MARINE ALGAL VEGETATION 131 



association are as follows: Chorda Filum, C. tomentosa, Chordaria 

 flagelliformis and Dictyosiphon foeniculaceus. Scytosiphon Lomentaria, 

 Castagnea virescens and Coilodesme bnUigera are also most nearly 

 related to this association. Some of the species occur in such abun- 

 dance that they may be said to form an association; this applies 

 more particularly to Chorda Filnm. A pronounced Chorda Filuiu- 

 association occurs in many places at a depth of almost 3--4 metres 

 (measured during low-water of spring-tide). The individuals are ex- 

 tremely long, about 6 metres and, to a great extent, float on the 

 surface at low-tide. The substratum is, as a rule, clayish with 

 pebbles here and there. This association is often almost pure, but 

 scattered individuals of Laminaria saccharina are not rare, although 

 they play no essential role in the vegetation. Chorda Filum also 

 grows above low-water mark in the lower littoral zone, but there 

 it does not really form associations, although it may grow luxuri- 

 antly in many places. 



Chorda tomentosa is also social and grows more luxuriantly 

 below low-water mark than above it. It often occurs in abundance 

 as a component of the sublittoral vegetation. 



Chordaria and Dictyosiphon foeniculaceus are species which grow 

 socially, and rather frequently a Chordarietum or a Dictyosipkonetum 

 is found, usually with a limited distribution both below low-water 

 mark and above it, especially in water-filled depressions in the 

 littoral zone. The remaining species which have been mentioned 

 are also of rather social growth in many places, both below and 

 above low-water mark, especially in pools. Coilodesme, for example, 

 was rather frequent in tide-pools in E. Iceland, and sometimes at 

 a very high level, but then the individuals were frequently inflated ; 

 in SW. Iceland the species grew at and below low-water mark in 

 company \vith Chorda Filum and Saccorrhiza. 



With the exception of the above-mentioned Chorda Fz7u/?i-asso- 

 ciation, this vegetation occurs usually in patches, distributed be- 

 tween other associations. Thus it is closely connected with the 

 Enteromorpha clathrata-association at the boundary between the 

 upper and lower littoral zones, and with the /?/?o(/yn?e/na-association 

 and the Monostroma /izscz/m-association at a depth of about 4 metres, 

 as has been previously mentioned. 



In the Faeroes a similar vegetation occurs as a part of the 

 Stictyosiphon-Sissociation (Borgesen, 12, pp.762 763). 



