DR. HOOKER ON THE DISTRIBUTION OF ARCTIC PLANTS. 277 
defeated 
opinions of my predecessors regarding them, I have found this a very tedious and unsa- 
tisfactory operation. 
Of all these sources of doubt 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 discussion of a multitude. ol 
details from which any generalization was hopeless ; the results in every case 
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; (me 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 Alj 
of these countries, and still more southern regions, of which there are only about 200. 
Glyceria flnitans, Atropis 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 Savi- 
fraga, J)raba, 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 Manunculus, of which the arctic species auriconms, aquatilis, and acns, 
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 J tola Mellarw , 
Arenaria, and Hieracium. This has often led to the grouping of names of p ants con- 
sidered as synonymous by some authors, varieties by others, and good species by a third 
class. Furthermore, 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 
unknown 
inhabit 
polar regions, are Soldanella in Europe, Swertia in Europe and the Himalaya, &c. 
2p2 
