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Early development of seed

The seed is developed from an ovule after fertilization. A seed is composed of a seed coat and an embryo. The embryo, which is a potential new plant is made up of a radicle, an embryonal axis bearing one (Monocotyledonous plants; E.g wheat, maize) or two cotyledons (Dicotyledonous plants; E.g pea).

The structure of a dicotyledonous seed:

The outermost covering of the seed, seed coat has two layers namely, the outer testa and the inner tegmen. On the seed coat, there is a scar called a hilum through which the developing seeds were attached to the fruit. Present above the hilum is a small pore called a micropyle.

The embryo is present within the seed coat along with the embryonal axis and two cotyledons. The cotyledons are often fleshy and full of reserve food materials. On either end of the embryonal axis, plumule and radicle are present.

In some plants such as castor, an endosperm is formed due to double fertilization. This endosperm functions as a food-storing tissue for the seed. However, the absence of endosperm in mature seeds of some plants renders them non-endosperm E.g bean, peas.

The structure of monocotyledonous seed:

The seed coat is membranous and generally fused with the fruit wall. The endosperm, usually present in monocotyledonous seeds is bulky and stores food reserves.

The outer covering of endosperm separated the embryo by a proteinaceous layer called the aleurone layer. The embryo is situated in a groove at one end of the endosperm.

In addition to this, the endosperm consists of one large, shield-shaped cotyledon called scutellum and a short embryonal axis with plumule and radicle on either side.

The plumule and radicle are enclosed in sheaths which are called coleoptiles and coleorhizae respectively.