The beginning of hormone research in the history of botany is discussed. Specific growth substances had been assumed to explain organ correlations in plants long before the term hormone was introduced into physiology. Progress in medical endocrinology did not initially have a particularly deep influence on physiology of plant development. Only a few botanists used the hormone concept without, however, having great resonance. Studies on phototropic responses led to the acceptance of growth regulating substances. But doubts arose if these plant (...) substances were comparable to animal hormones. For this reason the term 'phytohormone' is critically considered on the basis of Starling's classical hormone definition. (shrink)