Plant tissue culture, introduced unsuccessfully at the beginning of the twentieth century by Haberlandt, received full confirmation in the late Thirties by the works of Gautheret and Nobécourt, thanks to the discovery of auxin. A further special improvement--the free cell culture--, already fore-told by Haberlandt, was successfully achieved towards the mid-1950s by several physiologists thanks to coconut milk (cytokinin). The English physiologist Frederick Steward (who grouped an excellent American team of research during his twenty years stay at the Cornell University in Ithaca) was able to obtain complete cell differentiation from single cells cultured in vitro and demonstrate the totipotence of plant cells at any stage of development. The historical meaning of the research of Steward's team, accomplished between 1958 and 1970, rests on the concept of plant hormones as regulators of gene activity. In other terms, organogenesis was conceived as an epigenetically controlled series of events in which plant genes were "switched on" or "switched off" by special biomolecules. Steward's research paved the way for molecular plant physiology and inspired future research on the relation between cell receptors and specific hormones.