The Botany of Iceland - 01.12.1912, Page 82

IV. COMPARISON WITH NEIGHBOURING
FLORAL DISTRICTS.
In Table 61 is given a survey of tlie plant-geographical distribu-
tion of red and brown algæ coliectively, in certain subarctic
and boreal floral districts. These are so arranged that those
floras with the largest arctic element stand furthest to the left. Tlie
arctic and subarctic percentages decrease while the boreal percentage
increases to the right. The boreal-arctic group is practically similar
everywhere, which is also natural according to the geographical dis-
tribution of the group. The warm-boreal group is not represented
in the subarctic íloras, and the arctic group is quite infinitesimal
in SW. Iceland and Nordland, and is entirely absent from S. Iceland
and the Færöes. In regard to species, the cold-boreal group is ex-
tremely poor in East Greenland and Spitzbergen, somewhat richer
in West Greenland and considerably richer in E. Iceland.
By grouping the species, as is done above (cf. Börgesen and
Jónsson, 14), the character of the floral districts can be deter-
mined according to those groups which are richest in species. Thus,
I characterize a group as subarctic when more than half of its
species are reckoned to the subarctic group. In a similar manner a
district is boreal when more than half of its species belong to the
boreal groups (bor. arct., cold-bor., and warm-bor.).
Similarly, in an arctic district the species belonging to the arctic
group must constitute more than half of the number of species be-
longing to the district, and, in addition to the subarctic group, only
the boreal-arctic will be represented. Of the floral districts men-
tioned by Börgesen and Jónsson (14) none are arctic according
1 With the exception of Iceland the numbers of the species of red and brown
algæ are taken from Börgesen and Jónsson 1. c. (14, p. 22). In regard to East
Greenlaiul the numbers are corrected according to Rosenvinge (64), and to West
Greenland two species have been added: Ectocarpus maritimus and Chantransia
collopocla.