DR. HOOKER ON THE DISTRIBUTION OF ARCTIC PLANTS. 275 



There are also three plants peculiar to Greenland and Labrador, or the White or Rocky 

 Mountains, which have not hitherto been found elsewhere. They are ; — 

 Draba aurea (Rocky Mountains). 



Arenaria Graenlandica (White Mountains and Labrador). 

 Potentilla tridentata (Labrador). 



On the Arctic Froportions of Species to Genera, Orders, mid Classes. 



The observations which have hitherto been made on this subject, are almost exclusively 

 based on data collected on areas too small to yield general results. Especially in deter- 

 mining the influence of temperature in regulating the proportions of the great group of 

 flowering plants, it is of the highest importance to take comprehensive areas, both because 

 of the wider longitudinal dispersion of some orders, especially the Monocotyledons, and 

 the effects of local conditions, such as bog land, which determine the overwhelming pre- 

 ponderance of Cyperacece in some arctic provinces compared with others. 



The proportion of genera to species in the whole arctic phsenogamic flora is 323 : 762, 



or 1 : 2-8. j.. , ' -. ' ^.^ ; and that of orders to species 1 : 10-8 ; in the several pro- 

 vinces as foUows : — Gen. Gen. to Sp. Orders. Ord. to Sp. 

 Arctic Europe 277 



„ Asia 117 



„ West America 172 



„ East America 193 



„ Greenland 104 



Thus Europe presents the most continental character in its arctic flora, and West 

 America the most insular ; which may be attributable to the same cause in both ; namely, 

 the uniformity or variety of type. In West America we have, as in an oceanic island, a 

 great mixture of types (Asiatic, European, East and West American) and paucity of 

 species; in Europe the contrary. The proportions of species to orders are still more 

 various ; but here, again, Europe takes the lead decidedly. 



The proportions of genera and orders to species of all Greenland differ but little from 

 those of its arctic regions ; whereas the contrast between Arctic Eiirope and this, together 

 with Norway as far south as 60° N. lat., is very much greater. This is in accordance with 

 the observation I have elsewhere made, that the whole of Greenland is comparativelj^ 

 poorer in species than Arctic Greenland is. 



Gen. Sp. Ord. Sp. Gen. Sp. Ord. Sp. 



Arctic Scandinavia . . . 1:2-3 — 1 : 9*6 Arctic Greenland . . . . 1:2-0 — ^1:5-5 

 All Scandinavia . . . . 1 : 2-8 — 1 : 11-6 All Greenland 1:2-3—1:6-6 



The proportions of Monocotyledons to Dicotyledons are : — 



Arctic Flora 1:2-6 



Arctic Europe 1 : 2*3 



„ Asia 1:4-5 



„ West America 1 : 3-8 



„ East America 1:3-1 



„ Greenland . . . • 1:2-1 



All Greenland 1:20 



VOL. XXIII. . 2 P 



