42 



Tearhooh of the Department of Agriculture, 1921. 



Fig. 39. — Tlmathy is practically confined to the northeastern quarter of the United 

 States, except for a scattered acreage in the moister districts of the Rocky Mountain 

 Region. The western margin of the timothy acreage in the Dakotas, Nebraska, and 

 Kansas marks the beginning of the " Black-earth " belt, where lime has accumlated in 

 the subsoil, of dense alfalfa acreage, and of dry-farming practices (see Pigs. 6, 42, 

 and 10.3). The southern boundary of timothy follows approximately the line of 200 

 days in the frost-free season, or 77° mean " summer temperature. The districts of 

 densest production in northern Missouri, southern Illinois, eastern Ohio, and western 

 Pennsylvania have, in general, rather heavy and slightly sour soils. 



