The permeation of indoleacetic acid through the cuticle of the Avena coleoptile and its effects on the growth and the geotropism

The auxin production by the tip of the Avena coleoptile seems too high for a complete geotropic response (a curvature of 90 °) under the present experimental conditions (weak red light). It is sufficient for a maximum rate of geotropic curvature, but it is too low for a maximum rate of elongation. The entrance of indoleacetic acid through the cuticle is 2500-3000 times as difficult as that via the cut surface of a decapitated Avena coleoptile.