Like a true bulb, a corm is a stem base--but its tissue is solid, without scales. Roots grow from a basal plate at the bottom of the corm; the growth point is at the corm's top. Gladiolus and crocus are two familiar corms.
Each corm lasts for a single year. As it shrinks away after blooming, a new corm forms on top of it; many small increases, called cormels, may also be produced around the new corm's basal plate.