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A DISEASE OF BLACK OAKS CAUSED BY POLYPORUS 



OBTUSUS BERK. 



BY PKRLEY SPAULDING. 



Of the numerous fungi which attack living deciduous 



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trees by gaining entrance through wounds or dead branches, 

 Polyporus obtusus is not very generally known. The 

 disease caused by this fungus is quite destructive 

 locally to several species of oak trees which are of minor 

 importance as timber trees. Because so little seems to be 

 known of this fungus, and also because of the ever in- 

 creasing importance of the inferior timber trees, it has 

 seemed advisable to find out as much as possible concern- 

 ing this disease, which has been discovered in certain locali- 

 ties in central Missouri and northern Arkansas. The 

 disease which is caused by the fungus Polyporus obtusus in 

 living trees of Querent marilandica and Q. velutina has 

 been found only in the above mentioned places, but it is 

 more than probable that it is present in many others where 

 it has not been noted. Because of the insects which eat 

 the sporophores very rapidly, usually totally destroying 

 them and rarely leaving a single one intact for any length 

 of time, the damage caused by the fungus is very hard to 

 estimate and it is impossible to determine the percentage 

 of diseased trees. The thick, dark-colored, deeply fur- 

 rowed bark covers injuries very effectually so that it is 

 impossible to detect affected trees unless the sporophores 

 arc still upon them. 



Polyporus obtusus seems to occur only in North America. 

 In the United States it has been collected and reported 

 from widely scattered localities as follows : Alabama by 

 Mohr and Underwood & Earle ; Arkansas by Hedgcock and 

 Spaulding; Iowa by Holway, McBride, and von Schrenk; 



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