258 MANUAL OF TREE DISEASES 



Later they become yeUowish or brown. The upper surface 

 and the rounded edge and outer margin of the lower siu^ace 

 are hairy. The remainder of the under siarface is covered 

 with roundish or sinuous pores, the edges of which are irregular, 

 making the under surface rough. 



Cause. 



The soft heartwopd-rot of black oaks is caused by Polyporus 

 ohtusus. The spores borne within the tubes on the under sides 

 of the fruiting-bodies are blown about by the wind. Infection 

 usually takes place by the sporep entering the tunnels made 

 in the wood by the insect, Prionoxystus rohinim. From the 

 tunnels the mycelimn spreads upward and downward in the 

 wood. The fruiting-bodies are usually produced at the insect 

 burrow where infection occurred. For further details con- 

 cerning the life history and control of wood-rot fungi, see 

 page 64. 



References 



Spaulding, P. A disease of black oaks caused by Polyporus obtusus 



Berk. Missouri Bot. Garden Rept. 16 : 109-116, pis. 13-19. 



1905. 

 Schrenk, Hermann von, and Spaulding, P. Soft rot of oaks caused 



by Polyporus obtusus. In Diseases of deciduous forest trees. 



U. S. Dept. Agr. Bur. PL Ind. Bui. 149 : 41^2, fig. 5. 1909. 



White Piped Butt-Rot 



Caused by Polyporus croccus Fries ( = P. PUoUb Schw.) 



This wood-rot is found in oak and chestnut. The wood of 

 the roots and base of the trunk is most commonly affected, 

 although when dead branches are common it may be foimd in 

 the upper part of the trunk. It has proved destructive in 

 Arkansas, Virginia and New York and probably is generally 

 distributed throughout eastern and central United States. 

 The decayed wood is at first filled with white areas which en- 



