1052 



THE LIGHT FACTOR. 



INTENSITY 



CHAP. 28 



cence was observed by Wassink, Katz and Dorrestein (1942) in purple 

 bacteria. In the first place, they found no effect of carbon dioxide defi- 

 ciency at all when reductants were absent (fig. 28.29) — a condition that 

 cannot be duplicated in green plants. In the presence of thiosulfate or hy- 

 drogen, the effect of carbon dioxide deprivation was small but noticeable. 

 Figure 28.30A obtained in the presence of thiosulfate could be interpreted 

 as analogous to the findings of Franck and McAlister; here, too, 



o with CO2 

 A without COz 



INCIDENT INTENSITY, erg/cm'' sec. 



Fig. 28.28. Fluorescence and CO2 

 supply in diatoms (after Wassink and 

 Kersten 1945). 



UJ 



o 



z 



UJ 



o 

 to 



UJ 



cr 

 o 



14 



12- 



6- 



^12 3 



INCIDENT INTENSITY, erg/cm^ sec. 



Fig. 28.29. No effect of [CO2] on 

 fluorescence in purple bacteria when 

 reductant is absent (after Wassink 

 et al. 1942). 



the region of transition from the lower yield, (pi, to the higher yield, 

 (P2, appears to be shifted toward lower light intensities by the absence of 

 carbon dioxide. Figure 28. SOB obtained with hydrogen as reductant, on the 

 other hand, shows that the yield is enhanced by the absence of carbon di- 

 oxide only in a limited intensity region below 10 kerg; unexpectedly, the 

 relation is reversed at the higher light intensities, so that at 30 kerg the 

 fluorescence is about one-third stronger in the presence of carbon dioxide 

 than in its absence. 



(6) Reductants 



The influence of the concentration of reductants (thiosulfate, hydrogen, 

 etc.) on the shape of the fluorescence curves of Chromatium is illustrated 

 by figures 28.31-28.33. Comparison with figure 28.30 shows that the 



