The Botany of Iceland - 01.12.1930, Blaðsíða 141

STUDIES ON THE VEGETATION OF ICELAND
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temperate zones, to the soutli of, or below, the 20 per cent Ch
biochore.
The A group was again divided into 3 minor groups according
to the temperature requirements of the groups.
The A 1 group requires the highest temperature and is only
found in subarctic regions. 66° N. lat. in West Greenland was chosen
as a practical northern limit.
The A2 group does not require so high a temperature, yet
it does not occur in the most pronouncedly arctic regions. The
northern limit of the group in West Greenland lies south of 76° N. lat.
The A3 group is of common occurrence as far north as
northern Greenland, lience it is the group that thrives best in the
niost extreme cold.
While cold, i. e. a low temperature, together with a varying
sniount of heat is indispensable for the A groups, heat is indispen-
sable to the E group. In the latter group we may likewise distinguish
n series of types according to their temperature requirements. Hence
group E was divided into 4 minor groups of which E 1 required
most heat, E 4 least.
The species of the E 1 group have their northern limit in
Scandinavia that is to say, they belong to southern Scandinavia.
The E 2 group has no northern limit in Scandinavia, but
does not occur in Greenland.
The E 3 group is composed of Icelandic species which occur
•n Greenland, but soulh of 66° N. lat.
The E 4 group occurs in Greenland north of this line.
The distribution of the species groups in the various parts of
lceland as well as in the Icelandic altitudinal zones fully confirms
the above described distribution of the groups, both as regards quantitv
and as regards mere presence. Thus the A group occurs most
abundantly and witli the greatest number of species in the north
and in the highland tracts, whereas the E group is the dominant
g'oup in the lowlands and the south country.
Of the A sub-groups A 1 prefers the lowland, A 2 the lower
b'acts of the highland, and A 3 the upper tracts of the highland.
Of the E sub-groups E 4 is of common occurrence everywhere,
though there is an appreciable decrease in the upper tracts of the
highlands. E 3 occurs most frequently in the lowlands. E 2 and
especially E 1 occurs solely, and only in scattered specimens, in the
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