88 College of Forestry 
dimidiate sporophore form. Only small, white waxy bosses 
appeared and these spread irregularly in all directions, some- 
times uniting with one another; later they formed an inerus- 
tation over the surface of the branch. The white waxy bosses 
soon turned cream color and showed signs of pore formation 
on the exposed surface, while the surface next to the bark 
assumed the velvety zoned appearance so characteristic of the 
upper surface of a normal pileus. A piece of the pore- 
forming part, laid on a glass slide for an hour, yielded a good 
supply of spores. On the control a well-developed series of 
imbricate sporophores appeared. 
From these experiments it seems quite evident that the 
dimidiate form of the sporophore is not to be aseribed, either 
solely to the stimulus of light nor yet to that of gravity, but 
to the combined action of both. It is very evident, however, 
that the formation of pores, and thus spore production, is a 
response to the one tropism only — that of light. We see 
that light hkewise acts upon the sporophore as a morphogenic 
stimulus, and much more strongly than the tropism induced 
by gravity. 
Relation to Chemotropism.— Studies were made upon 
germinating spores and pure cultures of Polyporus parga- 
menus in order to determine whether the mycelium would 
respond to chemotropic stimuli. Spores were germinated in 
hanging drops of nutrient medium in which thin sections of 
yellow birch wood had been placed. The germ tubes, how- 
ever, continued to grow according to their own inclinations 
and the direction of growth did not seem to be influenced 
by the presence of a section of wood in the hanging drop. 
Bayliss (1908) observed the same behavior for Polyporus 
(Polystictus) versicolor. 
‘Transfers were made from pure cultures of Polyporus 
pargamenus to plates containing a rich malt agar, on top of 
which (in the center of each plate) a small, sterile block 
(4"x14”x1”) of yellow birch wood had been placed. 
The inoculations were made on the agar beside the blocks 
of wood, the whole experiment being performed under sterile 
conditions. In a few days the mycelium completely envel- 
