1050 



THE LIGHT FACTOR. I. IISTTENSITY 



CHAP. 28 



the reductant the yield is high even at Hght intensities as low as 1 kerg/cm.^ 

 sec. 



Figure 28.27 shows the transition from the low intensity yield, (pi, to 

 the high intensity yield, ipi- The yield in the upper figure becomes prac- 

 tically constant (v? = ^2) when the difference between the angles <p and <p2 

 in the lower figure ceases to be significant. 



ChL 



Chl 



■ 



Ic 



p J 



Fig. 28.27. Fluorescence intensity (F) and yield (<p) as function of 

 incident light intensity (schematic). 



Comparison of figure 28.32 with the light curves of photosynthesis of 

 Chromatium in the presence of thiosulfate (c/. fig. 28. 5B) indicates an ap- 

 proximate antiparallelism of (p and 7. The fluorescence yield, (p, begins to 

 rise at about 10 kerg in 1% thiosulfate (somewhat earlier in 0.05%), while 

 the first signs of saturation (i. e., of a decline of 7) are noticeable a little 

 above 10 kerg in 1% thiosulfate and at about 5 kerg in 0.067% thiosulfate. 



The green plants and algae discussed so far all showed an increase in (p 

 at high light intensities; different behavior was observed by Wassink and 

 Kersten (1945) in a species of diatoms. There, the yield of fluorescence 

 declined, in the presence of carbon dioxide, simultaneously with the satura- 

 tion of photos>Tithesis (i. e., <p2 appeared to be S7naller than c^i); the yield 

 (Pi remained uniformly high if the carbon dioxide supply was low (c/. fig. 



