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BOTANY Higher Secondary Second Year - Textbooks Online

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Tracheid<br />

conducting elements in angiosperms and they are absent in pteridophytes<br />

and gymnosperms. However, in Gnetum of gymnosperms, vessels occur.<br />

The main function of vessel is conduction of water and minerals.<br />

It also offers mechanical strength to the plant.<br />

Xylem fibres<br />

Bordered pit<br />

The fibres of sclerenchyma associated with the xylem are known as<br />

xylem fibres. They give additional mechanical support to the plant<br />

body. They are present both in primary and secondary xylem. Xylem<br />

fibres are dead cells and have lignified walls with narrow lumen. Xylem<br />

fibres are also called libriform fibres.<br />

Xylem parenchyma<br />

Vessel<br />

Bordered pit<br />

Simple pit<br />

Cytoplasm<br />

Nucleus<br />

Fig. 2.6. Kinds of xylem cells<br />

The parenchyma cells associated with the xylem are known as xylem<br />

parenchyma. Xylem parenchyma is the only living tissue amongst the<br />

consituents of xylem. The cell wall is thin and made up of cellulose. The<br />

xylem parenchyma cells store food reserves in the form of starch and<br />

fat. They also assist in conduction of water.<br />

75<br />

Xylem<br />

parenchyma<br />

Simple<br />

pit<br />

Xylem fibre

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