164 



I do not find any essential differences in the structure of leaves 

 from Arctic and from non- Arctic regions (Fig. 1). 



As regards the upper surface and the flanks, the outer 

 walls of the epidermis are thick and strongly cuticularized; 

 and the cuticle is striped longitudinally; the lateral walls are 

 wavy. The inner walls are characterized by a thick mucilagi- 

 nous layer which is noticeable along the whole of the upper 

 surface of the leaf and round the flanks, but ceases at the 

 entrance to the well-known "cavity" of the underside, formed 

 by the edges of the leaf closely approaching each other, being 



Fig. 1. Empetrum nigrum. 



Transverse section of a leaf; magnified. The parallel lines indicate 



the palisade-tissue, and the tinted part the spongy parenchyma with 



its lacimæ, indicated by white. K, Glandular hairs. Sp, Stomata. Disko. 



(A. M.) 



separated only by a narrow groove. This groove is closed 

 with long hairs, densely matted together, whereby is formed, 

 as has often been mentioned, "a calm space, free from wind." 

 Only in the cavity, which has thin outer-walls to its epidermal 

 cells, do stomata occur; their number is great; they lie trans- 

 versely to the length of the leaf and protrude slightly. Large 

 glandular hairs occur in the cavity. 



The chlorophyll-tissue consists of 2 — 4 layers of very short 

 palisade-cells and a rather lacunose spongy parenchyma. It is 

 transversed by a large median vein and several lateral veins. 



As is well-known, the flowers of Empetrum are exceedingly 



