50 WOODY TISSUES. 
interspaces (jig. 98). The woody portions of all plants consist - 
in a great part of this form of tissue. It is also found in the 
liber or inner bark mixed with parenchyma and certain vessels, 
and in the veins of leaves and those of other appendages of the 
stem and its divisions. 
Three kinds of prosenchymatous cells may be described 
which enter into the composition of Woody Tissues ; namely, the 
ordinary Wood-cells, Disc-bearing Wood-cells or Cells with Bor- 
dered Pits, and Liber-cells; these form respectively, by their 
combination, ordinary Woody Tissue, Disc-bearing Woody Tissue, 
and Woody Tissue of the Liber. 
a. Woody Tissue.—This, the ordinary kind of woody tissue, 
is composed of prosenchymatous cells or fibres of moderate 
length and lignified (fig. 96). A transverse section of these 
cells shows the thickening matter of their walls to be arranged 
in concentric layers, which are often so numerous as to almost 
obliterate their cavities (fig. 97). This kind of tissue occurs in 
the wood of most trees, except that of the Conifer and most 
other Gymnospermous plants ; and in the veins of some leaves, 
and those of certain parts of the flower. The peculiar manner in 
which these wood-cells are arranged with respect to one another, 
overlapping at their pointed extremities, and thus becoming 
firmly cemented, as it were, together, combined with the thick- 
ness of their walls, renders this tissue very strong and tough, 
and thus admirably adapted for those parts of plants in which 
it is found, and where such qualities are especially required. 
b. Disc-bearing Woody Tisswe—This tissue is composed of 
those wood-cells called cells with bordered pits, which have been 
already described on page 43 (figs. 82-86). This tissue consti- 
tutes generally nearly the whole of the wood of the Coniferz and 
most other Gymnospermous plants, as well as a portion of the 
wood of some other plants (see pages 44 and 83). These disc- 
bearing wood-cells are much larger than the other kinds of wood- 
cells, being often as much as 545 or 535 of an inch in diameter ; 
while the latter are frequently not more than 545, or on an 
average about ;3;; of an inch in diameter. 
c. Woody Tissue of the Liber or Bast Tissuwe.—This consists of 
cells much longer than ordinary wood-cells (figs. 99 and 157 b), with 
very thick walls (fig. 101), and owing to their not being lignified, 
or but partially so, they are softer, tougher and more flexible ; 
hence these are regarded as a peculiar kind of cell, and have re- 
ceived the distinctive name of Liber-cells, from their common 
occurrence in the inner bark or liber of Dicotyledonous stems. 
Such cells are also termed bast-fibres, and the tissue formed of 
them bast-tisswe, because the inner bark is also commonly termed 
bast. These cells are rarely branched (fig. 100). Besides the 
common occurrence of this tissue in the liber, it also occurs as a 
constituent of the jibro-vascular bundles of Monocotyledonous 
stems ; and of the fibrous coats of fruits. The veins which 
