Potentilla tridentata next appears to work its way into this 

 society. Potentilla fruticosa is often associated, but never abun- 

 dantly enough to be dominant. Arenaria grcenlandica, Carex 

 scirpoidea, Luzula spadicae melanocarpa, L. spicata and Juncus 

 articulatus are less prominent but normally associated forms. 

 This plant covering though sparce now acts as a retainer 

 of soil and humus washed from above and also adds to it by its 

 own decay. A humus and a power of hygroscopicity soon 

 develop sufficiently to support a less xerophytic society and the 

 next stage soon follows. 



(b). The Meadow Stage. Determined by the increasing 

 water content of the substratum the meadow encroaches with 

 rapidity upon the pioneer society. In many places the meadow 

 has entirely replaced it extending up to the very base of the walls 

 themselves (Fig. 6). It is thus that the stage once dominant 

 is now being gradually replaced by another of a higher 

 ecological type: a more successful society in the struggle for 

 existence. At the foot of the southwest wall of the Northwest 

 basin the pioneer society is a feature of the past, the Alpestrine 

 meadow entirely skirting the dripping face of this precipitous 

 wall. 



Among the first meadow forms to appear in the pioneer society 

 are Castilleja pallida, Prenanthes trifoliolata, Aster acuminatns, 

 A. radula, A. umbellatus, and Anaphalis margaritacea. Several 

 of the grasses now appear. Calamagrostis canadensis, C. 

 Langsdorfii, and Bromus ci licit us occur in great profusion, 

 Glyceria nervata, Agropyaum violaceum, and Agrostis rubra are 

 also common. With these grasses are associated Heracleum 

 ianatum, Habenaria dilatata, Arnica Chamissonis, Viola blanda, 

 V. canina, and Solidago macrophylla. As a whole this society 

 presents a striking meadow aspect, and one which appears quite 

 out of keeping with the surroundings. This society is quite 

 extensive, occurring wherever these conditions are repeated. 

 Here and in the Northwest basin, however, it reaches its typical 

 development. In this meadow society accumulation from wash 

 and decay are continually in progress. With fit conditions we 

 have the advent of another society. 



40 



