120 



PLANT .SOCIOLOGY 



snow. Air temperature — 17°C.; snow surface —15°; 5 cm. deep in 

 snow -11.3°; 12 cm. -9.2°; 23 cm. -8.4°; 42 cm. -3°; 52 cm. -1.6°. 



Under 1 to 2 m. of snow in the Alps the ground is rarely frozen. 

 Hence many species of plants continue to grow under the snow, and 

 some actually bloom. Soldanella alpina and S. pusilla were found 

 blooming under 0.5 m. of snow; so also were Crocus vernus, Scilla bifolia, 

 and Saxifraga oppositifolia (Braun-Blanquet, 1913) and in eastern 

 Europe Scilla sihirica (Keller, 1927). On Jan. 22, 1904, in the Mahxer 

 Alp near Chur (1,700 to 1,800 m.) under 50 to 120 cm. of snow (soil 

 moist, not frozen, 0°C.; air temperature 12°C.) the following species 



10 



15 



20 m. 



Fig. 66. — Parallelism in the zonal arrangement of certain acidophilous associations 

 according to the duration of snow cover. ^4, In the eastern Alps at 2,340 m.; a, associa- 

 tions of Carer curvula; b, Salix herbacea with some Care.r; c, Gnaphalium suplnum; d, 

 Salix herbacea; and e, Polytrichum sexangularc. (After Braun-Blanquet.) B, In 

 Sylene, Norway; o, associations of Juncus trifidus; b, Vaccinium myrtillus; c, Deschamp- 

 ■-ia Jlexuosa; d, Carex rigida; e, Salix herbacea; and /, Polytrichum sexangularc. (,Aft(r 

 Nordhagcn.) 



had green turgescent foliage: Luzula multijlora, Potentilla aurea, 

 Sicversia moniana, Trifoliurn thalii, Pirola minor, Vaccinium myrtillus, 

 Soldanella alpina, Gentiana kochiana, Ajuga pyramidalis, Galium 

 pumilum, Homogyne alpina, Hieracium alpinum. 



Snow Cover and Plant Communities. — The vegetation of the high 

 mountains and the far north may be simply classified according to its 

 relation to duration of snow (Fig. 66). This has been done in Scandi- 

 navia by Vestergren (1902) and by Fries (1913). In the high moun- 

 tains of central Europe also there arc pronounced snow-avoiding 

 communities on exposed ridges, e.g., Loiseleurietum cetrariosum, 

 Trifidi-Distichetum, Elynetum, Caricetum firmae, etc., and com- 



