FLUORESCENCE-TIME CURVES 



1403 



constant afterward. These results, even more than those of Kautsky and Eberlem 

 indicate a real effect of the momentarij oxygen concentration on the fluorescence curves of 

 Chlorella (whereas such effect seems to be almost nonexistent in the leaves of the higher 

 plants studied by Kautsky, McAlister and Myers). 



The observations of McAlister and Myers (1940) on the more pro- 

 nounced effect of carbon dioxide deficiency in nitrogen (compared with 

 air) were mentioned, and their explanation was given, on page 1393. 







10 



in No 



Chlorella 



_i 1_ 



J I 1 L- 



in N, 



Scenedesmus 



TIME, sec. 



I 2 



TIME, min. 



3 



(B) 



Fig 33 47. Anaerobic fluorescence induction curves of Chlorella and Scenedesrrms 

 at 25° C." (after Shiau and Franck 1947): 3.0 X 10^ erg/cm.^ sec. (A) First 3 sec; 

 (B) first 3 mins. Intensity units differ for the two algae. 



Shiau and Franck (1947) made extensive comparisons of fluorescence- 

 time curves of Scenedesmus and Chlorella in air and in very pure nitrogen. 

 The results obtained with the two species were similar. Figure 33.47 shows 

 the development of fluorescence during the first 3 minutes. In general, 

 the picture is similar to that in Wassink and Katz's figure (Fig. 33.46, 

 curves for nitrogen and air). About 15 minutes of darkness were needed 

 to repeat the anaerobic induction curve starting at the same high value. 

 These observers, too, found that, if oxygen from photosynthesis is permit- 

 led to accumulate, the difference between the two curves vanishes m 



