Allen and Jolivette—Light Reactions of Pilobolus. 567 
two to seven centimeters, there were more sporanges on a strip 
midway between the openings than on either strip 1 containing 
an opening. Even in these cases, however, the position of the 
openings could be located in the group] of sporanges on the 
glass by the presence of two more densely crowded areas. The 
sporanges between the openings were more scattered. Many 
lay far below the level of those on the strips which included the 
openings. The crescent shape of the whole group, which ap¬ 
peared in the preliminary experiment, first became apparent 
when the openings were five or six centimeters apart. The 
broad middle part, of the crescent resulted of course from the 
fact that in that region (as noted in the preliminary experi¬ 
ments) the sporanges were scattered through a greater vertical 
distance than were those in the immediate neighborhood of the 
openings. 
As. the openings were placed seven centimeters and more 
. apart, however, a marked decrease appeared in the proportion 
of sporanges found in the area between the openings. The 
single crescent-shaped group became gradually resolved into 
two. groups separated from each other by a broad region con¬ 
taining relatively few sporanges. From 70 to 80% of the total 
number were found on the strips containing the openings or 
within two centimeters to right or left, and the remainder were 
scattered over the areas between the openings. There were 
fewer in the middle areas, but there was no central vacant space. 
dSTot until the openings were 17 centimeters apart did a cen¬ 
tral space appear comparatively free from sporanges. At this 
stage in the experiments, the included angle between the two 
sets of light rays reaching the culture was 23°' or 24.° A 
noteworthy peculiarity lay in the fact that when the clear cen¬ 
tral space first appeared, it was not, as might be expected, only 
a centimeter or so wide, and thereafter a centimeter wider with 
each increase in the distance between the openings. On the 
contrary, the clear median space, when it first appeared, was 
about ten centimeters wide. When the centers of the openings 
were 15 centimeters apart, the sporanges in the vertical areas 
midway between the openings were, respectively, 
