Describe a water conducting tisue ?

Explanation

Xylem is water conducting complex permanent tissue and is also called wood. Earlier formed xylem elements are small in size and re referred to as 'Protoxylem' . Later formed xylem elements are quite large in size and referred to as 'Metaxylem' . Xylem comprises of four elements. namely.
(a) Tracheids (b) Trachea / vessels. (c) Xylem fibres (d) Xylem Parenchyma.
(a) Tracheids :- These are elongated dead cells with tapering ends found in pteridophytes and gymnosperm. In cross section they may appear polygonal or rectangular in shape with lignigied walls. Lignification may be annular , spiral, scalariform , reticulate in shape type . Tracheids are comparatively longer than trachea and measure about 1 mm to 120 mm in length. They are arranged one above the other to form canals in the plant body for water conduction . They are also mechanical in function.
(b) Trachea (x. vessels) : They are found in most of the angiosperms. There are dead cells and are shorter and wider than tracheids. However xylem vessels in trees in trees such as quercus and eucalyptus measure upto 2 mts in length respectively.
Xylem vessels are arranged one above the other similar to water pipes for conduction of water. As a consequence, end walls are absent ot they may have perforated endwalls. Xylem vessels protoxylem , usually exhibits annual and spiral thickening . Among xylem vessels protoxylem usually exhibits annual and spiral thickening wherease metaxylem shows scalariform ,reticulate and pitted thickenings. Because of lignification they are mechanical in function.
(C) Xylem fibres : These are similar to those of sclernohyma fibres, but are associated with xylem. They provide mechanical support to the plant body.
(d) Xylem parenchyma : These are the parenchyma cells associated iwth xylem. They are also called a wood parenchyma.
These are compactly arranged. Xylem parenchyma extend into xylem vessels and appear like ballons. These balloon like structures are called tyloses. They hider the ascent of sap.