Mention the post-fertilization changes that occur in a flower.

Hint:
Fertilization is the process by which the male gamete comes in contact with the female gamete. In angiosperms, the process is known as double fertilization, since one male gamete comes in contact with one ovum and the other one comes in contact with the polar nuclei to produce zygote and endosperm respectively. The process of fertilization is followed by various post-fertilization events.

Complete answer:
In angiosperm plants, the process of fertilization is followed by a series of events known as the post-fertilization events. Many changes take place in different parts of the flower, which facilitates the development of zygote.
Various major events which take place are as follows:
The accessory whorls of the flower, which are the sepals and petals.
The stamen of the female reproductive part falls off since the role of these whorls are limited for pollination.
The female gametophyte or ovule develops into the seeds, which encloses the fertilized zygote.
Later zygote gets developed into the embryo under constant division.
The endosperm is utilized by the zygote, and gradually decreases in amount. Ovules covered by the ovary of the flower enclosed in the pistil is retained.
And the ovary develops into the fruit.
The wall of the ovary gets converted into the pericarp, which provides a protective function to the fruit.

Note:
The embryonic development after fertilization involves different stages. The zygote is first divided into two cells named the basal and the terminal cells. The basal cell eventually gets developed into a structure called the suspensor, which functions as a connection to the parent tissue. It is a route of nutrition to the developing embryo from the parent tissue. The other cell known as the terminal cell gives rise to the pro embryo.