What do you understand by abscission ? How does it occur in plants?

Abscission is a natural separation or shedding of leaves, foliage branches, fruits, floral parts etc., from the plants.
(b) A special narrow zone develops in the area of abscission. It is called abscission zone. This zone is externally differentiated either by a shallow groove or by difference in colour of the surface
© Tyloses develop in xylem vessels while callose plugs develop in the area of sieve plates.
(d) Xylary tyloses reduce water supply to the organ causing water stress. As water stress increases, the callose plugs dissolve.
(e) The various nutrients present in the abscissing organ pass back into the plant.
(f) Two distinct layers develop in the abscission zone,
separation layer and protective layer.
(g) The protective layer is meant for dessication and
checking entry of pathways. Abscission occurs in the separation layer.