8. Plant Tissues and Anatomy - part 02 - Simple permanent tissues

 


8. Plant Tissues and Anatomy - part 02 - Simple permanent tissues


Permanent tissue : 

  • This is  group of  cells which have lost the capacity of division and aquired permanent size, shape and functions. 
  • It is due to different morphological,  physiological and functional changes that  occur  during maturation  of the cell. 
  • Depending upon types of cells, there are two types as -
  1. Simple permanent tissues and 
  2. Complex  permanent tissues.


Simple permanent tissues : 


  • These  are made up of only one type of cells carrying similar functions.  
  • This tissue is either living or dead. 
  • Following are the types of simple permanent tissues namely - 
  1. Parenchyma
  2. Collenchyma and 
  3. Sclerenchyma

1. Parenchyma  : 

  • Cells  in this tissue are thin walled, isodiametric,  round,  oval to polygonal or elongated  in  shape. 
  • Cell wall  is composed of cellulose.
  • Cells are living with prominent nucleus and cytoplasm with large vacuole. This is less specialized permanent tissue.
  • Parenchyma has distinct  intercellular spaces. Sometimes, cells may show  compact arrangement.  
  • The cytoplasm of adjacent cells is interconnected  through plasmodesmata and thus forms a continuous tissue.  
  • These cells  are distributed  in all the parts of plant body  viz. epidermis, cortex, pericycle, pith, mesophyll cells, endosperm, xylem and phloem.  
  • These cells store food,  water, help in gaseous exchange, increase  buoyancy, perform photosynthesis  and different  functions  in  plant body. 
  • Dedifferentiation  in parenchyma  cells develops vascular cambium and cork cambium at the time of secondary growth.


2. Collenchyma  : 
 

  • It is a simple permanent tissue made up of living  cells.  
  • The cell  wall is cellulosic but shows  uneven deposition of cellulose and pectin especially at corners.  
  • The walls may  show presence  of pits.  
  • Cells  are similar like  parenchyma containing  cytoplasm, nucleus and  vacuoles but small in size and without intercellular  gaps.  Thus appears to be compactly  packed.  
  • The cells are either circular, oval or angular in transverse section. 
  • Collenchyma  is living mechanical  tissue and serves different functions  in  plants.
  • It  gives mechanical strength to young  stem and  parts like   petiole  of leaf. 
  • It allows bending and pulling action in plant parts and also prevents tearing of leaf. 
  • Growth of organs and elongation are other functions. 
  • Collenchyma  is usually absent in monocots and roots of dicot plant.


3.  Sclerenchyma  :


  • It  is simple  permanent  tissue made  up of compactly  arranged thick  walled dead cells.  
  • The cells are living at the time of production but at maturity  they become  dead. 
  • As  cells are devoid of  cytoplasm their thickened walls are due to uniform  deposition  of lignin. 
  • Cells remain  interconnected through several pits. It is of two types viz. 
  1. fibres and 
  2. sclerids. 
1. Fibres 

  • Fibres  are thread-like, elongated and narrow structures with  tapering and  interlocking end walls. 
  • These are mostly in bundles, pits are narrow,  unbranched and oblique.  
  • They provide mechanical  strength. 

2. Sclerids
  •  Sclerids are usually broad, with  blunt  end  walls.  
  • These  occur singly  or in  loose groups and their  pits  are deep branched and straight. 
  • These are developed due  to secondary thickening  of parenchyma cells and provide stiffness only.


  • This tissue functions  as the  main mechanical tissue.  
  • It  permits bending, shearing and pulling. 
  • It gives rigidity to leaves and prevents it  from falling.  It also gives rigidity  to epicarps and seeds.
  •  Commercial  fibres are also produced from sclerenchyma fibres. e.g. jute, flax, hemp.

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