Lapas attēli
PDF
ePub

INTRODUCTION.

7

THAT part of the material world which bears the name of the Vegetable Kingdom, consists, like the Animal, of a vast multitude of species, whose outer and inner forms alike offer a prodigious diversity of modifications of one common simple plan of structure. Organic vesicles, usually extending into tubes of various kinds, exclusively constitute what we call Vegetation; but this simplicity of nature is attended by very complex details of arrangement, as is shown in trees, whose framework is knit together by countless myriads of such vesicles and tubes, entangled with an astonishing intricacy of simple arrangement.

Any living combination whatsoever of such vesicles constitutes a plant; but as the combinations themselves are countless, so are the resulting external forms; for, although two or three words may suffice to express all combinations whatsoever in their most general sense, as when the name of thallus is given to the simplest expansion of vegetable matter, while all the more complex forms are included under the name of axis and its appendages, yet ingenuity is exhausted in the attempt to distinguish by appropriate terms the manifold external forms assumed by that axis and the parts which it bears.

Hence it is that wherever the eye is directed it encounters an infinite multitude of the most dissimilar forms of vegetation. Some are cast ashore by the ocean in the form of leathery straps or thongs, or are collected into pelagic meadows of vast extent; others crawl over mines and illuminate them with phosphorescent gleams. Rivers and tranquil waters teem with green filaments, mud throws up its gelatinous scum, the human lungs, ulcers, and sordes of all sorts bring forth a living brood, timber crumbles to dust beneath insidious spawn, corn crops change to fetid soot, all matter in decay is seen to teem with mouldy life; and those filaments, that scum-bred spawn and mould, alike acknowledge a vegetable origin. The bark of ancient trees is carpeted with velvet, their branches are hung with a greybeard tapestry, and microscopical scales overspread their leaves; the face of rocks is stained with ancient colours, coeval with their own exposure to air; and those too are citizens of the great world of plants. Heaths and moors wave with a tough and wiry herbage, meadows are clothed with an emerald mantle, amidst which spring flowers of all hues and forms, bushes throw abroad their many-fashioned foliage, twiners scramble over and choke them, above all wave the arms of the ancient forest, and these too acknowledge the sovereignty of Flora. Their individual forms too change at every

b

step. With every altered condition and circumstance new plants start up. The mountain side has its own races of vegetable inhabitants, and the valleys have theirs; the tribes of the sand, the granite, and the limestone are all different; and the sun does not shine upon two degrees on the surface of this globe the vegetation of which is identical: for every latitude has a Flora of its own. In short, the forms of seas, lakes, and rivers, islands and peninsulas, hills, valleys, plains, and mountains, are not so infinitely diversified as that of the vegetation which adorns them.*

Botanists have gathered together these endless forms, have studied and arranged them, and calculated their numbers, which amount to more than 92,000 species: a mighty host whose ranks are daily swelled by new recruits.

This vast assemblage has not been gathered together in a few years; it is coeval with man, and we cannot but feel that the study of the distinctions between one plant and another commenced with the first day of the creation of the human race. The name indeed of Botany is modern; but its antiquity dates from the appearance of our first parents. We may assume it as a certain fact that the Vegetable Kingdom was the first to engage the attention of man, for it was more accessible, more easily turned to useful purposes, and more directly in contact with him than the Animal. Plants must have yielded man his earliest food, his first built habitation; his utensils and his weapons must alike have been derived from the same source. This could not fail to produce experience, and especially the art of distinguishing one kind of plant from another, if it were only as a means of recognising the useful and the worthless species, or of remembering those in which such qualities were most predominant. This would involve from the very beginning the contrivance of names for plants, together with the collection of individuals into species; and the mental process by which this was unconsciously effected gradually ripened into the first rude classifications that we know of. By placing together individuals identical in form and the uses they could be applied to, species were distinguished; and by applying a similar process to the species themselves, groups analogous to what we now call genera were obtained. The last step was to constitute classes, which were recognised under the well-known names of " grass, and herbs yielding seed, and fruit trees yielding fruit."

It is in the tropics that the prodigious diversity of appearance among plants is most strikingly exemplified. The beautiful forest scene, given as a frontispiece to this work, is copied from a plate in the Flora Brasiliensis of Dr. Von Martius, who describes it thus: "The landscape is divided into two unequal parts by a tree (*) rising to the height of 70 or 80 feet; it is Eschweilera angustifolia. It is overrun with ropes which eling around it, or hang down in various festoons; these ropes yield a milky white or yellowish juice when wounded, and probably belong to the Dogbanes or Asclepiads; other twiners, decorated with fine, large, beautifully green leaves, consist of species of Banisteria, Smilax, Serjania and Bignonia, voluptuously intertwined and entangled. A little above there is a tuft of the large leaves of Anthericum glaucum, and from the summit of all hangs down some unknown kind of Bromelwort. On the left stands a slender Acacia, whose bark is embraced by some parasitical climber; then comes the Couratari legalis, a high tree, whose timber is used in house-building; it forms a stem 60 or 70 feet high without a branch, and then spreads into a hemispherical head; owing to the slowness of its growth it is overrun with epiphytes. In front of the Acacia is a low tree with a close head and a shining bark; that is a Ficus americana, and Banisterias are shooting downwards from among its branches. Before this lie the bones of some fallen giant of the forest, overspread with great tufts of Anthericum and Epiphyllum phyllanthus. Close by, some Psychotria expands its large leaves and wide branches. A Heliconia and a Phrynium start from the mud and marshy foreground; a great patch of Anthericum umbellatum flourishes on the rotten trunk, and just in front is a group of Agarics, such as we see in the woods of Europe. The tall tree on the right of Eschweilera, with a smooth bark and pinnated leaves, is an Inga; next it is a small bush of Leandra scabra, behind which is a thicket of Palicuria and Renealmia nutans, backed by the Eriodendron leiantherum. The beautiful Palm to the right of them is Geonoma Pohliana. The foreground on the right is occupied by Ficus longifolia, conspicuous with its ample foliage, and loaded with epiphytes of various kinds, especially with Anthericum glaucum, umbellatum, and longifolium, and Caladium auritum. These and different kinds of Bilbergia have also taken possession of the rotten trunks in the neighbourhood. Near these is the white-barked Cecropia peltata, with large green leaves hoary with down on the under side." The cable-like climbers on the extreme right are not named by Dr. Von Martius.

But as human intelligence advanced, and a knowledge of things increased, such rude distinctions were improved, and when no means existed of appreciating the value of minute or hidden organs, the functions and existence of which were unknown, objects were at first collected into groups, characterised by common, external, and obvious signs. Theophrastus had his water-plants and parasites, pot-herbs and forest trees, and corn-plants; Dioscorides had aromatics, and gum-bearing plants, eatable vegetables and corn-herbs; and the successors, imitators, and copiers of those writers, retained the same kind of arrangement for ages. It was not till 1570 that

Lobel, a Fleming, improved the ancient modes of distinction, by taking into account characters of a more definite nature than those which had been employed by his predecessors; but he was soon succeeded by others, among the most distinguished of whom were Casalpinus, an Italian who wrote in 1583, the celebrated Tournefort, and especially our countryman, John Ray, who flourished in the end of the seventeenth century. The latter added much to the knowledge of his predecessors, and had so clear and philosophical a conception of the true principles of classification, as to have left behind him in his Historia Plantarum the real foundation of all those modern views which, having been again brought forward at a more favourable time by Jussieu, are generally ascribed exclusively to that most learned Botanist and his successors. Ray, however, laboured under the great disadvantage of being too far in advance of his contemporaries, who were unable to appreciate the importance of his views or the justness of his opinions; and who therefore, instead of occupying themselves with the improvement of his system, set themselves to work to discover some artificial method of arrangement, that should be to Botany what the alphabet is to language, a key by which the details of the science may be readily ascertained. With this in view, Rivinus invented, in 1690, a system depending upon the formation of the corolla; Kamel, in 1693, upon the fruit alone; Magnol, in 1720, on the calyx and corolla; and finally, Linnæus, in 1731, on variations in the stamens and pistil. The method of the last author has enjoyed a degree of celebrity which has rarely fallen to the lot of human contrivances, chiefly on account of its clearness and simplicity; and in its day it effected a large amount of good.

It was soon, however, perceived by those who studied the Vegetable Kingdom profoundly, that no improvement could be made in the knowledge of its true nature, of the best manner of arranging it, or even of the purposes to which it might be applied, unless the philosophy of the subject was investigated; and this became daily more apparent as the materials collected by botanical travellers accumulated. It was found that the few thousand ill-examined plants which inhabit Europe gave a most imperfect idea of the vegetation of the globe; that methods of classification which were tolerable so long as species were few, became useless, or an incumbrance as the number increased, and that no real progress in Botany, as a branch of science, could be hoped for so long as a few arbitrary signs were taken as the basis of all arrangement. The older Botanists knew little of vegetable physiology; and of the laws of vegetable structure they had at the most but a glimmering perception. Yet those subjects are the foundation of all sound principles of classification. The recognition of that fact immediately led to the investigation of new branches of knowledge, in which discoveries were daily made, and it has terminated in a universal adoption of the principles of Ray, improved and extended by the admirable views of Jussieu, as developed in his Genera Plantarum secundum Ordines

Naturales disposita,-a book of wonderful sagacity and most profound

research.

Since the appearance of that work Botany has assumed a new position in the ranks of science, and the evidence from which conclusions are to be drawn has multiplied beyond all that could have been anticipated. Twenty thousand species at the utmost could have been known to Jussieu in 1789; we have seen that the number actually on record at the present day amounts to more than 92,000. Vegetable Anatomy, the foundation of Vegetable Physiology, was at the former period in the state in which it had been left by Grew and Malpighi; it has since engaged the attention of the most acute and indefatigable observers, now armed with optical instruments of surprising excellence. The resources of Chemistry and Natural Philosophy have been enlisted in its cause; and the result is the accumulation of a prodigious mass of facts, the best mode of arranging which is the great problem that modern science has to solve.

That no artificial mode of classifying the vast materials of Botany could satisfy the human mind was clearly perceived and fully admitted by Linnæus himself, when he declared a Natural System to be the primum et ultimum in botanicis desideratum (Phil. Bot. § 77). That no insuperable obstacle to its attainment could exist in the nature of things became evident the moment that the work of Jussieu was before the world. That Botanist for the first time proposed distinctive characters for the groups of genera, which he called Natural Orders, and those characters were framed with such skill that a large proportion of his distinctions is still unaffected by the progress of modern discovery. The manner in which he obtained the distinctions of his Natural Orders was thus described by himself :—‘ -“ C'est ainsi que sont formées les familles très naturelles et généralement avouées. On extrait de tous les genres qui composent chacune d'elles les caractères communs à tous, sans excepter ceux qui n'appartiennent pas à la fructification, et la réunion de ces caractères communs constitue celui de la famille. Plus les ressemblances sont nombreuses, plus les familles sont naturelles, et par suite le caractère général est plus chargé. En procédant ainsi, on parvient plus sûrement au but principal de la Science, qui est, non de nommer une plante, mais de connoître sa nature et son organisation entière.”

The Natural Orders thus obtained were bound together into a system by adopting the important distinctions of Acotyledons, Monocotyledons, and Dicotyledons, and then by subdividing the two latter into Classes mainly characterised by the insertion of the stamens or the condition of the corolla; as will be more particularly explained hereafter.

It was not, however, to be expected that the views of Jussieu should be just in all respects, or that his scanty materials would enable him to form a plan of classification sound and perfect in all its parts. On the contrary, his system abounded in errors and imperfections, and, in fact, the latter years of his life were occupied in striving to improve and consolidate it. The same object has been sought by great numbers of those who have succeeded him, and every few years of late have witnessed the production of some scheme of classification which, although founded essentially upon the groundwork of Jussieu, differed nevertheless in numerous details. In another place, the principal of these schemes will be mentioned. It will be for the present sufficient to say that, beginning with Brown in 1810, and ending with Adolphe Brongniart in 1843, the mass of suggestions and improvements which has been collected renders comparatively easy the task of applying Jussieu's principles of classification to the vast multitudes of species now forming the Vegetable Kingdom.

The true principles of classification, however much they may have been amplified and refined upon, were in reality expressed by Ray, when he defined a Natural System to be that which neither brings together dissimilar species, nor separates those which are nearly allied. However much the words of this definition may have been varied, it still retains the very meaning given to it by its author. A species, said Jussieu, consists of individuals very much alike in all their parts, and retaining their resemblances from generation to generation. Those species are to be associated which correspond in the greater number of their characters; but one constant is of more importance than several inconstant characters. these two axioms hangs the whole principle of Natural classification.— (Genera Plantarum Præf.) And then he proceeded to show how a group of species combined upon this principle forms a Genus, of Genera an Order, and of Orders a Class; the same rules of combination being observed throughout, with this difference only, that the larger the group the fewer the characters by which it is limited (Quò generalior enim extat plantarum ordinatio quælibet, eò paucioribus utitur signis definientibus).

On

But it is far more easy to lay down principles than to put them in execution. The definition of Ray is perfect, but its application is surrounded with difficulty. The very first point to settle in attempting to carry out his views is by what rule the dissimilarity or alliance of species is to be determined. In fact, very different ideas of likeness or unlikeness are entertained by different observers. The common people can see no difference of moment between a Daphne, and a Cherry, and a Rhododendron, but call them all Laurels, although a Botanist fails to perceive their resemblance. On the other hand, there seems to the vulgar eye no connection between the Hemp plant and the Mulberry tree, and yet the Botanist brings them into close alliance. Nor are these conflicting views confined to the ignorant and the uneducated; such differences of opinion may be found among Botanists themselves. For instance, Linnæus joined Arum with Phytolacca under his Piperitæ, and Convolvulus with Viola under his Campanacei, combinations which modern Botanists entirely repudiate; and in like manner the association of Hugonia with Chlenads by Endlicher, of Nepenthes with Birthworts by Brown, of Planes with Witch Hazels by Adolphe Brongniart, of Vines with Berberries by the Author of this work, of Spurgeworts with Heathworts and Chenopods by Fries, are so many modern instances of peculiar views from which other Botanists withhold their assent.

It is therefore of the first importance to settle with something like precision what it is that constitutes likeness among plants, or, as it is technically called, their affinity.

The reason why the vulgar commit mistakes in judging of natural affinity is, because they draw their conclusions from unimportant circumstances, the chief of which are size, form, and colour. The similitude of size gave rise to the old notion that all trees made a class by themselves; which is as if in a classification of animals the horse, the lion, and elephant were placed in a different part of the animal kingdom from the rat, the cat, and the goat.. Form is another of the false guides which lead to error; if all round-leaved or square-stemmed plants are to be associated, so ought glass to be classed with the diamond when it is cut to the same shape. Colour is less a source of mistake, and yet it is sometimes unconsciously employed by the superficial observer, as when he calls all yellow-flowered Composites Marigolds, and all white-flowered vernal bushes Thorns. It

« iepriekšējāTurpināt »