¹ This symposium was held at the Fifty-seventh General Meeting of the Society of American Bacteriologists in Detroit, Michigan, on April 30, 1957. Participants were: Sol Spiegelman, Department of Bacteriology, University of Illinois, Urbana, Illinois; Dean Fraser and H. R. Mahler, Departments of Bacteriology and Chemistry, Indiana University, Bloomington, Indiana; Albert Frenkel, Donald D. Hickman and Lucille Smith, Department of Botany, University of Minnesota, Minneapolis, Minnesota, and Johnson Research Foundation, University of Pennsylvania, Philadelphia, Pennsylvania.