the liquid portion of their 
 food. If seeds of either of the above plants are inten- 
 tionally sown apart from other plants, it will be found 
 that after a very brief existence they die, having become 
 so far differentiated on the road towards parasitism, that 
 their roots cannot take in food direct from the soil, yet 
 in every example the leaves are still green and capable of 
 assimilation. It is interesting to note that in the earliest 
 condition, that is, immediately after the germination of 
 the seed, the young plants obtain all their food by the 
 typical method. In the tooth wort (Lathrcea squamaria) , 
 and the species of broomrape (Orobanche), the change 
 in the direction of parasitism has been carried much 
 further ; not only has the chlorophyll been completely 
 suppressed, but even the leaves themselves have become 
 reduced to mere scale-like structures of no functional 
 value, and the plant depends entirely on its host for its 
 supply of already assimilated food, the only trace of 
 individuality retained by such pronounced parasites 
 being the power of rearranging the food thus obtained 
 and building up the reproductive portion of their dege- 
 nerated structure. In extreme cases of parasitism, as 
 illustrated by the species of Rafflesia, natives of the 
 
 a 
 
82 BOTANY. [CHAP. n. 
 
 East Indian Archipelago, the vegetative part is reduced 
 to an absorbent portion that is completely buried in 
 the substance of the host ; the flowers, or reproductive 
 portion, on the other hand, often attaining enormous 
 dimensions, the flowers of Rafflesia Arnoldi measuring 
 nearly three feet in diameter. This loss of balance due 
 to a parasitic habit between the vegetative and repro- 
 ductive parts of plants, has its counterpart in the animal 
 world, where such parasites as the tapeworm are reduced 
 to the reproductive portion, and, like the last-named 
 animal, many parasitic plants belonging to the fungi 
 spend different periods of their existence or life-cycle on 
 different host-plants ; thus the common " rust " of wheat 
 and other cereals, Puccinia graminis appears in the 
 early summer on the leaves and stems as bright rust- 
 coloured streaks, hence the popular name ; if the spores 
 or reproductive bodies which constitute the rust-co- 
 loured powder be examined under the microscope, they 
 will be found to consist individually of a single cell with 
 a bright brown rough cell-wall ; these spores as soon as 
 mature, if carried by wind or rain on to other grass-leaves 
 or stems, germinate at once, the mycelium penetrating 
 into the tissues, where in a short time it produces similar 
 rust-coloured streaks, that burst through the epidermis 
 and appear on the surface, ready to be transported and 
 form the starting-point for a new colony ; in this manner 
 the rust spreads rapidly during the summer months, 
 and being a thorough parasite, robs the host of a consi- 
 derable amount of assimilated food originally elaborated 
 for its own use ; towards the autumn, the streaks on the 
 stem and leaves become somewhat darker in colour, and 
 if a portion of the powder is examined under the micro- 
 
CHAP, ii.] CHEMISTRY, ETC., OF PLANT LIFE. 83 
 
 scope, a number of spores as already described will be 
 seen, but mixed with these, and produced by the same 
 mycelium or vegetative portion of the fungus, will be 
 found spores of a totally different form and colour, each 
 consisting of two superposed cells furnished with a smooth, 
 brown cell- wall; as the season advances, the streaks 
 formed on the stem and leaves are almost black, and on 
 examination the spores will be found to consist entirely of 
 the last described two-celled kind, the one-celled first 
 formed kind having entirely disappeared. If the above 
 explanation has been understood, it will be seen that the 
 fungus during its development has completely changed 
 the nature of its spores or reproductive bodies not only 
 in colour and structure, but what is of more importance, 
 in function also ; the two-celled spores produced in the 
 autumn cannot germinate at once when mature, but pass 
 the winter in an unaltered condition, being carried to 
 the ground by the fall and decay of the leaves or stems 
 on which they are produced. The following spring these 
 spores germinate as follows : each cell of the spore 
 produces a short slender branch or germ- tube, that pro- 
 duces near its tip two or three very minute spores called 
 promycelium spores. These minute spores can only ger- 
 minate when carried by wind or some other means on to 
 the surface of the newly-expanded leaves of the common 
 barberry (Berberis vulgaris) ; when once located in this 
 position germination commences, and soon a slender 
 germ-tube is produced by the spore, that at once bores 
 through the epidermis of the leaf, and develops a 
 mycelium or vegetative portion at the expense of the 
 leaf; after a time the mycelium produces dense clusters 
 of yellow spores, at first arranged in chains, inclosed in 
 
84 BOTANY. [CHAP. n. 
 
 an external covering ; the whole cluster eventually bursts 
 through the epidermis of the leaf, the external covering 
 is ruptured at the top into a number of teeth that curl 
 backwards, the dense mass of golden-yellow spores being 
 now dry and powdery, and in this state are readily blown 
 away by the wind. This stage of the parasite is popu- 
 larly known as " cluster-cups," on account of the mem- 
 brane covering the spores more or less resembling a cup 
 with a toothed margin after bursting open, and in being 
 produced in clusters. Finally, the spores of the cluster- 
 cup stage must be carried by some means on to the 
 surface of a grass leaf or stem, where they at once 
 germinate, the germ-tube entering the leaf through a 
 stoma, where a mycelium is formed that gives origin to 
 the rust- coloured streaks consisting of the one-celled 
 spores that the description commenced with. Until 
 recently the three stages described above were considered 
 as totally distinct individuals. The term Heteroecism is 
 used to express the fact that a parasite passes different 
 phases of its life-cycle on different host-plants. The 
 above is not an isolated or exceptional example ; we have 
 in Britain alone numerous hetercecismal species of fungi, 
 the cluster-cup or Mddium stage being amongst the 
 most beautiful of microscopic objects. 
 
 Up to the present true parasites have been dealt with, 
 and in such instances everything is in favour of the 
 parasite, the host being in no instance benefited by the 
 presence of its unwelcome guest, but in some instances 
 we find that parasite and host have become so thoroughly 
 adjusted that both benefit mutually by the combination. 
 This condition of things is called mutualism or commen- 
 salism, and in the vegetable world is well shown in the 
 
CHAP, ii.] CHEMISTRY, ETC., OF PLANT LIFE. 85 
 
 large group of cryptogamic plants called Lichens, that 
 were until recently considered autonomous plants, as 
 their relations, the Algae and Fungi, are in reality. It 
 
 Fig. 24. Illustrations of the life-cycle of the parasitic fungus known 
 as "rust" on wheat and other grasses (Puccinia graminis). I. the 
 rust -coloured streaks of the fungus on stem and leaf of wheat plant 
 (natural size) ; II. spore of the spring stage, known as uredospores 
 (highly magnified) ; III. two-celled spore of autumn stage, known as 
 teleutospores (highly magnified) ; IV. a teleutospore germinating and 
 producing a promycelium bearing three promycelium-spores (highly 
 magnified); V. a leaf of the barberry bearing groups of the "cluster- 
 cup " or JEcidium, stage (natural size) ; VI. a portion of a barberry leaf 
 with a group of "cluster-cups" (slightly magnified); VII. a single 
 spore belonging to the secidium stage, called an cecidiospore (highly 
 magnified). 
 
 has, however, been clearly proved that every lichen is 
 what may be termed a compound organism, consisting 
 of a fungus and an alga leading a life of mutualism, and 
 
BOTANY. [CHAP. n. 
 
 together constituting the individual. The algal element, 
 being possessed of chlorophyll, assimilates carbonic 
 dioxide and forms organic carbon compounds, while 
 the mycelium of the fungus portion absorbs water con- 
 taining mineral substances in solution. The mycelium 
 of the fungal portion of the lichen clasps the cells of the 
 alga so closely that a transfusion of the substances 
 absorbed by the two respectively takes place ; but this 
 differs from a case of true parasitism, inasmuch as alga 
 and fungus mutually benefit. The fruit of every lichen 
 is formed entirely by the fungal element. The forma- 
 tion of a new lichen depends on the spores produced by 
 previous lichen germinating in contact with an alga the 
 cells of which are clasped by the mycelium of the germi- 
 nating spore, and growth or increase in size is effected 
 by the independent and contemporaneous growth of the 
 two individuals. This perfect balance and readjustment 
 of the division of labour between two originally distinct 
 plants to form a third possessing pronounced peculiarities 
 of its own, with a corresponding loss of individuality of 
 its components, is a marked illustration of the adapta- 
 bility of life, and is not an isolated example, as mutualism 
 in every phase of development exists in various divisions 
 of both the animal and plant kingdoms, and well authenti- 
 cated instances of mutualism between plants and animals 
 are also on record. 
 
 (2) Saprophytes. Plants that obtain their food from 
 dead organic matter, and are always destitute of chloro- 
 phyll, or at all events possess such minute traces as to 
 be of no functional value in assimilation, but is of interest 
 as one of the proofs of their having degenerated from 
 chlorophyll-bearing ancestors, other points of evidence 
 
CHAP, ii.] CHEMISTRY, ETC., OF PLANT LIFE. 87 
 
 in this connection being the close morphological or struc- 
 tural agreement with species that yet produce chlorophyll. 
 As examples of saprophytes may be mentioned the 
 numerous species of fungi popularly known as " toad- 
 stools" that grow on rotten wood, manure, etc., also 
 other species of fungi, as the common mushroom (Agaricus 
 campestris*), that grow on the ground, and which might 
 be supposed to feed on inorganic food like green plants; 
 but this is not the case, the mycelium of the fungus 
 absorbs organic food supplied by decaying vegetable 
 matter present in the soil. Amongst saprophytic flower- 
 ing plants found in Britain may be mentioned the bird's- 
 nest orchis (Neottia nidus- avis), and the coral-root orchis 
 (Corallorhiza innata) . 
 
 Typical parasites and saprophytes, having no chloro- 
 phyll, never remove carbonic dioxide from the atmosphere, 
 neither do they give out oxygen, but act like animals in 
 removing oxygen and giving off carbonic dioxide in the 
 act of respiration. Such plants are not influenced by light 
 in connection with nutrition. 
 
 Comparing saprophytes and parasites with plants pro- 
 ducing chlorophyll, it will be observed that the former 
 class save a considerable amount of labour by obtaining 
 their food more or less ready made, but this gain is more 
 than neutralized by a loss of individuality and freedom, 
 and are necessarily more limited in their distribution. 
 A green plant can establish itself wherever there is a 
 supply of moisture, proper soil, and a suitable tempera- 
 ture ; the atmosphere being everywhere is not a deter- 
 mining factor. The parasite requires all the above 
 conditions to enable its host to be present, plus the host; 
 and as many parasites have become so specialized as to be 
 
88 BOTANY. [CHAP. n. 
 
 able to procure their food from one particular kind of 
 host, it follows that its distribution is determined by that 
 of its host. Saprophytes, only requiring decomposing 
 organic matter, have a somewhat wider range, being 
 confined to those regions where life exists, but some 
 saprophytes appear to be partial to special kinds of 
 organic food. 
 
 Metastasis. The substance formed by assimilation in 
 the chlorophyll-grains, which is usually starch, sometimes 
 fat, or rarely cane-sugar; this constitutes the raw material 
 from which all the substances present in plant tissues 
 are formed. In this elaboration, oxygen, nitrogen, and 
 the various mineral substances taken from the soil are 
 also utilized. The most important and indispensable of 
 substances formed by the plant are those concerned in 
 the formation of the protoplasm and the cell-wall ; such 
 are called plastic substances. The plastic substances are 
 not used up entirely in the organs where they are formed, 
 but change their position and are either used up at once 
 in the formation of new cells, or are stored up as reserve 
 material for future use. The change in position of 
 elaborated material is usually accompanied by a change 
 in chemical composition for the purpose of facilitating 
 the transport. This is the process of Metastasis or Meta- 
 bolism. The solid starch formed in chlorophyll-grains is 
 converted into a glucoside,in which condition it can travel 
 along the stem, and is converted back into starch when 
 it reaches the specialized part destined to store it up 
 until required for use ; all seeds contain a supply of 
 reserve material for the purpose of furnishing the young 
 plantlet with its first food until it develops green leaves 
 and is able to assimilate for itself. Potato tubers, 
 
CHAP, ii.] CHEMISTRY, ETC., OF PLANT LIFE. 89 
 
 swollen roots, bulbs, and the trunks of trees also contain 
 reserve material for future use. During the process of 
 metabolism a great many products are formed that are 
 of no known use in plant economy, and may be termed 
 by-products of metastasis; as examples may be men- 
 tioned several volatile oils, acids, alkaloids, resinous 
 matters, etc. Degradation products, as the various kinds 
 of gum, are produced by the more or less complete 
 disintegration of cell-walls, and cannot be re-converted 
 back into plastic or formative material. 
 
CHAPTER III. 
 
 PROTECTIVE ARRANGEMENTS. 
 
 Origin of the Vegetable Kingdom. The struggle for existence. 
 Protection against climate. Protection against living enemies. 
 Saving of energy and expenditure of material exhibited in modern 
 modes of protection. 
 
 IT is generally admitted that the entire Vegetable King- 
 dom clothing the earth at the present day as also 
 those groups unsuccessful in the bitter fight for life, and 
 only known to us by their fossil remains have evolved 
 by a slow series of changes from the Algae or seaweeds, 
 hence the members of this group may be considered as 
 the pioneers of plant life. It is not intended to discuss 
 the various ideas respecting the origin of life, but 
 granted life to indicate the leading modifications that 
 have taken place in the members of the plant world and 
 to which are collectively due the enormous variety of 
 structure presented by plants at the present day. 
 
 Protection in the broader sense, as including all the 
 various arrangements and contrivances for enabling an 
 individual to do a given amount of work in a better 
 manner and with a less expenditure of energy and 
 material than heretofore, appears to be the one aim of 
 every member of the Vegetable Kingdom at the present 
 day. Self-sacrifice and philanthropy are factors not 
 
Fig. 25. Trunk and portions of the branches of a fossil called 
 Lepidodendron, illustrating a group of plants that formed vast forests 
 during the Carboniferous period, but which have been extinct now 
 for many geological ages. (Much reduced.) 
 
92 BOTANY. [CHAP. in. 
 
 exercised by plants in reality, although, as in some of 
 the higher members of the Animal Kingdom, sugges- 
 tions of these virtues are paraded by certain plants for 
 the purpose of accomplishing an object by surreptitious 
 methods. 
 
 The proofs of the evolution of all groups of plants 
 from seaweeds must be sought in more advanced works 
 than the present, where the evidence will be found more 
 convincing than is generally considered by those who 
 have never paid special attention to the study of plant 
 life. The fact that seaweeds still remain as seaweeds, 
 or, in other words, the reason why all the lower types of 
 plants have not evolved and got away from their primi- 
 tive starting-point, is not known ; neither is it known 
 why the half dozen children constituting a family do not 
 all exhibit exactly the same tendencies in every respect ; 
 we all know that such is not usually if ever the case, and 
 the variations of degree presented by the members of a 
 family should at least convince those most opposed to 
 evolution that all human beings are not cast in the same 
 mould, but that there must be a certain amount of internal 
 structural difference to account for the difference of exter- 
 nal manifestations ; for if the structure and composition of 
 every human being was absolutely identical, it would be 
 contrary to all experience to expect other than absolutely 
 identical results. The same argument in favour of in- 
 finitesimal differences between the members of a family 
 apply equally to the half dozen peas taken out of the 
 same pod, and if the truth of even the slightest amount 
 of variation is admitted as existing in the members of a 
 group, to what extent may this variation extend ? The 
 evolutionist's answer would be that the limits of varia- 
 
CHAP, in.] PROTECTIVE ARRANGEMENTS. 93 
 
 tion, as also its direction at different times and under 
 different conditions, are at present unknown. The per- 
 son opposed to evolution or the numerous class that are 
 quite indifferent on the subject and are only acquainted 
 with the traditional origin of all forms of life, while com- 
 pelled to admit a certain amount of individual variation, 
 argue that every given plant and animal was always what 
 it is at the present day, and ask, why do not the marked 
 changes from one form to another, that you ask us to 
 believe, still go on at the present day ? The first state- 
 ment, that things are now what they always were, is 
 simply expressing an opinion that finds no support in 
 nature ; if species had been the same in all time past, 
 then we should expect to find their fossil remains in the 
 rocks, but this is not the case ; what we do find is, as 
 already stated, in the early geological formations, the 
 remains of plants belonging to types that have long ago 
 become entirely extinct ; the same is true of animal 
 remains ; in other instances vast remains of plants occur 
 in a fossil condition, which, from their abundance and 
 structure, prove that geological ages ago they were far 
 more abundant and highly organized than their sur- 
 vivors are at the present day ; such groups may be said 
 to have long ago passed the maximum of their develop- 
 ment and are now on the decline. This condition of 
 things is illustrated by the group of plants known as 
 Gymnospermsj which includes the pines, firs, yews, 
 cycads, etc., characterized by the absence of fruit in a 
 botanical sense, and by the naked ovules or young seeds. 
 The Gymnosperms as a group were in the heyday of their 
 prosperity, and the monarchs of the vegetable world, 
 both on account of the high organization and size during 
 
Fig. 26. A cycad (Cyca$ circinalis), illustrating a type of plant life 
 that was abundant in early geological ages, but now on the wane, and 
 fast disappearing. The general habit resembles that of the modern 
 palms, but its affinities are widely separated from those plants. (Much 
 reduced. ) 
 
CHAP, m.] PROTECTIVE ARRANGEMENTS. 
 
 95 
 
 the Mesozoic period ; their decline is first indicated in 
 cretaceous times, and since that period up to the present 
 has been increasing. A few representatives yet remain, 
 but, as is well known, they do not stand in the first rank 
 of plants either structurally or numerically, being quietly 
 superseded by the group known as Angiosperms, charac- 
 
 7\ 
 
 T 
 
 L 
 
 Fig. 27. A portion of one of the large olive-brown seaweeds (Fucus 
 vesiculosus), showing the air-containing cavities, L, that act as floats 
 or buoys; T, thallus or vegetative portion; F, fruit-bearing tips. 
 (Natural size.) 
 
 terized by having the seed inclosed from the earliest 
 stage in a special structure, the fruit, and including the 
 great bulk of vegetation existing at the present day. 
 
 Submerged aquatic plants show the least amount of 
 specialization in connection with protection against either 
 enemies or climate, and in such primitive groups as the 
 Algae protective arrangements are almost entirely absent; 
 
96 BOTANY. [CHAP. m. 
 
 it is true that in some species the taste is very pungent, 
 but this does not avail them against the nibblings of cer- 
 tain molluscs. In other species specialized strands of 
 cellulose are present for the purpose of strengthening the 
 cell-walls and to neutralize the strain exerted on the 
 tissues by the movement of the water ; others, again, 
 have special contrivances in the way of hollowed-out 
 portions of the thallus or vegetative portion of the 
 plant that contain air for the purpose of enabling the 
 plant to float on the surface of the water, and thus ex- 
 pose itself to light in connection with the function of 
 assimilation. 
 
 Notwithstanding the primitive nature of the Algse as 
 a group, we find the leading ideas of plant life clearly 
 indicated within the group. In the simplest unicellular 
 or one-celled microscopic forms, the single cell is often 
 spherical, and even when we come to multicellular spe- 
 cies consisting of numerous cells, the same idea of 
 solidity is present; but in the higher groups we find 
 this weak point rectified, and the substance of the vege- 
 tative portion flattened out into comparatively thin sheets 
 leaves in fact in function for the purpose of exposing 
 the greatest amount of area possible from a given quan- 
 tity of material, thus enabling the organism to assimilate 
 a greater amount of food, an indispensable necessity for 
 the well-being of the individual. In connection with 
 reproduction, or the continuation of the species in time, 
 there is a sequence from the primitive asexual or vegeta- 
 tive mode to highly differentiated sexual methods, which 
 are so arranged as to render possible the invigorating 
 influence of cross fertilization; and from the algae up- 
 wards, the great variety of forms occurring in plant life 
 
CHAP, in.] PROTECTIVE ARRANGEMENTS. 97 
 
 are to a great extent due to the various successful and 
 unsuccessful modifications of the crude ideas of nutrition 
 and reproduction that were contemporaneous with the 
 appearance of the simplest members of the Vegetable 
 Kingdom. 
 
 The most complete and highly differentiated protec- 
 tive arrangements are met with in Phanerogams, and 
 even here the aquatic forms show least specialization in 
 this respect. Amongst terrestrial species the modes of 
 protection even against the same enemy are very varied 
 in the different species. Leaving for the present the con- 
 trivances for protection in connection with the repro- 
 ductive portion (that will be described later on) , we find 
 the various arrangements for protecting the individual to 
 fall under two headings protection against climate, and 
 protection against living enemies. As would be expected, 
 the two divisions meet and overlap at many points, for it 
 may be stated as a general rule that every case of spe- 
 cialization originates for the performance of a certain 
 specific function, and if the experiment proves a success, 
 and consequently becomes a permanent feature, further 
 modifications are superadded which may serve purposes 
 widely different from the original, and thus by various 
 modifications and amendments, such structures, that 
 originated in a simple form and for a specific purpose, 
 become extremely complicated, not only by the addition 
 or modification of parts that still perform functions of 
 service to the plant, but also by the remains in various 
 stages, of structures that at one time performed work of 
 real service to the individual, but which for some reason 
 or other have been superseded; but such structures, 
 when once fully evolved, cannot be at once arrested by 
 
 H 
 
98 BOTANY. [CHAP. in. 
 
 the plant when no longer of service, but remain for a 
 long time in a rudimentary condition. 
 
 (i.) Protection against climate. All climatic condi- 
 tions are not equally favourable for the development of 
 plant life, and as would be expected, in proportion as 
 plants have adapted themselves to live under more and 
 more unfavourable climatic conditions, the more marked 
 will be the modifications undergone to combat these con- 
 ditions. Taking as the typical plant structure living 
 under favourable conditions, we find in the majority of 
 instances a stem more or less erect, and bearing flattened 
 leaves, borne in a scattered manner on branches for the 
 purpose of exposing each leaf to the light, an indispen- 
 sable condition for the performance of its functions, as 
 already explained. A marked departure from this 
 general arrangement of stem and leaf is illustrated by 
 certain groups of plants that grow in very arid regions. 
 The cactus family, characteristic of and almost entirely 
 confined to the dry regions of Western North America, 
 is remarkable for the partial or complete suppression of 
 leaves, but to compensate for the arrest of these impor- 
 tant organs, the stem is furnished with chlorophyll, and 
 usually has prominent ridges or wings, for the purpose 
 of exposing a larger amount of assimilating surface than 
 would be the case with the ordinary cylindrical trunk. 
 Clusters of spines that originate from certain abortive 
 buds are usually present, and act as protective organs 
 against herbivorous animals that would otherwise browse 
 on the succulent and watery stems. In Central Africa a 
 similar habit is assumed by the members of a widely-sepa- 
 rated order of plants, the spurges ; in fact, so close is the 
 resemblance in habit that these plants are usually consi- 
 
CHAP, in.] PROTECTIVE ARRANGEMENTS. 99 
 
 dered as cactuses by travellers. The object of the above de- 
 scribed modification is obvious ; if ordinary leaves were 
 developed, the extreme heat and aridity would cause tran- 
 spiration of water to take place at a much greater rate from 
 the thin layers of tissue than could be supplied by the 
 roots, the leaves would consequently become flaccid and 
 unable to perform their functions, whereas when the entire 
 mass of tissue is embodied in a solid, succulent trunk 
 furnished with chlorophyll, less surface is exposed, and a 
 phase of life, if not the highest, is maintained. It is a 
 case of doing the best under the circumstances, and, as 
 would be expected, cactuses have not made any startling 
 development since they adopted their present mode of 
 life. As a rule, plants of dry regions are characterized 
 by thick fleshy leaves, and the stem remains green and 
 succulent, thus aiding the leaves in the functions of 
 assimilation, respiration, etc. 
 
 The most modern group of plants, the Angiosperms, 
 are divided into two primary divisions : Monocotyledons, 
 including the palms, lilies, grasses, sedges, etc., and 
 Dicotyledons, that includes all European forest trees 
 except the firs and pines that belong, as previously 
 stated, to the Gymnosperms, and the great bulk of 
 smaller flowering plants excepting the groups named 
 above. The broad features of evolution presented by 
 leaves can be well studied in the sequence presented by 
 the members of our own flora. In Monocotyledons, 
 geologically the oldest group, the leaves are generally 
 long and narrow and with the edge or margin entire 
 or uncut, as seen in grasses, sedges, daffodils, lily of 
 the valley, etc. Such structures agree literally with 
 the stock definition of a leaf, as given in antiquated 
 
100 BOTANY. [CHAP. in. 
 
 text-books " a flattened- out expansion of the stem ;" 
 and this is in reality what the typical leaf originally 
 is, an expansion of a plate of tissue containing all 
 the important elements of the stem, to which it is 
 attached by a broad base, with the fibro- vascular bundles, 
 or veins, sunk in the parenchymatous portion, running 
 in a parallel series and not forming a network; and 
 when the leaves grow erect, as in the grasses, irises, etc., 
 the two surfaces agree in structure ; in fact, it may be 
 said that the utility of the leaf was thoroughly realised 
 by monocotyledonous plants, and the fundamental idea 
 thoroughly developed, whereas in the dicotyledons those 
 improvements and finishing touches were evolved that, 
 surface area being equal, enables the perfectly- evolved 
 leaf of the Dicotyledon to do far more work than its 
 primitive monocotyledonous prototype. 
 
 In the dicotyledonous leaf there is often a more or 
 less elongated stalk or petiole that serves to carry the 
 leaf away from the branch producing it and placing it 
 under favourable conditions with regard to light. As a 
 rule, the leaves are placed horizontally, and exhibit 
 a bilateral structure ; that is, having the two sides diffe- 
 rently organized, as already explained, thus introducing 
 a division of labour not met with in the leaves of the 
 majority of Monocotyledons. The fibro-vascular bundles 
 are well developed, the larger branches being connected 
 by innumerable small veinlets, the whole forming a 
 complicated network best seen in the so-called C( skeleton 
 leaf/' This arrangement of the veins insures a supply 
 of material for assimilative purposes to every part of the 
 leaf, and also at once removes the assimilated material 
 from the leaf to be utilized at once in other parts of the 
 
CHAP, in.] PROTECTIVE ARRANGEMENTS. 
 
 101 
 
 plant or to be stored up for future use. Although the 
 points already enumerated show the higher development 
 of the dicotyledonous over the monocotyledonous leaf, 
 yet undoubtedly the greatest advance made by the leaves 
 of the group under consideration is that connected with 
 
 Fig. 28. Leaf of melon, a typical Dicotyledon, showing stalk or 
 petiole, prominent anastomosing veins forming a network and pro- 
 jecting from the under surface, also the cut edge or margin. 
 
 protection against both climate and living enemies. 
 The former only will be considered at present. In 
 Monocotyledons, the leaf, when once fully expanded, 
 remains rigid and motionless, its working surface being 
 constantly exposed to the chills of the night air and to 
 the dust settling down and covering up its chlorophyll 
 
102 BOTANY. [CHAP. in. 
 
 and stomata, for it will be remembered that leaves can 
 only perform their most important function, that of 
 assimilation, when exposed to light; hence it would be 
 a great advantage if leaves could pack themselves up 
 during the night when unable to work, and this point 
 has been reached by many Dicotyledons. The leaves of 
 many Dicotyledons are still rigid and incapable of pro- 
 tecting themselves by closing up at night or on dull days 
 when the light is insufficient to enable them to perform 
 their functions ; but the vast majority are moving in 
 this direction, the first indication of such a move being 
 an indication of toothing along the margin. From the 
 primitive phase of cut margin as illustrated by the 
 cherry or apple leaf, there is a sequence in the depth 
 of the indentations through the stage presented by the 
 ivy and the dandelion, until eventually we get the 
 cutting so deep that it reaches to the principal vein or 
 midrib of the leaf, and the portions of cut-up blade or 
 lamina are only attached to the midrib by the principal 
 vein of each portion of the leaf by a joint or articu- 
 lation that renders possible the movement of the 
 jointed portion called a leaflet; when this stage has 
 been reached the leaf is described as compound. There 
 are two types of compound leaf, the earliest being 
 illustrated by the dog-rose, and known as the pinnate 
 type, where several pairs of leaflets are arranged 
 at some distance apart along the midrib, the latter 
 being terminated by a single leaflet ; the leaves of 
 peas, beans, and laburnum belong to this type. The 
 second plan is where all the leaflets spring from the end 
 of the stalk like a fan, as in the horse-chesnut and lupin. 
 This last arrangement is brought about by the arrest or 
 
CHAP, in.] PROTECTIVE ARRANGEMENTS. 103 
 
 non- development of the naked portions of the midrib 
 between the pairs of leaflets in the pinnate type. 
 
 When a species has reached the stage of producing 
 compound leaves, the next step necessary for the folding 
 up of the leaf is the evolution of a certain amount of 
 irritability or re sponsion to external agents, as light and 
 heat, by the protoplasm. The closing of the leaflets of 
 compound leaves is usually influenced by the relative 
 
 Fig. 29. A digitately compound leaf of the horse-chestnut (dEscu- 
 lus hippocastanum). The young leaves are sensitive and close up at 
 night. 
 
 amount of light, providing the temperature is sufficiently 
 high. The closing and opening depends entirely on 
 changes taking place in the joints or articulations of the 
 leaflets and of the joint that connects the entire leaf to 
 the branch. These changes again are due to the move- 
 ment of water from the cells of one side of the joint 
 to the other, the movement of the water being set up 
 by the influence exercised by external agents on the 
 
104 BOTANY. [CHAP. m. 
 
 protoplasm. The closing and opening of leaves is well seen 
 in the wood sorrel (Oxalis acetosella), many of the clovers 
 (Trifolium) , etc., and more especially in what is popu- 
 larly known as the " sensitive plant " (Mimosa pudica), 
 where this faculty has become so thoroughly perfected 
 as to be not only influenced by the amount of light, 
 which usually causes the closed or " sleeping " condition 
 during darkness, and the " waking " or expanded con- 
 dition during the day, but to respond at once to the 
 slightest mechanical irritation, and in this case the trans- 
 mission of local irritation from one part of the plant to 
 another, equivalent to the transmission by nerve-power 
 in the animal world, causes every leaf on the tree to 
 close within a minute or two after the slightest touch at 
 any one point, even the irritation caused by touching a 
 leaf with, say, the point of a pencil. 
 
 The amount of work done by a given area of leaf 
 surface depends on the amount of light received by 
 every portion of that surface ; consequently the arrange- 
 ment of leaves from this point of view is of great impor- 
 tance. In many Monocotyledons, as the grasses, sedges, 
 and most bulbous plants, most or all the leaves spring 
 from one point near the ground ; this is also the case 
 with some Dicotyledons, as the dandelion, dog-daisy, 
 primrose, etc. Such an arrangement of leaves in the 
 form of a rosette is a primitive and comparatively im- 
 perfect method, inasmuch as some of the lower leaves, 
 after costing energy and material to make, are of little 
 service to the plant, being overshadowed by the upper 
 leaves ; this weak point was remedied to some extent 
 by the development of a tall stem that elevated the 
 leaves and exposed them to more favourable conditions 
 
Fig. 30. A tropical orchid (Oncidium Papilio] showing a rosette of 
 leaves springing from a very short stem near the root, hence called 
 radical leaves. (Reduced. ) 
 
106 BOTANY. [CHAP. iu. 
 
 for fulfilling their functions ; but in the cycads, screw- 
 pines, and palms, the leaves still retained the densely 
 crowded rosette arrangement, whereas in Dicotyledons 
 this difficulty was removed by lengthening the stem 
 between the individual leaves, which resulted in their 
 being scattered at distant intervals on the twig, as in 
 the ash, oak, rose, etc. 
 
 Plants belonging to cold regions are characterized 
 by having the leaves covered with a dense felt of soft 
 interwoven hairs for purposes of warmth. When such 
 plants are acclimatized to warmer regions, this protec- 
 tion in many instances is much reduced or completely 
 disappears. 
 
 The protection of the individual by various modifica- 
 tions that enables a given amount of leaf surface to do 
 the greatest possible amount of work, is very clearly 
 shown in the evolution of the stem or trunk. In Mono- 
 cotyledons, as already explained, the trunk is usually 
 unbranched, and bears at the top a dense rosette of large 
 leaves as in the palms ; one or two palms and the screw- 
 pines are exceptional in having a branched stem, but the 
 leaf arrangement is the same. In Dicotyledons we find 
 the main trunk broken up into numerous spreading 
 branches bearing many small leaves scattered at inter- 
 vals on the twigs, so that practically every inch of leaf 
 surface is fully exposed to the light, and consequently 
 there is no manufacture of leaf material that when made 
 cannot fully perform its functions on account of imper- 
 fect exposure to light. From geological evidence, the 
 earliest type of stem for the purposes of removing the 
 leaves beyond the reach of herbivorous animals, and at 
 the same time exposing them to light and air, was the 
 
Fig. 31. The screw-pine (Pandanus candelabrum], a Monocoty- 
 ledon that has developed a stem and assumed tree-like proportions, 
 but the leaves are still developed in dense terminal clusters. The 
 plants inhabit swamps, and the numerous roots sent down from the 
 stem are for the purpose of giving stability to the plant in the loose 
 mud. (Much reduced. ) 
 
108 BOTANY. [CHAP. in. 
 
 rigid, erect, woody trunk, an ancient type of which is 
 shown at fig. 25. This plan of structure, with various 
 modifications as it passed through Monocotyledons with 
 the single terminal bud, to the dicotyledonous plan of 
 breaking up into numerous branches and bearing an 
 indefinite number of buds, is even at the present day 
 most general, and certainly such a framework as seen in 
 the oak or the beech is a very effectual arrangement for 
 defying the elements under ordinary circumstances. In 
 the mode of arrangement of the branches there is a 
 gradual evolution or improvement observable, that is 
 most to the purpose that of equally exposing all the 
 leaves to light in the latest phase of plant development, 
 the dicotyledonous group. In the Gymnosperms, the 
 usual arrangement of the branches is in whorls or 
 verticils produced at intervals on the stem; these whorls 
 of branches grow out at right angles to the stem, and the 
 secondary branches all grow in the same plane forming 
 tier above tier, each one overshadowed by the tier above, 
 and consequently only receiving a comparatively small 
 amount of light as compared with the typical dicotyle- 
 donous arrangement as illustrated by the ash or the oak, 
 where the numerous primary branches start from the top 
 of the trunk and spread in every direction, the youngest 
 portions that bear the leaves being always produced at 
 the circumference of the head, consequently the great 
 bulk of the leaves are produced at the circumference 
 where they are fully exposed to light. In spite of the 
 many modifications and improvements, external and 
 internal, already indicated, the massive trunk idea 
 must be considered as a failure, its advantages being 
 neutralized by its extreme cost to the plant, for it must 
 
CHAP, in.] PROTECTIVE ARRANGEMENTS. 109 
 
 be remembered that every particle of the enormous 
 amount of material constituting the trunk and branches 
 of a tree have been converted by the plant into what 
 they are from inorganic matter derived from the air and 
 the soil, borrowed as it were for a purpose by the plant, 
 and retained so long as its own life-force predominates, 
 and all this enormous amount of work for the purpose of 
 protecting itself from enemies and securing the share of 
 light necessary for holding its own in the struggle for 
 existence. This arrangement also places the flowers or 
 reproductive organs in favourable positions for securing 
 cross-fertilization, and thus secures as far as possible the 
 continuance of the species in time. It may be asked, if 
 the development of the trunk has done so much for the 
 vegetable kingdom, what more can be desired. We are 
 not cognizant of the possibilities of life, not even plant 
 life ; and if all the above advantages can be secured with 
 a less expenditure of energy, it will by most people be 
 admitted as an improvement, and expressing plant ideas 
 from the human method of reasoning, many modern 
 plants have realised this fact, and have in part or entirely 
 forsaken the old-fashioned massive trunk idea, which may 
 be described as the method of accomplishing an object by 
 brute force, depending on sheer strength, regardless of 
 cost, and in its place developed a certain amount of sen- 
 sibility a step in the direction of the animal kingdom 
 manifested by the more highly organized protoplasm 
 possessing a greater control over other forces, as light 
 and heat, and utilizing them for its own advantage. It is 
 impossible in the space at command to trace all the 
 varied attempts in this connection, and all that can 
 be done is to indicate the modern methods that have 
 
110 BOTANY. [CHAP. in. 
 
 superseded the old-fashioned woody trunk. The long, slen- 
 der, weak-stemmed climbing and twining plants illustrate 
 the later method. As British examples, we may mention 
 the ivy, honeysuckle, convolvulus, etc. ; amongst exotic 
 plants, the vines, and those numerous forms that stretch 
 from tree to tree in tropical forests. Our roses and 
 brambles illustrate an incipient attempt in this direction, 
 their spines, that were in all probability protective 
 against animals, becoming in many species curved down- 
 wards, and serving as anchors that hook on to neigh- 
 bouring plants, and thus become elevated to a certain 
 extent at the cost of the neighbour. The method by 
 which the ivy clings to its support has been already 
 explained. Coming to such plants as the hop, where 
 the stem twines round a suitable support, we encounter a 
 higher stage of development due to the influence of 
 light, or rather to the more highly organized protoplasm 
 being enabled to utilize light to a greater extent than 
 plants lower down in the scale of life. The highest 
 stage of development reached by plants that have 
 adopted the long slender stem is illustrated by the grape- 
 vine and most of the peas and vetches. In such plants 
 the stem does not coil round a support, but is firmly 
 anchored by numerous slender threads known as tendrils 
 that become firmly coiled round the slender branches of 
 other trees. These tendrils are not new special parts 
 developed for this purpose in addition to the parts pre- 
 viously possessed by such plants, but are old parts 
 modified to serve this special purpose. The tendrils of 
 the vine are modified flower-stalks, those of the peas and 
 vetches in like manner are portions of the leaves. 
 Tendrils differ from twining stems in not coiling up 
 
Fig. 32. A species of passion-flower (Pussiflora caeriilea), showing 
 tendrils that are coiled up at the tip. (Natural size.) 
 
112 BOTANY. [CHAP, in, 
 
 under the influence of light and heat alone, this move- 
 ment depending on mechanical irritation. If the tendrils 
 of the passion-flower or those of the bryony (Bryonia, 
 dioica) are examined, it will be seen that in the young 
 condition they spread out from the stem either straight 
 or slightly curved, and remain for some time in this 
 condition, until the weak branch bearing them is brought 
 into contact with some neighbouring branch by the 
 wind or some other means, or in some plants the tendrils 
 themselves revolve, searching for a suitable body round 
 which they can coil. If the tendrils come in contact 
 with a flat surface or a thick branch, no change takes 
 place, but when made to touch a thin twig, the tendril 
 within a short time coils its tip round the support, and 
 then becomes rigid, so that it cannot be uncoiled without 
 breaking. This rigidity is necessary to prevent the 
 coiled portion being drawn out by the weight of its own 
 branch when moved by the wind. After the tip of the 
 tendril is firmly fixed to its support, the intermediate 
 portion undergoes a spiral contraction by which the 
 tendril is shortened. This spiral contraction of that 
 portion of the tendril between its base and tip is of value 
 from two points of view ; it gives elasticity, and conse- 
 quently greater strength, and also draws the branch 
 higher up so as to expose its leaves more fully to the 
 light. If a tendril that has become attached by the tip is 
 examined, it will be seen that one portion of the interme- 
 diate part is twisted in one direction and another portion 
 in the opposite direction, with an intermediate straight 
 part; but for this arrangement, it will be understood 
 that a body fixed at both ends and undergoing spiral 
 contraction would be ruptured. 
 
CHAP, in.] PROTECTIVE ARRANGEMENTS. 113 
 
 (2.) Protection against living enemies. The modifi- 
 cations undergone by plants necessitated by climatic 
 influence are not more varied than those required to 
 combat successfully the attacks of living enemies, and 
 the difficulty in the latter case is intensified by the fact 
 that, being possessed of life, and consequently possess- 
 ing the power of modification or adaptation to circum- 
 stances it follows that when a plant has evolved an 
 arrangement to ward off the attacks of its special enemy, 
 the latter in turn changes its tactics, and by a similar 
 modification often successfully overcomes the obstacle 
 placed in its way. There is no evidence in support of 
 the view that plants or animals were specially created to 
 serve as food for their neighbours, and wherever this 
 happens it always resolves itself into the condition of the 
 victim being overcome by the superior physical or 
 mental power of the victor. Man's mental development 
 has placed numerous members of both the plant and 
 animal kingdoms under his control, and this sphere of 
 influence has gone on increasing with the development 
 of that power. The same ideas are true of groups of 
 plants ; the forest tree type of vegetation with the 
 massive trunk and spreading branches at one time bid 
 fair to become the dominant race, but the sheer strength 
 method on which they depended has been superseded by 
 the greater adaptivity and more especially the greater 
 susceptibility of the protoplasm to external agents, in 
 the smaller members of the Vegetable Kingdom, and 
 many of these latter are now utilizing the trunks of the 
 older type as a means of support ; in some instances 
 strangulation of the trunk is effected by the modern 
 twiner, as in the honeysuckle, or is compelled by the 
 
114 BOTANY. [CHAP. in. 
 
 dominant parasite to surrender a portion of the food 
 elaborated for its own use. 
 
 Amongst the most prominent and general modes of 
 protection of vegetative parts against the attacks of 
 living enemies may be mentioned prickles, as in roses 
 and brambles, which may either be straight, and thus 
 prevent the nibblings of animals, or in more advanced 
 species, curved, thus enabling the weak stem to climb 
 and carry its leaves out of harm's way. 8 pines, that are 
 sharp-pointed abortive branches, serving the same pur- 
 pose as prickles, as in the common sloe or blackthorn 
 (Prunus spinosa). Rigid hairs on leaves and stem, as 
 in the borage (Borago officinalis) , and comfrey (Symphy- 
 tum officinale}. Stinging hairs, as in the common nettles 
 (Urtica dioica, and Z7. urens), in these cases the stinging 
 hairs are mixed on the leaves and stem with ordinary 
 rigid hairs, of which they are higher developments, dis- 
 tinguished by the lower or basal swollen portion of the 
 hair containing an irritating liquid that is ejected when 
 the tip of the hair is broken off. Sitter taste, often 
 accompanied by a strong scent, as in wormwood (Arte- 
 misia vulgaris), chamomiie (Anthemis nobilis) , and the 
 leaves and fruit of the walnut (Juglans regia). Poisonous 
 alkaloids, as in the species of Strychnos, which contain 
 two very poisonous alkaloids, strychnine and brucine, in 
 the root and the seeds; decoctions of species of Strychnos 
 are used by the Javanese and the natives of South 
 America to poison their arrows. Some of the species, 
 as Strychnos nux-vomica, are valuable medicines, depend- 
 ing on the strychnine they contain, which acts as a 
 powerful excitant of the spinal cord and nerves ; thus the 
 most effective protective arrangements evolved by plants 
 
CHAP, in.] PROTECTIVE ARRANGEMENTS. 115 
 
 can be turned to account, and consequently lead to the 
 destruction of the individuals they were designed to 
 protect. Our common arum (Arum maculatum) , popularly 
 known as " Lords and Ladies/' has an intensely acrid 
 substance present in the leaves, which effectually protects 
 it from the attacks of mammals and caterpillars, but not 
 from the attacks of parasitic fungi, which appear to be 
 
 Fig. 33. " Lords and 
 Ladies " (Arum macu- 
 latum), a plant that 
 protects its leaves from 
 mammals and insects 
 by the presence of an 
 acrid substance. (Re- 
 duced. ) 
 
 indifferent to all protective contrivances exhibited by 
 plants, nearly every plant supporting one or more of 
 these minute pests, the effects of which will be realized 
 by mentioning the potato disease, " rust " and " smut " 
 in the various cereals, and the hop disease, all due to 
 parasitic fungi. The leaves of many exotic evergreens 
 are often much injured by the presence of parasitic 
 lichens that spread over the surface. 
 
CHAPTER IV. 
 
 REPRODUCTION OF PLANTS. 
 
 Vegetative or asexual method. Sexual method. Gradual evo- 
 lution and advantages of the latter method. Alternation of genera- 
 tions. Cross-fertilization. Protection of reproductive portions of 
 plants. 
 
 IN many of the primitive types of plant life the 
 only known mode of reproduction is by fission 
 or cell division, as already explained in the case of 
 Pleurococcus vulgaris. In other simple multicellular 
 fresh-water Algae, as the species of Nostoc, that form 
 blue-green or brownish gelatinous masses on damp paths 
 and shady places after wet weather, the cells are arranged 
 in a single row, forming long filaments that are variously 
 contorted and imbedded in mucilage ; during the repro- 
 ductive phase these filaments break up into short pieces 
 which escape from the gelatinous matrix, each fragment 
 forming the starting-point of a new individual, the fila- 
 ment rapidly increasing in length by repeated fission of 
 its component cells. In vegetative or asexual repro- 
 duction the portion destined to form the starting-point 
 of a new individual always consists of one or more cells 
 formed by the ordinary method of cell-division, whereas 
 in the sexual mode the reproductive body is invariably 
 the result of the blending together of the protoplasm 
 
CHAP, iv.] REPRODUCTION OF PLANTS. 117 
 
 belonging to two distinct cells, respectively male and 
 female, which form a single cell. The above examples 
 illustrate the primitive form of asexual reproduction, 
 which involves the destruction or loss of individuality of 
 the parent plant, but commencing with the Algas and 
 running through most groups of Cryptogams we find a 
 higher asexual mode, where specialized and usually com- 
 paratively small portions of the individual are told off 
 for the purpose ; such portions fall away when mature, 
 and in many cases are not distinguished popularly from 
 sexually produced seeds. Although the sexual method 
 of reproduction is universal in phanerogams, yet the 
 primitive asexual method has not completely died out, 
 but manifests itself in a variety of ways. As examples, 
 the propagation of plants by cuttings, which may be 
 considered analogous to the breaking up of a Nostoc 
 into portions capable of reproducing the species or kind, 
 thus proving that all the essentials constituting the life 
 of the individual are present in the protoplasm of every 
 cell ; whereas in the great number of plants that cannot 
 be reproduced vegetatively by cuttings or other asexual 
 methods, the protoplasm has become more sharply diffe- 
 rentiated into series, one capable of governing the work 
 necessary for the existence of the individual, the vege- 
 tative portion, and incapable of exercising the functions 
 necessary for reproduction ; a second concerned specially 
 with reproduction, but with little capacity for vege- 
 tative work. The tubers of the potato and bulbs are 
 also asexual modes of reproduction still retained by 
 phanerogams. 
 
 Sexually formed reproductive bodies, known as seeds 
 in the higher plants, originate, as already stated, from a 
 
118 BOTANY. [CHAP, iv, 
 
 single cell that owes its important properties to the 
 mingling of the whole or a portion of the protoplasm of 
 two distinct cells ; this mingling of protoplasm consti- 
 tutes the act of fertilization. If the two cells concerned 
 in fertilization are produced by the same plant, self- 
 fertilization is the result ; if produced by distinct plants 
 of the same kind, cross-fertilization is effected. 
 
 Sexual reproduction is shadowed in amongst the 
 primitive types of Algae, under the form of motile 
 portions of protoplasm that escape from the cells and 
 swim about in the water by means of very delicate cilia 
 or prolongations of their protoplasmic substance ; such 
 cells are not furnished with a cell-wall, and after swim- 
 ming about for some time, approach each other in pairs, 
 which eventually blend together, withdraw their cilia, 
 and form a cell that soon secretes a cell-wall. This cell 
 either at once, or more frequently after a period of rest, 
 germinates and gives origin to the vegetative condition 
 of a new individual. This, the most primitive condition 
 of sexual reproduction, is known as conjugation. In 
 many cases the two conjugating cells are similar in 
 shape and size, and externally present no functional 
 differences ; in other forms one, presumably the male 
 element, is smaller than the other, the female ; but in 
 many instances bodies that usually conjugate become 
 inclosed in a cell- wall without doing so, and at the 
 proper time germinate and produce plants agreeing in 
 every respect with those originating from cells result- 
 ing from conjugation, proving that the sexual method 
 is not indispensable, but rather in the first phase of 
 evolution. Reproduction by conjugation occurs only 
 in certain groups of the Algaa and Fungi, and in the 
 
CHAP, iv.] REPRODUCTION OF PLANTS. 119 
 
 general evolution of sexual reproduction, one change has 
 been from that primitive condition where the two ele- 
 ments male and female are both motile, or possessed 
 of voluntary movement, to the condition attained by all 
 Phanerogams, where both are passive or motionless, and 
 in numerous instances their union, as will be explained 
 in detail, is effected by modifications of the plant that 
 enable it to utilize external agents for this purpose, as 
 the wind, or even members of the Animal Kingdom, 
 mostly insects. 
 
 A marked differentiation of sexes has been reached in 
 the common large olive-brown seaweeds included under 
 the generic name of Facus (Fig. 27), where the proto- 
 plasm of the female cell becomes divided into four or 
 eight portions depending on the kind examined ; when 
 ready for fertilization the wall of the cell splits, and the 
 separate portions of protoplasm each a cell without a 
 cell- wall escape into the water, but are entirely devoid 
 of voluntary movement ; at the same time the protoplasm 
 of the male cells divides into a large number of minute 
 cells, each furnished with cilia and without a cell- wall ; 
 these cells, called anther ozoids, escape into the water and 
 swim about until they come in contact with a passive 
 oosphere, fertilization being effected by the blending of 
 the two bodies. In Fucus, then, the point has been 
 reached where the female organ is passive or motionless ; 
 but the peculiarity of this batch of plants consists in the 
 female portion or oosphere escaping from the parent 
 plant before fertilization, a weak point, not to say a 
 decided mistake, and terminating abruptly with the 
 small batch of seaweeds where it originated, the weak 
 point consisting in the absolute necessity on the part of 
 
120 BOTANY. [CHAP. iv. 
 
 the fertilized body, on germination, to commence assimi- 
 lating food for itself from the very first, even before a 
 single additional cell could be added to its size, whereas 
 where the oosphere remains in contact with the whole 
 or a portion of the parent plant after fertilization, a 
 certain amount of food is supplied by the parent which 
 gives the germinating plant a start in life, in fact, 
 supplies it with a reserve of food that it can draw upon 
 until it has built up assimilating structures ; hence, other 
 things being equal, it is not to be wondered at that the 
 free oosphere idea is not dominant. 
 
 In some species of Fucus, in fact in most, a given 
 plant produces either antherozoids or oospheres only ; in 
 fact, the plants are male or female, hence cross -fertiliza- 
 tion is absolutely secured. 
 
 In the remainder of the Cryptogams, as the mosses, 
 ferns, and club-mosses, the oosphere is motionless and 
 remains in contact with the parent plant at least until 
 germination commences, the antherozoids in all cases 
 being motile, as in Fucus, and reaching the oosphere 
 through the agency of water, and this point more than 
 any other constitutes the distinction between Cryptogams 
 and Phanerogams, the two primary divisions of the Vege- 
 table Kingdom. This in turn explains the absence 
 from Cryptogams of those showy portions of the flower 
 so conspicuous in most Phanerogams, and evolved for 
 the purpose of attracting insects in connection with 
 fertilization, the methods of which will eventually be 
 described in detail. Eemembering that the primordial 
 types of plant life were aquatic forms, the advantage of 
 voluntary movements of the portions concerned with 
 fertilization in such is obvious, the male organs or 
 
CHAP, iv.] REPRODUCTION OF PLANTS. 121 
 
 anther old s swimming freely in the water until they 
 came in contact with the oospheres. The various at- 
 tempts of ancient aquatic types to establish themselves 
 on dry land was finally accomplished through the liver- 
 wort (Hepaticce) and moss (Musci) groups, which form a 
 connecting link between the primordial aquatic Algae 
 and the dry land vegetation of the present day ; never- 
 theless the mode of fertilization by means of motile 
 antherozoids that reached the oospheres by swimming 
 in water was so strongly stereotyped that, as already 
 stated, it held good through the liverworts (Hepaticce), 
 mosses (Musci), horsetails (Equisetacece), ferns (Filices) , 
 club-mosses (Lycopodiacece), and other groups consti- 
 tuting the Cryptogams, even after these groups had 
 become much modified in other respects to enable them 
 to live surrounded by dry air, and the tardiness dis- 
 played in effecting a corresponding change in the mode 
 of effecting fertilization is the main reason why the 
 above groups are more limited in their distribution, and 
 take a back place in the social scale of vegetation 
 growing on dry land at the present day. The drawback 
 alluded to is due to the fact that the sexual mode of 
 reproduction necessitates the presence of water to enable 
 the motile antherozoids to come in contact with the 
 oospheres ; hence Cryptogams are as a group confined 
 to damp situations, or the sexually produced repro- 
 ductive bodies are formed during the winter, as seen 
 in our mosses, that look bright and vigorous during 
 that period of the year, and shrivel up during the 
 summer if growing in dry situations, conditions that 
 are not followed by those members of the plant world 
 that have made most progress. 
 
122 BOTANY. [CHAP. iv. 
 
 It lias been already stated that on the evolution and 
 perfection of the sexual mode of reproduction, the more 
 antiquated asexual mode did not at once disappear, but 
 lingered on, and manifests itself even amongst the most 
 advanced of dry land plants, yet from a broad point of 
 view it is seen that the asexual mode of reproduction 
 degenerated in proportion as the sexual mode became 
 perfected ; and in many of the higher plants, where the 
 asexual mode is at the present day predominant, as in 
 many bulbous plants, this is due to a resuscitation of the 
 old method necessitated by surroundings being unfavour- 
 able for the continuance of the sexual method. 
 
 Amongst Cryptogams we find as a rule the asexual 
 and sexual modes of reproduction both present, and in 
 many groups occurring at definite periods in the life- 
 cycle of the individual. This regular alternation of the 
 two modes is known as Alternation of Generations, a 
 phenomenon clearly illustrated in the ferns and mosses. 
 It is generally known that towards the autumn the under 
 surface of the fronds of ferns bear dark brown patches, 
 either as rounded spots or elongated streak-like lines, 
 depending on the kind of fern examined ; these patches 
 consist of exceedingly minute one-celled reproductive 
 bodies called sporeSj that are produced in numbers in 
 special structures called sporangia. Each spore, when 
 placed under favourable circumstances, is capable of 
 germination and producing eventually a new fern plant. 
 On germination the spore first gives origin to a slender 
 filament which, by cell-division at the tip, soon expands 
 and forms a small structure lying flat on the ground 
 and rarely exceeding a quarter of an inch in diameter ; 
 this is called a prothallus, and constitutes the first or 
 
CHAP, iv.] REPRODUCTION OF PLANTS. 123 
 
 sexual stage in the life-cycle of the fern. All the cells 
 of the prothallus contain chlorophyll, and after existing 
 for some time doing vegetative work the reproductive 
 stage is entered upon; certain of the cells undergo a 
 series of changes, resulting in the formation of oospheres, 
 other cells giving origin to antherozoids. The oosphere 
 after fertilization is called an oospore, and lies perfectly 
 free in a special portion of the prothallus, but is not 
 organically attached to it in any way, secreting a new 
 cell- wall of its own after fertilization, and forms the 
 starting-point of the second (asexual) stage or genera- 
 tion, which closes the life-cycle of the fern. The oospore 
 by cell-division develops directly into what is popularly 
 considered as the whole of the fern plant ; that is, the 
 portion bearing green fronds, these in turn producing 
 the spores on the under surface, these spores are not 
 the result of sexual fertilization as in the case of the 
 oospore produced by the prothallus, but are purely 
 asexual or vegetative in origin, and on germination pro- 
 duce the sexual generation. Alternation of generations 
 first showed itself distinctly when plants succeeded in 
 establishing themselves on dry land, and in the mosses 
 and ferns the two generations are very sharply defined, 
 but in the last-named group this idea of having two 
 distinct phases in the life-cycle of the individual, con- 
 nected at one stage by a single cell the oospore 
 attained its maximum, and in the groups that followed, 
 as the club-mosses, selaginellas, quilworts, etc., the 
 sexual generation as a distinct and vegetative structure 
 became gradually suppressed, and in phanerogams has 
 altogether disappeared, the only remaining portion being 
 the indispensable sexual organs pollen grains and 
 
124 BOTANY. [CHAP. iv. 
 
 oospheres, the latter after fertilization forming by cell- 
 division the embryo or young plantlet, which is for some 
 time protected and supplied with food from structures 
 belonging to the asexual phase of the parent plant, the 
 whole forming the seed. From the above it will be 
 observed that the entire bulk of every phanerogam is 
 homologous with the asexual phase of those cryptogams 
 having distinct alternation of generations. 
 
 The advantages of the changes indicated depend on 
 the fact that in cases of cross-fertilization a greater 
 number of seeds are produced than by self- fertilized 
 plants of the same kind, and further, the seeds resulting 
 from cross-fertilization produce stronger and more 
 vigorous plants than those resulting from self-fertiliza- 
 tion ; consequently those groups of plants showing a 
 tendency to favour the sexual mode of reproduction, 
 being more robust than the other types, took possession 
 of the most favourable positions and spread at a much 
 greater rate than those cryptogams encumbered with 
 sexual and asexual phases, because the latter mode did 
 nothing towards invigorating the species, consequently 
 in phanerogams, as already stated, the presence of the 
 asexual mode of reproduction is either a remaining 
 vestige of the old idea, or its revival under conditions 
 unfavourable for the full development of the sexual 
 method of reproduction. 
 
 The term " flowerless plants," as often applied to 
 cryptogams, is misleading, in fact, not correct ; the idea 
 of a flowering plant being one that reproduces itself 
 sexually, a condition true of the great majority of 
 cryptogams, but, as already explained, the particular 
 method by which the antherozoid or fertilizing body 
 
CHAP, iv.] REPRODUCTION OF PLANTS. 125 
 
 reaches the oosphere does not necessitate the presence 
 of those showy and conspicuous portions that popularly 
 constitute the flower. The latter was considered by the 
 older botanists to be entirely absent, hence the origin of 
 the term " flowerless plants/' a mistake which, on account 
 of its being a mistake, still persists. 
 
 The progress made by the higher cryptogams in 
 getting away from their primordial aquatic habitat and 
 taking possession of the dry land has been noticed, also 
 the drawback to further extension in this direction 
 owing to the retention of the ancient mode of fertiliza- 
 tion, which depended on the presence of a certain amount 
 of moisture to enable the antherozoid to reach the 
 oosphere. This drawback was first overcome by the 
 group of plants known as Gymnosperms, the earliest of 
 phanerogams, where the fertilizing body, instead of 
 being a naked motile cell antherozoid consists of a 
 cell furnished with a cell-wall, and not possessed of 
 spontaneous movement, consequently the means of 
 reaching the oosphere for the purpose of effecting fer- 
 tilization depended on one of the two following methods. 
 (1) The stamens producing the pollen, and the pistil 
 containing the oospheres, or ovules, as they are generally 
 termed in phanerogamic plants, are placed in such close 
 proximity that the pollen falls directly on to the ovules 
 or stigma; or, (2) when the stamens and pistils are 
 produced at a distance from each other, the transporta- 
 tion of the pollen to the pistil depended entirely on 
 external agents, generally wind or insects. The first 
 method implied self-fertilization, the second, generally 
 cross-fertilization, and to the second method, which in 
 its most perfect and economical way is effected by the 
 
126 BOTANY. [CHAP. iv. 
 
 agency of insects, is due the evolution of those parts of 
 the reproductive structure possessing colour usually 
 the corolla scent, and nectar. 
 
 The typical flower of a phanerogamic plant, as shown 
 
 Fig. 34. Fuchsia globosa, a Phanerogamic plant with a complete 
 flower, that is, having the four whorls, calyx, corolla, stamens, and 
 pistil present. (Natural size.) 
 
 in the diagramic representation on p. 31, consists of four 
 whorls or verticils, the lowest on the axis or flower-stalk, 
 and outermost is the calyx, function protective; next the 
 'Corolla, function attractive, in the sense of acting as a 
 coloured advertisement indicating to insects the where- 
 
CHAP, iv.] REPRODUCTION OF PLANTS. 127 
 
 abouts of nectar their food the corolla is a feature of 
 the reproductive portion peculiar to phanerogams for the 
 purpose indicated above ; the equivalent of the calyx as 
 a protective organ being present in some cryptogams, as 
 mosses. Following the calyx and corolla are the stamens 
 and pistil, the essential organs. At the present day 
 the flowers of numerous plants do not possess all the 
 parts mentioned above ; of the two essential whorls, some 
 flowers have stamens only, and others of the same 
 species pistils only, but the order of arrangement of the 
 parts present, and the vestiges of the missing whorls in 
 a more or less rudimentary condition suggests that the 
 earliest flowers were hermaphrodite, that is, having 
 stamens and pistil present, and such were in all proba- 
 bility self- fertilized. 
 
 In Gymnosperms the flowers are unisexual, the stami- 
 nate and pistillate flowers being in some species present 
 on the same plant monoecious as in the Scotch fir 
 (Pinus sylvestris) , or the male and female plants are en 
 different plants dioecious as in the yew (Taxus baccata), 
 or as in the juniper (Juniperus communis) the male and 
 female flowers are sometimes on distinct plants, some- 
 times on the same plant, in fact, in cases where the sexes 
 are nominally separated at the present day it is not 
 unusual to meet with all stages of reversion to the old 
 bisexual or hermaphrodite type of flower, clearly indicating 
 the origin of the modern unisex'ual type as being due to 
 the suppression or non-development of one of the two 
 essential whorls for the purpose of preventing self- 
 fertilization. Many Angiosperms also have unisexual 
 flowers, monoecious as in the hazel, arum, etc., dioecious, 
 as the willows, poplars, and hop. The earliest idea in 
 
128 
 
 BOTANY. 
 
 [CHAP. iv. 
 
 connection with preventing self-fertilization, and con- 
 sequently securing cross-fertilization, was the evolution 
 of unisexual flowers, and this was not brought about 
 
 by the special formation of such 
 in addition to those already 
 existing, but, as already stated, 
 by the modification of the old 
 hermaphrodite form of flower. 
 So long as the two kinds of 
 flower stamina te and pistillate 
 were present on the same 
 plant, as in the hazel, the 
 prevention of self-fertilization 
 was not absolute, this point 
 being attained only when one 
 of the two sexes was completely 
 arrested on a given tree, as in 
 the willows, where the bright 
 yellow catkins of the goat wil- 
 low (Salix caprcea) , popularly 
 known as "palms'", are the 
 clusters of staminate flowers, 
 the trees of the same species 
 bearing the female catkins, that 
 are green and inconspicuous, 
 make but little show, and are 
 ignored for decorative purposes. 
 This early attempt to secure 
 cross-fertilization was certainly effective, but too ex- 
 pensive in many ways, and it will be seen that later 
 ideas in this direction were equally effective with a much 
 less expenditure of energy and bulk of material. All 
 
 Fig. 35. The hazel (Cory- 
 lus avellana), a monoecious 
 plant ; $ , pistillate flowers 
 having bright crimson pro- 
 truding stigmas ; <r, cat- 
 kins of staminate flowers. 
 (Natural size.) 
 
CHAP, iv.] EEPRODUCTION OF PLANTS. 129 
 
 the Gymnosperms and many monoecious and dioecious 
 Angiosperms are anemopliilous or wind-fertilized, that is, 
 fertilization depended on the pollen being carried by 
 the wind and brought in contact with the ovule or the 
 stigma. This uncertain method necessitated the produc- 
 tion of enormous quantities of pollen to insure fertiliza- 
 tion, the ( ' showers of sulphur " being in reality wind- 
 transported pollen of pine-trees brought to the earth, 
 and consequently wasted, by rain; this extravagant 
 primitive arrangement was succeeded by more econo- 
 mical and exact methods in Angiosperms. 
 
 Fig. 36. Portion of an ear 
 of wheat, an anemophilous or 
 wind-fertilized plant, showing 
 the protruding anthers sup- 
 ported on long, slender fila- 
 ments or stalks. (Enlarged. ) 
 
 In many anemophilous plants, as the hazel, willows, 
 poplars, etc., the flowers appear in early spring before 
 the leaves, as the presence of the latter would interfere 
 with the pollen being blown on to the stigma. In many 
 species the stamens are suspended beyond the flower on 
 long, slender stalks or filaments, thus enabling the wind 
 to scatter the pollen ; the stigmas are also often elon- 
 gated and project beyond the flower, and are rough with 
 hairs for the purpose of catching the pollen ; these pecu- 
 liarities can be well seen in the grasses and plantains 
 (Plantago) . 
 
 It is in the highest and most modern group of flower- 
 
 K 
 
130 BOTANY. [CHAP. iv. 
 
 ing plants Angiosperms that we meet with the most 
 profound modifications of the flower for the purpose of 
 securing cross-fertilization, insects being the agents em- 
 ployed in transferring the pollen from one plant to the 
 stigma of another plant of the same kind, and in this 
 group of plants the present form, colour, and fragrance 
 of flowers, also the secretion of nectar has gradually 
 evolved through the unconscious selection exercised by 
 insects in their search for food, which is furnished by 
 the sugary liquid or nectar present in many flowers, and 
 this object is the only one the insect has in view, the 
 transportation of pollen being an entirely unconscious 
 act ; and although in many plants that are visited by 
 insects, the chances of meeting with nectar are uncertain 
 as is the chance of cross-fertilization, yet in numerous 
 other instances the modifications that have taken place in 
 both the flower and the insect have resulted in what may 
 be called mutualism, differing only from the mutualism 
 between algae and fungi that form lichens in the two 
 organisms retaining their individuality and liberty of 
 action, yet so thoroughly interdependent that their indi- 
 vidual existence depends equally on the existence of 
 both ; that is, there are certain plants that have become 
 so thoroughly modified that fertilization can only be 
 effected by particular insects, the latter in turn being 
 able to obtain their food alone from the flower they can 
 fertilize. Looking at such a case of perfected mutualism 
 as that just indicated, naturally supports the old idea 
 of a preconceived arrangement and special creation of 
 two distinct forms of life adapted from the first to 
 mutually assist each other, but when we see on every 
 hand other forms of life exhibiting every phase from the 
 
CHAP, iv.] REPRODUCTION OF PLANTS. 131 
 
 crudest attempts in the direction of mutualism as defined 
 above, and further, when careful examination of those 
 members that have reached the highest known stage of 
 perfection in this respect, reveals the presence of degene- 
 rate organs and parts, clearly proving that such have 
 
 Fig. 37. Daffodil (Narcissus pseudo-Narcissus}. A regular or sym- 
 metrical flower having three sepals forming the outer whorl or calyx ; 
 three petals forming the second whorl or corolla, within which is a 
 tubular- shaped additional attractive organ with a frilled margin, the 
 corona, this in turn incloses six stamens and a single style supporting 
 the stigma at its tip. (Natural size. ) 
 
 attained to their present perfection by a series of changes, 
 then the force of the modern idea of evolution, or 
 gradual change of the entire organism or portions 
 thereof to successfully surmount new obstacles or to 
 benefit more from the forces at command, becomes 
 apparent. 
 
132 BOTANY. [CHAP. iv. 
 
 Cross-fertilization was undoubtedly the first and main 
 incentive in promoting the various changes that flowers 
 have undergone for the purpose of facilitating the visits 
 of insects ; but even if this were not the case, the idea 
 would be a success from the economical point of view, as 
 insect - fertilized flowers by their greater exactness of 
 arrangements insure fertilization with a much less expen- 
 diture of material than is the case with either wind- 
 fertilized or self-fertilized plants. In the latter class 
 the flowers are regular in form, that is, the sepals are of 
 equal size, as are also the petals, as illustrated by the 
 buttercup, wild rose, and tiger-lily, and in addition are 
 perfectly free from each other; in fact, the stamp of a 
 primitive flower is the perfect freedom from each other 
 of all its components, a character illustrated by our 
 buttercups ; the stamens in such plants are usually 
 numerous, the haphazard method of fertilization re- 
 quiring a very large amount of pollen to make certain 
 this indispensable process. In some flowers colour has 
 not yet been evolved, but this is usually the case, and 
 numerous flowers have not yet got beyond this stage, 
 which is the first step in the sequence leading up to the 
 fully evolved insect-fertilized flower. Along with the 
 advent of colour, we find as a rule arrangements for the 
 secretion of nectar, the production of which is confined 
 to specially modified portions of the flower called nec- 
 taries. Nectaries occur on different parts of the flower 
 in different plants. In the buttercup a nectary or honey 
 gland is present at the base or narrow point of attach- 
 ment of each petal on its upper surface ; in the colum- 
 bine, a plant belonging to the same order as the butter- 
 cup ( Ranunculacece) , we find each of the five petals 
 
CHAP, iv.] REPRODUCTION OF PLANTS. 133 
 
 prolonged downwards into a hollow horn-like projection 
 or spur, also a nectary ; and in other plants belonging to 
 the same order there is a sequence in the evolution of 
 the nectary from the comparatively unprotected form 
 presented by the buttercup, which is accessible to insects 
 that cannot fertilize the flower, to the elongated spur- 
 like form that secures the nectar from being sipped by 
 insects that cannot fertilize the flower, and at the same 
 time making it more accessible to those long " tongued" 
 insects, as bees, etc., that can effect this object. But, 
 as already mentioned, insects adapt themselves to cir- 
 cumstances as well as plants do, and we find adventurous 
 ants and minute beetles that have a taste for nectar, but 
 cannot fertilize the flower, overcome the difficulty placed 
 in their way by the plant in secreting its nectar at the 
 bottom of a long slender tube or spur, by venturing 
 down the narrow passage. This defeat is in turn 
 remedied in many plants by a further modification of 
 parts ; in the violets the opening to the spur is guarded 
 by the growth of two slender spines from two of the 
 anthers that pass down into the spur, these completely 
 prevent the bodily entrance of any small insect, at the 
 same time leaving sufficient space for the slender tongue 
 of the insect specially adapted to effect fertilization. 
 The common red dead-nettle prevents the entrance of 
 minute insects to the honey situated at the bottom of the 
 tube-shaped corolla by the development of a ring of 
 hairs that grow from the inside of the corolla-tube and 
 meet in the centre. Some short-tongued bees that can- 
 not reach the honey situated at the bottom of a long 
 spur or corolla-tube have acquired the habit of biting 
 through the corolla-tube and sipping the nectar. In the 
 
134 
 
 BOTANY. 
 
 [CHAP. iv. 
 
 common garden nasturtium (Tropceolum majus) the long 
 spur is a development of the calyx. Another advantage 
 
 C' 
 
 Fig. '"38. Lime (Tilia 
 Europcea). Showing a re- 
 gular and perfect flower, 
 with the parts (except 
 those of the pistil) free 
 from each other ; there is 
 no colour in the flower, but 
 bees are informed of the 
 proximity of a lime tree 
 by the strong scent; the 
 flowers also secrete large 
 quantities of nectar. The 
 flower-stalk is attached for 
 half its length to a leaf- 
 like bract that serves as a 
 dispersive organ of the 
 fruit when mature, becom- 
 ing dry and light, and be- 
 ing blown by the wind for 
 some distance, carrying the 
 fruit along with it. (Na- 
 tural size. ) 
 
 of the spur over the open nectary is that the nectar is 
 prevented from being washed away by rain. 
 
 So long as the flower is constructed on the buttercup 
 type, that is, regular in form, and all the parts free from 
 
CHAP, iv.] REPRODUCTION OF PLANTS. 135 
 
 each other, the power of self-fertilization is retained, and 
 this is the most general mode, although the presence of 
 colour, and in some cases of nectar also, attracts insects 
 which undoubtedly do in many instances effect cross- 
 fertilization. 
 
 The old method of securing cross-fertilization by 
 completely arresting the development of the stamens in 
 all the flowers on one tree and all the pistils in those of 
 another, is modified in most Angiosperms, who have 
 fallen back on the primitive hermaphrodite type of 
 flower, and by a double series of changes have succeeded 
 in preventing self-fertilization and secured the advan- 
 tages of cross-fertilization. Some of the most pronounced 
 contrivances for preventing self-fertilization are to be 
 found amongst our common wild flowers ; perhaps the 
 most general arrangement is in the stamens becoming 
 mature and shedding their pollen before the ovules of 
 the same flower are ready for fertilization, and this in 
 the majority of instances is the only thing absolutely 
 guarded against, although the pollen from one plant 
 must in many instances be conveyed by insects to the 
 stigmas of flowers belonging to a different plant of the 
 same kind, and thus effect cross- fertilization between 
 two distinct individuals. Flowers having the stamens 
 mature before the pistil are said to be proterandrous ; 
 examples, the geraniums, pinks, willow-herbs, and in fact 
 most flowers that have both stamens and pistil. In 
 comparatively few flowers the pistil is mature before the 
 stamens, as in the arum, figwort (Scrophularia nodosa), 
 plantain, etc.; such flowers are termed proterogynous . 
 In other examples the difference in position of the 
 stamens and pistil in the flowers of different individuals 
 
1-36 
 
 BOTANY. 
 
 [CHAP. iv. 
 
 of the same kind to some extent prevents self-fertilization, 
 and certainly favours cross-fertilization. If a number of 
 plants of the primrose or cowslip are examined it will be 
 found that all the flowers of a given plant have the 
 pistil at the top of the tube of the corolla and the stamens 
 halfway down the tube ; or, on the contrary, the stamens 
 
 Fig. 39. Oxlip (Primula elatior). A dimorphic flower. The left- 
 hand figure represents the long-styled form with the stigma, N, at the 
 top of the corolla-tube, and the stamens, s, halfway down the tube. 
 The right-hand figure shows the short-styled form with the stamens, 
 S, at the top of the tube, and the stigma, n, on a short style halfway 
 down the tube. (Slightly magnified. ) 
 
 are at the top of the tube and the pistil halfway down. 
 Such flowers are termed Heteromorphous, as distinguished 
 from Homomorphous flowers, that have in all cases the 
 stamens and pistil occupying the same relative positions. 
 Heteromorphic flowers that have two forms of flower 
 depending on difference of position of stamens and pistil, 
 
CHAP, iv.] REPRODUCTION OF PLANTS. 137 
 
 as in the primrose, are called Dimorphous ; those with 
 three forms, as loosestrife (Lyihrum salicaria), are called 
 Trimorphous. The facilities afforded by heteromorphism 
 in connection with cross-fertilization, is clearly shown 
 by the species of Primula, Fig. 39, which includes the 
 primrose and cowslip. An insect in obtaining nectar 
 from the base of the coralla-tube of a long-styled prim- 
 rose flower would dust its " tongue " with pollen at a point 
 which would exactly come in contact with the stigma 
 when it visited a short-styled flower. Conversely, 
 when visiting a short-styled flower the pollen would 
 adhere to that portion of the " tongue " that would come 
 in contact with the stigma of a long-styled flower. 
 
 A further guard against self-fertilization evolved by 
 many plants depends on the fact that the pollen of a 
 given flower when placed on the stigma of the same 
 flower is slower in forming pollen-tubes, and thus effect- 
 ing fertilization, than the pollen from another flower of 
 the same kind, and in some plants this idea is carried so 
 far that the pollen will not fertilize the ovules of the same 
 flower producing it, but when placed on the stigma 
 actually induces a toxic effect that results in the death 
 of the unfertilized ovules. 
 
 The sign that a plant has reached the stage of almost 
 or altogether entire dependence on insect aid for effect- 
 ing fertilization is indicated by the irregularity or unsym- 
 metrical structure of the corolla, accompanied by the 
 growing together to a greater or less extent of its 
 component petals. Several important groups of plants 
 belonging to this category have the corolla consisting of 
 petals of unequal size, and so arranged that a median 
 line divides it into two equal parts, but the petals are 
 
138 BOTANY. [CHAP. iv. 
 
 still free from each other. Well-known examples are, 
 violets (Violacece) ; peas, beans, and vetches (Legu- 
 minosce) ; and orchids (Orchidacece) . In the last-named 
 order there is a sequence from self-fertilized plants to 
 others that display the most perfect arrangements for 
 cross-fertilization met with in the Vegetable Kingdom. 
 Orchids belong to the same division of Angiosperms as the 
 lilies Monocotyledons and, like the latter, belong to the 
 type of regular flower with three free sepals, three free 
 petals, six stamens, and a pistil consisting of three carpels 
 grown together. The common tiger lily still shows this 
 structure, but the orchids, which may be said, as a group, to 
 have devoted their whole energy to the perfection of the 
 method of cross-fertilization with the greatest amount of 
 certainty combined with the minimum expenditure of 
 material, have developed an irregular flower. This 
 irregularity in the simplest type consists in the modifi- 
 cation of form of one of the three petals, the posterior or 
 uppermost; this modified petal is known as the lip or 
 labellum. In other species more of the sepals and 
 petals become changed, and there is a general tendency 
 on the part of the flower to become compressed laterally, 
 thus shadowing in the tubular type of flower, open at 
 the mouth and becoming narrower downwards towards 
 the point where the stamens and pistil are situated ; the 
 object of this arrangement being to compel the insect, 
 when sipping the nectar, to bring some portion of its 
 body in contact with the stamens or stigma as the case 
 may be. In such flowers the lowermost or anterior 
 petal is usually large, and stands out as a landing stage 
 on which the insect alights. A curious feature in the 
 evolution of the flower in orchids consists in the fact 
 
Fig. 40. An exotic orchid (Oncidium papilio). The flower is irregu- 
 lar, the sepals and petals together resemble a butterfly in shape ; 
 hence the botanical name. (Reduced.) 
 
140 BOTANY. [CHAP. iv. 
 
 that the petal forming 1 the labellum, intended as the 
 landing-stage for insects, appeared at the upper or 
 posterior part of the flower, and consequently proved 
 useless for the purpose intended, and although the 
 mistake was discovered, it appears that the line of 
 departure first taken could not be checked, and orchids 
 continue to grow the posterior petal as a landing-stage 
 and then, by a half-turn of the long, inferior ovary, 
 reverse the original position of the flower and bring the 
 labellum or landing-stage to the anterior or under side 
 of the flower, where it is of use to insects. In the great 
 majority of plants the pollen is dry and powdery, the 
 individual pollen-grains remaining distinct ; this is the 
 case in a few orchids, but in the great majority the pollen- 
 grains are stuck together in masses, two of which are 
 present in an anther which is situated above the stigma 
 in such a position that self-fertilization is impossible. 
 When a bee visits an orchid flower for the purpose of 
 obtaining the nectar situated in the spur that is a back- 
 ward continuation of the labellum, its head comes in 
 contact with the anther, and the two pollen masses 
 become attached to its head by a slender viscid stalk. 
 At the moment of removal the two pollen-masses stand 
 erect on the front part of the head of the insect, but in 
 a very short time bend forwards and downwards, in fact 
 bend downwards until they are as much below their 
 original level as the stigma of the orchid flower is below 
 the stamen. When the ovules are ready for fertilization 
 the stigma becomes viscid, and a bee carrying the 
 pollen-masses on its head, on entering a flower in this 
 condition, brings the pollen into contact with the viscid 
 stigma, to which it adheres. The mutualism between 
 
CHAP, iv.] REPRODUCTION OF PLANTS. 
 
 141 
 
 orchids and insects has become so perfect that in the 
 great majority of species there is only one fertile stamen 
 present, yet the whole working is so exact that cross- 
 fertilization is even more certain than is self-fertilization 
 in the case of allied groups having the full complement 
 of six stamens, and even if cross-fertilization was in 
 itself of no importance, the advantage of being able to 
 dispense with five stamens alone would compensate for 
 the evolution from the primitive type, as the change has 
 not necessitated the development of entirely additional 
 
 Fig. 41. Pollen-masses of an or- 
 chid. The upper thickened portion 
 consists of the pollen-grains stuck 
 together by a viscid gum-like sub- 
 stance that forms two slender stalks 
 terminating in a flattened portion 
 below. This flat part adheres to the 
 head of the insect. (Highly mag- 
 nified. ) 
 
 structures, but only a modification of parts already 
 present. 
 
 The type of having the petals more or less grown 
 together to form a tube is well illustrated by the white 
 dead-nettle (Lamium album"), where the five petals are 
 very irregular in shape and size, and grown together in 
 such a manner as to form two large lip-like portions, the 
 upper arched lip being formed of two petals, and 
 serving to protect the stamens and pistil from rain ; the 
 lower lip consists of three petals grown together, and 
 serves as a landing-stage for insects that visit the 
 flower. The stamens are four in number, the fifth pos- 
 
142 BOTANY. [CHAP. iv. 
 
 terior stamen present in less highly evolved allied 
 plants being completely arrested, a single long style 
 divided at the tip lies along with the stamens under the 
 large arched upper lip. The two lips of the corolla 
 become joined together at some distance down, and 
 form a curved tube, at the bottom of which the nectar or 
 honey is secreted. The above type of corolla is called 
 bilabiate on account of the two prominent lips, and is 
 characteristic of the large natural order of plants called 
 Labiatce, but occurs also in allied orders of plants, as 
 the figwort order (Scrophulariacece), etc. The dead-nettle 
 flower is proterandrous ; the stamens become ripe in 
 pairs. The first pair when ready to shed their pollen 
 curve downwards from under the upper lip and place 
 their anthers in such a position that they come in con- 
 tact with the back of an insect visiting the flower for 
 nectar, the pollen being dusted on to the insect's back. 
 After the pollen is removed the anthers shrivel up and 
 disappear, the second pair in turn bending down into 
 the position previously occupied by the first pair. Finally, 
 after the second pair of stamens have had their pollen 
 removed and disappeared, the pistil curves down from 
 under the upper lip and places its stigmas in the posi- 
 tion previously occupied by the anthers, consequently a 
 bee on entering the flower with pollen on its back, 
 obtained from another flower, unconsciously effects 
 cross-fertilization by bringing the pollen in contact with 
 the stigma. 
 
 The above arrangement for securing cross-fertiliza- 
 tion, although comparatively perfect in its way, is 
 eclipsed from every point of view by the contrivances 
 for this same object presented by the species of sage 
 
CHAP, iv.] REPRODUCTION OF PLANTS. 
 
 143 
 
 (Salvia), belonging to the same order of plants as the 
 white dead-nettle. The corolla of the sage flower is 
 formed on the bilabiate type, but owing to the certainty 
 
 Fig. 42. One of the sages (Salvia scalarea). In Fig. I., ob is the 
 large curved upper lip of the corolla ; n, the tip of the style with its 
 two stigmas ; s, an anther that has come clown upon the back of the 
 insect; Fig. II., s i and s 2, the two stamens; n, the tip of the 
 style showing the two stigmas ; r, the portion of the anther that the 
 insect's head comes in contact with in thrusting down the tube of the 
 corolla to reach the honey, when this part is pressed downwards it 
 causes the stamen to suddenly spring down upon the insect's back. 
 The lip or landing-stage has a second platform springing from its 
 under surface, on which the insect stands. 
 
 of securing fertilization the stamens are reduced to two, 
 and these two have each only one of the usual two 
 anther-lobes present, so that in reality there is only pre- 
 sent the amount of pollen produced by one normal anther. 
 
144 BOTANY. [CHAP. iv. 
 
 There is a lip on which the insect alights as in the dead- 
 nettle, but the special contrivance of the sage consists 
 in an arrangement by which the insect, in thrusting its 
 head into the tube of the corolla, causes the mature 
 anther to come suddenly down upon its back and shed 
 its pollen, after which it shrivels and disappears, the 
 second anther then being ready to act in a similar man- 
 ner. Eventually the style curves down as in the dead- 
 nettle. 
 
 The advantage of the latter method over that of the 
 white dead-nettle is aa follows. In the last-named 
 plant the stamens, when mature, curve down into posi- 
 tion and shed their pollen whether an insect visits the 
 flower or not, whereas in the sage the stamen remains 
 under the upper lip until mechanically forced down by 
 the presence of an insect ; then the force with which it 
 comes down on the insect's back causes the pollen to 
 escape from the anther. 
 
 Numerous other equally effective and interesting 
 arrangements for preventing self-fertilization, and at the 
 same time favouring cross- fertilization, exist; space 
 alone forbids a detailed description of such. In some 
 exotic plants, fertilization is effected by small birds. 
 
 The various colours of flowers are not, as might be 
 supposed, the result of chance, and without any special 
 object in view; but, remembering that the only known 
 use of colour in the flower is that of an advertisement 
 indicating their presence to insects or birds in connec- 
 tion with fertilization, so we find that the evolution of 
 colour is, as a rule, contemporaneous with that of struc- 
 ture bearing on fertilization. Yellow is the primitive 
 colour of flowers, and characteristic of those that are 
 
CHAP, iv.] REPRODUCTION OF PLANTS. 145 
 
 self-fertilized, or at all events retain that power as illus- 
 trated by buttercups and many regular flowers with the 
 component parts free from each other ; marked excep- 
 tions to this rule, however, are not rare, as in the prim- 
 rose and many of its allies, and more especially in the 
 composite plants, as the dandelion, hawkweeds, etc., also 
 in the common toadflax. The various shades of red 
 passing into purple follows yellow, and are characteristic 
 of flowers that have become irregular and more adapted 
 for insect-fertilization, as the red dead-nettle ; but here 
 again many regular flowers that are self-fertilized are 
 red. Pure blue is the rarest colour presented by 
 flowers, most so-called blue flowers having a more or 
 less decided red tinge, nevertheless blue or bluish-purple 
 colour is usually present in flowers that have advanced 
 structural arrangements for insect-fertilization, as seen 
 in monkshood, larkspur, etc.; but here again we have 
 an almost clear blue anemone (Anemone appenina) that 
 certainly belongs to the self -fertilizing batch, so with 
 many others. Sir John Lubbock has clearly demon- 
 strated that bees recognize certain colours, and it 
 appears that the colour of a flower is of use in indicating 
 to insects the presence of a meal or otherwise, their 
 only object in visiting it. The strongest proof of the 
 gradual evolution of colours in the sequence indicated 
 yellow, red, blue is shown in plants under cultivation, 
 where if a flower that is blue in a state of nature is cul- 
 tivated, which means being placed under a comparatively 
 new set of conditions, it not unfrequently produces 
 red and yellow varieties, whereas if a naturally yellow 
 flower is experimented with it never ascends to the 
 red or blue series. To appreciate fully this remark, it 
 
 L 
 
146 BOTANY. [CHAP. iv. 
 
 is necessary to understand that the changes induced by 
 cultivation, popularly considered to raise the plant above 
 its previous level of development, are in reality always of 
 a degenerate nature, causing the plant to fall back to a 
 lower level, or by developing to an extraordinary extent 
 one part of its structure at the expense of the remaining 
 portions, and so disturbing the natural balance of its eco- 
 nomy, that when neglected it never retains the abnormal 
 condition assumed under cultivation, but soon returns to 
 the wild or normal state. There are two principal objects 
 in view in cultivating plants ; utility, as sources of food, 
 etc., and in the second place, as affording pleasure by the 
 very varied combinations of form, and colour, and per- 
 fume afforded. From the first standpoint, it will be 
 seen that, as a rule, as already stated, one particular 
 part of the plant is alone of value, hence those methods 
 of cultivation are adopted that favour the development 
 of this particular part. As illustrations may be named 
 the disproportionate quantity of fruit desired, and this 
 too, to be of the first class, must be free from seeds ; in 
 the potato plant, the swollen tips of certain underground 
 branches potatoes are alone of value, hence the 
 whole object of the gardener is to get an abnormally 
 excessive development of this portion of the plant. 
 When gardeners and their employers are educated up to 
 the point of realizing that the constitution of a plant, as 
 that of an animal, can be overtaxed, and that this over- 
 taxation results in disease, as manifested by the potato- 
 disease, and in fact the diseases of most of our important 
 food-producing plants, which can in many instances be 
 proved to result from abnormal treatment, and a craving 
 to obtain more from the plant than it can yield without 
 
CHAP, iv.] REPRODUCTION OF PLANTS. 147 
 
 grave injury to itself, and consequent loss to its short- 
 sighted owner or " sweater." In the case of plants 
 grown for their beauty, a " double flower " is usually 
 considered the proper thing to produce ; this again is a 
 decided retrogression or degeneration, the stamens and 
 pistil under the unusual treatment termed cultivation, 
 fall back to the condition of flattened leaves from which 
 they evolved, and in consequence the flower is prevented 
 by this retrogression from performing the function for 
 which it was gradually evolved, hence the cultivated 
 plant could not possibly retain its changed character due 
 to cultivation, and at the same time hold its own in the 
 struggle for life unaided by man, any more than could 
 those miserable bandy-legged dogs that are so highly 
 prized on account of their very morbidity, and whose 
 only function seems to be that of indicating the calibre 
 of mind of the owner. 
 
 From what has been said respecting the complex 
 evolution of the flower in connection with insect-fer- 
 tilization, it might reasonably be supposed that a process 
 having effected such a complete revolution over pre- 
 viously existing modes of fertilization, and having also 
 reached such approximate perfection, would in a broad 
 sense, subject to minor modifications, endure for all 
 time; nevertheless, the evidence forthcoming does not 
 support this view, and we are perhaps at the present 
 day witnessing the maximum development of the insect- 
 fertilizing idea, with its necessary accompaniment of 
 brilliant colour and fragrance, which, like the preceding 
 period of wind-fertilized plants, will gradually pass away, 
 being superseded by a newer idea, which is already mani- 
 festing itself in various quarters of the globe, and is 
 
148 BOTANY. [CHAP. iv. 
 
 very clearly illustrated in our own wild violets. The 
 corolla in the violet is very highly differentiated for the 
 purpose of favouring insect-fertilization, although the 
 petals are not grown together, yet the corolla presents 
 the bilabiate type, with the lower lip standing out as a 
 landing-stage, there is a well-developed spur containing 
 nectar, and having the entrance guarded against the 
 entrance of small insects in a manner already described ; 
 the coloration passes in the various species from yellow 
 to very dark blue with just a tinge of red ; scent, as is 
 well known, is present in some species; in fact, the 
 whole structure of the flower shows that self-fertilization 
 was almost impossible, and that the visits of insects was 
 indispensable, yet all these elaborate arrangements have 
 not prevented the violets from evolving something even 
 more effectual and at the same time more economical in 
 connection with fertilization, and in reality the old- 
 fashioned coloured flower, evolved for aiding insect- 
 fertilization, is now of no use to the plant ; but, as pre- 
 viously explained, when a structure is evolved, it cannot 
 be at once arrested, even when completely superseded 
 and useless, and this is the condition that most of the 
 violets now find themselves in, encumbered with an old 
 effete type of arrangement for securing insect-fertiliza- 
 tion. The new type of flower present in many violets 
 appears later in the season than the old type of flower, 
 from which it differs fundamentally in being self-ferti- 
 lized, the sepals remaining closed until fertilization is 
 effected, petals are absent or rudimentary, the stamens 
 reduced to one or two, and containing only a small quan- 
 tity of pollen, but being placed in contact with the 
 stigma, fertilization is insured. These permanently 
 
CHAP, iv.] REPRODUCTION OF PLANTS. 149 
 
 closed, self- fertilized flowers are called Cleistogamous. 
 The pansy (Viola tricolor) is the only British violet in 
 which seeds are produced generally by the old type of 
 flower; in the others, as the dog violet (Viola canina*), 
 the sweet violet ( Viola odorata), etc., a few seeds may 
 occasionally be produced by the old type of flower, but 
 it has in reality been superseded by the cleistogamous 
 flower. The reversion to the self-fertilized method of 
 fertilization seems, and really is, unintelligible from the 
 present standpoint of knowledge, assuming that cross- 
 fertilization really invigorates and helps plants in the 
 struggle for existence, and judging from the proved 
 superiority of the offspring in the animal kingdom 
 resulting from parents having no blood -relationship, 
 this idea appears to be true ; nevertheless, in the case of 
 the violets and many other groups this is- certainly the 
 direction in which things are tending at the present 
 day. If it be eventually demonstrated that what appears 
 to be self-fertilization in cleistogamous flowers, by some 
 modification in the stamens and ovules, produces equally 
 vigorous offspring as by the method of cross-fertilization, 
 then the change becomes intelligible, as the plant would 
 save the enormous amount of material at present necessary 
 for the purpose of attracting and supplying insects with 
 food. It may not be the pleasantest of ideas to realize the 
 possibility of the gradual disappearance of the showy por- 
 tion of the flower,but we are, or think we are, a self-sacrific- 
 ing race, and would not begrudge the loss of our favourite 
 flowers, if shown to be of advantage, even to plants. 
 
 The various forms of Inflorescence, or massing of 
 flowers into dense clusters, have in many groups of 
 plants obviously been evolved, or, in other words, those 
 
150 BOTANY. [CHAP. iv. 
 
 modifications of inflorescence over previously existing 
 ones that favoured cross-fertilization, have predominated 
 in the struggle for existence, continually being carried 
 on amongst new structural departures from the older 
 forms. In the early types of flowers possessing colour, 
 the herald of all those various complications eventually 
 evolved for purpose of cross- fertilization, and which still 
 retain perfectly the power of self-fertilization, illustrated 
 by many of the lilies, geraniums, buttercups, roses, etc., 
 we find the flowers large and presenting a blaze of 
 colour, in fact division of labour and the formation of 
 communities for mutual good were ideas not evolved at 
 the early period of the cross-fertilization epoch, and why 
 the above-named plants along with numerous others 
 have never passed beyond this phase cannot at present 
 be explained ; however, numerous other plants have 
 broken away from the old extravagant state of things 
 where each individual flower had to do everything for 
 itself, and consequently assumed large dimensions for 
 the purpose of making its presence known to insects. 
 The line of departure consisted in reducing the size of 
 the individual flower, and at the same time in concen- 
 trating numerous flowers into a cluster, the gain being 
 an enormous saving of material, without sacrificing the 
 primary object of colour and scent as advertisements to 
 insects, this principle being equally effective in a large 
 quantity of small flowers massed together as in isolated 
 large flowers. A comparison of the dense mass of indi- 
 vidually small flowers forming the inflorescence of the 
 lilac (Syringa vulqaris) , with the large solitary flowers of 
 the red corn poppy (Pap aver rhceas^j will illustrate the 
 above-stated view. 
 
CHAP, iv.] REPRODUCTION OF PLANTS, 151 
 
 The maximum of development in the massing together 
 of minute flowers to form an effective mass has been 
 attained by the various members constituting the order 
 of plants known as Gompositce, represented by such well- 
 known plants as thistles, dandelions, daisies, chrysan- 
 themums, sunflowers, etc., where the head in all cases does 
 not consist of a single large flower, but of an enormous 
 assemblage of closely-packed small flowers. In addition 
 to the idea of concentration of small flowers met with in 
 Composite, we are also introduced to a high development 
 of division of labour in many instances. In the common 
 dog-daisy (Bellis petennis) the central yellow portion of 
 each head of flowers consists of minute yellow florets ; 
 these collectively form the disc, their function being 
 more especially to produce seeds, whereas the white 
 radiating portion of the head, each portion of which re- 
 presents a flower, serves for attractive purposes, the 
 florets being incomplete and not producing seed. Both 
 disc and ray florets have the petals adhering together, 
 but in the former the corolla is regular, in the latter 
 irregular. A similar division of labour is seen in the 
 inflorescence of the ox-eye daisy (Chrysanthemum leu- 
 canthemum) , sunflower (Helianthus annuus) y etc., whereas 
 in the dandelion (Taraxacum officinale), and the thistles 
 (Carduus), all the florets are fertile and of one shape, 
 showing no division of labour in the direction indicated 
 above. 
 
 In the case of scattered flowers, each flower originates 
 in the angle between & floral-bract or leaf-like structure, 
 and the stem, each flower with its floral-bract being 
 separated from those above and below by a naked portion 
 of flower-stalk ; in such cases the flowers are protected 
 
152 BOTANY. [CHAP. iv. 
 
 during the bud stage by the calyx. This arrangement 
 is met with in the inflorescence of the laburnum, red 
 currant, lupin, etc. Now, if we imagine all the naked 
 portions of flower-stalk between the flowers and their 
 floral-bracts to be removed or not developed, and at the 
 same time have the flowers sessile or without stalks, then 
 we get the crowded inflorescence characteristic of com- 
 posite plants as already described, which consists of a 
 dense cluster of sessile or stalkless small flowers crowded 
 at the top of a much swollen and flattened out flower- 
 stalk, each floret accompanied by its floral-bract, the 
 latter collectively forming the involucre, or outer row of 
 green leaves seen on the under side of the daisy, sun- 
 flower, etc., and which might at first be mistaken for a 
 calyx ; the involucre incloses and protects the entire 
 inflorescence during its early stage of development, hence 
 the calyx of each individual flower is not required to 
 perform its original function of protection, and in some 
 species, as the dog-daisy and nipplewort, has become 
 quite rudimentary, whereas in other species possessing 
 more aptness in turning things to account, have found 
 out a new use for the calyx, and utilize it as a dispersive 
 organ for the purpose of carrying away from the neigh- 
 bourhood of the parent plant the mature fruits. Under 
 this new form the modified calyx, which has given up its 
 cell-contents and become light and feathery for the pur- 
 pose of floating away its attached fruit, is known botani- 
 cally as the pappus, popularly as " clocks " in the 
 dandelion ; thistle-down is also a form of pappus, but it 
 is important to remember that every form of down or 
 dispersive arrangement for the purpose of scattering 
 seeds or fruits is not a pappus, that is, a modified calyx, 
 
CHAP, iv.j REPRODUCTION OF PLANTS. 
 
 153 
 
 the down of poplar-seeds, for example, having quite a 
 different origin. It is interesting to note that the 
 important features mentioned as characterizing the mem- 
 bers of the order Compositae the reduction in the size 
 of the flowers and their concentration into dense heads ; 
 the involucre as a protective organ ; and the pappus, a 
 dispersive organ, are not new factors added, but simply 
 modifications of organs previously existing ; and within 
 the order we have every transition 
 from the older and original function 
 of the parts enumerated above to 
 that of their complete modification ; 
 if this were not the case, it is very 
 doubtful whether we should ever 
 have been able to state that the 
 pappus is a modified calyx. This 
 is what is meant by the term evolu- 
 tion. The best proof that one or 
 more departures from the ordinary 
 track, evolved by a group of plants, 
 are of real service in enabling 
 the organisms concerned to better 
 maintain their position in the 
 struggle for existence, is shown by 
 their geographical distribution, and in this respect the 
 members of the natural order Compositse stand out pro- 
 minent. In addition to the points of advantage already 
 indicated, composite plants produce very minute fruits 
 that are easily carried by the wind and are thus dispersed 
 over wide areas ; their protective arrangements are also 
 well developed, and there is what may be termed an all- 
 round provision and tendency to meet circumstances and 
 
 Fig. 43. Fruit of 
 dandelion surmounted 
 by a stalked pappus. 
 (Slightly magnified.) 
 
154 BOTANY. [CHAP. iv. 
 
 make the best of whatever set of surroundings they may 
 encounter, the result being that there are at least ten 
 thousand known species, or about one-tenth of all known 
 flowering plants scattered over the surface of the globe. 
 
 It has been stated that ants and minute insects are 
 as a rule useless in effecting the cross-fertilization of 
 flowers, except in the case of some of the less differen- 
 tiated open kinds; and in the more highly evolved types 
 very varied arrangements are present for the purpose of 
 preventing such creeping insects from reaching the in- 
 florescence. Amongst such contrivances may be noted 
 the presence of a viscid substance on the stem, or the 
 presence of numerous hairs pointing downwards and 
 becoming longer and more numerous in the region of 
 the flowers, as in the cow-parsnip (Heracleum spliondy- 
 lium). In the wild teasel (Dipsacus sylvestris), the 
 opposite pairs of leaves are adherent to each other by 
 their margins for some distance, forming a receptacle 
 capable of holding a considerable quantity of water that 
 surrounds the stem just above the origin of the leaves, 
 and any insect creeping up the stem as far as the first 
 pair of leaves is confronted with this miniature pool, 
 which must be crossed before the stem can again be 
 reached ; and as there are usually from six to eight pairs 
 of leaves, each with its pool of water, it can be under- 
 stood that insects incapable of flight, and at the same 
 time not possessed of natatory powers, rarely reach the 
 inflorescence at the top of the stem. A similar contri- 
 vance is met with in other plants. 
 
 In concluding this portion of the subject allusion must 
 be made to the various modes by which the inflorescence 
 is protected against adverse climatic conditions, also 
 
Fig 44. Dwarf palm (Chamcerops humilis] ; showing the large 
 floral-bract or spathe that protects the inflorescence during its early 
 stage of development. The present species is the only palm indi- 
 genous to Europe, and it is confined to the southern portion, being 
 more abundant on the neighbouring shores of Africa. (Reduced.) 
 
156 BOTANY. [CHAP. iv. 
 
 against living enemies, during the early stage of develop- 
 ment, in fact in many instances until the flowers are 
 ready for fertilization. The involucre in Composite has 
 been already described. In the group of Monocotyle- 
 
 Fig. 45. Tornelia Fragrans, sometimes known by the name Mon- 
 stera deliciosa, a plant belonging to the Aroid family, showing the 
 large spathe covering the inflorescence. The fleshy spadix or stalk of 
 the inflorescence bearing perfumed and well-tasted fruits is constantly 
 sold in Mexican markets, where it rivals the pine-apple in estimation. 
 The leaves are very large, deeply cut into narrow segments, and 
 towards the centre irregularly perforated. (Much reduced. ) 
 
 dons the inflorescence is frequently protected by a single 
 large floral-bract called & spathe; this structure is well 
 seen in the palms, where it is frequently very large, 
 inclosing in some species a single inflorescence bearing 
 nearly 300,000 flowers. The spathe is also highly evolved 
 
CHAP, iv.] REPRODUCTION OF PLANTS. 157 
 
 in the arum family (Aroidece], and is a striking feature 
 in our " lords and ladies," the " Nile lily" (Richardia 
 ^Ethiopia*), where it is white, and the species of Gala- 
 dium, where it is often bright vermilion or crimson, 
 and performs an attractive as well as a protective 
 function. 
 
 A spathe also protects the flowers in the snowdrop, 
 daffodil, etc., and remains as a shrivelled brown mem- 
 brane, after the expansion of the inflorescence. In the 
 cow-parsnip the large inflorescence is at first inclosed 
 within the inflated leaf-stalk. 
 
CHAPTER V. 
 
 RELATIONSHIP AMONGST PLANTS. 
 
 Characters of importance in proving relationship. Primary 
 Divisions of the Vegetable Kingdom. Natural Orders of Plants. 
 What is a species ? 
 
 IT is not intended in the present place to enter into a 
 lengthened dissertation on the Classification of plants, 
 but solely to indicate in broad lines the most generally 
 acknowledged characters supposed to be of value in 
 indicating inter-relationship amongst plants. From 
 what has been already written it will have been realized 
 that evolution in the broader sense is recognized as the 
 cause of the great variety of morphological or structural, 
 and physiological or functional differences presented by 
 plants at the present day, as opposed to the older idea 
 of a special creation, in the sense of every plant having 
 existed from an ideal starting-point up to the present in 
 a comparatively unaltered condition. Having indicated 
 the principle of variation or evolution as affording the 
 basis on which plant affinity or relationship is founded, 
 it is necessary in the first instance to explain a few of 
 the most important terms employed by systematists 
 who deal with plant affinities. Although the modern or 
 so-called natural system of classification, as opposed to 
 the earlier artificial methods employed by Linnseus and 
 
CHAP, v.] RELATIONSHIP AMONGST PLANTS. 159 
 
 other writers, professes to take into consideration all 
 important characters in formulating the lines of true 
 relationship or descent, yet in reality the most advanced 
 natural systems derive most of their important characters 
 from the reproductive phase, and more especially those 
 furnished by the flower and the fruit, which necessarily 
 includes the seed. The structures present in a typical 
 flower have been already described and illustrated in a 
 diagrammatic manner in Fig. 7 ; the actual necessity 
 for the presence of a flower, as understood in Phanero- 
 gams, resulting from the compulsory change in the mode 
 of fertilization when plants established themselves on 
 dry land, has also been discussed, and it now remains 
 to show, that in spite of the distinct structural characters 
 presented by flowers, their componont parts are not new 
 additions to those possessed by cryptogams, but merely 
 modifications of previously-existing structures, in fact it 
 may be truly said that the reproductive portion of a 
 phanerogam is nothing more than a changed portion of 
 its older vegetative structure. The vegetative portion 
 of a plant developed above ground, leaving out of ques- 
 tion for the moment certain minor features, consists of a 
 stem bearing leaves, the latter being scattered or sepa- 
 rated from each other by internodes, a feature, from the 
 vegetative point of view, of prime importance, inasmuch 
 as it enables the individual leaves to secure the required 
 amount of exposure to light, a point on which the per- 
 formance of their most important function, that of 
 assimilation, depends. Leaves do not appear hap-hazard 
 on a twig, but develop according to a definite law, 
 known as acropetal development, which means that the 
 oldest leaf is situated at the base or oldest portion of the 
 
160 BOTANY. [CHAP. v. 
 
 twig, and the youngest nearest the tip or growing-point. 
 A young leaf never appears on a twig below, or lower 
 down, than another leaf that is already developed, and 
 when it is stated that the parts of a flower are modified 
 leaves, what is meant in reality is that the various whorls 
 of the flower follow the same acropetal law of develop- 
 ment as foliar organs or leaves, and not that sepals, 
 petals, stamens and carpels are in the young condition 
 leaves that afterwards change their functions. The 
 reversion of all the parts of the flower to foliar or 
 leaf-like organs, a not uncommon occurrence, supports 
 the above view. As in the case of foliage leaves it has 
 been shown to be an advantage that these should be 
 separated from each other by internodes, so in the case 
 of the flower it is a decided advantage that all the parts 
 should be concentrated ; this is effected by the suppres- 
 sion or non-development of the internodes of the stem, 
 and although this is in most flowers and inflorescences 
 the case, yet careful attention to the order of develop- 
 ment shows signs of the ancient idea of acropetal 
 development. If an expanding sunflower inflorescence 
 is watched it will be noticed that the ray florets do not 
 expand simultaneously all round, but that expansion 
 commences at one point and gradually works round to 
 that point, the first florets to expand occupying a position 
 in the concentrated arrangement corresponding to the 
 lowest and oldest leaves on an elongated stem, while 
 those that are latest in expanding correspond to the 
 youngest leaves on a lengthened twig. The same idea 
 is observed in the development of the various parts of 
 many flowers; the sepals, petals, and stamens, that 
 respectively appear to grow in whorls at the same level 
 
CHAP, v.] RELATIONSHIP AMONGST PLANTS. 161 
 
 of the stem, not appearing simultaneously but in suc- 
 cession. In many flowers well-developed internodes 
 are present between the respective whorls. The advan- 
 tages of concentration of the parts of a flower are 
 obvious. The sepals form a whorl that overlaps and 
 protects every internal part until ready to expand. The 
 concentration of the petals, in which the attractive fea- 
 ture of colour resides, makes the flower conspicuous at 
 a distance to an insect on the wing ; finally, during the 
 early self- fertilizing epoch the concentration of the 
 stamens in the immediate vicinity of the stigma was 
 imperative, and even when the self-fertilization method 
 was gradually superseded by that of cross- fertilization, 
 the various contrivances for preventing self-fertilization 
 did not necessitate the removal of the stamens from the 
 position occupied during the earlier condition of things. 
 Throughout the Vegetable Kingdom, and in connection 
 with every function, there is a decided stand against 
 radical and abrupt changes, in spite of, as one may 
 be allowed to express it, obvious advantages ; but at the 
 same time no impediment is placed in the way of modifi- 
 cations ; traits which, if manifested by ourselves, would 
 indicate a lukewarm confidence in the proposed change, 
 coupled with a determination not to completely forsake 
 an old tried method until the new idea had fully proved 
 its superiority. 
 
 Returning to the general build of a typical flower, we 
 meet with in early types, four whorls or verticils of 
 organs, calyx, corolla, stamens, and carpels, developed 
 in acropetal succession, the calyx being the oldest 
 whorl and consequently lowest down on the branch or 
 axis of the flower, and the carpels the youngest and 
 
 M 
 
162 BOTANY. [CHAP. v. 
 
 occupying the top or youngest portion of the stem, the 
 four whorls being, in every primitive flower, separated 
 by very short internodes. In the common field butter- 
 cup, which illustrates a simple and uncomplicated type 
 of flower, we meet with, commencing from below, a 
 calyx composed of five leaves or sepals, springing inde- 
 pendently from the stem, and perfectly free from each 
 other; such a calyx is termed polysepalous. Next we 
 come to the corolla, consisting of five yellow petals also 
 growing directly from the stem, and quite free from 
 each other hence called polypetalous. Within the 
 corolla, and consequently an internode higher up the 
 stem, is situated a considerable number of stamens, each 
 of which originates directly from the stem ; and finally, 
 at the tip or apex of the stem of the flower, we find a 
 number of closed leaves or carpels, each containing a 
 single seed, springing independently or free from each 
 other, from the tip of the floral axis ; the carpels collec- 
 tively form the fruit, and a fruit composed of free carpels, 
 that is, not grown to each other, is said to be apocarpous. 
 The above indicated sequence of development of the 
 four whorls constituting a flower is in reality the only 
 one that exists in the flower, but owing to the subse- 
 quent growing together of the components of any one 
 whorl, or of the different whorls with each other, we 
 meet with flowers exhibiting such different structural 
 peculiarities and appearances from those presented by 
 primitive types, as the buttercup, that unless the transi- 
 tions from one to the other are clearly traced, it is 
 difficult to realize that the two are built on the same 
 plan. If the flower of the primrose is next examined, 
 the sepals will be found cohering together and forming 
 
CHAP, v.] RELATIONSHIP AMONGST PLANTS. 163 
 
 a tube, the tips alone being free ; this type of calyx is 
 termed gamosepalous ; the petals are also grown to- 
 gether, forming a gamopetalous corolla ; five stamens are 
 present, which appear to grow from the inside of the 
 corolla-tube, and are described on this account as epi- 
 petalous ; finally the five carpels with their styles and 
 stigmas are completely grown together at every point ; 
 when the carpels are grown together the constituent pistil 
 is termed syncarpous. In the primrose, although there is 
 a growing together of components of the various whorls, 
 
 o 
 
 o 
 
 Fig. 46. Christmas rose (Hcl- Fig. 47. Primrose (Primula 
 leborm), showing the apocarpous vulgaris) showing the syncarpous 
 pistil. pistil. 
 
 yet the flower is regular, a still later type being illustrated 
 by the snapdragon (Antirrhinum), dead-nettle (Lamium) , 
 honeysuckle (Lonicera), etc., where the flower is irre- 
 gular, due to a difference in size and shape of the com- 
 ponent sepals and petals, for the purpose, already 
 explained, of facilitating the visits of insects. The 
 relative position occupied by the stamens, or rather the 
 particular portion of the flower from which they appear 
 to originate, is of primary importance in the classifica- 
 tion of plants, and requires to be clearly understood. 
 When the stamens grow directly from the thalamus or 
 
164 BOTANY. [CHAP. v. 
 
 axis of the flower, and are not in any way adherent to 
 any of the other whorls, they are said to be hypogynous. 
 This arrangement of the stamens is seen in buttercups, 
 
 Fig. 48. Red corn-poppy (Pa- 
 paver rhceas) showing the hypogy- 
 nous stamens originating directly 
 from the thalamus or axis of 
 the flower ; the superior pistil is 
 syncarpous, and surmounted by 
 several radiating, minutely vel- 
 vety stigmas. (Natural size.) 
 
 poppies, geraniums, etc., and in reality is the only 
 position from which stamens originate in every known 
 flower ; but in numerous instances the stamens, instead 
 of remaining perfectly free from the other whorls of the 
 flower, become adherent to a greater or less extent, and 
 in such cases appear at first sight as if they actually 
 started in the first instance from the organ to which 
 they are adherent. When stamens appear to grow from 
 the calyx, as in the roses, brambles, saxifrages, etc., 
 they are described as perigynous. When the stamens 
 appear to grow from the petals they are described as 
 epipetalous ; and, with very rare exceptions, the stamens 
 are always epipetalous when the corolla is gamopetalous. 
 Stamens that appear to originate from the top of the 
 ovary, as in the parsnip (Pastinaca sativum), and cicely 
 (Myrrhis odorata), are described as epigynous ; while 
 finally in the orchids, the one or two stamens present are 
 adherent to the style, and are said to be gynandrous. 
 The various positions occupied by stamens as described 
 above are not sharply separated from each other, but 
 connected by intermediate stages ; for example, in the 
 
CHAP, v.] RELATIONSHIP AMONGST PLANTS. 165 
 
 order known as Crassulacece, including the stonecrops 
 (Sedum), and houseleek (Sempervivum), it is in many 
 species a difficult matter to say whether the stamens are 
 hypogynous or perigynous ; the same is true of the 
 sundew order (Droseracece). In other instances the 
 stamens of a flower become more or less adherent 
 amongst themselves ; in the mallows and the hollyhock 
 all the filaments grow together, the anthers remaining 
 distinct, whereas in composite plants the anthers are 
 grown together, the filaments remaining distinct. All 
 the changes undergone by stamens from the fundamental 
 hypogynous position and perfect freedom from each 
 other, bear directly on the subject of insect- fertilization. 
 Returning to the pistil or central and terminal portion 
 of the flower, we find that the two conditions of apo- 
 carpous and syncarpous, depending on the freedom or 
 adherence of its component parts, called carpels, are 
 again connected by intermediate conditions as seen in 
 the saxifrages. The pistil varies considerably in struc- 
 ture and appearance in different plants, but the three 
 following parts, clearly shown in the primrose, fig. 46, 
 are usually present. The lower swollen portion, which 
 contains the ovules or unfertilized seeds, is the ovary ; 
 this is surmounted by a slender stalk-like body, the style, 
 which in turn is terminated by the knob-like stigma. 
 The ovary is the indispensable portion, which, after the 
 fertilization of the ovules then called seeds undergoes 
 important changes, often increasing considerably in size, 
 and is then known as the fruit; hence it will be observed 
 that ovule and seed are names applied to the same organ 
 at different stages of development ; the same remark 
 applies to the terms " ovary " and " fruit." The stigma is 
 
166 BOTANY. [CHAP. v. 
 
 the specialized portion of the pistil on which the pollen is 
 deposited ; while the use of the style, comparatively the 
 least important part of the pistil, and often entirely absent, 
 
 Fig. 49. Fuchsia globosa. The flower has an inferior ovary, the 
 calyx is coloured and gamosepalous, the sepals being united to form 
 a tube for about half their length, the four tips being free and spread- 
 ing ; the corolla is polypetalous. All whorls of the flower consist of 
 four parts or multiples of four ; there are four sepals, four petals, 
 eight stamens, and four carpels forming the syncarpous, inferior ovary. 
 (Natural size.) 
 
 as in the poppy, is for the purpose of placing the stigma 
 in the most favourable position for receiving the pollen. 
 A very remarkable change in the position of the ovary, 
 relative to the other whorls of the flower, requires notice. 
 
CHAP, v.] RELATIONSHIP AMONGST PLANTS. 167 
 
 It has already been stated that in primitive flowers, as 
 buttercups, poppies, etc., the pistil is situated highest up, 
 or terminal, on the central axis of the flower, and per- 
 fectly free from the other whorls ; when this is the case, 
 the ovary is said to be superior. If the flower of a snow- 
 drop, gooseberry, or Fuchsia is examined, the calyx and 
 
 Fig. 50. 
 carpel. 
 
 Pod of the pea, illustrating a fruit composed of a single 
 
 corolla will be found to originate from the top of the 
 ovary, the latter being apparently lowest down on the 
 axis of the flower ; in such cases the ovary is described 
 as inferior. It must be understood that there are not 
 two primitive types of flower structure, one with the 
 ovary superior, the other having the ovary inferior ; but 
 
168 BOTANY. [CHAP. v. 
 
 in reality the flower with an inferior ovary is a modi- 
 fication or evolution from the earlier type where the 
 ovary is superior. A transition stage, where the nor- 
 mally inferior whorls sepals, petals, and stamens have 
 only crept halfway up the ovary before becoming free 
 from it, is seen in some of the saxifrages, houseleeks, etc. 
 The appearance of the ovary when mature that is, the 
 fruit is in many instances so widely different from the 
 ordinary conception of a leaf-like structure, that unless 
 the transitional phases are indicated, it would be difficult 
 to realize the fact that the carpels or components of the 
 ovary are in reality modified organs originating, and, in 
 the early stage, presenting the characters peculiar to 
 leaves. This idea will be made clear by the examination 
 of the pod of a common pea, which is a carpel or leaf folded 
 so that its two edges meet and grow together, thus 
 forming a closed cavity, the ovary. The tip of the 
 carpellary leaf forms the stigma, and the ovules or young 
 seeds spring from the two margins of the carpel and 
 grow into the cavity formed by the closed-up carpel. In 
 the pea a single carpel constitutes the fruit, but in most 
 instances the fruit is composed of more than one carpel. 
 The fruit of the marsh marigold (Oaltha palustris) con- 
 sists of a number of carpels which, like that of the pea, 
 still remain comparatively unchanged and present a leaf- 
 like appearance ; and as these carpels remain free from 
 each other, the fruit, which consists collectively of all the 
 carpels belonging to one flower, is apocarpous. The 
 syncarpous ovary, on the contrary, is composed of two, 
 or generally more, carpels arranged in a whorl and 
 grown to each other by their edges. The number of 
 carpels forming a syncarpous ovary is in many cases 
 
CHAP, v.] RELATIONSHIP AMONGST PLANTS. 169 
 
 clearly indicated externally by grooves along the ovary 
 corresponding to the junction of the margins of the com- 
 ponent carpels, as in the tiger-lily, whereas in other 
 cases, as that of the hazel-nut, the " shell/' which is the 
 fruit consisting of two carpels, shows no external evidence 
 as to number of carpels forming it at maturity, and in 
 addition has become hard and woody, thus departing 
 from the leaf-like carpel of the pea. The object of 
 becoming hard and woody is for the purpose of protect- 
 ing the inclosed seed, popularly known as the " kernel." 
 
 Fig. 51. Fruit of the peach 
 (Persica vulgaris), cut open and 
 showing the structure of the fruit, 
 which includes the outermost 
 skin, the succulent portion, and 
 also the " stone," the seed being 
 the portion usually called the 
 "kernel." (Natural size. ) 
 
 Speaking of the " shell " of the hazel-nut as a fruit may 
 possibly cause some surprise, but the popular conception 
 of a fruit as being that of something good to eat, is not 
 in accordance with the botanical definition ; according 
 to the latter, the carpels at maturity constitute the fruit, 
 whatever their consistency and properties may be, and 
 the earliest function of the fruit in the ovary condition 
 is that of protecting the young ovules, and all subse- 
 quent changes in its condition are connected with either 
 continued protection of the seed, as in the case of the 
 hazel-nut, already mentioned, the walnut, cocoa-nut, etc. ; 
 
170 BOTANY. [CHAP, v. 
 
 or for dispersive purposes that is, by some means facili- 
 tating the removal of the fruit from the neighbourhood 
 of the parent plant, and depositing it in pastures new. 
 The contrivances for effecting dispersion are very varied, 
 and are mostly confined to those fruits that are indehis- 
 cent, or do not open in a definite manner at maturity for 
 the purpose of allowing the seeds to escape ; as examples 
 of such may be mentioned, peach, gooseberry, orange, 
 cocoa-nut, etc. The succulent and edible nature of the 
 group of fruits popularly known as stone-fruits, and many 
 others, is a dispersive contrivance ; the fruits are eaten 
 by animals, and consequently the seeds are dropped at 
 maybe a considerable distance from the parent plant; in 
 many such cases the seed is inclosed in a hard " shell/' 
 which is a specialized portion of the fruit for the object 
 of protecting the seed from harm during its passage 
 through the alimentary canal. The bright colours of most 
 edible fruits are attractive in function, indicating to birds 
 or mammals their whereabouts. In other instances the 
 surface of the fruit is furnished with hooked spines that 
 catch hold of the wool or hair of an animal, and are thus 
 dispersed ; the fruit of our common bedstraws (Galium) , 
 popularly known as t( cleavers/' illustrate this idea. In 
 another group of fruits, certain portions of the fruit are 
 flattened out into flat, wing-like portions for the purpose 
 of utilizing the wind as a dispersive agent; amongst 
 such may be mentioned the fruit of the ash, syca- 
 more, etc. 
 
 Fruits that open in a definite manner at maturity for 
 the purpose of allowing the seeds to escape are said to be 
 dehiscent ; examples, pea, wallflower, violet, poppy, etc. 
 In some instances the seeds are dispersed by the sudden 
 
CHAP, v.] RELATIONSHIP AMONGST PLANTS. 171 
 
 dehiscence or opening of the fruit, as in the wood- 
 sorrel (Oxalis acetosella) and the geraniums. 
 
 Important characters for classificatory purposes are 
 derived from the structure of the seed in Angiosperms. 
 Following the fertilization of the oosphere, important 
 changes take place in the ovule, one of which is the 
 accumulation of a certain amount of reserve material 
 
 Fig. 52. Fruit of the maple, showing wing-like flattened expansions 
 for the purpose of effecting removal from the tree by the wind. 
 (Natural size. ) 
 
 destined to serve as the first food for the young plantlet 
 on germination ; this arrangement is universal, as it will 
 be remembered that the assimilation of food depends on 
 the presence of green leaves, and the increase in size of 
 the tiny seedling up to the point of having leaves of 
 functional value is carried on entirely at the expense of 
 the material, known as endosperm, provided by the 
 parent plant. Contemporaneous with the appearance of 
 
172 BOTANY. [CHAP. v. 
 
 the endosperm in the ovule, and surrounding the fer 
 tilized oosphere now the oospore the latter by re- 
 peated cell-division assumes the form of a tiny plantlet 
 contained entirely within the ovule now the seed 
 and called the embryo j the development of the embryo 
 continues until the most important portions of the vege- 
 tative phase of the plant are formed, namely, a minute 
 stem or plumule, which is continued downwards as the root 
 or radicle, and in addition, either one or two minute 
 leaves or cotyledons. The presence of either one or 
 two cotyledons in the embyro depending on the species 
 examined is so constant that it constitutes one of the 
 most important characters used in breaking up the 
 Angiosperms into two primary divisions Monocoty- 
 ledons, where one cotyledon is present on the embryo ; 
 examples palms, grasses, sedges, lilies, etc. ; Dicotyle- 
 dons, where the embryo has two opposite cotyledons ; 
 examples buttercups, roses, peas, oak, hazel, etc. 
 
 The following arrangement illustrates the primary sec- 
 tions into which the vegetable kingdom is divided : 
 
 VEGETABLE KINGDOM. 
 
 I. Cryptogamia. 
 
 Asexual reproduction by cell-division, by motile 
 antherozoids, or in the higher groups by highly differen- 
 tiated spores. Sexual reproduction by oospheres that 
 are fertilized by motile antherozoids, water being the 
 agent that enables the antherozoids to reach the oosphere. 
 After fertilization, the oospore does not become dif- 
 ferentiated by cell-division into an embryo previous to 
 
CHAP, v.] RELATIONSHIP AMONGST PLANTS. 173 
 
 entering the resting stage. Alternation of generations 
 is often sharply marked. 
 
 The following are the most important groups or 
 natural orders of Cryptogams : 
 
 Seaweeds and their fresh-water allies (Algce) ; mush- 
 rooms, toadstools, puffballs, rusts, mildews, lichens 
 (Fungi) ; liverworts and mosses (Muscinece) ; ferns 
 (Filices) ; clubrnosses (Lycopodiacece) ; horsetails (Equise- 
 tacece) ; quillworts, salvinias, marsileas (Rhizocarpece). 
 
 II. Phanerogamia. 
 
 Sexual reproduction by oospheres that are fertilized 
 by passive or non-motile pollen grains ; these are brought 
 into contact with the oosphere by the agency of wind or 
 of insects, or the two sexes grow in immediate contact, 
 so that no external agency is required. The fertilized 
 oosphere by cell- division develops into a minute plantlet 
 or embryo while still inclosed within its protective 
 covering, the whole constituting the seed, which at 
 maturity enters the resting stage. Asexual reproduction 
 by spores. Alternation of generations absent. 
 
 To the present section belong all plants not enume- 
 rated under the preceding section, and popularly known 
 as flowering plants, on account of the usually conspicuous 
 flower; nevertheless, in very many phanerogams the 
 flower is comparatively inconspicuous, or very minute 
 and entirely devoid of colour, as in the grasses, sedges,, 
 and many forest trees. 
 
 In connection with the classification of plants, it is of 
 the greatest importance to bear in mind the fact that 
 the characters of sections given in books do not include 
 all the important features presented by the members 
 
174 BOTANY. [CHAP. v. 
 
 constituting the group, but only those that are most 
 pronounced and general, and for these reasons consi- 
 dered as being of value in indicating true relationship 
 and even these characters are not equally conspicuous 
 in all the included species, but gradually disappear and 
 are replaced by vestiges of other characters that in turn 
 become more pronounced, and constitute the leading 
 characteristics of a neighbouring section, hence book 
 characters only cover the most typical representatives of 
 a given allied group of plants, and it is often a matter of 
 personal opinion as to which of two or more sections 
 certain plants should be placed in, that occupy the 
 neutral or transitional line between one section and 
 another, by possessing, as stated above, the dying out 
 characteristics of one group, and the incipient indica- 
 tions of those which in the fully evolved condition con- 
 stitute the marked features of an allied group. 
 
 The above remarks apply to the two primary divisions 
 of the Vegetable Kingdom as given above. Cryptogams 
 and Phanerogams do not constitute two sections allied 
 to each other by the broad ties of plant individuality 
 only, such as the presence of chlorophyll and consequent 
 power of feeding on inorganic matter, but in the closer 
 affinity indicated by numerous points of agreement in 
 matters of detail; in fact, Cryptogams, as the oldest 
 section in point of time, appears to have emphasized two 
 points in its evolution that stand out conspicuously in 
 the higher types, namely, alternation of generations, 
 which implied the breaking up of the complete life- cycle 
 of an individual into two phases, one sexual, the other 
 asexual ; the second feature is the presence of motile 
 male bodies or antherozoids ; an additional negative 
 
CHAP, v.] RELATIONSHIP AMONGST PLANTS. 175 
 
 feature is the absence of high differentiation in the 
 fertilized body or oospore previous to immediate germi- 
 nation. The cutting down of one of the two phases or 
 generations the sexual one is carried to a very con- 
 siderable extent in Cryptogams, that is in plants that 
 yet have motile antherozoids, and consequently reach 
 the female part to be fertilized through the agency of 
 water ; but as plant-life extended from its original 
 aquatic habitat, water as the agent for bringing the 
 male or fertilizing body in contact with the female was 
 gradually superseded as already explained, by other 
 agents; consequently the male body lost its motility 
 and became transported by wind or insects. When 
 evolution reached the point where the sexual phase as a 
 distinct structure had been arrested, and the old motile 
 antherozoid replaced by non-motile pollen, also a higher 
 development of the fertilized oosphere resulting in the 
 formation of an embryo previous to immediate germina- 
 tion, then these combined characteristics constitute the 
 key-note to the botanist's conception of a Phanerogam, 
 as opposed to a Cryptogam, which it will be observed 
 turns in reality mostly on the particular way in which 
 the male or fertilizing body is conveyed to the female. 
 But Phanerogams did not appear with a spurt as a new 
 creation ; in other words, the features given above as 
 characterizing a Phanerogam did not appear simul- 
 taneously, and even in Phanerogams the rudimentary 
 remains of structures characteristic of Cryptogams, as 
 the prothallus or sexual generation, are still present in 
 Gymnosperms. On the other hand such features as 
 the highly developed embryo, characteristic of Phane- 
 rogams, is clearly indicated in some of the higher 
 
176 BOTANY. [CHAP. v. 
 
 Cryptogams, where the fertilizing body is still a motile 
 antherozoid. 
 
 It is not intended to enter further into the classifica- 
 tion of Cryptogams. The Phanerogams are divided into 
 the two following primary divisions : 
 
 PHANEKOGAMIA. 
 
 I. GymnospermeoB. 
 
 Fibro-vascular bundles open, arranged concentrically. 
 Ovules naked, produced on open carpellary leaves; 
 fertilization direct, the pollen coming in actual contact 
 with the ovule. 
 
 The following natural orders are all that are included 
 in the Gymnospermous division of Phanerogams : 
 
 Conifer ce, including firs, pines, cedars, yews, araucarias, 
 etc. The female inflorescence usually consists of a col- 
 lection of carpels crowded on a long axis and forming 
 a cone ; hence the name of the order. 
 
 CycadecB) including the cycads, zarnias, etc. The 
 species resemble tree-ferns and palms in general appear- 
 ance, having a more or less elongated trunk crowned by 
 a tuft of very large, much divided leaves. 
 
 Gymnosperrns are geologically the oldest group of 
 Phanerogams, and most nearly allied to their prede- 
 cessors, the Cryptogams, and still retain vestiges of 
 structural peculiarities that were well developed and 
 characteristic of the last-named group, such as traces of 
 the prothallus in the pollen-grain and ovule, the occur- 
 rence of several oospheres in the ovule, the formation of 
 endosperm previous to fertilization, etc. 
 
Fig. 53- Cycas circinalis, a gymnospermous plant belonging to the 
 order Cycadece, showing the palm-like habit. (Much reduced. ) 
 
 N 
 
178 BOTANY. [CHAP. v. 
 
 The species are trees or shrubs, herbaceous species 
 being absent. Finally, all are anemophilous, or wind- 
 fertilized. 
 
 II . Angiosp ermece . 
 
 Fibro-vascular bundles either closed and scattered or 
 open and arranged concentrically. Ovules developed 
 within the cavity formed by closed carpellary leaves; 
 fertilization consequently indirect, the pollen being re- 
 ceived on the stigma, where it forms a pollen-tube that 
 eventually comes in contact with the ovule. 
 
 Angiosperms as a group include the latest or most 
 modern types of plant evolution, and embody in many 
 groups the relative perfection of structure and adapta- 
 tion to circumstances which has taken geological ages 
 to evolve. The outcome of this evolution shows itself 
 in the elimination of many antiquated structures that 
 performed perfectly the functions required, but at too 
 great an expenditure of energy and material, and in all 
 the most highly differentiated groups, the outcome of 
 unconscious evolution tends towards one grand idea, 
 that of securing the greatest benefit with the least 
 possible outlay. Angiosperms include all flowering 
 plants, with the exception of the cycads and conifers, 
 enumerated under Gymnosperms; the various members 
 present all grades, from the tiniest wayside weed to 
 the forest tree, and in point of duration from a single 
 season to that of a period extending over centuries. 
 Wind-fertilization and self-fertilization are both still in 
 vogue, but in the great majority of species, insect- 
 fertilization is more or less completely relied upon, and 
 the enormous variety of floral evolution in connection 
 
Fig. 54. Livistonia australis, a palm with large fern-shaped leaves. 
 The palms, along with the screw-pines, are the only Monocotyledons 
 that assume tree -like proportions. (Much reduced.) 
 
180 BOTANY. [CHAP. v. 
 
 with this idea is certainly the most conspicuous of 
 features characteristic of Angiosperms. 
 
 Angiosperms in turn are divided into the two follow- 
 ing primary sections, depending on minor modifications 
 of the important structural characters of the group. 
 
 I. Monocotyledones. 
 
 Fibro- vascular bundles closed, scattered. Embryo with one coty- 
 ledon. Whorls of the flower in threes or multiples of three. 
 
 Other features characteristic of the present section 
 are the arrangement of the veins of the leaf, which are 
 usually described as parallel in arrangement, the complex 
 network, seen best in a "skeleton leaf" and charac- 
 teristic of the following section, being usually absent. 
 The general build of the leaf is also comparatively simple, 
 being usually long and narrow, as illustrated by grasses 
 and snowdrops, the margin as a rule is entire, the leaf is 
 not articulated to the stem, but after having performed 
 its functions remains hanging to the stem until it decays. 
 There is also an absence of so-called sensibility, or re- 
 sponsions in the way of movements to external stimuli. 
 The spathe, as already explained, is a form of floral 
 protection met with only in the present group. A 
 common mode of vegetative reproduction is by the 
 formation of bulbs, which generally consist of a number 
 of closely-packed modified leaves that are usually fleshy, 
 owing to the presence of store food materials, starch, etc. 
 The two outermost floral whorls, calyx and corolla, are 
 usually coloured, and together are often called the 
 Perianth. 
 
 The following are amongst the most characteristic 
 orders of Monocotyledons. Palmce, palms ; Liliacece, 
 
CHAP, v.] RELATIONSHIP AMONGST PLANTS. 181 
 
 lilies, hyacinths, tulips; Graminece, grasses, including 
 bamboos, sugar-cane, and the various cereals, as wheat, 
 rice, oats, maize, etc.; Orchidece, orchids; Iridece, iris, 
 gladiolus, etc. ; Amaryllidecp,, snowdrop, daffodil, snow- 
 flake, etc. 
 
 The plants belonging to the order Aroidece, including 
 our <f lords and ladies " (Arum maculatum) and the Nile 
 lily (Richardia cethiopica] , have the veins of the leaves 
 forming a network as in Dicotyledons. 
 
 II. Dicotyledones . 
 
 Fibre-vascular bundles open, arranged concentrically. Embryo with 
 two opposite cotyledons. Whorls of flower in fives or multiples of 
 five ; rarely in multiples of two. 
 
 The leaves in the present group attain a much higher 
 degree of specialization than in the Monocotyledons, and 
 there is a perfect sequence in the various species, from 
 the uncut simple leaf with an entire margin to the much 
 divided compound leaf possessed of the power of closing 
 and thus protecting its working surface when conditions 
 are unfavourable for the performance of its functions. 
 Protection against climate is often present in alpine or sub- 
 arctic species under the form of a dense coating of inter- 
 woven hairs, giving to the leaf the appearance of felt. In 
 the majority of species the leaves, whether simple or com- 
 pound, are articulated to the branch from which they 
 spring, and at the end of the season at once fall off, 
 leaving a clean leaf-scar on the branch. In <{ evergreen" 
 plants the leaves live for a longer period than one 
 season, and do not all fall away at one time, but the 
 old leaves fall away after new ones have become fully 
 developed. The modifications of leaves into tendrils, in 
 
182 BOTANY. [CHAP. v. 
 
 the case of weak- stemmed plants, and also as organs of 
 nutrition in insectivorous plants, have already been 
 noticed. 
 
 As a rule, so long as the corolla is polypetalous and 
 regular, and the stamens hypogynous, the latter are 
 numerous and the mode of self-fertilization predomi- 
 nates, whereas when special provision has been made 
 for favouring insect-fertilization, suggested by the irre- 
 gular gamopetalous corolla, the stamens never exceed 
 ten in number, far more frequently five only, and in 
 many instances even fewer, being reduced in the 
 sage, thyme, valerian, etc., to one or two. A marked 
 division of labour is usually present in the two outer- 
 most whorls of the flower, the calyx being green and 
 protective in function, the corolla coloured and attrac- 
 tive. In some cases, however, the calyx is coloured, 
 when it is described as petaloid, as in the Fuchsias 
 (fig. 49) ; in pendulous flowers the calyx is frequently 
 larger than the corolla and petaloid, becoming the most 
 conspicuous attractive whorl, or it is reduced to exceed- 
 ingly small proportions, so as not to interfere with the 
 attractive features of the corolla, as in heaths and the 
 harebell (Campanula, rotundifolia) . In many flowers the 
 corolla is entirely absent, and in such cases the calyx is 
 often brightly coloured, as in the marsh-marigold (Caltha 
 palustris^), wood anemone (Anemone nemorosa) , etc. 
 
 So far the groups considered have been of primary 
 importance, the result of certain characters being con- 
 stant in thousands of species, which, however, differ 
 widely amongst themselves in minor points of detail. 
 The most pronounced of these minor points constitute 
 in turn the characters of so-called Natural Orders. 
 
CHAP, v.] RELATIONSHIP AMONGST PLANTS. 183 
 
 In the Dicotyledons alone there are over two hundred 
 such Natural Orders, that is, Dicotyledonous plants can 
 
 Fig. 55- One of the honeysuckles (Lonicera glauca), a typical 
 Dicotyledon, having the corolla gamopetalous and irregular ; stamens 
 five, epipetalous ; ovary inferior. The opposite pairs of leaves are 
 connate, or grown together for some distance. (Natural size.) 
 
 be broken up into over two hundred groups, each cha- 
 racterized by the possession of certain structural features 
 
184 BOTANY. [CHAP. v. 
 
 in common, and at the same time not possessed by the 
 members of any other group. From the philosophical 
 point of view, supported by evidence of the mutation 
 and change in species that cannot be denied by the 
 bitterest opponents of evolution, it may be assumed 
 that the primary divisions of the vegetable kingdom 
 enumerated above originated as side branches from pre- 
 viously existing groups. From Cryptogams as the 
 starting-point of plant life we get, as already shown, 
 Phanerogams; the latter appearing as Gymnosperms, 
 that were followed later in time by Angiosperms ; the 
 latter again being first evolved as Monocotyledons, fol- 
 lowed by Dicotyledons. 
 
 It is important to understand that in the gradual 
 evolution of plants, the groups do not follow each other 
 in an unbroken sequence, by which is meant, the struc- 
 tural peculiarities characterizing a given group are not 
 evolved or supplemental to the characters possessed by 
 the most highly organized members of the group from 
 which it evolved, but in reality new groups originate 
 from the simpler and primitive members of the pre- 
 ceding or parent group, so that the early members of a 
 new group are for a time much simpler in organization 
 than the most perfect forms of the older ; but the new 
 group commences with what may be expressed as the 
 germ of a new idea, and if this new idea better enables 
 its members to hold their own in the struggle for exis- 
 tence, we find the new group gradually surpassing the 
 parent group in numbers and also in distribution in 
 space, due to the advantages derived from the posses- 
 sion of the new feature, which need not necessarily imply 
 increased complexity of structure, but, on the other 
 
CHAP, v.] RELATIONSHIP AMONGST PLANTS. 186 
 
 hand, as a rule, substitutes simplicity of mechanism 
 combined with accuracy of detail in place of what may 
 comparatively be termed a " rule-of-thurnb" arrange- 
 ment ; this idea is illustrated in both vegetative and 
 reproductive parts ; it is only necessary to mention com- 
 pound, sensitive leaves, and the various contrivances for 
 insect-fertilization as compared with antiquated leaves 
 and flowers. The extension of modern groups is illus- 
 trated by the subordinate position occupied at the 
 present day by cryptogams, once the only group in exis- 
 tence, and in like manner gymnosperms, the oldest of 
 the phanerogamic series, that were in turn monarchs of 
 the plant world, have yielded in numbers and position 
 to angiosperms, which at the present day take the lead, 
 due more especially to the scrupulous exactness with 
 which the law of " Division of Labour" is carried out. 
 
 The large divisions of phanerogams are in turn 
 broken up into so-called Natural Orders, characterized 
 by minor points of agreement ; and again, Orders are 
 divided into still smaller groups known as Genera, and 
 finally the different kinds or species constituting a genus 
 are distinguished from each other by less important or 
 what may be termed local characteristics. As to the 
 peculiarities of structure and otherwise that constitute a 
 species, there is a wide difference of opinion, but the 
 following gives an idea as to the scientific conception of a 
 species, that is, all those plants that at the present day so 
 resemble each other in structure and function as to 
 justify the idea that they have originated from a single 
 ancestor. 
 
CHAPTER VI. 
 
 FOSSIL PLANTS. 
 
 Vegetation of early Geological periods. Disappearance of groups 
 of Plants. The evolution of plants corroborated by Geological 
 evidence. 
 
 OWING to the minute size and delicacy of structure 
 of many of the early types of plant life belonging 
 to the Algae and Fungi, these would hardly be expected 
 to occur in a fossilized condition, nevertheless, certain 
 microscopic types of fungi, closely allied to the fungus 
 causing the potato disease at the present day, have been 
 detected in sections of fossil wood belonging to the Car- 
 boniferous period, and the microscopic group of Algae 
 called diatoms also occur in immense numbers in various 
 formations dating from the Carboniferous, where two 
 species occur that have passed down to the present day 
 without undergoing the minutest observable change in 
 any direction, and still exist in considerable numbers. 
 This at first sight appears directly opposed to the theory 
 of evolution, without, however, in reality being so, and 
 only proves that a change of environment is at least a 
 very important factor in promoting those modifications 
 of structure that eventually become sufficiently marked 
 to constitute what we term new species or groups. One 
 important feature clearly shown in the geological record 
 
CHAP, vi.] FOSSIL PLANTS. 187 
 
 is that each important group of plants commences in a 
 small way, that is, its components are comparatively few, 
 simple in organization, and comparatively limited in 
 distribution ; as the group evolves, we find that the 
 number of species increases at a comparatively rapid 
 rate, the same being true of the general organization 
 and distribution in space ; this goes on until a maximum 
 of development is reached, after which there is in every 
 instance a contraction as it were, indicated by a weeding 
 out and disappearance by degrees of those species least 
 able to hold their ground in the increased struggle for 
 life, accompanied by a general deterioration in structure, 
 and narrowing of the area of distribution. From the 
 above account it will be seen that the life-history of a 
 group of plants may be diagrammatically represented by 
 a spindle-shaped figure, its base or starting-point corre- 
 sponding to the first geological evidence of its existence, 
 then gradually widening out to its maximum point of 
 development, then again contracting, becoming thinner 
 and thinner, indicating its gradual decline, until the 
 present period is reached, for although in some cases 
 the living representatives are exceedingly few in num- 
 bers, limited in distribution, and degenerate in structure 
 compared with the same group at the period of its 
 maximum of development, yet every important group re- 
 presented in a higher stage of development during some 
 earlier geological epoch has existed up to the present 
 time, although sections or natural orders belonging to 
 certain groups have geological ages ago become quite 
 extinct, and are only known to us by their fossil remains. 
 In such cases the general structure and microscopic 
 details afford the proofs of affinity. 
 
188 
 
 BOTANY. 
 
 [CHAP. vi. 
 
 The following order of succession of Stratified Forma- 
 tions or Geological periods will enable the reader to trace 
 the gradual evolution of plant groups 
 
 Post-tertiary, 
 or Quar ternary. 
 
 J Recent and Prehistoric. 
 [Pleistocene or Glacial. 
 
 
 [Pliocene. 
 
 CaniozoiG, 
 or Tertiary. 
 
 J Miocene, 
 j Oligocene. 
 [Eocene. 
 
 
 [Cretaceous. 
 
 Mesozoic, 
 or Secondary. 
 
 I Jurassic. 
 I Liassic. 
 [Triassic. 
 
 Palceozoic, 
 or Primary. 
 
 [Permian. 
 | Carboniferous. 
 j Devonian. 
 [ Silurian . 
 
 Archcean. 
 
 Laurentian. 
 
 CRYPTOGAMS. 
 
 Algce. 
 
 The Algae, or seaweeds, geologically the oldest known 
 plants, first occur in the Laurentian series, and continue 
 to the present day. 
 
 Filices. 
 
 The ferns first appear in the Devonian, attain their 
 maximum of development towards the end of the 
 Carboniferous age, then, with the exception of a second 
 
CHAP. VI.] 
 
 FOSSIL PLANTS. 
 
 189 
 
 feeble attempt at extension about the commencement of 
 the Tertiary period, gradually diminish in importance 
 up to the present time. 
 
 Equisetacece. 
 The horsetails and their allies, amongst the earliest 
 
 
 Fig. 56. Neuropteris heterophylla, a fossil fern belonging to the 
 Carboniferous period. (Natural size. ) 
 
 of Vascular Cryptogams, appear late in the Silurian, 
 attain their maximum in the Carboniferous, and then 
 gradually decrease, being represented at the present day 
 by only one genus, including about twenty- five species ; 
 these are marsh plants of diminutive size and degraded 
 structure as compared with their forest- forming pro- 
 genitors of the Carboniferous period, such as Calamities*. 
 
190 BOTANY. [CHAP. vi. 
 
 Lycopodiacece. 
 
 The club-mosses are contemporaneous in their appear- 
 ance and period of maximum development with the 
 Equisetaceae, and like the latter assumed large dimen- 
 sions and formed forests during the Carboniferous age, 
 their remains contributing largely towards the forma- 
 tion of coal. At the present day the remaining members 
 of the group are few and of small size. 
 
 From the above it will be seen that all the groups of 
 Cryptogams attained their maximum of development 
 during the primary epoch, and mostly during the 
 Carboniferous period, which on this account has been 
 termed the age of Cryptogams. Several orders that 
 during that period formed extensive forests, as the 
 species of Sigillaria, Lepidodendron, Calamites, etc., 
 have long ago become extinct. 
 
 PHANEROGAMS. 
 
 Gymnosperms. 
 
 Ooniferce. 
 
 Conifers, the earliest of Phanerogams, first occur in 
 the Devonian rocks, their maximum extending through 
 the mesozoic period, after which a decline took place 
 that has continued up to the present time. 
 
 Cycadacece. 
 
 The Cycads appear in limited numbers in the Carboni- 
 ferous age, suddenly attain a wide-spread maximum 
 during the Jurassic period, of which they are highly 
 
CHAP, vi.] FOSSIL PLANTS. 191 
 
 characteristic ; this is followed by a slow decline through 
 the Cretaceous age, after which the falling-off in numbers 
 is rapid, but few surviving at the present day. 
 
 ANGIOSPEEMS. 
 Monocotyledon s . 
 
 The earliest known representatives of the most modern 
 group of plants appear in Permian rocks, attain their 
 maximum about the middle of the Tertiary epoch, and 
 at the present day are just on the decline. 
 
 Dicotyledons. 
 
 Dicotyledonous plants appear about the middle of the 
 Cretaceous age, and are still evolving, being more 
 numerous at the present day than during any previous 
 period. 
 
 It is interesting to note how comparatively soon in 
 every instance the maximum of development and exten- 
 sion in space, or geographical distribution, is attained 
 after the advent of a given group, compared with the 
 complete obliteration of the same after the maximum is 
 past. 
 
 The following paragraph from Dr. Geikie's " Class- 
 Book of Geology " is a fitting conclusion to the present 
 chapter. 
 
 " It is undoubtedly the greatest triumph of geological 
 science to have demonstrated that the present plants and 
 animals of the globe were not the first inhabitants of 
 the earth, but that they have appeared only as the 
 descendants of a vast ancestry, the latest comers in a 
 
192 BOTANY. [CHAP. vi. 
 
 majestic procession, which has been marching through 
 an unknown series of ages. At the head of this pro- 
 cession we ourselves stand, heirs of all the progress of 
 the past and moving forward into the future wherein 
 progress towards something higher and nobler must still 
 be for us, as it has been for all creation, the guiding 
 law." 
 
CHAPTER VII. 
 GEOGRAPHICAL DISTRIBUTION OF PLANTS. 
 
 Principal factors influencing the distribution of plants. British 
 Flora, past and present. Distribution of Cryptogams. Distribu- 
 tion of Phanerogams. 
 
 r I ""HE influence of temperature on plant life has 
 already been alluded to, and this factor is amongst 
 the most important in determining the distribution of 
 plants at the present day. The fact of certain groups 
 of plants occurring only in particular regions does not 
 prove that that particular region is the only one suited 
 to their requirements, as it has been proved in many 
 instances that when such locally occurring plants have 
 been introduced by human agency into new localities, 
 they have not only established themselves, but in several 
 instances have monopolized the new area, and more or 
 less completely driven out the previously-existing indi- 
 genous flora. Numerous common European weeds that 
 have been unintentionally introduced into new areas have 
 spread at an enormous rate, driving the native plants 
 before them, and causing serious inconvenience to the 
 settlers in such districts ; as an illustration may be men- 
 tioned the spread of the common thistle on the pampas 
 of Buenos Ayres, where at one time it almost completely 
 
 o 
 
194 BOTANY. [CHAP. VH. 
 
 covered thousands of acres with a rank growth, greatly 
 to the disadvantage of the sheep- farming industry. A 
 similar example on a smaller scale followed the accidental 
 introduction of the American water-weed into Britain, 
 which at one time threatened to choke up many of our 
 canals and rivers, but in both the above-mentioned 
 cases, and also in many others, after the first spurt made 
 by an alien on finding itself in what to it proves to be 
 virgin soil, a gradual decrease in its vigour of growth 
 and consequent distribution takes place, and it settles 
 down to the level of having to hold its own in the 
 struggle for existence, or in some instances almost 
 entirely disappears. Similar waves of inundation by 
 parasitic plants, more especially microscopic species of 
 fungi, have been observed, which after causing serious 
 devastation for a certain period, recede, either altogether 
 or to such an extent as not to materially influence the 
 continuance of the species of plant on which they are 
 parasitic. In connection with the above it is sufficient 
 to note the potato disease, due to the ravages of a 
 minute fungus known as Phytophthora infestans ; the 
 hollyhock disease, caused by an equally minute fungus 
 called Puccinia malvacearum; finally, the destructive 
 silk-worm disease known as (< muscardine " is also due 
 to the ravages of a minute fungus, Botrytis Bassiana, 
 which attacks and destroys the living insect. 
 
 As already stated, every plant of high organization is 
 much influenced by temperature ; in other words, a 
 certain amount of temperature is necessary to enable it 
 to perform all its functions properly. Hence we speak 
 of a palm region, cactus region, etc., meaning that the 
 particular group mentioned is highly characteristic and 
 
CHAP, vii.] DISTRIBUTION OF PLANTS. 195 
 
 abundant in the region indicated, but not at the same 
 time monopolizing the entire district. 
 
 The latitude of a place does not necessarily tell the 
 range of temperature, the isothermal lines, or those 
 running through places having the same mean annual 
 temperature, are in the region of the equator more or 
 less parallel with the lines of latitude, but as we recede 
 from the equator the two are widely separated, the 
 divergence depending on the proximity of the ocean, 
 mountain ranges, etc. The annual isotherm of 50 
 passes through latitude 42 30' in eastern America, 
 51 30' in England, and 40 in Eastern Asia ; nevertheless 
 the floras of these places are widely different, depending 
 on the fact that the mean annual temperature may be 
 the same in a place having a moderate summer and 
 winter temperature as in another having a very hot and 
 short summer and a very long cold winter. The last 
 mentioned distribution of heat is productive of a short 
 and sudden burst of floral glow as seen in the Swiss 
 Alps, or in high latitudes, as in Iceland, whereas the 
 first mentioned distribution of temperature favours a 
 prolonged activity of the different members of a flora, as 
 seen in England. 
 
 Light has already been shown to be indispensable to 
 the existence of all plants whose assimilation depends 
 on the presence of chlorophyll, but at the same time 
 this factor to some extent influences the distribution of 
 plants. Some kinds require full exposure to light ; 
 others flourish best in the shade. 
 
 The varying density of the atmosphere at different 
 elevations appears to produce little or no effect on plant 
 life, nor to be the cause of any morphological or physio- 
 
196 BOTANY. [CHAP. vn. 
 
 logical peculiarities. A comparison of arctic vegetation 
 growing but little above the sea-level with that growing 
 at an elevation of 17,000 feet in the Himalayas, where 
 15 inches of pressure were removed, showed no observ- 
 able difference in the habits and characters of such 
 plants as were common to the two regions. Again, the 
 common plants of the lowland portions of India that 
 bloom during the cold season are identical with the 
 same species that bloom at great elevations in the same 
 country during the alpine summer ; hence the variation 
 sometimes observable between lowland and alpine forms 
 of the same species does not depend on diminished 
 atmospheric pressure. 
 
 Moisture exerts a marked influence on the distribution 
 of plants as existing at the present time. The very 
 existence of life depends on the presence of water. The 
 plants of moist regions are often of a loose, spongy 
 texture with large, soft, smooth leaves, whereas those 
 characteristic of regions where there is but little mois- 
 ture in the air have the leaves firm and of a hard, dry 
 texture, as seen in many Australian plants, whereas in 
 very arid regions the leaves are often small and scanty, 
 and the stem covered with prominent spines. 
 
 Mountain ranges, deserts, and seas are unsurpassable 
 barriers to the migration and distribution of plants ; in 
 the case of mountains a two-fold difficulty is presented ; 
 the plants of low areas would be exposed to an increasing 
 degree of cold as they ascended, and at the same time 
 would have to struggle with the vegetation indigenous 
 to the regions on which they encroached, hence as a rule 
 the floras on the opposite sides of elevated mountain ranges 
 are often very distinct, not necessarily due, however, to 
 
CHAP, vii.] DISTRIBUTION OF PLANTS. 197 
 
 the impracticability of changing sides, but to the dif- 
 ferent climatal conditions usually present on the opposite 
 sides of a mountain range, depending on the relative 
 amount of heat and moisture present. Most fruits and 
 seeds quickly perish when immersed in sea-water ; the 
 fruit of the cocoa-nut is, however, an exception to this 
 rule, not suffering by prolonged immersion, and is fre- 
 quently carried for long distances by ocean currents, and 
 on being stranded under favourable conditions of tem- 
 perature, germinates at once ; by this means coral islands 
 often receive their first stock of palm trees. 
 
 The gradual adaptation of plants to particular condi- 
 tions, determined mostly by the relative amount of heat, 
 moisture, and light, has resulted in what is termed the 
 geographical distribution of plants, or the predominance 
 of certain plants in particular areas at the present day. 
 From geological evidence, as will be shown later on, the 
 areas that at the present day are characterized by certain 
 plants, were during earlier geological periods clothed 
 with vegetation which at the present time is only to be 
 met with in widely distant regions. This change is due 
 to the altered climatic conditions that certain areas have 
 undergone from time to time. A brief account of the 
 influence of climate and geographical changes on the 
 flora of a district may be to some extent realized from 
 a brief sketch of the compulsory migrations and whole- 
 sale destruction of consecutive floras that have from 
 time to time clothed the area known as Great Britain at 
 the present day. 
 
 The ancient flora, consisting chiefly of Cryptogams 
 and Gymnosperms, as Zamias and Cycads, that occupied 
 the site of what is now England must have been com- 
 
198 BOTANY. [CHAP. vu. 
 
 pletely obliterated during the latter part of the Creta- 
 ceous period, when all the land was submerged and 
 covered by a deep sea, in the bed of which the chalk was 
 slowly deposited. The comparatively uniform warm 
 temperature of the globe, indicated by the world-wide 
 diffusion of the same species in Palgeozoic and less con- 
 spicuously in Mesozoic time, at the commencement of 
 the tertiary period merged into the modern phase of 
 graduated and often extreme temperatures, and this 
 change of climatic conditions determined a corresponding 
 change in life. During the first two periods individuals 
 predominated ; that is, the luxuriant vegetation of early 
 times consisted of numerous individuals belonging to 
 comparatively few groups, whereas at the present day 
 groups or genera predominate, the comparatively homo- 
 geneous nature of the ancient flora being broken up 
 into numerous minor sections depending on the various 
 lines of departure taken by the ancient types in their 
 endeavours to accommodate themselves to the new 
 conditions. 
 
 At the close of the Cretaceous period great geographi- 
 cal changes took place, the bed of the Cretaceous sea 
 was gradually and irregularly elevated, and the present 
 site of England was once more dry land. During the 
 Eocene period the temperature of England, as of Europe, 
 was tropical, and the flora of our country during that 
 period has its nearest living representatives in the hotter 
 parts of India, Australia, Africa, and America. As 
 examples of the flora of that period may be mentioned 
 palms, aroids, cactuses, figs, eucalyptus, etc. All these 
 have long since disappeared from Europe, but their fossil 
 remains are abundant in eocene rocks. To this period 
 
CHAP, vii.] DISTRIBUTION OF PLANTS. 199 
 
 belongs the London clay, which contains many beauti- 
 fully-preserved fossils. Sheppey is also a noted locality 
 for fossils, the fruits of palms being common, accom- 
 panied by the remains of turtles and nautilus shells, etc. 
 The Bagshot Beds near Bournemouth, and Alum Bay in 
 the Isle of Wight, have seams of clay that are rich in 
 fossil leaves. 
 
 During Miocene times the British Isles appear to 
 to have been for the most part dry land, the Bovey 
 Tracey Beds occurring between Exeter and Teignmouth, 
 however, belong to this period, and contain the remains 
 of numerous plants, mostly leaves, the commonest being 
 that of a great coniferous tree, Sequoia Couttsice, which 
 appears to be closely allied to the gigantic Wellingtonia 
 Gigantea of California. Leaves of species of vine, 
 cinnamon, and fig are also common, pointing to a con- 
 tinuation of the warm climate of the previous period. 
 The flora that clothed the European Alps during this 
 period was not unlike the vegetation of the forests of 
 India and Australia at the present time. During the 
 latter portion of the Miocene age there are evidences of 
 a cooling down of the climate, the characteristic vege- 
 tation consisting of beeches, elms, poplars, hornbeams, 
 etc. 
 
 During the Pliocene age the flora shows a gradual 
 decrease of temperature, the tropical types of vegetation 
 of Eocene and Miocene times gradually retreating south- 
 wards, their place being taken by trees that still exist 
 here at present, as oaks, poplars, willows, alders, etc., 
 mixed, however, with forms that now occur in warmer 
 climates, as bamboos, sarsaparillas, magnolias, and figs. 
 In British rocks belonging to this period, which are 
 
200 BOTANY. [CHAP. vn. 
 
 almost entirely confined to Norfolk and Suffolk, the 
 fossil remains of cones of the Scotch fir, leaves of white 
 and yellow water-lilies, oak, hazel, bogbean, blackthorn, 
 etc., occur. During this period the geographical features 
 of Europe were very different to those of the present 
 time ; the Irish Sea and the English Channel had not 
 then been formed, and England at that time was con- 
 tinuous with the Continent by way of France and Spain, 
 the North Sea only extending as far south as Kent, the 
 Straits of Dover and the English Channel being formed 
 at a much later period. At this time the flora of Eng- 
 land was probably much the same as that of France, 
 Spain, and Portugal at the present day, and we have 
 remaining in the South of England a few plants that 
 have existed from that period. As examples of the 
 remains of this ancient flora may be mentioned the 
 marsh wood spurge (Euphorbia pilosa), found in Somer- 
 setshire, and at the present day a common species in 
 the Mediterranean region; the large-flowered butter- 
 wort (Pinguicula grandiflora), occurring in Ireland, and 
 Pinguicula lusitanica, found in a few places in the west 
 of England, are both characteristic Iberian plants. 
 
 The Pleistocene or Glacial period that followed the 
 Pliocene, almost completely obliterated the existing flora 
 of Great Britain, which along with the whole of Northern 
 Europe, was completely buried beneath an ice-sheet, in 
 many places several thousands of feet thick, driving south- 
 wards before it the flora and fauna of the northern 
 portion of Europe. At this period an arctic vegetation 
 spread over Northern and Central Europe, reaching as 
 far as the Pyrenees, and accompanied by characteristic 
 northern animals, as the reindeer, etc. In England the 
 
CHAP, vii.] DISTRIBUTION OF PLANTS. 201 
 
 ice-sheet did not pass south of the Thames valley, 
 consequently in the southernmost portions, the plants 
 already enumerated as remnants of the Pliocene age 
 managed to hold their own. During this period of 
 intense cold a new alpine flora was established in Wales 
 and Scotland, when the mountain summits of these coun- 
 tries were low islands, or members of chains of islands 
 that extended to Scandinavia through a glacial sea, and 
 a fair proportion of the Scotch Alpine flora arrived 
 during this period from the last-named area. 
 
 At the period when the arctic rigour of the glacial 
 period gave way to the present conditions of climate, 
 the area now occupied by the German Ocean was dry 
 land ; in other words, England formed a western exten- 
 sion of the continent, and along this route the great 
 bulk of our lowland flora, as existing at the present day, 
 reached us from the Germanic region of the mainland. 
 
 In a general view of the distribution of plants over 
 the surface of the globe as existing at the present day, it 
 is observable that there is far less adaptation to exist 
 under extreme climatic conditions amongst Cryptogams 
 than amongst Phanerogams. This is, to a great extent, 
 due to the fact that in Cryptogams the primordial 
 method of utilizing water as the agent for enabling the 
 antherozoid, or fertilizing body, to reach the oosphere 
 has been constantly adhered to in every group ; and 
 although Cryptogams can endure a greater amount of 
 cold than Phanerogams, being found in higher latitudes 
 and at greater elevations, on the other hand Phanerogams 
 are far more abundant in arid regions than Cryptogams. 
 
 Marine vegetation, with very few exceptions, consists 
 
202 BOTANY. [CHAP. vii. 
 
 of Algas, and in the sea there are fairly well defined 
 zones of vegetation. As a rule the green and olive- 
 brown groups of seaweeds are most numerous in cold 
 regions, whereas red seaweeds become more abundant 
 as the tropics are approached. The larger highly- 
 organized seaweeds do not grow at a very great depth, 
 but form a fringe round the shores. Amongst Alg89 we 
 meet with considerable variety as regards adaptation to 
 circumstances ; many species are true parasites, cases of 
 mutualism or commensalism between Algae and some of 
 the lower forms of animal life are on record. The 
 dimensions of Alg89 are very various, the diatoms are 
 unicellular and microscopic, whereas Macrocystis pyrifera 
 is frequently five hundred feet in length. The species 
 of Lessonia grow erect with the habit of forest trees, 
 forming in fact submarine forests. 
 
 Ferns occur in all climates between the polar regions, 
 where, however, few species occur, to the tropics, where 
 they are by far most abundant and attain their maximum 
 of development. Many genera are limited to equatorial 
 regions, or extend very little beyond ; on the other 
 hand, few genera are confined to a single continent. 
 The tree- ferns are tropical, although some species extend 
 to Tasmania and New Zealand. On the Andes they 
 grow along with the cinchona trees at an elevation of 
 four to eight thousand feet. The majority of ferns 
 thrive only under a peculiar combination of climatic con- 
 ditions, dry regions producing very few species ; damp, 
 shady places, with a comparatively equable temperature, 
 suit them best, consequently we meet with the greatest 
 percentage compared with the entire flora in insular 
 climates ; in fact, the smaller and more distant from 
 
CHAP, vii.] DISTRIBUTION OF PLANTS. 203 
 
 continents islands are, the larger is the proportion which 
 ferns bear to Phanerogamic plants. 
 
 The family of ferns has probably more fossil represen- 
 tatives than any other group of plants, and occur in all 
 fossiliferous formations from the Devonian upwards, 
 being especially abundant during the Carboniferous 
 period. The fossil species present the same broad 
 features as those existing at the present day ; no fossil 
 ferns have as yet been discovered that cannot be referred 
 to some existing type. 
 
 The distribution of Phanerogams may be studied from 
 two standpoints; latitude and altitude, the predomi- 
 nating factor in determining the distribution being in 
 both cases temperature, and a series of changes can be 
 traced in the lowland flora from the equator to the poles, 
 each zone being characterized by the predominance of 
 certain groups of vegetation that often give a feature to 
 the landscape. These zones of vegetation do not follow 
 the parallels of latitude, but are undulatory, correspond- 
 ing with the isotherm of the particular month in which 
 there is the greatest development of vegetable life. 
 
 In very high latitudes, lichens and mosses are only 
 met with, then follow grasses, species of saxifrage, 
 buttercup, woodrush, etc., species of rhododendron with 
 showy flowers are also present in the Arctic Zone. 
 Amongst trees the birch predominates, and extends 
 nearly to the North Cape; firs and pines are also 
 present. 
 
 In the Sub-arctic zone, including the northern parts of 
 Norway, Siberia, Iceland, and the Faroe Islands, firs 
 and willows are the predominating trees, and in some 
 localities are very much dwarfed, but in Siberia very 
 
204 BOTANY. [CHAP. vn. 
 
 extensive pine forests occur. Poplars and birches are 
 also present. Grasses and ling (Calluna vulgaris), also 
 junipers, are amongst the social or gregarious plants 
 that form features in the physiognomy of certain dis- 
 tricts in this zone in northern latitudes. In the 
 southern hemisphere the same zone embraces a few 
 barren islands. 
 
 The Cold Temperate Zone in the Northern Hemisphere 
 includes England, Northern France, Germany, etc. ; the 
 forest trees are all dicotyledons, amongst which conifers 
 predominate ; the heaths and grasses are the most con- 
 spicuous of social plants. This region is most favourable 
 for the cultivation of wheat. 
 
 The Warm Temperate Zone includes in Europe the 
 southern flora as far as the Pyrenees, also the mountains 
 of the south of France and the North of Greece, Asia 
 Minor, a zone extending between the Black sea and the 
 Caspian, Northern China, Japan, and a belt in North 
 America are also included. It is sometimes spoken of 
 as the zone of evergreen trees, and includes numerous 
 sub-tropical forms, as laurels, myrtles, figs, vines, etc. 
 The dwarf palm (Chamerops liumilis), a small species, is 
 the only European representative of the Palm order. 
 
 The Sub-tropical Zone extends from the tropics to 
 34 north and south latitude, with a mean annual tem- 
 perature ranging between 60 and 70 Fahr., and a 
 summer temperature between 74 and 83 Fahr. In this 
 zone vegetation is green throughout the year. It has 
 been called the region of Myrtacese and Lauraceee on 
 account of the predominance of species belonging to 
 these orders. Heaths and their Australian representa- 
 tives, epacrids, are also conspicuous. The arid regions 
 
CHAP, vii.] DISTRIBUTION OF PLANTS. 205 
 
 occurring in this zone have each a marked flora, as the 
 cactus group in Mexico, the euphorbius or spurges in 
 Africa, and numerous succulent and fleshy plants in the 
 Asiatic region. The date-palm also constitutes a feature 
 of the arid region in Egypt. 
 
 The Tropical Zone, extending from the i5th degree on 
 each side of the equator to lat. 23, having a mean annual 
 temperature of 7 3 to 79Fahr.,and a summer heat of 80 to 
 86 Fahr., is characterized by the abundance of tree-ferns 
 and numerous species of Ficus ; this zone is also the 
 head-quarters of the orders Piperacece and Melastomacece. 
 
 Equatorial Zone, extending 15 on each side of the 
 equator, has a mean annual temperature of 79 to 85 
 Fahr. ; the characteristic vegetation consists of palms, 
 bananas, arborescent grasses (as the bamboo, sugar-cane, 
 etc.), orchids, and species belonging to the order 
 Zingiberacece, as the ginger plant, etc. 
 
 Comparing the zones of altitude with those of latitude 
 the following gives a broad idea of the relative elevation 
 at which the groups previously mentioned occur. 
 
 Equatorial Region of palms and bananas extend from 
 the sea-level to 2,000 feet. 
 
 Tropical Region of tree-ferns and figs, 2,000 to 3,800 feet. 
 
 Sub-tropical Region of myrtles and laurels from 3,800 
 to 6,000 feet. 
 
 Warm Temperate Region of evergreen dicotyledonous 
 trees, 6,000 to 8,000 feet. 
 
 Gold Temperate Region of deciduous dicotyledonous 
 trees, 8,000 to 9,500 feet. 
 
 Sub-arctic Region of conifers, from 9,500 to 11,500 feet. 
 
 Arctic Region, characterized by bright-flowered rhodo- 
 dendrons, 11,500 to 13,500 feet. 
 
206 BOTANY. [CHAP. vii. 
 
 Polar Region of alpine plants, a few species of flower- 
 ing plants, mosses, and lichens, the last-named usually 
 being the last to appear in both latitude and altitude. 
 
 It must be clearly understood that the altitudes given 
 are merely approximate, and not of universal application ; 
 in fact, as a rule, when the same species occur on both 
 sides of a mountain, the altitude at which they occur 
 varies considerably on opposite sides. This will be 
 readily understood when the variation in the snow-line 
 is remembered. This in the Peruvian Andes exceeds 
 18,000 feet; in the Himalayas, in lat. 26 N., the snow- 
 line is about 18,000 feet on the north side and 15,500 feet 
 on the south side ; whereas in Norway it is under 
 4,000 feet, and close to the Arctic Ocean it is 2,000 feet. 
 
INDEX. 
 
 ACTION of plants on atmo- 
 sphere, 72. 
 
 Advantages and disadvantages 
 of parasitism, 87 ; of sapro- 
 phytes, 87. 
 
 Age of trees ascertained by 
 annual rings, 48. 
 
 AlgoB, 9. 
 
 Alternation of generations, 122. 
 
 Anemone appenina, 145. 
 
 Anemophilous, or wind-ferti- 
 lized plants, 24. 
 
 Anemophilous flowers, charac- 
 ters of, 129. 
 
 Angiospermce, characters of, 178. 
 
 Angiosperms, 31. 
 
 Animal kingdom, characters of, 
 6. 
 
 Annual plants, 25 ; rings, 48. 
 
 Antherozoids, 22, 34, 119. 
 
 Arum maculatum, 115, fig. 33. 
 
 Asexual reproduction, 22. 
 
 Assimilation, 61. 
 
 Bark, 48. 
 Bast-fibres, 51. 
 
 Bees, their power of recognizing 
 colours, 145. 
 
 Biennial plants, 25. 
 Bilabiate corolla, 142. 
 Birds' nest orchis, 87. 
 Bitter tastes, a means of protec- 
 tion, 114. 
 
 Bladderwort (Utricularia), 71. 
 Bramble, no. 
 Broomrape (OrdbancJie), 79. 
 Bryony (Bryonia dioica), 112. 
 Butterwort (Pinguicula), 71. 
 
 Cactus (Ecliinocacius Decaisne- 
 anus), 37, fig. 10. 
 
 Calamites, 189. 
 
 Calyx, 30; petaloid, 182. 
 
 Cambium, 47. 
 
 Carbonic dioxide, 54. 
 
 Carnivorous plants, 72 ; how 
 insects are captured, 76. 
 
 Carnivorous property an ac- 
 quired one, 74. 
 
 Carpels, 31, 162. 
 
 Cauline bundles, 44. 
 
 Cell of celandine, 33, fig. 8. 
 
 Cell-contents, 35. 
 
 Cell-sap, 38. 
 
 Cell-wall, 32. 
 
 Cellulose, 32. 
 
208 
 
 BOTANY. 
 
 Cephalotusfollicularis, 75. 
 Chemical composition of plants, 
 
 54- 
 
 Chlorophyll, 7, 35 ; grains, 63. 
 Christmas rose, fruit of, 163, 
 
 fig. 46. 
 Cilia, 22. 
 
 Cleistogamous flowers, 149. 
 " Clock " of dandelion, 53. 
 Collateral bundles, 44. 
 Colours of flowers, 144. 
 Commensalism, 84. 
 Compositce, 151. 
 Concentric bundles, 44. 
 Conditions under which life 
 
 exists, 16. 
 Coniferce, 176. 
 Conjugation, 118. 
 Convolvulus, no. 
 Corolla, 30. 
 
 Corylus avellana, 128, fig. 4. 
 Cotton, 51. 
 
 Cross-fertilization, 23. 
 Crypiogamia, characters of, 172. 
 Cryptogams, 23 ; occurrence of, 
 
 121. 
 Crystals in cells of beet, 36, fig. 
 
 9- 
 Cultivation of plants, objects of, 
 
 146. 
 Cycad (Cycas circinalis), 94, fig. 
 
 53- 
 
 Cycas, section through epider- 
 mis, 40, fig. 12. 
 
 CycadeoB, 176. 
 
 Daffodil, 131. 
 
 Dandelion, fruit of, 153, fig. 43. 
 
 Dead-nettle, 141. 
 Degeneration, 18. 
 Degradation products, 89. 
 Diagram of parts of typical 
 
 flower, 31, fig. 7. 
 Dicotyledons, 45. 
 Dicotyledones, characters cf, 
 
 ifi. 
 
 Dicotyledonous stem, section of, 
 49, fig. 15. 
 
 Dioecious, 127. 
 
 Dimorphous flowers, 137. 
 
 Direction of growth, what due 
 to, 69. 
 
 Distribution of plants, 192. 
 
 Division of labour in the inflores- 
 cence, 151. 
 
 Dodder (Cuscuta}, 79. 
 
 Dog-daisy (Bellis perennis), 151. 
 
 Double flowers, 147. 
 
 Drooping of plants, cause of, 
 68. 
 
 Ducts, 51. 
 
 Ear of wheat, 129, fig. 36. 
 
 Effect of vegetation on climate, 
 70. 
 
 Embryo, 124; structure of, 172. 
 
 Endosmose, 58. 
 
 Endosperm, 171. 
 
 Epidermis, 20; of Euonymous 
 Japonica, 39, fig. II. 
 
 Epigynous, 164. 
 
 Epipetalous, 163. 
 
 Evergreens, 181. 
 
 Evolution of all plants from sea- 
 weeds, 92; of colour in flowers, 
 145 ; of leaves, 99. 
 
IXDEX. 
 
 209 
 
 Exosmose, 58. 
 
 Eyebright (Euplirasia), So. 
 
 Fibro-vascular bundles, 20. 
 
 Figwort, 135. 
 
 Filament, 30. 
 
 Fission, n. 
 
 Flagellate Protozoa, 6. 
 
 Floral-bract, 151. 
 
 Flower, structure of, 30. 
 
 Flowerless plants, 124. 
 
 Foliar vascular bundles, 43. 
 
 Food constituents of plants, 55. 
 
 Fossil fern (Neuropteris hetero- 
 pliylla}, 189, fig. 56; funguses, 
 1 86; plants, 186; seaweeds, 
 1 86. 
 
 Fruit, 31. 
 
 Fruits, dispersion of, 170. 
 
 Fuchsia globosa, 126, fig. 49. 
 
 Fucus, 119. 
 
 Fucus vesiculosus, 14. 
 
 Fundamental tissue, 21, 42. 
 
 Fungus parasites, 79. 
 
 Gamosepalous, 163. 
 Genera of plants, 185. 
 Geological periods, 188. 
 Geotropism, 68. 
 Goat willow, 128. 
 Growth, definition of, 2. 
 Gymnosperms, 31, 125 ; age of, 
 
 93; characters of, 176. 
 Gynandrous, 164. 
 
 Hazel (Coryhis avellana), 25, fig. 
 
 35- 
 
 Heliotropic, positively, 66 ; 
 negatively, 67. 
 
 Heliotropism, 66. 
 Hepaticce, 20. 
 Hetercecism, 84. 
 Heteromorphous flowers, 136. 
 Homomorphous flowers, 136. 
 Honeysuckle (Lonicera glauca), 
 
 29, fig. 6. 
 
 Horse-chestnut leaf, 103, fig. 29. 
 Host, 79- 
 How plants obtain their food, 57. 
 
 Indian corn (Zea mays}, 19, fig. 
 
 3- 
 
 Inferior ovary, 167. 
 Inflorescence, 149 ; protection of, 
 
 154. 
 
 Inorganic matter, 4. 
 Insectivorous plants, 72. 
 Involucre, 152. 
 Iron necessary for chlorophyll 
 
 formation, 56. 
 
 Jute, 51. 
 
 Leaf, compound, 102 ; of melon, 
 1 01, fig. 28; structure, 61 ; 
 traces, 43. 
 Leaflet, 102. 
 
 Leaves, closing of, 104 ; evolu- 
 tion of, 99 ; uses of, 27. 
 Lepidodendron, 91, 190, fig. 25. 
 Lichens, nature of, 85. 
 Life-cycle of fern, 123. 
 Lilac (Syringa vulgaris}, 150. 
 Lime flower, 134, fig. 38. 
 Linen, 51. 
 Liverworts, 20. 
 I Livistonia australis, 179, fig. 54. 
 
210 
 
 BOTANY. 
 
 Lords and ladies, 115, fig. 33. 
 Lousewort (Pedicular is), So. 
 
 Maize, 19, fig. 3. 
 
 Maple, fruit of, 171, fig. 52. 
 
 Marchantia, 20. 
 
 Marsh marigold, fruit of, 168. 
 
 Medulla, 45. 
 
 Medullary rays, 45. 
 
 Melon leaf, 28, fig. 5 ; stem, 
 
 section of, 47, fig. 15. 
 Metabolism, 88. 
 Metals in plant tissues, 55. 
 Metastasis, 88. 
 
 Mistletoe (Viscum album], 80. 
 Monocotyledons, 44; characters 
 
 of; i 80. 
 
 Monoecious, 127. 
 Mother-cell of stoma, 39. 
 Multicellular plants, 13, 96. 
 Mushroom (Agaricus campestris), 
 
 87. 
 Mutualism, 84. 
 
 Natural orders of plants, 185. 
 Nile lily (Eichardia cethiopica), 
 
 157. 
 
 Nostoc, 1 1 6. 
 Nucleus, 32. 
 
 Oospore, 123. 
 
 Open bundles, 47. 
 
 Origin of varieties, 17. 
 
 Osmosis, 58. 
 
 Ovary, 164. 
 
 Ovule, 93. 
 
 Oxlip, 136, fig. 39. 
 
 Palisade-tissue, 62. 
 
 j "Palms," 128; dwarf, 155, fig. 
 44 ; stem, section of, 43, fig. 13. 
 
 Pansy (Viola tricolor), 149. 
 
 Pappus, 53, 152. 
 
 Parasites, 79. 
 
 Parasitism, an acquired habit, 
 80; stages of, 80, Si. 
 
 Passion-flower (Passiflora coe- 
 rulea), HI, fig. 32. 
 
 Pea, pod of, 167, fig. 50. 
 
 Peach, fruit of, 169, fig. 51. 
 
 Perennial plants, 26. 
 
 Perianth, 180. 
 
 Periderm, 41. 
 
 Permanent tissue, 44. 
 
 Petals, 30. 
 
 Petiole, 100. 
 
 Phanerogams, 3 1 ; differentiation 
 in, 97. 
 
 PJianerogamia, characters of, 173. 
 
 Phloem, 44. 
 
 Physical work, rays of light pro- 
 moting, 65. 
 
 Pioneers of plant-life, 16. 
 
 Pistil, 31. 
 
 Pitcher-plant (Nepenthes graci- 
 fo'*).77 fig- 2 3 5 structure of 
 pitchers, 78. 
 
 Pitted cells, 34. 
 
 Plant nutrition, effect on atmo- 
 sphere, 71. 
 
 Plants ben ding to wards the light, 
 66 ; bending away from the 
 light, 66. 
 
 Pleurococcus, 12, fig. i. 
 
 Pleurococcus viridis, 9. 
 
 Pollen, 30; grains, 123; masses 
 in orchids, 141, fig. 41. 
 
INDEX. 
 
 211 
 
 Pollination, 30. 
 Polypetalous, 162. 
 Polysepalous, 162. 
 Poppy, corn (Papaver Rhceas), 
 
 150; fruit of, 164, fig. 48. 
 Prickles, 114 ; of roses and 
 
 brambles, no. 
 
 Primary cortex, 45 ; wood, 51. 
 Primordial, or naked cell, 34. 
 Primrose flower, structure of, 
 
 137; fruit of, 163, fig. 47. 
 Promycelium spores, 83. 
 Protection against climate, 98; 
 
 against living enemies, 113. 
 Protective arrangements, 90. 
 Proterandrous, 135. 
 Proterogynous, 135. 
 Prothallus, 122. 
 Protoplasm, 32. 
 Protozoa, 6. 
 Puccinia graminis, life-history 
 
 of, 82, 85, fig. 24. 
 Purification of atmosphere by 
 
 plants, 70. 
 
 Rafflesia, 81,82. 
 
 Eaphides, 36. 
 
 Relationship amongst plants, 
 
 158. 
 
 Eeproduction in plants, 116. 
 Eeproductive phase of plant-life, 
 
 5- 
 
 Eespiration, 28, 70. 
 Eoot-hairs, 58. 
 Eoot, uses of, 26. 
 Eoots of seaweeds, 15. 
 Eose no. 
 
 Eotation of crops, 59 ; of proto- 
 plasm, 35. 
 Eush (Juncus), 33. 
 Eussia matting, 51. 
 Eust of wheat, life history of, 82. 
 
 Sage (Salvia scalarea), 143, fig. 
 42 ; mode of fertilization, 
 
 143- 
 
 Sap-cavity, 32. 
 Saprophytes, 86. 
 Scalariform cells, 34. 
 Seaweed (Fucus vesiculosus), 95, 
 
 fig. 2. 
 
 Seaforikta elegans, 46, fig. 14. 
 
 Secondary wood, 57. 
 
 Section of stem of BceJimeria 
 argentea, 52, fig. 18. 
 
 Seeds, 31. 
 
 Self-fertilization, 23. 
 
 Sepals, 30. 
 
 Sessile, 152. 
 
 Sieve-plates, 51. 
 
 Sieve-tubes, 51. 
 
 Sigillaria, 190. 
 
 Solar light, composition of, 65 ; 
 spectrum, 65. 
 
 Special creation, 7. 
 
 Species, 10; of plants, 185. 
 
 Spiderwort (Tradescantia 8 el- 
 lei), section of stem, 50, fig. 
 
 17. 
 
 Spiral vessels, 51. 
 Sporangia, 122. 
 Spore, 122. 
 Sports, 17. 
 Stamens, 30. 
 
212 
 
 BOTANY. 
 
 Starch, 35 ; test 01,64; of pota- 
 to, 64, fig. 20 1 ; chemical forma- 
 tion of, 3 ; of tapioca, 64, fig. 
 
 20 2 . 
 
 Stellate-cells, 32. 
 
 Stigma, 164. 
 
 Stomata, 20 ; action of, 67 ; 
 
 numbers of, on different 
 
 leaves, 40. 
 Strychnine, 114. 
 Style, 164. 
 
 Sulphur showers, 129. 
 Sundew (Drosera), 74. 
 
 Tendrils, action of, 112; of pas- 
 sion-flower, 112. 
 
 Thalamus, 163. 
 
 Toothwort (Lathrcea squa- 
 maria), 81. 
 
 Tornelia fragrans, 156, fig. 45. 
 
 Tracheides, 49. 
 
 Trimorphous flowers, 137. 
 Typical flower, structure of, 161. 
 
 Unicellular plants, 96. 
 
 Vacuoles, 34. 
 
 Vallisneria spiralis, cell of, 63, 
 
 fig. 19. 
 Variation, origin of, 17; in 
 
 plants, 92. 
 Vegetable kingdom, broad 
 
 features of, 7. 
 
 Vegetative phase of plant life, 5. 
 Venus 's fly-trap (Dioncea mus- 
 
 cipula), 73, fig. 21. 
 Vessels, 49. 
 Violet (Viola adorata), 149. 
 
 Water, movements of, 67. 
 Wood, 43. 
 
 Xylem, 44. 
 
 Yellow rattle (Rhinanthus}, So. 
 
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