8. Plant Tissues and Anatomy - part 08 - Anatomy of Dicot Stem (Sunflower)

 

8. Plant Tissues and Anatomy - part 08 - Anatomy of Dicot Stem (Sunflower)



Anatomy of Dicot Stem (Sunflower) : 
A  transverse section of dicot stem shows  the following structures :

  • Epidermis is single,  outermost  layer with multicellular outgrowth called  trichomes.  
  • A layer of cuticle is usually  present  towards the  outer  surface of epidermis.  
  • Cortex  is  situated below the epidermis  and is usually differentiated  into three  regions namely-
  1. hypodermis
  2. general cortex  and  
  3. endodermis  
1. Hypodermis :
  • Hypodermis is situated just below the epidermis and is made of 3-5 layers of collenchymatous  cells. 
  • Intercellular spaces are absent.
2. General cortex :
  • General cortex  is made up of several layers of large parenchymatous cells with intercellular spaces.  
3. Endodermis :
  • Endodermis is an innermost layer of cortex which is made up of barrel shaped cells. It is also called  starch sheath.
  • Stele  is the central core of tissues differentiated into  pericycle,  vascular bundles and  pith.  
  • Pericycle  is the outermost layer of  vascular system situated between the endodermis and vascular bundles. 
  • In sunflower, it  is multilayered  and also called  hard bast. 
  • Vascular  bundles  are conjoint, collateral, open, and are arranged in a ring. 
  • Each  one is composed of  xylem, phloem and  cambium. 
  • Xylem is endarch.  
  • A  strip of cambium is present between xylem and phloem. 
  • Pith  is situated in the center of  the young  stem and  is made up of large-sized parenchymatous cells with conspicuous intercellular spaces. 



D.   Anatomy of Monocot Stem : 


  • It differs from dicot.  
  • Epidermis  is without trichomes and  the hypodermis is sclerenchymatous.  
  • Vascular bundles are numerous and are scattered in ground tissue. 
  • Each  vascular bundle  is  surrounded by a sclerenchymatous  bundle  sheath. 
  • Vascular bundles are conjoint, collateral  and closed (without  cambium).  
  • Xylem  is endarch  and shows lysigenous cavity. 
  • Pith is absent. 
  • Secondary growth is also absent.

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