Thimann, Kenneth V

Thimann, Kenneth V(ivian)

(born Aug. 5, 1904, Ashford, Kent, Eng.—died Jan. 15, 1997, Haverford, Pa., U.S.) British-born U.S. plant physiologist. He received his Ph.D. from Imperial College in London. In 1934 he obtained and isolated pure auxin, an important plant-growth hormone and, with several coworkers, proved that auxin promotes cell elongation, formation of roots, and growth of buds, discoveries that led to the development of a widely used synthetic auxin, 2,4-D. Use of this and similar chemicals can prevent the premature falling of fruit and stimulate cut stems to grow abundant roots; because high concentrations of auxins are toxic to most plants, synthetic auxins are also effective weed killers.