Hormones and Root Formation

Portions of cuttings, some of which had been treated at the apex and some at the base with indoleacetic acid, showed large amounts of auxin in the bark immediately after treatment, but about 90 per cent of the auxin disappeared during the first day. 2. Very little auxin was recovered from the bark at the apex of cuttings which had been treated at the base with 0.001, 0.005, and 0.02 per cent solutions of indoleacetic acid. 3. Moderate amounts of auxin were recovered from the base when the cuttings were treated at the apex with these solutions; however, with the 0.02 per cent solution the amount recovered at the base was small as compared with that at the apex. 4. The 0.02 per cent solution applied at the base of lemon cuttings was the only treatment of those tested that gave significant increase in root formation on lemon cuttings over controls. 5. There was little difference in the amount of auxin recovered from treated apple and lemon cuttings, yet the apple cuttings did not form roots. It is assumed that apple cuttings are lacking in certain internal substances necessary for root formation. 6. Experiments involving removal of the treated base and treating of the new base indicate that the action of indoleacetic acid in root formation is primarily the mobilization of naturally occurring root-forming substances. 7. Evidence is presented which indicates that leaves of lemon cuttings supply a substance necessary for the differentiation of the root primordia and another for the outgrowth of these primordia. The former appears to be transported rapidly to the base under the influence of indoleacetic acid while the latter is transported slowly to the base.