360 Diseases of Economic Plants 



The trunk in cross-section shows rot at the center; the 

 wood becomes soft and pulpy. The decayed region is ir- 



yZ 



( 



Fig. 188. — Fomes igniarius upon maple. After von Schrenk. 



regular in outline and bounded by narrow black layers. The 

 tree is rarely hollow, but remains filled with the decayed 

 wood. Young trees which bear no dead branches to admit 

 the fungus are usually immune. 



