10 



STUDIES OF AMERICAN FUNGI. 



and live from year to year. They may therefore be found during the 

 winter as well as in the summer. The writer has found specimens 

 over eighty years old. The shelves or brackets are the fruit bodies, 

 and consist of the pileus with the fruiting surface below. The fruit- 

 ing surface is either in the form of gills like Agaricus, or it is honey- 

 combed, or spinous, or entirely smooth. 



Mycelium of the Wood Destroying Fungi. While the fruit bodies are 

 on the outside of the trunk, the mycelium, or vegetative part of the 

 fungus, is within the wood or bark. By stripping off the bark from 



Figure io. Polyporus borealis. Strands of mycelium extending radially in 

 the wood of the same living hemlock spruce shown in Fig. 9. (Natural 

 size.) 



decaying logs where these fungi are growing, the mycelium is often 

 found in great abundance. By tearing open the rotting wood it can 

 be traced all through the decaying parts. In fact, the mycelium is 

 largely if not wholly responsible for the rapid disintegration of the 

 wood. In living trees the mycelium of certain bracket fungi enters 

 through a wound and grows into the heart wood. Now the heart 

 wood is dead and cannot long resist the entrance and destructive 

 action of the mycelium. The mycelium spreads through the heart 

 of the tree, causing it to rot (Fig. lo). When it has spread over a 

 large feeding area it can then grow out through a wound or old knot- 



