Die Bedeutung tagesperiodischer Blattbewegungen für die Präzision der Tageslängenmessung

Summary

• 1. In Glycine max, the circadian leaf movements are synchronized with the 24 hr period in 12:12 hrs light-dark cycles even with light intensities of only 0.6–0.8 lx. The normal phase-angle difference between light-dark cycle and the circadian rhythm is already nearly reached with intensities of 10 lx.

• 2. In Phaseolus multiflorus, light with the intensities of moonlight, offered during the dark-period of 12:12 hrs light-dark cycles, is able to shift the phases of the circadian leaf-movement rhythm.

• 3. In Phaseolus, the transition of the leaves to the night-position reduces the intensity of moonlight reaching the leaf's upper surface to values below the threshold values for phase shifts.

• 4. The epidermis of the upper leaf surface in Parochetus communis has “ocelli”. The complicated transition of the leaves to their night-position results in a nearly complete darkening of these ocelli.

• 5. It is concluded that the circadian leaf movements prevent the interference of moonlight with the photoperiodic time measurement. Moreover, the leaf movements result in a very sharp increase or decrease of the light-intensity reaching the leaves' surface in the photoperiodically decisive range (between about 1 and 10 lx) during morning and evening twilight.