OXYGEX EXCHANGE DURING THE SHORT INDUCTION PERIOD 



1321 



In figure 33.3 the duration of flashes is indicated by the paler parts of the record, 

 flashes were produced by a revolving disc in front of an incandescent source (6000 meter- 

 candles). 



Bhnks and Skow associated the oxygen gush with the "inverse induction," observed 

 by Gaffron in the investigation of the influence of anaerobiosis on green algae (c/. chapter 

 6); and therefore emphasized that in their experiments, in consequence of respira- 

 tion and cathodic reduction, an anaerobic state was reached at the end of the dark period 

 in the layer between electrode and plant. However, the effects of anaerobic incubation 

 usually appear only after one or several hours in an oxygen-free medium (c/. section 6 

 below, and chapter 6). 



Blinks and Skow observed the oxygen gush not only with the leaves of a 

 higher land plant {Ricinus), but also with an aquatic plant (Potomageton) 

 and an alga {Ulva). They concluded that the gush is a general feature of 



E 40 

 o 



O 

 in 



CM 

 O 



g. 30 



o 



I- 

 < 



en 

 < 



01 



< 

 a. 

 a. 

 < 



20 



10 - 



10 



20 30 



TIME, min. 



40 



20 30 



TIME, min. 



Fig. 33.4. Induction in Fucvs after 16 hrs. in dark at 5.6° and 18.2° C. (after Stee- 

 mann-Nielsen 1942): (A) R = 0.45 mg. O./cm.^ hr.; (B) R = 0.25 mg. Oj/cm.^hr. 



the kinetics of photosynthesis. We will see below that Warburg and co- 

 workers reached a similar conclusion, and ascribed to it far-reaching 

 theoretical impUcations, but that other experiments indicate extreme vari- 

 ability of the gush in duration and volume, and thus argue against its inter- 

 pretation as an essential feature of photosynthesis. 



A more extensive, if less precise, study of induction in the evolution of 

 oxygen was carried out by Steemann-Nielsen (1942) with the multicellular 

 brown alga, Fucus serratus. He used Winkler's method of oxygen deter- 

 mination in water. Steemann-Nielsen incubated the thalli for as long as 

 16-17 hours before exposure to light, in streaming sea water. Neverthe- 

 less, the induction phenomena lasted for only about 10 minutes at 18° C. 



