The body slowly consumes away; the muscular tissues shrink and soften, and the haggard face and incipient delirium assure us that the work of death is going on at the nervous centres. If no help arrives, if the poor starving one is left to be "burnt with hunger," death sooner or later ensues, and the expression of the sacred text, which strikingly coincides with the philosophy of starvation, is realized; for the unhappy person is burnt alive. This effect is unquestionably principally due to the oxidizing influence of the atmosphere. Our "earthly tabernacle" is but a tent after all; a tent which each moment undergoes repair and waste. The structure which is the scene of such incessant conflicts between the powers of destruction and of reproduction, is already doomed. The balance cannot always be kept in equilibrio; equalization of the forces cannot always be secured. The surplus accumulates; the reparative powers give way before the onward march of the destructive. The body wastes down, as we say with old age, and when not actually hurried into the grave by disease, dies at last of exhaustion. Well is it for him who is able to say, with one of old, "I know that if the earthly house of this tabernacle be dissolved, I have a building of God, an house not made with hands, eternal in the heavens."* * 2 Cor. v. 1. CHAPTER VII. THE ATMOSPHERE AND VEGETATION. LET us now proceed to make inquiry as to the mutual relations subsisting between the air and the luxuriant vegetation which surrounds us. How and in what way are these blades of grass affected by the summer breathings which pass in wave-like movements over them? The direct connexion of animals with the chemistry of the atmosphere can, as a general rule, only be said properly to be immediately established when they first draw the breath of life, although undoubtedly they are indirectly the recipients of its beneficial influences in their previous condition of immaturity. In birds, however, and oviparous creatures generally, from the earliest dawn of the principle of life within the shell, this relation commences, only to cease with their death. The presence of the atmosphere is in like manner essential to the commencement of vegetative life. The seed can only begin to grow, or, in other words, to germinate, by A A virtue of its presence. Much, therefore, of the success of the florist, and, on a larger scale, of the agriculturist, depends upon this simple and often forgotten condition of things. The seed must have access to air. It is also necessary that it should be surrounded by a medium sufficiently but not too moist, and that a moderate degree of warmth should exist in the bed into which it is cast. It is a singular fact also, that while the luminous rays of light interfere with or even prevent this process, by some discoveries of Mr. R. Hunt it appears necessary that the actinic or chemical rays of the solar light should reach the seed in order to its germination. Placed in these favourable conditions, the seed absorbs moisture from the soil and oxygen from the air. A series of intricate chemical changes is immediately commenced, the gluten of the seed is altered, and its starch is converted into sugar for the nutriment of the young plant. Water and carbonic acid are also formed during this process, and in a short time the head of the young plant peeps above the soil. Passing by the less important period of vegetable infancy, we are led on to that far more interesting time when the plant and the atmosphere enter into new relations with each NUTRITION OF PLANTS. 355 other, on the fulfilment of which the most momentous results to all animate creation depend. In a previous section of this work it was stated that plants derive but a small proportion of their solid constituents from the soil in which they grow. It has been before mentioned that the chief solid material of a plant is its carbon; also that plants live with their roots buried in a material (vegetable mould) extremely rich in carbon. Yet, on the question being put, Do plants derive their carbon from the mould? the answer has been, Certainly not. This must now be proved. Experiment has shown that it is impossible for a plant to receive nutriment by its roots in any other but a soluble and perhaps a gaseous form. Be the nutrient material what it may, it must first be in one or other of these conditions before it can be appropriated by the vegetable economy. The rootlets cannot take up solid matter; nor, if they could, could the plant grow upon such a diet. If the hungry fibres wandered in their search for food through a mass of dry sawdust, or threaded their way through a pile of stones, they would find none,—because they would find nothing dissolved in such a situation. Applying this to our present subject, vegetable mould may be considered as almost in soluble. If its solubility were represented by figures, one part of good mould would dissolve in 100,000 parts of water. The same might be said of many stones; in fact, some show a considerably larger solubility. A plant, therefore, whose roots meandered through a mass of powdered stones, would be actually in a better condition, as regards its supply of soluble matter, than one planted in pure vegetable mould. It becomes clear, then, that while analysis fully confirms the fact that the vegetable soil abounds in one of the elements of wood, or in carbon, yet, at the same time, we are taught, that it is in such a condition as to be utterly useless to vegetation for food. The source of wood in plants is, consequently, not in the soil. Its true source is the atmosphere. This may excite surprise, and even challenge belief, but it is based upon the most incontestible evidence afforded by vegetable physiology. The wood of plants is derived from the thin air which they breathe thus air, or, more properly speaking, one of its ingredients, is actually the food of vegetation. The orchis-tribe, or, as they are commonly called, the "air-plants," furnish us with a beautiful illustration of this fact. These plants, in their native haunts, are found upon the branches of lofty trees, seated as it were in state, and surrounded with groups of flowers and leaves, : |