88 THE SCOTTISH BOTANICAL REVIEW 



Jerosch, namely, the presence of a felted coating of hairs 

 which entangles air when the plant becomes submerged by 

 occasional water, and so prevents flooding of the leaf. He 

 recalls the silky white sheen on such leaves as Gnaphalium, 

 Cerastium, Sibbaldia, and Alchemilla alpina when seen under 

 a shallow layer of flood-water. 



The evolution of the snow-flush vegetation is indicated in 

 E. Riibel's account. Anthelia, perhaps preceded by still lower 

 organisms,^ forms a humous turf, fairly stable and liable to 

 invasion by other species. Polytrichum follows later, and 

 more or less takes the place of Anthelia. Later still Salix 

 herbacea or Alchemilla assumes chief place. Riibel has 

 observed where the different sub-types occur beside each 

 other that Salix takes the higher and drier situations, 

 which in Switzerland adjoin the extensive plant association 

 of Carex curvula. Each of the stages of vegetation probably 

 indicate stages in the evolution of the habitat, since the later 

 vegetation will tend to give it increased stability. In time 

 the accumulation of sediment, humus, and vegetation may 

 be such that the snow-water is diverted to new situations, 

 where the sequence will begin over again. During the various 

 phases other species secure a footing and flourish well or ill 

 according as the habitat suits them. Riibel suggests that 

 Taraxacum and Cerastium cerastioides find in the snow-flush 

 that abundance of organic matter which they require ; in 

 Switzerland both are characteristic species of the " lair-flora," 

 that is, places manured by sheep, goats, or other animals, 

 where grasses like Poa annua flourish. Again, Carex 

 Lachenalii he has observed invading the snow-flush from 

 neighbouring marshes. All these observations point in one 

 direction : that the soow-flush is a series of migratory associa- 

 tions. These were recently defined in these pages (ii) (p. 8) : 

 " Migratory formations are of comparatively short persistence 

 on the same habitat, which sooner or later undergoes change 

 or destruction, with renewal elsewhere. Their associations 

 tend to rapid degeneration from plant invasion. All stages 

 of progressive successions of associations are encountered." 

 It seems to us that along these lines the somewhat complex 

 distribution of our arctic-alpine vegetation must be studied. 



^ Dr. Macvicar {in litt. ) informs me that Anthelia is preceded by an alga. 



