Geometry of Heliotropic and Nyctinastic Leaf Movements

Abstract

Leaves that show nyctinastic and helionastic movements are usually more steeply inclined during the night and near midday than in the early morning or afternoon. But leaf movement is complex and there are many different combinations of leaf folding, axial rotation, or inclination of the midrib that result in changes in total leaf inclination. The complexity of leaf movement and amount of total leaf inclination can be described by plotting axial rotation or folding angle as a function of the angle of inclination of the midrib. The use of this method of description of leaf movement indicates that the variation between types of leaf movement may be continuous and not simply classifiable as diaheliotropic or paraheliotropic. Furthermore, this paper introduces a new method for characterization of the geometry of leaf movement that uses correlation between axial rotation and elevation as a tool for identification and quantification of leaf movement.