THE POLYPORACEAE OF WISCONSIN. H 



thus becomes filled with small holes and becomes soft and brittle. The 

 fall wood is left more or less intact as a thin brittle shell, making the 

 growth rings more or less easily separable. 



The larger and more vigorous hyphae are usually found growing 

 lengthwise up and down the cells but are not as much tangled and 

 matted as the hyphae of Polyporus borealis figured by Hartig. The 

 horizontal hyphae are fewer in number, straighter and much thinner 

 than the others. They seem to be able to penetrate the radial 

 walls more easily than the tangential ones. Probably most of the ra- 

 dial distribution of the fungus takes place through the ray cells. The 

 hyphae in the ray cells are always quite small and never abundant, 

 although their action on these cells is always prominent. 



The hyphae do. not always pass through the pits of the cells but 

 appear to be able to penetrate the walls at any point. 



Polystictus pergamenus Fries. 



This is one of the commonest forms of the Polysticti, growing on 

 maple, willow, oak, birch and poplar. It is easily recognized by its 

 leathery consistency and purplish hymenium. The dissepiments are 

 usually torn into teeth or plates so that older specimens might often 

 be taken for species of Irpex. The hymenium turns brown with age. 

 The pilei are thin, profusely imbricated and laterally confluent. 



This species seems to be closely related to P. abietinus, described 

 above. The latter, however, is smaller, more hirsute and concentric- 

 ally sulcate and grows only on Coniferae, while P. pergamenus grows 

 only on deciduous trees. 



P. pergamenus is quite frequently found in living oak, maple and 

 poplar. The trees thus infected are always in a poor condition of 

 health and are often found in the last stages of life. On one side of 

 an oak tree even some of the large branches had pilei growing out of 

 their sides. The larger part of the tree was dead, and the rest was 

 not very vigorous. It was evident that this tree would soon be en- 

 tirely dead. On the side infected, the bark was cracking and loosen- 

 ing. 



Infection of living poplar is more rare, and then it is usually found 

 to be confined for the most part to the areas immediately surrounding 

 a wound. Nor does the bark seem to crack and loosen in poplar as 

 in oak and maple. It would seem that in the poplar the spread of 

 the fungus through the wood occurs after the death of the tree, or 

 at any rate the spread here is very slow. 



