ALPINE AND ARCTIC PLANTS 441 



period. We must bear in mind, however, that under certain 

 contingencies the high mountain summits might have been 

 clad in snow and ice, like Greenland, and the Alpine plants 

 might have been able to live only on their margins. 



Further, it would be easy to show that the Alpine plants of 

 Mount Washington would thrive under such conditions as 

 those supposed, at the sea level ; a low and equable tempera- 

 ture, with a moist atmosphere, being that which they most 

 desire, and their greatest enemy being the dry parching heat of 

 the plains of the temperate regions. Those of them, such as 

 Potentilla tridentata and Alsine Grxnlandica^ which occur in 

 low ground within the limits of the United States, are found 

 under shaded woods, in damp ravines, or on the moist sea- 

 coast ; and as we follow the coasts northward, we find these 

 plants, on these and on neighbouring islands, in lower latitudes 

 than those in which they occur inland. This is well seen in 

 Northern New Brunswick and in the south shore of the St. 

 Lawrence, where several northern species occur in shady and 

 moist localities. I have, for example, collected Cornus Suecica 

 and the Alpine birch in such places. When the summer mists 

 roll around the summit of Mount Washington, it is in every 

 respect the precise counterpart of an islet anywhere on the 

 coast of America, from Cape Breton to the Arctic seas, and 

 when winter wraps everything in a mantle of snow, all these 

 lands are in like manner under the same conditions. So, in 

 the Pleistocene period, though the islets of the White 

 Mountains may have experienced a less degree of winter cold, 

 they must have had very nearly the same summer temperature 

 as now ; and as this is the season of growth for our Alpine and 

 Arctic plants, it is its character that determines the suitableness 

 of the locality to them. 



Those stupendous vicissitudes of land and water which have 

 changed the aspect of continents, and swept into destruction 

 races of gigantic quadrupeds, have dealt gently with these 



