278 DR. HOOKER ON THE DISTRIBUTION OF ARCTIC PLANTS. 



may rank as good species, and its affinities and distribution be consequently open to doubt. 

 Thus under the arctic Stellaria longijies are included five other arctic forms {lata, Ed- 

 icardsii, pedunctilaris, liehecalyx and ciliatosepala) ; but amongst these forms some speci- 

 mens approach closely the American S. longifolia, Muhl, or slight varieties of it ; while 

 others resemble the European ;S'. Friesiana, Ser., others S. graminea, others certain 

 Tasmanian forms, and others, again, Chilian. My own impression is, that some of these 

 may prove but slight modifications of one common, very widely dispersed plant, between 

 all whose varieties no constant definalile characters will eventually be found ; but in the 

 present state of science I have abstained from including any of them, because to prove 

 this or disprove it, the whole genus wants a far longer and closer study than it has yet 

 received or than I can give it. Arenaria verna and its forms offer a very parallel case, 

 and these I have included more largely, because I have the published opinion of many 

 botanists to bear me out in doing so. Viola ejnj^sila, palustris and blanda, are thus in- 

 cluded, though they are more constant and have to a considerable extent different distri- 

 butions ; because I have found no differences of any moment between their normal forms, 

 because such as exist seem to me to be too slight to attach specific value to ; and because, 

 though well distinguished by Scandinavian botanists, they have not been so carefully col- 

 lected and studied in other parts of the arctic zone. Viola canina, Fragaria vesca, and 

 Sanguisorbla officinalis, afford other examples : all these arctic plants affect the temperate 

 plains rather than the mountains of the northern hemisphere. 



Turning to those arctic plants that chiefly affect the Alps of the temperate or tropical 

 zones, their limitation is quite as difficult ; alpine plants being as proverbially variable as 

 arctic. Many alpine plants are now considered to be only altered forms of lowland ones ; 

 and this affects the estimated distribution of every arctic species that is identified with an 

 alpine one. As an example, Saxifraga exilis is a very slight variety of S. cermia ; botli 

 are arctic and alpine plants, but S. cermia is considered by some botanists to be an alpine 

 form of the lowland S. granulata, whose limits and distribution are very difficult to settle ; 

 because it apparently passes into several oriental forms, which have been distinguished as 

 species. In this case I have not included S. granulata with S. cernua ; because the 

 latter is everywhere easily distinguished as a well-marked plant, having a restricted range 

 both in area and in elevation, which S. granulata does not share. At the same time I 

 am in favour of a hypothesis that would give these a common origin previous to the 

 glacial epoch. 



Other reasons for adopting the system of including very closely allied species are the 

 following : — When species have been founded in error ; this generally arises from their 

 authors having imperfect specimens, or too limited a series of them ; various species 

 founded by Brown on the first Arctic American collections come under this category, as 

 do Adams' Arctic Siberian species; the genera Banunciilus, Draba, Arenaria, sindPoten- 

 tilla, offer many examples : when the species, besides belonging to very variable genera, 

 are apparently identical both in the herbarium and according to their descriptions, and 

 present the same or a continuous distribution; of this Trientalis, Senecio, Aster, Erl- 

 geron, Merle iisia, Sedum, Claytonia, Turritis, and many others, afford examples. 



It may be asked what useful scientific results can ])c obtained from the study of a 



