BACTERIA IN THE INDUSTRIES 



175 



FIG. 55. R. mutabile from the root nodules of Trifolium helerodon, showing the ex- 

 treme form variation due to hyper-growth. The forms shown in Figs. 52, 53, 54," 55 

 and 56 are simply involution forms of the same species due to differences in environment 

 and host relationship. The chromatin bodies found in the hyper-nourished forms r (Fig. 

 54) are probably reserve products. 



^n=^ tf 

 W 



FIG. 56. FIG. 57. 



FIG. 56. Involution lorms of R. mutabile as they occur in artificial culture (beef 

 broth) . R. mutabile can be cultured quite readily upon a great variety ot culture media, 

 showing marked adaptability to variations of food supply and in environment. 



FIG. 57. Azotobacter agilis deeply stained. This organism is actively motile as 

 indicated by the pressure of numerous cilia. The closely related species A. chroococcum 

 is less actively motile. Both possess the power of free nitrogen assimilation to a high 

 degree, especially when cultured in a nitrogen-free medium. The organisms are large 

 (3 to 6ft in diameter) in the comparative sense. Clostridum pastorianum is also an active 

 free nitrogen assimilator, but differs trom the Azotobacters in that if forms spores, a prop- 

 erty which may render it highly valuable in economic agriculture as cultures in the 

 sporulating stage can be kept for a long time while the cultures of non-sporulating bac- 

 teria soon die off or lose their potency. 



