COMPOUND ORGANISMS 195 
bacteria-like organisms to which the name of 
Bacillus radicola has been given. 
The root becomes infected by this bacillus 
Fig. 22.—Root tubercles on the roots of the Kidney- 
bean plant. 
from the soil, in ordinary samples of which 
it is apparently always present. The bacillus 
enters through a root-hair, and when it reaches 
the interior of the cortex it multiplies there, 
