343 



The plant grows by preference in soil poor in humus. 

 In Arctic Norway it usually is not found below a height of 

 200—300 m. above tree-limit ; Norman regards it also as a decidedly 

 continental plant that is not common upon the islands. In 

 contradistinction to this, is the fact recorded by Düsen from 

 East Greenland, 74° — 75° N. lat. that it is found there growing 

 at shore-level and is never found at the head of fjords. 



Geographical Distribution. Arctic Russia, Lapland, 

 Finmark, Norway, Sweden, Beeren Eiland, Spitzbergen, Jan 

 Mayen, Iceland , the Færøes , the Alps, the Pyrenees, East 

 Greenland from 65^/2°N.L. north- 

 wards (Lange, Ddsén, see p. 342). 



Anatomy. Adventitious roots 

 of the first order. Epidermis 

 is thin-walled , and collapsed in 

 older roots. Exodermis is distinctly 

 marked ; the cells are somewhat 

 radially elongated, the radial walls 

 undulating. The epidermis and 

 the exodermis have suberized walls, 

 but the inner layer of the inner 

 wall of the exodermis is of cellu- 

 lose. The two outermost layers 



of cells of the cortex have somewhat coUenchymatously thick- 

 ened walls (Fig. 4|. The rest of the about 15-layered cortex 

 consists of thin-walled cells which are circular in transverse 

 section, and of large, usually 4 — 5 angled, intercellular spaces. 

 Large lysigenous lacunæ can often be seen. Next to the 

 central cylinder there are usually a few layers of smaller and 

 more closely-placed cells. All the cells of the cortex contained 

 a quantity of starch (middle of July), The endodermis is slightly 

 thickened and suberized; Caspary's dots are indistinct; the cells 

 are somewhat tangentially elongated. Pericycle is one-layered, 

 and the cells are isodiametric in transverse section. The vas- 



Fig. 4. R. glacialis. 



The outer layers of a root of the 

 first order (Jan Mayen), ep, Epi- 

 dermis; ex, exodermis. (^'^/i). 



