292 



CONTROL OF REPRODUCTION 



EFFECT OF SHORT DAYS ON COo METABOLISM IN THE LIGHT 



The CO2 metabolism during the light phase is shown in Fig. 3. Un- 

 der long-day conditions (broken lines) there is a marked photosyn- 

 thetic uptake of CO2. After exposure to short days (solid lines) the 

 rate of uptake of CO2 decreased during the early part of the light phase 

 giving way to a net CO2 production after pretreatment with 15 to 20 

 long nights. Thus, plants that have received 33 short days show a net 

 production of CO2 in the light and a net uptake of CO2 in the dark. 



40»r 



LONG DAY 

 SHORT DAY 



LIGHTS OFF 

 SHORT DAY 



LIGHTS OFF 

 LONG DAY 



Fig. 3. Carbon dioxide metabolism of Kolanchoe in light phase under 

 long-day conditions (broken lines) and after 1, 14, 21, and 32 long 

 nights (solid lines). Same plants as in Fig. 2. 



