The Biology of Polyporus Pargamenus Fries 85 
Relation to Gravity.— Under natural conditions the pileus 
is invariably horizontal while the hymenial tubes are vertical. 
It can be proved by simple experiment or by observations of 
instances of natural occurrence in the woods, that the pileus 
is diageotropic and that the tubes are positively geotropic. 
Trunks of trees that are covered with young pilei of 
Polyporus pargamenus, and then subsequently break off, are 
commonly met with in the woods. Quite frequently the 
trunks fall so that the margins of the pilei project vertically 
upward or at least come to le in a more or less perpendicular 
direction. Under these conditions all new growth from the 
margins of the pilei develops in such a manner that the upper 
surfaces of the subsequently formed portions of the pilei are 
brought into a horizontal plane. When this has taken place 
the pilei become diageotropie and now expand rapidly in a 
direction parallel to the earth’s surface. At the same time 
hymenial tubes develop from the lower surface of the newly 
formed portions of the pilei. They are positively geotropic 
and grow vertically downward. The original pilei, now in 
a vertical position, soon cease to grow and all new growth is 
concentrated in the new, horizontally forming portion of the 
pilei. It thus becomes evident that the stimulus of gravity 
strongly favors the growth of the horizontally placed por- 
tions of the pileus. In all cases the hymenial tubes develop 
and grow vertically downward, thus reacting in a positively 
geotropic manner. It has been noticed repeatedly in a num- 
ber of different species of polypores that newly formed sporo- 
phores, whose positions have become reversed through the 
overturn of the wood upon which they were growing, always 
would tend to restore themselves to their original and normal 
position in their subsequent growth. Spaulding (1911, 
p- 17) gives an account of an instance of this in the case of 
Lenzites saemaria (Wulf:) Fries. <A railroad tie, with a 
newly formed sporophore upon it, had been turned with its 
former surface underneath, so that the gills were on the 
upper instead of the under surface of the sporophore. When 
found the gills had just begun to produce a new growth of 
mycelium. On the sixth day new gills began to form on the 
