ENDOGENOUS DIURNAL PERIODICITY 



523 



within the cell population of the individual plant become evident. 

 But in other cases the single stimulus actually starts the oscillation in 

 the individual cells (unpublished data). 



With Phaseolus we found only wavelengths between 610 and 690 

 m^i to be effective for this synchronization (Biinning and Lorcher, 

 1957). Far red has an antagonistic effect. With cycles of red and far 



RED 



RED 



• FAR RED 



Fig. 19. Phaseolus muliifloriis, leaf movements; A, evocation of the 

 rhythm by red light; B-D, antagonistic effects of red and far red in 

 evocation and prevention of the periodicity. Broad black lines indicate 

 darkness. (Lorcher, unpublished experiments.) 



red, it is always the latter that determines whether or not the evo- 

 cation is estabhshed (Fig. 19). There is also evidence, both for 

 plants and animals, that the decline in amplitudes which customarily 

 occurs after 1 or 2 weeks of constant conditions is due to asynchrony 

 in the population of individuals or of cells inside the single individual. 



MODIFICATION BY LIGHT-DARK CYCLES 



The synchronization mentioned before means, of course, for the 

 majority of the cells a shifting of the phases. It is self-evident that this 



