The Biology of Polyporus Pargamenus Fries 101 
so much eroded that they break up into irregular fragments, 
among which can be detected portions of pitted walls and 
sealariform bars from the end walls of the vessel segments. 
Even those fragments of vessel walls retain their lignified 
nature until they become almost completely dissolved. 
Within any one center of decay the dissolution of the cell- 
walls progresses very uniformly, as shown by the fact that 
the distance from normal cell-walls to walls that have been 
completely decayed is often no more than thirty-five microns. 
An examination was made of prepared slides for the 
purpose of determining the relation of the mycelium to the 
wood. In the earlier stages of the decay the hyphe may 
follow the course of the vessels and wood parenchyma ele- 
ments for some distance before diverging, and again they 
may branch off profusely and enter the medullary rays. In 
the much decayed wood the mycelium is abundant in all the 
woody elements and branches profusely in all directions, 
perforating the walls of the woody elements at random. 
In the later stages of the decay it is evident that many of 
the hyphze deliquesce, or, at least, disappear in some way, 
for the perforated cell-walls are commonly seen but no hyphee 
can be found associated with them. The hyphe found in 
decaying yellow birch wood are exceedingly delicate and 
minute. No cross-walls or clamp connections were observed 
in them although failure to see these structures may have 
been due to the extremely small size of the hyphe. Dense 
plugs or mats of hyphee frequently occlude the vessels. These 
mats of hyphe are brown by reason of being incrusted with 
some decomposition product. 
From the above study it is evident that the first main 
chemical change which is brought about by the action of the 
fungus is that of delignification. It is due to this action 
that the elements lose their normal brownish color and appear 
as though bleached. At the beginning of delignification, the 
decay seems to be localized in small areas which appear as 
pockets in the wood after the woody tissue within them is 
completely destroyed. From the results obtained, it is 
apparent that delignification commences in the tertiary layer 
