Page:Popular Science Monthly Volume 22.djvu/198

186 constituent of the vegetable body. Our atmosphere is an enormous coal-mine, many miles in thickness, that can not be exhausted in thousands of thousands of years. The coal, indeed, is not found pure in the air, any more than the metal in the ore, but is in combination with oxygen as a transparent gas, carbonic acid, and a peculiar art is required to separate it.

In the mining districts, smelting-houses are erected beside the pits, where the noble metal is extracted from the impure ores. The green cells of the leaves combine the art of the miner with that of the smelter, and have the power of extracting the pure carbon from the atmosphere. In order to perform this work, they must be shone upon by the sun, for the sunlight alone can excite in them the marvelous faculty. Having extracted the carbon, they combine it with water and with the mineral substances that have been drawn from the soil, and prepare from them the living matters out of which the plant itself builds up its cells, and which, taken up into the body of an animal, is transformed by it into flesh and blood.

As bees do not at once consume all the honey they collect, but lay away a large portion of it in special cells for winter provision, so a portion of the cells in the plant are set apart for the storage of capital in anticipation of the necessities of the future. On the approach of winter the leaves discharge the greater part of what they have produced through the conducting vessels, which convey it to a subterranean magazine. The cells of the root-stock, the tubers, and the bulbs, protected from the frost by their covering of earth, are filled with starch, albumen, and other valuable food-material, which will be used again in the coming spring when they will be most needed, for the expansion of the leaves and flower-buds. When we eat a potato, we appropriate to our own nourishment the provision which the careful mother-plant has laid up in its cells during the previous year for the growth of the next spring; and we do what is substantially the same as when in the fall we rob bees of a part of the honey which they have gathered for the supply of their own state.

A necessary consequence of the short duration of the life of the single cell is that a part of the plant, the cell-village, in which the life processes are now active, is generally dead in the next year, and unfit for all work. Therefore the cell-state is subject to a constant mortality. The leaves which perform their work in the summer wither and drop off in the fall; the cells of the root, also, which then drew up the fluids from the soil, and those of the stem, which conducted it upward, have at the same time grown old—have become woody, as the botanist expresses it.

The greater part of the plant does not, in fact, survive the first year. Most herbs sprout in the spring, blossom in the summer, ripen their seed in the fall, and perish in the winter. Trees, on the other hand, bushes and shrubs, possess a regular economical administration.