=Wheat.=--The wheat of commerce is the seed of several species of cereal grass, one of which, _Triticum sativum_, is the ordinary cultivated plant. Wild species are found in the highlands of Kurdistan, in Greece, and in Mesopotamia, that are identical with species cultivated to-day. It is thought that the cultivation of the grain began in Mesopotamia, but it is also certain that it was grown by the Swiss lake-dwellers far back in prehistoric times. It is the "corn" Joseph's brothers sought to buy when they went to Egypt, and the records of its harvesting are scattered all over the pages of written history. [Illustration: THE GRAIN CROP--MODERN METHODS OF CULTIVATION AND HARVESTING] Of the one and one-half billion people that constitute the world's population, more than one-third, or about eight times the population of the United States, are consumers of wheat-bread; and this number is yearly increasing by twelve million. Moreover, each individual of this aggregate consumes yearly very nearly one barrel of flour, or about four and one-half bushels of wheat. In other words, it requires somewhat more than two billion three hundred million bushels of wheat each year to supply the world's demand.[23] As a matter of fact the world's crop is yearly consumed so nearly to the danger-line that very often the "visible supply," or the amount known to be in the market, is reduced to a few million bushels. Wheat will grow under very wide ranges of climate, but it thrives best between the parallels of 25 deg. and 55 deg. In a soil very rich in vegetable mould it is apt to "run to stalk." A rather poor clay-loam produces the best seed,[24] and a hard seed, rather than a heavy stalk, is required. In the latitude of Kansas the seeds planted in the fall will retain their vitality through the winter; in the latitude of Dakota they are "winter-killed," as a rule. Because of this feature two broad classes or divisions of the crop are recognized in commerce--the winter and the spring varieties. In general, the spring wheats are regarded as the better, and this is nearly always the case in localities too cold for winter wheat. There are exceptions to this rule, however. In the main, winter wheat ripens first, and is therefore first in the market.[25] [Illustration: WHEAT] In Europe the plain that faces the North and Baltic Seas, and that part which extends through southern Russia, yield the chief part of the crop, although the plains of the Po, the Danube, and Bohemia furnish heavy crops. Russia, France, Austria-Hungary, Germany, and Italy are all wheat states.