Root - Cork cambium or phellogen is formed from pericycle. It produces phellogen or cork on the outside and secondary cortex or phellogen on the inner side. This three together called periderm. Cortex and epiblema peel off. Cork or phloem is made of dead cells and lenticels are observed in different places.
Stem – Phellogen or cork cambium develops secondarily from the outer layer of cortex. Cells of phellogen divide outside as well as inside to form respectively cork or phellem and secondary cortex or phelloderm. Cork, cork cambium, secondary cortex are together called periderm.
Secondary cortex has radial arrangement of cells. Cork or phellem is made up of dead suberised and rectangular cells which are filled with air and tannins. Cork is protective. Bark is technically cork of dead cells outside phellogen and in non technical usage it means all tissues outside vascular cambium. The outer dead part of the bark is called rhytidome and inner part of the bark is living and made up of phellogen, secondary cortex and phloem. Outer part of the bark is peeled off either in sheets ( Eucalyptus), irregular strips (guava), sheet bark (Bhojpatra), bark of cinchona gives quinine and cinnamon provides spices.
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