CARBON DIOXIDE EXCHANGE DURING THE SHORT INDUCTION PERIOD 1349 



measure of the sluggishness of the apparatus, the true uptake perhaps being 

 highest at the very beginning of illumination.) The inhibition that follows 

 the gulp increased in diu-ation, and the separation of the successive inhibi- 

 tion waves became wider, as the dark period was extended (fig. 33.13A). 

 In tobacco leaves, for example, with ta = 2 minutes, the existence of the 

 two waves was revealed only by an inflection on the induction curve, while, 



CO2- 



content 



of gas 



Imin 



Fig. 33.13A. CO2 induction in lobacco leaves at 20° C. after 9, 5, 3 

 and 2 min. darkness; diaferometer record (after van der Veen 1949'). 



CO2- 



content 



of gas 



time 



Fig. 33.13B. CO2 induction curves of tobacco leaves at different temperatures; 

 diaferometer record (after van der Veen 1949'): ( f ) I'S^t on; ( | ) light off. 



at ^d = 5 minutes, the first inliibition peak was reached in about 1.5 min- 

 utes, and a well-separated second peak, 4.5 minutes later. Judging from 

 the shape of the induction curves after repeated short dark periods, the 

 factor causing the inhibition requires several minutes of darkness to be 

 built up (or else the factor responsible for activation in light survives in 

 the dark for several minutes) . 



The inhibition waves can be slowed down (fig. 33.13B) also by lowering 

 the temperature. The duration of the dark period needed to produce a 

 certain wave of inhibition decreases with increasing temperature. At 

 40° C, inhibition becomes more or less permanent. 



Figure 33.13C shows that the initial carbon dioxide gulp was unaffected 



