CULTURAL CHARACTERISTICS 297 



GROUP X. 

 Trailing wild bean, Strophostyles helvola. 



GROUP XL 

 Black, or common locust, Robinia pseudo-acacia. 



Hiltner and Stormer (1903), however, arranged the tubercle 

 bacteria into two groups possessing, according to them, well-defined 

 morphological and physiological differences. One of these groups 

 is included under the species Rhiz^b^um radicicola and the other 

 under Rhizobium beijerinckii. The former comprises the organisms 

 from lupines, serradella, and soybeans, whereas the latter comprises 

 all of the others. 



Grieg-Smith (1902) reports having found three races of the 

 nodule bacteria in the same nodule, while Gino de Rossi (1907) 

 reported the finding of two organisms which differ in that one forms 

 a large hyaline colony not developing well on beef and peptone 

 gelatin, while the other forms white non-transparent colonies on beef 

 gelatin. He believes that the one is morphologically, biologically, 

 and culturally widely different from Bacillus radicicola (Beijerinck). 



Cultural Characteristics. The nodule bacteria grow well on a great 

 variety of cultural media, perhaps best on a medium of ash-maltose- 

 agar or one of legume extract to which has been added a sugar, 

 dextrose, sucrose, or maltose, and dipotassium phosphate. 



In an agar stab typical drop-form colonies are produced at the 

 surface, while a thin gray growth follows the line of the needle. In 

 standard beef broth the growth of the organism is slow. The liquid 

 becomes cloudy, a gray-white ring is formed, and a thin membrane 

 covers the surface. Later a flocculent precipitate settles to the 

 bottom of the tube. In standard beef broth gelatin the growth of the 

 organism is at first funnel-shaped and then stratiform. Gelatin is 

 slowly liquefied, the process sometimes requiring two or three months 

 for completion. In gelatin stabs the growth sometimes seals over 

 the stab with a drop-form growth and liquefaction does not occur. 

 On the ordinary cultural media the organisms do not show any very 

 characteristic growth. The most noticeable difference between 

 various strains is the rapidity of development. Slight alkalinity to 

 +20 to +25 acid (Fuller's scale) with phenolphthalein is tolerated; 

 neutral to + 10 is best. 



The results obtained by Fred and Davenport clearly indicated 

 that the nodule bacteria from different plants behave differently 

 toward acid. They divided the legume bacteria into five groups 

 depending upon their sensitiveness to acid. 



1. Critical pn 4.9 Alfalfa and sweet clover. 



2. Critical pn 4.7 Garden pea, field pea and vetch. 



3. Critical pn 4.2 Red clover and common beans. 



4. Critical pn 3.3 Soybeans and velvet beans. 



5. Critical pn 3.15 Lupines. 



