30 H. JONSSON 



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 effect of the waves beating on the algae 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 Nans en, 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 



