TREES AND TIMBER 419 



1 to 25-30 cm. in diameter, nearly spherical, and consist 

 chiefly of immense numbers of white spines upon whose 

 surfaces the spores are borne. 



Heart rot (Fomes fulvus Fr.) . — In Missouri and Arkansas 

 this heart rot is found upon the river birch and a num- 

 ber of other trees. The wood is brown, and crumbles on 

 crushing. It extends from 3-4 m. above and below the 

 sporophores. These are pore-bearing, triangular in section. 

 The upper surface is very hard and bears fine, irregular 

 fissures parallel to the edge. When mature, the upper 

 surface is red-brown. The pores are barely visible without 

 a hand lens. 



Rot {Polyporus subacidus Peck). — This is a rot of dead 

 logs as well as living trees, which often enters through the 

 roots. 



The decayed wood is moist, spongy, and bears cavities 

 of various size and shape hned with a tough mycelial felt, 

 which is yellow inside. In early stages the wood is black- 

 spotted. The black spots later give way to larger white 

 spots surrounded by a straw-colored frayed region. The 

 sporophores are sheet-hke and bear shallow, straw-yellow 

 pores. 



Soft rot (Polyporus obtusus Berk.). — The black oaks (Q. 

 Marylandica and Q. velutina) are chiefly affected by this 

 rot, which is found in Missouri, Arkansas, Iowa, Tennes- 

 see, Mississippi, New Jersey, and Maryland. 



The causal fungus enters through the burrows of a wood 

 borer. The heartwood turns light yellow, then white, 

 and becomes brittle. Strings and sheets of white mycelium 

 are found in the wood. Death results either from diminu- 

 tion of water supply or from breaking of the trunk. 



