259 



The epidermis of the upper surface (Fig. 1 1 B and C) consists 

 of two kinds of cells, (1) large, somewhat straight-walled and 

 elongated cells, (2) irregularly-shaped cells with undulating walls. 

 The inner, lateral and outer walls are thin (the last about 2/z in 

 thickness). In the leaf-stalk the cells are greatly elongated, narrow 



Fig. tl. Saxifraga hypnoides. 



A (-/i), Leaf-form. B, Epidermis of the upper side of the leaf-stalk. C, Epidermis of the 



upper surface of the leaf. D, Hairs (see text). E, Epidermis of the lower surface of the 



leaf. (B, C, D and E ■'■"/i). 



and straight-walled. The stomata are placed on a level with the 

 leaf-surface and are distributed in groups of very variable size; 

 their apertures principally lie parallel with the longitudinal axis 

 of the leaf. All the epidermal cells between and in immediate 

 proximity to a group of stomata are smaller than the ordinary 



