The Botany of Iceland - 01.12.1912, Qupperneq 60

46
H. JÓNSSON
and in the Vestmannaeyjar, yet considerably liigher in the former
place. Grímsey has the fewesl wet days, and Berufjörður and Styk-
kishólmur have somewhat similar numhers.
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 Færöes 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 Færöes may
possibly be partly explained by this.
D. Winds.
The following figures show the annual percentage (Willaume-
Jantzen, 1. c.) of the winds: —
Berufjörður Grímsey Stykkishólmur Vestmannaeyjar
N 6 8 3 13
NE 24 18 18 3
E 4 20 20 23
SE 6 16 16 9
S 8 4 11 8
SW 15 5 10 10
w 4 12 7 8
NW 23 7 3 4
Calm 10 10 12 22
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