534 Wisconsin Academy of Sciences, Arts, and Letters. 
its sporanges when it is presented simultaneously with two 
sources of light of equal intensity? (41 What is the relative 
efficiency of light of elide rent colors presented successively or 
simultaneously in determining the direction in which the 
sporanges will he fired ? 
As early as 1874, Tode (22) discovered that Pilobolus dis¬ 
charged its sporanges with considerable violence toward a 
source of light. 
The reactions of fungi to light of different colors were stu¬ 
died by Sorokin (20). Cultures were grown on dung under 
double-walled bell jars in white, blue, and yellow light, and in 
the dark. He found that Mucor and Pilobolus show positive 
heliotropism in white light, and negative heliotropism in yellow 
light. The spores of Pilobolus are seldom scattered in the yel¬ 
low light. In Pilobolus, positive heliotropism is manifested 
through the firing of the sporange toward the light in question. 
In the dark, the hyphae of both genera grow upright and be¬ 
come much elongated. 
.Fischer von Waldheim (0) studied the light reactions of 
Pilobolus by the same methods and arrived at different results. 
In cultures kept in the dark, the sporangiophores stood out at 
right angles to the surface of the substratum, no matter whether 
the surface was horizontal or vertical. The organism behaved 
the same in yellow light, no negative reaction being observed. 
Brefeld (41, using the same methods, finds that sporangio¬ 
phores of Pilobolus microsporus are strongly positively helio¬ 
tropic in yellow light, although the sporanges never mature. 
By turning around every few hours a culture illuminated from 
one side, the sporangiophore bends successively back and forth 
and becomes zigzag in form. He concludes from this that the 
zone of growth is at or near the apex. 1 
Regel (19) also studied the bending reactions of Pilobolus 
cTystallinus as Well as those of Mucor mucedo. According to 
him, these molds are positively heliotropic in white, blue, yel¬ 
low, and red light. This is true for all light intensities and 
temperatures tried. The more refrangible rays are more effi- 
