736 



and the temperature and salinity will be constant or vary only 

 slightly. It is quite different in the littoral pools where the water 

 is but rarely renewed, perhaps even only in very stormy weather 

 in w^inter. Through the heat of the sun, the temperature of the 

 water may rise considerably and become lukew^arm. The salt water 

 will gradually be replaced by fresh w^ater and become brackish 

 or almost fresh. The water is usually anything but clean, as frag- 

 ments of dead algae are very often found in great quantities in the 

 high-lying pools. These fragments have been washed up by the 

 surf, and soon putrefy. 



But even if the alga? of the littoral pools come in many respects 

 under different biological conditions, in one respect, how^ever, and 

 that, of great importance, the conditions are similar, namely the alg^e 

 are always covered by water. In this respect they are under similar 

 conditions to those of the sublittoral algae and differ from the other 

 littoral algae-vegetation, w^hich is laid dry for a shorter or longer time 

 at low^ tide. Several otherwise sublittoral algae are also found in the 

 lower lying littoral pools. The light is certainly somewhat stronger 

 here than in the sublittoral region, but to the sublittoral algae w^hich 

 grow near the low^ water mark the difference will not be of great 

 consequence. In the littoral pools, w^here the light is darkened by 

 fallen rocks, one may even find some sublittoral algae w^hich are 

 otherw^ise generally found at a great depth. In the low lying pools 

 w^e find e. g. species of Delesseria, Porphyra miniata, Rhodomela 

 lycopodioides, Lomentaria clavellosa, Chcetomorpha Melagoniiim, Ulva 

 Lactiica^ etc. Rosenvinge has also reported these facts (71, p. 204) 

 and in this connection he discusses the question, whether the lit- 

 toral algae which are regularly laid bare at low tide can also grow 

 in littoral pools that are always filled with water. 



To this he answers as follows: » Observations now tell us that 

 a great many, perhaps most of the species that live in the littoral 

 region outside the pools, can also grow in the pools. « This agrees 

 with what has been observed on the coasts of the Faeroes. But 

 as pointed out by Rosenvinge, there are some littoral algae 

 which are never found in the pools. He mentions 8 species of 

 this kind, 7 of w^hich are also found on the Faeroes. These 

 7, viz.: Pilinia mariiima, Calothrix scopiiloriim , Urospora mirahilis, 

 Rhizocloniiim ripariiim, Bangia fiiscopiirpiirea , Porphyra iimbilicalis 

 and Ulothrix flacca, I never found in pools on the Faeroes, nor 

 the following littoral algae: Callithamnion arbasciila, Pliimaria ele- 



