2 BULLETIN 1020, U. S. DEPARTMENT OF AGRICULTURE. 
The investigation was confined to the wheat area of the central 
part of the American continent, the so-called Big Wheat Belt, 
extending from northern Texas on the south to Manitoba and Sas- 
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TKC/f/es '$?£>Ra//roac/s 
Fig. 1. — The wheat belt of the United States. 
katchewan on the north, and, in irregular contour, from the Missis- 
sippi Eiver on the east to the arid belt which runs south from east- 
ern Montana to New Mexico. There are two principal wheat-pro- 
