252 



Dr. Borgesen stales that llie slomala are equally abundant 

 on liolli sides (I. c, p. 225); he has however counted 17 upon 

 the upper surface, and 20 ui)(»n the lower per unit of surface 

 (I. c, p. 226). 



The mesophyll is fairly distinctly differentiated into a palisade- 

 layer and spongy parenchyma; in the specimens examined by 

 me there are three distinct palisade-layers (Børgesen found 2 — 3). 

 The presence of these three layers, which implies that the 

 specimens examined had been growing in comparatively ligli 

 localities, harmonizes excellently with Norman's above-mentioned 

 statement that the species occurs three times more commonly 

 on the sunny side than on the shady side (I have not seen 

 "shade-specimens," but Borgesen has evidently found them). 



The spongy parenchyma is loosely arranged and consists 

 of stellate cells (Fig. 6). The veins are accompanied by colour- 

 less, long-celled, usually one-layered bundle-sheaths. 



The hydathodes have convex epithema and are quite similar 

 in structure to those of 5. cernua\ they do not secrete lime. 



Borgesen found scattered glandular hairs; these consist of 

 a single row^ of cells, terminating in an undivided, obovate, 

 one-celled head. Holm (1. c. PI. X, Fig. 9) has figured a glandular 

 hair with a two-celled head, — a feature which I have not met 

 with. The hairs are more abundant upon the lower, and few 

 in number upon the upper, surface. 



The structure of the leaves is essentially the same in spe- 

 cimens from all the localities from which material has been 

 examined; thus. I have more closely investigated specimens 

 from Upernivik (July 10, 1887), Hold with Hope (July 10, 1891), 

 Julianehaab (June 14, 1887), Dyrefjord (June 10, 1895), and 

 Tromsø (June 28). The only deviation from the description given 

 above was observed in the specimens from Hold with Hope 

 and Dyrefjord, all of which contained a considerable quantity 

 of oxalate of lime as crystal-aggregates in the cells of the spongy 



