LKCT. XI.] ANATOMY OF LEAVES. 611 



disk of the leaf of common Sorrel, Rumex acetosa 

 (a. b. fig. 10. Plate 10), of the Primrose, Primula 

 (57.), and, very beautiful, on both surfaces of 

 Cactus opuntia (38.). 5. A quadrilateral pore, 

 osculum quadrilaterale, surrounded by an ele- 

 vated margin, as on both surfaces of the leaves 

 of Agave Americana (59-), and of all the other 

 species of the succulent tribe to which it belongs. 

 I cannot avoid remarking, in this place, the na- 

 tural separation, which may be traced by the 

 form of these apertures, between the Aloes and 

 the Agaves. In the former the pores are always 

 circular (60.), and in the latter they are inva- 

 riably quadrilateral (59.) 



61 



It is impossible to notice all the modifications 

 of these different species of the cuticular aper- 

 ture; I shall, therefore, only remark, that among 

 the varieties of the annulated aperture, we some- 

 times find the space between the pore, or the shield 

 and the enclosing ring, divided into distinct por- 



R R 2 



