seed (Q1495)

A mature or ripened ovule containing an embryonic sporophyte and a nutritive tissue (endosperm or perisperm) with stored food that sustains the initial growth of the embryo upon germination, except when such food reserve is stored instead in the cotyledon(s) of the embryo itself, these enclosed by one or two integuments (the testa), the whole serving as a propagule. A fertile seed (one containing a viable embryo) normally results from sexual fertilization of an egg by a sperm; however, fertile seeds are sometimes produced asexually by apomictic processes (e.g., parthenogenesis).