272 Elg. Warmim;. 



That the dorsiventrality can be displayed in the 

 various degrees of thickness of the epidermal cells of the 

 ventral and dorsal surfaces, has been stated above. It appears, 

 as already mentioned, to be correlated, with the direction 

 of the leaves (the epidermis of the surface which is turned 

 upwards or outwards being the highest). 



The epidermal cells are arranged more or less regularly 

 in longitudinal rows, at any rate in the narrow or linear 

 leaves (see e. g. Fig. 14, E and F; Fig. 15, E and F\ Fig. 16, 

 G, H and /; Fig. 18, H; Fig. 19, D and F; Fig. 20, G; and 

 Fig. 21, //, J and L). 



The lateral walls of the cells, when seen from above, 

 are sometimes highly undulating on both leaf-surfaces, 

 although more highly on that surface which limits the spongy- 

 tissue than on the other surface (Fig. 15, E and F)\ more 

 frequently the epidermal cells of the one surface have un- 

 dulating lateral walls, while those of the other have only 

 slightly undulating or quite straight walls; as also the cells 

 of this surface are more elongated (Fig. 14, E and F\ Fig. 16, 

 G, H and /; Fig. 19, D and F; Fig. 20, F and G ; Fig. 21, 

 H, J and L). The cells with very highly undulating walls 

 are moreover very short. The undulations indicate more damp 

 or more shady conditions. 



The Stomata are lower than the other epidermal cells, 

 and are placed on a level with the outer surface of the epi- 

 dermis, or even project slightly above it (this is shown in 

 many figures). Stomata may occur on both surfaces, some- 

 times almost equally in number. In other cases, the one 

 surface has no stomata or only a few. In some cases 

 they are most numerous on the dorsal surface, in others 

 on the ventral surface, for instance in Stellaria humijusa. 

 All these circumstances have been fully treated of by Vesque, 

 Börgesen, Wagner and Bonnier (see also Th. Holm). As 



