F. T. HAXO AND BEATRICE M. SWEENEY 419 



with time of irradiation ( Fig. 2 ) . When exposed to fluorescent hght of 

 700 ft-c intensity, maximum inhibition of luminescence was obtained 

 in 90 minutes, the final level of light emission being about equal to 

 that of cultures maintained continuously in the light. Preliminary 

 experiments with broad band pass filters intercepting the fluorescent 

 hght indicate that the blue-violet end of the spectrum is the most 

 effecti\e in suppressing luminescence. There is a suggestion of a small 

 effect of red hght, and a more detailed determination of the effective- 

 ness spectrum is planned. 



The inhibition of luminescence by light in Gomjaulax suggests a 

 photooxidation of one of the components of the luminescent system, 

 as in luminous bacteria and Cypridina extracts. The observation that 

 the maximum light emission of dark-adapted cultures increases with 

 the duration of the previous photosynthetic period implies that light 

 exerts a second effect on luminescence, probably through the building 

 up of photosynthetic products or interaiediates necessary for the 

 maintenance of the luminescent system. The decline in luminescence 

 capacity in the dark observed during the period 8-18 hours (Fig. 1) 

 may be interpreted as a progressive depletion of these substances. It 

 has been suggested that, as starvation proceeds, degenerative proc- 

 esses within the cell result in the release of additional reserves and 

 lead to the second peak observed in darkened cells. The final decline 

 in luminescence after 30 hours is associated with loss in cell viability 

 and death. This undoubtedly results from starvation, since Gomjaulax 

 is nutritionally dependent on photosynthesis. 



The above findings recall earlier reports (cf. Harvey, 1952) based 

 on visual observations that natural populations of dinoflagellates 

 show fluctuations in luminescence when brought into the laboratory. 

 In unialgal cultures of Gonyaulax polyedra maintained in the labora- 

 tory, luminescence is partially suppressed by exposure to bright light. 

 The ability to luminesce on stimulation is enhanced in darkened 

 cultures, and subsequently falls and rises before the cells die of 

 starvation. 



