ROT-FUNGI AND THEIR WORK 79 



at a wound or weakened spot, and push out sporo- 

 phores. The invasion of normal sapwood by 

 heartwood rots is, however, very slow, and it al- 

 most never happens that a tree is strangled and 

 killed by such a fungus. What the heart rots do 

 is to weaken the support of the tree, making it lia- 

 ble to destruction by storms. 



Perhaps the commonest and most destructive of 

 the fungi inhabiting the heartwood of trees is the 

 "white heart rot " (Fomes igniarius). It is 

 found in every part of the world. In this country 

 it most frequently attacks beech, aspen, willow, 

 maple, walnut, hickory, apple and oak. 



Entering through wounds or the stubs of dead 

 limbs, the fungus attacks the heartwood of the 

 tree. Von Schrenk and Spaulding give the fol- 

 lowing description of the effect of the fungus upon 

 the wood of the tree : ' The diseased wood is 

 very sharply bounded from the healthy wood by 

 black layers about one-eighth to one-sixteenth of 

 an inch in width. There may be but a single one 

 or there may be several arranged more or less 

 concentrically. Just outside of these layers there 

 is a layer consisting of from three to six annual 

 rings, which is darker in color than the normal 

 wood because of the infiltration into the same of 

 products of the decomposed wood. . . . The 

 black layers never exactly follow the annual rings 

 of growth. . . . The completely rotted wood is 



