214 BULLETIN 193. 



probably due to several causes, the resistance which it meets 

 from the wood, the action of tannic acids in the heart wood, as 

 well as to the small amount of air in the interior of the tree. 

 When sections of the trunk were cut, and piled together, the 

 mycelium at the cut surfaces grew very rapidly. The mycelium 

 here had access to air, and the moisture was conserved by the 

 cut surfaces being in contact. In this way it was easy to demon- 

 strate the presence of the mycelium in parts of the wood which 



73. Polyporus igniarius,from maple. 



to the eye appeared sound. The mycelium grew out from the 

 wood into the moist air, along the concentric annual rings, and 

 the medullary rays, so that within 24 hours the location of the 

 mycelium at these points was plainly demonstrated and photo- 

 graphs taken at this time marked the location of the mycelium 

 in the infected areas. In several days time, however, the 

 mycelium spread out between the cut surface forming thin sheets 

 of " punk." 



POLYPORUS IGNIARIUS. 



This species occurs on broad leaved trees. It is known on the 

 apple, oak, alder, beech, birch, maple and other species. The 

 fruit bodies are hoof-shaped, very hard, almost stony, the upper 

 surface black, while the lower surface, the fruiting surface, is 

 brownish. The upper surface is marked by concentric furrows 



