From Seed to Seed:
Stems are the aboveground structures that bear the plant's leaves and flowers. The stem provides a host of services to the plant:
Many familiar garden plants' stems are soft and green; these are called
stems. Examples include the stems of annuals
like impatiens and lettuce, and perennials such as hostas and lupine.
The stems of trees and shrubs also start out soft and green, but
become woody as they mature. (Recall our earlier discussion about secondary
growth producing wood.)
Stems contain vascular tissues-the "circulatory system" of the plant. Similar to our blood vessels, vascular tissues form an intricate network of veins that carry fluids throughout the plant. Large cells of the xylem (ZY-lem; Gr. xylon = wood) form a conduit for transporting water up from the roots. The smaller cells of the phloem (FLOW-em; Gr. phloos = bark) primarily transport sugars produced in the leaves, but are also involved in some water movement.
In herbaceous stems, the xylem and phloem are contained in vascular bundles.
A plant's shoot system consists of its aboveground stems, plus any branches and leaves.
Now let's put it all together...
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Copyright 2001, National Gardening
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