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Xylem

Xylem is a water-conducting tissue in plants, first introduced by Nageli in 1858. It consists of various cell types, including tracheary elements (tracheids and vessel members), fibres, and parenchyma cells, which perform functions such as support and food storage. There are two types of xylem based on development: primary xylem from procambium and secondary xylem from vascular cambium.

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Xylem Farah Naz #19 Life Sciences IUB
Xylem • Term introduce by Nageli(1858). • Greek xylos meaning wood.
• A group of cells which are similar in Origin and function but of more than One type in structure.
Functions of xylem • Water conducting tissue • Along with phloem make vascular tissue • Provide support to plants
Elements of xylem • 1)Tracheary elements These are nonliving cells, provide support and conduct water. Two types, (a)Tracheids: elongate, tube like cell, tapering, rounded or oval ends, hard lignified walls. (b)Vessels members: long, cylindrical, tube-like structures with lignified walls.
Elements of xylem • (2)Fibres: thick walls, evolve from tracheids and provide mechanical strength. Two types, • (a)Fibre-tracheids: medium thickness walls, have reduced boardered pits. • (b)Libriform fibres: very thick walls, have reduced simple pits.
Elements of fibres • Parenchyma cells: living cells, in woody plants, store of food in starch form. Two types: • (a)Axial parenchyma: derived from fusiform initials, have tracheary elements and fibres. • (b)Ray parenchyma: derived from ray initials of cambium, xylem ray cells.
Types of xylem • Developmentally, xylem have two types • (1)Primary xylem: derived from procambium, developing from embryo, non-woody plants. • (2)Secondary xylem: from vascular cambium, second stage of plant development, in woody plants.
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