273 



These structural features are: — 



(1) Functionless (permanently closed) stomata. 



(2) Functionless hydathodes (the water-pores being 

 closed). 



(3) Light-orientated (obliquely placed) palisade-cells. 



I have investigated specimens of this species from two 

 localities, viz. Siberia (July 24, 1878, Kjellman) and Nova 

 Zembla (Th. Holm). They were all alike. 



Saxifraga tricuspidata Retz. (Figs. 21 and 22.) 



Saxifraga tricuspidata Retz. a is usually found upon heaths 

 and is xerophytic in the choice of its habitat, and this xero- 

 phytism is distinctly impressed upon the structure. 



The leaf is narrov^f (Fig. 21 A)^ fairly thick, and, at the 

 apex, is trifid . and bears three hydathodes. The epidermis of 

 the upper surface (Fig. 22) consists of fairly straight-walled 

 cells, which at the base of the leaf are nearly isodiametric, 

 but become more and more transversely elongated towards the 

 apex of the leaf. The cells are not elongated along the midrib. 

 Pits are present in the lateral walls. The outer walls are thick, 

 with distinct cuticle (Fig. 22 B]. Stomata are evenly distributed 

 over the greater part of the leaf-blade, they are most nu- 

 merous on the more exposed parts of the leaf, but are few 

 in number at the base. They are somewhat prominent. Along 

 the margin of the leaf are numerous irregularly-multicellular 

 hairs. Glandular hairs occur, with long, club-shaped apical 

 glands (Fig. 21 B). 



The epidermis of the lower surface (Fig. 22) along the margin 

 is, in structure, precisely similar to that of the upper surface — 

 also in regard to its stomata. Along the middle of the leaf 

 the cells are more -elongated and the stomata few in number 

 (more abundant, however, towards the apex of the leaf); Børge- 

 sen states that there are two per unit of surface, while the 



