750 



most natural to determine the boundary line where the brown 

 algæ leave off, and where only a pure or alniost pure Florideæ- 

 vegetation is left. But while we still know so little of the algæ- 

 vegetation at greater depths, it seems to me most natural, as men- 

 tioned before to determine the sublittoral region as one, and, in agree- 

 ment with Rosenvinge (1. c. p. 237), »to move the lower boundary 

 line of the sublittoral region from the curve of 20 fathoms to the limit 

 where the algæ-vegetation disappears. Thus the elittoral region will in- 

 clude that part of the bottom of the sea which is destitute of algæ«^ 



a. Exposed Coasts. 

 The Phymatolithon-Association. 



This association begins at about the lowest water mark, or a 

 little above, and probably extends down to a depth of several fathoms. 

 My observations are, however, not exact, as Phijmatolithon poly- 

 morphum which forms this association is almost always covered 

 by the Alaria, etc. and is therefore not easily observed. Still I have 

 seen that it may be found in caves several fathoms below low 

 water mark as well as at and even over the highest water mark. 

 It covers the rock with a whitish or slightly pink , glabrous crust, 

 but as mentioned before it is mostly covered by various larger algæ, 

 especially the Alaria. 



This association grows on the most exposed coasts. Its stone-like 

 consistency, and its firm hold on the rocks, serve to protect it from 

 the surf. Simmons mentions a Lithothamnion- formation (p. 251) 

 which probably agrees with this association. It is true that, ac- 

 cording to his report, it is found almost only in the littoral region 

 (»ausnahmsweise bis an die Fluthgrenze hinaufreichend und sich bis 

 an oder zuweilen etwas unter die Ebbengrenze streckend,«) but later 

 he has corrected this. 



The sublittoral Corallina-Formation. 

 The littoral Cora//mrt-formation stretches sublittorally, as men- 

 tioned before, down to a depth of several fathoms^. Here the Co- 



^ »at flytte den lavere Grænse for den sublitorale Region fra 20-Favne Kurven 

 til den nedre Grænse for Forekomst af Algcvegetation overhovedet, saa at den eli- 

 torale Region kommer til at omfatte den Del af Havbunden, der er blottet for Ve- 

 getation«. 



- In my flora (8, p. 402), I have stated this depth as 1—2 fathoms. According 

 to my later observations, it may however reach to at least 4 fathoms. 



