January 22, 2016

Junior Inter Botany 8 Marks Question from Chapters 12-13

Q: Describe the T.S of dicot stem.
A: The transverse section of a dicot stem shows: Epidermis, Cortex and Stele.
Epidermis: The epidermis is outer most protective layer covered by a cuticle. It may bear multicellular trichomes and stomata. It helps in protection, transpiration and
gaseous exchange.

Cortex: The cortex is the region between epidermis and stele. It is differentiated into: 1) Hypodermis 2) General cortex 3) Endodermis
The hypodermis is present below the epidermis and made up of collenchyma. It gives mechanical strength to young stems.

General cortex is parenchymatous with intercellular spaces. It helps in assimilation and
storage. The inner most layer of cortex is endodermis also called starch sheath. It
stores starch.

Stele: The stele is the central conducting cylinder and occupies large area in the stem.
It is differentiated into: 1) Pericycle 2) Vascular bundles 3) Medulla 4) Medullary rays
Pericycle is in the form of a semi lunar patch of Sclerenchyma above the vascular bundle.
The vascular bundles are arranged in a ring (eustele). Each vascular bundle is collateral, conjoint, open (cambium present between xylem and phloem) with endarch xylem.
Xylem is present towards centre and phloem towards periphery separated by cambium. Pith is large and parenchymatous at the centre and radiates as medullary rays in between the vascular bundles.

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