SUCH A VOLUMINOUS literature has grown around auxins that it is neither possible nor advisable to include a comprehensive survey of it within the scope of a short paper. The reader is referred to Boysen Jensen's (1936) book, which treats the subject very exhaustively. In experiments with heteroauxin (indole-3-acetic acid) the Avena-coleoptile test has been used by most workers as a standard, and the bending of the coleoptile has been freely ascribed to the " hormone-like " property of this substance. Yet we have no satisfactory explanation for the fact that the same substances which seem to induce growth in coleoptile, foliage leaves, hypocotyls, and stems inhibit the elongation of the roots. But roots are not the only organs to be suppressed; Le Fanu (1936) found that the axillary buds of Pisum sativurn on single-node stem cuttings were inhibited when the ends were placed in heteroauxin solution, and when whole shoots were placed in this solution the growth of the young stem was inhibited; similarly, buds of cuttings were inhibited when heteroauxin was applied below or above the bud. Solacolu and Constantinesco (1936) observed that within the limits of concentration used, heteroauxin prevented the development of the radicle and the plumule during the germination of Ricinus and Phaseolus, and that tumors were produced at the level of the collar or along the axis of the hypocotyl. Most data on the effect of auxins have been obtained within a few hours of the initiation of the experiments. What would happen if the time were extended? Since this is possible largely by pure culture methods, the work presented in this paper follows microbiological technique. About one hundred different fungi, seven different unicellular green algae, and corn seedlings were used as test plants. Fungi are particularly well suited for experiments with growth-promoting substances because many of them 'iIi not grow in a medium consisting of dihydrogen potassium phosphate, 0.5 g., magnesium sulfate, 0.5 g., ammonium nitrate, 1 g., and dextrose, 5 g. in 1000 cc. of distilled water. Consequently, one can readily observe whether or not a given substance is capable of inducing growth. Many other fungi grow readily in such a synthetic medium. The following representative fungi of the first group were tested in our work: Allomyces javanicus, Basidiobolus ranarum, Blakesleea trispora, Chaetocladium brefeldii, Conidiobolus villosus, Dasyobolus immersus, Dicranophora fulva, Pilaira moreaui, Plectospira gemmifera, Phytophthora cactorum, Pythium polymastum, Pythiomorpha gonapodioides, Phycomyces nitens, Saproleqnia diclina, and Thamnidium chaetocladioides. Of the second group of fungi the following, among many others, were used: