BIOL 1001 Lecture Notes - Lecture 2: Vessel Element, Tracheid, Lignin

• School: Louisiana State University-Alexandria
• Department: Biology
• Course: BIOL 1001

Document Summary

Therefor, tracheids are considered to be more primitive than vessel members. Vessel members are present in the xylem of all angiosperms except order ranales (e. g. magnolis purpurea) where the xylem contains only tracheids. For this reason (and others), the order ranales is considered, phylogenetically, to be the most primitive order of angiosperms. Tracheary elements are elongated, non-living cells (i. e. without protoplast), principally concerned with the water transport and also have a supporting function. Usually, tracheary elements are without intercellular spaces and the thickening of their walls is even. They are classified into tracheids and vessel members. Tracheids are pitted and relatively longer than vessel members. Each xylem vessel arises from a vertical row of meristematic cells. Generally, the tracheary elements of the secondary xylem are shorter than those of the primary xylem. Secondary xylem of gymnosperms is distinguished by the absence of vessels (except genetales).