256 THE ANATOMY OF STEMS. 



are exemplified in trees and shrubs ; but as the struc- 

 ture of the parts differs according to the age of the 

 plant, it is requisite to examine them, both as they 

 appear in the young plant or yearly shoot, and in the 

 trunk and branches of older subjects. 



If the young shoot of any tree or shrub, the Horse 

 Chesnut for example, be cut either transversely or 

 longitudinally, the parts which have been enumerated 

 are rendered evident to the naked eye. If the sec- 

 tion be transverse, it is seen to consist of a central 

 spongy or cellular portion, which is the pith, enclosed 

 within a ring of more solid consistence, which is 

 the wood, and this, again, is em r 'roned by another 

 circle ol an intermediate degree of firmness, which is 

 the bark. 



The Bark. In the shoot we are now examining, 

 cut in the autumn, the bark when separated from the 

 wood is about the 16th part of an inch in thickness, 

 and appears to the naked eye, composed of 4 distinct 

 parts. 1. A dry, leathery, fawn-colored, semi-trans- 

 parent, tough membrane, which is the cuticle ; 2. 

 a cellular layer which adheres, although not very 

 firmly, to the cuticle, and is named the cellular integ- 

 ument ; 3. a vascular layer ; and 4. a whitish layer, 

 apparently of a fibrous texture, which is the inner 

 baric; and of a more complicated structure than the 

 other layers. 



1. The Cuticle. This term is employed to dis- 

 tinguish it from the thin unorganized pellicle already 

 described under the name Epidermis, as one of the 

 general components of the vegetable structure ; and 

 which is, in fact, the exterior part of the cuticle. 



The cuticle may be raised from the cellular integ- 

 ument by the point of a knife, and this is the best 



