Pharmacognsy

• Decortication in Quillaia and Cinnamon

  Done for reasons such as containing low percentage of / or no active constituents, containing an undesirable number of tannins or coloring matter or other undesirable constituents
• Fracture is the behavior of the bark when broken transversely and gives an idea about the nature of the tissues present
• Rhytidome is not frequently present in commercial barks, being removed during preparation. It is formed of dead, usually collapsed tissue including the epidermis, some cortical parenchyma, and even other deeper tissues
• Preparation of the bark


  The bark can be separated from the stem, its branches, and the root by making two transverse circular incisions at suitable distances, connected by a longitudinal incision, then the bark is stripped off and dried by sun heat in open air
• Types of fracture

  • Short: When breaking quickly and straight across and the fractured surface is almost smooth e.g. Pomegranate
  • Brittle: When easily broken into fragments
  • Fibrous: When resisting during breaking and fibrous projections protruding from the broken surfaces
  • Even or smooth: When breaking with smooth surfaces
• Cork is a protective tissue of secondary origin, developed from a secondary meristematic layer, the phellogen or cork cambium, by repeated division. It is formed of suberized sometimes lignified dead cells
• Bark structure

  • The commercial bark may consist of tissues including Rhytidome, Periderm (cork, phellogen, and phelloderm), Primary cortex, Pericycle, Primary phloem, Secondary phloem
• Types of tissues in plants

  • Cal parenchyma
  • Cork
  • Phellogen
  • Phelloderm
  • Cortex
  • Pericycle
  • Phloem
  • Medullary Rays
• Cortex


  Also called primary cortex, composed of parenchyma cells, may contain various types of cells like collenchymatous, fibers, mucilage cells, starch grains, and calcium oxalate crystals
• Formation of Phellogen

  1. Developed by the activation of parenchyma

  2. Produces rows of cork cells to the outside and unsuberized cells forming the phelloderm to the inside
• Phloem


  Characterized by sieve tubes, companion cells, phloem parenchyma, may contain oil cells or mucilage cells, parenchyma usually contains starch granules and calcium oxalate crystals
• Difference between stem bark and root bark
• Classification of barks

  • Aromatic Barks
  • Non Aromatic Barks
  • Alkaloid containing Barks
  • Tannins containing Barks
• Periderm

  Consists of phellogen, cork, and phelloderm
• Pericycle


  Varies in extent, may be parenchymatous or sclerenchymatous, may contain pericyclic fibers
• Formation of Cork

  1. Developed from a secondary meristematic layer, the phellogen or cork cambium, by repeated division

  2. Formed of suberized sometimes lignified dead cells
• Medullary Rays

  Parenchymatous, may become lignified and pitted, may vary in width, may be uniseriate or multiseriate
• Official Medicinal Barks


  • Cinchona bark
  • Cinnamon bark
  • Pomegranate bark
  • Quillaia bark
  • Frangula bark
  • Cascara bark
• Non-official medicinal bark :

  -Canella -Cassia
• Official Barks

  • Outlines
  • Cascara
  • Frangula
  • Cinchona
• The term bark as employed in pharmacognosy is the part of the trunk stem, branches or roots of woody plants, like trees and shrubs
• Shapes of barks

  • Smooth
  • Ridges
  • Cracks
  • Flat
  • Curved
  • Recurved
  • Channeled
  • Single quill
  • Double quill
  • Compound quill
• Barks are usually dried by sun heat in open air
• Fracture


  1. Behavior of the bark when broken transversely and the character of the exposed surfaces

  2. Examples of fracture: Short, Brittle, Fibrous, Even or smooth
• Types of barks

  • Stem bark
  • Root bark
• The outer surface of the stem bark is usually lighter in color than the inner due to discoloration by sun – light
• The two surfaces of stem bark have nearly the same color
• The outer surface of stem bark shows epiphytes
• The surface of the root bark is devoid of epiphytes
• The stem bark is much thicker and may be flat, curved or quilled, but the root bark may be irregularly quilled or twisted
• In the preparation of commercial barks, part or whole of the tissues outside the secondary phloem may be removed in a process called decortication
• In Quillaia and Cinnamon, decortication is done for specific reasons
• Cork is a protective tissue developed from the phellogen or cork cambium, by repeated division
• Cork is formed of suberized sometimes lignified dead cells
• The phellogen by division produces rows of cork cells to the outside and unsuberized cells forming the phelloderm to the inside
• The phellogen, cork, and phelloderm constitute the periderm
• The phelloderm or secondary cortex is developed from the phellogen on its inner surface
• The cortex, also called primary cortex, is absent in many barks due to decortication, e.g., Cinnamon
• The cortex is composed of parenchyma cells and may have outer collenchymatous layer as in Oak
• The cortex may contain scelerieds as in Cascara, fibers as in Oak, or mucilage cells as in Cassia