METABOLIC ASPECTS OF PHOTOPERIODISM 



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LONG DAY 

 SHORT DAY 



LIGHTS 

 SHORT 



OFF 

 DAY 



LIGHTS OFF 

 LONG DAY 



LIGHTS ON 



Fig. 2. Carbon dioxide metabolism of Kalancho'e in dark phase under 

 long-day conditions (broken lines) and during the 1st, 15th, 22nd, and 

 33rd long nights (solid lines). 



dark period after exposure to an increasing number of short days. As 

 the number of short-day cycles is increased, there is a marked increase 

 in the abihty of the plant to fix CO2 in the dark. The maximum fixation 

 usually occurs 1 1 to 12 hr after the onset of darkness, after which the 

 rate of CO2 uptake decreases to about zero before the lights come on 

 at 8:00 A.M. 



