148 
ISLAND-FLORAS 
available at higher and higher levels. This explains how so 
many northern forms occur on the mountains of the tropics, 
and so many arctic genera on those of Europe, and also 
why there are so many species identical on the different 
European and even American mountain-ranges, these being 
in fact species derived from the arctic region in the glacial 
period. 
I sland= Floras 1 . The flora of such an island as Great 
Britain, recently detached from a continent, is much like 
that of the continent ; but in true oceanic islands, such as 
the Sandwich Islands, the Canaries, the Azores, St Helena, 
&c., the flora is peculiar, containing a considerable propor- 
tion of endemic forms ; a study of these floras has led to 
many important conclusions upon migration, distribution, 
&c. The endemic forms are sometimes of specific rank 
only, in which case it seems probable that the isolation of 
the island cannot have lasted very long, or that it cannot 
have been long inhabited by plants ; sometimes of generic 
rank ( e.g . see Bencomia, Brexia, Commidendron, Lodoicea, 
&c.), and in one case (Lac/oris ferna?idezia?ia from Juan 
Fernandez) even of ordinal rank. They illustrate the 
important conclusion that geographical isolation involves 
the production of new forms. The most striking examples 
of this are seen in such archipelagos as the Galapagos 
Islands, where almost every island has its own endemic 
species. 
The flora of an island may be derived from many 
sources ; islands detached from continents begin with a 
flora like that of the continent, whilst islands formed by 
volcanic agencies or coral-animals begin with no flora and 
become gradually occupied by plants with dispersal-methods 
capable of transporting their seeds to it. Thus in the island 
of Krakatoa, which was completely denuded of vegetation 
by the eruption of 1883, small algae and ferns were first to 
arrive, and then coast-plants and those distributed by birds. 
Besides the more modern forms, such islands as the Azores 
possess many plants whose presence probably dates from far 
x Wallace, Island Life ; Hemsley, Botany of Challenger Expedition , 
vol. I, 1885 ; Schimper, Die indomalayische Strand-flora \ Treub in Ann. 
Buitenz. 1, vii. Penzig in do., 2, ill. on Flo 7 -a of Krakatau ; Willis and 
Gardiner, Botany of the Maldives, Ann. Perad. I, 1902, p. 45. 
