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amino acids is a Vell known phenomenon in animals and has been interpreted as the detoxication of otherwise poisonous substances. The formation of indoleacetylaspartic acid is the first instance of a similar reaction in plants which has come to the attention of the authors. The significance of the reaction in the physiology of the pea is not yet understood. However, the marked difference between plant species with respect to the biosynthesis and utilization of indoleacetylaspartic acid suggests an approach to the problem of selective herbicidal action which may prove useful. The authors wish to acknowledge the technical assistance of A. W. H. Van Ysselstein. LITERATURE CITED 1. ANDREAE, W. A. Communicated at the Congr. Intern. Bot., 8th, Paris. Sect. 11/12: 151. 1954. 2. BoIssoNNAS, R. A. A new method of peptide synthesis. Helv. Chim. Acta 34: 874-879. 1951. 3. JERCHEL, D. and STAAB-MiLLER, R. Analytical characteristics and growth activity of homologs and peptides of indole-3-acetic acid. Zeits. Natturforsch. 9b: 411-415. 1954. 4. TANG, V. W. and BONNER, J. The enzymatic inactivation of indoleacetic acid. II. The physiology of the enzyme. Amer. Jour. Bot. 35: 570-578. 1948. 5. SIEGEL, S. M. and GALSTON, A. WV. Experimental coupling of indoleacetic acid to pea root protein in vivo and in vitro. Proc. Nat. Acad. Sci.. U. S.

The stimulatory effect of indole compounds on fruit-setting of several horticultural crops (7,8,18) was soon established following the identification of indole-3-acetic acid as a plant growth hormone (12). Strangely enough, however, for the stimulation of parthenocarpy many related compounds, some analogs of indole-3-acetic acid, were found more effective (7,8,11,23,25,27,32). MIeanwhile, extracts of corn kernels in the milk stage were described as having a fruit-setting potency much greater than could be accredited to indole-3-acetic acid alone (9,26). Recently the fruit-setting factor derived from the ethanol extracts of immature corn kernels was characterized by REDEMANN et al. (16) as the ethyl ester of indole-3-acetic acid and was found to induce parthenocarpic fruit development in the tomato when applied in dilutions of 1 part in 10,000. Thus, the fruitsetting activity was multiplied almost 100-fold compared with the free acid or the salts of heteroauxin.Recent studies concerned with the relation of chemical structure to activity, the relative instability of indole-3-acetic acid, the enhancement of activity by the addition of chlorine to the ring structure of certain growth substances, the role of growth substances in in vitro culture of tomato fruits (14) and finally, the scant attention directed toward halogenated or otherwise substituted indole compounds in biological activity testing suggested a more detailed evaluation of this chemical group of compounds with respect to the comparative induction of parthenocarpic fruit development in the tomato.Methods A known quantity of the compound was dissolved in anhydrous, peroxide-free ether and diluted to the desired concentration. An aliquot of this solution containing the required amount of the compound was added to a known quantity of anhydrous lanolin and stirred until solution was complete. The ether was removed by immersing the containers of the solution in a hot water bath. For higher dilutions the same procedure was followed with smaller aliquots.Estimation of the fruit-setting activity of the various indole compounds consisted of applying 1, 0.1, 0.01, and 0.001% lanolin solutions of each chemical to the ovary of the tomato flower from which the stamens had been 1 Journal article no. 1385 of the Michigan Agricultural Experiment Station.

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