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 
Fic. 1. The Tundra in Northern Russia, summer conditions. The 
illustration 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 
willows, 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, 
B2 
