Moi plu)l()g\ ol Nodule Ikiclcria 



215 



the hraiichiug lonns arc not degeneration lornis, but may be looked 

 upon as normal and necessary stages in the life cycle of the organism 

 with specific biological functions. Some in\'estigators cjuestion, how- 

 ever, the reproducibility of the bacteroids. 



Unbanded 

 nonmotile rods 



Motile rods 



Swarmers 



Banded rods 

 (bacteroids) 



Coccoid forms 



Preswarmers 

 Fig. 89. The life cycle of Bacilhis radicicola (from Tliornton and Gangulee). 



Five stages in the life cycle of the root-nodule organism are now 

 recognized : 



1. Nonmotile, preswarmer stage, observed in cultures kept in a 

 neutral soil solution. 



2. Larger, nonmotile coccus, obtained in the presence of certain 

 carbohydrates and phosphates. 



3. Motile, swarmer stage, the cell becoming ellipsoidal and devel- 

 oping high motility. 



4. Rod form, resulting from the finther elongation of the swarmsr, 

 with decreasing motility. 



5. Vacuolated stage produced in absence of carbohydrates, the 

 chromatin dividing into a number of bands. These bands become 

 rounded and escape from the rod as the coccoid preswarmer. 



