253 



parenchyma near to the bundle-sheaths of the veins at the 

 base of the leaf. 



As may thus be seen, the structure of the leaf is distinctly 

 mesophytic or perhaps even hygrophytic; the prominent stomata 

 upon both leaf-surfaces, the thin-walled epidermis, and the loose 

 structure of the spongy parenchyma show this. The agreement 

 between the structure of the leaf and the character of the habitat, 

 as it has been described to me by M. Porsild, is unmistakable. 



Saxifraga hieraciifolia W. K. (Figs. 7 and 8). 



Saxifraga hieraciifolia W. K. occurs in precisely the same 

 localities as S. nivalis (according to verbal information from M. 

 Porsild), and it should be expected to have a structure similar 

 to that of the latter; that it has it will be more clearly proved 

 by wliat follows. 



The leaf is long-stalked, oval, with distant teeth and a 

 hydathode at the apex of each tooth (Fig. 7). The thickness is 

 slight, less than in S. nivalis. 



The cells of the epidermis of the upper surface (Fig. 8 Ä 

 and C) have undulating walls, and rounded, wavy contours; all the 

 walls are thin, with cuticle very slightly developed. The stomata 

 are numerous, and prominent. Scattered glandular hairs occur 

 which consist of a single row of cells with a one-celled head. 



The epidermis of the lower surface (Fig. 8 В and D) is 

 essentially like that of the upper; but the undulating outline of 

 the lateral walls is more acutely angled. Stomata are numerous, 

 and prominent. Børgesen writes that there are as many upon 

 the upper as upon the lower surface, but yet, at the same 

 time, records seven upon the upper and twelve upon the lower 

 surface per unit of surface. 



The mesophyll (Fig. 7 B, С and D) is distinctly differentiated 

 into palisade-tissue and spongy parenchyma. Borgesen found 

 2 — 3 layers; my specimens showed two; nowhere in the leaf 

 are they placed obliquely. The cells of the spongy parenchyma 



XXXVI. 17 



