Page:Popular Science Monthly Volume 76.djvu/530

526 cultivated; the correlative branches are the Forest Service and the Bureau of Plant Industry. The fourth pertains to the fauna, both wild and domesticated, correlative respectively with the Biological Survey and the Bureau of Animal Industry, together with the ancillary insect life, correlative with the Bureau of Entomology. Adjunct lines of work pertain to certain molecular relations, treated in the Bureau of Chemistry and the Office of Public Roads; to quantitative or economic relations, treated in the Bureau of Statistics; and to ecologic relations, treated largely in the Office of Experiment Stations. In each line the primary purpose is to discover facts and relations connected with development or growth; the secondary purpose is to redirect and control the course of natural development, and the ultimate purpose is to progressively artificialize the earth with its life and growth for the benefit of men and nations. In every line the constant effort is to increase the efficiency of the better and to either improve or eliminate the worse, and this in the light of all knowledge and the exercise of all natural and human power.

The immediate basis of life and growth on the earth is the soil; it yields substance for the flora, which in turn sustains the fauna. At the same time it is itself derived from cruder earth-matter largely by the action of plants and animals, and its chief elements of fertility (such as nitrates and potassates and phosphates) are organic derivatives. Thus the primary law of the soil is cumulative enrichment through interaction with floras and faunas; to this law it has normally conformed throughout the geologic ages; and the primary duty of the soil specialist is to accelerate and intensify the natural progress, and thereby to increase soil efficiency. Now the efficiency of soils depends wholly on the associated water and air (unless indeed these be considered integral parts of the soil), of which the former especially maintains a sort of circulation, dissolving earth-salts, conveying plant-food into and through the circulatory systems of the living and growing plants, and carrying the acids of growth and decay back to the earth-matter to hasten its solution—so that the active agency or principle of soil efficiency is the soil water. The normal processes are sometimes interrupted or impeded by abnormalities: Certain organic derivatives are excretory, and poisonous to the plants yielding them and sometimes to others; climatal and other natural conditions in connection with cultural changes sometimes disturb the circulation of soil water, or permit surface erosion and leaching to impoverish or even completely remove the soil; and unsuitable plants sometimes gain such foothold as to exclude organisms better adapted to normal enrichment of the soil. Accordingly, the soil work comprises (1) examination and classification of soils with respect to materials and potentialities; (2) determination of the soil water and its movements