—EEO 
1906] FULTON—CHEMOTROPISM OF FUNGI - 103 
in the water was in all directions, directly downward, as well as 
radially in a horizontal plane. The value of the control cultures, 
which were duplicates in all respects excepting that the dishes were 
only partly filled with water, was vitiated by the accumulation of 
condensed moisture in comparatively large drops about the openings 
in the plates. This caused an unmistakable turning toward the 
holes, which was not so decided, however, as in the test cultures. 
It is evident from these results that all of the fungi tested in this 
regard are, under the conditions of experiment, positively hydro- 
tropic; but Mucor stolonifer may under certain conditions show a 
negative hydrotropism. This response to a hydrotropic stimulus 
probably accounts in large measure for the constant turning toward 
protected layers from those more exposed, which latter may have 
become drier through evaporation. 
A sharp distinction between bedwieeneis and Pacareries on 
the one hand, or between hydrotropism and osmotropism on the ’ 
other, cannot in all cases be made, although these phenomena in 
typical cases are quite distinct. The phenomena here reported are 
probably due primarily to differences in the moisture content of 
the layers, and not to water currents, either molar or molecular. 
For this reason the term hydrotropism has been applied, which is not 
in agreement, however, with the current view (PFEFFER, 27, p. 592), 
that in the case of the fungous mycelia heretofore studied, osmo- 
tropism and rheotropism, but not hydrotropism, have been estab- 
lished. It is further recognized that chemical rather than other 
properties of water furnish the effective stimulus, in which event 
hydrotropism would properly be regarded as a special kind of chemo- 
tropism. : 
Aerotropism.—Under the conditions prevailing in some of the 
experiments above described, there was doubtless an inadequate 
supply of oxygen, as when a medium poor in oxygen was enclosed 
between impervious plates. There was then a very decided tendency 
for the hyphae to turn toward the edges of the plates. The obser- 
vation of this phenomenon from time to time suggested that the 
fungi might show an aerotropic sensibility, either as a positive 
reaction to oxygen, or as a negative reaction to carbon dioxid. 
In order definitely to test the matter, experiments were arranged 
