THE PERIODIC ASPECT 



559 



ments an external factor which changed with the 24-hr cycle of the 

 solar day. I assume that this was air pollution, which easily penetrates 

 into physiological darkrooms unless carbon filters have been installed. 

 In addition, there seems to be an autonomous cycle of 10-hr duration, 



10 



20 



30 



40 50 60 70 



TIME (hr) 



80 



90 



100 



At 14° C 



TIME 



Fig. 3. Leaf movements of the primary leaves of Phaseolus in complete 

 darkness and in constant temperature. Abscissa, time in hours after initial 

 light exposure of 1 hr. 



which may be independent of temperature, but this is definitely a 

 secondary cycle. 



Recently Hamner and Nanda (unpublished) have found excellent 

 evidence of the existence of the Biinning cycle in the photoperiodic 

 induction of the soybean. When they carried out experiments in the 

 Earhart Laboratory at different temperatures, they found that whereas 

 at 23° the cycle length was 24 hr, at 17° it was 30 hr and at 10° it was 

 36 hr. These points coincide with Biinning's and my own data (see 



