"Attention is again called to the fact that the is the original source of 98½% per cent of the materials found in the green plant; the carbohydrates, fats and being composed of elements supplied in the form of water and gas. These substances are furnished free of cost in humid climates, the supply being practically beyond control, and their use by the plant results in no impoverishment of the land. The subject of practical importance to the farmer is the supply of the other 1½% per cent of the plant, consisting of nitrogen and the ash elements which are derived directly from the solid particles of the soil. It has been shown that seven of these elements are essential to plant growth. Experience has proved that only three of these elements (i.e. , and ) are likely to become exhausted, or, in other words, that nothing is gained by adding to the soil any of the other elements of . This is due to the fact that the plant uses nitrogen, phosphoric acid and potash in rather larger quantities than the other elements, and that they exist in smaller quantities in the ground, and not because they are any more essential to vegetation. Occasionally soils are found that are actually deficient in , but in most cases lime is present in sufficient abundance for the growth of the plant."