FLUORESCENCE-TIME CURVES 



1385 



light, and accelerated by higher temperature. (For confirmations, see 

 sections b and c.) At constant light intensity and temperature, height B 

 must increase with the duration of incubation, until the accumulated 

 amount of "precursor" will l:>e so high that the rate of its photochemical 

 activation ceases to depend on this amount {i. e., probably, until it occurs 

 with a quantum yield of unity). 



UJ 



o 



z 



LJ 

 O 



CO 

 bJ 



o 



13 



1100- 



900- 



700- 



500 



20 



40 60 80 



TIME, sec. 



Fig. 33.25. Height of fluorescence peak (B in fig. 33.19) 

 in relation to dark rest (after Franck and Wood 193G). 



(A) (B) (C) 



Fig. 33.2G. Induction in wheat in normal air and strong light (after 

 McAlister and Myers 1940): (A) 40 min. light, 12 min. dark; (B) 2 min. 



dark; (C) 1-2 min. 

 CO2 uptake. 



dark. Upper curves, fluorescence; lower curves. 



These predictions can be compared with the experimental results of 

 Franck and Wood (1936), who found the height of B to rise Unearly with 

 duration of the dark rest, until the latter reached about 60 seconds (c/. 

 fig. 33.25). After this, the height of B continued to increase for a long 

 time (as shown by experiments with plants that have rested overnight), but 

 so much more slowly as to suggest an entirely different fluorescence-pro- 

 moting i-eaction. This result bears obvious similarity to the effects of the 



