EDWIN BROUN FRED 



335 



NITROGEN NUTRITION 



The process of nitrogen fixation is carried out by the bacteria within the nodule. 

 The plant furnishes the carbohydrate and the bacteria the combined nitrogen. Just 



TABLE I 



what causes the rapid autolysis of the bacterial cells within the nodule is not definitely 

 known. It is reported' that the presence of a bacteriophage brings about the rapid 



Not inoculated Inoculated 



Fig. 3. — Effect of root-nodule bacteria on the growth of clover 



dissolution of the bacteria within the nodule, and thus the proper equilibrium is main- 

 tained between the higher plant and the bacteria. 



The intimate relationship between the nodule and nitrogen content of the plants 

 is shown by the results of chemical analyses. Young nodules of plants are much richer 

 in nitrogen than the rest of the root, while at a later period the nodules are much 

 lower in nitrogen. Analyses of lupine nodules and roots at various stages during 

 the growth of the plant illustrate this point (see Table I).' 



Concerning the nature of the nitrogenous compounds of nodules, it has been 

 found that about 50 per cent are soluble in water. ^ Of the protein-free soluble nitrogen 



' Gerretsen, F. C, Grijns, A., Sach, J., and Sohngen, N.L.: Ccntralbl.f. Baktcriol., Abt. II, 60, 

 311. 1923; Grijns, A.: Doctor's thesis, p. 104. Wageningen, Holland: Veenman & Zonen, 1926. 

 ^ Stoklasa, J.: Landw. Jahrb., 24, 827. 1895. 

 3 Strowd, W. H.: Soil Sc, 11, 123. 1921. 



