AVAVE LENGTH 



105 



seedlings of Avena to a carbon arc spectrum for a certain 

 time. The seedlings were then placed in the dark and 

 after the proper time it was ascertained which part of the 

 spectrum had induced heliotropic curvatures. By vary- 

 ing the duration of time of exposure to the spectrum it 

 was found that with a minimal time of exposure only 

 certain blue rays, namely, those of a wave length of 478 w> 

 caused heliotropic bending, while with longer exposure 

 longer waves also became efficient. In this way the mini- 

 mum duration of exposure for various parts of the spec- 

 trum was ascertained. Table IX gives his results. 



TABLE IX 



The red and yellow parts of the spectrum were ineffec- 

 tive for the intensity and time limits used and the optimum 

 of efficiency was in the blue, in the region between 466 

 and 478 w. 



A shorter series of experiments was made on the fruit 

 bearers of Phy corny ces, with the following results : 



44 to 47 per cent, of the Phycomyces showed heliotropic 

 curvatures 



after 192 seconds of illumination at 615 ju,i» 

 after 192 seconds of illumination at 550 titi 

 after 16 seconds of illumination at 495 /xti 

 after 32 seconds of illumination at 450 pp 

 after 64 seconds of illumination at 420 ti/i 



