104 BOTANICAL GAZETTE [FEBRUARY 
in which the growth toward holes in mica plates could be observed 
when the plates separated normal non-nutrient gelatin from non- 
nutrient gelatin saturated with carbon dioxid on the one hand, and 
from normal non-nutrient gelatin on the other. The fungi used 
were Penicillium glaucum, Sterigmatocystis nigra, Mucor mucedo, 
Botrytis vulgaris, Monilia fructigena, Monilia sitophila, and Phy- 
comyces nitens. In no case was the percentage of turning toward 
the carbon dioxid gelatin greatly different from that toward the 
_control gelatin. 
As a further test, a layer of gelatin containing spores was placed 
below a perforated mica cover for a Van Tieghem cell, and a per- 
forated mica plate, small enough to fit inside the cell, was placed 
below the gelatin. A layer of normal gelatin was spread below this 
last plate, and a layer of carbon dioxid gelatin above the cover. 
This preparation was sealed to the cell rim, and the whole placed 
* under a bell jar practically filled with carbon dioxid and kept at 
a room temperature of 21-24° C. Efforts were made to have the 
moisture conditions equal within and without the cells; and the 
exposed gelatin layers, which served very well as indicators, showed 
no difference in this respect until after the observations on the majority 
of the preparations had been made, although there was drying of 
the outer gelatin layer by the time the more slowly growing fungi 
had reached the proper stage. The same fungi were used in this 
experiment as in the preceding one, with the addition of Mucor 
stolonifer. In most instances the turning toward the gelatin con- 
taining carbon dioxid and exposed to an atmosphere of carbon 
dioxid, was as great as toward normal gelatin; the growth, however, 
was less vigorous in the former case. In those preparations in 
which there was less turning toward the carbon dioxid gelatin, this 
gelatin had become evidently rather dry. 
It is to be concluded, therefore, that the observed turning toward 
the edges of preparations is not due primarily to aerotropic sensi- 
bility. The experiments also negative the supposition that the 
observed repellent influence of growing hyphae may be due to the | 
consumption of oxygen or to the production of carbon dioxid by 
the fungus, or to both. 
oO Z rah Al ck 
& 
tt RE Fe Te he 
g the fact that osmotropism is 
