The Botany of Iceland - 01.12.1930, Síða 142

132
H. M0LHOLM HANSEN
lowlands. These plants find the most favourable conditions of growth
round the hot springs.
The circling investigations closely confirm these results. The
A percentage of the formations is higher in the highland than in
lowland tracts, and higher in North Iceland than in South Iceland.
The same applies to the sub-groups, A 1 showing a steady decrease
in quantity from the lowlands to the highlands: at Bjork and
Lækjamót the average A 1 percentages are 12.1, at Lýngdalur the
A 1 percentage is 9.1, and at Arnarvatnsheiði it is 5.8.
A 2 occurs more frequently in the highlands than in the low-
lands, and more frequently in North Iceland than in South Iceland,
this is the case too with A 3, only in an even more marked degree.
The E sub-groups show similar relations. E 4 occurs with equal
frequency in the highland and lowland tracts. E 3 occurs most
frequently in tlie lowlands, especially in tlie south country. The
same applies in even greater degree to E 2 and especially to E 1.
Table 26 shows the numerical values and their variations accord-
ing to altitude and district.
Table 26 shows the distribution of the species groups
in the scale of moisture.
The A group shows the same depression on moderately moist
soil as the chamaephytes; from Zone IV the A percentage shows
an increase, both upwards in the mo and downwards in the mýri.
In Zone VII, the flói, the A percentage reaches its lowest value.
The individual sub-groups show different relations; while the
A 3 group decreases steadily as we pass downwards in the scale
from mo through jaðar to mýri, the reverse is the case with the
two other groups, so that the increase of A in the lower section
must be ascribed to A 2 and A 1. These relations are most plainly
illustrated in the lowland series: Bjork, Lýngdalur, and Lækjamót.
The individual sub-groups of E play a very different part in
the composition of the vegetation. E 4 occurs in the greatest quan-
titj% then successively E 3, E 2, and E 1.
While E 4 and especially E 3 must be said to prefer the damper
section of the scale, the reverse is the case with E 2 and E 1 which
only occur in the mo formations. In the Lækjamót series, however,
E 2 forms an exception to this rule, for, similarly to E 4 and E 3,
this group increases with increasing moisture of the soil.
Even if the 7 sub-groups cannot perhaps be said to form a
continuous scale of adaptation to decreasing temperature, this is at