17. Earliest use of grains. Although we may be sure that the cultivation of the grains began many years before the time of our earliest records concerning them, we have no means of knowing how long ago they were first planted as a crop; nor have we any definite knowledge of how any one of them first came to be cultivated. Still there is good reason to suppose that before the advantages of planting were discovered, it was the custom to gather the wild grain when it was ripe, just as certain savage tribes do with other grains at the present day. Thus it would happen naturally that the sort of grain which grew wild in a given locality would be the one first cultivated in that region, whence its cultivation would spread in course of time to other parts of the world. In Figs. 16 to 21 are indicated the region which is now believed to have been the native home of each cereal, and the range of its present cultivation. As will be seen by a comparison of the maps, five of the cereals are natives of the Old World, maize alone belonging to the new. All six, however, are cultivated successfully in America, and to-day the markets of the world are supplied largely by grain raised in the United States.