ALPINE AND ARCTIC PLANTS 443 



dency to vary, and none to adapt themselves to new forms in 

 the sunny plains below. This is especially noteworthy on 

 Mount Washington and the neighbouring peaks, because the 

 soil of these is the same with that of the valleys. Several of 

 the plants peculiar to these hills, as the black crowberry 

 (Empetrum nigntm), for instance, even when other conditions 

 are favourable, shun rich calcareous soils, and affect those of 

 granitic origin. In many cases the difference in soil is a suffi- 

 cient reason for the non-occurrence of such plants, except on 

 certain hills. At Murray Bay, and on the shores of Lake 

 Superior, the plant above named occurs only on the Lauren- 

 tian gneiss. In Nova Scotia, its relative, Corema Conradi, is 

 confined to the granite barrens of the south coast. Many such 

 plants skirt the whole Laurentian range from Labrador to Lake 

 Superior, but refuse to extend themselves over the calcareous 

 plains of Canada. But in the White Hills the soil of the 

 river alluvium is the same micaceous sand that fills the crevices 

 of the rocks in the mountains, and hence there is no obstruc- 

 tion, in so far as soil is concerned, to the diffusion of plants 

 upward and downward in the hills. In like manner there is 

 every possible condition as to moisture and dryness, sunshine 

 and shade, in both localities. These circumstances are of all 

 others the most favourable to such variation as these plants 

 are capable of undergoing. The case is the same with that 

 which Hugh Miller so strongly puts in relation to the species 

 of algae that occur at different distances below high water mark 

 on the coast of Scotland, each species there attaining a certain 

 limit, and then, instead of changing to suit the new conditions, 

 giving place to another. So it is on Mount Washington ; and 

 this, whether we regard the lowland plants that climb to a cer- 

 tain height, and there stop, the plants that are common to the 

 base and summit, or the plants that are confined to the latter. 

 I have already referred to the evident struggle of the spruces 

 and firs, and the plants associated with them, to ascend the 



