r9r4] JOLIVETTE—PILOBOLUS 99 
4. Sporangium-formation may start during a reaction; in such 
cases the reaction is delayed for some time. 
5. Incase the reaction toward light isinterrupted by sporangium- 
formation, it is resumed again a little before or about the time when 
the vesicular bulb is beginning to form. 
6. After the sporangium is formed, the growing and curving 
portion is located immediately beneath the vesicular bulb. 
The reaction of Pilobolus when exposed simultaneously to two 
equal sources of light 
The effect of exposing a culture of Pilobolus simultaneously to 
two equal sources of white light was studied. For this purpose 
a light-proof box, measuring 120 cm. long by 60 cm. wide by 60 cm.. 
high, was used. The box was made of pine and was painted a dull 
black on the inside. Running horizontally across one end, 20 cm. 
from the bottom, was an opening 10 cm. wide. Into the opening, 
which was prepared with rabbeted edges, was introduced a gal- 
vanized iron strip containing two openings 1 cm. in diameter and 
g cm. apart. The culture was placed at a distance of 25 cm. 
from the central point between the openings and on a level 
with them. It was placed with its surface vertical and facing 
the side of the box containing the openings. 
The object of the experiment demanded that the light from the 
two openings be equal, but I know no methods of obtaining abso- 
lutely equal light intensities. We can only know that they are 
approximately equal. In order to obtain as nearly as possible 
equal illumination at the two openings, one light of measured 
intensity was placed equidistant from the two openings of the 
box and 40 cm. in front of it. Two mirrors were so adjusted that 
the culture intercepted the single spot of light formed by the con- 
vergence of the two sets of light rays. The light from either mirror 
was excluded from the opposite opening by means of the following 
device. At right angles to the edge of the box, along a line equi- 
distant from the two openings, was placed an upright piece of board 
measuring 60 cm. high by 30 cm. wide by 1 cm. thick. At right 
angles to the first piece and parallel to the end of the box was nailed 
a second piece measuring 60 cm. high by to cm. wide by 5 mm. thick. 
