The nature and composition of the soil play an important part in determining whether cotton can be grown upon it in sufficient quantities to make it a profitable crop for commercial purposes. The agricultural chemistry of cotton is yet in its infancy and much has still to be learned on the subject ; but it would appear that those soils, which are most favourable, contain nitrogen, phos phoric acid, potash, lime, and magnesia, in sufficient quantities to satisfy the demands of the plant. Nevertheless, some of these may be present in very small quantities on good cotton land, while other lands, seeming to possess all the necessary constituents, fail to yield a crop. The texture of the soil is of importance, chiefly from its influence on the water supply. If the rainfall is con siderable, a heavy soil may become waterlogged ; on the other hand, a sandy soil, unable to retain moisture, will only yield a poor crop if the rainfall is low. Thus, although no particular soil is typical of the cotton belt, one which is continuously moist, but not wet, is the most suitable.
TOBACCO.—Although the tobacco plant thrives both in tropical and temperate countries, the quality of the tobacco obtained from it varies greatly according to the climatic conditions under which it is cultivated. Within tropical regions, where both heat and moisture are abundant, the very finest tobaccos are produced. A second zone of cultivation lies to the north of this first one, and is bounded by the isotherm of 75° F. for the month of July. This zone includes
the greater part of the United States, one of the chief tobacco producing regions of the world. In the southern hemisphere there is a corresponding belt. The third region, and one which yields a coarse tobacco without aroma, lies in the northern hemis phere only, between the isotherms of 75° F. and 65° F. for the month of July.
Soil is a very important factor in the cultivation of tobacco. In Cuba, for example, differences in the soilbetween one valley and another are sufficient to cause great differences in the quality of the product. A light and sandy soil grows plants, the leaves of which are fine in texture and possess a light and delicate aroma, while a clay or other heavy soil produces plants with thicker and coarser leaves. As a general rule, valleys covered with the debris of granitic and gneissic rocks are among the most suitable lands for the cultivation of tobacco, as they are rich in potash. The presence of humus is an advantage.
The cereals, other than rice, have a very wide extension, as they have in many cases been adapted to regions in which they are not indigenous. On the whole, it may be said that they have their greatest development in the lands which have been cleared of deciduous forest, and in the hygrophilous grasslands of the temperate zone, although they spread to a considerable distance on either side of these regions.