Reproductive structure in plants that consists of a plant embryo, usually accompanied by a supply of food (endosperm, which is produced during fertilization) and enclosed in a protective coat. Seed embryos contain one or more cotyledons. In typical flowering plants, seed production follows pollination and fertilization. As seeds mature, the ovary that enclosed the ovules develops into a fruit containing the seeds. Most seeds are small, weighing less than a gram; the smallest contain no food reserve. At the opposite extreme, the seed of the double coconut palm may weigh up to about 60 lb (27 kg). Seeds are highly adapted to transportation by animals, wind, and water. When circumstances are favorable, water and oxygen penetrate the seed coat, and the new plant begins to grow (see germination). The longevity of seeds varies widely: some remain viable for only about a week; others have been known to germinate after hundreds or even thousands of years.

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