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1 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 ‘‘cavily” 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 lacune, 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 
