Xylem
/ˈzaɪləm/
Definition
Xylem is the plant vascular tissue that carries water and dissolved minerals from the roots to stems and leaves. It also helps support the plant because many xylem cells have thick, lignified walls, meaning they are strengthened with a rigid woody material. Xylem occurs in roots, stems, and leaf veins, and differs from phloem, which transports sugars and other organic nutrients.
Biological Role
- Water movement to leaves: It carries water and dissolved minerals from roots to stems and leaves, supporting photosynthesis, cooling through transpiration, and the pressure that keeps many non-woody tissues firm.
- Support in woody plants: Its thickened cell walls add strength, especially in shrubs and trees. Much of what is called wood is largely xylem, so it is central to trunk and branch stability.
- Link to growth rings: In many temperate trees, new xylem produced each growing season forms visible annual rings. Ring patterns can reflect changing growing conditions such as moisture and temperature.
- Pathway for stress and disease: Blockage or damage can reduce water flow and cause wilting, dieback, or poor growth. Some vascular diseases spread through xylem, which helps explain fast decline in affected plants.