26o PSYCHROPHYTES sect, ix 



Characteristic of tropical fell-field is the occurrence of pygmy-trees, 

 which render it different from other formations belonging to this class. 

 Tropical fell-field thus approaches tropical savannah, but differs from 

 this in the frequent presence of cushion-hke plants. 



Antarctic Fell-fields. 



The climate of antarctic islands shows a strong likeness to that of 

 tropical high mountains, in that the difference of temperature in the 

 different seasons is slight. There is a long season during which the 

 temperature rises a few degrees above o C. On Kerguelen the winter 

 has a mean temperature of 2 C, and the summer one of 64 C. On 

 South Georgia only the three coldest months show mean temperatures 

 below C, yet the mean temperature of the warmest month is only 

 5-3 C. This explains the close resemblance between tropical and 

 antarctic fell-fields. 



In South Georgia fell-field is essentially formed by scattered tufts 

 of Poa caespitosa (tussock-grass).^ The tussocks are from i to i| metres 

 in height, and at the base are surrounded by withered leaves. Between 

 the tussocks only few other species grow. On the Falkland Isles the 

 tussock-grass is also common. But the fell-field is much richer in forms 

 here. There occur evergreen dwarf-shrubs, Chiliotrichum amelloideum, 

 Pernettya empetrifolia, which often give rise to true heath. In addition 

 we find here the peculiar, cushion-like umbelliferous Azorella caespitosa.^ 

 This assumes the form of a dirty-green, hemispherical cushion, which is 

 more than a metre in height and is extraordinarily hard. The periphery 

 is composed of numerous little shoots, which are all equally tall and are 

 densely clothed with scale leaves. These shoots adhere so closely and 

 firmly to the intervening old leaves and shoots that it may be difficult 

 to remove a fragment of the plant even with the aid of a knife. Dusen 

 describes ' Bolax-heath ', as a ' heath ' composed of Bolax glebaria, Comm. 

 (Azorella caespitosa, Vahl) occurring in tracts south of Rio Grande : 

 the cushions of Azorella fuse together nearly everywhere, thus forming 

 an almost uninterrupted, compact, very hard vegetable covering, which 

 extends over wide areas.^ Lichens, mosses, e. g. Racomitrium, and 

 other plants may spread over these cushions. 



To this vegetation that of fell-field on high mountains in New Zealand 

 is allied. Here the majority of species are xerophytic cushion-plants, 

 which grow scattered about and seem everywhere to be deserting the 

 rocks. Especially remarkable are the ' vegetable sheep ' plants which 

 are species of Raoulia and Haastia. Dense cushions are also produced 

 by Celmisia viscosa, species of Veronica, Hectorella, and others.* 



Mountain-steppe. 



In drier districts on high mountains there occurs a type of fell-field 

 that approximates to steppe in many respects. 



Europe. On Etna the presence of tragacanth-shrubs is a true sign 

 of an affinity with steppe. 



^ Concerning the characteristic tussock-formation, see Chapter XLVIII. 

 * See Gobel, 1891; Schenck, 19056. ' Dusen, 1905. * Diels, 1896, 1905. 





