REVERSION IN ORIENTATION TO LIGHT 381 



There was considerable difference in the results obtained in 

 the different tests, but taken as a whole they show conclusively 

 that photosynthesis was most rapid in the diffuse white light and 

 less rapid in the other illuminations in the following order: 

 yellow, red, blue, green, darkness. 



These results, consequently, demonstrate that photosynthesis 

 was more rapid in the red and the yellow light used in these 

 experiments than in the blue and the green. And since the blue 

 and the green were more effective in producing reversion in the 

 sense of orientation than the red and the yellow, it is evident 

 that the effect of light on reversion is not determined by photo- 

 synthesis unless the photosynthesis which occurred during the 

 exposure to white light in making the tests in the dark-room is 

 involved. This, however, does not seem probable since all of 

 the aquaria were exposed to the same illuminations. Moreover, 

 essentially the same results were obtained in observations in 

 which the aquaria were exposed to green light produced by nieans 

 of passing the beam of light in the dark-room through a satu- 

 rated solution of chlorophyl in 95 per cent alcohol. Now, since 

 photosynthesis is reduced to a minimum in green light produced 

 in this way and since the reactions of the colonies in the different 

 aquaria were essentially the same as in white light, it is evident 

 that photosynthesis during exposure in the dark-room is of no 

 practical consequence. The conclusions, therefore, that rever- 

 sion in the sense of orientation is not determined by photosynthe- 

 sis appears to be valid. 



The region in the spectrum of maximum stimulating efficiency 

 lies in the green near wave-length 524 mm for Pandorina (Mast, '17, 

 p. 509) and in the blue-green near wave-length 494 mm for Vol vox 

 (Laurens, '18). The results of the experiments described above 

 indicate that the regions of maximum efficiency in producing re- 

 version in the sense of orientation in Pandorina and Volvox prob- 

 ably have the same location as the regions of maximum stimu- 

 lating efficiency. If this is true, it is probable, although by no 

 means certain, that the processes involved in stimulation are 

 also involved in reversion. 



