] 28 H. .IONSSON 



noted that, when the semi-littoral species occur in the upper littoral 

 zone, they are usually confined to the pools, a fact which proves 

 that they do not essentially belong to the upper littoral zone. 



b. The Semi-littoral Zone. 



The upper boundary of this vegetation is just at the lower 

 boundary of the Focus-belt. The vegetation covers the lower littoral 

 zone, and extends, usually in the form of stragglers, below the limit 

 of low-tide, down between the uppermost extensions of the vegeta- 

 tion of the Laminaria-be\\, which in many places reach right up 

 to the limit of low-tide. The semi-littoral communities consequently 

 grow side by side with the Laminarm-associations below the limit 

 of low-tide, to a depth of about 10 metres; they also occur as epi- 

 phytic vegetation on the Laminarice at the depth mentioned. 



Thus, the semi-littoral zone is that between the lower edge of 

 the Focus-belt and the Laminaria-be\t. The breadth of the zone 

 depends on the slope of the coast. If the coast is steep the zone 

 is narrow, but if the coast slopes gently, it is broad. In this zone 

 no single dominant community of extremely social and large species 

 occurs, like, for example, the Focac'ece-community in the littoral 

 zone, and the La/m'nar/acece-community in the sublittoral zone. The 

 zone appears to lie too low for Fucacece and too high for La- 

 minar iacece. 



Green and brown algae occur in abundance in the semi-littoral 

 zone, but the Rhodophycew are most richly represented. The semi- 

 littoral associations occur both laid bare during low-tide and also 

 continuously submerged to the depth mentioned. 



It is easy to follow the upper boundary of the zone, even in 

 places where the Fucacea: are absent. The lower boundary can also 

 be ascertained with comparative ease, if the large Laminariaz only 

 are followed, and if the observer is not led astray by the small La- 

 minariai, which may occur in the depressions and pools of the 

 lower littoral zone. 



The semi-littoral zone comprises several associations which play 

 a rather considerable part in the vegetation. 



By authors who describe the algal vegetation on coasts where 

 there is a change of tide these associations are generally considered 

 to belong partly to the littoral and partly to the sublittoral vegeta- 

 tion. On coasts where there is no tide, the littoral vegetation has, 



