40 College of Forestry 
form, which is more abundant even than the first, is generally 
fhanmer and less distinctly tomentose. Indeed, it is sometimes 
nearly or quite smooth, and it often appears to become smoother 
with age. Instead of being concentrically sulcate it is generally 
more or less marked with narrow delicate zones. There are also 
fine radiating lines or striations which are more perceptible in 
the smoother specimens. The color is generally grayish pallid 
or subochraceous. The pores are usually seriately placed, espe- 
cially toward the margin, and though variable in color they are 
commonly tinged with purple when fresh and young, as in the 
preceding form. As in that form also they become paler with 
age. This is the form recently published under the name Poly- 
porus pseudopargamenus, Thum. When the pileus is narrowed 
toward its base so that its length is greater than its breadth it 
is Polyporus elongatus, Berk. It occurs on a great variety of 
deciduous trees, but is most frequent on birch, maple, oak and 
chestnut. The first form is most common on poplar though not 
limited to it. I have not found either growing on pine. “These 
two forms run into each other by such insensible graduations that 
it is not possible to draw any satisfactory line of distinction 
between them, and therefore, the conclusion must be that both 
are forms of one species, Polyporus pergamenus.” 
Relation of Environmental Factors to the Morphologie 
Variation of the Sporophores.— All plants, especially fungi, 
manifest fluctuating variation in all their characters. Such 
variations are largely, if not entirely dependent upon the 
environment. Differences in the kind of food elements sup- 
plied, due to the occurrence of fungi on a great variety of 
hosts in different stages of decay will give rise often to sporo- 
phores of variable appearance. Changes in the amount of 
water available and the length of time that an optimum 
supply remains available are manifested in the resulting 
form of the sporophores. Variations in the degree of humi- 
dity as determined by the growth site or environment, ch- 
matic conditions, temperature, ete., are reflected in the 
variation of size, shape, and other morphological characters 
of the sporophores. Probably the greatest factor of all, how- 
ever, is that of the growth position of the sporophores on 
the substratum. This factor alone is probably responsible 
for greater variation in the appearance of the sporophores 
of fungi than all the others combined. Only when we fully 
realize the importance of environmental factors in influencing 
the morphology of the sporophores can we appreciate the 
value of a broader conception of our species of fungi. 
