xylem and phloemBiology presentation9-fDone by : Rohan & jimit

Nature of XylemIt has Xylem parenchyma as only living part. Others are tracheids, vessels, xylem fibres which all are dead.

Nature of Xylema. Tracheids: Elongated cells with sloping walls enclosing a large empty cavity. The walls of trachieds are thickened by a complex chemical compound called lignin.

Nature of Xylemb. Vessels: Cylindrical tube-like

structures formed by a row of cells placed end to end. The transverse wall between the cells partly or almost completely dissolve to form a continuous channel or water pipe. These also have lignified walls.Trachieds and vessels are Named according to the Manner in which lignin has been deposited. E.g. annular, Spiral, scalariform

Nature of PhloemIt consists of sieve tubes,Companion cells, phloemparenchyma and which all are

living parts. Bast fibres alone are composed of dead cells.

Nature of Phloem1.Sieve tubes: Thin-walled

elongated cells placed end toend forming a slender tubular structure. Cytoplasm of one sieve element is continuous with other because of pores present at transverse end walls of cells. Nuclei is absent.

Nature of Phloemb. Companion cells: Theseare small in size, have dense cytoplasm and

a large elongated nucleus and are associated with sieve tubes.

It remains connected with companion cells by pores.

These are absent in ferns and gymnosperms(fir, cycas, pine)

c. Bast fibers: Sclerenchyma cells in phloem are Bast fibers. These alone are composed of dead cells.

d. Phloem Parenchyma: It is ordinary parenchyma. It is absent in monocot stems.

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Occurrence of xylem and phloem

xylem• In root, stem and

leaf of the higher plants. They occur together with phloem to form vascular bundle.

phloem

• Phloem is found in all parts of plant like roots, stems and leaves.

functions of xylem and phloem

xylem•Tracheids and vessels transport water and minerals upwards from the roots to the stem and leaves.

phloem•The sieve tubes are used for the longitudinal transmission of prepared food materials from the leaves to the storage organs and growing parts of plant.

functions of xylem and phloem

Older xylem tissue form the

wood and do

not take

part in conduc

tion. Their walls being

lignified, they give

mechanical

strength to the plant.

Phloem fibres

provide

mechanical

strength .

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