X FLOWERS AND FORESTS OF THE FAR WEST 221 



long to quite peculiar American genera are only 14 in 

 number. 



In considering how this curious similarity of the alpine 

 species of the two continents has been brought about, we 

 must go back to a time anterior to the glacial epoch, 

 when a rather mild climate prevailed in much of what is 

 now the Arctic regions. The present Arctic flora, or its 

 immediate ancestors, was then probably confined to the 

 highest latitudes around the North Pole, together with 

 the higher mountains which were immediately contiguous 

 — such as Greenland, then only partially or not at all ice- 

 clad, Spitzbergen and Nova Zembla, and some of the 

 mountain peaks of Alaska and North-Eastern Asia. At 

 this time the Rocky Mountains, the European Alps, and 

 even Scandinavia supported in all probability only alpine 

 forms of the plants of the surrounding lowlands, such as 

 are now everywhere intermingled with the widespread 

 Arctic species. As the cold came on, and the ice-sheet 

 crept farther and farther over the two continents, the true 

 Arctic plants were driven southward, disj^lacing the indi- 

 genous flora, which could not withstand the increasing 

 severity of the climate, and occupying all the great 

 mountain ranges on the lower side of the ice-fields and 

 glaciers, and also such of the peaks as rose permanently 

 above the ice-sheet of the glacial epoch. As the cold 

 period gradually passed away, these hardy plants kept 

 close to the gradually retreating ice, and in this way 

 mounted to the higher peaks of many mountains from which 

 the ice and even perpetual snow wholly passed away. 

 Thus it is that so many species are now common to the 

 Rocky Mountains and the European Alps; and, what 

 seems more extraordinary, that identical plants occur on 

 the summits of the isolated Scotch and Welsh mountains, 

 and also on the White Mountains of New Hampshire and 

 some of the mountains to the south of them. 



Before passing on to sketch the flora of the Avest coast 

 of America, we may briefly notice the more prominent 

 differences between the Rocky Mountain flora and that 

 of our European Alps, such differences as must strike 



