1320 



INDUCTION PHENOMENA 



CHAP. 33 



In the experiment recorded in the figure the lower surface of a castor 

 bean leaf {Ricinus) was pressed tightly against a stationary mercury elec- 

 trode. The oxygen was down to nearly anaerobic levels due to respiration 

 and reduction by the electrode. The leaf was then illuminated (through 

 the agar) with light of about 7500 meter candles during the shaded parts 

 of the record : in a after a 10 minute dark period, in h after 34 seconds, etc., 

 as shown in the figure. We note the immediate, brief gush of oxygen. Verti- 

 cal lines are time marks, 1 minute apart; arrows indicate beginning of 





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Fig. 33.3. O2 liberation in light after dark intervals of the order of 1 sec. (after Blinks 

 and Skow 1938). (a) 0.45 sec. light, 1.35 sec. dark; (b) 0.9 sec. light, 0.9 sec. dark; (c) 

 0.7 sec. light, 1.1 sec. dark; (d) later portion of c, with long dark period in last half of 

 record. O2 production begins within the period of the galvanometer, and is nearly con- 

 stant during the flash, or slightly higher at the beginning. Time marks are 0.2 sec. 

 apart. Full height in d represents O2 content of water in equilibrium with air. 



illumination. (Similar records were obtained with a platinum electrode 

 and with marine algae (e. g., Ulvd) without stomata or gas spaces.) 



In accordance with Warburg's and van der Paauw's data the inhibition begins to 

 disappear after about 1 minute of illumination, and oxygen hberation is well under way 

 toward the end of the second minute. 



Figure 33.3 shows that, even after dark intervals of only 1 second, the oxygen evolu- 

 tion during the first half second of illumination is slightly faster than in the second half 

 second; this may or may not be the first sign of the "gush" and subsequent inhibition 



