The Biology of Polyporus Pargamenus Fries 141 
menus produces a type of decay in which the destructive 
changes at first are confined to localized areas of the wood 
but later spread so that the whole mass of the wood is soon 
involved. The pocket formation is not so pronounced at first 
in the earlier stages of the decay but becomes a conspicuous 
feature of the late stages as explained in the descriptions of 
the decay of individual woods. With the progress of the 
decay the destruction of the woody substance tends to be 
completed within the numerous individual pockets so that in 
the late stages of the decay practically no sound wood is left 
except the narrow zones separating the pockets. The pockets | 
are not sharply defined until the late stages of the decay for 
in the intermediate stages they are more or less filled with a 
mass of partially reduced woody elements which remain in 
position next to the unchanged wood. In the late stages of 
the decay, however, the pockets frequently coalesce into 
larger ones separated by a mere membranous layer of resis- 
tant wood and become devoid of all contents save for a few 
vessel segments which resist. decay unusually long. Micro- 
scopic sections of wood in this stage of decay show that the 
pockets are separated only by a thin zone of resistant wood 
from one to several cells wide (Plate XXIV, Figs. 1 and 2). 
This was especially marked in the sections studied in con- 
nection with the decay of yellow birch, bitternut hickory, and 
hemlock. In the sections of decayed sugar maple wood 
studied this resistant zone of wood was less pronounced and 
contained abundant masses of matted fungal hyphz within 
the lumina of the elements of this resistant zone. In some 
of the sections of decayed chestnut oak wood studied the 
resistant zones of wood demarking the pockets had completely 
disappeared and in their place was left a reticulum or net- 
work of matted fungal hyphz occupying the position for- 
merly held by the resistant zones of wood. In fact sugges- 
tions of this transformation could be seen occasionally in 
certain sections of the other woods. In connection with the 
microscopic descriptions of the individual decays of the five 
woods studied in full detail mention was made of mats of 
hyphee within the wood, particularly in the vessels, which 
