"Seed and fruit is potentially this and that kind of body," De anima, II, i, 11. The seed before animation is not dead matter: we are probably right in ascribing to it a certain lower form of life (Bödder, Psychologia Rationalis, nn. 557, 558, pp. 394, 395). But inasmuch as it has not yet the more perfect life of the creature that is born of it, St Thomas calls it, in reference to this life which is to follow. "only potentially alive."
Of God and His Creatures: 2.57