230 CONTROL MECHANISMS IN CELLULAR PROCESSES 



movement in Phaseolus, has reported that a few compounds— colchi- 

 cine, urethane, and ethyl alcohol— show effects upon the period. 



Before describing the inhibitor studies, some few details will be 

 given concerning the nature of the rhythms we are studying and 

 the techniques used. As shown in Fig. 9-1, we have observed sev- 

 eral different rhythms in Gonyaulax. With cells maintained on an 



FLASHING 



GLOW LUM.AND 



60- 



40 



in 

 o 



2C- 



LUMINESCENCE 1. 



PHOTOSYNTHES«S-N 



36 48 



TIME, HOURS 



Fig. 9-1. The several rhythms and their phase relationships in Gonyaulax. 

 All measurements were made with cells maintained in alternating light and dark 

 periods of 12 hours each, the dark periods being indicated by the black bars 

 on the abscissa. The light intensity during the light period was 960 foot candles, 

 and temperatures varied from a maximum of 26° C during the light periods to a 

 minimum of 23° C during the dark periods. Cell densities were uniform in all 

 aliquots, about 11,000 cells per milliliter. Ordinates: on left, counts per second 

 incorporated, corrected for background and controls; on right, luminescence or 

 divisions in arbitrary units. Abscissa: time in hours. For the measurement of 

 rate of incorporation of C^'Oiv two flasks, each containing 20 ml of cells, were 

 removed and incubated in the light at an intensity of 960 foot candles for 

 15 minutes, in the presence of 12.5 microcuries of C'^. At the same time appro- 

 priate controls were incubated in the dark. Luminescence measurements and 

 measurements of cell division were made with aliquots removed at the times 

 indicated. 



artificial day-night schedule of 12 hours light and 12 hours dark, the 

 maximum in the typical bioluminescence, i.e., flashing induced by 

 stimulation, occurs in the middle of the dark period ( Sweeney and 

 Hastings, 1957). 



There exists also a rhythm in the photosynthetic capacity of the 

 cells, shown by the curve whose maximum falls in the light period. 

 Cells were assayed for their photosynthetic capacity under standard 

 conditions at various times (Hastings and Astrachan, 1959). This 



