LECT. XI.] ANATOMY OF LEAVES. 607 



than the epidermis which covers it, can be demon- 

 strated only as they appear in a vertical section. 

 They are either spheroidal or oval ; and are found 

 generally empty, or filled with a colourless fluid. 

 I have not been able to detect any immediate com- 

 munication between them and the cells of the pa- 

 renchyma, or even between one and another. In 

 the greater number of leaves the cutis contains one 

 layer only of cells ; but it may contain several 

 layers, as Mr. Francis Bauer * has demonstrated 

 is the case in the genus Hsemanthus; and I have 

 found that this is the case, also, in the leaf of 

 commpn Oleander, Neriurn Oleander. 



The slits or apertures which have been already 

 noticed as existing on one or both surfaces of all 

 leaves, were first described by Grew as orifices; but 

 afterwards regarded by the elder M. De Saussure 

 as glands, and by M. Von Gleichen, who ex- 

 amined them in the leaves of Polypody, as the 

 anthers of the Fern tribe. The more correct ob- 

 servations of Hedwig and of Decandolle, however, 

 have confirmed the opinion of Grew; and, indeed, 

 it is only necessary to examine them, under a good 

 microscope, to be satisfied that they are real 

 pores -f-. In the leaves of trees and of some other 



* Tracts relative to Botany, Lond. 1805. 



f It is extraordinary that Senebier, who searched for these 

 apertures in the leaves of a great variety of plants, never could 

 detect them. Vide Phys. veg. i. p. 4-56. 



