60 



DISEASES OF DECIDUOUS FOREST TREES. 



ing trees, and should, in the opinion of the writers, be considered as 

 saprophytic forms. (See fig. 8.) 



DECAY CAUSED BY STEREUM FRUSTULOSUM. 



Stereum frustulosum (Pers.) Fr. and other species of Stereum 

 cause the destruction annually of large quantities of structural tim- 

 bers. The fruiting bodies of this fungus are very insignificant and 

 generally escape the attention of the casual observer. They appear 

 in the form of small, slightly elevated gray spots on the surface of 

 decaying wood. In the majority of instances they look like sheets 

 of cracked mud, the individual pieces separated by the cracks vary- 



Fig. 9. 



A piece of oak timber rotted by Stereum fruxtulosum. The fruiting bodies are the lighter 

 colored, irregular, small bodies which are seen thickly scattered over the surface. 



ing in size from one-sixteenth to one-fourth of an inch in diameter. 

 Figure 9 shows a piece of red oak (Q-uercus rubra L.) with the fruit- 

 ing bodies of this fungus. 



Wood decayed by Stereum frustulosum can always be recognized 

 by the peculiar pocket-like formation in the mass of the wood. Fungi 

 like Polystictus versicolor produce a form of rot in which the entire 

 mass of the wood is affected. Stereum frustulosum, on the other 

 hand, causes changes in the wood fiber in localized areas of the wood. 

 The holes are more or less lens shaped and are separated from one 

 another by sound layers of wood fiber. The lining of the holes is 

 usually composed of a layer of white cellulose fibers. Stereum frustu- 



149 



