The Botany of Iceland - 01.12.1912, Side 44

30
H. JÓNSSON
it, but when the water falls it counteracts the tidal wave; this circum-
stance is of great importance on exposed coasts where the wind blows
frequently, as it shortens the period of desiccation. These move-
ments in the sea are naturally somewhat irregular, but the irregu-
larities are quite equalized in the long run, and therefore the effect
of these movements may very well be regarded as constant. The
high-mark which the water leaves on the coasts is due to the tide
and to these movements jointly.
A frequent sea-wind has a favourable effect on the vegetation
in the zone laid bare by the tide, as mentioned above, but where
a frequent land-wind is blowing the effect is the reverse, as this
counteracts the rise of the tidal wave and accelerates its fall, whereby
the period of desiccation is prolonged.
The eífect of the waves beating on the algæ is great. In ex-
posed places, that is in places where the swell is heavy, the plants
must be able to withstand the drag of the waves. The species
which grow in these places therefore have a tough, leathery and
narrow frond, whereas species in quiet waters have a delicate frond,
often broad and brittle. The consistency of the frond thus accom-
modates itself to the force of the beat of the waves, and in partially
exposed places, or in places where the beat of the waves is not
strong, but yet fairly considerable, we find the consistency of the
frond to be about midway between what it is in exposed and in
calm places.
Like all other movements of the sea, the waves also are of
great importance to the algal vegetation by the fact of their con-
stantly providing fresh particles of water.
c. Currents (Fig. 2). Along the coast of Iceland the warm water
of the Atlantic Ocean meets the cold water of the Arctic Ocean.
The Gulf Stream washes the south coast of the country and sends
an arm northward along SW. Iceland and NW. Iceland, and along
the entire north coast warm water can be traced (the eastern arm
of the Irminger Current) to Langanes; and from thence the arm
turns toward the south along the coast of E. Iceland (Nielsen, 52,
p. 13), where it mixes with water from the East Iceland polar cur-
rent, which comes from the Norwegian Sea (Helland-Hansen
and Nansen, 27, p. 287, where the current is called the East
Iceland Arctic Current). In this manner characteristic coast-water
arises at E. Iceland. Regarding this Nielsen (52, p. 13) writes that
the Irminger Current “gives the waters over the coast shoal of East