162 
PHARMACOGNOSY. 
and this is commonly differentiated into two distinct 
parts — one next to the cambium, in which life-processes 
take place, contains the greatest amount of active prin- 
ciples, and is known as the inner bark ; another, 
external to this, having a greater or less development 
of corky layers in among more or less obliterated 
sieve and parenchymatious cells, is known as the outer 
bark. Tbe term bark is sometimes restricted to this 
outer layer, but this is more or less confusing and has 
not been generally adopted. The term bork is fre- 
quently applied to the outer corky layers and the 
dead tissues inclosed by them. The term periderm is 
applied to all the tissues produced by the phellogen, 
the older layers of periderm being included in the 
bork. 
In a few cases the wood alone is employed in medi- 
cine and, like the bark, may be differentiated into two 
layers — the one next to the cambium, in which the 
ascent of the cell-sap takes place, known as the sap- 
wood, and another within this which may contain 
resinous, coloring and other substances, and denomi- 
nated as heartwood, the latter being the part usually 
employed in medicine and the arts. 
The pith being in the nature of a reserve layer may 
contain various of the carbohydrates. Sassafras pith 
furnishes an example of this, being used in medicine 
on account of the mucilage it contains. 
The following artificial classification may be found 
of assistance' in the study of the drugs of this class: 
I. Barks. 
1. With periderm. 
A. Yellowish red to dark brown. 
a. Fracture short. 
a Aromatic odor and taste. 
Dark brown Cinnamomum 
Reddish brown Sassafras 
