16 THE POLYPORACEAE OF WISCONSIN. 



Many large white pine trunks when cut down show the characteristic 

 rot due to this fungus, but when the trunk is examined minutely one 

 fails to find the fruiting bodies. Occasionally swellings or lumps 

 called "punk knots" by the lumbermen are seen some distance up the 

 trunk on infected trees. "When cut open, it is found that these knots 

 are found by the healing over of the ends of broken branches. These 

 old branch stubs are usually very much decayed, and together with a 

 mass of yellowish-brown mycelium, fill the cavity of the knot. In a 

 few instances small sporophores were found growing out of the end 

 of the punk knots. In all instances where pilei were found on white 

 pine, they occurred at places where a branch had been broken off. 

 On hemlock and tamarack the pilei appeared at other places on the 

 trunk as weU. This agrees with Von Schrenk's observations (Bull. 25, 

 page 36). Another striking feature is the fact that no matter how 

 much or how little the trunk is decayed, or over how great an area the 

 infection had spread in the white pine, the sporophores, if found at 

 all, are never very large. They seldom exceed an inch in length and 

 an inch and a half in width. On tamarack, on the other hand, pilei 

 were found measuring five inches long by twelve inches wide, and at- 

 tached by a base at least six inches in thickness, the tubes showing in 

 some cases eight strata. Probably the tamarack is more prolific than 

 the white pine in producing fruit bodies, because its sapwood is less 

 resistant than that of the pine and the growing mycelium easily ^gets 

 close to the periphery, so that there is only a thin shell through which 

 it must break in order to get to the surface. The question remains 

 why the sapwood of the pine should be more resistant. The main dif- 

 ference between the sapwood and heartwood is the greater abundance 

 of free resin in the former. This free resin seems to be an obstacle to 

 the spread of the fungus, probably because it quite effectively shuts 

 off the supply of air and moisture without which the plant cannot 

 grow. As a matter of fact, 'there is always more or less resin flowing 

 out of old punk-knots and places where old branches have been broken 

 off and are in the process of healing over. 



Atkinson mentions that the "gum running from all the knot-holes" 

 is regarded as a sure sign of heart rot. When, then, the mycelium 

 does get to the surface, which usually occurs through the small heart- 

 wood of a dead branch, only a limited amount of growth takes place 

 and the resulting pileus is small. On the other hand, the mycelium 

 easily penetrates the sapwood in the tamarack and the decay extends 

 to the bark. Between the bark and the wood there are somtimes 

 formed cushions of brown mycelium with pore-bearing surfaces, but 



