8 BULLETIN 191 



portance from the point of view of its ability to continue the forma- 

 tion of fruiting bodies on fallen trees and thus greatly to increase the 

 spread of the disease. 



Growth of mycelium. Von Schrenk (2) states that destruction 

 of the wood, at least, ceases upon the fall of the tree, but that whether 

 the fruiting bodies on fallen trees do or do not function to any great 

 extent remains an open question. That the growth of the mycelium 

 (the thread-like tubes which penetrate the wood and nourish the fun- 

 gus, tubes which in their function are analogous in a way to the roots 

 of higher plants) in fallen trees is dependent almost entirely upon 

 moisture conditions, was proved conclusively by the writer by taking 

 uniform slabs of diseased pine, placing them in various conditions of 

 moisture and- watching the progress of the growth of the mycelium 

 and the destruction of the wood. Slabs placed under cover where con- 

 ditions are such as are found ordinarily where lumber is seasoned, 

 showed no further growth of the fungus. The wood dried out and 

 its pithy appearance assumed a more open character. On the other 

 hand, slabs of the diseased wood left in contact with the ground, or 

 near moisture, showed abundant growth of the mycelium, which ex- 

 tended even to the surface of the wood. Whether infected wood left 

 in such conditions ultimately would or would not form functioning 

 fruiting bodies, is undetermined. However, it is believed that trees 

 which fall in the woods as a result of permeation by the fungus do 

 not fall ordinarily under such conditions as tend to favor the con- 

 tinued growth of the mycelium. The trunk of the tree is more likely 

 to be attacked by fungi such as Lenzites sepiaria and other saprophytes 

 that can live in a drier situation. 



Method of attack. Any tree wound which opens up a way to ex- 

 posed heart-wood enables the red rot fungus to germinate and the 

 mycelium to penetrate the wood. Once the mycelia have gained en- 

 trance, they spread rapidly, both up and down the trunk, along the 

 tracheids (i. e. wood cells used simply as water carriers) longitudinally, 

 and more slowly across radially. 



Resistance. Apparently the only resistance offered by the tree 

 takes the form of a free exudation of pitch. In the younger trees this 

 discharge is sufficiently large to hinder the progress of the mycelium 

 while the lessened amount of pitch which is exuded by the older trees 

 accounts for the increased destruction. 



It is stated by Von Schrenk (2) that the mycelium of Trametes 

 Pini flourishes in both the heart-wood and sap-wood of spruce, hem- 



