DR. HOOKER ON THE DISTRIBUTION OF ARCTIC PLANTS. 255 
On the Local Distribution of Plants within 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. Prom 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 River, 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° N. 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. Phoenogamic 
plants, however, are probably nowhere found far north of lat. 81°. 70 flowering plants 
are found in Spitzbergen ; and Sabine and Ross collected^) 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 collector, found 23 at Melville Bay and Wolstenholme 
and Whale Sounds, in the extreme north of Baflin's Bay (lat. 76°, 77° N.). Parn, 
James Boss, Sabine, Beechev, and others, together found 60 species on Melville Island, 
and Lyall 50 on the islands north of Barrow Straits and Lancaster Sound. About 80 tun e 
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 
