46 



H. JONSSON 



and in the Vestmannaeyjar, yet considerably higher in the former 

 place. Grimsey has the fewest wet days, and BerufjorQur and Styk- 

 kisholmur have somewhat similar numbers. 



It is in the spring and the summer especially that the desicca- 

 tion, during the period of exposure, may have an injurious effect 

 in the zone laid bare along the coast. The amount of cloud is of 

 course important, since clouds diminish the danger of desiccation, 

 but the mean figures are not sufficiently elucidatory. Bright sunny 

 days are not propitious to the vegetation left exposed, especially if 

 several such days occur in succession ; and if this takes place at 

 neap-tide, the vegetation which is found above Pelvetia-Fucus spiralis 

 is in danger. Although the weather in Iceland varies greatly, longer 

 periods which are damp or dry often occur. Clear days are not 

 uncommon in the spring and summer, and periods of even a week 

 or more of bright weather are not rare. On bright sunny days in 

 summer the temperature may rise rather high; I have measured 

 20° C. on such a day in a pool in the littoral zone, in the plant- 

 covering itself, and the temperature of the air may rise even higher. 



The periods of bright and dry weather are certainly of impor- 

 tance as regards the upper limit of growth of the algal vegetation 

 during the summer. The Faeroes are probably less favoured by 

 clear weather than Iceland, and the difference in the upper limit 

 of growth of the algal vegetation in Iceland and in the Faeroes may 

 possibly be partly explained by this. 



D. Winds. 



The following figures show the annual percentage (Willaume- 

 Jantzen, I.e.) of the winds: — ■ 





BerufjorSur 



Grimsey 



Stykkisholmur 



Veslmannaeyjar 



N 



6 



8 

 18 



3 

 18 



13 



NE 



24 



3 



E 



4 



20 



20 



23 



SE 



6 



16 



16 



9 



S 



8 



4 



11 



8 



s w 



15 



5 



10 



10 



w 



4 



12 



7 



7 

 3 



8 



NW 



23 



4 



Calm 



10 



10 



12 



22 



