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and the temperature and salinity will be constant or vary only 

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

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

 in winter. Through the heat of the sun, the temperature of the 

 water may rise considerably and become lukewarm. The salt water 

 will gradually be replaced by fresh water and become brackish 

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

 ments of dead algæ 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 algæ of the littoral pools come in many respects 

 under different biological conditions, in one respect, however, and 

 that, of great importance, the conditions are similar, namely the algæ 

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

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

 littoral algæ-vegetation, which is laid dry for a shorter or longer time 

 at Iow tide. Several otherwise sublittoral algæ are also found in the 

 lower lying littoral pools. The light is cerlainly somewhat stronger 

 here than in the sublittoral region, but to the sublittoral algæ which 

 grow near the Iow water mark the difference will not be of great 

 consequence. In the littoral pools, where the light is darkened by 

 fallen rocks, one may even find some sublittoral algæ which are 

 otherwise generally found at a great depth. In the Iow lying pools 

 we find e. g. species of Delesseria, Porphyra miniata, Rhodomela 

 lycopodioides, Lomentaria clavellosa, Chætomorpha Melagonium, Ulva 

 Lactuca, etc. Ros en vinge has also reported these facts (71, p. 204) 

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

 toral algæ which are regularly laid bare at Iow tide can also grow 

 in littoral pools that are always fdled 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 Ihe coasts of the Færoes. But 

 as pointed out by Ro sen vinge, there are some littoral algæ 

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

 this kind, 7 of which are also found on the Færoes. These 

 7, viz.: Pilinia maritima, Calothrix scopnlornm , Urospora mirabilis, 

 Rhizocloniiim riparium, Bangia fuscopiirpiirea , Porphyra iimhilicalis 

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

 the following littoral algæ: Callithamnion arbuscula, Plumaria e/e- 



