Rosaceæ. 



109 



ern Greenland, in the valleys within the fjords, dispersed 

 through Betula and Salix copses; it grows also in N. America. 

 The leaves are smooth. The epidermis shows strong 

 €uticular stripes, strongest upon the upper surface, and upon 

 the lower surface stronger along the margins (Fig. 41, A, C, 

 D). The outer^wall of the upper epidermis is about 4.5 ^м 



Fig. 41. Sorbus americana. 



л, Transverse section of the leaf, ß, Transverse section of tlie epidermis 

 of the upper surface showing a cell with highly mucilaginous inner \vall. 

 C, Surface view of the upper epidermis of the leaf. D, Section parallel to 

 the surface of the lower epidermis of the leaf ; the cuticular folds of some 

 of the cells are shown as in C, usually each epidermal cell has its own sys- 

 tem of folds. E, Section of the spongy parenchyma of the leaf parallel 

 to the surface. — A, B. C, D, E "Vi- Ivigtut in Greenland. 



thick, of the lower about 2.5 a. Some of the cells in the upper 

 epidermis have highly mucilaginous inner walls, and such 

 cells are often particularly large (Fig. 41, B), compare p. 57. 

 Stomata occur, with the exception of the water-stomata on 

 the leaf -teeth, only on the lower surface; they are on a level 

 with the surface. There are two layers of palisade-tissue of 



