DR. HOOKER ON THE DISTRIBUTION OF ARCTIC PLANTS. 
263 
The plants which 
exclusively Arctic in Europe, are the following 
widely distributed in Temperate America or Asia, but almost 
Ranunculus Pallasii, Asia and America. 
Trollius Asiaticus, Asia. 
Parrya macrocarpa, Asia and America. 
- arctica, Asia and America. 
Stellaria longipes, Asia and America. 
Potentilla emarginata, America. 
Epilobium latifolium, Asia and Ameri 
Sedurn quadrifidum^ Asia, 
Saxifraga 
edtefolius 
Ligularia Sibirica, Asia. 
Mulgedium Sibiricurn, Asia, 
Cassiopeia tetragona, Asia and America. 
Gentiana detonsa, Asia and America. 
Plenrogyne rot at a. Asia and America. 
EritricMum aretioides, Asia and America. 
Gymnandra Pallasii, Asia. 
Castilleja pallida, Asia and America. 
Veronica macrostemon, Asia. 
Pedicularis flammea } America. 
Pinguicula villosa, Asia and America. 
Koenigia islandica, Asia and America. 
Salix polaris, Asia and America. 
Picea orientalis, Asia. 
Larix Ledebourii, Asia. 
Platanthera hyperborea, America. 
- obtusata, America. 
Deyeuxia Deschampsioides , Asia and N.W. Ame- 
rica. 
Dupontia Fisheri, America. 
The works upon which I have mainly depended for the habitats of the Arctic European 
plants are Wahlenberg's * Flora Lapponica,' Ledebour's * Flora Rossica,' Fries' * Summa 
vegetabilium Scandinaviae,' and * Mantissae,' and various admirable treatises by Andersson, 
Nylander, Hartmann, Lindblom, Wahlberg, Blytt, C. Martins, Ruprecht, and Schrenk. 
For Spitzbergen plants I have depended on Hooker's enumeration of the Spitzbergen 
collections made during Parry's attempt to reach the north pole, Capt. Sabine's collection 
made in the same island, and on Lindblom and Beilschmied's ■ Flora von Spitzbergen ' 
(Regensburg, Flora, 1842). 
For the southern distribution of the Arctic European plants, I have further consulted 
Nym 
ans excellent 'Sylloge,' Ledebour's * Flora Rossica,' Grisebach's 'Flora Rumelica 
Grenier and Godron's ' Flore de France,' Parlatore's ' Flora Italiana,' Koch's ' Synopsis 
Florae Germanise,' Munby's ( Catalogue of Algerian Plants,' A. Richard's of those of 
Abyssinia, Visiani's 'Flora Dalmatica,' Delile's 'Flora iEgyptiaca,' Boissier's noble 
'Voyage Botanique dans l'Espagne,' and Tchihatcheffs 'Asia Minor,' besides numerous 
local floras of the Mediterranean regions, Madeira, the Azores, and Canaries. 
2. Arctic Asia.— This, which for its extent, contains by far the poorest flora of any 
on the globe, reaches from the Gulf of Obi eastwards to Behring's Straits, where it merges 
the West American. The climate is marked by excessive mean cold 
the Obi 
the isotherm of 18° cuts the arctic circle in its S.E. course, and at the eastern extremity 
°f the province the isotherm of 20° cuts the same circle, while the centre part of the 
district is all north of the isotherm of 9°. The whole of the district is hence far north 
of the isotherm of 32°, which descends to 52° N.L. in its middle longitude. The extremes 
of temperature 
are also very great 
the June isotherm of 41° ascending eastward 
through its western half to the Polar Sea, whilst the September isotherm of 41° descends 
nearly to 60° N.L. ; whence the low autumn temperature must present an almost insuper- 
able obstacle to the ripening of seeds within this segment of the polar circle. 
