14 THE POLYPORACEAE OF WISCONSIN. 



Since neither the pilei of the fungus nor its characteristic rot was 

 found in living trees, it appears that it is strictly saprophyte attack- 

 ing the wood only after the tree is dead. The effect, however, on 

 the cells is not much different from that of Fomes pinicola as deseibed 

 by Von Schrenck and by Hartig. 



In general, the pilei seem to grow out of cracks in the wood, and 

 the decay also follows these cracks to some extent. Wherever there 

 is abundant mycelium, and especially in the neighborhood of pilei, the 

 wood is often colored a sepia brown by a coloring matter which ap- 

 pears also to be dissolved out by the rain. This coloring matter is 

 very soluble in ammonium hydrate. Wood containing the mycelium 

 or the coloring matter turns very dark, almost black, when treated 

 with ammonia, as does also the pileus. 



The wood destroyed by this fungus becomes brown, paler than in 

 the case of the rot produced by Fomes carneus and F. pinicola, but 

 otherwise it looks quite similar. The wood becomes cracked and 

 shrunken. This cracking occurs for the most part transversely and 

 longitudinally, sometimes also radially, forming irregular cubical frag- 

 ments. In advanced stages the wood can be rubbed to a fine powder 

 with the fingers. The cracking is evidently due to the shrinking, as 

 Hartig suggests, probably because of the removal of moisture and cell- 

 wall substances by the fungus. 



Nothing definite can be stated about the method and time of infec- 

 tion, nor as to the rapidity of development. It seems certain, how- 

 ever, that infection takes place in the openings that occur in the wood, 

 such as cracks and holes, and in the porous ends of rough transverse 

 cuts. In such places the pilei will be found, and in the neighbor- 

 hood the wood shows the effects of the fungus. Bridge timbers that 

 become cheeked from weathering are always in danger of attack by 

 this fungus. I have never found it on well painted timber, unless 

 it showed cracks or holes. 



The earliest stages of decay that were studied were found in a piece 

 of hemlock out of which a pileus one and one-half inches broad, and 

 one inch long was growing through a hole in the bark one-quarter 

 inch deep, made by a bark borer. The wood underneath this pileus 

 for a distance of three inches above and below this hole, and one inch 

 in width, showed stages of decay. To a depth of about one-quarter 

 inch the wood was turning brown but showed white spots and stripes. 

 Underneath this to a depth of nearly three-quarters of an inch the wood 

 had its natural color but was mottled with whiter spots and stripes. 

 These white spots and stripes are in the summer wood, and the darker 



