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144 H. JONSSON 



about the limit of low-tide, down to a depth of about 30 metres. 

 Small individuals may be found in the lowermost water-filled de- 

 pressions of the littoral zone. Compared with the other commonly 

 distributed Lommarza-speeies, L. digitata and L. hyperborea, then L. 

 saccharina generally keeps nearest to the coast, especially the more 

 leathery, shallow- water form. In shallow depths the succession can 

 be perceived distinctly, but with regard to greater depths conclu- 

 sions must be drawn from what is brought up by the dredge. The 

 succession usually is, that while L. saccharina keeps nearest to the 

 land L. hyperborea extends deepest. 



As is well known the species varies very much, according to 

 the depth and the degree of exposure. A form with leathery, thick 

 fronds with a rough surface occurs near land on somewhat ex- 

 posed coasts in those depths where the effect of the beat of the 

 waves is distinctly observable. At greater depths another form oc- 

 curs, the deep-water form, with long, broad and comparatively thin 

 fronds; and in protected localities inside the fjords of E. and W. 

 Iceland a third form occurs at a depth of 4 — 20 metres. This form 

 (f. latifolia) is long-stemmed, with comparatively very broad lamina 

 and an entirely smooth surface. As each of these forms grows very 

 socially the character of the association varies in accordance with 

 the depth and the exposure. 



The Laminaria digitata-association. This association is 

 very common everywhere along the coasts where there is a rocky 

 substratum, from a depth of about 4 to about 25 metres. On rocky 

 coasts, however, small specimens occur just at the limit of low-tide, 

 and there represent a kind of boundary. Small individuals may 

 occur also in water-filled depressions in the lowest part of the 

 littoral zone. 



The tendency of Laminaria digitata is to vary in the same 

 manner as L. saccharina, and thus the character of the association 

 differs according to the depth and the degree of exposure, as the 

 forms, individually, grow socially. The typical appearance of the 

 association is determined by the deep-water form, or the typical 

 form, which seems to grow most luxuriantly at a depth of about 

 10 — 20 metres. Here the species attains its greatest length and, as 

 a rule, the stipe is so strong that it is able to raise the much- 

 divided lamina from the bottom. 



Just as the forms are connected with one another by inter- 



