Page:Popular Science Monthly Volume 22.djvu/188

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armed with the most effective aids supplied by modern science, has only recently remarked, after a long time, that any change has taken place.

In reality every living body is subject to an uninterrupted change, which goes on in an appointed course. Life is like a stream, which gushes out of a hidden spring; slowly increases, flows on for a time with even strength, finally with diminishing velocity, to disappear in the sea of eternity. We designate the course of changes which every living being, plant, and animal, as well as man, goes through, as its development. Development begins with the moment of birth and ends with death.

But with the death of the single being its race does not disappear; the property dwells in every living being by which a part of it can drop off from the whole, continue to develop itself independently, be nourished and rejuvenated by a change of matter. We call this dropping off of a part, capable of development, from the whole, propagation; with propagation is transferred the history of development; the separated part, which we denote as an egg or spore, a seed or embryo, a bud or spawn-knob, passes in substance through the same course of changes as the whole from which it has been separated. Like arises from like; the children resemble their parents, and, as these again resemble their ancestors, the character of the species is kept up essentially unchanged, in spite of the perishability of individuals, through all the generations.

That life is nothing but a constant development and an uninterrupted rejuvenation is expressed in the plainest and clearest manner in the world of plants. It is, indeed, not easy to comprehend the life of plants aright, and many regard the term as a figure of speech, not properly applied. Plants, they say, do not feel or move; they have no consciousness, no soul, like animals; how can we speak of their life? If motion, feeling, and consciousness alone constituted life, there might be some doubt as to whether plants lived, though it would still be worth while to inquire whether these higher attributes were really wanting in plants. Darwin has lately shown, in connection with many older observations, that all the parts of plants participate in a regular circling motion, and that single organs show sensibility enough to make them comparable with the brains of the lower animals. But when, instead of the highest acts of life, we confine ourselves to its general and essential manifestations, it becomes undoubtedly clear that plants are living in the same sense as animals and men. Only plants are distinguished, not from animals generally, but from the higher animals that rank nearest to men, and from which our conceptions of animal life in general have been formed, in that in them unity, or individuality, is expressed in a much more imperfect manner. The mammal, bird, fish, insect, is a separate, single, and indivisible being. Its members are fixed and limited in number; not one of them can