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Bulb  [ Botany ]

Dictionary of botanic terminology - index of names

  A thick, rounded, underground storage organ consisting of layered, fleshy leaves and membranes.  
A bulb is an underground  stem, usually globular, containing a complete embryonic plant inside, with tiny flowers, stems, leaves, and roots. The contents of the bulb are often enclosed in protective, fleshy scales emerging from the top which are held together by a small basal plate. The scales are modified leaves that contain enough nutrients to sustain the plant through dormancy and early growth. The fleshy leaves are storage organ that store food and water, they may be loose and open. In many bulbs, a paper-thin tunic protects the scales. Fibrous roots emerging from the bulb's basal plate. Examples include the tulip, narcissus, and onion.
During the growing season; the upper part of the plant dies as the weather becomes cold or dry. The bulb remains dormant (living but inactive) underground until the weather warms and water is available. At the start of the new growing season, roots grow from the bottom of the bulb and a bud grows from the stem. The food and water in the bulb tissues nourish the fast-growing bud. The bud develops into a plant that will blossom (producing seeds above ground) and then die back (above the ground) at the end of the growing season; this cycle continues year after year. Many bulbs require a period of low-temperature dormancy before they sprout new buds and roots

Types of Bulbs:
There are two main types of bulbs. One type has a thin paper-like covering that protects its fleshy leaves (for example, the onion). The second type, called a scaly bulb, does not have a papery covering and looks as though it is composed of a group of angular scales (for example, the true lily).

See: storage organ




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