ILLUSTRATIONS. 



Page. 



Fig. 1. Map of the central part of the semiarid portion of the Great Plains, 



showing average annual precipitation 12 



2. A field of wheat on summer-tilled land, Phillips County, Colo., 1909. . 27 



3. A summer-tilled field where winter wheat will be grown, adjacent to 



the field shown in figure 2 29 



4. A field summer-tilled by listing instead of plowing, Rawlins County, 



Kans., 1909 30 



215 

 6 



