Secondary thickening in Dicot root

The growth in thickness by the activity of secondary tissues is called secondary thickening
Stelar secondary growth by vascular cambium
  • Formation of cambial ring
  • The conjunctive tissue between xylem and phloem develops into cambium. Strips are later joined to form a complete cambial ring.
  • The cambium produces secondary phloem to the outside and secondary xylem to the inside.
  • More secondary xylem is produced due to more activity of vascular cambium to the outside.
Extra stelar Secondary growth or Periderm formation by cork cambium
  • The formation of more and more secondary tissues exerts a pressure on cortex and epidermis
  • The epidermis gets ruptured and is replaced by another protective tissue developed in the
  • cortex from the cork cambium is the periderm. Periderm consists of meristem called phellogen or cork cambium. Cork cambium produces cork or phellum to the outside and phelloderm or secondary cortex to the outside. Periderm has specialised openings called lenticels on its surface for gaseous exchange. Often not prominent in dicot root.
Secondary thickening in dicot rootImportant points:
  • Secondary vascular tissues are present
  • Formation of cambial ring
  • Cambial ring is wavy at the beginning later become circular
  • The cambium is completely secondary in origin
  • The cambium produces secondary phloem to the outside and secondary xylem to the inside.
  • Cork cambium is present and produces cork to the outside and secondary cortex to the inside forming periderm.
  • Primary Vascular bundles are radial and xylem is exarch
  • Number of xylem and phloem groups limited (2-6 or 8)
  • Common material: Carica Papaya
Read more: Difference between Secondary Growth in Dicot stem and Dicot Root
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