What is the xylem of a tree?
What is the xylem of a tree?
The xylem, or vascular system (deciduous trees), or tracheid system (coniferous trees), is one of two types of transport tissue in plants, including trees. And it plays a crucial role in it transport of water and minerals from the roots to the rest of the plant. In the xylem there is a predominance of upward water transport and mineral transport.
The xylem consists of several types of specialized cells that work together to perform these essential functions.
When viewed in cross-section of a tree trunk, the xylem is located between it cambium and the center of the trunk. The cambium is a thin layer of actively dividing cells located just inside the bark (phloem).
The xylem forms the bulk of the wood mass of the trunk and extends from it cambium to the center of the trunk.
In this context, the xylem is the area that extends from just inside the cambium (the thin line separating the phloem from the xylem) to the central part of the stem. Including both the sapwood (younger xylem that is still active in transporting water) and the heartwood (older xylem that mainly provides structural support).
The young xylem is essential for transporting water and minerals from the roots to the leaves and other parts of the tree.
Composition of the xylem
The xylem consists mainly of the following cells and structures:
Tracheids (in conifers)
Elongated, dead cells with thickened cell walls and tapered ends. They are present in all vascular plants and are the primary water-conducting cells in most conifers.
Barrels or Barrel Elements (on deciduous trees)
These cells combine to form long tubes that efficiently transport water and dissolved minerals. They are characteristic of deciduous trees (angiosperms) and some gymnosperms.
Wood fibers
These provide structural support to the tree. Although they are not primarily involved in water transport, they contribute to the strength of the xylem tissue.
Parenchymal cells
Living cells in the xylem involved in the storage and lateral transport of nutrients and water within the xylem tissue.
Tip: read what it is difference between xylem vessels and tracheids.
Functions of the xylem
Water and mineral transport
The main function of the xylem is transporting water and dissolved minerals, which are absorbed from the soil, from the roots to the leaves and other parts of the tree.
This upward transport is driven by transpiration in the leaves, during which water evaporates and exits through the stomata. This creates a negative pressure, which helps to draw the water up through the xylem. And enables trees to transport water and nutrients from the ground to great heights.
This transport is essential for photosynthesis, growth, and other metabolic processes in the tree.
Structural support
The xylem contributes to the structural integrity of the tree. The thickened cell walls of tracheids and wood fibers provide strength and resistance to gravity and mechanical stress.
Storage
Although not the primary function, the parenchyma cells within the xylem can serve as storage sites for starch and other nutrients.
Wood formation
The xylem is also responsible for the formation of wood in trees. As the xylem tissue matures and its function for water transport decreases, it becomes part of the heartwood of the tree, which contributes to the thickness growth of the trunk and branches.