126 



alpina; it is deciduous, hairs are absent, and there is only a 

 waxy covering. 



The upper and lower epidermis are only slightly thickened 

 and have no specially cuticularized layer beneath the cuticle ; 

 the lateral walls are slightly undulating. The stomata are con- 

 fined to the lower surface and do not project. 



The palisade-tissue consists of 1 — 2 layers of cells, with 

 a height of as much as 100//, and it is somewhat unequally 



developed , the lower 

 layer being less deve- 

 loped when the upper 

 consists of long cells. 

 The cells of the spongy 

 parenchyma are more 

 elongated in the vertical 

 than in the horizontal 

 direction and often 

 branch but slightly; the 

 intercellular spaces are 

 large. The whole of the 

 mesophyll is loosely 

 built. In the material at 

 my disposal I have not 

 observed any difference 

 between Danish, Sub- 

 arctic, and Arctic spe- 

 cimens. 



The stem. The 

 primary cortex consists, 

 according to Segerstedt, "of a few layers of cells of which 

 the outermost have scanty chlorophyll-contents with walls 

 thicker than those of the inner, which are loosely con- 

 nected and the contents of which are colourless." The epidermis 



Fig. 37. Vaccinium uliginosum. 

 Transverse section of stem X 180. (Phot.) 



