8. Plant Tissues and Anatomy - part 05 - Wood

 

8. Plant Tissues and Anatomy - part 05 - Wood


Wood : 

  • During favourable conditions,  spring ood  (early wood) is formed which has broader xylem  bands, lighter  colour, tracheids with thin wall and wide lumen,  fibres are less  in  number,  low  density.  
  • Whereas,  during unfavourable season  autumn ood  (late wood) is formed which has  narrow xylem band, darker in colour, lumen is narrow and walls are thick with abundant fibres are present of high density. 
  • Tracheary elements of heartwood are plugged by in-growth of adjacent parenchyma cells  i.e. tyloses.  
  • They are filled  by oils, gums, resins, tannins called as extractives.  
  • Thus inner non-functinal,  durable  part which is resistant to  pathogens is called  duramen  or heartwood. 
  • Outer light, functional part of secondary xylem, cells are living, no deposition, lighter  and less durable, more susceptible to pathogens and involved  in conduction  of sap is called  as  sap ood  (alburnum). 

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