328 FOUNDATIONS OF BOTANY 



for not less than nine months of the year. The flowers 

 are often showy and appear very quickly after the brief 

 summer begins. Mosses and lichens are abundant, the 

 latter of economical importance because they furnish a 

 considerable part of the food of reindeer. 



400. Mountain or Alpine Vegetation. In a general way 

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



FIG. 232. A Plant of Arctic Willow. (About natural size.) 



concerned, is like that of traveling into colder regions. 

 It was long ago suggested, in regard to Mount Ararat, 

 that on ascending it one traversed 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 mountains are 

 very commonly forest-covered. The altitude up to which 

 trees can grow (or as it is commonly called in this country 

 the " timber line ") is somewhat over twelve thousand feet 



