Page 126 - Pharmacognosy-I (02-06-06-102)

3- Splintery : if sharp and jagged projection are formed.
4- Fibrous : if fine fibrous threads extend from the broken
surface.
5- Laminated : if breaks into tangentially arranged layers.
Structure of Bark :

In the preparation of commercial barks, part or whole of
the tissues outside the secondary phloem, may be removed by
decortication as they are either :

- lacking the medicinally active constituents of the drug, or
- containing an undesirable amount of tannin or of colouring
matter or;
- containing an undesirable constituents as in case of
cinnamon which have bitter taste.

The commercial bark may consist of all or some or the
following tissues, commencing from outside.

1- Rhytidoma :
-It is not frequently present in commercial bark; being usually removed
during the preparation.
-It is formed of alternate layers of dead cork cells lined with suberin,
making them highly impermeable to water and gases and other collapsed
dead tissues of cortex or phloem.

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