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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    the maintenance of animal and plant life respec- tively. Every one acquainted with the merest rudiments of human physiology knows that animals require a due supi)ly of oxygen for the maintenance of their vital functions (p. 218); and that plants, on the other hand, demand carbonic acid as their gaseous food. Could this rule be made absolute, as the lawyers have it, the test of the exact nature of a living being might be referred to the capability of the former to inhale oxygen and to emit car- bonic acid, as a part result of its bodily waste. The plant, on this showing, might conversely be known by its power of reversing this operation, and by its inhaling carbonic acid and giving out oxygen as the result of its vital chemistry. But is it true that all plants absorb carbonic-acid gas, and exhale oxygen 1 Let us refer the matter to the chemist and botanist as arbitrators, and let them detail the results of their experience. As you walk in a garden on a bright summer's day, your eye is pleased with the grateful green of the vege- tation around. The botanist tells you that this green colour—of all hues the most grateful and re- freshing to the human eye—is to be taken as a test of a plant's capacity to subsist on carbonic acid. Wherever you see a green leaf—no matter whether it forms part of a stately ti-ee, or exists in a lowly blade of grass—the botanist will inform you that thex'e the great operation of plant-life may proceed ; and that within the leaf-tissues, carbonic-acid gas, through the exercise of the vital chemistry of the plant, is being sj^lit up or decomposed into its constituents—carbon and oxygen. The carbon, he will further tell you, is retained by the plant to serve for food, whilst the oxygen is liberated, and passes back to the atmosphere to afford food for the animal. But our botanical friend would also inform us that before the green colouring-matter can thus decompose the carbonic acid, it must be subjected to the action of light. Light forms, in fact, the second condition required for the performance of this chemical act on the part of the plant; the presence of chlorophyll being the first condition. What, then, will happen when the daylight fades, and darkness falls on the plant world 1 His reply is that in the dark the green plant becomes an animal, and, like its living neighbour, breathes oxygen and emits carbonic acid. Hence this distinction of inhaling carbonic acid and exhaling oxygen on the part of the plant is only a functional one, and at best one of temporary nature. Depending on it alone, we should be compelled to call a buttercup or any other green vegetable, a plant in the light, and an animal in the dark. Further, it is a distinction which does not hold good for the whole vegetable kingdom, and in this latter phase it must also be regarded as imsatisfactory. All plants are not green, and such as want the green hue are therefore found to be incapable of utilising carbonic acid. A mushroom, a toadstool, and others of their fungoid neighbours, have, in con- sequence of their lack of green colouring-matter, no partiality for carbonic acid. Habitually and nor- mally, they are therefore animals in all essential particixlars relating to their breathing; since they inhale oxygen and emit carbonic acid at all times, and whether in the darkness or in the light. It is time, however, to call a halt to this process of scientific fault-finding, and to the task of showing how completely worthless most of the distinctions which the naturalists of bygone days drew between animals and plants, have been rendered by the pro- gress of scientific research. Are all distinctions, then, of no avail in this task of separating one group from the other, and are we litex'ally unable to say at the present time of some organisms, This is an animal, and that is a plant 1 To these ques- tions an afiirmative answer must be returned. There are some lower forms of life—and the Monads are of them—which may either be one or the other. So hopeless have some biologists become of drawing distinctions between animals and plants, that they have proposed to construct what has well been termed a kind of biological No Man's Land — a teiritory belonging neither to the animal world nor to the plant world, but composed of vmcertain living units, which are at home in neither king- dom. Such is the Regnum Protisticum of some writers. By most biologists, however, this ar- rangement has not been received with favour, for the construction and admission of this neutral territory or refuge for the destitute, seems to amount to a tacit avowal of our absolute incapacity to separate out its members into their proper grades in the two kingdoms of living nature.
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