284 Eduard Riibel 



ing leafy shoots. The influence o£ dimate is minimal. Differences 

 in temperature are still of some influence, but rather on the 

 floristic composition than on the ecology. Salt content divides 

 groups; also the rooting in mud or fixation on stone. Therefore 

 we have four large groups or orders — the mud-rooting sweet- 

 water Potametalia or Limnaeas, the mud-rooting salt-water 

 Enalids, the stone-fixed Limno-Nereids or Encyonematetalia, 

 and the Halo-Nereids; and to be added to these are the swim- 

 mers Pleuston or Hydrocharitetalia. 



Warm water knows as Limnaea the beautiful Victoria regia 

 with its associates; colder water, the lake roses (water lilies) 

 Nymphaea and Nuphar; in the alpine belt, Sparganium angusti- 

 folium and Hippuris vulgaris and Ranunculus flaccidus; in the 

 north, Stratiotes aloides; in America, Eriocaulon septangulare 

 or Elodea canadensis; in Lake Titicaca, Ceratophylls and Pota- 

 mogetons; in deeper waters, Charas and Nitellas. EnaUds are the 

 shore-covering subaquatic sea-grass meadows of Zostera manna 

 and Z. nana; in the Mediterranean, Posidonietum oceanicae. 

 Chlorophyceae and Cyanophyceae cover the stones of lake 

 shores, as Limno-Nereids. Halo-Nereids are plentiful. In north- 

 ern Europe live the well-studied algal communities of Fucaceae, 

 Laminariaceae, and others. I never forget the amusing California 

 community of sparse Pelagophycus gigantea with their myste- 

 rious floating heads, and the subaquatic dwarf-palm forest of 

 Postelsia palm ae for mis. 



Ecologically, we have to place here also the Pleuston, the float- 

 ing sargasso meadows of the ocean, and the water lens, Lemne- 



tum, of ponds. 



ig.Sphagniherbosa: Moss moor (Hochmoor).— These com- 

 munities depend on aerial water rather than telluric; they form 

 swamps and produce their substratum by their own vegetation. 



