STABLE AND MIGRATORY i'LANT FORMATIONS 1 39 



surrounding- forests that one must necessarily ask how all 

 these trees come here. The greater part of them do not 

 occur anywhere but in swamps or similar watery places. 

 Swamp forest is completely bare in the rainy season, and it 

 occurs in typical form in places, which in the rainy season 

 are covered by water up to 4-5 feet (sometimes even 7 feet). 

 It consists, like rain-forest, of several tiers : tall trees 

 60-70 feet high, small trees, shrubs, and plants clothing the 

 ground " (i). 



Alder and sallow swamps are widely distributed in this 

 country, and patches of fenland still characterise some of 

 our lower river courses. The fenland growth is apparently 

 dependent on certain topographic factors regulating the 

 water level and protecting the area from erosion and silt. 

 For its full development fenland may have somewhat similar 

 climatic requirements as the moorland, but owing to its 

 developmental relations to physiography, is probably capable 

 of forming far beyond the moorland climatic province. The 

 physiographic relations of the swamps, fen. and the woodlands 

 known as " Carr," which are found in our principal fen 

 district of East Norfolk, are set forth in the " Types of 

 British Vegetation," to which the reader should refer. 



Within the tidal way of our rivers, the reed belt generally 

 consists of different species to those found further up stream. 

 Fringing belts of Scirpus laaistris, Sparganiuui ramosiun, 

 Heleocharis palustris^ Carex aquatilis, and others, with back- 

 waters and swamps of TypJia, Alisma, Phaiaris, etc., give 

 place to such species as Scirpus inaritiuius, Carex salvia, 

 Scirpus triqueter, and others (39). Alluvial meadows with 

 Poa, Dactylis, Holc?is, Aira ccsspitosa, etc., to others with 

 Hordcuin jjiaritivuun, Broinus mollis var. glabrescens^ or mari- 

 time forms of Phlceum pratense, Agrostis, and Triticuvi. 

 Marshes with Juncus effusus, Jtaicus acutifiorus , Iris Pseiida- 

 corus, Alopecurus geniculatus, etc., are represented by others 

 with [uncus Gerardi, J. viaritimus or J. baliicus, Plantago 

 vtaritima, Triglochin niaritiuium, etc., and from this we pass 

 seaward to the salt-marshes of the estuarine mud-flats covered 

 by the high spring tides. 



These have a close physiographic relation to those parts 

 of the coast-line where the rivers deliver their burden of sands 



