18 CHEMICAL COMPOSITION OF FIBRE. 
part of their structure, they may be reduced into pulp for 
paper-making. 
Woody Tissue or Fibre.—Within the cellular tissue are found 
the above-described vessels, and along with them what is called 
woody fibre or tissue. This, together with some vascular 
bundles, constitutes collectively the chief part of the wood of 
plants, and gives support to the whole vegetable fabric. These 
woody fibres consist of elongated cells or tubes with tapering 
extremities, which overlap each other, and by their union 
longitudinally form the fibres which are extracted for economic 
purposes. But when so obtained, they are seldom separated 
into their ultimate fibres, but, rather united together into 
bundles of fibres. These are found in the wood, in the inner 
‘ork, and in the leaves of plants. 
These woody fibres are extremely slender and transparent, 
but tough. Like the membrane of the cells, that of the fibre 
is also without pores, but permeable to fluids, and becomes 
thickened by the internal deposition of layer within layer, of 
matter which surrounds the cavity of the cell. In length these 
constituent cells of the fibre do not exceed from one third to 
one line. The bast cells of flax and hemp are long, but it is 
difficult to measure them exactly, as it is impossible to ascertain 
where one cell terminates and another begins. When moist- 
ened, “considerable swelling takes place, principally in the 
direction of the breadth, and only in a small degree in the 
longitudinal direction.” 
The original membrane which forms the basis of the fibre- 
cell is composed of carbon, hydrogen, and oxygen. But, as 
Mohl has observed, ‘‘ the combination of cell-membrane with 
inorganic substances, is a very general condition. In almost 
all plants, a skeleton (the ash), corresponding to the form of 
the membrane, and composed of the alkalies, earths, and 
metallic oxides which kad been deposited in it, remains behind 
after the cell has been burnt. The younger an elementary 
organ is, the more abundant, in general, the alkalies appear to 
be ; the older it is, the more exclusively the earths and metallic 
oxides seem to be combined with its substance.” Hence the 
best fibres are found in the young bark of plants, or in fleshy 
leaves; and therefore, plants when grown for their fibre, are 
generally sown and grown close together. This is done in ore: 
