261 



is like that of the upper, only the hairs of the former are 

 glandular (upon the leaf-stalk, however, non-glandular hah's occur). 



Along the margin of the leaf-stalk there are numerous 

 hairs similar to those upon the upper surface of the leaf. 



The mesophyll (Fig. 12) is differentiated to about the same 

 degree as in S. groenlandica: the palisade-cells are short (in the 

 specimens investigated very indistinctly, or not at all, obliquely 

 placed) and the layer passes fairly gradually into the spongy 

 parenchyma. The latter is loose and lacunose in the middle of 

 the leaf, but immediately within the lower epidermis it becomes 

 very compact and polygonal, and is almost without intercellular 

 spaces. 



The veins are without mechanical tissue, and are accom- 

 panied by a bundle- sheath of elongated cells one-layered on 

 the whole. 



The hydathode is well-developed, with convex epithema, 

 and it opens upon the upper side of the leaf-margin and does 

 not secrete lime (Fig. 12 i). 



The description here given is based upon the investigation 

 of specimens gathered by F. Borgesen at Velbestad (the Færøes), 

 July 5, 1895; that is the only material I have had at my disposal. 



Saxifraga groeulandica L. (Figs. 13, 14 and 15). 



Saxifraga groenlandica L. is common everywhere on the 

 heather moors and upon the rocky flats of Greenland, and 

 ascends to the mountain heights there and also in Norway 

 (Warming, Norman). Grows almost as commonly on the sunny 

 side as on the shady side upon the mountains; and usually 

 in dry localities. 



The leaves are deeply palmately cleft, the leaf-stalk is 

 broad and flat. A hydathode occurs at the apex of each segment. 

 Glandular hairs occur fairly numerously upon both surfaces. 



The epidermis of the upper surface (Figs. 13 B and 15 A 

 and 5) has everywhere thin-walled cells; the latter, upon the leaf- 



