Volume 1

Science for all / edited by Robert Brown.

Date:
[1877?-1882?]
Catalogue details

Licence: Public Domain Mark

Credit: Science for all / edited by Robert Brown. Source: Wellcome Collection.

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    of life more and more confusing—as well as in animals of higher grade. And a starchy sub- stance known as cellulose (p. 52), of which the walls of plant-cells are composed, is found abun- dantly in the outer layer or covering of the bodies of those Molluscoid animals named Sea- squirts or Ascidians (Fig. 5). Sugar and starch, known to every one as vegetable products of characteristic kmd, are now ascertained to be manufactured in a perfectly regular fashion by animals, which, as it would seem, are bent on the close imitation of the chemistry of plants. And stranger still, it would appear that the chemical and vital processes of animals are imitated by plants; for it has been shown that in the develop- ing seed of a vetch there exists a principle, or ferment, as it is called, allied to the sweet- bread juice or pancreatic secretion of animals. By means of this secretion, the young plant as it springs from the seed is able actually to digest the starchy and nitrogenoxis matters within its reach. The digestion of flies by the Venus' fly-trap (Dioiicea) and by the Sundew (Drosera), as de- scribed in another paper (p. 240), also ilhistrate the imitation of the animal processes by plants. And just as the chemist inci'eases our diffi- cidties by showing us the similarity in substance of animal and plant bodies, so also does the micro- scopist fail us when we apply to him for aid in separating the two groups of living organisms. If animals and plants are to be regarded as alike in composition, they are no less similar in essential structure. Place the tissues of animals under the microscope, and they are seen to be composed of the minute bodies to which the name of cells is given. Examine plant-tissues, and cells again appear as the units of which tlie plant as a whole is built lip. And once again, if the lower animals and plants be microscopically compared, their sub- stance, which defies separation by the art of chemistiy, equally defies divoi-ce at the hands of the microscopist. The protoplasm of lower animal and plant bodies is literally indistinguishable. If the germ of the higher plant, and that from which the higher animal springs, be examined by the micro- scope, the difierences which become so apparent in after-life are seen to disappear in a primary resemblance, so close in all points, that the task of separation appears simply hopeless. It may now be said that, granting the futility of the foregoing methods of scientific examination in enabling us to say wherein lie the essential features of the animal and the plant, the j^resence of nerves. and the power of receiving and of acting upon sen- sations, might be regarded as a characteristic of tho animal as distingTiished fi'om the non-sensitive jilant. But in a previous paper (p. 179) it has been shown that the Venus' fly-trap, the sensitive plant, and other i^lants, ai'e highly sensitive; and we then ad- vanced reasons in our opinion of greater force than any that may be given to the contrary, in supjiort of the proposition that sensation was univei'sally diflused through living nature. Wherever the primitive life-substance of protoplasm exists, it may be held that there sensation is present— lowly-developed it may be, but still undoubtedly manifested, as we may see when we regard the movements in the cells of lower plants, or the better-defined acts of animalcules. The arguments for the universal recognition of sensation as an invariable concomitant of life itself are both reasonable and well founded on analogy. The assertion that animals may be invariably known by the possession of a mouth and stomach is disproved by the consideration that many parasitic animals—for example, the tape-worms, the male wheel-animalcules or Botifera, and many animalcules—are destitute of, it may be, the veriest rudiments of a digestive apparatus. The animal commissariat in such cases is conducted essentially on the principles of the plant; such animals in most cases living by the absorption of fluid matters in the absence of an alimentary system. It may be admitted that it is a charac- teristic of most animals that they can feed on solid matters, and as a rule on living matter only; whilst their plant-neighbours are comjielled to subsist on sloj^s ■—that is, liquid and gaseous food, or in- organic matter derived from the soil and atmosphere; the liquids, however, containing solid matters in solution. But there are some lower plants allied to the Fungi which present us with exceptions to these latter rules. Many parasitic plants feed on the juices of other j'lants—that is, on living matter. And what shall we say of yEtlialium, the so-called flowers of tan, a fungus growing in tan-pits, which not merely begins to exhibit independent movements at certain periods of its existence, but at these periods appears to sub- sist on solid food, like a veritable animal ] Thus even a single example—and JEtlialium is not alone in respect of its singular habits—may vitiate a dis- tinction which, as applied to the generality of plants, is of sufiiciently stable kind. Connected with the subject and question of the food of the two groups of living beings, is that of the gases necessary for
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