The Botany of Iceland - 01.12.1912, Qupperneq 139

MARINE ALGAL VEGETATION
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in the Færöes (Börgesen 1. c., p. 718) as it does in Iceland, with
this difference, however, tliat the species extends higher upwards
in tlie Færöes and, also, frequently grows in fresh-Water in the
latter place.1 Sphacelaria britannica grows similarly in the Færöes
(Börgesen, 13, p. 432).
According to Foslie (18) a similar shade-vegetation appears to
occur in northern Norway.
This vegetation is a natural upward continuation of tlie semi-
littoral Polysiphonia nrceo/a/n-associalion mentioned below.
cc. The Vegetation of Tide-Pools.
Where there is a rocky coast, depressions of varying sizes occur
everywhere in the littoral zone. These depressions may be divided
into two groups: The tide-pools of the upper littoral zone, and the
tide-pools of the lower littoral zone. The plant-growth in these tide-
pools does not form a vegetation-unit, and is chiefly composed of
species either scattered or of social growth which belong to the
littoral or semi-litloral communities; tliey are, however, here treated
separalely in order to further characterize the iilustration of the
littoral zone given in the above description.
Tide-Pools of the Upper Littoral Zone. Of these the
uppermost, which are almost on the level of Fncus spiralis, are of
the greatest interest, as they often contain species, or forms of
species, which do not occur elsewhere in the littoral zone. These
species are Cladophora sericea f. and Fucus inflatus f. linearis.
The water in the uppermost pools is not replenished with the
recurrence of each high-tide, and this is especially the case in calm
wealher during neap-tide; if, simnltaneously, dry weather occurs,
the water evaporates, and tliis the vegetation cannot endure l'or any
lenglh of time. In rainy weatlier, on the other hand, the pools are
filled witli fresh water, and should this happen during neap-tide
the salinily would be insufíicienl l'or any of the species to exist.
At spring-tide the water in the pools becomes mixed with a fresh
supply of sea-water, and Ihe vegelalion then lives, for a lime, under
good conditions. Thus, there are times during which the conditions
in the pools are not favourable to algal life.
Cladophora sericea grows very socially in many places and, in
1 When I visited tlie Færöes in October, 1897, I was at first surprised to
flnd /?. Rothii growing in streams at and above tlie upper limit of tlood-tide; sucb
a situation for it in Iceland was unknown to me.