538 



RHYTHMS IN PLANTS AND ANIMALS 



12:12 light-dark 



v. 



continuous light 

 A**^ day 



Fig. 2. PeriWa. Diurnal changes in quantity of chlorophyll h during 

 light-dark cycle and in continuous light. (Bunning, Mitrakos, and Eber- 

 hardt, unpublished data.) 



At any rate, if there are diurnal changes in chlorophyll content, it 

 might well be possible that other pigments are involved too. With 

 these aspects in mind, experiments with Chenopodium amaranticolor 

 may be of some interest (Fig. 3). 



.-x--»«--y-* 



Fig. 3. Chenopodium amaranticolor. Influence of light breaks during 

 light and dark period on length of inflorescence. The plants were offered 

 10 short-day cycles (10 hr light, 14 hr dark). Length of the inflorescence 

 in the controls 12 mm. Light breaks in light period 200,000 kiloerg/cm^, 

 in dark period 20,000 kiloerg/cm-. Determination of inflorescence 

 length 15 days after beginning the experiment. (After Biinning and 

 Konitz, 1957.) 



Offering 10: 14-hr light-dark cycles, again we found the well-known 

 inhibiting effect of breaks with red light (10 or 15 min). This effect 

 was strongest 7 hr after the beginning of the dark period, but in order 



