288 Eduard Riibel 



soil, Salicornia perennis and Atriplex portulacoides. On the 

 Mediterranean shores, Salicornia fruticosa is the main plant; in 

 southwestern Australia, Salicornia australis; on Java, Ipomoea 

 pescaprae; on the Moluccas, Canavalia; on Asiatic shores, Spini- 

 fex squarrosus. 



2^.Mobilideserta: Wander deserts. — The desert character o£ 

 open vegetation is caused by the mechanical action of the un- 

 stable substratum. The mobility of the soil is a peculiar factor 

 with formidable influence on the vegetation, demanding a par- 

 ticular ecology against its being torn away or buried. According 

 as the mobility of soil is caused by wind, by gravity, by water, or 

 by man, there are different groups : shifting dunes, steep screes, 

 and shifting river alluvions. Ammophiletum arenariae is the 

 main shifting-dune association all over Europe and America, 

 with more or less slight variations. The English Lancaster coast 

 has a foredune dominated by Agropyron junceum; Michigan, 

 one dominated by Calamovilfa Ion gi folia. Salt-water and sweet- 

 water dunes are closely related. 



The calcareous Alps have a fine sliding rubble vegetation 

 around the Thlaspeetum rotundifolii, with Trisetum disticho- 

 phyllum, Papaver alpinum sendtneri (white), and other plants, 

 a fine scree on the Pilatus, for example. The eastern central Alps 

 have an association with the pretty yellow Papaver aurantiacum. 

 On the screes on Mount Garfield in the Rocky Mountains I saw, 

 especially. Paronychia and Silene acaulis. 



On alluvial ground in the Swiss Alps, Myricaria germanica is 

 dominant from the plain up to 2000 meters altitude. In the higher 

 localities on glacial river alluvium a subassociation is dominated 

 by the red big-flowering Epilobium fleischeri. 



Somewhat similar to the alluvium turned over about once a 

 year by the high waters are the artificially turned-over soils, the 



