The physiology of plant hormones was one of the most dynamic fields in experimental biology in the 1930s, and an important part of T. H. Morgan's influential life science division at the California Institute of Technology. I describe one episode of plant physiology research at the institution in which faculty member James Bonner discovered that the B vitamin thiamin is a plant growth regulator, and then worked in close collaboration with the Merck pharmaceutical firm to develop it as a growth-boosting (...) agrichemical. This episode allows one to draw continuities between certain fields of life science in the United States circa 1940 and the biotechnology industry today, and also foregrounds a number of similarities between plant physiology of the late 1930s and the molecular biology of the period. (shrink)