The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
26. After that (there takes place) conjunction (of the soul) with him who performs the act of generation.
The conclusion arrived at under the preceding Sûtra is confirmed also by scripture stating that the souls, after having entered into plants, 'become' beings performing the
act of generation, 'for whoever eats the food, whoever performs the act of generation, that again he (the soul) becomes.' Here again the soul's 'becoming' he who performs the act of generation cannot be taken in its literal sense; for a person becomes capable of generation a long time after his birth only, viz. when he reaches puberty. How then should the soul contained in the food eaten enter into that condition in its true sense? Hence we must interpret the passage to mean only that the soul enters into conjunction with one who performs the act of generation; and from this we again infer that the soul's becoming a plant merely means its entering into conjunction with a plant.