36 Martin J. Prucha 



in a particular species of legume enables such organisms to produce more 

 abundant nodules in a shorter length of time than bacteria isolated from 

 some other legume and grown upon nitrogen-free media. While this is of 

 considerable practical importance, and will probably always make it neces- 

 sary to distribute the specific organism for the specific crop, it does not in 

 any way indicate that the bacteria found in the nodules of beans, peas, 

 clovers, etc., are separate species. The most that can be maintained is 

 that there is a slight physiological difference due to the long association 

 with a plant of a peculiar reaction which enables the bacteria more easily 

 to penetrate the host upon which they have been accustomed to grow. 

 These slight racial characteristics can readily be broken down by culti- 

 vation in the laboratory, and it is entirely possible to secure a universal 

 organism capable of producing a limited number of nodules upon all the 

 legumes which now possess these growths." 



Hopkins (1904) found that the organism from sweet clover readily 

 inoculates alfalfa. 



Nobbe and Hiltner (1900) undertook to train the nodule-forming 

 organism of peas and that of beans so that the former may cause nodules 

 on beans and the latter on peas. They succeeded in doing this, and 

 drew the following conclusions: 



1. The nodule-forming organism from peas can be trained to produce 

 nodules on beans, and that from beans to produce nodules on peas. 



2. Although some nodules are produced in both cases, the organisms 

 do not assimilate any nitrogen at first. 



3. If the pea organism that caused nodules on beans is isolated and 

 beans are inoculated with it a second time, the organism then infects the 

 beans more readily than at the first inoculation and its power to assimilate 

 nitrogen is increased. The organism of beans behaves in the same manner 

 when made to infect peas. 



Kellerman (1912) reports that Mr. Leonard has succeeded in securing 

 abundant inoculation on soy beans, lupines, and alfalfa from an organism 

 of a culture originally isolated from the alfalfa nodule and kept on an 

 artificial medium in the laboratory for about six years. Kellerman, 

 therefore, is of the opinion that the nodule-forming organisms of all the 

 Leguminosae should be considered as a single species. 



The evidence from the investigations mentioned above points to two 

 conclusions: (1) that, with some exceptions, the nodule-forming organism 



