Some Factors influencing the Abschission of Debladed Leaf Petioles

1. Experiments with various deblading patterns in Coleus do not confirm in all respects the auxin gradient theory about abscission. Indications are obtained that in order to render abscission possible there should be a sufficient auxin production (or auxin induced growth) on the proximal side of the abscission zone. 2. Placing the plants in a horizontal position induces an accelerated fall of debladed petioles. This effect is only clear if a certain quantity of auxin (or auxin induced growth) is present at the proximal side of the abscission zone. Some preliminary experiments on the clinostat suggest that the accelerated fall is induced, at least for the greater part, by the transversal component of gravity. The effect is supposed to be connected with an increased growth in thickness in horizontal stems. The consequences of the results for practical fruit growing are discussed. The author wishes to thank Dr M. H. van Raalte for his constant interest and valuable suggestions.