DR. HOOKER ON THE DISTRIBUTION OF ARCTIC PLANTS. 27*) 
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flora whose specific limits are in so vague a condition ? the answer is, that thoi 
much is uncertain, all is not so ; and that if the species thus treated conjointly really 
express afiinities far closer than those which exist between those treated separately, a 
certain amount of definite information, useful for my purpose, is obtained; and it is a 
matter of secondary importance to me whether the plants in question are to be con- 
sidered species or varieties. Again, if, with many botanists, we consider these closely 
allied varieties and species as derived by variation and natural selection from one parent 
form at a comparatively modern epoch, we may with advantage, for certain purposes, 
ird the aggregate distribution of the very closely allied species as that of one plant. 
When sufficient materials shall have been collected from all parts of the arctic and sub- 
arctic areas, we may institute afresh the inquiry into their specific identity or difference, 
by selecting examples from physically differing distant areas, and comparing them with 
others from intermediate localities. An empirical grouping of allied plants for the pur- 
poses of distribution may thus lead to a practical solution of difficulties in the classification 
and synonymy of species. 
My thus grouping names must not therefore be regarded as a committal of myself to 
the opinion that the plants thus grouped are not to be held as distinct species ; I simply 
treat of them under one name, because for the purposes of this essay it appears to me 
advisable to do so. Every reflecting botanist must acknowledge that there is no more 
equivalence amongst species than there is amongst genera; and I have elsewhere* endea- 
voured to show that, for all purposes of classification, species must be treated as groups 
analogous to genera, differing in the number of distinguishable forms they include, and 
of individuals to which these forms have given origin, and in the amount of affinity both 
between forms and individuals. My main object is to show the affinities of the polar 
plants, and I can best do this by keeping the specific idea comprehensive. It is always 
easier to indicate differences than to detect resemblances, and if I were to adopt extreme 
_ iews of specific difference, I should make some of the polar areas appear to be botamcally 
very dissimilar from others with which they are really most intimately allied, and from 
which I believe them to have derived almost all their species. A glance at my catalogue 
Will show that, had I ranked as different species the few Greenland forms of European 
plants (called generallv by the trivial name Gr<enlandica), I should have made that flora 
appear not only more different from the European than it really is,but from the American 
also ; and that the differences thus introduced would be of opposite values, and hence de- 
ceptive, in every case when the European species (of which the Grccnlanchca is often not 
even a variety or distinct form) was not also common to America. t '. ■ . . . 
I wish it then to be clearly understood that the catalogue here appended is intended to 
include every species hitherto found within the arctic circle, together with those most 
closely allied forms which I believe to have branched off from one common parent 
withm a comparatively recent geological epoch, and that immediately previous to the 
m period or since then. Further, I desire it to be understood that I claim no 
finality in bringing these closely allied forms together ; from the appended notes, it 
I be seen that there is scarcely one of them that has not been treated as a synonym, 
* Essay on the Australian Flora ; introductory to the Flora Tasmanica, p. v. &e. 
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