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 longipes are included five other arctic forms (Iceta, Ed- 
vyrdsii, peduncular is , hebecalyx 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. grcmmea, 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 definable 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 epipsila, 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 
Sanguisorbia 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. cernua ; both 
are arctic and alpine plants, but S. cernua 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 Ranunculus, Braba, Arenaria, and Poten- 
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, Fn- 
geron, Merteasia, Sediim, Claijtonia, Turritw, and many others, afford examples. 
It may be asked what useful scientific results can be obtained from the study of a 
