“Soils rich in humus have for their chief constituent the brown substance that results from the decaying of leaves and other vegetable matter. Turf land stands first as rich in humus. Turf is a dark, spongy substance that forms in moist lowlands from the accumulation of vegetable refuse, especially mosses. Turf, or peat, as it is also called, is used for fuel. To turn such a soil to account, it must first be made wholesome by drainage, it must be mellowed by paring and burning and by the addition of sand and marl, and a proportion of lime must be mixed in to hasten the decomposition of all vegetable matter. Turf lands are recognized by their sphagnei, great mosses that grow with their roots in the water; and by their flax-like sedges, from the tops of which hang beautiful tufts of down having the softness and whiteness of the finest silk.” CHAPTER VI POTASH AND PHOSPHORUS “Let us burn a plant, no matter what kind. The first effect of the heat is to produce carbon, which, mixed with other substances, constituted the plant. If combustion continues, this carbon is dissipated in the air in the form of carbonic acid gas, and there remains an earthy residue which we call ashes. Here then are two kinds of material, carbon and ashes, which without exception enter into all plant-life. The plant did not create them, did not make them out of nothing, since it is impossible to obtain something from nothing. It must, then, have derived them from some source. We shall take up before long the subject of coal and its origin, and shall find that it comes chiefly from the atmosphere, whence the leaves obtain carbonic acid gas, which they decompose under the action of the sun’s rays, retaining the carbon and throwing off the air in a condition fit for breathing. The vegetation of the entire earth thus finds its principal nutriment in the atmosphere, an inexhaustible and increasingly abundant reservoir, because the respiration of animals, putrefaction, and combustion are continually giving forth as much carbonic acid gas as the combined plant-life of the earth can consume. To maintain the fertility of his fields, therefore, the farmer need not give a thought to the subject of carbon; with no assistance from him his growing crops find in the air all the carbonic acid gas they require. There remains for our consideration, then, the residue left after combustion, the ashes in fact, a mixture of various substances of which we will now examine the most important.