Which tissue in trees carries water upward from roots to leaves? Xylem is the vascular tissue that transports water and dissolved mineral nutrients upward from roots to stems and leaves.
Xylem forms a continuous network through a tree. Its main conducting cells, vessels and tracheids, are typically dead when mature, leaving hollow or interconnected pathways through which xylem sap can move. The tissue also provides structural support; much of the wood in a tree is secondary xylem.
The principal driving force is transpiration. As water evaporates from leaf surfaces, cohesion between water molecules and adhesion to xylem walls help pull an unbroken column of water upward. Root pressure and capillary effects can contribute, but the tree does not pump water upward with a heart-like organ.
Xylem is commonly confused with phloem. Xylem mainly carries water and inorganic ions from roots toward the canopy, while phloem distributes sugars and other organic substances made by photosynthesis. The word xylem comes from the Ancient Greek word for wood, and botanist Carl Nägeli introduced the term in 1858.