HOOKER ON ARCTIC PLANTS. 211 



besides numerous local floras of the Mediterranean regions, Madeira, 

 the Azores, and Canaries. 



2. Arctic Asia. — This District, which, for its extent, contains 

 by far the poorest flora of any on the globe, reaches from the Gulf 

 of Obi eastward to Behring's Straits, where it merges into the 

 West-American. The climate is marked by excessive mean cold ; 

 at the Obi the isotherm of 18° cuts the Arctic Circle in its S.E. 

 course, and at the eastern extremity of the province the isotherm 

 of 20° cuts the same circle ; while the central 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 insuperable obstacle 

 to the ripening of seeds within this segment of the Polar Circle. 



The warming influence of the Atlantic currents being felt no 

 further east than the Obi, and the summer desiccation of the vast 

 Asiatic continent, combine to render the climate of this region 

 one of excessive drought as well as cold, whence it is in every 

 way most unfavourable to vegetation of all kinds. 



The total number of species hitherto recorded from this area 

 is 233 :— 



Monocotyledons - - 42 ) _ , . - 



Dicotyledons - - - 191 i ~ ' 



The proportion of genera to species is 1 : 2. Of the 233 species, 

 217 inhabit Siberia, as far south as the Altai or Japan, &c. j 104 

 extend southwards to the Himalaya or mountains of Persia ; none 

 are found on the mountains of the two Indian peninsulas, and 85 

 on those of Australia and New Zealand. All but 37 are European, 

 and nine of these are almost exclusively Arctic. [The table fol- 

 lows, page 264.] 



Thus out of 37 non-European species only 12 are confined to 

 Asia, the remaining 25 being American. On the other hand, 

 there are only 22 European species in Arctic Asia which are not 

 also American, which scarcely establishes a nearer relationship 

 between Arctic Asia with Europe than with America. [The 

 table follows, page 264.] 



In other words, of the 233 Asiatic species 196 are common to 

 Asia and Europe, 22 are confined to Asia and Europe, 25 are 

 confined to Asia and America only, and 12 are confined to Asia, 

 of which three are peculiar to the Arctic Circle. 



The rarity of Grramineas, and especially of Cyperaceae, in this 

 region is its most exceptional feature, only 21 of the 138 Arctic 

 species of these orders having hitherto been detected in it. Crypto- 

 gamic plants seem to be even more rare ; Woodsia Ilvensis and 

 Lastrea fragrans being the only Filices hitherto enumerated. 

 Further researches along the edge of the Arctic Circle would 

 •doubtless add more Siberian species to this flora, as the examina- 

 tion of the north-east extreme would add American species, and 



o 2 



