The Biology of Polyporus Pargamenus Fries 187 
to this extent that they respond to the cellulose test with 
chlorzinc-iodine. The corners of the middle lamelle, where 
they are thickest, are the last portions to disappear under the 
dissolving action of the fungus. 
Within the individual pockets or decayed areas the various 
classes of elements disappear in a definite order, depending 
upon the thickness of their walls in conjunction with their 
degree of lignification. In general, in the dicotyledonous 
woods studied, the thick-walled but little lignified wood pro- 
senchyma elements are the first to disappear. In the decay 
of yellow birch wood the uniseriate pith-rays sometimes 
disappear before the other elements. It is highly probable 
that, in the case of living trees at least, the rapidity with 
which the pith-rays are attacked and destroyed depends 
largely upon the time of year that the wood was attacked 
by the fungus. If a tree was attacked at a time when large 
amounts of reserve food was stored in the pith-ray cells, it is 
quite likely that the smaller medullary rays at least would 
be the first elements to be attacked and dissolved by the 
mycelium. After the wood prosenchyma elements have dis- 
appeared the next element to go usually is the uniseriate 
pith-rays. The order in which the other elements disappear 
is subject to considerable variation in the different woods. 
In those woods containing but scanty wood parenchyma this 
element disappears before the multiseriate pith-rays. In 
those woods containing well-developed wood parenchyma this 
element disappears simultaneously with the multiseriate 
pith-rays. In those woods having no very large pith-rays, 
such as yellow birch and bitternut hickory, the vessels are 
the last element to disappear within the individual pockets. 
In those which contain broad pith-rays, such as sugar maple 
and chestnut oak, the broad pith-rays resist decay longer than 
the vessels. In general it may be stated that the vessels 
resist decay longer than any other one element excepting the 
broad medullary rays. Where the vessels occurred in groups 
they frequently separated from one another before they 
became entirely dissolved. The vessel walls behave very 
similarly to the middle lamellee; they are very uniformly lig- 
