ANATOMY OF FLOWERING PLANTS

 

Sclereids :

• Spherical, oval or cylindrical in shape.
• Highly thickened dead cells with very narrow cavities (lumen).
• Commonly found in fruit walls of nuts; pulp of guava, pear and sapota; seed coats of legumes and leaves of tea.

Complex tissues :

• Made of more than one type of cells and these work together as a unit.
• Xylem and phloem constitute the complex tissues in plants.

Xylem :

• Functions as conducting tissues for water and minerals from roots to stem and leaves.
• Provides mechanical support to the plant.
• It consists of four different kinds of elements:-
  • Tracheids
  • Vessels
  • Xylem fibres and
  • Xylem parenchyma.
  
  
• Tracheids :
  • Elongated or tube like cells.
  • Thick and lignified walls and tapering ends.
  • Cells are dead and without protoplasm.
  • Inner layers of cell walls have thickenings which vary in forms.
  
  
• Vessels.
  • Is a long cylindrical tube-like structure made up of many cells called vessel members.
  • Each with lignified walls and a large central cavity.
  • Cells are devoid of protoplasm.
  • Vessel members are interconnected through perforations in their common walls.
  • Presences of vessels are the characteristics of the angiosperm.
  
  
• Xylem fibres :
  • Have highly thickened walls and obliterated central lumen.
  • Either septate or aseptate.
  
  
• Xylem Parenchyma :
  • Cells are living and thin-walled.
  • Cell walls are made up of cellulose.
  • They stored food materials in the form of starch or fat.
  • Also store materials like tannins.
  • The radial conduction of water takes place by the ray parenchymatous cells.
  
  
• The primary xylem is of two types-
  • Protoxylem
  • Metaxylem.
  
  
• The first formed xylem elements are called protoxylem.
• The later formed primary xylem is called metaxylem.
• Endarch: the protoxylem lies towards pith and metaxylem towards the periphery of the organ ( in stem)
• Exarch: in root the protoxylem lies towards periphery and metaxylem lies towards the centre.

Phloem :

• Transports food materials usually from leaves to other part of plant.
• It is composed of four elements:-
  • Sieve tube elements.
  • Companion cells.
  • Phloem parenchyma.
  • Phloem fibres.
  
  
• Sieve tube elements :
  • Long tube like structure arranged longitudinally
  • Associated with companion cells.
  • End walls are perforated to form sieve plates.
  • A mature sieve element possesses peripheral cytoplasm and a large vacuole but lacks nucleus.
  • The function of sieve elements controlled by nucleus of companion cells.
  
  
• Companion cells :
  • Specialized parenchymatous cells.
  • Closely associated with sieve tube elements.
  • Connected with sieve tube element by pit field.
  • Helps in maintaining pressure gradient in the sieve tubes.
  
  
• Phloem parenchyma :
  • Made up of elongated tapering cylindrical cells
  • Have dense cytoplasm and nucleus.
  • Cell wall made of cellulose and has pits through plasmodesmatal connections exist between the cells.
  • Store food materials and other substances like resins and latex and mucilages.
  • It is absent in monocotyledons.

 

CBSE Biology (Chapter Wise) Class XI ( By Mr. Hare Krushna Giri ) 
Email Id : [email protected]