The Biology of Polyporus Pargamenus Fries 121 
early wood of the growth ring remain fairly intact until 
practically all of the elements of the late wood have become 
considerably broken down. However, even these elements 
undergo digestion earlier than the occasional large multi- 
seriate pith-rays. Even in thoroughly decayed wood these 
large pith-rays still remain hard and resistant, while the rest 
of the wood can be powdered readily by rubbing it between 
the fingers. It will be noticed here again that the elements 
in general disappear in a definite sequence which depends 
upon the degree of lignification exhibited by them. The 
individual cells of the multiseriate medullary rays probably 
are no more lignified than the large vessels, but their greater 
resistance to decay i is to be attributed to the fact that they 
contain a greater mass of lignified tissue than do the vessels, 
and hence they are not penetrated so readily by the fungal 
hyphe. Although the broad medullary rays do not occur so 
closely together as in sugar maple wood, they are much 
broader than the rays of the latter wood and would offer a 
very efficient barrier to the spread of the decay within the 
trunk in any other than a radial or perpendicular direction. 
The outermost rows of tangentially flattened cells in the 
growth ring are no more lignified than the other elements 
of the late wood and do not appear to resist decay any longer 
than the other elements. In the decay of sugar maple wood 
it will be remembered that the reverse circumstance occurred. 
Longitudinal sections of decayed wood usually exhibit a 
great abundance of matted erowths of hyphe. In the later 
stages of the decay the network of resistant wood bounding 
the pockets lar gely disappears and in its place zones of matted 
fungal hyphe occur, often forming a reticulum through the 
wood. (Plate XXV, Fig. 2.) The mats of hyphe extend 
through the elements in all directions, crossing the vessels 
and even the large pith-rays. As a rule they are practically 
free from incrustations of brown decomposition products. 
As in the decay of sugar maple and bitternut hickory wood 
the fungal hyphze apparently do not exert any solvent action 
upon the crystals of calcium oxalate commonly occurring in 
the wood parenchyma cells. 
