characteristic undergrowth. Advancing from the edge of this 

 forest to the flat glaciated tops are islands of Krummholz spruce 

 and fir with single trees beyond. In several places the heath is 

 thus completely spanned. The fusion of these islands makes the 

 destruction of this heath in the near future a certainty. Why 

 this rock society is so extremely xerophytic, perhaps even more 

 so than the summits, can perhaps be explained by no other reason 

 than by its excessive dryness. due to an almost perfect drainage. 

 There is also little retention of water, and humus accumulation 

 is necessarily slow. These conditions all contribute to extreme 

 xerophytism at first, but once a soil is formed succession will fol- 

 low as rapidly as upon the mountain. 



B. THE ALPESTRINE MEADOW SOCIETIES. 



This plant society furnishes one of the strongest evidences of 

 the edaphic theory that has ever come under the writer's obser- 

 vation. On a substratum, otherwise very xerophytic and which 

 would normally support an Alpine-Tundra society, occurs, by 

 virtue of its location and exposure, a mesophytic Alpestrine 

 meadow society. Situated at the base of the dripping west walls 

 of the North basin, and so presenting a warm south and south- 

 eastern exposure, it possesses in these two conditions edaphic 

 factors which determine its existence. 



Passing out from the base of the cliff, several well defined 

 plant zones are successively traversed. Situated at the base of a 

 precipitous cliff and upon a sharp talus slope the soil is largely 

 accumulated from the slopes above. By snow-slides and heavy 

 rains a residual soil of gravel and humus is washed down and 

 forms the substratum for these plant societies. Three very 

 distinct stages or zones appear to-day. By a study of this hori- 

 zontal zonation we may arrive at an understanding of the vertical 

 succession. 



(a) . The Pioneer Stage. Upon the first accumulation of soil 

 which lodges in cracks, crevices, gorges, on miniature shelves, 

 and at the base of the dripping walls, Scirpns cccspitosus first 

 makes its appearance, and often becomes very abundant. Cam- 

 panula rotundifolia, forming vast beds, follows Scirpus. With it 

 is associated Solidago Virgaurea alpina. (Fig. 6). 



39 



