262 MANUAL OF TREE DISEASES 



pear on the surface of the outer bark of affected roots. The 

 largest roots may be rotted to the center and the decayed wood 

 is finally spongy and easily crushed. 



The sporophores of the causal fungus form on exposed roots 

 when the tree is blown over or at the very base of the trunk, 

 arising at the surface of the ground. They are large, irregu- 

 larly shaped masses of a corky or woody texture (Fig. 51). 

 When developing, they are watery, and large drops of water 



Fig. 51. — Frui ting-body of Polyporus dryadeus, 



often form on the outer growing margin. These drops leave 

 depressions in the surface. The upper surface is uneven 

 and light brown, changing with age to darker brown and 

 black. The under part is oblique to the surface of the 

 ground in the thicker forms and more or less horizontal in 

 the thinner forms. The pores in the under surface- are 

 soon stuffed with mycelium, making them invisible. The 

 outer margin of the sporophore is thick and rounded. In- 

 sects soon destroy the under surface and outer margin but the 



