INITIAL STEPS IN PHOTOSYNTHESIS 



307 



pension was reduced to obtain more light per unit area of the sus- 

 pension of algae. The photosynthetic rate was measured by observing 

 the change of oxygen content in the closed system by means of an 

 analyzer measuring the paramagnetic property of oxygen. At the 

 same time, the change of CO2 was observed as a reference by an in- 

 frared CO2 analyzer. To saturate the photosynthetic yield, two 1-kw. 

 projection lamps and a 400-watt photospot illuminated the suspen- 

 sion of algae through three sheets of infrared absorbing glass with a 

 water-cooling sj^stem. In front of the cell, which contained 25 ml. of 



-0-0- 



SATURATION TEST WITH 

 FLASHING LIGHT 



10 



15 



20 



'rel 



Fig. 1. Saturation test with flashing Ught. 



algal suspension, a sectored disc was rotated. Six kinds of discs were 

 used; they have 1, 2, 3, 4, 6, and 9 open sectors of the same size in a 

 disc which is 40 cm. in diameter. The size of opening was made so as 

 to obtain equal dark and light periods with a 9-hole disk. Therefore, 

 dark periods relati\'e to the light period in these discs are 17, 8, 5, 

 3.5, 2, and 1 , respectively. If the rotating rate is fixed, the light period 

 (te) is the same for all discs, but the dark periods (to) can be changed by 

 changing the disc. From a set of data with a single rotation rate, one 

 can obtain the change of yield per flash as a function of dark period 

 for a fixed light period. The light period was changed by changing the 



rotation rate. The light periods were 



1 / 



/ 360, 



V180, V90, and V45 second. 



An important requirement in this experiment is that the photo- 



