1907] HASSELBRING—FORM-STIMULUS IN FUNGI 257 
stalked at the back and bearing the gills on the upper surface (jigs. 1 
and 2). It will be seen that the gills are not, as in all other Agari- 
caceae, on that surface of the pileus which is continuous with the 
stipe, 7. ¢., the lower surface, but on the opposite side, which corre- 
sponds to the dorsal surface of other mushrooms. In this respect 
Schizophyllum stands alone, at 
present, among the Agaricaceae. 
The growth of the fungus on the 
klinostat enables us to interpret 
the structure of the normal dorsi- 
ventral fruit-body. 
The youngest primordia arise 
in the form of minute cups. If 
these are allowed to develop on 
the klinostat, the tendency of the 
pileus to develop equally on all 
portions shows itself. If, how- 
ever, the fungus grows out more 
or less horizontally from the sub- 
stratum, as it normally grows, 
the lower half of the pileus ceases 
to develop, while the upper half 
grows into a fan-shaped fruit- 
body. The pileus may be re- 
garded as a funnel with the gills 
on the inside, having its lower 
half cut away and the upper half 
flattened out so as to expose the 
gills in their normal position Schizophyllum commune. Fic. 1.— 
toward the earth. The inhibition Stalked symmetrical fruit-body grown on 
of growth of the lower half is ai ae ae nit 
ultimately due to gravity, since de of branch lying on the ground, show- 
on the klinostat all portions de- ing symmetrical structure. X I. 
velop equally. The same effect 
is produced when the fruit-bodies grow on the lower side of sticks, 
as they often do in nature. Such specimens expand symmetrically 
on the margin, producing a rotate fruit-body attached at the back 
