42 H. JONSSON 



3. THE AIR. 



The climate is of special importance to that part of the algal 

 vegetation which is exposed during low-tide. The temperature is 

 possibly of least importance in a climate where high and very low 

 degrees of temperature do not occur, or are, at any rate, rare. The 

 degree of humidity of the air and the cloud-covering are, on the 

 other hand, highly important to the algal vegetation which is left 

 dry. The movements of the air are also of importance, especially 

 as it produces movements in the sea. 



A. The Temperature. 



The following means (19 years) 1 from a number of stations on 

 different parts of the coast are here given for the elucidation of the 

 thermal conditions. 



Papey 



Grimsey 



SW. Iceland 



Stykkisholmur - 2.2 0.8 8.9 3.9 2.9 



S. Iceland 



Vestmannaeyjar 1.1 3.8 9.7 5.2 5.0 



Eyrarbakki -2.0 2.1 10.2 3.5 3.5 



From the figures given above it will be possible to form an 

 opinion of the thermal conditions in the places mentioned, and 

 these are altogether such that an algal vegetation left dry can thrive 

 everywhere along the coast. The extremes will not have a sufficiently 

 injurious effect on the vegetation for it to be noticeable in the long 

 run. High degrees of temperature, about 20 C for example, occur 

 rarely in the summer, and will have no permanent effect. Very low 

 degrees of temperature in the winter will not injure the vegetation 

 left dry to any extent worth mentioning, as it is then partly pro- 

 tected by snow (at the very top) and partly by ice. 



I do not consider the cold in the winter injurious to the vege- 

 tation which is left dry, as the algae certainly endure being frozen 

 fairly well. At least I have seen uppermost in the littoral zone, 



Willaume- Jantzen, Meteorologiske Middeltal og Extremer for Fseroerne, 

 Island og Gronland, Kjobenhavn, 1899. 



