CHAP. LXVII SUBGLACIAL FELL-FIELD FORMATIONS 261 



Africa. On the Canary Isles the peak-region lying above the clouds 

 is desert almost devoid of plant-life. Here and there grow hemispherical 

 shrubs of Sparto-cytisus nubigenus, which are almost the only plants 

 that one sees. 1 



Asia. On high mountains in central Asia, above the forest in the 

 cloud-belt, there extend alpine steppes whose flora is a remarkable 

 admixture of steppe-plants and alpine forms. In Tibet, Rockhill found 

 at a great altitude a vegetation consisting of scattered tufts of grass, 

 rhubarb, and Allium senescens. 



South America. The punas of the Andes must be regarded as moun- 

 tain-steppes. 2 In summer their temperatures are higher than those of 

 the paramos. At Potosi even in November the mean temperature is 

 14-2 C. Nevertheless in the dry rarefied air the fluctuations of tempera- 

 ture are so great that brooks may freeze at almost any time of the year. 

 Snow mostly falls in summer but never remains lying for a whole day, 

 even when it is a foot in depth. During night-time radiation from the 

 soil is so intense that rime may be formed at a time when the temperature 

 of the air is 6-7 C. Strong winds dry everything up. Dead animals 

 last like mummies and do not undergo putrefaction. The vegetation is 

 mainly formed by a grass, Stipa Ichu. Its setaceous tufts are 35-50 centi- 

 metres in diameter and nearly always inclined away from the prevailing 

 wind. During most of the year the tufts of grass are blackened as if burnt 

 by the sun. In addition to grasses the ptinas display numerous xerophytic 

 perennial herbs and undershrubs, which assume the forms of rosette- 

 plants and cushion-plants. Bulbous and tuberous plants also occur. 

 Even the Cactaceae give rise to cushions. The punas are poorer in 

 plant-life than the paramos. Cactaceae which are absent from the latter 

 are common here. 3 Here, too, grow herbs with enormously long roots, 

 often a metre in length, and with reduced assimilatory shoots, which are 

 only a few centimetres in length and bear rosettes of woolly or glandular- 

 haired leaves that lie flat on the ground. 4 In the Argentine Andes, 

 Fries 5 distinguished three kinds of shrub-steppes : Hoffmanseggia- 

 association, Cactus-association, and Azorella-association. 



1 Schroter, 1908. * Seep. 259. * Tschudi; Gobel, 1891. 



* Benrath ; Weberbauer, 1905. ' Rob. Fries, 1905. 



