342 



C. S. French 



Green (567 m^ ) 



Red (680 m^) 



_1 I 1- 



10 20 30 40 50 60 

 Light intensity^ relative units 



Fig, 5. The decrease in photosynthetic rate at low sec- 

 tor speed at different intensities of red and green 

 light. 



A particularly interesting difference in the response to single 

 flashes of 50 ms given at 21.5 sec intervals is illustrated in 

 figure 6. Here we see two different manifestations of the en- 

 hancement effect. The top curve shows green flashes given with 



-Red liglit background— ► 



_Green light bQcl<ground_ 



f^^■''^''^^^^^^^^^__J^^A^^^J 



jj-mJ 



_L 



Green flashes 



Red flashes 



10 

 Time, minutes 



15 



20 



Fig, 6. The rate of oxygen exchange following 50 ms 

 flashes given repetitively with and without complemen- 

 tary background light. 



and without a continuous red background. The spike height, that 

 is, the initial rate of Oo evolution, is increased by the continu- 

 ous red light. The time during which O2 is produced after the 



