703 



weaker, but yet ralher while light, which reaches it. Tlie Floridecc 

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

 the Faeroes, must likewise ])e supposed to get a some perhaps ra- 

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

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



As the epiphytes on stipes of Laminaria hijperborea have always 

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

 ward (more will })e said of this in connection with the Laminaria 

 hyperborea-assoc'iixiion) , it is certainly solely due to a regard for 

 light. The fact is, that those at the top are algae wanting much 

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

 generally found in greater depths. Similar observations have been 

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

 that the epiphytic algae 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 tlie colour of the algae, especially to the Floridece. Floridece 

 growing in deep w^ater or in the sliade are of pure, bright red 

 colour; most Floridece growing littorally are of a dark reddish-brow^n 

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

 Ceramium acanthonohim, Gigartina mamillosa, Polysiphonia iirceolata, 

 Porphyra iimhilicalis, Chondriis crispiis and others, whereas the same 

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

 bright F/o/zc/eop-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 Floridece are found on exposed 

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

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

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

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

 the fact that, in conformit}' with the Gaiduko w-Engelmann's 

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

 how^ever, also be some truth in the explanation given by Berthold, 

 who supposes that, as the algae 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 tlieir thallus; moreover the foam of the surf also 

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

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

 Chondrus crispus, Rhodymenia palmala, Odonthalia dentala become 



