148 H. JONSSON 



mates to surf. In deep water the Laminaria fronds will always 

 moderate the motion. 



In shallow water, especially where the bottom can be seen, it 

 is easy to observe the under-vegetation, but in deep water one has 

 to rely upon the specimens brought up by the dredge. 



The under-vegetation is not divided according to the various 

 associations of the upper vegetation, but seems to possess the same 

 character wherever it is observed. In S. Iceland (the Vestmannaeyjar 

 and Eyrarbakki) Phymatolithon polymorphum occurs in great abun- 

 dance, covering the bottom entirely for large distances near the 

 coast as an undergrowth. It is mainly composed of crustaceous, 

 membranaceous, and more or less branching Floridece. 



A. Crustaceous Algse. In several places in N. and E. Iceland 

 I found a luxuriant under-vegetation formed of Lithothamnion Iceve, 

 L. circumscriptum and L. glaciate. Among these species the first men- 

 tioned especially seemed to be widely distributed both on the bottom 

 of an Alaria and a Laminaria association. In E. Iceland Lithothamnion 

 flavescens and L. foecundum in addition, like Clathromorphum compac- 

 tum, were very frequent on a Lamz'narza-association-bottom. Together 

 with these species occurred Peyssonellia Rosenvingii, Cruoria arctica, 

 Lithoderma and others, as in the crustaceous algal vegetation (seep. 155). 



B. Membranaceous and Branching filamentous spe- 

 cies. The upper layer, with which are also associated inter- 

 mingled species, varies considerably according to the depth. In 

 addition to a number of the species which extend further down- 

 wards, various semi-littoral species may thus occur in the upper 

 part of the Laminaria-be\t A number of the species which grow 

 on the Laminaria stems may also occur on the bottom between 

 the Laminarice. 



Here it is really a question of several associations; the lowest 

 layer, as mentioned, is the crustaceous alga-association; the second 

 layer is composed in its upper part of semi -littoral associations, 

 which meet the associations which extend deeper and are mainly 

 associations of Rhodophycea* ; and the uppermost layer is the Lami- 

 narza-association. The species are named where these associations 

 are mentioned, and are therefore omitted here. 



The Epiphyte-vegetation. Epiphytes very frequently occur 

 on the stipes and laminae of the Laminariacex, and it is a parti- 

 cularly common occurrence for old stems of Laminaria hyperborea 

 to be entirely overgrown, for the epiphytic vegetation is much more 



