Auxin precursors retard abscission when applied to debladed petioles of Coleus blumei Benth. The d and l forms of tryptophan are equally effective in retarding abscission. Tryptamine is more effective than is tryptophan. Both compounds apparently are converted to auxin through an aldehyde intermediate. The evidence presented suggests that a major pathway of tryptophan metabolism proceeds through tryptamine, as can be demonstrated by the use of amine oxidase inhibitors in the petiole tissue. Cell free preparations of the tissues metabolize tryptophan-1-(14)C with the release of carbon dioxide. The rate of tryptophan mtabolism in abscission tissue is 5 times that in distal petiole tissue. Radioactivity is associated with basic indole conversion products as well as with neutral and acidic fractions. The radioactivity is most concentrated in the neutral fraction. The results indicate that the Coleus petiole itself is capable of producing auxin.