1464 PHOTOSYNTHESIS IN INTERMITTENT LIGHT CHAP. 34 



once in each flash). The relation is reversed at 0° where the Emerson- 

 Arnold period is considerably longer than the duration of the flash. The 

 experiments in which Eb is to be measured by the maximum flash yield 

 with the help of flash bulbs must therefore be performed at low temperature. 



At 0° C, the maximum anaerobic flash yield of a suspension of Scenedes- 

 mus was found to be 2.3 X 10~^ ml. in a carrier gas (nitrogen) without ex- 

 tra carbon dioxide (beyond that produced by respiration and fermentation 

 of the algae), and 3 X 10~* ml. in the presence of added carbon dioxide. 

 The difference is so small as to suggest that (as expected in Franck's theory) 

 the concentration of carbon dioxide has no effect on the maximum flash 

 yield. (More precise confirmation obviously remains desirable.) 



At room temperature, the flash yield as determined by this method was 

 not only somewhat higher than at 0° C. (this was mentioned before), 

 but also was much more dependent on the carbon dioxide supply. Both 

 observations are explicable by reference to the fact that the duration of the 

 flash at 20° is longer than the working period of the yield-limiting catalyst. 



Emerson and Arnold (1932) found that the maximum flash yield is af- 

 fected by chlorophyll deficiency (fig. 34.18). This dependence is another 

 aspect of the problem discussed in chapter 32, section 2, in connection with 

 the similar effect of fChl] on P"^^^- in continuous light. We concluded 

 there — from the fact that the parallelism of [Chi] and p™"""- was absent in 

 many plants, and not ahvays present even in Chlorella— that no direct 

 relation exists between these two magnitudes, but that a depression of 

 P'"*"' occurs when the decrease of [Chi] is brought about by treatment 

 (such as iron starvation) that also reduces the concentration of other 

 catalytic components of the photosynthetic apparatus, such as the usually 

 rate-limiting catalj^st, Eb- The same hypothesis could explain the paral- 

 lelism between [Chi] and the maximum flash yield, p™*^-. 



The effect of narcotics on p""^""-^ also noted by Emerson and Arnold 

 (1932), and illustrated by figure 34.19, could be similar to that of carbon 

 dioxide deficiency. By enveloping the sensitizer molecules, narcotics 

 could cause a dissipation of the energy of a considerable proportion of the 

 absorbed light quanta. In this case, a higher flash energy would be re- 

 quired to produce flash saturation in the presence of narcotics, but the 

 saturation level would be the same as in the nonpoisoned state. This is 

 not clearly confirmed by figure 34.19. Explanation could be the same 

 as suggested in the case of [CO2] — failure to reach true saturation in the 

 inhibited state; but it is also possible that narcotics inhibit not only the 

 sensitizer, but also the limiting catalyst, Eb (since their influence is not as 

 specific as that of the "catalyst poisons"). In this case, the flash saturation 

 yield will be affected qualitatively in the same way as the yield of non- 

 saturating flashes. We recall that in chapter 12, part B, we made the same 



