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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 ?
Identification of TLC profile of ethanol extract 70 % of Dayak onion bulbs showed Rf value varied to 0.10, 0.28, 0.44, and 0.87.
Also, Hansen [8] reported reductions in amino acid content of onion bulbs as the plant ages.
asperellum 47.73 (c) (*) Means with different superscript are significantly different at 5% level of significance using DMRT Table 3: Percent growth inhibition of crude extracts of Trichoderma species Crude extract concentration ([micro]l/ml) Growth inhibition (%) TA100 9.23 (e) TA500 24.40 (a) TA1000 8.69 (e) TL100 9.00 (e) TL500 14.49 (c) TL1000 12.00 (d) TH100 11.22 (d) TH500 15.58 (b) TH1000 11.53 (d) (*) Means with different subscript are significantly different at 5% level of significance Table 4: Disease severity of the onion bulb Treatments Mean of Lesions Grading Control (uninoculated and untreated) (mm) Scale C.
Onion bulb formation is the most common change in CMT1A [10-13].
Table II.-Impact of plant spacing on thrips population, onion bulb weight, yield/plot and yield/hectare in onion field plots.
Once onion bulbs begin to form, ample watering can help dilute the flavor compounds in the onions, resulting in a milder taste.
* to abridge the gape of poverty through introducing the most promising and economically feasible intervention like maintenance of recommended plant population of certified onion bulb seed, one of the effective and possibly successful agriculture venture considered as a case study in Malakand Division.
Scallions, or green onions, are simply immature yellow onion bulbs. Chives may have always grown wild.
Fronting Brias' algae-like screen are Gonzales' onion bulb lamps, made of paper and arurog for Roche Bobois.
The pathogen infects the basal stem plate of the onion bulb and degrades it ultimately kills the whole plant (Cramer 2000).