8. Plant Tissues and Anatomy - part 07 - Anatomy of Root, Stem and Leaf

 

8. Plant Tissues and Anatomy - part 07 - Anatomy of Root, Stem and Leaf


Anatomy of Root, Stem and Leaf : 
A.   Anatomy of Dicot Root : 


  • The transverse section of a typical dicotyledonous root shows following anatomical features.  
  • The outermost single layer of  cells without cuticle is  Epiblema.  
  • Some of its cells are prolonged into unicellular  root hair. 
  • Next to it is the  Cortex  which  consists of several layers of typical  parenchymatous cells.  
  • After the death of epiblema, outer layer of cortex become cutinized  and is called  Exodermis. 
  • The cortical  cells  store food and water.  The innermost layer of cortex  is called  Endodermis. 
  • The cells are barrel-shaped and their radial walls bear Casparian strip or Casparian bands composed of suberin. 
  • Near the protoxylem, there  are unthickened  passage cells.  
  • A  single layer  of parenchymatous  Pericycle  is present just below endodermis which bounds the stele or vascular cylinder.  
  • Stele  consists of 2 to 6 radial vascular bundles. 
  • Xylem is exarch. 
  • Based on the number  of groups of xylem  and phloem, the stele may be diarch to hexarch. 
  • A  parenchymatous  connective  tissue or conjunction tissue is present between  xylem and phloem.
  • The central part of stele or vascular cylinder is called  Pith.  
  • It is narrow  and made up of parenchymatous  cells,  with  or without intercellular  spaces.  
  • At later stage, a cambium ring develops between xylem and phloem which causes secondary growth in thickness. 
B.   Anatomy of monocot root  :


  • It resembles that of a dicot root in its basic plan.  
  • However, it  possesses more  than six  xylem bundles (polyarch  condition). 
  • Pith is large and well-developed.  
  • Secondary growth is absent.


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