Proof of the subapical differential growth of the flanks in the Chara rhizoid during graviresponse

The displacement of resin spheres attached to the tip of the gravitropically bending Chara rhizoid was measured by means of time-lapse photography. The relative growth of the flanks which at the beginning of stimulation were opposite to each other, was calculated during the earliest response time. The physically upper subapical flank section continues growing after stimulation at a decreasing rate. The growth of the opposite lower flank section is inhibited immediately after stimulation by the position of the statoliths. As soon as the statoliths are displaced in a basal direction, the growth of this section is transiently promoted. The gravitropic downward bending of the Chara rhizoid is by bowing, not by bulging.