Instructor in Biology, Soochow University, Soochow, China(1932-1940)
Technical Assistant, Arnold Arboretum of Harvard University, Cambridge, Mass., U. S. A.(1941-1943)
Professor of Biology, Soochow University, Soochow, China(1946-1947)
Professor of Botany and Head of the Department, National Taiwan University, Taipei, Taiwan(1947-1950)
Professor of Biology and University Director of Biology, The Chinese University of Hong Kong(1964-1965)
The Morris Arboretum, University of Pennsylvania, Philadelphia, PA, U.S.A.
Research Associate (1952-1955), Taxonomist (1955-1970), Director (1971-1974)
University of Pennsylvania, Philadelphia, PA, U.S.A.
Associate Professor of Botany (1958-1963), Professor of Botany (1963-1973), John Bartram Professor of Botany and Horticulture (1974-1979), Emeritus(1979－)