A study of the autotropic straightening reaction of a shoot previously curved during geotropism

Abstract

Abstract The growth of marked zones on horizontal sunflower and maize shoots was measured over long periods. Subsequent to a period of geocurvature, a period of autotropic straightening occurred in most zones of these shoots. The patterns of differential growth causing this straightening were determined. The straightening appeared in the more apical zones initially and subsequently in the basal zones. The magnitude of the differential growth causing the straightening in any zone was similar to that which caused geocurvature in the same zone. It was found that autotropic straightening became evident in some zones before those zones had reached a vertical orientation thus it is suggested that gravity is not directly involved in the initiation of autotropism.