VESSELS OR DUCTS.—PITTED VESSELS. bl 
form the framework of leaves are also in part composed of this 
kind of tissue. 
These bast-fibres are called bast-tubes by some botanists, who 
regard them not as elongated cells, but as true vessels formed 
like them by the coalescence of rows of cells, the partition walls 
between them having become absorbed, so that their cavities 
communicate and form a continuous canal. These liber-cells, 
bast-fibres, or bast-tubes, must not be confounded with sieve- 
vessels or sieve-twhes (see page 55), which are also frequently 
termed bast-vessels from their common occurrence in the liber. 
From the peculiar qualities of the woody tissue of the liber it 
is admirably adapted for various manufacturing purposes ; thus 
Hemp, Flax, New Zealand Flax, Pita Flax, Sunn, Jute, China 
Grass, and many other fibres, are all composed of the liber 
tissue of different plants, and will afford good illustrations of the 
value of such fibres as textile materials. This Jiber tissue also 
when macerated so as to separate the cells from one another is 
made into a mash from which the best kinds of paper are made. 
Inferior sorts of paper are prepared from the ordinary woody 
tissue of many plants, but they lack the toughness of papers 
made from the liber, and are brittle and tear more easily. 
The different kinds of woody tissue are commonly associated 
with other organs, which are also of an elongated tubular 
character, but larger than the prosenchymatous cells of which 
the woody tissues are composed. These constitute the vessels 
of plants, and must now be described. 
3. VESSELS.—These have also been frequently termed ducts 
by authors. The essential character of a vessel is that it is 
composed of several cells, which are united end to end, and the 
septa dividing them more or less completely absorbed. The 
component cells may be either very long and narrow, or they 
may be short and broad. 
There are several varieties of these vessels, which are known 
as pitted, spiral, annular, reticulated, and scalariform, the char- 
acters of which depend upon the component cells out of which 
they have been formed, and which have already been described. 
They contain air or water. 
But besides these vessels we have also other varieties, which 
are commonly distinguished under the names of sieve-tubes or 
sieve-vessels, laticiferous vessels, and vesicular or utricular vessels. 
These are closely related to one another from the nature of their 
contents, their chief function being to act as reservoirs of 
nutrient fluids or secretions, and also as carriers of the nutri- 
ent fluids to those parts of plants where they are required. 
a. Pitted or Dotted Vessels.—A pitted vessel is formed from 
a row of cylindrical pitted cells placed end to end (fig. 102), the 
intervening partitions of which have become more or less ab- 
sorbed, so that their cavities communicate and form a continuous 
canal (fig. 103). The origin of pitted vessels from a row of cells 
E 2 
