536 Wisconsin Academy of Sciences, Arts, and Letters. 
in the region of optimum illumination the vertical position of 
the sporangiophore is clue to geotropism. 
Graenitz (10) repeated Brefeld’s experiments on Pilobolus 
and Coprinus and corroborated his results. 
Steyer (2d), like Oltmanns, found that Phycornyces is nega¬ 
tively or positively heliotropic according to the intensity of the 
light used, and that plants grown in the light are less sensitive 
than those grown in the dark. He determined the region of 
the sporangiophore which was sensitive to light by allowing a 
horizontal slit of light to strike the sporangiophore at different 
places. He found that the zone of growth (the portion of the 
sporangiophore just beneath the sporange) alone is the sensi¬ 
tive region, and that the rapidity of the reaction is dependent 
on the rate of growth. Steyer showed further that during arti¬ 
ficial inhibition of growth by ether, the sporangiophore is in a 
position to perceive a light stimulus. He exposed the fungus 
to light while it was under the influence of ether. Ho visible 
reaction took place. The culture was then placed in the dark 
and the effects of the ether were allowed to disappear. The 
plant then reacted to the light stimulus which it received when 
under the influence of ether. 
The more recent literature dealing with the physiological 
efficiency of various colors, the effects of simultaneous stimula¬ 
tion, and related topics will be taken up below in the discussion 
of our own results. 
Methods 
In our experiments we used cultures of Pilobolus grown in 
two-inch flower pots. The experiments were made in light- 
proof boxes painted black inside and provided with one or 
more openings for admitting light. A movable pane of glass, cut 
to fit the inside dimensions of the box, was placed either against 
the end containing the opening or parallel to it and nearer the 
culture. Sporanges discharged from the culture toward the 
source of light were intercepted at any desired distance by the 
.glass plate and remained attached to it. The sporanges could 
easily be seen with the naked eye. From cultures of the size 
