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( Ovule)
Ovule literally means "small egg." In seed plants, the ovule is the structure that gives rise to and contains the female reproductive cells. It consists of three parts The integuments forming its outer layer, the nucellus (or megasporangium), and the megaspore-derived female gametophyte (or megagametophyte) in its center. The megagametophyte (also called embryo sac in flowering plants) produces the egg cell for fertilization. After fertilization, the ovule develops into a seed. In flowering plants, the ovule is located within the actual flower, the part of the carpel known as the ovary, which ultimately becomes the fruit. Depending on the plant, flowers may have one or multiple ovules per ovary. The ovule is attached to the placental wall of the ovary through a structure known as the funiculus, the plant equivalent of an umbilical cord. Different patterns of ovule attachment, or placentation, can be found among plants In parietal placentation, the ovules are attached to the outer ovary wall, whereas in free central placentation, they are attached to a central column within the ovary. In axile placentation, they are attached to radial spokes within the ovary. In gymnosperms such as conifers and similar plants, the ovules are borne unenclosed on the surface of an ovuliferous (ovule-bearing) scale, usually within an ovulate cone (also called megastrobilus). The ovule is composed of diploid maternal tissue that gives rise to the haploid tissue of the female gametophyte. The maternal tissues of the ovule include the integuments and the nucellus. The next "generation" formed within the ovule are the haploid megaspore and megagametophyte, or embryo sac. After fertilization of the egg cell and formation of a zygote, the ovule contains the embryo of the next sporophyte generation and, in flowering plants, the triploid endosperm.
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