Plant hormone; recognized as the principal auxin of higher plants. Prepd by the reaction of indole with potassium glycolate at 250°: Johnson, Crosby, J. Org. Chem. 28, 1246 (1963). From indole and chloroacetic acid: Shagalov et al., US 3320281 (1967). Reviews: Leopold in The Hormones vol. IV, G. Pincus et al., Eds. (Academic Press, New York, 1964) pp 1-66; Thimann in The Physiology of Plant Growth and Development, M. B. Wilkins, Ed. (McGraw-Hill, New York, 1969) pp 1-45.