Allen and Jolivette—Light Reactions of Pilobolus. 577 
Three experiments were performed with the culture ten centi¬ 
meters from the openings. In the first experiment (Table 
XII), 21 out of 126 sporanges were intercepted by the second 
glass; in the second, 19 out of 144; and in the third, 11 out of 
99. The average thus intercepted in the three experiments 
is 14%. 
Three similar experiments were performed with the culture 
25 centimeters from the openings. In the first, 40 out 126 
were on the second glass (30%) ; in the second, 31 out of 124 
(40%) ; and in the third, 122 out of 317 (38%). The average 
percentage for the three experiments is 36, or 22% more than 
when the culture was 10 centimeters from the openings. 
The respective beams of light reaching a given sporangio- 
phore from the two openings do not differ greatly in intensity, 
a 
Fig. 16. Diagram of horizontal cross section of box used in table XII. 
whatever the position of the sporangiophore in the culture', yet 
the majority of the sporanges are shot toward the nearer open¬ 
ing, that is, toward the source of the stronger illumination. It 
is evident that very small differences in light intensity are per¬ 
ceived by the sporangiophores. 
Table XII. — Showing to what extent sporanges are thrown to the farther of 
two simultaneously presented lights. 
10 cm. from culture to 
openings. 
25 cm. from culture to 
openings. 
On first 
glass. 
t 
I 
105 
125 
88 . 
86 
93 
195 
On second 
glass 
aimed at 
right 
opening. 
On second 
glass 
aimed at 
left 
opening. 
Total. 
Per cent on 
second 
glass. 
r 
14 
126 
16.7 
10 
9 
144 
13.2 
6 
5 
99 
11.1 
27 
13 
126 
30.1 
18 
13 
124 
40. 
63 
59 
317 
38. 
