Allen and Jolivette—Light Reactions of Pilobolus. 535 
cient in causing heliotropic curvatures than are the less refran¬ 
gible. 
USToll (18) used in studying the light reactions of Pilobolus 
a box with an opening at one end through which daylight could 
enter. Inside the box, be placed a culture with the surface 
sloping toward the opening. According to Noll, the grouping 
of the sporanges about the opening after their discharge showed 
that they were directed toward the center of the opening. His 
schematic figure of the sporangiophores just before being dis¬ 
charged shows that those on the part of the culture furthest 
from the opening were pointed far above the opening. He,, 
however, says nothing about this in his description. No state¬ 
ment is made to show whether or not he believes that the spor¬ 
angiophores have aimed high in order that the sporanges may 
not fall below' the opening. Noll believes that the final position 
of the sporangiophore is not a resultant of a heliotropic and of 
a geotropic reaction, but that it is due to light alone. 
Oltmanns (16) describes experiments with PJiycornyces to 
determine whether there is an optimum light intensity for its 
reactions. For these experiments he used a box one meter in 
length and twenty-five centimeters in breadth and height. He 
placed an arc light before the opening at one end of the box, 
and intercepted the heat rays by placing a fiask of running 
water between the light and the box. The cultures were placed 
at ten centimeter intervals along the median line of the box. 
A negative reaction was shown by those at from twenty to 
thirty centimeters distance, and a positive reaction by those at 
from seventy-five to eighty centimeters distance. Those between 
these extremes were straight. This intermediate region, ac¬ 
cording to Oltmanns, is the region of optimum light intensity. 
Somewhat later, the region in which the sporangiophores did 
not bend was between sixty and seventy centimeters. Still 
later it receded to from fifty to sixty centimeters from the light. 
Oltmanns concludes that the more accustomed the sporangio¬ 
phores become to the light the higher is the optimum light in¬ 
tensity ; that is, the nearer to the light will be the region where 
the sporangiophores remain straight. He also' concludes that 
