The Seed

After fertilization, the ovules mature into seeds. A seed consists of two parts: a seed coat and an embryo. A radicle, an embryonal axis, and one (as in wheat, maize) or two cotyledons make up the embryo (as in gram and pea).

Structure of a Dicotyledonous Seed:

The seed coat is a seed's outermost coating. The outer testa and the inner tegmen are the two layers of the seed coat. The hilum is a scar on the seed coat that was used to adhere the developing seeds to the fruit.The micropyle is a tiny pore located above the hilum. The embryo, which consists of an embryonal axis and two cotyledons, is contained within the seed coat. The cotyledons are usually plump and rich in food reserves. The radicle and the plumule are located at the two ends of the embryonal axis. The endosperm developed as a result of multiple fertilization in some seeds, such as castor, is a food-storing tissue and is referred to as endospermic seeds.The endosperm is absent in mature seeds of plants such as beans, gram, and pea, and these seeds are referred to as non-endospermic.

Structure of Monocotyledonous Seed:

Monocotyledonous seeds are usually endospermic, but some, such as those found in orchids, are not. The seed coat of cereal seeds, such as maize, is membranous and usually united with the fruit wall. The endosperm is a thick substance that stores food. A protein layer termed aleurone separates the embryo from the endosperm's outer covering. The embryo is tiny and rests in a groove on one end of the endosperm. It consists of a scutellum, a big shield-shaped cotyledon, and a short axis with a plumule and radicle. Coleoptile and coleorhiza are sheaths that surround the plumule and radicle, respectively.

Figure 22: Structure of a dicot and monocot seed