What is seed ? Describe structure of dicotyledonous and monocotyledonous seed with diagram.

$\rightarrow$ Seed : The ovules after fertilisation develop into seeds.
$\rightarrow$ A seed is made up of a seed coat and an embryo.
$\rightarrow$ The embryo is made up of a radicle, an embryonal axis and one (as in wheat, maize) or two cotyledons (as in gram and pea).
$(a)$ Structure of a Dicotyledonous seed :
$\rightarrow$ The outermost covering of a seed is the seed coat.
$\rightarrow$ The seed coat has two layers, the outer testa and the inner tegmen.
$\rightarrow$ The hilum is a scar on the seed coat through which the developing seeds were attached to the fruit.
$\rightarrow$ Above the hilum is a small pore called the micropyle.
$\rightarrow$ Within the seed, coat is the embryo, consisting of an embryonal axis and two cotyledons. The cotyledons are often fleshy and full of reserve food materials.
$\rightarrow$ At the two ends of the embryonal axis are present the radicle and the plumule.
$\rightarrow$ In some seeds such as castor the endosperm formed as a result of double fertilisation, is a food storing tissue.

$\rightarrow$  In plants such as bean, gram and pea, the endosperm is not present in mature seeds and such seeds are called non-endospermous.

$(b)$ Structure of Monocotyledonous seed :

$\rightarrow$ Generally, monocotyledonous seeds are endospermic but some as in orchids are nonendospermic