278 



about live times as common upon the southern side as upon 

 the northern, while it scarcely ever occurs on the eastern 

 and western sides i Norman, I, c, pp. 294 — 95). 



The leaves are in a dense rosette, which somewhat recalls 

 Semperviviim. Each of the teeth upon the leaves is provided 

 with a hydathode (Fig. 23 A). The leaves are fairly thick. 



The epidermis of the upper surface (Fig. 23 B and Fig. 24) con- 

 sists of polygonal, straight-wailed, usually transversely elongated 

 cells; the lateral walls are rather thick (3—4;/), with numerous 

 thin-walled parts (pits). The outer wall is thick (8 — 10/^), with 

 a strong cuticle; stomata occur abundantly, but are absent 

 towards the base, are more numerous upon the exposed parts 

 of the leaves, and are all surrounded by 4 — 6 small cells; 

 they project above the leaf-surface (Fig. 23 B). 



The epidermis of the lower surface (Fig. 24) consists of 

 elongated cells which are similar in structure to those upon the 

 upper surface. The stomata are absent from along the whole 

 of the middle band and from the base of the leaf, exactly as 

 in S. Aizoon (a specimen from Kobbefjord — which see); but 

 they are numerous along the margin, where the epidermal cells 

 are less elongated, and are decidedly most abundant upon the 

 lower side. Along the margin of the leaf-base there are some 

 thick, irregularly-multicellular iiairs (Fig. 23 C). 



The mesophyll consists of remarkably homogeneous cells; 

 the palisade-cells are somewhat longer than the cells of the spongy 

 parenchyma, and approximately barrel-shaped (Fig, 23). They are 

 placed, especially towards the apex, obliquely to the epidermis, 

 and there are numerous, rather large intercellular spaces 

 between them. Below, the palisade merges imperceptibly into 

 the more isodiametric, unbranched cells of the spongy paren- 

 chyma, between which the intercellular spaces are still larger. 

 The vascular bundles are without stereom, but are surrounded 

 by a (usually one-layered) bundle-sheath which contains tannin. 

 Sphaerocrystals, the nature of which has not been more 



