AUTOBASIDIOMYCETES 



459 



The mycelium evidently establishes itself in a saprophytic man- 

 ner upon dead branches or in the decayed wood about knot holes, 

 thence gaining entrance to the heartwood of the main trunk. 

 After growing for years in the latter, it may develop sporophores 



Fig. 227. Polyporus sulphureus on White Oak, showing Nature of 

 Decay. (Photograph by Geo. F. Atkinson) 



where wounds occur, permitting the vigorous mycelium to reach 

 the surface readily. In other cases the path of the mycelium of this 

 fungus evidently extends directly to the surface, killing the wood 

 as it progresses. Sporophores may then be developed on the 

 otherwise uninjured bark surface. In general, the growth of the 

 mycelium causes a prompt decay of the wood, the latter becoming 



