The dependence of amplitude and shape of the circadian leaf movement inoxalis acetosellaandoxalis regnelliiupon the strength of the zeitgeber

Abstract

Abstract The amplitude of the leaf movement in Oxalis acetosella and Oxalis regnellii strongly depends upon the strength of the Zeitgeber. In this paper the strength of the ZG was lowered by reducing the light‐intensity steps to ratios of 10: 1 (3000: 300 lux) or 4.3: 1 (1300: 300 lux). Under such conditions O. acetosella exhibited as little as 15% of its maximal amplitudes in one of the experiments. The reduction of the amplitude was accompanied by changes in the shape of the movement. The usual shape similar to a square wave was left by reflecting more or less pulse‐like movements of leaf spreading and folding. The pulses resembled direct reactions upon the light‐intensity steps and sometimes were followed by an outfading series of short‐term oscillations. In one case O. acetosella behaved differently in spreading and folding movement. The results support the concept that under experimental conditions of high mean light intensities the leaf movements of the two species are excited externally by the ZG. ...