266 



DR. HOOKER ON THE DISTRIBUTION OF ARCTIC PLANTS. 



longitude of the Mackenzie by that of 12° 5' ; whilst the Jnne isotherm of 41° ascends 

 obliquely from S.AV. to N.E., from the Aleutian Islands to the mouth of the Mackenzie, 

 and passes south of this province ; the June and the September isotherms of 41° and 32° 

 both traverse it obliquely, ascending to the N.E. 



The vast extent of the Pacific Ocean and its warm northerly currents greatly modify 

 the climate of West Arctic America, causing dense fogs to prevail, especially throughout 

 the summer months, whilst the currents keep the ice to the north of Behring's Straits. 

 The shallowness of the ocean between America and Asia, north of lat. 60°, together with 

 the identity of the vegetation in the higher latitudes of these continents, suggests the 

 probability of the land having been continuous at no remote epoch. 



The number of phsenogamic plants hitherto found in Arctic West America is 364 

 /Monocotyledons 76 ■!_ _ \ 

 VDicotyledons 288 J ' / 

 The proportion of genera to species is 1 : 1'7. Of these 364 species, almost all but the 

 littoral and purely arctic species are found in West Temperate North America or in the 

 Eocky Mountains, 26 in the Andes of Tropical or Subtropical America, and 37 in Tem- 

 perate or Antarctic South America. Comparing this flora with that of Temperate and 

 Arctic Asia, I find that no less than 320 species are found on the north-western shores 

 and islands of that continent, or in Siberia, many extending to the Altai and the Himalaya. 

 A comparison with Eastern Arctic America shows that 281 are common to it, and the 

 following 38 are found in Temperate, but not Arctic East America. 



Anemone alpina. 



Pennsylvanica. 



Hutchinsia calycina (Rocky Mountains only 



and Asia). 

 Sisymbrium humile (R. M. and As.). 

 Draba oligosperma (Rocky Mountains only). 

 Lathyrus palustris (Europe, Asia, East and 



West America). 

 Spirtea salicifolia (Eur., As., E. & W. Am.). 

 Potentilla fruticosa (Eur., As., E. & W. Am.). 



Pennsylvanica (Eur., As., E. & W. Am.). 



Comarum palustre (Eur., As., E. & W. Am.). 

 Montia fontana (Eur., As., & W. Am.). 

 Saxifraga Sibirica (Asia and Labrador only). 



Dahurica (Asia and Rocky Mounts, only), 



bronchialis (Europe, Asia, & R. Mounts.). 



Archangelica officinalis (Europe, Asia, America). 

 Ligusticum Scoticum (Eur., As., Am.). 

 Cornus Suecica (Eur., As., Am.). 

 Galium rubioides (Eur., As., Am.). 



Senecio resedBefolius (Eur., As., Am.). 



pseudo- Arnica (Asia and America). 



Cassandra calyculata (Europe, Asia, America). 

 Gentiana arctophila (Rocky Mountains only). 



prostrata (Europe, Asia, America). 



tenella (Eur., As., Am.). 



Veronica scutellata (Eur., As., Am.). 

 Pedicularis palustris (Eur., As., Am.). 

 Atriplex patula (Eur., As., Am.). 

 Corispermum hyssopifolium (Eur., As., Am.). 

 Corallorhiza innata (Eur., As., Am.). 

 Luzula spadicea (Eur., As., Am.). 



spicata (Eur., As., Am.). 



pilosa (Eur., As., Am.). 



Juncus balticus (Eur., As., Am.). 

 Carex lagopina (Eur., As., Am.). 



Gmelini (America only). 



cryptocarpa (Europe, Asia, America). 



stricta (Europe, America). 



Hierochloe borealis (Europe, Asia, and America). 



These, it will be seen, are for the most part north temperate plants, common in many 

 parts of the globe, and which are only excluded from Eastern Arctic America by the 

 greater rigour of its climate. 



