SHADE TREE AND TIMBER DESTROYING FUNGI. 217 



there appear several different stages. The outer one is marked 

 by the dark discolored area, the next is pale yellowish white, the 

 wood being quite soft, and an older and more advanced area at 

 the centre of the heart. These different stages in the process 

 of decay from the centre to the periphery are usually limited by 

 the black line, which is bordered by a more or less well defined 

 corona of color darker than the area upon which it is advancing. 



76. Young trunk of maple nearly killed by Polyporus 

 igniarius. 



In many cases these areas of decay progress very irregularly, 

 and the figure becomes complicated and confused, especially in 

 the later stages of the decay of a tree, so that dark lines extend 

 very irregularly. 



An examination of several maple trees bearing the Polyporus 

 igniarius gave evidence that the peculiar discoloration of the 

 wood, accompanied the mycelium of this species of fungus, and 

 might perhaps be sufficient to identify the species even where no 

 fruit form of the fungus was present. An examination of the 



