Investigations of the Geotropic Curvature of the Avena Coleoptile

Abstract

AbstractThe geotropic reaction in Avena coleoptiles is studied as a function of the stimulation time. The direction of the stimulation with respect to the vascular bundles must be defined when studying geotropic responses.It is found that the threshold time to evoke geotropic response is less than half a minute, i.e., at least ten times lower than the presentation time usually reported in the literature. An extrapolation procedure can be used to give a so‐called extrapolated presentation time tb, which is intimately related to the logarithmic part of the geotropic response curve and has a physical meaning in the reciprocity rule.The problem of the duration of the true threshold time for stimulation with 1 g is discussed.An experiment indicates that it is not necessary for mass particles (“statoliths”) to settle on the lateral cell wall in order to start the geotropic reaction chain.The slope of the logarithmic part of the geotropic response curve is independent of the transverse force applied to the coleoptiles. Support is given to the view that the slope is determined by the number of sedimenting mass particles.