TEXTURE OF VEGETABLES. 197 



rye, and most kinds of grass, the cuticle is of the highest 

 importance, for it supports their stalks and secures them from 

 injuries. In these, and still more abundantly in some others, 

 Sir Humphry Davy has discovered the existence of a flinty 

 earth ; and it is this which makes the ashes of burnt straw 

 one of the best materials which can be employed in giving 

 its finest polish to marble. The fruit of the peach and the 

 leaf of the mullein have a cuticle covered with dense and 

 rather harsh wool. 



Immediately under the cuticle of leaves and young stems 

 is found a substance called the cellular integument. It is 

 of a pulpy texture and the seat of colour. No plants are 

 destitute of it, for it is the seat of operations indispensably 

 necessary to healthy vegetation. When the cellular integu- 

 ment is removed, the outer surface of the hark presents it- 

 self, which in plants or branches that are only one year old, 

 consists of one simple layer ; but in the older branches and 

 trunks of trees, it consists of as many layers as they are 

 years old. The bark contains a great number of woody 

 fibres, running for the most part longitudinally, which give 

 it tenacity, and in which it differs very essentially from the 

 parts already described. In the bark, the peculiar virtues or 

 qualities of particular plants chiefly reside. Here we find 

 in appropriate vessels the resin of the Fir, the astringent 

 principle of the Oak, the fine and valuable bitter of the Pe- 

 ruvian Bark, and the exquisitely aromatic oil of the Cinna- 

 mon. Immediately under the bark is situated the wood, 

 which forms the great bulk of trees and shrubs. When cut 

 across it is found to consist of numerous concentric layers. 

 LinnjEus and most writers believe that one of these circular 

 layers is formed every year, the hard external part being 

 caused by the cold of winter ; consequently, that the exact 

 age of a sound tree when felled may be known by counting 

 these rings. That the bark produces wood seems to have 

 been proved beyond dispute, for plates of tin-foil have been 

 introduced under the barks of growing trees, the wounds 

 carefully bound up, and after some years, on cutting them 

 across, the layers of new wood have been found on the out- 

 side of the tin. 



The centre or heart of the vegetable body, within the 

 wood, contains the pith. Its texture is precisely similar to 

 that of the cellular integument, being composed of cells 



