A seed is a small embryonic plant enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the motherplant. The formation of the seed completes the process of reproduction in seed plants (started with the development of flowers and pollination), with the embryo developed from the zygote and the seed coat from the integuments of the ovule.The new seed formed in plant structures is called fruits.

Seed structure

A seed contains the embryo from which a new plant will grow under proper conditions. Seeds also usually contain a supply of stored food and is wrapped in the seed coat or testa. Seeds are very diverse in size. The dust-like orchid seeds are the smallest with about one million seeds per gram. The embryo has one cotyledon or seed leaf in monocotyledons, two cotyledons in almost all dicotyledons and two or more in gymnosperms. The radicle is the embryonic root. The plumule is the embryonic shoot. The embryonic stem above the point of attachment of the cotyledon(s) is the epicotyl. The embryonic stem below the point of attachment is the hypocotyl.In angiosperms, the stored food begins as a tissue called the endosperm, which is derived from the parent plant via double fertilization. The usually triploid endosperm is rich in oil or starch and protein. Seed functions
Seeds protect and nourish the embryo or baby plant. Seeds usually give a seedling a faster start than a sporling from a spore gets because of the larger food reserves in the seed.One important function of most seeds is delaying germination to allow time for dispersal and to prevent all seeds from germinating at once when conditions are favorable. Staggering germination prevents all seeds from germinating at once and being wiped out by bad weather or herbivores. Seed dormancy is defined as a seed failing to germinate under environmental conditions optimal for germination. It is often confused with seed quiescence, which is a seed failing to germinate because environmental conditions are inappropriate for germination. Many cultivated seeds lack dormancy but do not germinate in seed packets simply because there is insufficient moisture.

Economic importance
Many seeds are edible. The majority of human calories comes from seeds, especially from cereals, legumes and nuts. Seeds also provide most cooking oils, many beverages and spices and some important food additives.Seeds are used to propagate many crops such as cereals, legumes, forest trees, turfgrasses and pasture grasses.Some seeds are also poisonous. One of the deadliest poisons, ricin, comes from seeds of the castor bean. Another seed poison is strychnine. Other poisonous seeds are those of yew, wisteria, apple, horse-chestnut and peach.The world's most important clothing fiber grows attached to cotton seed. Other seed fibers are from kapok and milkweed.Many important nonfood oils are extracted from seeds. Linseed oil is used in paints.

Oil from jojoba and crambe are similar to whale oil.Seeds are the source of some medicines including castor oil, Tea Tree Oil (Melaleuca Oil) and the discredited cancer drug, Laetrile.Many seeds have been used as beads in necklaces and rosaries including Job's tears, Chinaberry and rosary pea. However, the latter two are also poisonous.