96 PLANT GEOGRAPHY 



is thus crowded into six or eight weeks, annual plants 

 are all but absent, and many of the prevalent herbaceous 

 perennials do not ripen seed. Large low-lying areas are 

 covered by mosses and lichens, the latter predominating 

 on the poor porous sand derived from granitic rocks and 

 constituting dry tundra, whilst the mosses may or may 

 not retain more moisture and form wet tundra. Three 

 factors, the continuous daylight during the period of 

 vegetation, the low temperature, and, above all, the 

 cold of the soil, combine to retard growth, and the 800 

 species of this region are consequently mostly low-growing 



FIG. 7. Salix polaris, the Dwarf Arctic Willow (nat. size). 

 (From Graebner's " Pflanzengeographie") 



and xerophytic. Many of them, such as the Saxifrages 

 and Papaver nudicaule L., assume a cushion-like habit; 

 have leathery, cuticularised leaves, as in the cases of 

 A ndromeda tetragona L. , or Diapensia lapponica L. ; or 

 become succulent like Saxifraga opppsitifolia L. ; hairy, 

 as are Dry as octopetala L., Loiseleuria procumbens Desf., 

 and Salix lanata L. ; or coated with wax, as is Salix 

 reticulata L. ; or have their leaves rolled up, as in 

 Hierochloe alpina Rcem. and Schul. Numerous and 

 relatively large flowers are the rule; but few are scented. 

 Characteristic types, in addition to those already 

 mentioned, are Cladonia rangiferina, the Reindeer-moss 

 lichen, species of Polytrichum, Empetrum nigrum L., 

 Car ex, Ranunculus, Pyrola, Eriophorum, and Poa. The 

 most numerously represented orders are Cyperacea, 

 Graminecs, Caryophyllacece, Cruciferce, and Composites. 



