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 pecuUar 

 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 the bark is called the Jiher ; it is here only, 

 that the essential, vital functions, are carried on ; this integument is 

 so called from liher, 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 g-2>d/u?g- 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, arid which of course retains its vital power, re- 

 mains inactive between the wood and the outer layers of the bark, 

 until the warmth of spring causes the ascent of the sap. After pro- 

 moting the development of buds, and the grov/th of new Avood and 

 bark, the liber hardens and loses its vital energy, like that of the 

 preceding year. 



Fig. lis, at yl, represents a young dicotyledonous stem, cut trans- 

 versely ; the inner circle surrounds the pith ; the wood extends to 

 the hark, which at a appears darkly shaded. 



At jB, is a section of the same stem magnified ; a &, is the bark, 

 b ?■, 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 cellular in- 

 tegument ; aid 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- 



Whatis said of the Cortes'?— 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 1— Alburnum 



