1350 



INDUCTION PHENOMENA 



CHAP. 33 



by heat pretreatment. It persisted even after the cells had been heated to 

 47-53° C, reducing steady photosynthesis to zero. In this way, the gulp 

 can be completely separated from normal photosynthesis. It then proves 

 to be independent of the dark period (between 1 minute and 1 hour) and 

 temperature (between 6 and 30° C). The gulp depends on hght intensity; 



time 



Fig. 33.13C. Effect on CO2 induction curve of 3 min. preheating of leaves to 43° C. 

 (after van der Veen 1949'): (I) normal; (II) preheated. Diaferometric record. 



CO2- 

 content 

 of gas 



^^'~V 



"VA 



A 



\ 20001 \ 10 0001 \ 20 000 1 [ 

 a b c 



Fig. 33.13D. CO2 uptake by heat pretreated Sciadopitys needles after 

 successive e.xposures to different illumination (2, 10, 20 klux), and its release 

 in dark (after van der Veen 1949i). Diaferometer record. 



stepwise increase in illumination produces a sequence of gulps, with satura- 

 tion at about 20 klux. The gulp can be produced in filtered red light, show- 

 ing it to be chlorophyll-sensitized. After switching the light off, the carbon 

 dioxide taken up in the gulp (or gulps) is released in a gush in the dark (fig. 

 33.13D). In many of these details (but not, for example, in its independ- 

 ence from the length of the dark period) , the phenomenon reminds one of the 

 ''Emerson-Lewis effect" — with a reverse sign. 



