560 



RHYTHMS IN PLANTS AND ANIMALS 



40n 



30- 



I- 

 <s> 



UJ 



^.0 



o 



.Photoperiod 



Nycfinasty 

 Phaseolus 



1 I 1 1 I 



10 20 30 



TEMPERATURE (°C) 



Fig. 4. Relationship between autonomous cycle lengths (the ordinate in 

 hours) as a function of temperature. Crosses, data of BUnning (1932) 

 for nyctinastic movements of Phaseolus leaves. Squares, similar data for 

 Phaseolus leaf movements from Fig. 3. Circles, length of internal photo- 

 periodic cycle for soybean, after Hamner and Nanda (unpublished). 



Fig. 4). Therefore I think that we can conclude that in higher plants 

 in general the Biinning cycle has a temperature coefficient of 1.2—1.25. 



From the preceding it must be obvious that plants from a warm 

 climate will not have synchronization of their internal cycle with the 

 solar cycle at relatively low temperatures. We actually find that such 

 plants grow very poorly and often die within a few months when 

 grown at 4°, 7°, or 10°. Perhaps most significant is the fact that the 

 first symptoms of abnormal growth are lack of chlorophyll formation 

 in the newly formed leaves and ultimately complete cessation of 

 growth in the growing point. Tomatoes turn yellow at 4°, tobacco and 

 Begonia at 4° and 1°, Saint paiilia and Coleus at 10°. 



To test whether death of warm-climate plants in cool temperatures 

 can be attributed to a lack of synchronization between internal and 

 external daily cycles, Saintpaulias and Begonias were grown at 10° in 

 both a 24- and a 32-hr light-dark cycle, getting during one-third of the 

 cycle artificial light at 1000 ft-c. Very soon the Begonias, and after 

 several months, the Saintpaulias, died in the 24-hr cycle, but growth 

 was very healthy in the 32-hr cycle (see Fig. 5). 



