E. V. Wulff —82— Historical Plant Geography 



Chief T3rpes of Discontinuous Areas: — 



1. Arctic-Alpine Type. — This type of discontinuous area is charac- 

 terized by species distributed, on the one hand, in the Alps and other 

 mountains of central and southern Europe and, on the other, in arctic 

 regions, in northern Europe and Asia, in the Altai Mts., and in North 

 America. A few examples will illustrate the nature of this t3fpe: 



Salix herbacea. Pyrenees, Alps, Apennines, Sudetes Mts., Car- 

 pathian Mts., Siebenbiirgen, the Balkans — the Urals, northern and 

 arctic Europe, mountains of England and Scotland, northern and arctic 

 Siberia, northern and arctic North America. 



Ranunculus pygmaeus. Central Alps, western Carpathians — north- 

 ern Scandinavia, arctic Europe, Siberia, and America, and the Rocky 

 Mts. as far south as 55° N. 



Thaliclrum alpinum. Pyrenees, Alps — Wales, Scotland, the Cau- 

 casus, northern and arctic Europe, Asia, and America, mountains of in- 

 terior Asia, Rocky Mts. as far south as Colorado, Newfoundland, and 

 Anticosti Island. 



2. North Atlantic Type. — Plants distributed in North America and 

 Europe (including the British Isles) and divided into two sections by 

 the northern part of the Atlantic Ocean. Some of the species in this 

 group are found also in isolated spots in Asia, including eastern Asia. 

 Exceptionally interesting examples of this tj^e are the areas of species 

 found only in Ireland and North America, such as Eriocaulon septangu- 

 lare and Spiranthes romanzoffiana. Other examples are: 



Lycopodium inundatum. Northern and central Europe — North 

 America. 



Carex flava. Almost all of Europe, Anterior Asia — North America. 



3. Asturian Type. — This type of area was noted as long ago as 

 1835 by Watson and later by Forbes for such species as Daboecia 

 polifolia, Saxifraga geum, and 5. umbrosa, distributed in Ireland and 

 then in southwestern France, the Pyrenees, Asturia, Cantabria, and 

 Portugal (as regards Dabeocia, also on the Azores). A similar distri- 

 bution has been established by Scharf for a number of animals. 



Such a discontinuity in the areas of these few species is all the more 

 interesting since it resembles the discontinuity in many areas, where 

 one portion embraces the British Isles and the other southwestern 

 Europe and frequently also northern Africa (e.g., the area of Anagallis 

 tenella). 



4. North Pacific Type. — This type of area is characterized by 

 species now found, on the one hand, in Asia, particularly its eastern 

 part (including Japan and Sakhalin), sometimes also in Europe, and, on 

 the other, in North America, usually in the western (Pacific) section 

 but in some cases in the eastern (Atlantic) section or in both sections. 

 Discontinuous areas of this type are occupied by plants belonging 

 either to one and the same species or to closely related species, the 

 distinguishing characters of which arose as a result of prolonged iso- 

 lation. In some cases the discontinuity in area has been established by 

 the finding, in isolated regions, of species very close to those now living. 

 As examples of this type we may take the areas of distribution of the 

 following plants: 



