In the 1530s-1550s, anatomy and botany renewed their method based on direct observation of things and their position with respect to the Ancients based on the translation and critical edition of ancient treatises, in particular Galen and Dioscorides. Charles Estienne and André Vésale can serve as a touchstone for understanding the issues involved in reformed anatomy and botany. Following in the long tradition of Plato and Galen, Vesalius and Estienne advocated a unity of life between man and plant at the level of the natural faculty. Both practised botany and conceived of nutrition as a single form of life shared between plants and humans. Their conception of a univocity of life shared by plants and humans is rooted in an institutional context and based on a scientific method; but more fundamentally, it results from theoretical arguments that ground it in an ontology of life. Mots clés plant nutrition circulation analogy epistemic Domaines Philosophie