52 College of Forestry 
susceptibility of the sporophores to variation induced by 
various ecological factors.” 
In the absence of any cross inoculation data, it has been 
regarded best for the present to include the poroid forms, 
including both the thick western plant with long tubes on 
species of Populus that has been called Polyporus (Cortolus) 
subchartaceus by Murrill (1907, p. 24) and the thinner 
plant with shorter tubes occurring on the wood of Populus 
and Salix both in the eastern and western United States 
under Polyporus pargamenus. 
The sporophores of Polyporus pargamenus grow through 
only a limited period. When drought or cold weather inter- 
venes, growth is interrupted. However, this and similar 
tough forms of leathery consistency are able to withstand 
severe conditions and continue growth after such interrup-. 
tions so that they are perennial in the sense that they grow 
from year to year. Growth of the sporophore in this and 
similar thin, leathery forms is limited mainly to the mar- 
ginal hy phee and ordinarily the pileus does not increase in 
thickness. The areas representing the increase in the width 
of the pileus during the different periods of growth usually 
are demarked by more or less distinct suleations. Upon a 
plentiful supply of moisture, after periods of long drought, 
the pilei frequently renew growth for a time. The result is 
that one frequently finds specimens that are concentrically 
suleate with a broad, bright-colored margin which is in 
strong contrast to the dark-gray color of the older growth. 
Each portion of growth does net represent annual erowth, 
but does represent periodic growth which took place between 
periods of drought. This and similar species are said to be 
annuals in that they do not form more than one layer of 
pores although exceptions occur occasionally. Growth, how- 
ever, may begin at any month of the year so long as condi- 
tions favorable to growth occur, and continues even during 
the winter months at intervals when the sporophores are not 
frozen. 
%* Such an experiment would take at least two, and probably more, 
years’ work to complete. Jor this reason it has not been attempted in 
the present investigation. 
