The Biology of Polyporus Pargamenus Fries Dd 
sulcations appearing commonly on pilei are indicative of 
the alternation of decidedly wet and dry periods of growth. 
The faint zoning which always is present on this and similar 
rapidly growing, thin pilei are indicative of mimor changes 
in the humidity of the air — in many cases doubtlessly they 
are due to the check in growth resulting from the fall in 
temperature which takes place during the night. This is 
especially apt to be true where we have a succession of cold 
nights and warm days. 
Pilei frequently are found that are exceedingly thin and 
papery, these being pale-colored with scanty pubescence. On 
the surfaces of these pilei the zones of growth and bands of 
color show up very strikingly. In some instances the whole 
surfaces ate shining and have a silky appearance. In, gen- 
eral, however, the pilei are much thicker and darker 
colored; also villous or velvety. Such pilei usually assume 
a dark-gray or grayish-brown coloration with age and the 
zones of growth and bands of color are very inconspicuous 
after the pilei have weathered for a time. Not infrequently 
one finds both combinations within the same pileus. In this 
ease the grayish, weathered part represents the original 
growth while recent growth is shown by the lighter colored 
area that has grown out from the old, d: rk-colored: one, 
possibly some months after the cessation of growth by the 
older part. 
The biological significance of the velvety hairs which 
occur on the upper surfaces of the pilei of many species of 
fungi is a matter of doubt. According to Buller (1909, 
p- 113) they form a capillary system for the purpose of 
rapidly disseminating any drops of water which may fall 
on the pileus. This explanation, while unsubstantiated, 
least seems plausible for a drop of water let fall on the dry 
pileus is absorbed almost instantly by conspicuously hirsute 
pulei such as Polyporus abietinus Fr. and Polyporus hirsutus 
Fr. In more glabrous pilei, for example in sparingly pube- 
seent pilei of Polyporus pargamenus, the absorption of 
water dropped on the surface was much slower. In addition 
to this the pubescence may be of the same use as is that of 
