DR. HOOKER ON THE DISTRIBUTION OF ARCTIC PLANTS. 279 



flora whose specific limits are in so yague a condition ? the answer is, that thougli 

 much is uncertain, all is not so ; and that if the species thus treated conjointly really 

 express affinities 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, 

 regard 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 tliat, for all purposes of classification, species must be treated as groups 

 analogous to genera, difi"ering in the number of distinguishable forms they include, and 

 of individuals to which these forms have given origin, and in the amount of affinity botli 

 lietween forms and individuals. My main oliject 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 

 views of specific difference, I should make some of the polar areas appear to be botanically 

 very dissimilar from others with which they are really most intimately allied, and from 

 which I believe them to liave 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 generally by the trivial name Grcenlandica), 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 Grcenlandica is often not 

 even a variety or distinct form) was not also common to America. 



I wish it then to be clearly understood that the catalogue here appended is intended tcj 

 include every species hitherto found within the arctic circle, together A\ith those most 

 closely allied forms which I believe to have branched off from one common parent 

 within a comparatively recent geological epoch, and that immediately previous to the 

 glacial period or since then. Further, I desire it to be understood that I claim no 

 originality in bringing these closely allied forms together ; from the appended notes, it 

 will 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. &c. 



