Explain the various Xylem elements.

Xylem is a complex tissue of plants, which means that it includes more than one type of cell.

Tracheids are the chief water-conducting elements in gymnosperms and seedless vascular plants. They can also be found in angiosperms. Tracheids are elongated cells, closed at both ends. Their ends are tapering. The walls of tracheids are opened by numerous pits that are, either round, oval, gap- or groove-shaped. Water passes from cell to cell via pits.

 

Vessels are the chief water-conducting elements of angiosperms. Vessels are generally thought to be more efficient water conductors than tracheids. Vessels are very long tube-like structures formed by a row of cells placed end to end. The length of the single tube can be as long as several meters. Vessels are marked by characteristically structured secondary wall coatings (lignin) at the inner surface of the primary walls. Vessels are shorter and wider than tracheids.

 

Xylem parenchyma is the only living xylem element. It stores food and helps in sideways conduction of water. 

Xylem fibres are mainly supportive in function. Xylem fibres can be regarded as derivatives of tracheids. Their walls are more stable than those of the tracheids.