60 TEXTURE OF VEGETABLES. 



the entire bark, and in all they are its most essential 

 portion. 



The exterior and old " layers are coarse and loose 

 in their texture, exhibiting individually a conspicuous 

 and indurated, but very irregular net-work, composed 

 of bundles of longitudinal fibres, not ascending the stem 

 directly but winding more or less around the axis of the 

 plant. 



As the layers recede from the circumference, the 

 net-work which they form is finer though still very ir- 

 regular, and their texture more compact. But al- 

 though irregular, the meshes of the different layers 

 often correspond, forming an aperture that extends as 

 far as the meshes coincide, but diminishing in size as 

 it penetrates towards the centre. In the trunks of 

 aged trees, such as the Oak and Elm, the apertures 

 thus formed, widen into large gaps and chinks, exhibit- 

 ing still in their distribution the rough traces of the 

 net-work of the original layer, now laid bare by the 

 decay of the epidermis and cellular integument."* 



But in the bark of young trees and young branches, 

 these apertures are occupied by a cellular substance, 

 more or less indurated, which pervades the fibres of 

 the net-work and binds them together, but these fibres 

 being less perishable than the intervening substance 

 remain entire long after it has wasted away. 



The inner layer, that which lies contiguous to the 

 wood is termed Liber, from its having been employed 

 in ancient manuscripts. It is more delicate than the 

 others and also more important ; whether we regard 

 its uses in the economy of vegetation, or its subservi- 

 ency to the wants of man. 



* Keith. 



