What Are The Cell Types In Xylem And Their Functions

Xylem is a complex tissue composed of four main cell types. The first two are the primary water-conducting cells.

1. Tracheids: These are long, thin, spindle-shaped cells with tapering ends. They are dead at maturity and have thick, lignified walls. Water does not pass through an open tube but moves from cell to cell through small, thin areas in the wall called pits. Tracheids are found in all vascular plants and also provide structural support.
2. Vessel Elements: These are shorter, wider, barrel-shaped cells. Like tracheids, they are dead at maturity and lignified. They are stacked end-to-end to form a continuous, hollow tube called a vessel. Their end walls, called perforation plates, are partially or completely dissolved, allowing for a much more efficient, lower-resistance flow of water. These are the main water-conducting cells in angiosperms (flowering plants).
3. Xylem Fibers: These are long, slender cells with extremely thick, lignified walls. They are also dead at maturity. Their primary function is not water transport but structural support for the plant, adding strength and rigidity.
4. Xylem Parenchyma: These are the only living cells found in xylem. They are standard plant cells with thin walls, a nucleus, and cytoplasm. Their functions include storage (of starches and fats) and lateral (sideways) transport of water and minerals within the stem or root.