1868.] HOOKER — ARCTIC FLORA. 345 



collections of Drs. Lyall and Wood formed in Vancouver Island 

 and British Columbia ; for the Californian, Mexican, and Cordillera 

 floras generally, to the herbarium at Kew, the works above men- 

 tioned, and the various memoirs of Torrey and of Gray on the 

 plants of the American Surveying Expeditions. 



4. Arctic East America (exclusive of Greenland). — 

 This tract of land is analogous to the Arctic Asiatic in many 

 respects of position and climate, but is very much richer in species. 

 It extends from the estuary of the Mackenzie River to Baffin's 

 Bay, and its flora differs from that of the western part of the 

 continent, both in the characters mentioned in the notice of that 

 province, and in possessing more East American species. The 

 western boundary of this province is an artificial one ; the eastern 

 is very natural, both botanically and geographically ; for Baffin's 

 Bay and Davis Straits (unlike Behring's Strait) have very deep 

 water and different floras on their opposite shores. 



The arctic circle is crossed in the longitude of the Mackenzie 

 River by the isotherm of 12 Q , which thence trends south-eastward 

 to the middle of Hudson Bay ; and in the longitude of Davis 

 Straits it is crossed by the isotherm of 18^-°. The June isotherm 

 of 41° descends obliquely from the shores of the Arctic Sea, near 

 the mouths of the Mackenzie, to the northern parts of Hudson 

 Bay, south of the arctic circle; and the September isotherm of 

 41° is everywhere south of the circle. Hence, the western parts 

 of this province 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 Spitzbsrgen, of which nothing certain 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 



* It is a well-known fact that the temperature always rises rapidly 

 with the north (as well as other) winds over all this Arctic American 



