222 MANUAL OF TREE DISEASES 



sapwood. The reddish colored decayed wood splits into small 

 cubes with plate-like sheets of mycelium filling up the cracks 

 between. This wood-rot is similar in its effect on the different 

 kinds of trees and is more fully described imder oak diseases, 

 page 247. 



Root-Tubercles 



Caused by Bacillus radicicola Beijerinck 



Locust roots often show small globose swellings. These 

 structures are abnormal lateral rootlets which are inhabited 

 by the nitrogen-fixing bacterium. The bacteria gain entrance 

 to the root through the root-hairs. They multiply in the cortex 

 cells and stimulate the tissues to over-growth. A discussion 

 of the relation between the host and parasite will be found 

 imder alder diseases, on page 88. 



