Xylems

Xylems are the vascular tissues in seed plants that transport water and dissolved minerals from roots to leaves and shoots. They provide structural support through lignified cell walls.

Xylem is composed of hollow, dead cells called tracheary elements—tracheids and vessel elements—that form continuous tubes for water movement. Xylem also includes living xylem parenchyma and, in many species, sclerenchyma or xylem fibers that strengthen the tissue.

Development: Xylem originates from the plant's procambium in the embryo and primary growth; secondary xylem is produced by the vascular cambium during secondary growth, forming wood.

In angiosperms, vessel elements and tracheids conduct water; in gymnosperms, tracheids are predominant and vessels may be absent.

Transport mechanism: Water ascent follows the cohesion-tension theory, driven by transpiration and root pressure, with negative pressure pulling water upward through the conduits. Embolism can disrupt flow, but plants have mechanisms to restore function.

Ecology and uses: Xylem structure influences drought tolerance and hydraulic conductivity; the secondary xylem forms wood used in construction and industry, while xylem anatomy informs paleoclimate studies.