The Biology of Polyporus Pargamenus Fries 148 
position products has accumulated. This brown substance 
tends to occlude the lumina of the cells and collects in part 
on the fungal hyphe and partly in and on the cell-walls so 
that these become brownish-black. As stated before, warm 
nitric acid removes these substances entirely, leaving the 
wood almost colorless. In the decay by Polyporus parga- 
menus of those woods studied there is only a slight aceumu- 
lation of these partially decomposed substances midway 
between adjoining pockets. ‘That this accumulation of the 
partially decomposed substances is not sufficiently great to 
arrest the decay at this point is shown by the anastomosing 
of adjacent pockets with one another in the later stages of 
the decay. It is evident, however, that even the slight accu- 
mulation of decomposition products midway between two 
adjoining pockets has a decided tendency to retard the 
advancement of the decay, since such infiltrated substances 
are more difficult for the fungus to assimilate than those 
constituents which have not been oxidized. Owing to this, 
the cell-walls of those cells, that have become infiltrated with 
by-products of the decomposition, which otherwise would be 
an important source of nutriment for the growth of the 
fungal hyphz, have assumed through chemical decomposition 
a form more difficult to assimilate. On these grounds it is 
to be expected that the network of resistant wood left between 
the original centers of infection would be more resistant to 
decay than the centers of initial decay, owing to the tendency 
for resistant by-products of the decomposition to accumulate 
midway between the centers of initial decay. 
The results obtained from the detailed study of the decay 
of five species of wood of dissimilar structure indicate that 
the decay may progress to a varying extent within different 
woods. Such a study requires the securing of abundant 
material so that sections may be made from each wood in 
all of its various stages of decay. While it is not claimed 
that all stages of the decays of each of the five different 
woods were studied, sufficient sections of each were included 
so that the general course of the decay of each of these woods 
could be ascertained. In the decay of yellow birch and bit- 
