12 A MANUAL OF FARM GRASSES 



as forage, but they enrich the land upon which they are 

 grown. By means of bacteria-like organisms inhabiting 

 the nodules upon the roots, leguminous plants are able to 

 gather nitrogen from the air. Part of this accumulated 

 nitrogen is stored in the foliage but a part remains in the 

 roots. This portion is added to the soil when the roots 

 decay, and becomes available for the following crop. 

 Thus it is that clover benefits the wheat that is grown 

 later on the same soil. 



OTHER FORAGE PLANTS 



Aside from the two great groups already mentioned, 

 there are few plants cultivated for forage. The most 

 important are those of the mustard family of which the 

 rape and turnip are examples. Another group occa- 

 sionally cultivated are the salt bushes. 



FORAGE CROP AREAS 



The forage crop areas of the United States are classi- 

 fied on the basis of temperature and rainfall. All forage 

 plants are limited to rather definite conditions of heat 

 and moisture and a knowledge of the adaptability of the 

 different species is necessary in choosing plants for differ- 

 ent regions. The chief areas are the Cool Humid 

 Region, the Warm Humid Region, the Semiarid Region, 

 the Arid Region, and the Region of Winter Rains. These 

 areas overlap in places and become indefinite in others 

 but in the main they are fairly distinct. 



COOL HUMID REGION 



This area includes the northeastern states, extending 

 south to the southern border of Virginia and Kentucky 



