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In seed plants, the ovule ("small egg") is the structure that gives rise to and contains the female reproductive cells. It consists of three parts: The integument(s) forming its outer layer(s), the nucellus (or remnant of the megasporangium), and female gametophyte (formed from haploid megaspore) in its center. The female gametophyte—specifically termed a ''megagametophyte''—is also called the embryo sac in angiosperms. The megagametophyte produces an egg cell (or several egg cells in some groups) for the purpose of fertilization. After fertilization, the ovule develops into a seed. == Location within the plant == In flowering plants, the ovule is located inside the portion of the flower called the gynoecium. The ovary of the gynoecium produces one or more ovules and ultimately becomes the fruit wall. Ovules are attached to the placenta in the ovary through a stalk-like structure known as a funiculus (plural, funiculi). Different patterns of ovule attachment, or placentation, can be found among plant species, these include:〔(Kotpal, Tyagi, Bendre, & Pande. Concepts of Biology XI. Rastogi Publications, 2nd ed. New Delhi 2007. ISBN 8171338968. Fig. 38 Types of placentation, page 2-127 )〕 *Apical placentation: The placenta is at the apex (top) of the ovary. Simple or compound carpel. *Axile placentation: The ovary is divided into radial segments, with placentas in separate locules. Ventral sutures of carpels meet at centre of ovary. Placentae along fused margins of carpels. Two or more carpels. (e.g. ''Hibiscus'', ''Citrus'', ''Solanum'') *Basal placentation: The placenta is at the base (bottom) of the ovary on a protrusion of the thalamus (receptacle). Simple or compound carpel, unilocular ovary. (e.g. ''Sonchus'', ''Helianthus'', Compositae) *Free-central placentation: Derived from axile, as partitions absorbed, leaving central axis ovules. Compound carpel, unilocular ovary. (e.g. ''Stellaria'', ''Dianthus'') *Marginal placentation: Simplest type. There is only one elongated placenta on one side of the ovary, as ovules are attached at the fusion line of the carpel's margins . This is conspicuous in legumes. Simple carpel, unilocular ovary. (e.g. ''Pisum'') *Parietal placentation: Placentas on inner ovary wall within a non-sectioned ovary, corresponding to fused carpel margins. Two or more carpels, unilocular ovary. (e.g. ''Brassica'') *Superficial: Similar to axile, but placenta on inner surface of multilocular ovary (e.g. ''Nymphaea'') In gymnosperms such as conifers, ovules are borne on the surface of an ovuliferous (ovule-bearing) scale, usually within an ovulate cone (also called megastrobilus). In some extinct plants (e.g. Pteridosperms), megasporangia and perhaps ovules were borne on the surface of leaves. In other extinct taxa, a cupule (a modified leaf or part of a leaf) surrounds the ovule (e.g. ''Caytonia'' or ''Glossopteris''). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「ovule」の詳細全文を読む スポンサード リンク
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