page_title: Tissue (biology)
section_title: Xylem
hierarchical_section_title: Tissue (biology) / Plants / Permanent tissues / Complex permanent tissue / Xylem
caption_attribution_description: English: Cross section of 2 year old Tilia Americana, with xylem rays featured.
context_page_description: In biology, tissue is a cellular organizational level between cells and a complete organ. A tissue is an ensemble of similar cells and their extracellular matrix from the same origin that together carry out a specific function. Organs are then formed by the functional grouping together of multiple tissues.
  The English word "tissue" derives from the French word "tissu", meaning that something that is "woven", from the verb tisser, "to weave".
  The study of human and animal tissues is known as histology or, in connection with disease, as histopathology. For plants, the discipline is called plant anatomy. The classical tools for studying tissues are the paraffin block in which tissue is embedded and then sectioned, the histological stain, and the optical microscope. Developments in electron microscopy, immunofluorescence, and the use of frozen tissue-sections have enhanced the detail that can be observed in tissues. With these tools, the classical appearances of tissues can be examined in health and disease, enabling considerable refinement of medical diagnosis and prognosis.
context_section_description: Xylem consists of:
  Xylem tracheids
  Xylem vessel or trachea
  Xylem fibres or Xylem sclerenchyma
  Xylem parenchyma
  Xylem serves as a chief conducting tissue of vascular plants. 
  It is responsible for the conduction of water and mineral ions/salt. 
  Xylem tissue is organised in a tube-like fashion along the main axes of stems and roots. It consists of a combination of parenchyma cells, fibers, vessels, tracheids, and ray cells. Longer tubes made up of individual cells are vessels tracheids, while vessel members are open at each end. Internally, there may be bars of wall material extending across the open space. These cells are joined end to end to form long tubes. Vessel members and tracheids are dead at maturity. Tracheids have thick secondary cell walls and are tapered at the ends. They do not have end openings such as the vessels. The tracheids end overlap with each other, with pairs of pits present. The pit pairs allow water to pass from cell to cell.
  Though most conduction in xylem tissue is vertical, lateral conduction along the diameter of a stem is facilitated via rays. Rays are horizontal rows of long-living parenchyma cells that arise out of the vascular cambium. In trees and other woody plants, rays radiate out from the center of stems and roots and appear like spokes on a wheel in cross section. Rays, unlike vessel members and tracheids, are alive at functional maturity.
caption: Cross section of 2-year-old Tilia Americana, highlighting xylem ray shape and orientation.
exif: {"Image Orientation": "Horizontal (normal)"}