The tendency of a plant or animal to be attracted or repelled by an external stimulus, as of the sunflower in turning toward light, or of roots in turning away from light.

【生物】向性(动植物对外界刺激而起反应之倾向；如向日葵之向日及细根之避日；日用于复合字，表明刺激之性质；如thermotropism)。