Senescence as an active developmental cellular process in the growth and functioning of a flowering plant, is indicated in :

Explanation

(c) : Senescence is the process of ageing which is caused by cellular breakdown, increased metabolic failure, increased entropy etc. It occurs in the period between reproductive maturity and death. Cell division followed by cell enlargement and differentiation, precede the actual separation. Senescence of cell in distal region lead to lignification of cell wall. Tylose formation in tracheary element and callose deposition in sieve elements which occur in advance of abscission (i.e. senescence) finally, lead to actual separation. Thus, vessels and tracheid (trachery elements) differentiation indicates senescence.