290 



CONTROL OF REPRODUCTION 



Fig. 1. Gastight plant chamber used to study COa-metabolism of Kalcm- 

 cho'e blossfeldiana. Description in text. 



which they were transferred to 8-hr photoperiods (short days). The 

 gas exchange was then measured under short-day conditions after the 

 plants had received an increasing number of short days. 



EFFECT OF SHORT DAYS ON COo METABOLISM IN THE DARK 



In Fig. 2, the data for the COi- metaboHsm during the dark phase are 

 presented. The broken Hnes show the CO2 uptake during two succes- 

 sive nights under long-day conditions. When the lights go off at mid- 

 night (24 hr) photosynthesis ceases, but there remains a small, though 

 significant, net dark uptake of CO2. When the lights come on at 8:00 

 A.M., photosynthesis resumes and there is a marked increase in the 

 rate of uptake of CO2. This behavior is what would be expected from 

 a succulent plant. 



The solid lines show the corresponding behavior during the 16-hr 



