280 



the former having less markedly differentiated palisade-tissue 

 than the latter. This somewhat indistinct differenlialion also found 

 by me in the Arctic specimens of S. Cotijledon at my disposal agrees 

 closely with characters found by Bonnikr in Arctic specimens ; 

 the same investigator (Rev. gén. d. bot.. Tome VI, p. 514) has 

 demonstrated this feature very distinctly in S. oppositifolia (see 

 below). His figure of the Arctic leaf of this latter species is good 

 and agrees closely with the results of my investigations. 



Saxifraga Aizoou Jacq. (Figs. 25, 26 and 27). 

 Saxifraya Aizoon Jacq. occurs upon sunny cliffs, and 

 sometimes upon rather wet moraine, and is xerophytic. Its whole 



Fig. 25. Saxifraga Aizoon. 



The leaf: A {-n), Leaf-form. B, Epidermis of the upper surface. C, Marginal hairs. 



D, Longitudinal section (•'"/i). 



