Phase Shift Effects in the Kalanchoë Petal Rhythm due to Two or More Light Pulses

The circadian petal rhythm of Kalanchoë blossfeldiana Poellniz was studied theoretically and experimentally. Results of experiments in which (i) two light pulses and (ii) repeated light pulses were given to the flowers are compared with predictions based on a previously published feedback model. In this model both the amplitude and the phase of the rhythm are affected by light pulses. Results from the present phase shift studies are shown to be in good agreement with the model. The results are also discussed in relation to a constant amplitude model like that suggested by Pittendrigh for the eclosion rhythm of Drosophila.