Effect of Double Red Light Interruptions on the Photoperiodic Response of Pharbitis nil

In previous papers (2, 3) it was suggested that 2 endogenous circadian rhythms were associated with the photoperiodic response of Pharbitis; one was initiated by the beginning of the light period (lighton signal) and the other was initiated by the beginning of the dark period (light-off signal). Both of these rhythms had alternate phases of sensitivity to light; during 1 phase red light was inhibitory to flowering and during the other phase red light could be stimulatory. Since even a brief period of illumination gives the plant both a light-on and light-off signal the question arises as to whether or not the intensity of the light and the duration of the photoperiod affects the intensity or effectiveness of the 2 rhythms produced. Furthermore, if light is given during the dark period out of phase with the rhythm which had been induced by prior treatment, how much light is required to interfere with or damp that preinduced rhythm ?