INFLUENCE OF VARIOUS FACTORS ON FLASH YIELD 



1461 



catalyst available for their transformation; it only slows dovm the rate of 

 this transformation. 



The maximum flash yield becomes dependent on temperature when, at 

 the higher temperature, the duration of the flash ceases to be short com- 

 pared with the working period of Eb (Franck, Pringsheim and Lad 1945). 



At 4.7° C, the shape of the curve is not as close to exponential as at 

 20.7°, but indicates a linear beginning. This change is similar to that caused 



UJ 



Z3 



oc 



UJ 

 Q. 



W 



(/) 

 UJ 



X 

 H 

 Z 

 >- 

 W) 



o 



(- 

 o 



X 



a. 



20 40 60 80 



CARBON DIOXIDE CONCENTRATION, m./l. 



Fig. 34.15. Effect of [CO2] on photo- 

 synthesis in continuous and flashing 

 light (24 flashes/sec.) (after Emerson 

 and Arnold 1932). 



10 



12 



2 4 6 8 



DARK TIME, sec. 



Fig. 34.16. Course of dark reaction at 

 two different concentrations of CO2 (after 

 Emerson and Arnold 1932). 



by cyanide poisoning (fig. 34.12), and could therefore be quoted in sup- 

 port of Franck 's hypothesis that, at low temperature, the cyanide sensi- 

 tive carboxylation reaction (catalyzed by Ea) replaces the cyanide-resist- 

 ant finishing reaction (catalyzed by Eb) as the main yield-limiting factor 

 (cf. chapter 31). 



The effect of changes in the concentration of carbon dioxide on photo- 

 synthesis in flashing light offers an interesting problem. As shown by 

 figure 34.15, Emerson and Arnold (1932) found the "carbon dioxide curves" 

 in flashing light to be similar to those in continuous light. However, half 

 saturation occurred in flashing light (ta = 0.04 second) considerably earlier 

 than in continuous light. This is natural, since carbon dioxide saturation 

 must ensue as soon as the carbon dioxide supply reaction — which proceeds 

 at a uniform rate throughout the dark periods — supplies enough material 

 to cover the A • CO2 consumption of saturating flashes, which is consider- 

 ably lower than that of saturating continuous light. Less easy to explain 

 is figiu-e 34.16, which shows the flash yield in relation to the length of 



