266 DR. HOOKER ON THE DISTRIBUTION OF ARCTIC PLANTS. 
longitude of the Mackenzie by that of 12° 5' ; whilst the June isotherm of 41° ascends 
obliquely from S.W. 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 phgenogamic plants hitherto found in Arctic West America is 364 
/Monocotyledons 76 
VDicotyledons 288 = 
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 
Rocky Mountains, 26 in the Andes of Tropical or Subtropical America, and 37 in Tern- 
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. 
Pennsylvania. 
Senecio resedaefolius (Eur., As., Am.). 
Arnica 
Hutdnnsm calycma (Rocky Mountain, only Cassandra ealyculata (Europe, Asia, America). 
and Asia), 
Sisymbrium humile (R. M 
Mountains 
Mountains 
prostrata (Europe, Asia, America) 
t *u i . ^ ' •"* — ~~ tenella (Eur., As., Am.)- 
Lathyrus palustns (Europe, Asia, East and Veronica scutellata (Eur., As, Am.). 
V> est America). r> j- i • , . „ 
*„• „ ,. ., .. ' , „ Pediculans palustns Eur., As., Am.), 
fcpiraea sahcifoha Eur., As., E. & W. Ami a*,;~i H. m . . \ ' 
W 
Atriplex patula (Eur., As., Am.). 
ur 
an 7 , 7 ,r a ' " ^^ Corall °' hi - *»»»* (Eur., As., Am.) 
jj-o run, palustre (Eur., As., E. & W. Am.). Luzula spadicea (Eur., As., Am.). 
Wr'l S t a (E " r ' A8 -' & T W - Am ->- — S picata (Eur., As, An,). 
Saxuraga S.bmca As,a and Labrador only). _ pilosa L,A, aJ. 
Archangelica officinalis (Europe 
Mounts, on! 
urope, Asia, & R. Mount 
ur 
pilosa (Eur., As., Am.). 
Juncus balticus (Eur., As., Am.). 
Carex lagopina (Eur., As., Am.). 
Gmelini (America only), 
ryptocarpa 
Cornus Suecica (Eur., As., Am. . cryp oca , ^^ Asi 
Galium rubioides IE,,,.. *.•■*'-, ."I - 8tr,cta ( E »™pe. America) 
Hierochloe borealis (Europe, Asia, and America). 
pa^of 1*1!* S6en ; ar u- fOT * he m ° St Part north tem P erate P 1 ^ common in many 
S£££22. :w e ch are only escluded from Eastern *»* *"*• * the 
