DR. HOOKER ON THE DISTRIBUTION OF ARCTIC PLANTS. 255 



On the Local Distribution of Flants loitlmi the Arctic Circle. 



The greatest number of plants occurring in any given arctic district is found in the 

 European, where 616 flowering plants have been collected from the verge of the circle to 

 Spitzbergen, From this region vegetation rapidly diminishes in proceeding eastwards 

 and westwards, especially the latter. Thus, in Arctic Asia only 233 flowering plants have 

 been collected; in Arctic Greenland, 207 species; in the American continent east of 

 the Mackenzie Eiver, 379 species ; and in the area westwards from that river to Behring's 

 Straits, 364 species. 



A glance at the annual and monthly isothermal lines shows that there is little relation 

 between the temperature and vegetation of the areas they intersect, beyond the general 

 feature of the scantiness 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 Ice- 

 land, 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 temperatures 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° jST. lat. in the meridian of Behring's Straits, where the flora is comparatively 

 luxuriant ; and the June isothermal of 32", which traverses Greenland 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 com- 

 bined with the ocean temperature and consequent 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 therefore 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. Pha-nogamic 

 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, 15 miles further to the north. Suther- 

 land, a very careful and intelligent coUector, found 23 at Melville Bay and Wolstenholme 

 and Whale Sounds, in the extreme north of Baffin's Bay (lat. 76°, 77° N.). Parry, 

 James Boss, Sabine, Beechey, and others, together found 60 species on Melville Island, 

 and Lyall 60 on the islands north of Barrow Straits and Lancaster Sound. About 80 liave 

 been detected on the west shores of Baffin's Bay and Davis's Straits, between Pond Bay 

 and Home Bay. To the north of Eastern Asia, again, Seemann collected only 4 species on 



