Page 128 - Pharmacognosy-I (02-06-06-102)

- In such cases, the sclerenchyma ring is accompanied, on the outside by
pericyclic fibres.

7- Primary phloem :
- It is usually collapsed and even becoming indistinguishable or totally
absorbed. It is called ceratenchyma.
8- Secondary phloem (Inner bark) Characterized by:
-The presence of sieve tubes and phloem parenchyma, traversed by
medullary rays.
- The phloem commonly contains bast fibers (phloem fibres) and
sometimes sclereids, oil cells.
- The parenchyma usually contains starch granules and sometimes
calcium oxalate crystals.

Medullary rays :

- Formed of rectagular and radially elongated parenchymatous cells.
- The cells commonly contain starch granules and occasionally calcium
oxalate crystals.
- They appear in transverse sections as radial straight, curved or wavy
lines or as radial narrow bands. Medullary rays being formed form one
cell (uniseriate) to many cells thick (multiseriate) ranging form 3-4
cells.

Phloem fibres :

- Are dead, very much elongated, polygonal cells, with tapering end.
They occur either isolated or in short files.

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