FOREST INSECTS AND FUNGI 



133 



commonly more or less hoof shaped, the thickness being about 

 equal to the width. The upper surface, at first smooth, becomes 

 concentrically marked with age. They grow to great age as 

 indicated approximately by the number of layers. The lower 

 surface is gray to reddish brown; the edge yellowish brown. 



The spores enter the tree trunk through some wound, as an 

 old branch stub. The fruiting bodies usually form at the point 

 of original infection. It is not uncommon to find a dozen of 

 these bodies on the trunk of an aspen. Examinations by 

 Spaulding have proved that the fungus continues to thrive after 

 the death of its host. 



Fig. 47. An oak broken off by the wind. The base of the tree was honeycombed by a 

 fungus which entered through old fire scars. Wind cannot uproot an oak but fre- 

 quently breaks off weakened trees. 



A tree affected with white rot may live for a number of years, 

 especially such long-lived species as oak and beech. But with 

 such trees as aspen where the disease may encroach upon the sap- 

 wood, the trees may be killed by the disease. The death of 

 trees is a minor result of the disease compared with the great 

 destruction of wood which it causes. 



Two methods of prevention are possible: one consists in the 



