Qua corona usus, duplici colore foliorum geminos labores (superorum) inferorumque testatus est. See also Isidore of Seville, Etymologiae 17.4.45: "The white poplar is named because its leaves are white on one side and green on the other. It is therefore two-colored, having marks as if of day and night, which correspond to the times of the rising and setting of the sun" (translation by Priscilla Throop).
