30 



OUTLINE OF PLANT GEOGRAPHY 



In the strictly arctic regions, trees are completely wanting, 

 and the shrubs reduced to prostrate mats, scarcely rising above the 

 level of the ground. The bogs and tundra are largely occupied 

 by dense growths of mosses and lichens, among which the grasses, 

 sedges, and low shrubby growths are scattered. Where conditions 

 are favorable there may be seen herbaceous plants, which from 

 their perennial subterranean roots or tubers quickly start into 

 growth in the summer and adorn the barren ground with their 

 showy flowers. Among the characteristic flowers of the far north, 



Fig. 1. — Willow thickets on the upper Killik River, North Alaska. 



Photo., Dr. Philip S. Smith. 



are species of buttercups, anemones, primroses, cinquefoil (Po- 

 tentilla), saxifrages, poppies (Pa-paver nudicaule), and whitlow 

 grass (Draba) . 



Of the woody plants, dwarf willows and birches are characteris- 

 tic, and several of the heath family; e. g., Rhododendron, Cassiope, 

 Vaccinium, Empetrum. The only conifer of the arctic regions 

 is a dwarf juniper. 



While a good many species are pretty strictly confined to the 

 arctic zone, others like some species of cotton grass (Eriophorum) 

 and some of the heath family, e. g., Rhododendron lapponicum, 

 Cassiope tetragona, extend into the colder parts of the temperate 

 zone. Other characteristic arctic species, like the pretty moun- 



