bulb, thickened, fleshy plant bud, usually formed under the surface of the soil, which carries the plant over from one blooming season to another. It may have many fleshy layers (as in the onion and hyacinth) or thin dry scales (as in some lilies)—both of which are highly modified leaves. Many popular outdoor and house plants, such as the tulip and the narcissus, are grown from bulbs, often out of their usual flowering season by forcing (i.e., by exposing them to a cold treatment). Not true bulbs, but often so called, are the corm of the crocus and the gladiolus, the tuber of the dahlia and the potato, and the rhizome of certain irises. All such organs are specialized subterranean stems serving for food and water storage and asexual reproduction.
See J. E. Bryan, Bulbs (1989).