564 Wisconsin Academy of Sciences, Arts, and Letters. 
that the right-hand opening was closed by a black pad. Figure 
13 shows the result. 
If, when subjected to two simultaneous beams of light, a 
sporangiophore reacts to but one, and if the reaction to that 
stimulus is in no way influenced by the presence of the other, 
then Figure 13 should be comparable in every detail to the 
left half of Figure 12. The absolute number of sporanges in 
a given area would vary of course with the total number dis¬ 
charged in the course of the experiment, but the percentages in 
the corresponding areas should be subs t anti ally equal. 
For convenience in comparing the results of the two experi¬ 
ments, the field is first divided into right and left halves by a 
vertical line midway between the two openings. Each half is 
then subdivided into three areas by vertical lines tangent to the 
right and left edges of the openings. The sporanges in each 
area were counted and the percentage was calculated of the total 
number included in each area. To make Figure 13 directly 
comparable to the left half of Figure 12, the total percentage 
for Figure 13 was made 50 instead of 100. 
Table YIII — Tabulation of results shown in figures 12 and 13. 
Left half of field. 
Right half of field. 
Total 
To left 
of open¬ 
ing 
On open¬ 
ing or 
below 
To right 
of open¬ 
ing 
To left 
of open¬ 
ing 
On open¬ 
ing or 
below 
To right 
of open¬ 
ing 
Sporanges. 
8 
40 
17 
19 
46 
13 
143 
%...,. 
5.6 
28 
11.9 
13.3 
32.1 
9.1 
Sporanges. 
42 
204 
82 
328 
6.4 
31.1 
12.5 
As the table shows, there is a very close correspondence be¬ 
tween the two experiments as to the proportional number of 
sporanges in each area. 
There is, however, one difference between the results of the 
two experiments which the table does not show. When there 
is but one source of light, (Fig. 13), the sporanges which strike 
the target at the lowest level fall, of course, approximately be¬ 
low the opening. When there are two sources of light, the 
