252 MANUAL OP TREE DISEASES 



The under surface is brown as is the inside structiu-e, including 

 the granular core. 



Cause. 



The white pocketed rot of oaks and poplars is caused by the 

 fungus Polyporus Rheades which is also known by the name 

 P. dryophUics. The sporophores described above are annual. 

 The rot may be confined largely to the branches and upper 

 part of the trunk or the tree may be rotted from the base to top. 

 Infection occurs most commonly in broken branches, from 

 which the mycelium extends down into the trunk. When in- 

 fection takes place through dead side branches or at the base 

 of the tree, through fire scars, the rot may extend the entire 

 length of the trunk. For fuller details concerning the life 

 history of wood-rot fungi and the nature of the decay caused 

 by them, see page 64. 



References 



Hedgeock, G. G., and Long, W. H. Heart-rot of oaks and poplars 

 caused by Pol3TM>rus dryophilus. Jour. Agr. Res. 3 : 65-80, pis. 

 8-10. 1914. 



Sehrenk, Hermann von, and Spaulding, P. Pii)ed-rot of oak and 

 chestnut. In Diseases of deciduous forest trees. U. S. Dept. 

 Agr. Bur. PL Ind. Bui. 149 : 39-40, pi. 5. 1909. (Note : The 

 piped-rot of oak described is due to P. Rheades and that of chest- 

 nut to P. croceiis.) 



Hartig, R. Polyporus dryadeus Fr. In Die Zersetzungserschei- 

 nungen des Holzes etc., pp. 125-128, pi. 17. 1878. .(This is a 

 discussion of the rot due to P. Rheades and not P. drya^us.) 



String and Rat Butt-Rot 



Caused by Polyporus Berkeleyi Fries 



This heartwood-rot of the base of oak trees is found through- 

 out eastern and central United States. It is not known to be 

 as common or destructive as several of the other wood-rots of 

 oaks. Mature and over-mature trees are affected. It is never 

 found in the tops of trees but is limited to the base of the trunk 



