Morophogicslly, the seed is the integuments, mature, megasporangium, which is developed from fertilized ovule and contains an embryo. A seed may have 1 or 2 covering called seed coats- outer, thick, hard, testa and thinner, thin tegmen.
There are two types of seeds. The kernel may also contain endosperm, present in endospermic or albuminous seeds like cereal, castor, coconut, etc. in exalbuminous or non-endospermic seeds like gram, pea, mustard, etc, the endosperm is entirely consumed by the embryo.

1 Classification of seeds

There are one cotyledon in monocots and two cotyledons in dicots.
In some seed below the seed coat, a very thin membrane is found over kernel called perisperm. The embryonic axis differentiated into radical and plumule.
In monocot seeds, the radical is protected by a sheath called coleorhiza, and the coleoptile protects the plumule.

Figure: monocot seed

Seed