188 College of Forestry 
practical purposes, particularly for the convenience of the 
critical worker. 
The usual form of the fructification is distinct from that 
of its near relative Polyporus abictinus, with which it is often 
confused. These two species are to be distinguished defi- 
nitely only by the combined use of their respective morpho- 
logical characters, since the knowledge of the habitat 
(whether on coniferous or dicotyledonous wood), while suf- 
ficient in most cases, will not always serve as the deciding 
criterion. 
The concentric suleations, as well as the zones of color 
and pubescence, on the pilei are to be regarded as expressive 
of differences in the local climatological and atmospheric 
conditions existing at different times during the growth of 
the pilei. 
The pores of the sporophores are evolved successively from 
the center of growth or point of attachment outward, the 
basidia and spores beginning to form while the pilei are still 
young, and continuing their dev elopment throughout the hfe 
of the pilei.. As a result of this successive dev elopment of 
the basidia the spores are shed intermittently over long 
periods. 
The extreme drouth resistance of the fructifications is 
indicated by the following criteria: (a) By the ability of 
the sporophores to resume growth after withstanding long 
periods of dessication; (b) by the ability of the sporophores 
to revive and shed viable spores after being kept in a state 
of dessication for at least a year; and (c) by the ability of 
the spores to germinate and produce infectious mycelium 
after having bea shed and kept in a state of total dessication 
for as long as ten months. 
Darkness is conducive to the most vigorous vegetative 
growth but retards sporophore formation. The dimidiate 
form of the sporophore is not to be ascribed either solely to 
the stimulus afforded by light, nor to that by gravity, but to 
the combined action of both. The formation of pores and 
the production of spores, however, depends entirely on light. 
No chemotropism of the mycelium could be detected; it seems 
