230 



Bulletin 193. 



of the bark and cambium, or growing region, at this spot. Tliis 

 wound was too large and the tissues too much bruised to permit 

 rapid healing over. It offered therefore a sure infection court 

 tliroui^h which the mycelium entered. 



This also shows that the healing has been going on for a long 

 time from the margin of the wound. But the wound is so large, it 

 is yet far from being healed. Had it later healed over, it conld 

 nut, of course, save the tree from destruction because the wound 

 parasite was already permanently established in the intei'ioi-, ur 

 heart, wood. Thus the wound which a-ave entrance to the funii-us 

 mycelium also offers a place for its exit in the formation of the fruit 

 body. 



From the time the mycelium entered the trunk at this wound, 



rvav.' ± ' 



-|R5S5Wr9TTr 



\ 



60. — Polyporus horealis. Disintegration of wood. 



which must have been from 25 to 40 years ago, the mycelium gradu- 

 ally made its way into the heart, and from there grew downward into 

 tlie roots and upward through the heart to the top of the tree. Its 

 presence on the roots was determined by the occurrence of the 

 fruit bodies from a few places on exposed parts of the large roots 

 while external evidence of its having reached the top of the tree 

 was shown by a numl)er of dead limbs in the top, some of which 

 had fallen. Evidence of its having reached the top was also found 

 on cutting down the tree, and taking out sections at different points 

 in the trunk. Here was found an abundance of mycelium and the 

 heart wood was in an advanced stage of decay. 



The mycelium advances in certain definite directions in the wood 



