703 



weaker, but yet ralher white light, which reaches it. The Florideæ 

 growing near the surface of the sea, in the often very lofty caves on 

 the Færoes, must Hkewise be supposed to get a some perhaps ra- 

 ther weak, but still white light, besides the still weaker, reflected, 

 blue or green light, that comes up from the sea. 



As the epiphytes on stipes of Laminaria hyperborea have always 

 been found to be growing in a precise order, from the top down- 

 ward (more will be said of this in connection with the Laminaria 

 hijperborea-assoc'mWon), it is certainly solely due to a regard for 

 light. The faet is, that those at the top are algæ wanting much 

 light, and those further down, overshadowed by the latter, are algæ 

 generally found in greater depths. Similar observations have been 

 made by Berthold in the Mediterranean (5, p. 421— 422), showing 

 that the epiphytic algæ on a stem of Cystosira are likewise arranged 

 according to their requirements of light. 



Light is likewise, as before mentioned, of no small importance 

 to the colour of the algæ, especially to the Florideæ. Florideæ 

 growing in deep water or in the shade are of pure, bright red 

 colour; most Florideæ growing littorally are of a dark reddish-brown 

 often of an almost blackish shade, e. g. Callithamnion arbiiscula, 

 Ceramium acanthonotiim, Gigartina mamillosa, Polysiphonia iirceolata, 

 Porphyra umbilicalis, Chondrus crispus and others, whereas the same 

 species, when they find themselves in the shade, will recover their 

 bright F/oric/eæ-colour. According to Berthold (5, p. 416—417) the 

 same thing has been observed in the Bay of Naples. This author 

 likewise points out, that many more Florideæ are found on exposed 

 than on sheltered coasts. This is in perfect agreement with my 

 observations made on the coasts of the Færoes. That the Flori- 

 deæ are thus found growing littorally in great numbers on ex- 

 posed coasts, must naturally in the first instance be attributed to 

 the faet that, in conformity with the Gaidukow^-Engelmann's 

 theory, they are of a reddish-browai colour. There may surely, 

 however, also be some truth in the explanation given by Berthold, 

 who supposes that, as the algæ are constantly stirred by the surge, 

 and thus incessantly turning other sides to the light which reaches 

 them, the influence of the light can only be of short duration on 

 each part of their thailus; moreover the foam of the surf also 

 lends some shade. Possibly many of these algæ are in different 

 degrees adapted to stand the intense light; several species, e. g. 

 Chondrus crispus, Rhodymenia palmata, Odonthalia dentata become 



