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Dicotyledonous Stem

 

Epidermis

  • It is the outermost layer formed of a single layer of cells.
  • It forms the protective layer of the stem.
  • It has a thick waxy layer called cuticle over the external surface.
  • It bears trichomes and a few stomata.

Cortex

  • The cortex is heterogeneous and differentiated into several sub- zones.
  • The outer zone is called hypodermis and is composed of a few layers of collenchymas cells. It provides mechanical strength to the stem.
  • The middle cortical layers are composed of thin walled chlorenchyma and parenchyma cells.
  • The innermost layer is the endodermis. It is single layered, composed of barrel-shaped cells and rich in starch grains. Hence it is also called starch sheath.

Pericycle

  • It is the region between the endodermis and the vascular bundle.
  • It occurs in the form of semilunar patches of sclerenchyma cells.
  • Since it is found above the vascular bundle, it is also known as bundle cap.

Vascular bundles

  • They are few in number, and are arranged in the form of a ring.
  • They are conjoint, open (cambrium present) with endarch protoxylem.

Medullary Rays

  • It is composed of a few layers of elongated cells lying between two vascular bundles.
  • It acts as a pathway for the radial conduction of food and water.

Pith

  • It is the central portion of the ground tissue.
  • It is composed of loosely arranged parenchyma cells.
  • Their main function is storage.

 

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