138G 



INDUCTION PHENOMENA 



CHAP. 33 



duration of incubation upon the induction losses of oxygen and carbon di- 

 oxide, illustrated by figures 33.6 and 33.9. 



Wassink and Katz (1939) found, similarly, with Chlorella, that the 

 height of B can be maintained, in successive light flashes of 10 seconds dura- 

 tion, if these flashes are separated by dark intervals of at least 2 minutes. 

 The required intervals were much shorter in cells grown in glucose solution 

 and having strong respiration than in cells grown in an organic medium 

 and having w^eak respiration, thus confirming the surmise that the inhibitor 

 is removed by an oxidation process. 



These results of Franck and Wood, and of Wassink and Katz, are in 

 satisfactory agreement with determinations of Warburg, McAlister and 

 others, which gave a value of about 1 minute for the dark interval required 

 to repeat the induction curves of oxygen liberation and carbon dioxide 

 absorption (c/., e. g., fig. 33.9). The observations of Aufdemgarten 

 (figs. 33.10b and 33.11b) indicated a somewhat longer regeneration period of 

 the "precursor" (>4 minutes), while McAlister and Myers noted (c/. 

 fig. 33.26) that, in wheat in normal air, no burst of fluorescence at all oc- 

 curred after 1 minute darkness, and only a faint burst was noticeable after 

 2 minutes. 



(b) Light Intensity 



Like induction losses of O2 and CO2, induction of fluorescence is not ob- 

 served in weak light (fig. 33.27). (There are as yet no observations on 





lij 



o 



2 

 liJ 

 O 

 (/5 



LU 



tr 

 o 



ID 



10- 



10 



20 30 



TIME, sec. 



40 



50 



Fig. 33.27. Fluorescence time curves of 

 Ulva lactuca for different light intensities 

 (after Kautsky and Franck 1943): first 50 

 sec. of illumination; 20° C; ordinary air. 



LIGHT INTENSITY, erg/cm.' sec. 



in 



Fig. 33.28. Fluorescence outburst 

 relation to light intensity in Hydrangea 

 (after Franck, French and Puck 1941). 



whether the CO2 gush, which occurs even in weak fight, is accompanied by 

 variations of fluorescence.) With increasing light intensity, ascending 



