[Sidenote: Size of the various crops.] =The Value of American Agricultural Products.=—The largest cereal crop produced in the United states is corn; the total in some years runs as high as three billion bushels. This is more than twice the amount of corn grown in all the rest of the world. Oats come next, with about one and one-half billion bushels in the best years, and wheat third, with a round billion or thereabouts. Cotton is the largest staple crop, with an annual yield of from ten to fifteen billion bales, each bale containing five hundred pounds. Of this nearly half is exported. More than twelve million cattle are received each year at the great abattoirs, besides an equal number of sheep and twice as many hogs. The value of this enormous agricultural production, if stated in dollars and cents, would be misleading because prices change from year to year; the fluctuations are often considerable within a very short period of time.[157] But in any case the contribution which agriculture makes to the yearly income of the nation is enormous. Upon it the national prosperity depends in a very great measure. [Sidenote: How the war stimulated American food production.] =American Agriculture and the War.=—American agriculture had a very important part in winning the World War. As this great struggle progressed the task of providing food for the Allied armies and for the civilian populations became month by month more difficult. Men were drawn off the farms of Europe to fight and the fields went uncultivated; practically the whole of Belgium and a considerable part of France were in the hands of the enemy; no supplies could be drawn from remote parts of the world such as Australia, South America, or the Far East because the available ships were needed to carry troops and munitions; so the American farmer had to speed up production in order to save the situation. When America entered the war the Allies had practically reached the end of their resources in foodstuffs; their populations were living under a rigid system of food rationing. Under the stimulation of this great emergency American agriculture rose to the occasion and the increased production of foodstuffs, together with the savings which were made through the observance of “wheatless” and “meatless” days enabled the United States not only to maintain an army of two million soldiers in France but to contribute largely to the food supplies of the Allied armies and civilian populations as well. The supply trains which fed the American army in France (and never on a single day did they fail to reach the front), started from Kansas City and Chicago, not from Brest or Havre. The American farmer was the great factor in this service of supply. [Sidenote: An example of _increasing returns_.]