104 ANATOMY OF VEGETABLES. 



action of air and light, and in which the various secre- 

 tions principally take place. 



This part is interposed between the cuticle and the 

 true bark. 



3. Cortex. Immediately under the cellular integu- 

 ment and next to the wood we find the inner or true 

 bark. Jt consists of but one layer in plants or branch- 

 es of only one year old. In older branches or the 

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

 are years old. The innermost layer is called the liber. 

 It is in this layer only that the essential vital functions 

 are carried on for the time being ; after which, it is 

 pushed outwards with the cellular integument by the 

 successive formation of new layers, and with the cel- 

 lular integument finally becomes a lifeless crust. 



The inner bark of some species of trees separates 

 when macerated in water into the several layers of 

 which it is composed ; each layer, in some cases, ap- 

 pearing perforated like lace. The Lime-tree or Bass- 

 wood is one of the finest examples, in which the fibres 

 are soft and tenacious like hemp, and have been manu- 

 factured. 



All these layers, in a living state, are closely con- 

 nected by the cellular texture which pervades the vege- 

 table body generally, as well as by transverse vessels 

 which pass through them. The principal vessels of 

 the bark are the longitudinal ones 5 they are called 

 cortical vessels. 



In the bark the peculiar virtues of particular plants 

 chiefly reside, especially in several of its internal lay- 

 ers nearest the wood. 



II. Wood. 



When the bark is removed, we come to the wood* 

 which makes the principal bulk of a trunk of a tre^ or 

 shrub. When cut across, it is found to consist of a 

 number of concentric layers, called grains, PL 3, fig* 

 17, c. very distinct in most trees of our northern cli- 



