The stem makes up the largest parts of
some kinds of plants. For example, the trunk,
branches, and twigs of trees are all stems. Other
plants, such as cabbage and
lettuce, have such short stems and large leaves that they appear to have no stems at
all. The stems of still other plants, including
potatoes, grow partly underground.
Most stems suport the leaves and flowers
of plants. The stems hold these parts up in the
air so they can receive sunlight. Stems also
carry water and minerals from the roots to the
leaves, and they carry food from the leaves to
the other parts of the plant. The cells that
carry water make up what is called the xylem
tissue of a plant. Cells that transport food form
the plant's phloem tissue.
Stems that grow above ground
are called aerial stems, and those
underground are known as subterranean.
Aerial stems are either woody or herbaceous.
Plants with woody stems include trees and shrubs.
These plants are rigid because they contain large
amounts of woody xylem tissue. Most herbaceous
stems are soft and green because they contain
only small amounts of xylem tissue.
Many common flowers sprout from
underground stems. Some of these subterranean
stems are rootlike structures called bulbs,
corms, rhizomes, or tubers.
Jonquils, lilies, and tulips grow from bulbs,
crocus and gladiolus plants from corms. Many
grasses and wild flowers grow from rhizomes,
which are long and slender and spread
horizontally. Tubers, such as those of the
familiar potato plant, are shorter and thicker.
At the tip of each stem or twig
is a terminal bud. When these buds grow,
the plant grows taller. Other buds, called lateral
buds, form farther back along the stem. Some
of these buds grow into branches, and other
become leaves or flowers. The place at which a
lateral bud forms is called a node. Tiny
leaflike coverings known as bud scales
protect the growing ends of some buds.
World Book Encyclopedia
Chicago: World Book-Childcraft International,
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