Editing Tissue (biology) (section)

==== Complex permanent tissue ====
The complex permanent tissue consists of more than one type of cells having a common origin which work together as a unit. Complex tissues are mainly concerned with the transportation of mineral nutrients, organic solutes (food materials), and water. That's why it is also known as conducting and vascular tissue. The common types of complex permanent tissue are:
* [[Xylem]] (or wood)
* [[Phloem]] (or bast).

Xylem and phloem together form vascular bundles.

===== Xylem =====
{{Anchor|Ray cell}}
[[Xylem]] (Greek, ''xylos'' = wood) serves as a chief conducting tissue of vascular plants. It is responsible for the conduction of water and inorganic solutes. Xylem consists of four kinds of cells:
* [[Tracheid]]s
* [[Vessel element|Vessels]] (or tracheae)
* Xylem fibers or Xylem sclerenchyma
* Xylem parenchyma

[[File:Xylem rays (Tilia Americana).jpg|thumb|right|Cross section of 2-year-old ''[[Tilia americana]]'', highlighting xylem ray shape and orientation]]

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 cellssels 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  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.{{cn|date=August 2022}} Rays are horizontal rows of long-living parenchyma cells that arise out of the vascular cambium.

===== Phloem =====
[[Phloem]] consists of:
* [[Sieve tube]]
* [[Companion cell]]
* Phloem fiber
* Phloem parenchyma.

Phloem is an equally important plant tissue as it also is part of the 'plumbing system' of a plant. Primarily, phloem carries dissolved food substances throughout the plant. This conduction system is composed of sieve-tube member and companion cells, that are without secondary walls. The parent cells of the vascular cambium produce both xylem and phloem. This usually also includes fibers, parenchyma and ray cells. Sieve tubes are formed from sieve-tube members laid end to end. The end walls, unlike vessel members in xylem, do not have openings. The end walls, however, are full of small pores where cytoplasm extends from cell to cell. These porous connections are called sieve plates. In spite of the fact that their cytoplasm is actively involved in the conduction of food materials, sieve-tube members do not have nuclei at maturity. It is the companion cells that are nestled between sieve-tube members that function in some manner bringing about the conduction of food. Sieve-tube members that are alive contain a polymer called callose, a carbohydrate polymer, forming the callus pad/callus, the colourless substance that covers the sieve plate. Callose stays in solution as long as the cell contents are under pressure. Phloem transports food and materials in plants upwards and downwards as required.