The Effect of Caffeic Acid on the Epinastic Curvature of Isolated Petioles of Coleus sp. in Comparison with the Effect of Gibberellic Acid and Indoleacetic Acid

The isolated petioles of Coleus show a distinct dependence on indoleacetic acid in the development of the epinastic curvature, in aqueous medium. Under the same experimental conditions gibberellic acid shows no effect or an inhibition only. Caffeic acid tested in concentrations between 10—11 and 10—3 evoked varying responses. In winter-grown plants the curvature vs. concentration curve shows two small maxima, which are not evident in the response of summer-grown plants. The interaction of indoleacetic acid and caffeic acid is tested and discussed in elation with the question of the endogenous auxin in Coleus.