The analogy of human beings to plants is widespread in ancient medical and biological writing, clustering, in particular, in embryological texts. But the stakes of the analogy and what it makes visible are raised, as more attention is paid to vegetal life as an ontological category in Plato and especially in Aristotle: are we simply like plants, or are we, in some critical way, plants ourselves? In this chapter, I closely examine the plant analogy in the Hippocratic embryological writings and in Galen's embryological corpus. I argue that already in the Hippocratic material we can begin to see an interest in vegetal life as defined by the capacity to attract nutriment and, thus, to sustain life. In Galen, this self-nourishing form of life comes to define the human at the earliest stage of its development, even as the nature of plant life remains obscure.