1911-12.] BOTANICAL SOCIETY OF EDINBURGH 43 



Another interesting adaptation is noted by Brockmann- 

 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 Gnaphaliv/m, 

 Gerastium, Sibbcddia, and Alchemilla aZpina when seen 

 under a shallow layer of flood-water. 



The evolution of the snow-flush vegetation is indicated 

 in E. Rubel's account. Anthelia, perhaps preceded by 

 still lower organisms, 1 forms a humous tuft, fairly stable 

 and liable to invasion by other species. Polytrichum 

 follows later, and more or less takes the place of Anthelia. 

 Later still SaZix 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 Garex 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 sedi- 

 ment, 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 Taraxacv/m 

 and Cerastiv/m cemstioides 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 Poo annua flourish. Again, 

 Garex LachenaUii he has observed invading the snow- 

 flush from neighbouring marshes. All these observations 

 point in one direction : that the snow-flush is a series of 

 migratory associations. These were recently defined by 

 C. B. Crampton (11) (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 pro- 



1 Mr. Macvicar (in litt.) informs me that Anthelia is preceded by an 



