The Seed

· The Seeds develop from ovules after fertilization.

· A seed consists of a seed coat and an embryo.

· The embryo is made up of a radicle, an embryonal axis and one (wheat, maize) or two cotyledons (gram and pea).

Structure of a Dicotyledonous Seed:

• The outermost covering of a seed is the seed coat.

The seed coat consists of two layers:

· The outer testa

· The inner tegmen

• The hilum is a scar on the seed coat through which the emerging seeds were attached to the fruit.

• Above the hilum is a small pore called the micropyle.

Structure of dicotyledonous seed

• Inside the seed coat is the embryo, containing an embryonal axis and two cotyledons.

• The cotyledons are often fleshy and full of reserve food materials.

• At the two ends of the embryonal axis are present the radicle and the plumule.

Structure of dicotyledonous seed

• In some seeds such as castor the endosperm formed as a result of double fertilisation, is a food storing tissue.

• In plants such as bean, gram and pea, the endosperm is not present in mature seeds and such seeds are termed non-endospermous.

Structure of Monocotyledonous Seed:

• Normally, monocotyledonous seeds are endospermic but some are non-endospermic, as in orchids.

• In the case of seeds of cereals, like maize the seed coat is membranous and generally attached with the fruit wall.

• The endosperm is large and stores food and its outer covering separates it from the embryo by a proteinous layer called aleurone layer.

• The embryo is small and situated in a groove at one end of the endosperm.

• It consists of one large and shield shaped cotyledon known as scutellum and a short axis with a plumule and a radicle.

• The plumule and radicle are enclosed in sheaths which are called coleoptile and coleorhiza.

Structure of a monocotyledonous seed