204 BULLETIN 193. 



in the several photographs. A section through the entire fruit 

 body (Fig. 57) shows the radiating lines formed by the general 

 direction of the mycelium in the caps from their common origin 

 in the tree trunk. 



One of the photographs gives us a clue to the manner in which 

 the mycelium of the fungus entered this particular tree. The 

 log, lying in the foreground, close by the trunk of the affected 

 tree, tells the tale. This tree in its descent, years ago, struck 

 the slightly projecting base of the standing hemlock, and 

 knocked off a large area of the bark and cambium, or growing 

 region, at this spot. This wound was too large and the tissues 



60. Polyporus borealis. Disintegration of wood. 



too much bruised to permit rapid healing over. It offered there- 

 fore a sure infection court through 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 

 could not, of course, save the tree from destruction because the 

 wound parasite was already permanently established in the 

 interior, or heart, wood. Thus the wound which gave entrance 

 to the fungus 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, 

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

 gradually made its way into the heart, and from there grew 

 downward into the roots and upward through the heart to the 



