418 DISEASES OF ECONOMIC PLANTS 



at maturity it is brittle. This fungus abounds on knots 

 and stumps. 



The rotted wood resembles a red-brown charcoal and 

 bears concentric and radial cracks due to shrinkage follow- 

 ing the decay. In these cracks are large sheets of fimgous 

 wefts. 



Diseased trees should be cut and burned to prevent 

 infection. 



Piped rot {Fungus sp.). — The oak, chestnut, beech, and 

 birch are susceptible to this rot. The sporiferous stage of 

 the causal fungus has not been recognized. The rot, 

 limited to the heartwood, is characterized by irregular, 

 small, pocketlike patches of white fiber.' These regions 

 first appear in the wood as small, lenticular areas which 

 increase, coalesce, and change into small pockets. These 

 frequently become filled with a dark, red-brown myce- 

 lium. The speckled character of the wood is a distinctive 

 mark. 



'^ Heart rot {Fomes nigricans Fr.). — The birch, willow, 

 and aspen, from Maine to Oregon, are affected. 



The rotted heartwood is reddish brown and very soft 

 and spongy. The disease eventually progresses into the 

 sapwood, reaches the bark, and kills the tree. 



The pore-bearing sporophores are few, hoof-shaped, large, 

 25-30 cm. wide, and woody, much like those of Fomes 

 igniarius. 



White rot (Hydnum erinaceus Bull.). — Although upon 

 many species, oaks are chiefly affected. The rotten wood 

 is soft and wet and with numerous holes full of light yel- 

 low floccose mycelium. The fleshy sporophores are white, 



' Von Schrenk, H., U.S. Dept. Agr. Bur. Plant Indus. Bui. 149. 



