The promoting effect of an increased acidity of the medium on the straight growth of decapitated coleoptiles as well as the inhibiting effect on their geotropic curvature, that are observed when these coleoptiles are supplied with limiting amounts of indoleacetic acid, are to be ascribed to a decrease in the degree of dissociation of this auxin and to the circumstance that it penetrates more easily into the protoplasm in the molecular form, with the result that the internal auxin level is raised. With abundant indoleacetic acid — which prevents a geotropic reaction — the pH of the medium did not change the rate of elongation. '1 he above conclusion is supported by the fact that when the non-dissociated indoleacetonitrile was supplied to the coleoptiles a decrease of the external pH from 7.8 to 3.8 produced no effect on these processes. From these results it is further concluded that during the experimental period (75 minutes) the pH of the cytoplasm was not affected by a change of the pH of the surrounding solution. The author is indebted to Prof. Dr. V. J. Koningsberger and to Dr. H. P. Bottelier for stimulating discussions.

Acta botanica neerlandica

CC BY 3.0 NL ("Naamsvermelding")

Koninklijke Nederlandse Botanische Vereniging

L. Anker. (1958). The Influence of the pH on the Growth and the Geotropism of decapitated Avena Coeloptiles supplied either with Indoleacetic Acid or with Indoleacetonitrile. Acta botanica neerlandica, 7(1), 69–76.