The substance that triggers the fall of mature leaves and fruits from plants is due to
(a) auxin
(b) gibberellin
(c) abscisic acid
(d) cytokinin
Answer: C
Solution: Abscisic acid is a plant hormone that plays an important role under stress conditions. It promotes senescence of leaves and causes abscission of flowers and fruits by forming a layer of abscission. This layer disconnects the living tissue of leaf from the other parts.