769 



of course perish. They are, however, of no importance for the deter- 

 mination of the lowest deptli at whicli the algæ-vegetation mav be 

 found; in this connection we are only interested with the fixed algæ- 

 vegetation. It is, however, difficult to determine how deep this limit is. 

 It varies much in the ditTerent seas and depends on how far down 

 a sufficient amount of light may reach. The light reaches farthest 

 down in the tropics, where the rays of the sun strike the surface 

 of the sea almost vertically. In higher latitudes the rays strike 

 the surface more and more slantingly, and therefore do not reach 

 so far down. According to Berthold, a rich vegetation of deep 

 w^ater algæ was still found at a depth of about from 120 to 130 

 metres in the gulf at Naples, and according to Rodriguez, the 

 very lowest limit of the vegetation is 160 meters at Minorca (com- 

 pare Sauvageau: Remarques sur les Sphacélariacées, p. 235). In the 

 tropics the algæ-vegetation probably grows at a still greater depth. 

 According to Ros en vinge, the lower limit of the algæ-vegeta- 

 tion in Greenland is about the curve of from 20 to 30 fathoms. 

 As I have before indicated, this almost agrees with what has been 

 observed at the coasts of the Færoes. Naturally, local conditions 

 often cause the vegetation to disappear above this depth ; there 

 may for instance be plenty of Plankton, or the bottom may at a 

 certain depth turn into mud or sand, which makes it unfit for the 

 algæ. This is perhaps the case on the coasts of Bohuslån, where 

 the algæ-vegetation, according to Kjell man, hardly grows any 

 farther down than a depth of 20 fathoms. 



III. 

 GENERAL CHARACTER OF THE ALGÆ-VEGETATION. 



Upon the whole the algal vegetation on the Færoese coasts must 

 be considered specially vigorous and luxuriant. That stunted forms 

 may be found in unfavourable localities, such as the upper part of 

 the beach or the heads of inlets, where the water becomes brack- 

 ish or almost fresh, is of no consequence in comparison with the 

 luxuriance which otherwise characterizes the vegetation. We could 

 not easily imagine any locality better fitted for developing a vigo- 

 rous algæ-vegetation than the Færoes, where the nature of the 

 coast, the situation in the midst of a large ocean, and the climate, 

 all serve to facilitate the growth of the algæ. 



