1868.] HOOKER — ARCTIC FLORA. 357 



treating several very closely allied species and varieties as one 

 aggregate or collective species. This appears at first sight to be 

 an evasive course ; but as it offered the only satisfactory method 

 of solving the difficulty, I was obliged, after many futile attempts 

 to find a better, to resort to it, and hence I feel called upon to 

 enter more fully into my reasons for doing so ; premising that all 

 my attempts to treat each variety, form, and subspecies as a 

 distinct plant involved the discussion of a multitude of details 

 from which any generalization was hopeless ; the results in every 

 case defeated the object of this paper. 



Of the plants found north of the arctic circle, very few are 

 absolutely or almost exclusively confined to frigid latitudes (only 

 about 50 out of 762 are so), the remainder, as far as their 

 southern dispersion is concerned, may be referred to two classes ; 

 one consisting of plants widely diffused over the plains of Northern 

 Europe, Asia, and America, of which there are upwards of 500 ; 

 the other of plants more or less confined to the Alps of these 

 countries, and still more southern regions, of which there are only 

 about 200. Glyceria fluitans, Atropls maritima, and Senecio 

 campestris are good examples of the first, as being high arctic and 

 boreal but not alpine ; while most of the species of Saxifraga, 

 Draba, and Androsace, are examples of the second.* Both these 

 classes abound in species, the limitation of which within the arctic 

 circle, and the identification of whose varieties with those of plants 

 of more southern countries, present great difficulties. 



Those plants of the temperate plains which enter the arctic 

 regions are often species of large, widely dispersed, and variable 

 genera, most or all of whose species are very difficult of limitation ; 

 as Ranunculus, of which the arctic species auricomus, aquatilis, 

 and acris, are each the centre of a nceud of allied temperate 

 species or varieties, as to whose limits no two botanists are agreed ; 

 and the same applies to the species^ of Viola, Stellar ia, Arenaria, 

 and Sieracium. This has often led to the grouping of names of 

 plants considered as synonymous by some authors, varieties by 

 others, and good species by a third class. Furthermore, such 



* Conversely the only arctic genus unknown in the Alps of the middle 

 temperate zone is Pleuropogon, and the only alpine genera containing 

 several species which inhabit the highest Alps of the north temperate 

 zone, but not the polar regions, are Soldanclla in Europe, Siccrtia in 

 Europe and the Himalaya, etc. 



Vol. III. X Xo. 5. 



