341 



C. S. French 



SOME EFFECTS OF MONOCHROMATIC FLASHING LIGHT IN PORPHYRIDIUM 



Further effects of flashing light selected in wavelength to 

 activate preferentially one or the other pigment system were seen, 

 A striking difference between green and red was found in the vari- 

 ation of photosynthetic rate as the speed of the sector was va- 

 ried. This kind of a flashing light experiment, in which both the 

 length of the flash and the dark time vary together, has an advan- 

 tage over the independent variation of either, in that the total 

 amount of light given the cells per minute remains constant. 

 Measured changes in the steady-state rate are far less susceptible 

 to errors from unexpected causes than are calculations of yield 

 per flash from widely differing rates. The interpretation of the 

 results is, however, not as straightforward as for experiments in 

 which only the dark time was changed. Figure 4 shows such an 



60 



20 - 



10 



, Green - 567 m/i 



_L 



_L 



J L 



10 



12 



6 8 



Sector speed, revolutions per second 



14 



16 18 



Fig, 4. The variation of photosynthetic rate of Porphy - 

 ridium with sector speed in two colors of flashing light. 

 Conditions: artificial sea water, 5 per cent CO2 in air, 

 about 23° C, sector opening about 1.2 per cent of circum- 

 ference. 



experiment in which the intensities were adjusted to give the same 

 rate in green and in red at the highest sector speed. With red 

 light the rate was more strongly influenced by the distribution of 

 the light in time than it was with green light. 



At low light intensity the differences between the rates with 

 high and low sector speeds are large. However, at higher inten- 

 sity the differences become smaller as is evident from figure 5, 



