596 



PRINCIPLES OF SOIL MICROBIOLOGY 



controversy. It was shown conclusively 151 that leguminous plants (cow- 

 pea and soybean) fix atmospheric nitrogen through their roots and not 

 through their leaves, as it had been assumed in some cases. In the 

 earlier part of the growth of the plant, the roots contain the larger part 

 of the nitrogen while, at the time of harvest, 74 per cent of the nitrogen 

 of cowpeas and soybeans was found in the tops. The fixation of the 

 nitrogen takes place in the early stages of growth of the seedling, some- 

 times within fourteen days. 



A study of the composition of leguminous plants 152 established the 

 presence of various amino acids and amides. Inoculation was found to 

 increase the protein content of the plant, often without even increasing 

 the crop yield. 



TABLE 60 



Influence of inoculation and fertilization vpon yield, alkaloid and nitrogen content 



of Lupinus angustifolius 



The formation of branching forms, or bacteroids, in the nodule is due 

 largely to specific nutrition, especially to the presence of alkaloids. 

 Plants depending largely upon the bacteria for their nitrogen show a 

 high alkaloid content; plants which obtain their nitrogen from inorganic 

 nitrogenous compounds, especially lupines, are poor in alkaloids. 153 



Table 60 shows that inoculation resulted in a large increase in the 

 nitrogen content of the plant, but this is accompanied by a still larger 

 increase in its alkaloid content. When sterile plants obtain their 



161 Whiting, 1915 (p. 590). 



152 Schulze, E. Ueber den Umsatz der Eiweissstoffe in der lebenden Pflanze. 

 Ztschr. physiol. Chem., 24: 18-114. 1895; 30: 241-312; 48: 387, 396. 1906. 



153 Weber, E. tlber den Einflusz der Stickstoffernahrung auf den Bitterstoff- 

 gehalt der Lupine. Inaug. Diss. Leipzig. 1920. 



