OXYGEN EXCHANGE DURING THE SHORT INDUCTION PERIOD 1319 



burg with Chlorella. Figure 33.1 shows the oxygen evolution as a function 

 of time. The induction lasts approximately the same time (5 minutes) 

 between 1740 and 282,000 lux; it is unaffected (at the higher light inten- 

 sity) by changes in CO2 concentration (from 2 to 29 X 10^^ mole/1. ). 



The curves in figure 33.1 were calculated by means of an interpolation formula: 



(33.1) log [(Pmax. + P)/(Pmax. - P)] = Kt 



where t = time. This equation, according to Smith, also fits the experimental results 

 of Warburg, van der Paauw and Briggs. 



21 



jit> 



t 



^ 



t 



V. 

 t 



Fig. 33.2. O2 liberation during induction period in Ricinus leaf (after Blinks and 



Skow 1938). 



The first investigation in which the oxygen liberation during the induc- 

 tion period was followed by a direct "differential" method was that of 

 Blinks and Skow (1938-). They used the polarographic method described 

 in chapter 25 (page 850). To avoid time lags, a small-surface platinum or 

 mercury electrode was pressed against a thallus or a submerged leaf. With 

 a polarization potential of 0.5 volt, the current was proportional to the 

 oxygen concentration in the thin layer between plant and electrode. The 

 capacity of this layer was so small that fluctuations lasting for less than 0.02 

 second could be recorded. The "time resolution" in Blinks and Skow's 

 experiments was thus a thousand times higher than in the manometric 

 experiments of Warburg, van der Paauw and Smith. Where the latter 

 noted only a smooth increase in oxygen liberation in the first 2 to 5 minutes 

 of illumination, the polarographic curves now revealed an initial "gush" of 

 oxygen, which was over in a few seconds (fig. 33.2). 



