A lecture. The observed growth effects following the application of auxins to plants may in certain cases be in-direct, resulting from small direct effects on the root system of the young plant (Avena). This complicates the analysis of the process. Further, auxins may promote or inhibit growth according to the conc. used and the organ acted upon, while the same substances also produce effects other than simple growth, such as root formation (illustrated on Vitis cuttings). The action of auxins is evidently exerted on a fundamental process or "master reaction" in the cell. Analysis of this reaction, both through the chemical structure of auxins and through study of the intimate nature of the process, is discussed.