Page 165 - Pharmacognosy-I (02-06-06-102)

WOODS

INTRODUCTION

Definition : Wood, in pharmacognosy as well as in commerce, may be

defined as all that portion of the axis of woody plants lying inside the
cambium line. Hence it consists mainly of secondary xylem. The wood
is obtained from the trunks, branches or roots of the dicotyledonous trees
or shrubs.

Kind of Wood : The wood may be :

1- Sap Wood :
- It is usually pale in colour, containing living cells and reserve food

materials, e.g. starch, functioning both as conductive ans as support.
2- Heart wood:
-It is usually dark coloured. It consists of lignified dead cells (no

reserve food materials). It functions only as support.

Structure of Wood :

The wood consists mainly of thick-walled cells which are all lignified and
thus the wood will wholly acquire a deep red colouration when treated
with phloroglucin and hydrochloric acid. The elements present in the
wood are fibres, tracheids, vessels, wood parenchyma and medullary
ray cells.

Annual rings : Owing to the climatic variations, the cambial tissue,

exhibits a periodical seasonal activity. This results in the formation of
alternate cylindrical layers of wood, each corresponds to one year growth,
thus called annual rings.

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