538 Wisconsin Academy of Sciences, Arts, and Letters. 
with openings of different sizes and with the cultures at vary¬ 
ing distances from the source of illumination. We first at¬ 
tempted to determine the influence of the size of the opening 
upon the accuracy of aim. 
The first experiment was made with white light admitted 
through a, circular opening one centimeter in diameter. An ap¬ 
paratus was used similar to that described by IsToll (17). A 
dark' box 121 centimeters long, 27 centimeters wide and 28 
centimeters high was used. The opening for the light was in 
one end. The box was placed with this end facing toward, and 
about 30 centimeters from, a south window. Direct sunlight 
did not strike the cultures. Within the box the well-watered 
culture, five centimeters in diameter, was so placed and sup¬ 
ported that its surface was vertical, squarely facing the Open- 
Fig-. l. Target consisting of four concentric circles. The inner circle is 1 cm. in 
diameter. The circles are 1 cm. apart. 
ing, at a distance of 20 (centimeters, and with the center of the 
culture on a level with the center of the opening. A glass on 
which the sporanges were to be caught was placed inside the 
box directly in front of and against the opening. 
The target used in recording the position and relative distri¬ 
bution of the sporanges consisted of four concentric circles, the 
radius of ea.eh being greater by one centimeter than that of the 
next circle within. The innermost circle (the bulks eye), one 
centimeter in diameter, was of the same size as the opening in 
the box. The areas marked off by the circles were numbered 
consecutively from one to five, beginning with the bulks eye 
(Fig. 1). Area 5 included all outside of area 4. By mteans 
of this target the percentage of the sporanges which landed 
upon the illuminated opening and within definite limits out- 
