570 PHOTOPERIODISM IN INVERTEBRATES 



FLASHING AND GLOW RHYTHMS 



Gonyaulax cultures have been found to emit light even if they are 

 not stimulated. If a cell suspension is left undisturbed in front of the 

 sensitive photomultiplier tube and the output is recorded on a chart, a 

 record such as that shown in Fig. 3 is obtained. The closely spaced 



Fig. 3, Photograph of a tracing from the automatic graphic chart, re- 

 cording luminescence from undisturbed cultures. Ordinate, light intensity; 

 abscissa, time, each division being equal to 1 hr. The changes in the base- 

 line level represent the course of a steady dim light emission. The vertical 

 traces result from flashes similar to the one illustrated in Fig. 1. Tempera- 

 ture, about 23 °C. 



vertical lines represent flashing, which we think may result from cells 

 bumping into one another or into the side of the tube. It is not due to 

 external stimulation, i.e., vibration of the building, etc. Since the pat- 

 tern shown, covering 18 hr (Fig. 3), is essentially repeated with 

 approximately a 24-hr period, there is an evident rhythm in the flash- 

 ing of undisturbed cell suspensions. It is our opinion that this rhythm 

 of flashing is another manifestation of the rhythm of luminescence as 

 measured by deliberate stimulation (described in the previous section), 

 rather than a distinct and separate clock-controlled process. We have 

 not made extensive studies of this flashing rhythm, but the records ob- 

 tained serve to indicate that the important factors in the rhythm of 

 luminescence include both ( 1 ) a variation in the sensitivity of the cell 

 to stimulation — the frequency of flashing is always much greater dur- 

 ing the night phase than during the day phase; and (2) a variation in 



