The Botany of Iceland - 01.12.1928, Qupperneq 25

THE AERIAL ALGÆ OF ICELAND
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freely over the country in most places. Even in the woods, which
only cover very small areas and consist of quite low trees or bushes,
there can hardly be much shelter in the winter. Whether it is the
mechanical effect of the wind or its desiccating power, or both in
conjunction, that decide the issue, can hardly be determined with
certainty as long as sure data concerning the force of the wind and
the degree of moisture in the atmosphere are not to liand. As
known, these two kinds of meteorological data are the most diffi-
cult to ascertain, just as also the local conditions of quite small
areas may play an extremely important part.
It might be expected that deep mountain ravines would afford
shelter from the wind, and this is undoubtedly the case; but steep
ravines are not very common in Iceland where, on the contrary,
the broad U-shaped valleys prevail. I saw a narrow ravine sheltered
from the wind in the so-called »Stóra Gjá« to the east of Mývatn,
but as tliere were neither trees nor woodwork of any description
there, I had no opportunitj^ of observing how algæ might have
developed on these substrata. It is a characteristic fact that most
of the samples of algal vegetation from woodwork come from Isa-
fjörður, which lies in a very deep valley surrounded by high moun-
tains on all sides, and from Reykjavík where the high and com-
paratively closeljr built houses will be able to afford some degree
of shelter.
I may further point out that the highest mountain regions of
Norway present a similar lack of tliis community of algæ (Strom
1926, p. 17). In a thesis (Nr. 7) in his doctors dissertation (1910)
Helgi Jónsson makes the following statement:
»The cold itself does not seem injurious to liibernating plants
in cold climates, whereas desiccation by frequent, stormy winds is
extremely fatal.« True, this statement is made witli reference to
the phanerogams only, but there can hardly lie any doubt that it
applies equally lo the aerial algæ.
2. Brickwork.
The old farms of Iceland were all built of turf and wood, but
recently brick-built houses have become inore and more common.
On the lower part of the walls layers of green algæ are often met
with and seem to me to occur with as great frequency as in Den-
mark. Evidently the algæ find better life-conditions on the walls than