Page 127 - Pharmacognosy-I (02-06-06-102)

2- Cork :
- It is a protective tissues formed of dead polygonal cells, usually uniform
in shape and arranged in radial rows; Cork cells may be suberised or
lignified.
- The cork usually appears dark brown in colour due to the presence of
amorphous brown or reddish cell contents which are rich in tannin.
- The cork and dead tissue outside it constitute the outer bark.

3- Phellogen :
- It produces cork to the outside and phelloderm to the inside.

4- Phelloderm :
- It is formed of unsuberised cells, arranged in short radial rows.
-The phelloderm may be wholly parenchymatous, collenchymatous or
sclerenchymatous.
- It may constitute the whole cortical part of the bark as in root-barks,
and thus called secondary cortex.

5- Primary cortex :
- It is absent in many barks either due to decortication or due to
exfoliation produced by the deep formation of phellogen as in case of all
root-barks.
- It is formed of parenchyma and may contain sclereids, oil-cells,
laticiferous structures.
- The cells usually contain starch granules, and crystals of calcium
oxalate.

6- Pericycle :
- It may be parenchymatous or sclerenchymatous.

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