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The Biology of Polyporus Pargamenus Fries 119 
the dissimilar structure and microchemical reactions of the 
various elements we would expect the multiseriate pith-rays 
to resist decay even longer than the comparatively thin-walled 
vessels. Of the individual elements the middle lamell 
would resist decay longer than the secondary layers of thick- 
ening of the respective elements. The least resistant layers 
would be the secondary and tertiary layers of the wood fibers. 
Macroscopic Appearance of Decayed Wood.— The macro- 
scopic appearance of decayed chestnut oak wood shows 
essentially the same type of decay that occurs in the other 
woods. Numerous fine black zones are to be seen in decayed 
trunks, when the decay has not progressed too far. Their 
occurrence is the same as in the other decayed woods 
described, namely, surrounding areas of undecayed wood and 
demarking them from the surrounding decayed wood. The 
black zones occurring in decaying chestnut oak (or other 
oak) wood usually are thinner and less conspicuous than 
those which predominately occur in the decay of most other 
dicotyledonous woods. The decayed wood examined was 
very friable but by no means in the last stages of decay. 
The pockets occurring in the decayed wood were somewhat 
inconspicuous owing to the heterogeneous structure of the 
wood. They were clearly visible, however, after the surface 
of the wood was moistened. Owing to the broad pith-rays 
of this wood its decay is quite comparable to that of sugar 
maple wood. The effect of the broad pith-rays in retarding 
the decay from spreading in any other than a radial direc- 
tion is even more strongly exemplified in chestnut oak wood 
than that of sugar maple. The multiseriate pith-rays of 
chestnut oak wood are exceptionally thick, high, and broad, 
many of them extending unbroken from the pith to the 
bark. Unlike sugar maple wood, however, they do not le 
so closely together. Nevertheless, they are important factors 
in forcing the decay to spread mainly in a radial direction, 
since, owing to their lignified nature, they are not attacked 
and penetrated nearly so readily as the other elements of the 
growth ring. As a result of this unequal spread of the 
fungus the decayed wood tends to rupture far easier in a 
