BACTERIA FIXING ATMOSPHERIC NITROGEN 137 



Group V: Group IX: 



Glycine hispida (Soja max), soybean Amorpha canescens, lead plant 



Group VI: Group X: 



Phaseolus vulgaris, garden bean Strophostyles helvola, trailing wild 



Phaseolus mullifiorus, scarlet runner bean 



Group VII: Gr ° U P XI: „ 



Lupinus percnnis, lupine Robtma pseudo-acacia, black or com- 



Ornithopus saliva, seradella mon locust 



Group VIII: Group XII: 



Amphicarpa monoica, hog peanut Dalea alopecuroidcs, wood's clover 



An interchangeability between the soy bean and cowpea has been 

 demonstrated 164 in the laboratory, however. Field tests from other 

 sources do not indicate such relationship. Various explanations for the 

 specificity, based on soil reaction, climate, etc., have been proposed. 

 Burrill and Hansen properly suggested that it may be a case of specific 

 enzymes produced by the bacteria or of differences in the root-sap, 

 which cannot be detected by chemical methods. So far we have to 

 depend on cross inoculation and serological tests for the specific separa- 

 tion. No morphological differences have yet been established, ex- 

 cept the division into two groups suggested by Lohnis and Hansen; 

 we do not know whether we are dealing here with different species 

 or mere biological races. 



The application of serological reactions has brought out the fact 

 that various strains of bacteria may form nodules on the same plant, 

 but only one serological type is found in the same nodule. 165 Other 

 investigators 166,167 also found that not all strains of Bad. radicicola 

 of one leguminous plant are identical. This suggested the existence of 

 various biotypes even for the same plant. The existence of two general 

 types of the organism which can form nodules on the soy bean, identical 

 morphologically but different physiologically and especially serologi- 

 cally, has been demonstrated. 167 



These results are probably due to the fact that a bacterial culture is 

 actually a population in which the different cells have variable proper- 

 ties. Although morphology may not be sufficient to demonstrate any 



164 Leonard, L. T. Nodule production kinship between the soybean and cow- 

 pea. SoilSci. 15: 277-283. 1923. 



165 Bialosuknia, W., and Klott, C. Badania nad Baklerium radicicola. Roczn. 

 Nauk. Rolniczych. 9: 288-335. 1923. 



166 Stevens, 1923-25 (p. 135). 



167 Wright, 1925 (p. 127). 



