Thursday, 29 April 2021

Protoxylem lies towards the centre of the stem while metaxylem

 Protoxylem lies towards the centre of the stem while metaxylem



Protoxylem lies towards the centre of the stem while metaxylem occurs towards the side of cambium. Such a type of xylem is called éndarch xylem. Protoxylem has narrow small elements while metaxylem has larger and broader elements. Vessels occur in the form of a few radial rows. Tracheids occur in between the radial rows of vessels.

 Xylem fibres are also present here and there. Xylem parenchyma is present mostly towards the outer side of vascular strand. Xylem conducts water and mineral salts. Vessels and tracheids constitute the tracheary elements. However, most of the conduction is carried out by vessels.

 Tracheary elements of protoxylem have annular and spiral thickenings while those of metaxylem have pitted thickenings. Along with conduction of sap, the tracheary elements provide mechanical strength.

 Xylem fibres are purely mechanical in function. Xylem parenchyma stores food. It also helps in lateral conduction of sap. Medullary Rays : They are nonvascular areas present in between the vascular bundles. 

 They are made up of radially elongated Theychymatous cells. Cells are larger than those of cortex. Medullary rays take part in radial conduction of materials - food, water, (7) gases, etc. However, intercellular spaces are very few.

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