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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).

The Columbia Electronic Encyclopedia™ Copyright © 2013, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



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.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


A short, subterranean stem with many overlapping fleshy leaf bases or scales, such as in the onion and tulip.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


In lighting, see lamp bulb, light bulb.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.


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
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
References in periodicals archive ?
These hair strands act as conductors to allow light to pass through and penetrate deep into the skin to zap hair bulbs, connective tissues and stem cells.
A new set of primers that allows amplification of a larger DNA fragment, associated to a hot-start PCR reaction, resulted in an efficient amplification from a single hair bulb added directly to the PCR mix.
The color comes from a pigment called melanin (mel-a-nin) which is produced by special cells in the hair bulb. This bulb lies inside the follicle (fol-li-cle), a tiny pit buried deep inside your scalp.
The outer root sheath varied from a single to double layer of cells just above the hair bulb. In sections where it consisted of a double layer, more peripheral cells presented with oval shaped nuclei, while the cells in direct contact with the inner root sheath had flattened nuclei (Figures 1(b), 1(d), and 1(f)).
Hair bulb melanocytes were situated in the basal region of the hair matrix, resting on a basement membrane which separates it from the dermal papilla, as in a general description of the mouse by Boissy [8].
Human anagen scalp hair bulbs were examined by light microscopy to investigate the anatomical effects of mechanical plucking [9].
Histopathologically hair shafts hair bulbs and sebaceous and sweat glands were observed in the epidermis and dermis of the choristoma.
Melanocytes, melanin granules, hair bulbs, adipose tissue and sebaceous glands were observed in corneal epithelium and propria histopathologically.
Hair bulbs have been suggested as a reservoir for beta-HPVs (15), and this may also be true for MCPyV.
The cells in the skin's dermal layer, where hair bulbs lie buried, sometimes become cancerous.
The student wanted to try applying a certain fluorescent staining technique, which Wells originally developed for looking at the cells of human hair bulbs, to the hairs on plant stems.
L'Oreal researchers also studied how African hair forms curls by growing in vitro cultures of isolated hair bulbs. They made a surprising discovery: The same hair shaft contains two different genetic programs.