614 CONSERVATIVE ORGANS. [LECT. XI. 



direction throughout; but in the majority of 

 leaves they have no regular arrangement, and as- 

 sume different directions. In herbaceous plants 

 we generally find them on both surfaces of the 

 leaves; but in ligneous plants they are scarcely 

 ever seen on the upper surface. They are never 

 situated on the costae, nor on the edges of the leaf. 

 But these demonstrations make us acquainted 

 with the superficial aspect only of the foliar aper- 

 tures, beyond which it is surprising that no Phy- 

 tologist has yet attempted to push his investiga- 

 tions; although it is by no means difficult to 

 determine their structure by the aid of the micro- 

 scope. Placing a very thin vertical slice of a 

 leaf of the Clove Pink, Dianthus Caryophyllus, 

 cut in the direction of the axis of the leaf, under 

 the microscope, we find that the aperture (e. 41. 

 p. 602) which is thus divided in its longitudinal 

 diameter, is a short cylindrical tube penetrating 

 completely through the cutis, and terminating in 

 a cul de sac, which is impressed into a vesicle 

 (f.) that appears to communicate with the oblong 

 cells (d.) immediately beneath the cutis. But al- 

 though the aperture penetrates the cutis, there is 

 no opening through the epidermis (.), which, on 

 the contrary, enters into the tubular part of the 

 pore and lines it throughout. In another slice of 

 the same leaf, cut so as to divide one of the aper- 

 tures in its cross diameter (42. p. 602), we per- 



