164 College of Forestry 
a few find suitable conditions and give rise to mature plants. 
Moreover, spores are microscopically small and hence cannot 
contain very much nutriment. They cannot, therefore, with- 
stand unfavorable conditions for germination for such pro- 
tracted periods as can most seeds of seed- bearing plants. 
While spores frequently can pass through a long resting 
period and are capable of germination at the end. of this 
period, after germination has begun the spore usually can- 
not resist unfavorable conditions. After a consideration of 
these facts it becomes apparent that the fungi in general must 
necessarily be very prodigal of their spores, so that they are 
produced in enormous numbers. 
The relation of the fungus to its host is a definite one. 
The question of the spores gaining entrance, however, is 
somewhat problematic. But few of even the parasitic fungi 
can gain entrance unaided through the bark which envelops 
the entire living trunk, since the fungal hyphee are incapable 
of forcing their way through layers of cork. When unin- 
jured, the bark therefore serves as an efficient barrier to the 
entrance of even the parasitic fungi. For its entrance io 
the living tree Polyporus pargamenus 1s dependent upon 
human, organic, or inorganic agencies, usually gaining en- 
trance through mechanical injuries to the host. There is 
no reason to believe that the fungus studied here can gain 
entrance to a living tree unaided by one of these methods 
of entrance, since the writer’s experience has shown that 
there must be some condition conducive to infection, such 
as a broken branch or other form of wound, a drying out 
and consequent death of the cambium as a result of fire. 
When the cambium of a tree is killed and the underlying 
sapwood exposed by a broken branch, blazing, or some other 
form of mechanical injury, the wood immediately under- 
lying the wounded area soon becomes functionless and dead. 
The weathering action of the elements softens this wood, it 
retains moisture readily, and affords an ideal environment 
for the development of a spore. The spores that are blown 
there by the wind germinate and send out their mycelial 
filaments, which slowly penetrate the dead wood. Some 
