Minnesota Plant Diseases. 



241 



tree attacked by a Stereum. The progress of the myecHum up- 

 ward in the stem is indicated by the size of the fruiting bodies, 



which are largest 

 in the neighbor- 

 h o o d of the 

 wound and dimin- 

 ish gradually 

 away from the 

 wound. 



Oak attacked 

 by Stereum hir- 

 sutum Fr. is 

 known as white- 

 piped or yellow- 

 piped oak. The 

 wood becomes 

 brownish at first. 

 Lo ng i tu dinal 

 white or yellow 

 streaks then arise 

 where, under the 

 influence of the 

 fungus mycelium, 

 the wood loses 

 its woody charac- 

 ter. The whole 

 block then grad- 

 ually undergoes 

 further decompo- 

 sition. In a cross 

 section of the 

 wood these 

 streaks are seen 

 as whitish specks 

 which have given 



Fig. 117.— A Stereum wound parasite (a species of Stereum). 

 The fungus obtained entrance in the wound at the base 

 of the tree (an oak), and, as shown by the fungus fruit- 

 ing bodies, is gradually progressing upward. This tree 

 died about a year after the photograph was taken. 

 Original. 

 16 



