347 



The leafis somewhat succulent; the upper surface is glabrous 

 and the lower somewhat hairy with long (as much as 2 mm.), flaccid 

 hairs. The structure of the leaf is decidedly dorsiventral; in 

 the majority of the leaves three distinct palisade-layers (Fig. 

 7, A) were found, the height of the cells of which was about 

 three times the breadth : the palisade-cells were slightly inclined 

 towards the leaf-apices. There is an abrupt transition from 

 the palisade to the spongy parenchyma which is extremely 

 loose in structure and consists of abundantly branching cells. 



л - с 



Fig. 7. R. glacialis. 



A, Transverse section of leaf (Jan Mayen). Б. Surface section of the uppermost layer of 



the palisade-tissue (Tromsö). С, Surface section of spongy tissue (Tromsö). ср. Epidermis 



pal, palisade-cells, /, intercellular spaces {A, about ^h; B, C, "'"/i). 



The vascular bundles are surrounded by a sheath containing 

 chlorophyll, and are entirely enclosed by the mesophyll; even 

 above the principal vein three palisade-layers occur. The 

 epidermis of both the upper and lower surface contains chlo- 

 rophyll; the outer walls are slightly thickened. The stomata 

 are situated on a level with the epidermis (Fig. 8, D). The 

 cells of the upper epidermis have almost straight walls while 

 those of the lower epidermis are somewhat undulating (Fig. 8, 

 A^ B). There are about three times as many stomata upon 

 the upper as upon the lower surface. Тн. Kesvoll found 78 



