Vascular bundles (fascicles) are the component of the stelar system in higher plants and their main function is the conduction of water, minerals and food materials. Typically the vascular bundle composed of xylem and phloem arranged together as bundles. In a young stem, both in dicots and monocots, the xylem of vascular bundles are differentiated into PROTOXYLEM and METAXYLEM based on the structural and functional difference of their elements. The present post describes the similarities and differences between Protoxylem and Metaxylem in a primary vascular bundle of a young stem.
Similarities between Protoxylem and Metaxylem
Ø Both protoxylem and metaxylem can conduct water and minerals.
Ø Both components contain living and dead cells.
Ø Both are developed from the primary meristem, the pro-cambium.
Ø Both contain tracheids, vessels and parenchyma.
Ø Protoxylem and metaxylem develop only in primary vascular bundles.
Differences between Protoxylem and Metaxylem
Sl. No. Protoxylem Metaxylem 1 First formed part of xylem in the vascular bundles. Metaxylem is the xylem part formed after the protoxylem. 2 Matures before the plant organs have completed their elongation. Matures after the completion of growth of the plant organ. 3 In the stem, protoxylem is arranged towards the centre. In stem, it is arranged towards the exterior 4 In the root, it is arranged towards the periphery. In root, it is arranged towards the interior 5 Composed of very less amount of tracheary elements. Composed of more tracheary elements then protoxylem. 6 Contain large amounts of parenchyma. Contain less amount of parenchyma 7 Tracheary elements are with a very narrow lumen. Cells of the tracheary elements are with large lumen than that of protoxylem. 8 Show annular or spiral thickening in their secondary wall (primitive type). They show reticulate or pitted thickening (advanced type). 9 Subjected to stress and strain during the maturation of the plant Not subjected to stress and strain 10 In monocot stem, protoxylem elements fuse together to form a cavity Metaxylem elements do not form the lysigenous cavity 11 Fibres absent in protoxylem Fibres present in metaxylem 12 Tyloses are not formed in protoxylem Tyloses may present in metaxylem 13 Less efficient in the conduction of water and minerals More efficient in the conduction of water and minerals
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