M. FOSLIE. [1905 



I consider it superfluous to enter more fully upon the reasons 

 which have induced me to reducing the species so considerably 

 as done below. My motives will in part appear from the remarks 

 made concerning each single species. I had so to speak to choose 

 between two ways — either to establish a still larger number of 

 feebly differentiated boreal-arctic species, than already done, or to 

 reduce as below, and at the same time found some new forms. 

 As I have indicated, I choose the latter way. It may, however, 

 seem as if I have gone too far in this reduction. But as I have 

 been unable to draw sure lines, I think the reduction must be 

 considered compulsory, even if some species are to be taken in a 

 rather wide sense. This reduction also corresponds with the view 

 of recent authors concerning the mutual relationship of other alga?, 

 e. g. the species of Fucus; for in these too a strong reduction has 

 urged itself, the great variation of these algas being really condi- 

 tioned only by certain hydrographic circumstances This is parti- 

 cularly the case with Fucus inflatus. The Laminarise may also 

 be instanced, which in the boreal-arctic areas show an extreme 

 power of variation. If we have in hand a reduced form of e. g. 

 Laminaria digitata from the interior of one of the larger fjords 

 on the coast of Norway and another extreme form of the same 

 species from certain localities on the open shore, we should believe, 

 if we had not seen the intermediate forms, that we had in hand 

 species rather widely different 1 ). In the Lithothamnia is found a 

 similar power of variation, which is scarcely greater in any other 

 place than in these very areas. It is, however, to be observed 

 that in several cases this variation is not conditioned by the same 

 hydrographic circumstances as in the alga? mentioned above. As 

 to the Lithothamnia, besides, other circumstances can play impor- 

 tant parts. 



1) A form peculiar in this respect, or rather biologically, is Pelvctia canali- 

 culata f. radicans Fosl. New or crit. Norw. Alg. pi. 1, fig. 2. The lower 

 part of the frond is somewhat creeping, provided with rhizoids more or 

 less numerous, connecting the particular individuals to one another, and 

 penetrating about 1 cm. into the clay. It has only once been met with 

 in pools of probably brackish water along the lower part of the river 

 Rindelven at the inner part of the Trondhjem Fjord. 



