The Biology of Polyporus Pargamenus Fries 167 
decay and insect attacks in trees. The fire may have 
occurred many years ago and all signs of it been hidden by 
subsequent growth, but during the two or more years that it 
took the tree to heal over the scar insects and spores of fungi 
which produce rot in trees entered at this open wound on 
the butt and, in the case of the rots, have been at work ever 
since, gradually destroying the wood of the trunk (Plate 
XXXI, Fig. 2.) Thus it is that within a few months after 
the fire the sporophores Polyporus pargamenus are found 
growing on the dead bark and the decay caused by the fungus 
extends rapidly throughout the deadened area. 
The small fire-scar may, and usually does, heal over so 
that within a few years no evidence of a fire or injury to the 
trunk can be seen from the outside. The rot, however, con- 
tinues to grow for years, speedily causing the death of the 
tree upon the decay of the cambium and the sapwood. After 
the death of the tree the fungus continues its ravages of 
decay in the sound wood remaining, thus ruining the tree 
for most commercial purposes. Every time a tree is reached 
by a fire sufficiently hot to kill a small area of the inner bark 
and sapwood, an opportunity is given for attacks by this and 
other wood-destroying fungi. 
There are, however, certain physical factors upon which 
the growth of fungi and the consequent destruction of the 
wood is dependent. For example, all fungi require a certain 
supply of nutriment, moisture, and air, the amount of each 
varying with the individual species and the environmental 
conditions for growth. If deprived of the requisite amounts 
of any one of these the fungus ceases to develop and eventu- 
ally dies. It has been established that no chemical reaction 
takes place between substances except in the presence of 
water. As the decay of wood is largely dependent upon the 
chemical reaction of certain enzymes, secreted by the my- 
celium of the fungus, upon the various constituents of the 
cell-walls of the woody tissue, it follows that water must be 
present wherever there is decay. Water is essential for plant 
growth, and when there is no moisture no plants can develop, 
hence no decay can occur. Warmth also is conducive to the 
