xl INTRODUCTION TO BOTANY. 



between the ramifications of the nerves of leaves. The herba- 

 ceous integument constitutes the part known by the name of 

 cork in the cork-tree, (quercus suber.) Within its substance, 

 is effected the decomposition of the carbonic acid', (fixed air,) 

 absorbed by the plant from the surrounding air. The carbon 

 remains within the vegetable, the oxygen, (pure part of the air,) 

 being set free, is expelled from it. This decomposition takes 

 place only when the plant is exposed to the rays of the sun ; the 

 carbonic acid is given out unchano;ed when the vegetable is 

 not under the influence of that body. This organ, (the herb, 

 integ.) is partly renewed every year. At the return of spring, 

 it invites the sap to ascend towards the buds, and thus becomes 

 one of the most powerful causes of their developement. The 

 herbaceous integument is the part, observed on removing the 

 epidermis, or outermost covering of branches ; for examples 

 the common elder, (sambucus.) 



§. 3. Of the Cortical Layers. 



These are sometimes very difficult to recognise. Placed 

 under the herbaceous integument, they are applied to the 

 outer layers of the liher, (the true bark,) from which they can 

 hardly be distinguished. 



§. 4. Of the Liber. 



This is found between the cortical layers, on its outside, 

 and the woody body which lies within it. It consists of a 

 vascular net-work, whose elongated meshes are filled up with 

 cellular tissue. By maceration, it may be separated into 

 distinct layers. The liber is capable of being reproduced. 

 To the viscid substance poured out from the denuded^ 

 (stripped,) parts to reproduce the liber, the name of camhmmi 

 has been given. The cambium is considered by many to be 

 nothing more than the descending and elaborated sap. The 

 liber is indispensable for the process of vegetation ; for exam- 

 ple, a graft will not succeed, unless its liber be in contact with 

 that of the tree on which it is inserted : a cutting, stripped of 



' See Parke's Chemical Catechism, last edition. The clearest and most 

 entertaining work on Chemistry, with which I am acquainted. 



