FORAGE PLANTS 21 



from the air to the soil, thus increasing the soil fertility. 

 This transfer is accomplished by means of organisms con- 

 tained in nodules upon the roots of legumes, these organ- 

 isms, which are allied to bacteria, being able to extract 

 free nitrogen from the air. The accumulated nitrogen 

 is in part passed on to the host plant. After the removal 

 or death of the latter, the roots or such portions as remain 

 in the earth return to the soil in a form available for 

 absorption such nitrogen as was stored in them. For this 

 reason the fertility of soils is increased by the growing of 

 legumes, the following crops being correspondingly 

 improved. The various grasses cultivated for forage are 

 usually grown in combination with legumes either simulta- 

 neously or successively, in order to increase the nutritive 

 value of the product and at the same time to retain the 

 fertility of the soil. 



16. Miscellaneous. — The third group of forage plants 

 includes all plants that do not belong to the grasses or 

 the legumes. Certain plants of the mustard family, 

 especially rape (see Farmers' Bulletin No. 164), are cul- 

 tivated for forage. Most of the plants of this group, with 

 the exception of rape, are native range plants, deriving 

 their importance from their presence in arid or semi- 

 arid regions. The most important of those found in 

 America are the salt bushes (species of Atriplex) (see 

 Farmers' Bulletin No. 108), winter fat {Eurotia lanata 

 (Pursh) Moq.) and the prickly pear cactuses (species of 

 Opuntia). The cultivation of the opuntias has recently 

 been undertaken in the southwestern states and gives 

 much promise (see Farmers' Bulletin No. 483). Species of 

 Plantago, known to ranchmen as Indian wheat, are 

 important winter grazing plants for sheep in the desert 

 regions of Arizona and California. 



