13] VEGETATIONAL TYPES OF POLAR LANDS 417 



particularly to the coolness of the ' warm ' season and to the frequency 

 and persistent strength of the winds — and also to the isolated 

 situation which makes immigration extremely difficult. Almost the 

 entire Continent belongs to the zone of * perpetual frost ', only a 

 few peripheral areas having a ' tundra climate ', though this is 

 enjoyed by most of the subantarctic islands. 



Only two species of vascular plants, a Grass and a Caryophyll, are 

 at all well known from the Antarctic Continent (a segregate of the 

 Grass is claimed by some to constitute a third species), but there 

 are fairly numerous Lichens, Mosses, and Algae, many of which are 

 widespread. The microthermic vascular flora of surrounding 

 islands, however, includes a fair number of more or less circumpolar 

 species. Characteristic components of this flora are Colobanthus 

 crassifoUus and Lyallia spp. (the former being known from the 

 Antarctic Continent, and both belonging to the Caryophyllaceae), 

 Pringlea antiscorbutica (the Kerguelen Cabbage, belonging to the 

 Cruciferae), Acaena spp. (Rosaceae), Azorella spp. (Umbelliferae), 

 and the Grass Deschampsia antarctica (also found on the Antarctic 

 Continent). Mixed with various hardy cryptogams, these and other 

 vascular plants form a thin tundra which, with increasing luxuriance, 

 extends northwards over the Antarctic Islands and into much lower 

 latitudes — for example in southern South America. Nevertheless 

 this * subantarctic ' tundra occupies only a tiny area when compared 

 with its arctic counterpart. Like the latter, it includes some 

 shrubby plants, mostly of cushion-form, and often tussocky Grasses, 

 as on South Georgia. 



The Antarctic Continent is largely covered by the world's greatest 

 ice-cap and consequently is a vast polar waste. Only here and there, 

 on ice- and snow-free spots of the shore or inland ' oases ', on steep 

 walls of rock or stony slopes, and on mountain-peaks protruding 

 from the ice, are found the Lichens, Mosses, and Algae mentioned 

 above — the vegetation at the best being in general far poorer than 

 is to be found in all but the most barren of arctic habitats. Even 

 Bacteria appear to be relatively few in number. Most of them, and 

 many of the largest known patches of macroscopic vegetation, have 

 been found in the Graham Land sector of western Antarctica below 

 the 68th parallel of S. latitude. Here, in the most suitable situations 

 within areas of favoured climate, may be found the two or three truly 

 antarctic vascular plant species and patches of cryptogamic vegeta- 

 tion that are locally more or less closed — particularly with such 

 Mosses as Brachythecium antarcticum and species of Grimmia and 



