Complex Permanent Tissue Notes | Free Biology Study Materials

Complex Permanent Tissue Notes

This article we will discuss about Complex Permanent Tissue:- Xylem and phloem

  • Complex tissues are made of more than one type of cells and they are heterogenous
  • They are also known as vascular tissue or conducting tissue
  • Complex tissues are absent in gametophytes
  • Complex tissues are of two types:- Xylem and Phloem


  • The term xylem was introduced by nageli (1858)
  • Xylem is conducting tissue which conducts water and mineral nutrients upwards from the root to the leaves
  • Xylem besides conduction also provide mechanical strength
  • They are composed of four different types of cells
  • The elements of xylem are xylem tracheids, xylem vessels, xylem fibres and xylem parenchyma

Elements of xylem

i) Tracheids

  • Tracheids are dead and lignified cells
  • Tracheids are elongated cell, thick walls with tapering end
  • They are placed one above other and all separated by cross walls which bear bordered pits
  • The deposition of lignin on cell wall is responsible for formation of different types of thickenings
  • Types of thickening in tracheids are annular, spiral, scalariform, reticulate and border pitted
  • Tracheids are found in pteridophytes, gymnosperms and xylem of dicotyledons
  • Function: Conduct water, dissolved salts and also give mechanical support

ii) Vessels

  • Vessels are dead and lignified cells
  • Vessels are short cells, pipe like structure and thick walled with wide lumen
  • Usually they have simple pits
  • The deposition of lignin on cell wall is responsible for formation of different types of thickenings
  • Types of thickening in vessels are annular, spiral, reticulate and pitted thickening
  • The end walls of vessel elements are called perforation plates
  • The perforation may be simple or multiple
  • Function: Conduct water, dissolved salts and also give mechanical support

iii) Xylem fibres

  • Xylem fibres are dead and lignified cells
  • Fibres are long, thick walled and tapering ends
  • Lumen is highly reduced
  • They are generally not fount in gymnosperm wood
  • Function: They give support to vessels and tracheids

iv) Xylem parenchyma

  • Xylem parenchyma are living and thin walled cells
  • Cell walls are made up of cellulose
  • Function: Store food materials and radial conduction of water


  • The term phloem was introduced by nageli
  • Phloem is conducting tissue which conducts food materials from the leaves to other parts of the plants
  • First formed phloem is protophloem and later formed phloem is called metaphloem
  • They are composed of four different types elements
  • The elements of Phloem are sieve elements, companion cells, phloem fibres and phloem parenchyma

Elements of phloem

I) Sieve Elements

  • Sieve elements are living cells with protoplasm
  • They are food conducting cells
  • Nucleus absent in the sieve elements
  • Two types of sieve elements are found in the phloem

a) Sieve tubes

  • Sieve tube occurs in angiosperms
  • They are rows of cells arranged one above other to form long pipes
  • In sieve tubes the sieve area is located on end wall called sieve plate
  • During unfavourable conditions the cytoplasmic strand is ensheathed by the callose material in the sieve area and transport of food material is stopped

b) Sieve Cells

  • Sieve cells occur in phloem of ferns & gymnosperms
  • These are primitive type of sieve elements
  • Sieve cells are elongated with tapering end
  • Sieve pores are present all over sieve cells

II) Companion cells

  • Companion cells are living cells associated with the sieve tubes
  • They are present only in angiosperms and are absent in pteridophytes & gymnosperms
  • Companion cell and sieve tube are the sister cells because both of them originated from same mother cell
  • They are contains both nucleus and cytoplasm
  • Special type of cells are attached with sieve cells in gymnosperm and pteridophytes in place of companion cells.
  • These cells are called Albuminous cells or Strasburger cells

III) Phloem parenchyma

  • They are living cells with thin walled
  • Phloem parenchyma cells in generally store up food materials and help in conduction of food
  • Phloem parenchyma is totally absent in monocot plants
  • Two types of parenchyma occurs in phloem
  • Axial parenchyma:- Present in primary phloem and they store starch
  • Ray parenchyma:- Present in secondary phloem and useful for radial conduction of food materials

IV) Phloem fibres

  • This is only the dead component of phloem
  • They possess lignified cell wall with pits on their wall
  • Phloem fibres are very long, soft and silky in appearance, hence have immense economic importance
  • These fibres provide mechanical support to the plants

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