Allen and Jolivette—Light Reactions of Pilobolus. 565 
lowest sporanges strike in tliei neighborhood of the vertical 
line midway between the two openings. In Figure 12, the 
sporanges as a whole are arranged roughly in the form of a 
crescent with the convex side below and the points of the cres¬ 
cent upon the openings. This crescent shape has been repeat¬ 
edly noted in other experiments of a similar nature. The 
sporanges which are aimed directly at one or the other of the 
two openings fall very little below. Why the few sporanges 
which drop far below the level of the openings should be the 
ones which aim between the two openings is unexplained. It 
may be that the weaker, inferior individuals are less sensitive 
to light than the rest, and that they perceive in the two lights 
but one general source of illumination, and aim accordingly. 
The majority of the sporanges aim at one source of light 
or the other and aim as accurately at the one chosen as though 
the other did not exist. In general, it appears that under the 
conditions of the experiment, a sporangiophore reacts to one 
only of two simultaneous lights. 
In the next series of experiments, we studied the variations 
in the distribution of the sporanges as the distance between 
the two openings varied. A light-proof wooden box was con¬ 
structed, provision being made in one end for two openings 
which could be shifted so as to be placed at any desired dis¬ 
tance apart but always at the same level. The interior of the 
box was painted black. Daylight was used in these experi¬ 
ments, and the box was placed before a south window with 
the end containing the openings facing south. The position of 
the box was not changed during the series of experiments. 
Within the box, the culture, in a two-inch flower-pot, was sup¬ 
ported on a black stand. The flower-pot lay on its side, with 
the surface of the culture vertical and facing the end of the 
box containing the openings. The center of the culture, was on 
a level with the center of the openings. In the experiments, 
the distance between the openings (measured from the center 
of one opening to the center of the other) wias varied between 
2 and 26 centimeters, but the distance from the culture to each 
