THE POLYPORACEAE OF WISCONSIN. 9 



there was a narrow strip of wood not yet infected, extending from 

 the base of the trunk to the living branches. On the other side, the 

 characteristic rot was co-extensive with the fungus. Frequently the 

 tops are dead in trees infected with this fungus, but in all of these 

 cases it was found that the fungus had actually spread to the top in- 

 stead of encircling the trunk at the point of infection. Another tree 

 which was wounded some thirty feet from the base was cut down to 

 determine whether the fungus spreads downwards. Upwards from 

 the wound traces of the fungus were found to a distance of some 

 twenty feet, but downwards it had spread less than ten feet. From 

 this it would seem that the fungus spreads upwards more rapidly 

 than downwards. 



Trees killed by the fungus often remain standing for many years 

 before they are blown down. This is because the heartwood is usu- 

 ally sound. One tree trunk was found near Star Lake in which the 

 sap wood was decayed by P. abietinus and the heartwood by Pomes 

 pinicola. This trunk was about twelve inches in diameter but I eas- 

 ily broke it off and by stepping on it, crumbled it into minute pieces. 



The general effect of P. abietinus on fir, spruce, and tamarack, is 

 the same as that on hemlock, but the percentage of infected trees is 

 much less than for hemlock, being least in white pine. Stumps and 

 branches of red pine were quite frequently found infected. Very 

 often the white mycelium was found spreading in strands between 

 the bark and the wood. In these cases the bark loosens easily from 

 the wood. Often when the pileus grows out of a hole made by a bark 

 borer, the white mycelium is found spreading in every direction be- 

 tween the bark and the wood, the greater growth being upward. The 

 cambium being destroyed, the bark becomes loosened and that part of 

 tree dies. 



Whenever there are cracks in the wood, it is found that the myce- 

 lium follows them very readily and pilei are formed at the openings 

 of the cracks where the mycelia issue in strands. This would seem 

 to show that the mycelium spreads most easily in the direction of least 

 mechanical resistance. The hyphae which run lengthwise through 

 the cells are always the largest and best developed. These large hy- 

 phae pierce the end walls of the tracheids quite easily. The end walls 

 are perhaps less resistant than the lateral walls. Whether the path of 

 sap flow has something to do with the direction of the growth of the 

 hyphae, is difficult to determine. There does not seem to be any 

 spread of the fungus in the bark. 



The rot produced by the fungus is characteristic and unlike any 

 other rot I have observed, though in some respects it resembles the 



