THE GONYAULAX CLOCK 



579 



10 



20 30 



40 50 60 70 

 TIME - HOURS 



90 



Fig. 7. Phase shift of the luminescence rhythm by single light perturba- 

 tions. The lower curve is the control left in the dark all the while. Previ- 

 ous to the time shown all cultures were in LD conditions. Zero time was 

 the end of the last light period. The upper two curves show the response 

 of cells kept under identical conditions, with the exception of a 6-hr light 

 exposure (1400 ft-c) given at the times indicated by the bars on the time 

 axis (middle, from IVz to 8Vi hr; upper, from 6 to 12 hr). Temperature, 

 21.2°C. 



shorter exposures of the same intensity. In this system the amount of 

 phase shift increases Hnearly with time up to a maximum, which is ob- 

 tained with a 2V2-hr exposure to bright light (> 1000 ft-c). This 

 response is evidently somewhat complicated by the differences in sensi- 

 tivity with time in the old cycle, as noted above. 



High hght intensities are more effective in shifting the phase than are 



