114 
PHYSIOLOGICAL VIEWS. 
a species of sea-weed, and some other succulent plants, appear to 
be altogether composed of cellular texture. 
3d. Cortex. Immediately under the cellular integument, we find 
the true bark, which, in plants that are only one year old, consists of 
one simple layer ; but in trunks of older trees, it consists of as many 
layers as the tree has numbered years. The cortex is formed of 
bundles of longitudinal fibres called cortical vessels. The pecuhar 
virtues or quahties of plants chiefly reside in the bark. Here we 
find the resin of the fir, the astringent principle of the oak, and the 
aromatic oil of the cinnamon. 
The inner layer of tlie bark is called the liber ; it is here only, 
that the essential, vital functions, are carried on ; this integument is 
so called from liber, a book, on account of its fine and thin plates, 
which are thought to bear some resemblance to the leaves of a book. 
This substance, by its development, produces new roots, branches, 
leaves, flowers, and fruits.^ It is composed of a kind of net- work, 
which has been compared to cloth ; the elongated fibres represent- 
ing the warp, and the cellular texture the filling up. It has been ob- 
served that the cambium descends between the liber and the wood, 
and that a layer of new liber, and of new wood, are every year 
formed from that liquid ; as the new layer of bark is formed, the old 
one is pushed outward, and at length, losing its vital principle, it be- 
comes a lifeless crust. The natives of Otaheite manufacture gar- 
ments from the liber of the paper mulberry. The liber of flax is, by 
a more refined process, converted into fine linen. This part of the 
bark is important to the life of vegetables ; the outer bark may be 
peeled off without injury to them, but the destruction of the liber is 
generally fatal. 
The operation of girdling trees, which is often practised in new 
countries, consists in making, with an axe, one or more complete 
circles through the outer bark and the liber of the trunk. Trees 
seldom survive this operation, especially if it be performed early in 
the spring, before the first flow of the sap from the root towards the 
extremities. 
During the repose of vegetation, that part of the liber most re- 
cently organized, and which of course retains its vital power, re- 
mains inactive betv/een the wood and the outer layers of the bark, 
until the warmth of spring causes the ascent of the sap. After pror 
moting the development of buds, and the growth of new wood and 
bark, the liber hardens and loses its vital energy, like that of the 
preceding year. 
Fig. 118, at A, represents a young dicotyledonous stem, cut trans- 
versely ; the inner circle surrounds the pith ; the wood extends to 
the bark, which at a appears darkly shaded. 
At B, is a section of the same stem magnified ; a 6, is the bark, 
b i, the wood, and i k, the pith. 
The divisions of the bark may be seen as follows; ac, represents 
the cuticle, or the dry, disorganized part ; . at c d, is the cellidar in- 
tegument ; at d b, is the cortex, the extreme part of which, at b, is the 
liber. 
Wood. The wood (lignum) consists of two parts, alburnum or 
sap-wood, and perfect wood. 
The alburnum is so called from albus, white, on account of the 
paleness of its colour. This is the newly formed wood, and consti^ 
What is said of the cortex 7— Liber— Annually renewed— Girdling— What ultimate- 
ly becomes of the liber ?— Describe a dicotyledonous or exogenous stem— Of how 
many parts does the wood consist 7— Alburnum. 
