1380 



INDUCTION PHENOMENA 



CHAP. 33 



depressions, the first of them marked A in figures 33.27 and 33.33B.) 

 Sometimes this bulge develops into a maximum and can then l)e con- 

 fused with the second main wave of fluorescence. 



Even while we do not believe, with Kautsky (1943), that each ripple on 

 the induction curve indicates a new photochemical reaction in the main 

 sequence of photosynthesis, the persistent occurrence of these details 

 shows that they are not accidental, but indicative of a complex interplay of 

 activation and deactivation processes. 



5 10 



TIME, sec. 

 Fig. 33.23. Effect of mechanical injury on fluorescence curve of a 

 leaf {Saponaria officinalis) (after Kautsky and Franck 1943): air, 20° C, 

 40 meter candles (about 4 X 10* erg/cm. ^ sec). 



Certain conditions appear to favor the occurrence of induction curves 

 of "type I" (fig. 33.19) or "type 11" (fig. 33.20). Curves of type I, with 

 a peak value, (pm, twice or three times as high as the steady yield, ip, appear 

 to be more common with higher land plants, while induction curves of 

 type II are more often encountered with algae. Thus, figure 33.19a was 

 obtained with wheat, and figure 33.19b with Hydrangea, while figure 33.20 

 was given by Wassink and Katz (1939) for Chlorclla. Kautsky and U. 

 Franck (1943) observed, in the green alga Ulva lactuca, curves with a com- 

 paratively weak first fluorescence wave (even in very strong light, the ratio 

 <Pm/(p was not higher than 1.6), and a second wave more or less comparable 

 in height with the first one (fig. 33.27). 



Kautsky and Hirsch (1934), who studied 22 species, concluded that 

 ferns and higher aquatic plants, as well as algae, show a more rapid decay 

 of the first wave of fluorescence than is commonly observed with land plants. 



The experiments of Franck, Pringsheim and Lad (1947) make it likely 

 that the difference between unicellular algae and leaves is based, at least 

 in part, on the different density of packing of the cells. The induction 

 phenomena in algal suspensions may, for the same reason, depend on the 

 density of the suspension. 



