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Lignin fills the spaces in the cell wall between cellulose, hemicellulose, and pectin components, especially in vascular and support tissues: xylem tracheids, vessel elements and sclereid cells. [citation needed] Lignin plays a crucial part in conducting water and aqueous nutrients in plant stems.
Xylem also contains two other type of cells: parenchyma and fibers. [7] Xylem can be found: in vascular bundles, present in non-woody plants and non-woody parts of woody plants; in secondary xylem, laid down by a meristem called the vascular cambium in woody plants; as part of a stelar arrangement not divided into bundles, as in many ferns.
Lignin has also been shown to prevent the infection of cells. Plant cells will increase the production of lignin generating enzymes when stressed by some pathogens, further lignifying the secondary cell wall. Increased lignin content is particularly effective at resisting vascular pathogens that use the secondary xylem to spread. [9]
Sclerenchyma is the tissue which makes the plant hard and stiff. Sclerenchyma is the supporting tissue in plants. Two types of sclerenchyma cells exist: fibers cellular and sclereids. Their cell walls consist of cellulose, hemicellulose, and lignin. Sclerenchyma cells are the principal supporting cells in plant tissues that have ceased elongation.
Casbury pointed out that this structure may be composed of lignin or suberin. Later scholars mostly thought it was suberin. [21] It was not until the 1990s that after analyzing the Casparian strip of several plants, it was found that lignin was the main component, but many textbooks have not been updated. [4]
Wood is primarily composed of xylem cells with cell walls made of cellulose and lignin. Xylem is a vascular tissue which moves water and nutrients from the roots to the leaves. Most woody plants form new layers of woody tissue each year, and so increase their stem diameter from year to year, with new wood deposited on the inner side of a ...
Between the xylem and phloem is a meristem called the vascular cambium. This tissue divides off cells that will become additional xylem and phloem. This growth increases the girth of the plant, rather than its length. As long as the vascular cambium continues to produce new cells, the plant will continue to grow more stout.
A tracheid is a long and tapered lignified cell in the xylem of vascular plants. It is a type of conductive cell called a tracheary element. Angiosperms use another type of conductive cell, called vessel elements, to transport water through the xylem.