86 CHAP. XI. PHENOMENON OF PHOTOSYNTHETIC INDUCTION 



60 minutes increased it from 450 seconds to 510 seconds, i.e. 

 only 1 • 1 times ; the induction-period had thus practically 

 reached the limit. 



To make allowance for any change that may occur 

 during the experiment, the series of operations were next 

 carried through a complete cycle and the determination 



Fig. 25. Cyclic Curve showing effect of Increasing (lower curve) 

 and Decreasing (upper curve) Periods of Darkness on Induc- 

 tion-period 



made with periods of darkness increasing as 1, 5, 10, 20, 40, 

 60 minutes, and decreasing in the reverse order, 40, 20, 10, 

 5 and 1 minute. The results are given in Table XIIIa (p. 85) . 



The induction-period is thus seen to increase with 

 increasing duration of previous darkness. The curve is 

 straight up to 20 minutes, but afterwards it tends to become 

 horizontal, the increase of induction-period reaching the limit 

 (ng. 25). 



It may be urged that the increase in the induction- 



