A structure found in seed plants (gymnosperms
and angiosperms) that develops into a
seed after fertilization
of an egg-cell within it. In gymnosperms (conifers) the ovules are unprotected,
being borne on the inner surface of the female cone; in angiosperms (flowering
plants) the ovule is protected by the megasporophyll which forms a closed
structure (carpel) within which they form
singly, or in numbers. Each ovule is attached to the carpel wall by a stalk
or funicle which arises from its base (chalaza). A mature angiosperm ovule
consists of a central mass of tissue, the nucellus,
surrounded by one or two protective layers, the integuments, from which
the seed coat is ultimately formed. Integuments enclose the nucellus except
at its apex, where there is a small passage, the micropyle.
Within the nucellus is a large oval cell, the embryo sac developed from
a megaspore, containing the naked egg-cell.