Complex Permanent Tissue

Complex Permanent Tissue

Complex Permanent Tissue

Complex Permanent Tissue are the tissue that are composed of different types of cells thus forming heterogenous mass. All different types of cells of complex permanent tissue work together as an unit to perform set of related function-conduction or transportation. Since, function of complex permanent tissue is conduction so called as vascular( i.e conduction) tissue.On the basis of function , it’s of two types :- Xylem and Phloem.

  1. Xylem(Gr. xylol=wood) : It is the type of complex permanent tissue function of which is conduction of water or minerals from roots to various parts for which there are 4 different types of cell components :
  1. Trachieds : It is the major component of xylem. They are dead , elongated with both the end pointed . Cell wall is very thick , lignified but with lumen. Its major function is conduction of water and minerals . Secondarily it also gives mechanical support for which it develops secondary wall (liginified) in various ways according to which it is classified :-

Types of Tracheids

Types of Tracheids

 

  1. Vessel or Trachae : It is also the major component of xylem as its major function is conduction of water and minerals . It is totally absent in lower vascular plants (pteridophyte and gymnosperm except Gnetales) . Vessel is predominantly found in the xylem of angiosperm . Unlike tracheids, vessel is also not a single cell rather is a pipe like structure that is made by end to end fusion of several small , dead, thick walled lignified cells each called vessel cells. Due to dissolution or perforation of end wall like tracheids , vessel also develops secondary wall variously on the basis of which it is divided .
  2. Xylem Fibre : They are dead cells , thicked walled , spindle shape sclerenchyma fibre that develops intermixing with other compnents of xylem . It provides mechanical support to plant.
  3. Xylem Parenchyma : They are ordinary parenchyma i.e living cell and thin walled which develops along with other component of xylem . Its function to assist in slow conduction of water and minerals.

Types of Xylem

Types of Xylem Cells

 

Types of Xylem

  1. On the basis of time of development and structure
    • Protoxylem (Gr ; proto=first ,xylem=wood) : It is the first formed xylem consist of smaller tracheary elements(i.e tracheids and vessels) with annular and spiral thickening
    • Metaxylem : It is later formed xylem consist of bigger tracheary elements having scaliform , reticulate or pitted thickening.
  2. On the basis of position of protoxylem
    • Exarch : Proto xylem develops towards the periphery of axis.
      Ex : found in all roots
    • Endarch : Proto xylem develops towards center of axis .
      Eg : found in all stem and leaf .
  1. Phloem ( Bast) : It is a type of complex permanent tissue function of which is conduction of organic food from leaf to the various parts for which there are 4 different types of cells .

Phloem cells

 

  1. Sieve tube : It is the major component of phloem because it is conducting elements for organic food materials . It is tube like structure made up of end to end fusion of many small cells , each called as sieve cells . Plate formed at the end of each sieve tube has minute pore as sieve , hence the plate is called as sieve plate. Each sieve cell is a living , thin walled cell with a cellulosic cell wall having peripheral cytoplasm but devoid of nucleus. Each pore of sieve plate get pluged during callose(unsaturated carbohydrate) during passive season .
  2. Companion cell : It is a specialized parenchyma which get associated with each sieve tube . Companion cell is elongated , narrow living cell with a conspicuous nucleus and get connected with sieve tube with the help of pore called plasmodesmata . It is believed that nucleus of companion cell will control metabolic activities of sieve tube cell (cell without nucleus ).
  3. Phloem or Bast Parenchyma : It is ordinary parenchyma cell which get associated with other component of phloem . Its function is to store food and slow conduction of the food .
  4. Phloem or Bast fibre : They are sclerenchyma fibre which are dead , highly thicked wall lignified cells which develop associating with other component of phloem . It provides mechanical support to plant .

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