140 H. JONSSON 



continuous, although only as far as the substratum is favourable 

 for its development. By reason of the nature of the substratum, 

 both the upper and the lower boundaries often have an irregular 

 course, and stragglers from the main body of the vegetation often 

 occur. Those Laminar iaceie which occur in the low-lying tide-pools 

 must be regarded as stragglers from the Laminariacew - community 

 which exists below. In the same way there are stragglers which 

 extend outwards into deep water, as some members of the com- 

 munity have been found at a depth of 40 metres. The community 

 occurs both on exposed coasts and on those which are partly ex- 

 posed, as well as on sheltered coasts. It is composed of perennial 

 species with, as a rule, strongly developed organs of attachment, a 

 stem-like stipe and, as a continuation of this, a lamina or leaf-like 

 portion which is originally undivided, but in some of the species, 

 is later divided by longitudinal slits into many lobes. The species 

 are the largest of all the algal species in the northern seas: the}' 

 grow both in pure associations and highly intermingled with one 

 another. The community may be said to resemble a "forest" on 

 the sea-bed; sometimes the "forest" is pure, sometimes mixed, and 

 it has its undergrowth, its "stem" epiphytes and its "leaf" epiphytes. 

 The species which occur are Saccorrhiza dermatodea, Laminaria- 

 species and A/arz'a-species. Like the Fucacece-community in the lit- 

 toral zone, the Laminariacea;-commumty is composed of a few species 

 of very social growth, and, just as the Fucacece-community forms the 

 greater part of the bulk of the vegetation in the littoral zone, so 

 does the Laminariaceoe-commumty below the limit of low-tide. If the 

 range of the associations differs in depth this will be mentioned 

 when they are described. 



The Associations of the La minariacese Community 

 occur in many places in fairly regular succession from the coast 

 out towards the deep sea. Thus, often quite close to the coast, 

 Laminaria saccharina or Alaria esculenta is found occurring in very 

 great abundance in pure or mixed associations; be3'ond is found a 

 belt of Laminaria digitata; and deepest of all Laminaria hyperborea. 

 But the order is not always so regular, and at lesser depths it is 

 frequently seen that the species occur socially on small areas of 

 the substratum, sometimes one species being dominant and some- 

 times another. The species may also occur scattered amongst one 

 anolher, especially at lower depths. There is a difference in the 



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