Natural and Forced Circadian Oscillations in the Leaf of Trifolium Repens

Abstract

The leaves of white clover (T. repens) exhibit typical circadian characteristics with an endogenous period, T, of 25-27 hr. Oorresponding oscillations are observed of the torque exerted by leaflets prevented from closing. The mean variation in torque during a cycle was 339 � 13 dyne cm. When leaves were subjected to light-dark cycles at constant temperature, entrainment was obtained for periods from 0�7 to 1� 4T. Phase shifts were observed ranging from a lag of 40� for O' 7T to an advance of 130� for 1� 4T. The pulvinus was shown to be both the photoreceptor and the site of the endogenous timer.