OAK DISEASES 257 



shelves. The fungus finds entrance into the tree where heart- 

 wood is exposed at fire-scars, branch wounds and the like. 

 While usually found in the base of the trees, it sometimes oc- 

 curs in the tops. The sapwood of the living tree is not affected, 

 but when the tree is felled the mycelium grows into the sapwood 

 and causes a similar decay. 



Control. 



In the forest this rot can be controlled by preventing fires, 

 which are responsible for the scars that furnish a ready en- 

 trance point for infection. Likewise it is essential to remove or 

 burn dead and diseased oaks that are standing, as well as cull 

 logs, for on these the sporophores will continue to form for 

 several years. These measures will also keep several of the 

 other butt-rots and heartwood-rots of oaks under control. 



Reference 



Long, W. H. A honeycomb heart-rot of oaks caused by Stereum sub- 

 pileatum. Jour. Agr. Res. 5 : 421-428, pi. 41. 1915. 



Soft Heartwood-Rot 



Caused by Polyyorus ohtusus Berkeley 



Black oaks in eastern and central United States are affected 

 by this heartwood-rot. Several trees are usually found affected 

 in a group where the disease occurs. 



Symptoms. 



The affected heartwood is lighter in color than the normal 

 wood and finally becomes almost white. The wood does not 

 check and retains its normal fibrous character. It, however, 

 is weak and breaks easily. The rot progresses rapidly and the 

 trunks are weakened so that they snap off during wind-storms. 



The fruiting-bodies appear annually on the side of the trunk. 

 They are more or less hoof-shaped and at first white and spongy. 



