THE NORTHERN VEGETATION COMPARED, ETC. 143 



sea to any height along the slopes of a mountain. In both these 

 directions there is a striking agreement in the order of succession of 

 the phenomena, so much so, that the natural products of any given 

 latitude may be properly compared with those occurring at a given 

 height above the level of the sea ; for instance, the vegetation of 

 regions near the polar circles, and that of high mountains near the 

 limits of perpetual snow under any latitude. The height of this limit, 

 however, varies of course with the latitude. In Lapland, at 67° north 

 latitude, it is three thousand five hundred feet above the level of the 

 sea ; in Norway at lat. 60° it is five thousand feet ; in the Alps at 

 lat. 46° about eight thousand five hundred ; in the Himalaya at lat. 

 30° over twelve thousand ; in Mexico at lat. 19° it is fifteen thou- 

 sand ; and at Quito under the equator, not less than sixteen thousand. 

 At these elevations, in their different respective latitudes, without 

 taking the undulations of the isothermal lines into consideration, 

 vegetation shows a most uniform character, so that it may be said 

 that there is a corresponding similarity of climate and vegetation be- ■ 

 tween the successive degrees of latitude and the successive heights 

 above the sea. As a striking example I may mention the fact of the 

 occurrence of identical plants in Lapland in lat. 67° at a height of 

 about three thousand feet and less above the level of the sea, and 

 upon the summit of Mount Washington in latitude 44° at a height 

 of not less than six thousand feet, while below this limit, in the 

 wooded valleys of the White Mountains, there is not one species 

 which occurs also about North Cape. 



There is nevertheless one circumstance which shows that cUmatic 

 influences alone, however extensive, taking for instance into account 

 all the above-mentioned agents together, will not fully account for the 

 geographical distribution of organized beings, as their various limits 

 do not agree precisely with the outlines indicating the intensity of 

 physical agents upon the surface of the earth. A few examples 

 may serve to illustrate this remark. The hmit of forest vegetation 

 round the Arctic Circle, does not coincide with the astronomical 

 limits of the Arctic zone ; nor does it agree fully with the isother- 

 mal hne of 32° of Fahrenheit ; nor is the limit of vegetation in 

 height always strictly in accordance with the temperature, as the Ce- 

 rastium latifolium and Ranunculus glacialis, for instance, occur in the 



