1348 INDUCTION PHENOMENA CHAP. 33 



transient gulp is sometimes superimposed upon the slower burst. Figure 

 33. 6D (c/. also fig. 33.13), for example, shows a distinct carbon dioxide 

 gulp in the first minute of illumination, paralleling a simultaneous oxygen 

 burst (reminiscent of Blinks and Skow's, and Warburg's, findings); but 

 a carbon dioxide burst supersedes the gulp in the second minute and lasts 

 through the third and fourth minutes; only after that does the ratio Qp 

 become close to 1. In many other runs, the "positive" induction effects 

 were much less prominent than in fig. 33. 6D, or totally submerged under a 

 much bigger carbon dioxide burst (c/. fig. 29. 3B). 



The dependence of the burst on cell concentration, even in the region of 

 nearly complete fight absorption (in which the rate of photosynthesis is 

 almost independent of cell density), indicates, according to Emerson, that 

 it is due to the emptying of a "reservoir" filled up during the dark period, 

 and is not directly related to the kinetics of photosynthesis. It seems that 

 most if not all the transient gas exchange phenomena are highly sensitive 

 to conditions such as temperature, cell density and carbon dioxide concen- 

 tration, while the steady rate of photosynthesis (in the light-limited state), 

 is, in good approximation, independent of all of these factors. 



Emerson and Lewis suggested that the "induction loss" of carbon di- 

 oxide consumption in strong light (as observed, e. y., by McAlister and 

 Aufdemgarten) may be merely another aspect of the carbon dioxide gush. 

 The maximum volume of the gush is in fact about equal to the induction 

 loss as measured by McAlister (page 1335). However, McAhster's induc- 

 tion losses were measured in 0.3 or 0.03% CO2, a concentration region 

 where the carbon dioxide gush should be negligible. 



Pending further clarification of the relation between the two effects, it 

 seems advisable to consider the carbon dioxide gush and the carbon dioxide 

 induction loss as two independent effects. 



Van der Veen (1949^, too, studied the carbon dioxide uptake during the 

 induction period, using a "diaferometer" — a heat conduction meter similar 

 to that of Aufdemgarten. With an entirely different plant material — 

 leaves of tobacco and needles of Sciadopitys — he obtained results very 

 similar to those found by Aufdemgarten with unicellular algae. He, too, 

 observed curves that began with a brief carbon dioxide "gulp"; a wave of 

 inhibition followed, decaying within 3-5 minutes to a steady rate. Some- 

 times the approach to the steady level was interrupted by another, or 

 several, waves of inhibition. 



The initial carbon dioxide gulp was small in normal air, and increased 

 with carbon dioxide enrichment of the atmosphere; its time course was 

 not much affected by the length of the dark period, or temperature varia- 

 tions. The highest rate of carbon dioxide uptake was reached in 1/2 to 

 3/4 minute under all the conditions used. (This might have been the 



