1056 



THE LIGHT FACTOR. I. INTENSITY 



CHAP. 28 



110 



100 



90 



80 



.t: 70 



o 



LU 

 O 



O 



in 

 'J 

 <r 

 o 



3 



60 



50 



40 



30 



20- 



- 8 



oK 



O 30° C 



A 12° C 



• 28° C 



A 14° C 



* 116x10^ 



INTENSITY, erg/cm^ sec. 



Fig. 28.36. Fluorescence of chlorophyll in suspensions of 

 Chlorella at different temperatures (after Wassink, Ver- 

 meulen, Reman and Katz 1938). 



servation in chapter 33, in dealing with "induction" phenomena; here we 

 note that, even after the burst was over, the steady yield of fluorescence 

 remained greater at 0° C. than at room temperature (fig. 28.37c, levels A 

 andE). 



This temperature effect could be observed only in a certain medium 

 range of intensities (e. g., at 5 and 27 kerg/cm.^ sec, cf. figs. 28.37b and 

 c); but not in high light (e. g., 220 kerg/cm.^ sec, cf. fig. 28.37a); or low 

 light (e. g., 1.8 kerg/cm.^ sec, cf. fig. 28.37c). In other words, a decline 

 in temperature appeared to have no effect on the steady fluorescence levels, 

 (Pi and (p2 {cf. fig. 28.27), but caused the transition from (pi to ^2 to occur at 

 lower light intensities (fig. 28.38). (Figs. 28.37 to 28.45 are on pages 

 1058-1061.) 



The effect of temperature on the light curves of fluorescence was also 

 observed by Wassink and Kersten (1945) with diatoms. Figure 28.39 

 shows that the peculiarity noted in the fluorescence curves of the same 



