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The Epic Interactive Encyclopedia 1998
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Epic Interactive Encyclopedia, The - 1998 Edition (1998)(Epic Marketing).iso
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Xylem
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INFOTEXT
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1992-09-02
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A tissue found in vascular plants, whose main
function is to conduct water and dissolved
mineral nutrients from the roots to other
parts of the plant. Xylem is composed of a
number of different types of cell, and may
include long, thin, usually dead cells known
as tracheids, fibres, thin-walled parenchyma
cells, and conducting vessels. In most
flowering plants water is translocated
through the vessels. Most gymnosperms and
pteridophytes lack vessels and depend on
tracheids for water conduction. Non-woody
plants contain only primary xylem, derived
from the procambium, whereas in trees and
shrubs this is replaced for the most part by
secondary xylem, formed by secondary growth
from the actively dividing vascular cambium.
The cell walls of the secondary xylem are
thickened by a deposit of lignin, providing
mechanical support to the plant; see wood.