596 Wisconsin Academy of Sciences, Arts, and Letters. 
A comparison of the reactions of 'Pilobolus toward each of 
two colored lights nsed simultaneously gives results in har¬ 
mony with those obtained when similar lights were used separ¬ 
ately. The reaction is most accurate toward the blue light 
when the latter is used in combination with the white, the 
yellow or the red. A larger percentage of the sporanges strike 
the glass at the opening in the blue light. The reaction 
toward the white light is a little less accurate than that toward 
the blue, as is shown when the white light is used simultan¬ 
eously with the blue, red and yellow. A comparison of the 
average percentages reaching the respective openings in the 
whole series of experiments (Table XV) shows plainly that a 
larger percentage strikes the opening in the blue than in the 
white light. The average percentage striking the opening in 
the blue light was 57.9; that in the white light 47.3. The 
reaction toward the yellow light is much less accurate than that 
toward either the blue or white, while the reaction toward the 
red light is the least accurate of all. 
We have found that when the culture is exposed to blue and 
white lights simultaneously, the ratio of the total number of 
sporanges bred toward the respective lights is 4 to 7 in favor 
of the white light, although, as our previous experiments, just 
cited, had shown, the sporangiophores are aimed, if anything, 
rather more accurately toward a single blue light than toward 
a single white light. The results with the simultaneous blue 
and white lights seem to show that the relative intensity of the 
light is a prime factor in determining the reaction. The in¬ 
tensity of the white light used is greater than that of the blue, 
since the blue glass cuts out a large portion of the spectrum, 
thereby diminishing the intensity of the light. It must be 
left to further investigations to determine whether the number 
of sporanges bred respectively toward the simultaneously act¬ 
ing blue and white lights is proportional to the relative inten¬ 
sities of the two lights. 
The ratio of the total numbers of sporanges bred respectively 
toward simultaneous blue and yellow lights was 9 to 1 in favor 
of the blue. These results are in harmony with those ob- 
