LEGUMES 



205 



264. How legume plants add nitrogen to the soil. Nearly 

 everyone who has lived in the country has heard men speak of 

 clover as a fertilizer. It was not until the latter part of the 

 last century, however, 

 that the cause of the 

 beneficial action of leg- 

 umes was discovered. 

 A careful examination 

 showed that upon the 

 roots of these plants 

 are nodules which are 

 literally filled with bac- 

 teria. It was demon- 

 strated that these bacteria 

 had the power to pene- 

 trate the root, causing 

 the nodules to form, 

 and then to take up free 

 nitrogen and supply it 

 to the plant in a form 

 which the plant can use. 

 It is therefore possible 

 to maintain and even 

 to increase the quantity 

 of nitrogen in the soil 



FIG. 95. How legumes get their nitrogen 



The peanut is an important crop plant in several 

 mid-southern states. Its large and abundant root 

 tubercles contain many bacteria which gather nitro- 

 gen from the air of the soil ; and its fruit is a favored 

 article of food. (Photograph from Virginia Experi- 

 ment Station) 



through the growing of 

 legumes. 



265. Inoculation for 

 legumes. Different leg- 

 umes have different 

 kinds of bacteria which 

 live on their roots. The kinds of bacteria which grow well on 

 clover roots, for example, do not grow well on other legume 

 roots. Not all soils are supplied with the kinds of bacteria 

 which cause nodules on the roots of a particular legume, and 

 it is often necessary to supply them. This is especially true 



