The Botany of Iceland - 01.12.1930, Síða 164
154
H. M0LHOLM HANSEN
snow-bare soil Ch thrive best, the deeper the snow-
covering tbe more does the Cb percentage decrease, while,
on tbe other hand, the H percentage increases, and where
tlie snow-covering is deepest, H play the most prominent
part. This distribution must be regarded as a consequence of the
geographical distribution of the life í'orms. Ch, the arctic life-form,
thrive best where the cold has the strongest effect, while the more
temperate life-form, H, shows a preference for conditions in which
there is tbe greatest protection from the cold.
From tbis rule of the distribution of tlie life-forms in tbe Ice-
landic scale of snow-covering there is an interesting, though merely
apparent, devialion, as will appear from a close investigation of
conditions in the individual localilies. In the higlilands the rule
applies throughout, the slighter the snow-covering, the higher tlie
Ch percentage fthough in the very lowest class there occurs an in-
crease), and in the lowlands too it holds good if we consider the
relation between melar and mo, i. e. between snow-bare and snow'-
covered soil. In olher respects conditions in the lowlands seem to
go against the rule, Ch playing the most prominent part where the
snow-covering is deepest and of the longest duration, whereas this
group decreases when the depth of the snow-covering decreases.
The Ch percentage in the Elyna mo, the comparatively snow'-bare
formation at Bjork, is 28, whereas, in the Arctostaphylos mo, the
relatively snow-covered formation, it is 39. In the mo at Lýngdalur
the Ch percentage is 26, in the geiri 35, and in mosathembur only
10. At Thrasaborg the values for mo and geiri are 25 and 34 re-
spectively.
This difference in the disíribution of Ch in the highland and
the lowdand scale of snow-covering is due to the fact that the Ch
vegetation in the lowdands consists especially of E species, whereas,
in the highland tracts, it consists of A species. This disagreement
thus handsomely confirms the distribution of the species groups in
the scale of snow-covering.
Raunkiær examined the variations in the biological spectra
in sections from southern towards norlhern regions (1908, 1911) and
showed that some life-forms, Ph, K, and Th, decrease in quantity,
while others, Ch, increase and others again, H, undergo no appre-