324 BOTANICAL GAZETTE [may 



ing, more important ecologically than physiographically, is the enlarg- 

 ing of the cracks or joint planes in the smooth floor of the cafions, by 

 disintegration of their edges and the deposit, in or near the cracks, 

 of the fine disintegrated material. Stream erosion has so far pro- 

 duced practically no effect upon the topography of the upper portions 

 of the canons. 



III. Vegetation 



In considering the vegetation of the higher mountain region, we 

 naturally divide it into two great formations: the alpine grassland, 

 and the forest, and place the division between these at timberhne. In 

 general this arrangement is a right one for the region, but in studying 

 the vegetation dynamically w^e are compelled to recognize an exception 

 in the wet meadows of the caiions. Above timberhne wc find two 

 types of grassland: the dry meadow, occupying the exposed slopes 

 and ridges; and the wet meadow, in the upper portions of the glacial 

 canons. The former is a true climatic grassland. The latter, how- 

 ever, as will be shown, is probably not permanent grassland brought 

 about by climatic factors, but is a stage in the forest succession, and, 

 conditions remaining the same, will become forest after the lapse 

 of sufficient time. In this paper the term ''alpine grassland" will 

 be used to include both dry and wTt meadow. \\c will consider first 

 the development of these tw^o types of alpine meadow" and second, 

 the forest formation in its successional relation to them. 



A. THE ALPINE GRASSLAND 



I. 



The dry meadow 



(fis- 



cover a large part of the area above timberline— an area which is 

 practically coextensive with the flat summit of the range and the 

 slopes similar to it, which, as has been said, are covered with a layer 

 of broken fragments. While this layer of broken material protects 

 the bed rock from further weathering, the fragments themselves are 

 continually disintegrating under the influence of frost and of lichens. 

 Disintegration by Hchens is an important process here as is evidenced 

 by the thick crust of these plants upon every stone. 



Every stage in the development of the dry meadow may be seen 

 on the summit of the range. On the more elevated portions, where 



