Thimann, Kenneth Vivian

▪ 1998

      British-born plant physiologist (b. Aug. 5, 1904, Ashford, Kent, Eng.—d. Jan. 15, 1997, Haverford, Pa.), isolated and purified the plant hormone auxin and identified it as a chemical messenger with principal roles in regulating plant growth. After receiving (1928) a doctorate in biochemistry from Imperial College, University of London, Thimann joined the faculty of the California Institute of Technology in 1930 and began conducting research to isolate the universal growth substance that was known to control plant growth toward light and against the force of gravity. A few years earlier Dutch plant physiologist Frits Went had extracted the growth-stimulating substance from seedlings. Thimann demonstrated that auxin not only stimulated cell growth but also exerted an inhibitory effect on it. He identified the three main functions of auxin—cell elongation (with James Bonner), root formation (with Went), and bud growth (with Folke Skoog). Thimann's elucidation of the chemical structure of auxin allowed the hormone to be synthetically manufactured and put to use for a variety of purposes in farming and horticulture. For example, by spraying fruit trees with auxin prior to harvest, growers could prevent the premature falling of fruit (especially apples). Auxin was also found useful in promoting the joining of grafts and, in high concentrations, in controlling weeds. Thimann also investigated other aspects of plant physiology such as the formation of pigments in plants, the role of various wavelengths of light in photosynthesis, and the mechanisms involved in plant aging. He continued his research at Harvard University (1935-65) and moved to the University of California, Santa Cruz, where he served (1965-72) as the founding provost of Crown College. He was a member of the U.S. National Academy of Sciences and the American Academy of Arts and Sciences and published more than 300 research papers and a number of influential books, including Phytohormones (1937; with Went) and Hormone Action in the Whole Life of Plants (1977).

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