294 



CONTROL OF REPRODUCTION 



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16 20 24 



TIME OF DAYlHRS.) 



LIGHTS ON 



LIGHTS OFF 



10 MIN. 

 INTERRUPTION 



LIGHTS ON 



Fig. 4. The diurnal variation in CO^ metabolism of Kalanchoe after 35 

 long nights with (broken lines) and without (solid lines) 10-min interrup- 

 tions of the long dark period by 1500 ft-c. The interrupting light was 

 given at midnight (24 hr). 



