578 Wisconsin Academy of Sciences, Arts , and Letters. 
When the culture was 25 centimeters from each opening 
(Table XII), 36% of the sporanges were shot towjard the more 
distant opening, while only 14% were shot toward the more 
distant opening when the culture was 10 'centimeters away. 
This is easily explained. As th© culture is moved further from 
the Openings, being kept equidistant from them, the amount of 
light from the respective openings; reaching any particular 
sporangiophore not in the median line of the culture becomes 
more nearly equal. The ratio approaches 1:1 as a limit as the 
distance increases. When the culture is placed at a consider¬ 
able distance from the openings, then, sporanges from the whole 
surface of the culture contribute to the group at each of the 
openings. 
The Response of Pilobolus to the Simultaneous Stimuli 
of Two Differently Colored LightsJ 
The relative efficiency of lights of different colors in causing 
heliotropic reaction in Pilobolus has already been considered 
in connection with the question of accuracy of aim. It was 
found that the reactions to white and blue lights were the most 
precise; that those to yellow light were much less so; and that 
the reactions to red light were very vague and indefinite. The 
behavior of Pilobolus was next studied when subjected simul¬ 
taneously to lights of two different colors. 
The cultures were placed in a box 38 centimeters long, 17 
centimeters wide and 23 centimeters high. In the middle of 
each end was a circular opening two centimeters in diameter. 
The same blue, ruby, yellow and colorless glass plates were used 
as in the foregoing experiments, and in addition potassium bi¬ 
chromate and copperoxide solutions contained in parallel-walled 
flasks. The plates of colored glass were placed one against each 
opening, precautions being taken to prevent the entrance of 
light around their edges. When solutions were used, the flat 
flasks were placed close against the opening and on the outside 
of the box, black pads encircling the opening ensuring the ex¬ 
clusion of all white light. Against the inside of each end of 
the box was placed a plate of colorless glass to catch the spor- 
