1344 



INDUCTION PHENOMENA 



CHAP. 33 



flashes lasting only 0.04 second were recorded as distinct peaks on the pH 

 curves. 



The unexpected result of Blinks and Skow's measurements was the ob- 

 servation of a gush of acidity in the first moment of illumination. This 

 gush was particularly strong after a prolonged dark rest, and could then be 

 observed several times in succession — although with a declining strength — 

 even after dark intervals of only a few seconds duration. Figure 33.12 

 shows three repetitions of the gush in a pond lily leaf (in this case, the dark 

 intervals were of the order of 1 minute). 



I Light I Dark 



^ y 



■/• 



Minutes 



1 



'3 



Fig. 33.12. 

 Skow 1938). 

 mata). 



Acidity change on illumination of pond lily (Castalia) (after Blinks and 

 Glass electrode pressed against upper surface of leaf (side that has sto- 



A temporary decrease of pH occurs immediately on illumination, pre- 

 ceding the regular rise of pH (alkalinity increase) due to assimilation of car- 

 bon dioxide. The anomalous pH decrease is most marked on the first 

 illumination (after a long dark period) and becomes progressively less on 

 successive exposures after shorter dark intervals. 



Upon darkening, after a period of illumination, an alkaline gush was 

 found to precede the regular increase in acidity due to respiration. The 

 "acid gush" was observed by Blinks and Skow with marine algae (e. g., 

 Stephanoptera) , fresh water plants (e. g., Potomageton and Castilia) and land 

 plants, and thus seems to be of fairly general occurrence. 



