8. Plant Tissues and Anatomy - part 09 -Anatomy of Leaf

 

8. Plant Tissues and Anatomy - part 09 -Anatomy of Leaf


Anatomy of Leaf :  

  • Dorsiventral Leaf  is very common in dicotyledonous  plants where the mesophyll tissue is differentiated  into 

  1. palisade and 
  2. spongy parenchyma.  

  • The leaves are commonly horizontal  in orientation  with distinct upper and lower surfaces.  
  • The upper surface which faces the sun is darker than the lower surface. 


V. S. of  Typical dicot leaf : 

  • Upper  epidermis  consists of a single layer  of tightly  packed  rectangular, barrel shaped, parenchymatous cells  which are devoid of chloroplast.  
  • A distinct  layer of cuticle lies on the outside of the epidermis. 
  • Stomata are generally absent. 
  • Between upper and  lower epidermis, there is chloroplast-containing photosynthetic tissue called  Mesophyll. 
  • Mesophyll  is differentiated  into -
  1. palisade tissue and 
  2. spongy tissue.  
Palisade parenchyma 
  • It is present  below upper epidermis and consists of closely packed elongated cells. 
  • The cells contain abundant chloroplasts and help in photosynthesis.  
Spongy parenchyma
  • It is present below palisade tissue and consists of loosely  arranged irregularly  shaped cells  with intercellular  spaces.  
  • The  spongy  parenchyma cells contain chloroplast and are in contact with atmosphere through stomata.
  • Vascular system is made up of a number of vascular  bundles  of varying  size  depending upon the venation. 
  • Each one is surrounded by a thin layer of parenchymatous cells called bundle sheath.  
  • Vascular bundles are closed and xylem towards upper epidermis and phloem towards  lower epidermis. 
  • Cambium is absent hence no secondary growth in the leaf. 
  • Lower  epidermis  consists of a single layer of compactly  arranged rectangular, parenchymatous  cells.  
  • A  thin layer of cuticle is also present.  
  • The lower epidermis  contains a large number of microscopic pores called stomata.  
  • There is an air-space called substomatal chamber at each stoma. 

Isobilateral  Leaf :  
  • In this leaf both the surfaces are equally  illuminated  as both the surface can face  the  sun, and show similar structure.  
  • The two surfaces are equally  green. 
  • Generally  monocotyledonous plants  have isobilateral leaves. 
A typical monocot leaf : 

  •  resembles  a dicot  leaf in its anatomical structure. 
  • However, it shows stomata on both the surfaces and mesophyll is not differentiated  into palisade and spongy tissue. 
  • It has parallel veins.  
  • These are conjoint, collateral and closed.

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