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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 cormcorm,
short, thickened underground stem, usually covered with papery leaves. A corm grows vertically, producing buds at the upper nodes and roots from the lower surface. Corms serve as organs of food storage and in some plants (e.g.
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 of the crocus and the gladiolus, the tubertuber,
enlarged tip of a rhizome (underground stem) that stores food. Although much modified in structure, the tuber contains all the usual stem parts—bark, wood, pith, nodes, and internodes.
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 of the dahlia and the potato, and the rhizomerhizome
or rootstock,
fleshy, creeping underground stem by means of which certain plants propagate themselves. Buds that form at the joints produce new shoots.
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 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).



a modified, usually subterranean shoot with a greatly shortened stem and fleshy scalelike leaves.

Bulbs store water and nutritive substances (primarily sugars); they are also a means of vegetative renewal and reproduction. In some plant species, bulblets develop in the inflorescences (onions and meadow grasses) or in the leaf axils of aboveground shoots (lilies and toothworts). Bulbs can function as storage organs for approximately one year (annual bulbs of tulips, onions, and fritillary) or longer (perennial bulbs of narcissus, snowdrop, and hyacinth). After their nutrients have been used, dry scales form protective outer coverings. Scaly bulbs have narrow scales that touch the bulb only at their bases (lilies); tunicated bulbs have broad enwrapping scales (onions).

According to the manner of growth, two types of bulbs are distinguished. Monopodial, or intermediate, bulbs renew themselves at the expense of the terminal bud of the bulb stem (snow-drop, narcissus, and belladonna lily). In plants with sympodial, or determinate, bulbs, the inflorescence and aboveground parts develop from the terminal bud, but the bulb regenerates at the expense of the bud located in the axil of a scale (tulips, onions, and hyacinths). In sympodial bulbs the mother bulb is replaced annually by daughter bulbs. If not one but two or more buds are active, the bulb reproduces vegetatively. In garlic plants several cloves form in the axils of the bulb scales and are arranged in a row, thus constituting complex bulbs.



A short, subterranean stem with many overlapping fleshy leaf bases or scales, such as in the onion and tulip.


In lighting, see lamp bulb, light bulb.


1. a rounded organ of vegetative reproduction in plants such as the tulip and onion: a flattened stem bearing a central shoot surrounded by fleshy nutritive inner leaves and thin brown outer leaves
2. a plant, such as a hyacinth or daffodil, that grows from a bulb
3. See light bulb
4. a rounded part of an instrument such as a syringe or thermometer
5. Anatomy a rounded expansion of a cylindrical organ or part, such as the medulla oblongata
6. Nautical a bulbous protuberance at the forefoot of a ship to reduce turbulence
References in periodicals archive ?
Photographer James Morgan who came up with the idea, backed by Cunard, to put Captain Oprey on the bulbous bow said safety was paramount, with two safety craft standing by during the photo-shoot, but he remained sure-footed throughout.
Other comet grains came apart when they hit the gel, creating a bulbous hole at the surface before narrowing to a turnip shape.
Their bulbous ends are filled with carbon monoxide.
Plant bearded, beardless and bulbous irises in prepared sites.
The Miami building--a white-and-blue box that might otherwise be mistaken for a warehouse, except for the bulbous antennae and satellite dishes on the roof--is Terremark's hub.
The trail looks like it's on Mars, and we follow a dotted white line up and over the bulbous rock formations, often on the very edges of white-knuckle precipices.
While the Cardinals Stadium's unique bulbous exterior borrows from the barrel cactus, a fixture of the surrounding desert landscape, the naked steel lattices and skeletal framework of the NYSCC bears a purposeful resemblance to a prominent fixture on the West Side waterfront: the George Washington Bridge.
Inside their containers, bulbous, dismembered feminine bodies hung in space to evoke "the future of mannequins," according to one dude who smoked incessantly beside me, banging on a bongo.
On the other hand, there is the case of the Chevy SSR Concept, which was translated fairly undiminished into the SSR production vehicle, the retro-truck with the bulbous, curvaceous surfaces: "The concept vehicle for the SSR was done in a computer.