GAS EXCHANGE DURING THE LONG INDUCTION PERIOD 



1361 



posed above as explanation of induction losses following transition from 

 saturating (but not excessive) to limiting light. 



The time required for reactivation is about the same, whether a certain 

 degree of deactivation had been reached by brief exposure to excessively 

 bright light, or moderate exposure to moderately strong light; it becomes, 

 however, much longer if deactivation by bright light had been pushed so 

 far as to prorluco almost complete suppression of photosynthesis. 



5. Gas Exchange during the Long Induction Period 



When Osterhout and Haas (1918) first described the induction of photo- 

 synthesis, they left the plant {Ulva lactuca) in the dark overnight and ob- 

 served, in the morning, a gradual increase in the rate of carbon dioxide 

 consumption, which lasted for about 1.5 hours. 



6 8 10 12 14 16 18 20 



TIME.hr 



Fig. 3.3.14. Long induction 

 in Fontinalis after 14 hours 

 darkness for four plant speci- 

 mens (after Harder 1930). 



8 10 



14 16 



TIME.hr. 



20 



22 



Fig. 33.15. Induction curves of sun-adapted 

 and shade-adapted Fontinalis plants (18° C.) (after 

 Harder 1933). Adaptation to sun: several months 

 in an aquarium with southern exposure. Adapta- 

 tion to shade: 6 days in shaded aquarium. 



Comparison with the results of Warburg, van der Paauw, McAlister 

 and Aufdemgarten shows that what Osterhout and Haas observed must 

 have been the long, rather than the short, induction; more precisely, it 

 was a superposition of the two phenomena. Many of the subsequent in- 

 duction studies also were made under conditions that must have led to the 

 superposition of the two induction effects, often with the long induction 



