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VI Marine Algal Vegetation and Sea-grass Vegetation 95 



Account of the Marine Algal Vegetation and the Sea-grass Vegetation ... 98 



A. The Marine Algal Vegetation 99 



a. The Littoral Zone 99 



aa. The Photophilous or strictly Littoral Communities 99 



1. The Prasiola stipitata-association 100 



2. The Community of Filiform Algae 102 



3. The Community of Fucacea? 106 



4. The Enteromorpha-association 120 



5. The Acrosiphonia-association 121 



bb. The Shade-vegetation 123 



6. The Hildenbrandia-association 123 



7. The Rhodochorton-association, the Sphacelarietum bri- 

 tannici and the Polysiphonietum urceolatse 123 



cc. The Vegetation of Tide-Pools 125 



b. The Semi-littoral Zone 128 



8. The Monostroma-association 129 



9. The Chorda-association 130 



10. The Community of Rhodymenia 132 



11. The Polysiphonia urceolata-association 133 



12. The Community of Corallina 135 



13. The Crustaceous alga-association 138 



c. The Sublittoral Zone 139 



14. The Community of Laminariacea? 140 



15. The Desmarestia-association 151 



16. The Deep-water Community of Floridea? 152 



17. The Lithothamnion-association 154 



18. The Community of Crustaceous Alga? 155 



B. The Sea-grass Vegetation 157 



The Zostera-association 157 



VII Differences in the Vegetation in East and South Iceland 159 



VIII Some Notes on the Biology of the Alga? along the coast of Iceland 166 



1 . Duration of Life . 166 







2. Periodical Changes 169 



3. Littoral Winter-vegetation of Reykjavfk 180 



Bibliography 183 



