1914] JOLIVETTE—PILOBOLUS QI 
Study of the reactions of the individual sporangiophore 
to a single. light 
In the earlier experiments (2), and also in those on simultaneous 
light stimulation in this paper, I was concerned with a large 
number of sporangiophores and with the net result of the reaction. 
This set of experiments was inaugurated for the purpose of following 
in detail the stages in the reaction of the individual sporangiophore 
toward light. The horizontal microscope was employed for this 
purpose. 
A culture of Pilobolus in a 5-cm. flower pot was used. The pot 
was supported in an upright position. A thin glass Petri dish, 
measuring 5 cm. in diameter and 4 cm. in height, was placed over 
the top of the flower pot to keep the culture from drying. A 
16-c.-p. carbon filament incandescent light was placed at a dis- 
tance of 30 cm. from the culture, with the central point of the fila- 
ments 5 cm. above the level of the surface of the culture. The 
experiments were performed in the dark room and no other light 
had access to the culture. A horizontal microscope was placed 
with the tube on a level with the surface of the culture and at right 
angles to the direction of the light rays reaching the culture, so that _ 
any bending toward the light could be observed. A micrometer 
scale was placed in the ocular of the microscope in order to measure 
the change of position of the sporangiophore. In favorable cases 
several sporangiophores could be observed in the field of the 
microscope. 
The first culture used in these experiments was put in place 
at 7:15 P.M. The sporangiophore had been exposed to the after- 
noon light and had grown straight out toward it, making an angle 
of 45° with the vertical. The culture was placed with the sporangio- 
phores leaning away from the light, so that the angle between the 
light rays and the sporangiophore was about 135°. At the time 
when the experiment was set up, the young sporangiophores showed 
no signs of the sporangial swelling or vesicular bulb. 
Two sporangiophores were observed during a period of 3 hrs. 
on the evening of May 18, 1910, and sketches were made at inter- 
vals during the reaction. The exact time when the reaction of the 
