196 Parr .— The Response of Pilobolus to Light . 
increase from red to violet. At no time was there found in this series 
of experiments any intermediate minimum such as Wiesner obtained in 
yellow (1879) and Dandeno in green (1903), nor a maximum, as reported 
by Guillemin (1857) in the violet and in the red, by Dandeno in yellow, and 
by Blaauw (1909) in indigo. 
50 55 60 6^ 70 75 
Fig. 4. Graphs (from data in Tables II, VI, and VII) showing presentation times on Pilobolus 
in relation to frequency of light waves. Abscissae represent the presentation times in minutes, and 
ordinates the frequency of the light waves. 
The slope of the graphs from the violet towards the red shows that the 
response of the organism has a very marked relation to wave-frequency. 
Calculation of this relation shows that the product of the square root of the 
frequencies and the presentation time is so nearly uniform as to warrant 
attention later (cf. Nernst, 1899; Verworn, 1913). The results of this 
calculation are given in Table VIII. 
