Phototropism of stems, roots and coleoptiles

Abstract

Cylindrical plant organs placed in a gradient of visible light energy generally react by growing toward or away from the brighter light (Fig. 1). Such bending or curvature, due to unequal growth rates on the two sides of the differentially illuminated organ, is referred to as phototropism. While the basic phenomenon must have been familiar to botanists and laymen throughout the ages, it was first subjected to searching inquiry in the late 17th century, and the analytic interpretation of the mechanism by which curvature is produced has been restricted to the last seventy-five years. The earlier work, which cannot, for reasons of space, concern us here, is well reviewed by Wiesner (1881), Sachs (1890), Pringsheim (1912) and Boysen-Jensen (1936).