Write short note.
Xylem: Xylem is the complex tissue as it consists of both parenchymatous and sclerenchymatous cells. It is composed of four elements:
(a) Tracheids: It is a non-living, elongated cell with tapering ends. The wall is highly thickened with lignin, except at certain circular spots known as pits.
(b) Vessel: It is a non-living cell with lignified walls. Tracheids and vessels are the main conducting elements in the xylem.
(c) Xylem parenchyma: It consists of living cell and performs the function of storage.
(d) Xylem fibre: It is a non-living, thick walled cell which provides mechanical support.