This chapter examines the use of vegetal analogy in late Renaissance physiology through the case of the German physician Daniel Sennert. It is centered on Sennert’s explanation of generation, in particular the transmission of life through the vegetative soul within the seed, as developed in his early works on medicine and alchemy, the _Institutionum medicinae libri V_ and _De chymicorum…liber_. This chapter first summarizes Sennert’s account of generation and the seed’s “formative force” according to Aristotle and Galen, as well as his appraisal of the medical debates on the origin of the seed’s soul and form. Then, the next part explores Sennert’s own interpretation of the origin of forms, for which plant physiology served as a common denominator of his medical, alchemical and theological inclinations. Finally, this chapter considers how Sennert attempted to harmonize his reasoning with the Paracelsian account of generation, seed and life.