THE NEW BOTANY.* THE Darwinian theory, which has thrown so
abundant a light upon the zoological, is less potent in respect of the botanical phenomena of biological science. Plants gain their livelihood, so to speak, after a far simpler fashion than all but the lowest animals do ; they only exceptionally feed upon each other, and possess no organs enabling them to seek food or pursue prey. Hence natural selection has had less material to work upon in the vegetable than in the animal kingdom ; and while in the latter a complex and varied morphology is the outcome of the struggle for existence, in the former the survival of the fittest depends chiefly upon facts belonging to the domain of chemistry and physics. These considerations render intel- ligible the imperfections of botanical classifications, compared with the elaborate systems of zoology, to which, besides, the study of developmental forms lends a powerful aid that various circumstances refuse to the sister-science. Nevertheless, the progress made by the latter branch of natural science during the last two decades is in some respects even more striking than what has been achieved in zoology. A generation ago,
• Lectures on the Physiology of Plaids. By B. H. Vines, D.Sc.. F.H.B. Cambridge : University Press.—A Counts of Practical Instruction in Bo'ane. By F. O. Bower, M.A., F.H.B.. and S. H. Vines. D.Sc.. F.H.B. With a Preface by W. T. Thiselton Dyer, 0.55.0., F.R.P. London: Macmillan and Co.
botany was mainly a categorisation of plant-forms under so-called natural systems, based principally upon external characters, and its biological interest was comparatively small. Sir Joseph Hooker, by his classical inquiries into the distribution of plants in space and time, opened new and most important fields of speculation and research, and the patient labours of German botanists have almost created the science of vegetable physiology, which the energy, ability, and insight of the authors of the works before us have brought to the forefront of biological studies in this country. The position, though but newly won, is well deserved. For it is not too much to say that the origins of life are more likely to be closely approached among the complicated physical and chemical phenomena of plant-life than among any that engage the attention of men of science.
The reasons are obvious. Not only do plants stand in nearer relation to the inorganic world than animals, but physiological botany is far more susceptible of the fruitful process of experi- mentation than animal biology. The conditions of their existence can be modified almost indefinitely, and the results observed with an exactness not attainable in the case of animals ; while their habits, natural and induced, can be studied with a close- ness and continuity obviously impossible where organisms for the most part constantly changing their position in space, form the subject of investigation. The agenoies of light, gravity, and temperature can be applied, modified, or withdrawn at the will of the experimentalist, and the effects of crossing and interbreeding determined with an accuracy that leaves little to be desired. In a word, the vast majority of the vegetable forms of life can be interrogated by experiment and observation to an extent limited only by the knowledge and patience of the observer ; and what obscurity may attend the answers lies rather in their biological significance than in their substance.
In some respects, the commonest roadside weed is a more wonderful example of Nature's handiwork than the most com- plicated and specialised animal form. The internal as well as the external morphology of plants is comparatively simple; but therein, in truth, lies the marvel. They exhibit mobility and contractility without the vestige of a muscular tissue; they show no trace of a nervous system, yet the impulse of the faintest touch is in some instances transmitted throughout their fabric almost instantaneously ; their juiccs are distri- buted with the aid of no active circulatory apparatus ; and they elaborate from almost elemental materials an infinite number of highly complex substances that form the foods, the remedies, and the poisons of humanity. Each individual plant is, in fact, a most wonderful chemical workshop. Within it, without the aid of either special organs or special tissues, synthetic and analytic processes are carried on of unparalleled and inimitable complexity and delicacy, upon the maintenance of a certain equilibrium between which the vitality of the plant depends. But that vitality does not seem thus to originate. It resides in a mere speck of protoplasm, which hands on the spark from generation to generation where the race is perpetuated by spores or seeds ; and in all other cases also, the workshop, devoid of apparatus, starts upon a like basis of protoplasm, differing from all other known forms of matter in that indefinable property which we term vitality. It is only this vital protoplasm that possesses a truly synthetic capacity ; dead, or rather lifeless, protoplasm seems to be the mere passive material of analytical processes chiefly, perhaps, of an exoteric character.
Of Dr. Vines's carefully and clearly written volume, in which, for the first time in the English language, the subject of the " Physiology of Plants " has met with adequate treatment perhaps the most interesting chapters are those dealing with the synthetic and analytic processes we have alluded to,—in other words, with what is known as the constructive and destructive metabolism of plants. The term " destructive," by the way, though fully warranted by scientific usage, is hardly a happy one, the so-called destructive phenomena of living organisms being merely molecular or elemental rearrangements necessary to their full life. Old Izaak Walton, in his amusing panegyric of water, cites with approval the common opinion of his time that plants feed wholly on that element ; and modern science has shown that in a certain sense the theory is true. For water, though only one of the foods of plants, is the vehicle of all the rest,—of the carbonic acid of the atmosphere, and of the phosphorus, sulphur, nitrogen, lime, potash, and iron they derive from the constituents of the soil by absorption in a state of solution through the fibrils of the root. An instruc- tive woodcut on p. 133 of Dr. Vines's volume represents an
experiment that shows how essential are these elements to a thriving plant. Five plants of buckwheat were grown in as many bottles containing various saline solutions. The plant grown in the central bottle of the group, which was filled with a solution in which all the above elements were present, attained a bulk from ten to a hundred times as great as that of the plants grown in the other bottles, in which one or more of the elements were lacking. It is curious that iron playa a part in the economy of plants not unlike that assigned to it in animal physiology; and plants, like animals, deprived of iron, lose their colour, and fall into a condition of chlorosis. Of the organic constituents of the plant-cell, the most important are the nitrogenous proteids, or albumen-like substances, and the carbo-hydrates, or compounds of carbon, oxygen, and hydrogen—sugar, starch, and cellulose. The elucidation of the mode of formation of these substances, mainly from nitro- genous salts, carbonic acid, and water, is the most interesting, and at the same time the most difficult, problem of vegetable chemistry. The process is at first a synthesis, a building-up of nitrogenous protoplasm ; but the steps of the process are very difficult to follow, or even to imagine. Nevertheless, what all the resources of our laboratories are unable to accomplish, daisies and dandelions live by doing daily. The carbo-hydrates result from the analytical metabolism of protoplasm, itself a mixture of various substances in a state of continuous molecular change. The average atmosphere contains only one twenty-five hundredth part by volume of carbonic acid, which the cella of the leaves, and probably of all the green parts of plants, nevertheless con- trive to absorb by solution in the water they bold. So far the process is a physical one, and intelligible enough. The next and succeeding steps are chemical ; but there our definite knowledge ends- Dr. Vines has exhausted the literature of the subject, the very difficulty of which adds to its fascination, and with abundant knowledge and acuteness, presents and discusses the various theories that have been put forward. We must refer the reader to his pages for an account of them, and can here only indicate very briefly the part played in the process by chlorophyll, the green colouring-matter of plants. This nitro- genous substance, not identical, but mixed up with the protoplasm of the cell, and aggregated in distinct masses—the chlorophyll- corpuscles, which have been also found in some animals—begins its work by absorbing certain of the rays of light, especially the red and the blue. The energy thus disengaged seems to set the protoplasm in chemical motion, and to induce such changes in it as enable it to construct organic substance out of its own materials, together with the carbonic acid dissolved in the ambient fluids. Chlorophyll, therefore, must be regarded rather as a physical assistant than as a chemical operator in the plant- laboratory; it is the servant, not the comrade, of protoplasm ; and the chlorophyll-corpuscles, in relation to their function, may be considered, perhaps, as in some measure comparable with the red corpuscles of the blood.
While the " Lectures " demonstrate the great importance and interest of their subject as a branch of biological inquiry, the smaller volume is an admirable guide to the manipulative study of the minute anatomy and micro-chemistry of plants, which afford the only sure basis of a physiology of the vegetable kingdom. Here we may take advantage of the occasion to point out how admirably fitted is the study of plant-life to serve as a means of acquiring that scientific training which, at no distant period it may be hoped, will form an indispensable element in all secondary and higher education. A few bottles of re-agents and of mounting and preservative fluids, a microscope magnifying up to about six hundred diameters (costing from £4 to R5), and some simple accessories, constitute all the necessary apparatns ; while almost every important fact may be demonstrated with materials obtainable from any green- grocer or seedeman, or from common gardens and roadsides. No science can be so easily pursued, even within the narrow limits of a London house ; its study is free from every kind of offensiveness, and with the aid of a small greenhouse and a few square yards of garden ground, researches as extensive and important as those of Darwin may without difficulty be carried out. Botany, the kind of botany we have now in view, is especially a science of experiment and manipulation—that is, one in which the reflective and inventive faculties are in constant exercise—while its problems are among the most important with which the biological inquirer can concern himself. The publica- tion of these two volumes, which we have not, of course, attempted to review, seems to indicate a growing interest in the branches of biology they deal with, and cannot fail greatly to facilitate and encourage the study of the attractive and im- portant science to which they form so valuable a contribution. The " Course" is intended to meet the needs of working inquirers ; but the " Lectures " have a wider aim, and will be read with profit and interest by many who cannot personally follow Sir Thomas Browne's injunction to-
" Rally the scattered causes ; and that line
Which Nature twists be able to untwine."
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