Anatomy of the Dicotyledonous Roots

·         The Dicotyledonous Root

·         Rhizodermis or Epiblema

§  Outermost layer aka rhizodermis (epidermis in stems) made of a single layer of parenchyma cells which are arranged compactly without intercellular spaces, with no stomata or cuticle

§  Root hair is always single celled

§  Protects inner tissues of the root

·         The Cortex

§  Consists of only parenchyma cells loosely arranged with intercellular spaces to make gaseous exchange easier

§  These cells may store food reserves

§  The cells are oval or rounded in shape

§  Sometimes are polygonal due to mutual pressure

§  Cortical cells are devoid of chloroplasts but starch grains are stored in them

§  The cortical cells also possess leucoplasts

§  Inner most layer of the cortex is endodermis

§  Endodermis is made up of single layer of barrel shaped parenchymatous cells

§  Stele is completely surrounded by the endodermis

§  The radial and the inner tangential walls of endodermal cells are thickened with suberin

§  Casparian strips

§  Casparian strips are absent in the endodermal cells located opposite to the protoxylem elements

§  These thin-walled cells without Casparian strips are called passage cells through which water and mineral salts are conducted from the cortex to the xylem elements

§  Water cannot pass through other endodermal cells due to the presence of Casparian ·         

The Stele

§  Include all the tissues present inside endodermis

§  The stele includes pericycle and vascular tissues

§  The Pericycle

§  Pericycle is generally a single layer of parenchymatous cells found inner to the endodermis

§  It is the outermost layer of the stele

§  Lateral roots originate from the pericycle

§  Thus, the lateral roots are endogenous in origin

§  The Vascular Tissues

§  Vascular tissues are in radial arrangement

§  Xylem and phloem are separated by a conjunctive tissue

§  If conjunctive tissue is composed of parenchymatous tissue then, the xylem is in exarch condition

§  If number of protoxylem points is four, then, the xylem is called tetrarch

§  Each phloem patch consists of sieve tubes, companion cells and phloem parenchyma

§  Metaxylem vessels are generally polygonal in shape but in monocot roots they are circular thickenings

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