8. Plant Tissue and Anatomy - part 06 - Cork cambium and secondary growth

 

8. Plant Tissue and Anatomy - part 06 - Cork cambium and secondary growth



Cork cambium and secondary growth: 

  • Increase in diameter of stem by secondary growth is mainly due to the activity of vascular cambium  present the  outer cortical layer.  
  • When epidermis  gets ruptured, it becomes necessary  to  replace these cells by new cells. Phellogen  (cork cambium)  develops in extrastelar  region  of stem. 
  • The  outer  cortical cells of cortex become meristematic and produce a layer of thin walled, rectangular cells.  
  • These cells cut off new cells on both sides.  
  • The cells produced on outer side develop phellem  (cork) wheras on the inner side produce phelloderm (secondary cortex).  
  • The cork  is  impervious in nature  and does not allow entry  of water due to suberized walls. Secondary cortex is  parenchymatous in nature.
  •  Phellogen,  phellem  and phelloderm constitute  periderm.  
  • Activity of cork  cambium develops a pressure on the other cells  and these cells die. 
  • Bark is non-technical term refering to all cell types found  external to vascular cambium  including  secondary phloem. 
  • Bark of early season is soft and of the late  season is hard.
  • Lenticles  are aerating pores present as (raised scars) the  surface of bark.  
  • These  are portions of periderm, where phellogen activity is more, lenticles are means for gaseous and water vapour exchange. 
  • Monocot stems lack cambium  hence secondary growth does not take place. 
  • But  accessory cambium development in plants like,  Dracena,  Agave, Palms and root of sweet potato  show presence  of  secondary  growth. This  is  called  as anomalous secondary  growth

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