ROUGH-BARKED AND SMOOTH-BARKED WHITE OAKS. 83 



Michigan may account for the fact that some of the oaks escape com- 

 plete infestation, and this may explain the peculiar sculpturing which 

 has already been noted. 



The white oak seems most frequently attacked, and the other species 

 about in the order named. It may be added that the fungus seems to do 

 no harm whatever to the tree, as it does not penetrate the bark to the 

 living tissues, but gets its needs supplied wholly from the outer layers. 

 The work of the fungus must proceed slowly since the borders of the 

 infested areas are rather indefinite. 



The same, or a closely related fungus, occurs upon the bark of other 

 species of trees than the oaks, and it is possible that all the species with 

 thin, flaky bark are attacked by it and that the flaking may be due to 

 the action of the fungus. The above considerations make it apparent 

 that it is not safe to consider any one form of bark typical of a given 

 species, until a thorough study of the type has been made. 

 C. A. Davis, 



Department of Forestry, University of Michigan, 

 Ann Arbor. 



