ANATOMY OF LEAVES. 305 



consist of two distinct layers ; the exterior of vvhicli 

 is a fine, transparent, apparently unorganized pellicle, 

 and the interior vascular and cellular. 



The true epidermis, or the delicate pellicle which 

 forms the outermost covering of the leaf, is described 

 by Saussure as being perforated by the slits or pores 

 which may be found on one or both of the surfaces of 

 every leaf; but on minute examination it appears, 

 that it is not perforated by them, but enters into them, 

 as well as into every gland opening on the surface of 

 a leaf, as a lining membrane ; and is, in fact, the cov- 

 ering of every part of the vegetable texture, which 

 would otherwise come in contact with the air. If, 

 however, it cover every part of the surface of the leaf, 

 and is an imperforated membrane, by what means, it 

 may be asked, does the fluid which exhales so freely 

 from the leaves escape ? It is not easy to answer this 

 question ; but as we can scarcely form an idea of a mem- 

 brane perfectly free from pores, even in a living body, 

 transmitting fluids ; we may conclude that, although 

 no pores are visible in this membrane, even when it is 

 examined under the microscope, yet, it does not fol- 

 low that no pores exist; and, in accounting for the 

 transudation of the fluids, which the leaf throws off, we 

 must always bear in mind, that the functions of living 

 bodies are influenced by different powers from those 

 which regulate the operations connected with inert 

 matter. 



The second or interior cuticular layer is seen 

 through the epidermis, and consists of a vascular net- 

 work resting upon a layer or layers of cells. The 

 lines forming the meshes which characterize the cutis 

 of leaves, were first described by Hedwig as vessels, 

 originating in the circumference of the pores ; an 

 opinion supported by the elder Saussure and M. Kie- 

 ser ; and which is confirmed by the microscopical ex- 

 2G* 



