The auxin production of the physiological tip of the Avena coleoptile and the repression of tip regeneration by indoleacetic acid (not by naphthylacetic acid and 2,4-dichlorophenoxyacetic acid)

The physiological tip of a decapitated Avena coleoptile is equivalent to the tip of the intact coleoptile as far as the regulation of the growth and the geotropic reaction is concerned. The regeneration of the physiological tip is completely inhibited by indoleacetic acid, even in concentrations below 0.01 mg/1. The auxin analogues naphthylacetic acid and 2,4-dichlorophenoxyacetic acid do not repress the auxin synthesis.