A Graphic Smnmary of Americo/n Agricultv/re. 



33 



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Fig. 30. — About half the acreage of spring wheat iu 1919 was in the Spring Wheat 

 Area, where it constituted 40 per cent of the acreage of all crops, and most of the other 

 half was located in the adjoining portion of the Great Plains Region. A secondary but 

 important center of production is located in the subhumid portions of Washington and 

 Oregon. The southern boundary of the Spring Wlieat Area is determined largely by the 

 northern boundary of winter wheat, which is, in general, more i>roductive and more 

 profitable where it can be grown. The northern limit of spring wheat is approximately 

 the mean summer temperature of 58°, which is found iu the United States only iu the 

 western mountains. 



