Abscission: (ab-ˈsi-zhən) The controlled separation of leaves, flowers, and fruit from plants.*
In autumn, leaves detach at the abscission zone, a layer of cells at the base of a leaf petiole, flower, or fruit stalk, the weakening of which causes the organ to separate from the plant.*
*Capon, B. (2005). Botany for gardeners (Revised ed). Portland: Timber Press.