82 THE SCOTTISH BOTANICAL REVIEW 



more and more restricted to sheltered places beside blocks. 

 Here the most conspicuous plant association is RJiaco^nitrium. 

 lanuginosuni with Carex rigida and other mat-forming plants, 

 but at frequent intervals the darker patches occur. The summit 

 ridge shows many tracts of this black mossy crust, and in the 

 " Cernua Corrie " there is one large patch at the rough wall 

 near the ruins of the Ordnance hut. One has also recollec- 

 tions of other summits where this dark-crusted humous 

 surface is a feature. 



The Swiss botanists recognised these patches and tracts as 

 " Schneetalchen," a term introduced by Oswald Heer in 

 1836. In L. Schroter's " Taschenflora " (3) the word is trans- 

 lated as " snow- valley, " but as English equivalent "snow- 

 gutter" or "snow-flush" more nearly expresses the kind of 

 little runnels suggested by the original term. The vegetation 

 of these snow-flushes has been described by authors like 

 Kerner, Christ, Stebler, and Schroter. The more recent 

 observations of Brockmann-Jerosch (4) indicate that, before 

 dealing with the vegetation, attention should be directed to the 

 topographical and physical factors that bring about its evolu- 

 tion. Anyone who has seen the snow melting on the higher 

 hills can recall the early emergence of rocks or snow-bleached 

 green slopes and knolls. In Switzerland and the Tyrol 

 these are bedecked with flowers while the snow still lies a few 

 yards away. Day by day the snow-patches decrease, becom- 

 ing more limited to the lower depressions or sunless slopes. 

 The snow-water soaks through the turf seeking the lower de- 

 pressions till it flows from below the snow and streams away 

 to still lower levels. Thus in troughs and depressions of 

 undulating ground and along the foot of slopes or escarp- 

 ments there is a system of temporary water-courses which, so 

 long as the snow is melting, are more or less under water. 

 The summer rain-water will tend to follow the same course, 

 but with this difference that the larger supply of ice-cold 

 water is replaced by more occasional trickles of warmer 

 surface-water. On steep slopes these streamlets descend with 

 some force and carve out little stream-beds (snow-water 

 channels), but on gentle slopes or flats or in depressions the 

 force of the flow is not sufficient to erode ; the water wanders 

 slowly through the turf and deposits accumulated suspended 



