268 DR. HOOKER ON THE DISTRIBUTION OF ARCTIC PLANTS. 
descends obliquely from the shores of the Arctic Sea, near the mouths of the Mackenzie, 
to the northern parts of Hudson's Bay, south of the arctic circle ; and the September 
isotherm of 41° is everywhere south of the circle. Hence the western parts of this pro- 
vince are very much warmer than the eastern ; so much so, that the whole west coast and 
islands of Baffin's Bay lie north of a southern inflection of the June isotherm of 32°, 
which passes north of all the other polar islands ; the Parry Islands have an analogous 
temperature of 40°. The warmth of the western portion of this tract is no doubt mainly 
due to the influence of the Pacific Ocean being felt across the continent of West America ; 
though possibly also to the presence of a comparatively warm polar ocean, or to Atlantic 
currents crossing the pole between Nova Zembla and Spitzbergen, of which nothing cer- 
tain is known *. Be this as it may, the comparative luxuriance of the flora of Melville 
Island is a well-known fact, and one inexplicable by considerations of temperature, if 
unaccompanied by a humid atmosphere. The whole region is of course far north of the 
isotherm of 32°, which, in the longitude of its middle district, descends to Lake "Winnipeg, 
in lat. 52°. 
That portion of this province which is richest in plants is the tract which intervenes 
between the Coppermine and Mackenzie Rivers ; east of this, vegetation rapidly diminishes, 
as also to the northward. The flora of the Boothian Peninsula, surrounded as it is with 
glacial straits, and placed centrically among the arctic islands, is perhaps the poorest of 
any part of the area ; those of Banks' Land and Melville Island to the N.W. being con- 
siderably richer, as are those of the shores of Lancaster's Sound and Barrow's Strait, and 
the shores of Baffin's Bay to the north and east f. 
The pluenogamic flora of Arctic East America contains 379 species 
Monocotyledons. 92 
Dicotyledons. . 287 
1 
The proportion of genera to species is 1 : 2-0. Of these 379 species, 323 inhabit Temperate 
North America, east of the Rocky Mountains ; 35 the Cordillera ; and 49 Temperate or 
Antarctic South America. Comparing this flora with that of Europe, I find that 239 (or 
two-thirds) species are common to the arctic regions of both continents, whilst but little 
more than one-third of the Arctic European species are Arctic East American. Of 105 
non-European species in Arctic East America, 32 are Asiatic ; leaving 73 species confined 
to America, of which the following are furthermore confined to the eastward of the Rocky 
Mountains and Mackenzie River : 
Corydalis glauca. Lathyrus ochroleucus. Vaccinium Canadense. 
Sarracenia purpurea. Rubus triflorus. Dracocephalum parviflorum 
Viola cucullata. p runus Virginiana. __„ o 
Silene Pennsylvania. Heuchera Richardsoni. EhJgnus argentea 
Arena™ Michauxii. Cornus stolonifera. Urtica dioica. 
Polygala Senega. Grindelia squarrosa. Salix cordata. 
* J 4 ■ a well-known fact that the temperature always rises rapidly with the north (as well as other) winds over all 
this Arctic American area. 
Douglasia arctica. 
t Details of these florulas will be found in the volume of the « Linnean Journal/ under the notice of Dr. Walker's 
collections, made during the voyage of the Fox. 
