244 



the leaf-surface and also with scattered, long-stalked glandular 

 hairs. Børgesen (1. с, pp. 225—26) states that the stomata are 

 most numerous upon the upper surface, where there are 10 

 per unit of surface, while on the lower surface only 8. 



The epidermis of the lower surface has even more strongly 

 undulating walls; it is otherwise very slightly developed (as upon 



Fig. 2. Saxifraga cernua. 



A, Epidermis of the upper surface of the leaf. B, The same in vertical section. C, Epidermis 



of the lower surface of the leaf (in a solitary cell several crystal-aggregates are seen). D, 



Lower epidermis in vertical section. E, Hair from the lower surface of the leaf ('^-/i). 



the upper surface) and is provided with stomata, placed slightly 

 above the level of the leaf-surface, and short-stalked glandular 

 hairs exactly similar in appearance to those upon the margin 

 of the leaves (Fig. 2 E). 



The mesophyll is very loosely arranged, with large and 

 numerous intercellular spaces (Fig. 1 C). The palisade-cells form 

 indistinct rows and, in the greater part of the leaf, are placed 

 almost vertically within the epidermis while towards the apex of 

 the veins they are placed somewhat obliquely — a circumstance 



