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

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.