Plants, then, are living things, and as we proceed we shall find them born, or “germinating,” growing up as young plants, maturing as adults, and finally dying, and their particles resolving into their elements. There is more than one application of the text, “Man is but as a flower of the field.”
In the Geological section we noticed the progressive stages of the vegetable creation, and if we turn back to those pages wherein the various epochs of the earth’s formation are enumerated, we shall see how plant-life developed. Thus we find in the Cambrian the first traces of vegetable life in the weeds of primeval seas. The Silurian strata and the Devonian furnish us with many fossils of marine algæ, and if we examine the succeeding periods we shall find a progressive increase and development; pines and tree-ferns in the sandstone, and most of the plants (by which term we include all varieties) were different from those at present existing in the earth.
Fig. 735.—Branch of the oak.
We spoke of climate lately, and referred to the vegetation having an influence upon it. The same is true of the effect of climate upon vegetation. The conditions of plant-life depend upon climate, as it partly depends upon plant-life. But of all the necessary conditions the first created thing is the most necessary—light. Without light the plant is nothing.
Fig. 736.—The pine.
Plants have many points of similarity with animals. They live, they possess organs, their compositions contain similar substances, such as carbon and albumen, and close chemical analyses have found the existence of the elements oxygen, nitrogen, hydrogen, and carbon in animals and plants. Therefore water must play a conspicuous part in all. Professor Huxley puts this question in his usual clear fashion. He says:—
“It is a very remarkable fact that not only are such substances as albumen, gluten, fibrin, and syntonin known exclusively as products of animal and vegetable bodies, but that every animal and every plant at all periods of its existence contains one or other of them, though in other respects the composition of living bodies may vary indefinitely. Thus some plants contain neither starch nor cellulose, though these substances are found in some animals; while many animals contain no horny matter and no gelatine-yielding substance. So that the matter which appears to be the essential foundation of both the animal and the plant, is the proteid united with water, though it is probable that in all animals and plants these are associated with more or less fatty and amyloid (starchy and saccharine) substances, and with very small quantities of certain mineral bodies, of which the most important appear to be phosphorus, iron, lime, and potash. Thus there is a substance composed of water, plus proteids, plus fat, plus amyloids, plus mineral matters, which are found in all animals and plants. When these are alive this substance is termed Protoplasm.”
