133G 



INDUCTION PHENOMENA 



CHAP. 33 



duction develops rapidly as the dark time increases to little more than a 

 minute; when fully developed, it accounts — at room temperature — for the 

 loss of about one molecule of carbon dioxide for two molecules of chloro- 

 phyll. (McAhster estimated that the induction losses of oxygen in the ex- 



Fig. 33.8. Effect of intensity of illumination on the induction period in wheat 

 (after McAHster 1937). Numbers are rates of CO2 exchange by respiration or 

 assimilation (true) in mm.' per 10 miii. First arrow, beginning of experiment; 

 second, switch from dark to light; third, return to darkness. Dotted line shows 

 return to initial position at end of experiment. 



periments of van der Paauw and Smith were of the same order of magni- 

 tude.) At low temperatures, the induction loss may be three to five 

 times larger (c/. fig. 33.7). A second induction-enhancing dark process 

 becomes apparent when the dark period is extended to several hours ; this 

 process leads to a stationary state after about 7 hours in darkness, and then 

 accounts for an induction loss of about five molecules of carbon dioxide 



