Write the changes a fertilized ovule undergoes within the ovary in an angiosperm plant.

Explanation

Immediately after fertilization the secondary nucleus starts developing into a triploid endosperm while the zygote starts developing into embryo. The integuments form the seed coat. The zygote divides only when certain amount of endosperm is formed. This is an adaptation to provide assured nutrition to the developing embryo. The first division of zygote is transverse and produces hypobasal cell towards micropyle and epibasal cell or embryo cell towards the chalaza.The hypobasal and the remaining cells constitute the suspensor which pushes the embryo into the endosperm to receive nutrition for the development of embryo. The first cell of the suspensor towards the micropylar end becomes swollen and functions as a haustorium. The last cell of the suspensor at the end adjoining the embryo is called as hypophysis which gives rise to the radicle. The epibasal cell or embryo cell undergoes two vertical divisions and one transverse division to form eight cells which are arranged in two tiers epibasal (terminal) and hypobasal (near the suspensor). The epibasal cell forms the two cotyledons and the plumule. The hypobasal cells produce the hypocotyl except its tip. Embryo depicts globular, heart shaped and ultimately torpedo shaped structures. The various stages of development of embryo are depicted in diagrams drawn below: