ON THE FORMATION OF ADVENTITIOUS ROOTS IN CUTTINGS OF COLEUS IN RELATION TO THE EFFECT OF INDOLEACETIC ACID ON THE EPINASTIC CURVATURE OF ISOLATED PETIOLES

A bstract The epinastic curvature of isolated petioles of Coleus shows a dependence upon the concentration of indoleacetic acid in the ambient medium. In low concentrations (between 10 −9 and 10 −7 ) of indoleacetic acid, a small maximum followed by a small minimum in the curvature vs . concentration curve can be seen. Between 10 −7 and 10 −5 indoleacetic acid there is a concentration dependent increase of the curvature. In higher concentrations the curvature diminishes, and a discolouration of part of the petiole occurs. These phenomena occur in concentrations that promote the formation of adventitious roots. The possibility of a correlation of injurious conditions with the formation of adventitious roots has been investigated, using stem cuttings of Coleus . Exuberant formation of adventitious roots after a treatment with high concentrations of indoleacetic acid was accompanied by necrosis in the lowest part of the cutting. Sulphuric acid, potassium hydroxide and mercuric chloride alone, were shown to cause a promotion of the formation of adventitious roots when applied in concentrations that cause necrosis in the lowest part of the cutting without being lethal to the whole cutting.