[Response-curves of the circadian rhythm in Phaseolus]

In Phaseolus multiflorus light interruptions were applied at different phases of the circadian cycles in leaf movements. The results were as follows. 1. The relation between the intensity of the light and the extent of the phase shift is qualitatively different with delays than it is with advances. These results suggest a difference in the nature of the primary processes in the two cases. 2. The response-curves for effects of white light (without far-red) published earlier are mainly due to the direct effect of the red component of this light on the leaf joint. 3. Far-red effects result in a quite different response-curve, with a strong dominance of the advances (shortening of the cycles). This effect occurs only after light absorption in the blade of the leaf. The leaf joint is indirectly influenced by the far-red. The direct effect of far-red on the leaf joints is only very little. 4. The difference in the effects of continuously applied far-red (shortening of the periods) and red (lengthening of the periods) is a consequence of the differences between these response-curves.