Saturday, 22 May 2021

Metaxylem vessels have pitted thickenings while protoxylem

Metaxylem vessels have pitted thickenings while protoxylem



  In smaller vascular bundles xylem is compact and without distinction of protoxylem and metaxylem. In larger, vascular bundles, xylem is endarch. Protoxylem cavity is often formed. Both protoxylem and metaxylem have oval or rounded vessels arranged in the form of V or Y-shaped configuration.

 Metaxylem vessels have pitted thickenings while protoxylem vessels have annular or spiral thickenings. number of other grasses, mesophyll forms concentric layers around the vascular bundles that possess large sized centrifugally arranged chloroplasts in bundle sheath cells.

 This arrangement is called Kranz anatomy. The anatomy is tropical conditions. It is also found in some an evolutionary adaptation to dicot leaves. Midrib : It is the widest or thickest part of the leaf. Similar but less prominent thickenings occur in the region of other large veins.

 A shallow groove is present in the upper or adaxial surface while a broad ridge is present on the abaxial surface. Mesophyll is absent. The ground tissue is parenchymatous with sclerenchymatous patches towards both the sides. A number of conjoint, collateral and closed vascular bundles are embedded in the ground tissue. 

Reasons for Identification : (i) Presence of larger sized bulliform cells on upper surface. (ii) Flat structure. (iii) Undifferentiated mesophyll. (iv) Presence of bundle sheath with chloroplasts. (v) Vascular bundle with xylem towards upper side and phloem towards lower side, (vi) Xylem vessels rounded.It is formed of sieve tubes and companion cells.protophloem and metaphloem. 


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