484 PLANT GEOGRAPHY 



463. Arctic vegetation. The seed plants of the arctic flora 

 are mostly perennials, never trees, though many of the species, 

 as the willow, alder, and birch, belong to groups that are trees 

 in other regions. By the large bulk of the underground por- 

 tion as compared with that of the part above ground, they are 

 adapted to a climate in which they must lie dormant for not 

 less than nine months of the year. The flowers are often showy 

 and appear very quickly after the brief summer begins. Mosses 



FIG. 369. A plant of arctic willow 

 About natural size 



and lichens are abundant, the latter of economical importance 

 because they furnish a considerable part of the food of reindeer. 

 464. Mountain or alpine vegetation. In a general way the 

 effect of ascending a mountain, so far as vegetation is concerned, 

 is like that of traveling into colder regions. It was long ago sug- 

 gested in regard to Mount Ararat, that on ascending it one trav- 

 ersed first an Armenian, then a south European, then a French, 

 then a Scandinavian, and finally an arctic flora. Up to a certain 

 height, which varies in different latitudes, the slopes of moun- 

 tains are very commonly forest-covered. The altitude up to 



