Development and Structure of Seed

Development and Structure of Seed:

After fertilization in the female gametophyte, zygote divides repeatedly by mitosis and develops into an embryo. At this stage, ovule changes into seed. The formation of seed completes the process of sexual reproduction in seed plants.

Angiosperm seeds consist of three distinct parts;(1) the embryo formed from zygote, (2) the endosperm tissue formed from endosperm nucleus, and (3) the seed coat which develops from the wall of ovule.

Seed coat develops from the integument, originally surrounding the ovule. It may be a paper-thin layer or thick and hard. Seed coat protects embryo from mechanical injury and from drying out. There is a scar on seed coat, called hilum. It is where the seed is attached to ovary wall. At one end of hilum, there is micropyle. This is the same opening through which the pollen tube entered ovule. Seed uses it for the absorption of water.

Embryo is actually an immature plant. It consists of a radical, a plumule and one or two cotyledons. The radical of embryo develops into new root while the plumule develops into new shoot. The embryonic stem above the point of attachment of cotyledon is called epicotyls. The embryonic stem below the point of attachment is hypocotyls. With is seed, there us as tore of nutrients for the seeding that will grow from embryo. In angiosperms, the stored food is derived from the endosperm tissue. This tissue is rich in oil or starch and protein. In many seeds, the food of the endosperm is absorbed and stored by cotyledons.