Circadian Clock in Photoperiodic Time Measurement: A Test of the Bünning Hypothesis

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Science  08 Sep 1967:
Vol. 157, Issue 3793, pp. 1182-1185
DOI: 10.1126/science.157.3793.1182


A technique has been developed for effectively separating the direct inductive effect of a light signal from its effect on the phase of the rhythm of sensitivity to photoperiodic induction. With this technique it has been shown that a 75-minute pulse of light per day, when appropriately positioned with respect to the circadian activity cycle of the sparrow Passer domesticus, is sufficient to produce a response normally produced only by long days. The results cannot be interpreted in terms of a requirement of an absolute amount of either darkness or light and offer strong confirmation of Bünning's hypothesis concerning the mechanism of photoperiodic time measurement.