Internal Structures of the Dicot Stem

·         Internal structure of dicotyledonous stem consists of Epidermis, Cortex and Stele.

·         Epidermis

§  It consists of a single layer of parenchymatous rectangular cells

§  Epidermal cells are compactly arranged without intercellular spaces

§  Epidermis is covered on the outside by cuticle made up of waxy substance

§  The cuticle checks/controls transpiration

§  Stomata may be present at irregular intervals

§  A large number of multicellular hairs occur on the epidermis

·         Cortex

§  Cortex lies below the epidermis

§  The cortex is differentiated into three zones

§  The first zone (Hypodermis)

·         Lies below the epidermis, consists of a few layers of collenchymacells

§  The second zone

·         Lies inner to the hypodermis

·         Consists of a few layers of chlorenchyma cells

·         Some resin ducts also occur in this zone

§  The third zone

·         Consists of parenchyma cells

·         The innermost layer of the cortex is the endodermis

·         Made of barrel shaped cells arranged compactly without intercellular spaces

·         Rich in starch grains, hence “starch sheath”

·         The Stele

§  In the central part of the stem inner to the endodermis

§  It consists of pericycle, vascular bundles and pith

§  Vascular bundles are arranged in a ring around the pith

§  Pericycle

§  Layers of cells between endodermis and vascular bundles

§  Vascular Bundles

§  Consist of xylem, phloem and cambium

§  Xylem and phloem in stem occur together to form the vascular bundles

§  These vascular bundles are wedge shaped

§  The vascular bundle is conjoint, collateral, open and endarch

§  Phloem

§  Consists of sieve tubes, companion cells and phloem parenchyma

§  Phloem conducts organic food materials from the leaves to other parts of the plant body

§  Cambium

§  Consists of brick shaped and thin walled meristematic cells

§  Form new cells during secondary growth

§  Xylem

§  Consists of xylem fibres, xylem parenchyma, vessels and tracheids

§  Vessels are thick walled and arranged in a few rows

§  Conducts water and minerals from the root to the other parts of the plant body

§  Pith (medulla)

§  It is the large central portion of the stem

§  It is composed of parenchyma cells with intercellular spaces

§  The pith extends between the vascular bundles and form primary medullary rays

§  These extensions of the pith between the vascular bundles are called

                                 It stores food 

Selective-focus Photography of Orange Petaled Flower


Evans, W. C. (2009). Trease and Evans Pharmacognosy. India: Reed Elsevier Limited.

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