Page 124 - Pharmacognosy-I (02-06-06-102)
P. 124
DIAGRAM SHOWING A TYPICAL ARRANGEMENT OF
THE TISSUES OF BARKS:
A typical arrangement of the tissues:
1- Cork.
2- Cork cambium or phellogen.
3- Phelloderm or secondary cortex.
4- Inner part of primary cortex.
5- Pericycle.
6- Primary phloem.
7- Secondary phloem.
8- Medullary rays.
Outer Surface : Usually exhibits important features :
1-Epiphytes :
a- Lichens : grayish thalloid structure.
b- Liver worts : consist of very small slender stems to which
small leaves are attached in one plane.
c- Mosses : slender stem bearing spirally arranged leaves.
2- Lenticels : they are breathing pores for exchange of gases,
placed transversely, the shape and abundance of which may
help in distinguishing the bark.
3- Cracks and fissures : arise owing to continued increase in
growth and to the lack of elasticity.
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