Embryology

It is one of the branches of biology which deals with the formation and development of the embryo.

The events from initiation of the flower buds to be full development of the embryo are generally considered under embryology.

In the earlier stages of embryo development there is no fundamental difference between monocotyledons and dicotyledons. Ultimately, the embryo germinates and produces a new individual.

The zygote divides first by a transverse wall into two cells, the upper cell or the cell lying towards the micropylar end known as suspensor cell while the other cell is known as the embryonal cell. The embryonal cell takes part in the formation of an embryo while the suspensor cell gives rise to suspensor. The suspensor cell divides transversely and the embryonal cell divides longitudinally resulting in a proembryo composed of four cells. The four celled proembryo undergoes further division so as to form eight cells or octants. Out of the eight cells, four cells away from the suspensor give rise to plumule and the two cotyledons, the other four cells give rise to hypocotyl. The lowest cell of the suspensor divides to give rise to the radicle.

The primary endosperm nucleus (PEN) starts dividing even before the zygote nucleus divides. There are three types of endosperm formation.

Nuclear type

In this type of endosperm, the PEN undergoes repeated division and produces numerous free nuclei. The nuclear division is not followed by wall formation.

Cellular type

In this type of endosperm, the nuclear divisions are followed by wall formation with the result that the embryosac may have several chambers. Some of the chambers may have more than one nucleus.

Helobial type

This is an intermediate type of endosperm formation between the nuclear and cellular types. In this, the first division is accompanied by wall formation but the subsequent divisions are nuclear.