| Abstract: | Abstract— The timing mechanism in plant photoperiodism seems to involve two endogenous circadian rhythms: a light-on (dawn) rhythm and a light-off (dusk) rhythm. Following a period of darkness light may affect flowering without affecting the rhythms, or it may affect flowering by rephasing the rhythms. A hypothesis is presented concerning the mechanism of the interaction between illumination and endogenous rhythms based upon correlations between leaf movements and flowering responses in various photoperiodic treatments. The possible role played by phytochrome in the response is considered in relation to the effects of light quality on the responses. |
