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.