256 BOTANICAL GAZETTE [APRIL 
for their development. In these cases the development of the pileus 
is retarded or suppressed, so that it is probable that here light acts as 
something more than a tropic stimulus. BULLER (/. c.) has recently 
shown, however, that the lamellae of Lentinus develop first and most 
vigorously on the lower side of the young fruit-body when it arises 
obliquely from the substratum, and that this unilateral development 
is due to the effect of gravity. Here we have a change in form due 
to the effect of gravity. It is probable that the eccentricity of the 
stalks of tree- and stump-inhabiting forms is directly due to such 
action of gravity, for when some of these forms, like Pleurotus ulma- 
rius, develop on the upper side of a fallen trunk they are symmetrical. 
In Polystictus cinnabarinus, as in other shelf-forms, the fruit- 
bodies increase in size by growth at the margin. The hyphae near 
the lower side of the growing margin turn downward and produce 
the hymenophore. The epinastic growth (if this term, originally 
applied only to dorsiventral organs, may be employed) of these 
hyphae is due to their positive geotropism, for on the klinostat they 
grow uniformly in all directions. The organization of the hymeno- 
phore itself is not dependent upon gravity, for when this force is 
equalized all the hyphae form hymenial tissue. The differentiation 
of the fruit-body into an upper sterile and a lower fertile region is also 
due ultimately to the influence of gravity. All the hyphae are poten- 
tially fertile, but the development of a hymenium by the upper 
hyphae is inhibited finally by gravity. How this sterilization is 
brought about is another question. It is probable that the direct 
_ cause is to be sought in the mechanical or chemotropic influences of 
the hyphae upon each other. Since experiments were conducted 
both in light and in dark, it is evident that light is not a factor in this 
case. 
The form of the more highly organized Schizophyllum is influenced 
in a less degree. It is evident that the general organization of the 
fungus is quite independent of the stimulus of gravity. There is one 
interesting phase, however, that needs to be considered. The fruit- 
bodies of this fungus are typically dorsiventral and laterally attached, 
yet on the klinostat they originate as small funnel-shaped bodies 
with the lamellae on the inside of the funnel; and when allowed to 
develop fully, the funnel expands and develops into a lobed disk, 
