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A thick, rounded,
underground
storage organ consisting
of layered, fleshy
leaves and
membranes. |
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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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