118 TRANSFORMATION OF NITROGEN BY SOIL MICROBES 



in the presence of the bacteria, or whether both share equally in 

 the reaction, is speculative. There are thus many points of 



A B C 



Fig. 55. — Nodules of cowpeas (A), soybeans (B), and lima beans (C) 

 (from Lohnis and Leonard). 



difference between fixation by symbiotic and non-symbiotic bac- 

 teria, but the actual chemical reactions involved may not be unhke. 



The nodules pro- 

 duced on roots of 

 different legumes may 

 be quite different in 

 appearance, but the 

 ^^__^^ / general shape is quite 



^F* .^S^C^ constant in any one 



species of plant. On 



some of the beans the 



nodules are fairly 



large and spherical, 



and seldom occur in 



clusters (Fig. 55). 



Nodules on many of 



the clovers and alfalfa 



are small elongated 



swellings, sometimes 



branching or occurring in clusters (Figs. 56 and 57). The nature 



of the plant and the soil conditions affect the location of the 



nodules. Under conditions particularly favorable for inoculation, 



Fig. 56.— Nodules of alfalfa (A) and vetch (B) 

 (from Lohnis and Leonard). 



