DR. HOOKER ON THE DISTRIBUTION OF ARCTIC PLANTS. 277 



opinions of my predecessors regarding them, I have foimd this a very tedious and unsa- 

 tisfactory operation. 



Of all these sources of douht and error, the most perplexing has been the well-known 

 variability of polar plants ; and in the existing state of the controversy upon Mr. Darwin's 

 hypothesis, it requires to be treated circumspectly. In several genera, I have not only 

 had to decide whether to unite for purposes of distribution dubious or spurious arctic 

 species, but also how far I should go in examining and uniting cognate forms from other 

 countries, which, if included, would materially affect the distribution of the species. 

 These questions became in many instances so numerous and complicated, that I have 

 often resorted to the plan of 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 discitssion 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 con- 

 sisting 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 fiuitans, Atropis maritima, and Senecio campestrls are good examples of the 

 first, as being high arctic and boreal but not alpine ; while most of the species of Saxi- 

 fraga, 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 Rammmihis, of which the arctic species auricoimis, aqitatilis, and acris> 

 are each the centre of a noeud of allied temperate species or varieties, as to whose limits 

 no two botanists are agreed; and the same applies to the species of Viola, Stellaria, 

 Arenaria, and Sieracinm. This has often led to the grouping of names of plants con- 

 sidered as synonymous by some authors, varieties by others, and good species by a third 

 class. Purthermore, such genera are often represented in the temperate regions of two 

 or more continents (and some of them in the south temperate zone also) by closely allied 

 groups of intimately related species. This always complicates matters extremely ; for an 

 arctic species, being generally in a reduced or stunted state, may be equally similar to 

 alpine or reduced forms of what in two or more of these geographically sundered groups 



* 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 Soldanella in Europe, Swertia in Europe and the Himalaya, &c. 



2 P 2 



