SECT. I. THE EPIDERMIS. 311 



the best of all leaves for a beginner to commence 

 his observations upon is, perhaps, that of common 

 Sorrel, Rumex Acetosa, of which the cuticle is so 

 easily detached from the pulp that it may be 

 obtained in large portions, merely by tearing the 

 leaf in two, either in a transverse or longitudinal dU 

 rection. 



The longitudinal direction of the fibres and 

 meshes of the net-work forming the basis of the 

 epidermis is., as represented by Hedwig and Com- 

 paretti, generally verticle, or at least it follows the 

 longitudinal direction of the plant. But although 

 this is the rule, it has, like most other rules, its ex- 

 ceptions ; as may be exemplified in the epidermis of 

 the stem of the Currant and Cherry-tree, in which 

 the longitudinal direction of the fibres and meshes 

 is not vertical but horizontal, extending in a line 

 that encircles the body of the plant, and gives to 

 the epidermis a tenacity that is greatest in the ver- 

 tical direction of the stem. 



According to all of the foregoing descriptions the 

 epidermis is represented as consisting of at least 

 two if not more layers, which, in the stem of many 

 plants, are very easily distinguished, particularly in 

 that of the Paper Birch as exemplified by Du 

 Hamel. The same thing may be also exemplified 

 in the stem or branches of the Currant, Ribes ru~ 

 brum ; the outer layer of the epidermis of which, 

 after acquiring from age a tinge of brown, splits 

 into a number of fragments that spontaneously de. 



