ovules

An ovule is a plant structure that develops within the ovary of a flower or on the scales of a gymnosperm cone and, after fertilization, becomes a seed. It contains a megasporangium (nucellus) surrounded by one or two protective integuments and is connected to the parent plant by a funiculus. The opening through which a pollen tube may enter is the micropyle.

During megasporogenesis, a megaspore mother cell undergoes meiosis to produce a haploid megaspore, which then develops into the female gametophyte (embryo sac in angiosperms). In most flowering plants the typical embryo sac is eight nucleate and seven celled, containing the egg cell, two synergids, three antipodal cells, and a central cell with two polar nuclei. Fertilization involves two sperm cells delivered by the pollen tube: one fuses with the egg to form a zygote, and the other fuses with the polar nuclei to form endosperm (double fertilization). In gymnosperms, the ovule generally contains a female gametophyte that serves as nutritive tissue for the developing embryo.

An ovule becomes a seed after fertilization; the integuments develop into the seed coat, and the nucellus is reduced or consumed as the embryo and other tissues mature. In gymnosperms the nutritive tissue is the megagametophyte rather than endosperm. The ovule is typically attached to the ovary wall by a funiculus, and its position within the ovary is determined by placentation (such as axile, parietal, or basal).

Function and significance: ovules enable sexual reproduction and genetic variation, giving rise to seeds that support dispersal and dormancy. They are central to agriculture, as seed formation underpins many crops.