Growth Inhibitor Production by Root Caps in relation to Geotropic Responses

Abstract

JUNIPER et al.¹ have drawn attention to the importance of the cap in the geotropic response of Zea mays roots. They found that removing the cap abolished the downward curvature of horizontally placed roots even though the roots continued to elongate. This important finding suggested that the root cap might be (a) the site of the graviperception mechanism, (b) the source of growth regulating substances involved in the geotropic response, or (c) both (a) and (b). Our aim was to determine whether the cap was the source of growth regulating substances involved in the geotropic response of the primary root of Zea mays, var. Giant White Horse Tooth.