HISTORY OF PILOBOLUS 



39 



phores showed curvatures. The mean wave-lengths to which the 

 cultures were exposed were as follows : 708 and 667 (red) ; 631 and 



750 



700 



650 



600 



550 



500 



450 



BO 



55 



60 



65 



70 



75 



Fig. 14. — Graph showing presentation times in relation to frequency 

 (not wave-length) of light waves in heliotropic experiments on 

 Pilobolus. The time required to cause one-half of the spor- 

 angiophores in a culture to bend toward the light is seen to decrease 

 as the light employed changes from red (long waves with Zow fre- 

 quency) through orange, yellow, green, blue, and indigo to violet 

 (short waves with high frequency). The graph also shows that 

 Pilobolus responds heliotropically to the light of all the regions 

 of the visible spectrum. Reproduced from Rosalie Parr's The 

 Response of Pilobolus to Light (Annals of Botany, Vol. XXXIT, 

 1918). 



