8. Plant Tissues and Anatomy - part 01 - Tissue and Classification of Meristem

 

8. Plant Tissues and Anatomy - part 01 - Tissue and Classification of Meristem


Tissue :    
  • Anatomy is the study of internal structure  of organism. 
  • Organs are made up of  group  of  cells.  
  • A  group  of  cells  having essentially a common function and origin is called as tissue. 
  • Plant tissues are grouped as [on the basis of its ability to divide ]

  1. meristematic  tissue and 
  2. permanent  tissue 
Meristematic Tissue  : 

  • It  is  a  group of young cells.  
  • These  are living cells with ability  to divide in the regions where they are persent.  
  • These are polyhedral or isodiametric  in shape without intercellular spaces.
  • Cell wall is thin, elastic, mainly composed of cellulose.  
  • Protoplasm is dense with distinct  nucleus at the center  and vacuoles if present, are very small. 
  • Cells show  high rate of metabolism.  These cells are immature.

1. Classification of Meristem :   [ Based  on Origin] :

  1. Primordial  meristem
  2. Primary meristem 
  3. Secondary meristems

1. Primordial  meristem :
  • Primordial  meristem or  promeristem is also called  as embryonic meristem.  
  • Usually occupying very  minute area  at  the tip of  root and shoot.  
2. Primary meristem :
  • Originates from the  primordial  meristem  and occurs  in  the plant body  from the beginning, at the root and shoot apices. 
  • Cells are dividing and different permanent tissues are produced from primary meristems.  
3. secondary meristems :
  • Secondary meristematic  tissues develop from living permanent tissues during later stages of plant growth; hence are called as secondary meristems.  
  • This tissue occurs in the  mature  regions of root and shoot of many plants.  
  • Secondary  meristem  is always lateral (to the central axis) in position e.g. fascicular cambium, inter fascicular  cambium, cork cambium. 

2.Classification of Meristem :   [ Based  on Position] :

  1. Apical meristem 
  2. Lateral meristem
1. Apical meristem :
  • Produced from promeristem and forms  growing point of apices of root, shoot and their  lateral  branches. 
  • It brings  about increase in length of plant body and called as apical initials. 
  • Shoot apical meristem  is terminal  in position whereas in root it is subterminal i.e. located  below the root cap. 
2. Intercalary meristematic  :
  • Intercalary meristematic tissue is present in the  top or base area of node.  
  • Their  activity  is mainly seen in monocots.These  are short lived.
3. Lateral meristem :
  • Present  along the sides of central axis of organs. 
  • It takes part in increasing girth of stem or root. eg. intrafascicular cambium. 
  • It is found in vascular bundles of gymnosperms and dicot angiosperms. 
3. Classification of Meristem :   [ Based  on Function] :

  1. Protoderm
  2. Procambium
  3. Ground meristem

1. Protoderm :
  • Young growing region of the plant has  Protoderm  that forms protective  covering like  epidermis  arround the  various organs. 
2. Procambium :
  • Meristem called  Procambium  is   involved in developing  primary vascular tissue.  
3. Ground meristem :
  • The other structures like cortex, endodermis, pericycle  medullary rays, pith are formed from the region of  Ground meristem. 
  • These  are three groups of meristem based on function.

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