ipoS] COOPER— ALPINE VEGETATION IN COLORADO 331 



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more streams meandering through it (fig. 5). These streams often 

 run over the rock itself, since the current has so far kept their beds 

 free from sediment. Prominent plants growing in these wet meadows 

 are as follows : 



Lycopodium selago L., L. annotinum L., Carex (several species) dominant, 

 Caltha rotundifolia (Huth) Greene, Sedum rhodanthum A. Gray, Sicversia 

 turbinata (Rydb.) Greene, Kalmia microphylla (Hook.) Heller, Primula Parryi 

 A. Gray, Gentiana frigida Haenke, G. plebeja Holmii Wettst., Swertia congesta 

 A. Xels,, Elephantella groenlandica (Retz.) Rydb., Crepis alpicola (Rydb.) 

 A. Nels. 



Later a few shrubs make their appearance. Bclula glandidosa is 

 by far the commonest of these, and Dasiphora fruticosa and Salix 

 chlorophylla are frequent. 



Where a stream flows amoi 

 gently sloping rock surface, plants themselves arc instrumental in 

 forming small basins. Fine material accumulates around the rock 

 fragments, and in this mosses obtain a foothold. From the rock 

 fragments as centers mats of moss spread out, and these coalescing 

 partially dam up the stream, so that more fine material is deposited 

 The development of the meadow then progresses as in the natural 

 rock basins. Frequently the damming-up of its course deflects a 

 portion or all of the stream, and in its new course it encounters other 

 debris where the process is repeated. These little meadow patches 

 often coalesce to form areas of quite respectable size. The turf mats 

 that start from the cracks also sometimes become Joined to these, and 

 thus in various ways considerable areas on the canon floors obtam a 

 solid covering of herbaceous vegetation {figs. 4, 6). Ledges on the 

 canon walls, where water trickles over them, are covered with a turf 

 n^at similar in composition to that upon the canon floor {fig. j)- 

 ^^Tiere cascades occur, principally at the great "steps," there is 

 naturally an abundant vegetation, consisting of mosses, sedges, and 

 other herbs growing within the influence of the spray (fig- 5); ^^^ 

 lake basins are so large and deep that comparatively little filling has 

 been accomplished. The shallower portions along the shore are 

 PartiaUy converted to meadow, and where a lake occurs at the base o 

 a "step" good-sized alluvial cones extend out into the water at the 

 upper ends. Of course this is not the case with the highest lake., 

 where very little alluvial matter is available. 



