236 FERNOW 



interesting fact to the plant geographer is that the forest 

 flora of this interior region is entirely different from that 

 of the coast region, being in its species essentially the same 

 as our northeastern Atlantic boreal flora. 



Intervening between the Pacific and Atlantic forest 

 flora, is the high, somewhat triangular-shaped plateau, 

 enclosed by the coast ranges and the more northern 

 mountains, some 15,000 square miles in extent according 

 to I. C. Russell, 1 a region of absolute, stern, silent, 

 motionless winter, covered with snow and ice all the 

 year round, without a vestige of life. 



Again, skirting the coast of Bering Sea from Kuskokwim 

 Bay northward and along the Arctic Ocean, is the tundra 

 a belt of treeless country, though not entirely devoid of 

 woody vegetation, varying from a hundred miles or less 

 to several hundred miles in width. 



Lastly we recognize as a different type the forestless 

 region of grassy slopes and snow covered peaks which 

 the Alaska Peninsula and the Aleutian and other islands 

 west of the I53d degree of longitude exhibit. 



To explain this distribution of the arborescent flora, 

 both climatic and physiographic conditions must be ad- 

 duced. It is easily understood that the mechanical barrier 

 which the ice- and snow-bound mountain ranges interpose 

 should effectively separate the Pacific and Atlantic forest 

 flora. But to the westward toward the Alaska Peninsula 

 and the Aleutian and other islands no such mechanical 

 barrier exists, hence other causes must be found to ex- 

 plain the limits of distribution. 



The separation of the coast and interior floras seems in 

 general complete, although an exchange of species may 

 occur here and there across the mountain passes and 

 along the river courses. Thus, a paper-barked birch ap- 

 pears in numbers at the head of Lynn Canal, 1,000 feet 



1 Am. Journal of Science, 3d series, Vol. XLIII, p. 171, 1892. 



