The Tenth International Conference on Plant Growth Substances was held July 22-26,1979 at the Wisconsin Center of the University of Wisconsin-Madison under the joint sponsorship of The International Plant Growth Substances Association (IPGSA) and the Graduate School of the University. More than 500 persons, including 423 regis tered participants, attended the Conference. Financial support was generously provided by the organizations listed under Acknowledg ments. The Conference was planned and hosted by a Local Committee in response to a request from Professor Dennis Carr, Secretary of IPGSA, in 1976, that the Tenth Conference be held on this campus in 1979. To achieve comprehensive, systematic coverage of the subject and yet provide maximum opportunity for individual contributions by partici pants, reports were presented under ten topics, each with sessions of oral reports and poster demonstrations. Chairmen appointed by the Local Committee organized the material to be presented and arranged for a series of integrated, invited reports on each topic. They presided and led discussions at the sessions, and they also greatly assisted in the editing of the invited reports which are presented in full in these Pro ceedings. Unfortunately it was economically impractical to publish all reports, but the 244 submitted abstracts have been printed and dis tributed to participants.

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Origin and Development of Plant Growth Substance Research.- Darwin and the Movement of Plants: A Retrospect.- The Development of Plant Hormone Research in the Last 60 Years.- Auxins.- Homeostatic Control of Concentrations of Indole-3-Acetic Acid.- The Mechanism of Transmembrane Auxin Transport and Its Relation to the Chemiosmotic Hypothesis of the Polar Transport of Auxin.- Purification and Properties of Membrane-Bound Auxin Receptors in Corn.- Auxin and H+-Excretion: The State of Our Knowledge.- Auxin-Induced Changes in Noncellulosic Polysaccharides of Cell Walls of Monocot Coleoptiles and Dicot Stems.- Auxin-Regulated Elongation: A Summary Hypothesis.- Auxin-Induced Specific Changes in the Pattern of Protein Synthesis in Soybean Hypocotyl Sections.- Auxins Summary of Other Reports.- Cytokinins.- Metabolites of Cytokinins.- Cytokinin Action on Enzyme Activities in Plants.- Presence and Possible Functions of Cytokinins in RNA.- Probing the Cytokinin Receptor Site(s).- Gibberellins.- Partial Syntheses of Isotopically Labelled Gibberellins.- Metabolism of Gibberellins in Immature Seeds of Pisum sativum.- GA-Biosynthesis: The Development and Application of Cell-Free Systems for Biosynthetic Studies.- The Physiology of Gibberellin-Induced Elongation.- Ethylene.- Ethylene and Seeds.- Ethylene Metabolism and Its Possible Physiological Role in Plants.- Mechanism and Regulation of Ethylene Biosynthesis.- Enzymes of Ethylene Biosynthesis.- Abscisic Acid.- Introductory Comments: Abscisic Acid in the Physiology of Plants.- A Role for Abscisic Acid in Drought Endurance and Drought Avoidance.- Abscisic Acid and Other Naturally Occurring Plant Growth Inhibitors.- Regulation of Abscisic Acid Metabolism.- Studies on the Role of Abscisic Acid in Stomatal Movements.- New GrowthFactors.- New Growth Factors Summary of Session.- Hormonal Regulation in Plant Reproductive Development.- The Hormonal Control of Tuberisation in Potato.- Inhibition of Flowering in Short-Day Plants.- Inhibition of Flowering in Long-Day Plants.- Regulation of Flowering in the Grapevine (Vitis vinifera L.).- Hormonal Regulation of Sex Expression in Plants.- Growth Substances: Roles in Fertilization and Sex Expression.- Hormonal Regulation of Morphogenesis.- The Hormonal Regulation of Morphogenesis in Mosses.- Hormonal Control of Morphogenesis in Cultured Tissues.- Agricultural Uses of Plant Growth Regulators.- Agricultural Uses of Plant Growth Substances: Historical Perspective.- Applications of Gibberellins in Agriculture.- Ethylene and Ethylene Physiology.- Applied Uses of Growth Substances Growth Inhibitors.- Growth Regulator Use in Commercial Apple Production.- Uses of Plant Growth Substances in the Production of Sugarcane: A Practical Case History.- Plant Growth Substances in Commercial Uses of Tissue Culture.- Symposium on Plant Movements.- Circumnutations, Rhythms and Light-Regulated Movements in Plants.- Phototropism as a Phenomenon of Inhibition.- Hormonal Control of Root Georeaction: Some Light Effects.- Action Potentials and Rapid Plant Movements.- The Role of Action Potentials in the Control of Capture Movements of Drosera and Dionaea.- On the Mechanism of Contact Coiling of Tendrils.- Movement by Bacteria: On the Mechanism of Sensory Transduction in Bacterial Chemotaxis.- Participants.