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ON THE FIBRES OF EXOGENOUS PLANTS. 
We have already noted the great differences in point of 
internal structure, between what botanists call Endogenous 
and Exogenous growth, a distinction which we have shown to 
be useful even for practical purposes. Exogenous plants may in 
general be at once known even by their leaves, of which the vena- 
tion is reticulated or net-like, and not parallel as among the 
Endogens ; and therefore the fibres, united to each other in 
meshes, cannot be separated from the leaves for economical 
purposes, but must be obtained from other parts of these plants, 
where the said fibres lie nearly parallel to each other, as, for 
instance, in the bark. 
The peculiar structure of Exogens may also be seen on 
making a transverse section of the stems or branches, for in- 
stance, of the trees of European climates. There we may see 
rings of wood and layers of bark. But in annual stems, we see 
in the centre a circle of white cellular tissue, called pith, and 
round it a layer of wood-like matter, which in some plants is 
called boon, or shove. This is surrounded by layers of cellular 
tissue, which, examined longitudinally, form a tubular sheath, 
inclosing the other parts. It is in some plants composed of long 
and tough elongated cells or fibres, which are sometimes called 
bast, and is covered externally by a delicate skin or cuticle. 
It is these bast fibres which are separated from the Flax and 
Hemp plants, and familiarly known by these names. 
If we proceed to examine the transverse section of an 
Exogenous branch or tree, we see a number of rings, propor- 
tioned to its age. In the centre we observe the pith, which is 
usually small when compared with the bulk of wood. There 
may also be observed a number of lines, usually lighter coloured, 
radiating from the centre towards the circumference. These 
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