ENDOGENOUS DIURNAL PERIODICITY 513 



Table I. Phaseolus mitltiflorus, Leaf Movements. 

 Temperature before Recording, 20° C (Bunning, 1931) 



Temperature, °C Length of Periods, hr 

 15 29.7 



20 27.0 



25 23.7 



30 22.0 



35 19.0 



or even while this low temperature is still prevailing, the delay of the 

 clock is compensated (Tables II, III). The cycles may even, for 

 several days, become shorter than they are normally (Bunning and 

 Leinweber, 1956; Leinweber, 1956). It would appear that the 

 processes of compensation are working too actively during this period. 

 (For explanation see Addendum.) 



Table II. Phaseolus, Leaf Movements at 15° C; 



Temperature for Several Hours 1° C; Length of 



Periods (After Leinweber, 1956) 



Extending these experiments for a still longer period of time enables 

 plants and animals to become adapted to the new temperature: 

 temperature dependence can no longer be observed. This phenomenon 

 has been described by several research workers. I may mention the 

 experiments of Pittendrigh (1954) on Drosophila, of Bruce and Pit- 



Table III. Pcriplancta americana, Rhvthm of Activity; 



Length of Periods, hr, at 22° C after Chi'lling 12 hr to 5° C 



(Bunning, unpublished data) 



