top-soil. When the use of the land is needed, Nature's way is costly, for it costs time.
Other ways are quicker. Stable manures and garbage can be hauled from near-by towns; seaweed and mineral fertil izers, such as phosphates and lime, can be bought and applied. Subsoil plowing is practised to make available new layers of soil that are just as important as new acres added to the sur face. Leguminous crops like peas and clover, which have the power of extracting nitrogen from the air, are cultivated, and either plowed under or fed to animals in the fields. If the roots of such plants are inoculated with bacteria their nitro gen-making power is greatly increased. The progress of sci ence and of skill in agriculture is going far to maintain present food areas on the average in undiminished efficiency. In many respects the productivity of land may be even fur ther increased. If we did not have to reckon on a great increase of population in the world, the problem of a continu ing supply of land to grow food would be a relatively minor one.
§ 5. Land for products other than food. The problem of the supply of agricultural land is first, and most often, thought of in connection with the supply of staples like corn and wheat used for food. But it relates also to the supply of all other organic materials that have to be constantly produced, such as teas, coffee, spices, fruits, sugar, etc.; meats, fats, hides, bones, feathers, bristles, etc., from cattle, swine, sheep, or poultry; materials for textiles, as flax, linen, cotton, including those that must be obtained by the use of animals, as is the case with silk and wool; vegetable oils, as cottonseed, linseed, olive, and turpentine; animal oils, as lard, tallow; and thou sands of other materials. Each of these kinds of goods has its own peculiar need of area and fertility, and its peculiar in fluences on the maintenance or exhaustion of the soil. Each must be separately studied, and thus has developed in each natural science its economic department—economic geology, industrial chemistry, economic botany, economic zoology and its more special branches, called economic entomology, eco nomic ornithology, etc. In the case of many organic prod
ucts the amount available promises to continue adequate for the needs of the future; in the case of others, scarcity makes itself much more quickly felt.
§ 6. Destruction of the natural forests. The forests have been used with less regard for future uses than have agricul tural lands. Moreover, a conservative policy with regard to forests has been less tardily adopted, because the necessity of it was more tardily brought home to men. To the barbarians of Roman times, sparsely peopling the lands, and with few uses for timber, the primeval forests of Europe must have seemed as certainly renewable as the waters of the rivers or as inexhaustible a stock as the sand of the seashore. Left a century untouched by man, any land once naturally covered with trees would revert to a state like that of the primeval forest. Under the economic conditions of barbaric times the forests were self-replenishing sources of supply. They ceased to be so, in full measure, as population increased. The con sequent curtailment of the rights of peasants to the free use of wood began to cause social and political troubles early in the Middle Ages. Until the eighteenth century scarcely any systematic beginning was made in the cultivation of the forest growth. Until a few generations ago in European countries, and until the present moment in most parts of America, tim ber has been cut with no attempt to maintain an undiminished stock.
Germany and France began in the eighteenth century to turn attention to systematic forest culture, but England, with exceptional transportation, could more cheaply get timber from Norway and from North America. The magnificent forests of America were a source of ready income to the set tlers, affording immediately saleable exportable goods in the form of ship timber, masts, shingles, staves, pitch, and tur pentine. A bountiful supply of lumber has always been a large element in the prosperity of the American people.