[GPI]

A bulb is an underground vertical shoot that has modified leaves (or thickened leaf bases) that are used as food storage organs by a dormant plant.

A bulb's leaf bases generally do not support leaves, but contain food reserves to enable the plant to survive adverse conditions.
The leaf bases may overlap and surround the center of the bulb as with lilies, or may completely surround the inner regions of the bulb, as with the onion.
A modified stem forms the base of the bulb, and plant growth occurs from this basal plate.
Roots emerge from the underside of the base, and new stems and leaves from the upper side.

Other types of storage organs (such as corms, rhizomes, and tubers) are sometimes erroneously referred to as bulbs.
The correct term for plants that form underground storage organs, including bulbs as well as tubers and corms, is geophyte.
Some epiphytic orchids (family Orchidaceae) form above-ground storage organs called pseudobulbs, that superficially resemble bulbs.

Plants that form true bulbs are all monocotyledons, and include:

* Onion, garlic, and other alliums, family Alliaceae.
* Lily, tulip, and many other members of the lily family Liliaceae.
* Amaryllis, Hippeastrum, Narcissus, and several other members of the amaryllis family Amaryllidaceae.
* Two groups of Iris species, family Iridaceae: subgenus Xiphium (the "Dutch" irises) and subgenus Hermodactyloides (the miniature "rock garden" irises).



Corm

A corm is a short, vertical, swollen underground stem of a plant (usually one of the monocots) that serves as a storage organ to enable the plant to survive winter or other adverse conditions such as summer drought and heat (estivation).
A corm consists of one or more internodes with at least one growing point, and is typically surrounded by protective skins or tunics.
Inside, a corm is mostly starch-containing parenchyma cells.
Corms can be dug up and used to propagate or redistribute the plant (see, for example, taro).

Externally, they are often similar in appearance to bulbs, and erroneously called by that name, but internally their solid tissue easily distinguishes them from bulbs, which are visibly layered.

Cultivated plants that form corms include;

* Many plants of the family Iridaceae grown for their flowers, including Crocus, Gladiolus, Iris, and Montbretia
* Many plants of several families grown as root vegetables; see that article for a list.



Tuber

A tuber is a part of a rhizome thickened for use as a storage organ.
It is usually, though not always, subterranean, such as a potato. This modified stem forms at the end of a lateral branch.
Auxiliary buds are located at the nodes. When the buds develop, adventitious roots and rhizomes form below them.

This article is licensed under the GNU Free Documentation License http://www.gnu.org/copyleft/fdl.html It uses material from the Wikipedia article http://en.wikipedia.org/wiki/Bulb
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[Lilith]

I remember way back in high school, our biology teacher was talking about bulbs, and someone asked about potatoes. He told us they were tubers...turgid tubers, in fact. For some reason, that sent the whole class into hysterical fits of laughter. We were all laughing so hard, we were nearly in tears. Poor man was just dumbfounded.