Explanation of Plates. 



Plate I. 

 Effect of Pyropolyporus igniarius (L.) Murrill upon a living tree. 

 Cross section of the trunk of a silver maple (Acer saccharinum Linn.) 

 which bore but one fruiting body, this being the only external indica- 

 tion of disease. Note the thin black zones surrounding the completely 

 decayed wood; also the place of entrance of the fungus at the upper 

 left-hand corner, produced by the rotting of a dead lateral branch. 

 Photo by courtesy of the U. S. Bureau of Plant Industry. 



