701 



brown algæ gencially disappear at a depth of a])oul 15 — 20 fa- 

 thoms, leaving an almost pure vegetation of Florideæ, with the 

 exception of some green, and bluish-green algæ, living in testa, 

 and, however, often turning reddish liere. On the beach, especially 

 in its lower part, as well as in the upper part of the sublittoral 

 region, where light is still intense, a vigorous vegetation of lirown 

 algæ is found. To tliese must be added several algæ, especially 

 some green and bluish-green at the upper part of the beach, and 

 at the lower part several red algæ. 



That this distribution is principally, perhaps solely due to 

 light, its quantity as well as its quality, may easily be proved by 

 an investigation of the algæ -vegetation of one of the numerous 

 caves on the coasts of the Færoes. When rowing into such a 

 cave, it will be observed, that the species of algæ, common at 

 the entrance, gradually disappear and are replaced by a great many 

 difTerent sublittoral Florideæ, directh^ under the surface of the 

 w^ater^. This will be more thoroughly explained later on, when 

 the cave vegetation is dealt with. This faet has also been men- 

 tioned by several investigators, e. g. Berthold and Falkenberg 

 (18, p. 220). But whilst Berthold only seeks the cause of the 

 distribution of algæ in the intensity of light, Gaidukow^ main- 

 tains that it is entirely due to its quality. Founding his opinion 

 on Engel mann's well known investigations as w^ell as on his own, 

 Gaidukow has recently in an interesting and instructive paper 

 (35) clearly shown, that the distribution of the algæ is not so much 

 due to the intensity as to the colour of the light. The faet is, 

 that the green and bluish-green algæ grow uppermost, as the red 



' In this connection it should however not be forgotten, that it seems as 

 if some sublittoral species on the shores of the Færoes are only to be found at a 

 certain depth. never directly under the surface of the sea, not even in dark piaces, 

 e. g. several species of Lithothamnion, CallophylUs laciniata, RhodophijUis dichotoma, 

 Antithamnion Pliimnla, Desmarestia aculeata and D. viridis, etc. As to Greenland, 

 some species are likewise nientioned by Rosen vinge (71, p. 228) as never occurring 

 near the surface of the sea. He thinks that this is due to the faet, that temperature 

 and salinity both become less variable as the depth increases. Several of these algæ 

 may however be found littorally in other districts. Kjellman for instance states, 

 that Desmarestia aculeata and D. viridis can occur in the littoral region, on the 

 west coast of Norwa}-, and Antithamnion boreale is sometimes met with littorally 

 in the Norwegian Polar sea. Le Jolis (58) writes that CallophylUs lacinata is to 

 be found at the lowest part of the beach. As these algæ do not appear on the 

 shores of the Færoes at such a high level, even in the caves, it is most probabU' 

 due to the faet that they cannot bear the strong surf here. 



45* 



