Page 21 - Lesson Notes-Morphologyof flowering plant

and an embryo. The embryo is made up of a radicle, an embryonal axis and one
(wheat and maize) or two cotyledons (gram and pea).
Types of Seeds
Seeds can be classified into two different types based on the number of cotyledons
and presence or absence of endosperms, i.e., dicotyledonous and
monocotyledonous seed.
i.Dicotyledonous Seed
Gram seed is a dicot seed formed in a small pod or legume. The outermost covering
is the seed coat. An endosperm is absent.
Seed can be studied under two heads, i.e., external structure and internal structure.
It is light or dark brown in colour. Its surface may be smooth or wrinkled. A small
oval scar present at the side called hilum. It is the point where the stalk or funicle of
the seed is attached to it. A narrow ridge called raphae runs from hilum to chalaza
inside the furrow. A small pore called micropyle present between the hilum and
pointed end.
The outermost covering of the seed is seed coat. The outer hard and leathery layer
of the coat is called testa and the inner thin and membranous layer is the tegmen. In
some seeds, the tegmen and testa are fused.

The seed coat encloses the embryo, which is differentiated into a radicle, a plumule
and cotyledons. The radicle develops into root and plumule into shoot. Cotyledons
may be one or two to serve as reserve food.
Hypocotyl is a part present between the point of attachment of cotyledon and
radicle. Epicotyle is present between point of attachment of cotyledons and plumule.
In some seeds, such as castor seeds, the endosperm is formed as a result of double
fertilisation, which is a food storing tissue. In plants like bean, gram and pea, the
endosperm is not present in mature seeds (i.e., non-endospermous seeds).
ii- Monocotyledonous Seed
The monocotyledonous seeds are endospermic but some as in orchids are non-
endospermic. In the cereals, such as maize, the seed coat is membranous and
generally fused with the fruit wall.
Structure of Monocotyledonous Seed
The endosperm is bulky and stores food. The outer covering of endosperm
separates 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
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 respectively.