THE TUNDRA AND ITS FAUNA 



19 



abundance of mosses and lichens, which do not die 

 down in winter, and are therefore permanently avail- 

 able as pasture for the herbivorous mammals. It is 

 well known that the lichen popularly called reindeer 

 moss (Cladonia rangiferina), which occurs over wide 

 areas, forms a very important part of the winter food 



Fig. 1. The Tundra in Northern Kussia, summer conditions. The 

 iUastration shows the undifferentiated nature of the drainage, and 

 shows also that at this season pasturage is freely available for 

 herbivorous mammals. 



of the reindeer. Other areas are clad in hair moss 

 (Polytrichum), or bog moss (Sphagnum). Among the 

 higher plants we may note the presence of dwarf 

 wiUows, birches, alders, &c., whose branches stick up 

 through the snow, and whose buds and seeds are of 

 great importance as part of the food of the ptarmigan 

 and the snow-bunting. In the more favourably situated 

 regions berry-bearing shrubs occur, such as crowberries, 



B 2 



