79 6 



ZONES AND REGIONS [Pt. Ill, Sect. V 



than in the Baltic. It is also always free from ice in the North Sea, but 

 in the Baltic is occasionally frozen during winter. These differences are 

 reflected in the vegetation. Thus, on the southern coast of Norway exposed 

 to a powerful alternation of ebb and flow, the emerging belt bears a more 

 abundant vegetation than does the submerged belt ; whereas the reverse is 

 the case on the coasts of the Kattegat, where tides are weaker and ice more 

 frequent l . 



As in the Mediterranean Sea, only the rocky parts of the emerging belt 



Fig. 485. Desmarestia aculeata, (Linn.) Lamx. Na- 

 tural size. After Kjellman in Engler und Plantl, Die 

 natiirlichen Pflanzenfamilien. 



Fig. 4S6. Laminaria digitata, f. 

 Cloustoni. Above, the old frond ; 

 below, the new thallus-fiond. One- 

 third natural size. From Stras- 

 burger's Text-book of Botany. 



are occupied by vegetation, whilst shingly, sandy, and muddy soils, owing 

 to the breakers, remain bare of vegetation. Here also many species are 

 characteristic of situations that are alternately exposed to the air and under 

 water. Eucus vesiculosus, for instance, appears chiefly in the emerging 

 belt and alone covers wide tracts. Species of Ulva are also not wanting. 

 Associated with similar conditions are Kjellman's Nemalion-formation, 

 which on the Kattegat is mainly composed of Nemalion multifidum ; 



1 Kjellman, III. 



