290 Eduard Riibel 



an alpine-niveai belt association dominated by the firm cushions 

 of Androsace helvetica, accompanied by Draba tomentosa and 

 others. The corresponding siliceous-rock vegetation gravitates 

 in the subalpine belt around Aspleniiim septentrionale and sev- 

 eral Sedum and Sempervivum species, and in the alpine around 

 Androsace mtdtiflora, Fhyteuma carestiae (eastern), Ph. humile 

 (western), and Primula hirsuta. 



2^. Saxideserta: Stone {and wood) deserts. — This is the Litho- 

 phyte vegetation of stones and wood, especially bark, growing 

 direcdy on firm, not disintegrated substratum. Bark vegetation 

 is similar to and often identical with the stone vegetation, espe- 

 cially with calciphobes (Gams). Mosses, and especially lichens, 

 cover the rocks as well as bark in multicolored mosaic. The com- 

 munities have been well studied in Fenno-Scandinavia by Ser- 

 nander, DuRietz, Hayren; in die Swiss Alps by Eduard Frey, 

 Ochsner, Gams. The other large group are the Algetalia, algal 

 communities coloring more or less perpendicular rocks, espe- 

 ciallv Gloeocapsae and related species. 



26.Aquerrantia: PhytoplanI{ton {water floaters). — This com- 

 munitv consists of microphytes free-floating in the water. Com- 

 munities specialize with the content of salt, oxygen, humus. ^\lso 

 the snow contains its own kryoplankton according to its more 

 solid consistency, and the floating of this growth is less mobile. 



2'j.Solerrantia: Phytedaphon {soil ^oa^^y) .—Microphytes, 

 myxomyceae, schizomycetes, mucorineae, form communities in 

 the soil. They neither root nor adhere. One may call it a floating 

 on soUd ground, just as the chemical engineer speaks of "solid 

 solutions!' 



2S.Aererrantia: Phytaeron {air ^o^/dr/) .—Microorganisms 

 float freely in the air; their connection is extremely loose, wind 

 causes rapid changes, yet perhaps they occur in groupings. 



