328 DR. HOOKER ON THE DISTRIBUTION OF ARCTIC PLANTS. 
specimens from arctic habitats, are to me unavailable characters ; Koch also keeps them 
distinct, and characterizes them by their leaves. 
E. linear e, Muhl. Pries keeps this distinct from palustre, L, both being found in 
Lapland. It is referred to palustre, var. j3, in the * Flora Bor.-Am,' in Torrey and Gray's 
Flora, and in Asa Gray's Manual. 
Callitriche verna, L. I have treated this as one collective species, including autum- 
nalis, following Bentham' s idea. Fries keeps this and autumnalis, L, distinct, giving 
Lapland as a habitat for both. Bentham unites them. A. Gray and most authors keep 
them distinct. 
Myriophylltjm spicatum, L., is not Lapponian according to Fries, though Lapland and 
Asiatic Russia are given as habitats by Ledebour. 
IIipptjris montana, Led. I have not seen this plant, which, judging from Ledebour's 
description, would appear undoubtedly to be only a starved state of S. vulgaris. S. ma- 
ritlma, Hellen, is reduced by "Wahlenberg, Fries, and Koch to a variety of vulgaris ; on 
the other hand, it is retained as a species by Brown, Ruprecht, ■ Flor. Bor.-Am.,' and 
Torrey and Gray. Both this and vulgaris are arctic. 
Ceratophyllum. Owing chiefly to imperfect materials, I am obliged to treat Cerato- 
phyllum as consisting of one collective species. The specimens I have examined do not 
present such definite characters in the fruit as the descriptions of authors would seem to 
imply. Bentham regards submersum and demersum as forms of one ; Torrey and Gray 
suggest that there is but one American species ; Fries, Koch, and Watson keep these two 
distinct. Neither of them are Arctic European or Asiatic, though found in Arctic 
America. 
Claytonia lanceolata, Pursh, arctica, Adams, and sarmentosa, C. A. M., are undoubt- 
edly trifling varieties of one plant, neither constant inter se nor as to locality. 
Montia fontana, L. The absence of this cosmopolitan plant in all parts of Temperate 
America east of the Rocky Mountains, except Labrador, is one of the most remarkable 
facts in botanical geography. Newfoundland is given as a habitat by Le Pylaie ; but this, 
hke that of Calluna vulgaris, wants confirmation. M. rivularis, Gmel., is reduced to a 
variety by Fries and Torrey and Gray. 
Sedtjm elongatum, Led. I do not know this plant by authentic specimens. Ledebour 
gives it as a doubtful species, confounded with S. Rhodiola by Chamisso, Hooker and 
Arnott, and Torrey and Gray. 
S euphorbioides, Schl. Of this I know nothing ; according to Ledebour it is pro- 
bably a variety of the Siberian S. algidum, Led, itself very near to quadrifidum, Pall. 
Ribes propinquum, Richardson. This does not differ from B. rubrum, L., to which it 
is reduced as var. /3 by Trautvetter and Meyer in » Flora Ochotsk.' 
Ciirysosplexiuii tetmndrum, Lund, is noticed by Fries as a varietv of alternifolium, 
also occurring in Lapland. I have not seen authentic specimens. 
Parkassia obtusiflora, Rupr., appears nothing but a smaU specimen of palustris, U 
