LECT. XI.] ANATOMY OF LEAyES. 601 



leaf which we have examined, there is sufficient 

 reason for believing that it is as much a distinct 

 layer as the cuticle in the human body, although, 

 in the leaf, it cannot be readily detached from the 

 interior layer of cutis. It is described by Saussure 

 as being perforated by the slits or pores which, I 

 shall soon demonstrate to you, are found on one or 

 both of the surfaces of every leaf; but we shall 

 find, on minutely examining these, 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 

 covering of every part of the vegetable texture, 

 which would otherwise come in contact with the 

 air. If, however, it cover every part of the sur- 

 face of the leaf, and is an imperforated mem- 

 brane, by what means, it may be asked, does the 

 fluid which exhales so freely from the leaves es- 

 cape? It is certainly not easy to answer this ques- 

 tion ; but as we can scarcely form an idea of a 

 membrane perfectly free from pores, even in a 

 living body, transmitting fluids ; we may conclude 

 that, although no pores are visible in this mem- 

 brane, even when it is examined under the mi- 

 croscope, yet, it does not follow 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 



