THE INDUCTION-PERIOD 85 



this period of darkness was that, on re-exposure, instead 

 of the bubble appearing after 20 seconds, it appeared after 

 25 seconds. One minute's darkness increased the induction- 

 period to 45 seconds, 10 minutes' darkness to 160 seconds, 

 20 minutes' darkness to 270 seconds, 30 minutes' darkness 

 to 385 seconds, 40 minutes' darkness to 450 seconds, and 

 60 minutes' darkness to 510 seconds. The results are given 

 in the following tabular form. 



Table XIII. — Photosynthetic Induction-Period under 

 Increasing Periods of Previous Darkness 



These results show that while an increase of the period 

 of darkness from to 20 minutes increased the induction- 



Table XIIIa.- 



-Effect of Cyclic Variation of Periods of Darkness 

 on the Induction Period 



period from 20 seconds to 270 seconds, or nearly fourteen- 

 fold, a similar increase in the period of darkness from 40 to 



