136 H. JONSSON 



the autumn and winter, both because the light is feeble, and be- 

 cause the increased high seas following stormy weather to some 

 extent compensate for the difference in height. But it is in the 

 spring and summer that it is most evident that Corallina has 

 really extended too high up. According to Borge sen's description 

 (12) it appears to extend still higher up in the Faeroes. 



In the Cora//z/?a-association an abundant epiphytic vegetation 

 may occur, both of small algae like Chantransia and of larger algae 

 such as Monostroma Grevillei, Spongomorpha vernalis, Acrosiphonia 

 albescens and also the Lea//?esza-associations. Furthermore, Ceraminm 

 rubrnm, Cystocloniam, Delesseria sinaosa and D. sanguined occur, and 

 other red algae, often in great quantities. When to this is added 

 the fact that Gigartina is often abundantly intermingled with those 

 already mentioned, it is easily seen that this mixed vegetation as- 

 sumes quite a different character, according as to whether the 

 brown-red Gigartina and Ceraminm or the light-green Monostroma 

 and Spongomorpha predominate. This characteristic appearance dif- 

 fers entirely from the usually monotonous appearance of the Coral- 

 lina-belt. This epiphytic vegetation must be considered to form as- 

 sociations which do not really belong to the CoraZ/zna-vegetation in 

 any other respect than that of having it for a substratum. 



The Gigartin a-associatioii is widely distributed on very 

 exposed coasts; it often is of very great breadth and, as already 

 frequently mentioned, extends in under the Fncacece as undergrowth. 

 Where the exposure is less, it does not reach so high; but yet, in 

 the lower littoral zone there is, as a rule, a distinct Gigartina-be\t< 

 which most frequently occurs above the limit of low- tide. The 

 GzV/ar/z/ia- vegetation extends also below the limit of low-tide, but it 

 seems to belong most closely to the lower littoral zone. The belt 

 is quite characteristic, and can often be seen from a distance, as 

 the colour is in strong contrast to that of the Fncaceoe-co mm unity. 

 The species is of very social growth and is usually dominant where 

 it occurs; not rarely, however, a few species occur intermingled 

 with it, especially in the Vestmannaeyjar and at OndverSarnes, two 

 very exposed localities. In the Gigartina-be\\. Corallina may occur 

 lo\vest, Callithamnion Arbnscnla is sometimes plentifully intermixed 

 with the Corallina and occurs also in abundance as an epiphyte, 

 and Ceraminm acanthonolnm occurs rather frequently and often 

 abundantly. In the Vestmannaeyjar Callithamnion scopnlornm occurs 

 rather frequently as undergrowth. In addition, Ceraminm rnbrnm, 



