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 (Hurotia lanata 
(Pursh) Mogq.) 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. 
