Germination is the onset of growth of the embryo, usually after a period of dormancy. There are two types of germination according to whether or not the cotyledons grow above ground or remain below it. In epigeal germination the hypocotyls (or part of the shoot axis just below the cotyledon elongates, and the cotyledons are carried above the ground. In hypogeal germination the internodes just above the cotyledons (the epicotyl) elongates, then the cotyledons remain below ground. Epigeal germination occurs in castor, groundnut and cowpea plants, hypogeal germination occurs in maize, grain seed, yam bean etc.