Seed - Function, Structure and Types

A seed is a reproductive part of a flower. It is developed from a fertile ovule. It encloses embryo and stores food for its development. A seed is the ripened ovule which contains an embryo and its food source is covered by a protective coat. Seeds are the product of the ripened ovule, after fertilization by pollen and some growth within the mother plant. Under suitable conditions seed germinates and gives a baby plant. 

Function of Seed

a) A seed takes part in germination as a result a new young plant is produced.

b) The cotyledons of seeds store the food materials and helps in the germination of seeds.

c) Seed often contains large amount of reserve food such as starch, oil, proteins and fats.

Structure of Seed

A typical seed is differentiated into a protective covering seed coat and embryo. The seed coat is differentiated into outer thick testa and the inner thin larger tegmen. Testa has a tiny aperture called the micropyle. Micropyle allows the entry of water into the seed. An embryo is defined as a young miniature plant enclosed within the seed coat. The embryo of a mature seed consists of cotyledon and embryo axis. Embryo axis is the young or mature plant differentiated into radical, plumule, mesocotyl, hypocotyl and epicotyl. 

Radical is present at the lower side of embryonic axis and later it develops into a root system. Plumule is at the upper side of the embryonic axis and it develops into a shoot system. Cotyledons are also called seed leaves. They are either two (in dicotyledonous plant) or one (in monocotyledon plant) in number. Cotyledons are leaf like structures which generally store food and supply it to the developing embryo at the time of germination of the seed. On one side of the seed is a scar called hilum. It represents the point of attachment of the seed with its stalk. The region between the radical and the plumule below the point of attachment of the embryo to the cotyledon is known as the hypocotyls. The region above this point is the epicotyls.

Types of Seed                                 

There are 2 types of seeds.

a) Monocotyledon: The seed having only one cotyledon are called monocotyledon. For example; rice, wheat, maize, etc.

 b) Dicotyledonous:  The seed having two cotyledons are called dicotyledonous. For example, pea, bean, gram, mango, etc.