222 



Nitrogen Fixation— Symbiotic 



early stages of growth of the seedling. The mechanism of the fixa- 

 tion process has been elucidated by Virtanen as follows: 



The presence of various amino acids and amides in leguminous 

 plants has been used as substantiation of the above concept. These 

 acids are believed to be excreted from the plant into the soil and 

 are made available for the growth of nonleguminous plants. The 

 data presented in Table 50 tend to substantiate these conclusions, 

 with which Wilson, however, could not fully agree. 



Table 50. Growth and Nitrogen Content of Red Clover, Peas, Barley, 

 AND Wheat Plants in Quartz Sand (from Virtanen) 



* Culture of l)arley liarvesled at mucli cariicT stage tiiaii oilier cultures. 



