Tyepes of Xylum,Tracheids,Vessels or Tracheae,Xylem parenchyma,Xylem fibres,Primary xylem,Secondary xylem,Annular tracheids, Spiral tracheids,Reticulate tracheids,Pitted tracheids

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Home >> Biology >> Morphology and Anatomy of Flowering Plants >> Types of Xylum

Tyepes of Xylum
1. Tracheids
The tracheids are elongated, angular, lignified dead cells with tapering ends. Their walls are variously thickened for mechanical strength and for movement of water from one tracheid to another. Their types are
(a) Annular tracheids, Tracheids having thickenings in the form of ring.
(b) Spiral tracheids. Lignin is deposited in the form of a continuous spiral.
(c) Reticulate tracheids. In them the thickenings form a network.
(d) Pitted tracheids. In them the thickenings from a network.
(e) Pitted tracheids. The entire wall is uniformly thickened leaving small areas called pits.

In tracheids of angiosperms the pit cavity is uniform throughout its depth (simple pit) while in gymnosperms tracheids develops bordered in which the primary wall develops a small pad in middle called torus and the secondary wall overhangs the rim of the pit as a dome shaped border.

Annular	Spiral	Scalariform	Reticulate	Pitted
Types of Wall Thickenings in Tracheary Elements

Bordered Pits Shown in Surface and Sectional View

1. Border	2. Torus
3. Pit Aperture	4. Pit Membrane 5. Bordered Pit

2. Vessels or Tracheae
Vessels are similar to tracheids in structure and function. But unlike tracheids they are not one celled but are tube like structures containing a number of vessels joined end with their oblique walls dissolved. These are the characteristic of angiosperms.

3. Xylem parenchyma
These are parenchymatous cells which occur in xylem. They may be thin or thick walled. Xylem parenchyma store food and also assist in conduction of water.

4. Xylem fibres
These are sclerenchymatous fibers associated with xylem. They are lignified walls and provide mechanical support. Xylum is of two types. These are (a) Primary xylem (b) Secondary xylem.

(a) Primary xylem
This xylem develops from Procambium of root and shoot apex and the xylem element is called protoxylem. It consists of small tracheids and vessels.



Vessel Types

[A-B. wide with simple perforation plate, C. vessel with scalariform perforation plate, D-E. narrow vessels with simple perforation plate and tail either on both (D) or one (E) end F. a narrow vessel with reticulate perforation plate.]



Xylem Fibres and Parenchyma Cells

[A fibre tracheid. B. librifrom fibre. C. axial parenchyma cell. D, E. ray parenchyma cells.]

(b) Secondary xylem
Xylem which develops as a result of secondary growth is secondary xylem element is called metaxylem. It consists of large sized tracheids and vessels.

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Anatomy of Flowering Plants Tissue and Meristematic Tissue Classification of Meristematic Tissue Apical Meristems of Stem and Root Permanent Tissue Simple Permanent Tissue Complex Tissues - Xylem Types of Xylum Complex Tissues - Phloem Classification of Permanent Tissue on Basis of Their Functions Types of Vascular Bundles Anatomy of Monocot Stem - Maize, Primary Structure of Stem Anatomy of Dicotyledonous Stem - Sunflower Stem Secondary Growth in Dicot System Origin and Activity of Cambium Origin and Activity of Cork Cambium Heart Wood and Sap Wood Primary Structure of Monocot Root Primary Structure of Dicot Root Secondary Growth in Dicot Roots Origin and Activity of Vascular Cambium Origin and Activity of Cork Cambiums Internal Structure of Dicot Leaf Internal Structure of Xerophytic Leaf Internal Structure of Monocot Leaf - Isobilateral Leaf