LECT. XI.] ANATOMY OF LEAVES. 615 



ceive that the vesicle (/*.) appears to be double ; 

 from which it is probable that it is this vesicle, 

 seen through the transparent substance of the 

 cutis, which gives the appearance of the shield 

 in the superficial view of the aperture. As we 

 find that, in the superficial view of these apertures, 

 the character varies considerably in different 

 plants, so this form of the tube and the vesicle is 

 also variously modified ; but the general charac- 

 ter is nearly the same, with a very few exceptions, 

 throughout the vegetable kingdom, as far, at 

 least, as my observations extend. Thus in the 

 Agave (59- p. 611), the superficial form of the 

 aperture is very different from that in Dianthus 

 (40. p. 602) ; but if we examine it in a transverse 

 section of the leaf, although we find the general 

 structure of both agreeing, inasmuch as the aper- 

 tures of both are lined with the epidermis, pene- 

 trate the cutis, and have at their bottom the vesi- 

 cular ring ; yet we perceive that that of the Agave 

 differs from that of Dianthus, in terminating in a 

 large dilated cell (66. f.), which is found always 



R R 4 



