MARINE ALGAL VEGETATION 125 



in the Faeroes (Borgesen 1. c, p. 718) as it does in Iceland, with 

 this difference, however, that the species extends higher upwards 

 in the Faeroes and, also, frequently grows in fresh-water in the 

 latter place. 1 Sphacelaria britannica grows similarly in the Faeroes 

 (Borgesen, 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 the semi- 

 littoral Polysiphonia urceo/a/a-association 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-littoral communities ; they are, however, here treated 

 separately in order to further characterize the illustration 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 Fucus 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 

 weather during neap-tide; if, simultaneously, dry weather occurs, 

 the water evaporates, and this the vegetation cannot endure for any 

 length of time. In rainy weather, on the other hand, the pools are 

 filled with fresh water, and should this happen during neap-tide 

 the salinity would be insufficient for any of the species to exist. 

 At spring-tide the water in the pools becomes mixed with a fresh 

 supply of sea-water, and the vegetation then lives, for a time, 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 the Faeroes in October, 1897, I was at first surprised to 

 find R. Rothii growing in streams at and above the upper limit of flood-tide; such 

 a situation for it in Iceland was unknown to me. 



