46 College of Forestry 
The poroid form of Polyporus pargamenus apparently is 
confined to species of Populus and Salix. The writer has 
made collections of this poroid form on Populus grandiden- 
fata and P. tremuloides ix Pennsylvania and New York, 
and has examined numerous specimens of this form on 
western species of Populus. Recently a specimen of the 
poroid form on Salix, collected at Madison, Wisconsin, 
came to the writer’s attention. Since he had never 
observed this form of the plant on wood of any other 
genus than Populus he was skeptical of the determination 
since, from the appearance of the accompanying bark and 
wood, it may have been either Populus or Salix. Since 
the wood of these genera can not be distinguished 
macroscopically the writer made radial microtome sec- 
tions to study the structure of the medullary rays which 
afford the chief distinguishing character, the rays of 
Salix being heterogeneous, whereas those of Populus are 
homogeneous. A microscopic examination of the prepared 
sections showed that the marginal cells of the rays were 
upright in contrast to the radially elongated or procumbent 
cells composing the interior of the rays, thus proving the 
wood to be Salia rather than Populus. It is evident, there- 
fore, that the poroid form of Polyporus pargamenus occurs 
on both Populus and Salix, but apparently is confined to 
these two genera of the family Salicacew. The writer wishes 
to have it distinctly understood, however, that, in addition 
to the poroid form apparently confined to wood of the genera 
Populus and Salix, the typical hydnoid form of Polyporus 
pargamenus is also found occasionally on these hosts. 
The poroid forms of Polyporus pargamenus found in the 
eastern and middle western United States depart markedly 
from the typical form of the plant. The upper surface of 
the sporophores of these forms varies from light to dark gray, 
depending on the age of the sporophores. It is zonate but 
lacks the more or less conspicuous multicolored zones which 
commonly occur in most specimens of Polyporus parga- 
menus, and is more rigid and hirtose than the usual form 
of the plant. Like the latter, however, it frequently has 
