1868.] HOOKER — ARCTIC FLORA. 331 



land, 207 species ; in the American continent east of the Mackenzie 

 River, 379 species ; and in the area westward from that river to 

 Behring's Straits, 36-4 species. 



A glance at the animal and monthly isothermal lines will show 

 that there is little relation between the temperature and vegetation 

 of the areas they intersect, beyond the general feature of the scanti- 

 ness of the Siberian flora being accompanied by a great southern 

 bend of the annual isotherm of 32° in Asia, and the greatest 

 northern bend of the same isotherm occurring in the longitude of 

 west Lapland, which contains the richest flora. On the other 

 hand, the same isotherm bends northwards in passing from Eastern 

 America to Greenland, the vegetation of which is the scantier of 

 the two ; and passes to the northward of Iceland, which is much 

 poorer in species than those parts of Lapland to the southward of 

 which it passes. 



The June isothermals, as indicating the most effective tempera- 

 tures in the arctic regions (where all vegetation is torpid for nine 

 months, and excessively stimulated during the three others), might 

 have been expected to indicate better the positions of the most 

 luxuriant vegetation : but neither is this the case ; for the June 

 isothermal of 41°, which lies within the arctic zone in Asia, where 

 the vegetation is scanty in the extreme, descends to 54° N. lat. in 

 the meridian of Behring's Straits, where the flora is comparatively 

 luxuriant; and the June isothermal of 32°, which traverses Green- 

 land north of Disco, passes to the north, both of Spitzbergen and 

 the Parry Islands. In fact, it is neither the mean annual, nor the 

 summer (flowering), nor the autumn (fruiting) temperature that 

 determines the abundance or scarcity of the vegetation in each 

 district, but these combined with the ocean temperature and con- 

 sequent prevalence of humidity, its geographical position, and its 

 former conditions both climatal and geographical. The relations 

 between the isothermals and floras in each longitude being there- 

 fore special, and not general, I shall consider them further when 

 defining the different arctic floras. 



The northern limits to which vegetation extends varies in every 

 longitude ; and its extreme limits are still unknown ; it may, indeed, 

 reach to the pole itself. Phsenogamic plants, however, are probably 

 nowhere found far north of lat. 81°. 70 flowering plants are found 

 in Spitzbergen ; and Sabine and Boss collected 9 on Walden Island, 

 towards its northern extreme, but none on Boss's Islet, fifteen miles 

 further to the north. Sutherland, a very careful and intelligent 



