MIDDDE EUROPE. 



269 



Gadeceau (1909) has distinguished the following serai zones and associations 

 about the lake of Grande-lieu in France: 



1. Central or lacuster zone, (1) limnaean with three associations, Caricetum, 

 Myriophylletumi and Nymphaeetum, (2) oligorhizous with two associations, 

 Hydrocharetum and CeratophyUetum. 2. Marginal or paluster zone with 

 thxee groups of associations: (1) amphiphytes with four associations, Ldtto- 

 relletum, Heleocharetum, Limosequisetum, and Heterophylletum, (2) heliophytes 

 with three associations, Sdrpetum, Phragmitetum, Typhetum, (3) distropho- 

 phytes with four associations, Magnocaricetum, Myricetum, Juncetum, and 

 Agrostidetum. 3. Extra-marginal or Silvester zone with two groups of associ- 

 ations, (1) psammophytes with two associations, Gynodactyletum and Piisillae- 

 juncetum, (2) pelophytes with three associations, Ericetum, Ulicetum, and 

 Qtiercetum. 



Massart (1910), in his comprehensive and thorough treatment of the vege- 

 tation of Belgium, has touched the successional relations completely, though 

 he has not been primarily concerned with development. The general course 

 of the hydrosere and xerosere is indicated by the following table (115, 210) : 



Open asaocia- Mobile littoral dunes. Mobile interior dunes. Schistose rocks . . Calcareous 

 tions. rocks. 



Closed dry as- f Fixed littoral dunes . . Fixed interior dunes 1~ , , 



sociations. iDry pannes Dry heaths Dry swamps. . . _ j"'''^^'^'!"- 



i-11 J 1- -J (Wet pannes Wet heaths Wet swamps. 



Closed humid Peatbogs Peatbogs. 



afisociation8.|p„^^g p„^^ p^^^^ 



Baumann (1911 : 474) has made a detailed analysis of the structure of the 

 serai zones of Lake Constance: 



The iimermost zone consists of Chara, NiteUa, and some Fantinalis, at a 

 depth of 6 to 17 m. The next zone lies at a depth of 2.5 to 6 m., and is com- 

 posed of Potamogeton, Myriophyllum, Ceratophyllum, and Helodea. The 

 Nuphar zone, at a depth of 0.7 to 3 m., is characterized by Nuphar, Nymphaea, 

 Potamogeton natans, Ranunculus, etc. The next zone consists of Phragmites 

 and Sdrpus, usually alternating but often mixed, and frequently marked 

 by communities of Typha, Phalaris, Glyceria or Polygonum amphibium. The 

 pleuston or free-swimming communities are the Lemnetum, Ceratophylletum, 

 and Zygnemetum. The flood zone is characterized by a large number of con- 

 socies and socles drawn from various stages of the hydrosere, such as Phrag- 

 mites, Litorella, Hdeocharis, Potamogeton, Hippuris, etc. The sequence in 

 the reed-swamps is Phragmitetum, Magnocaricetum, and Molinietum, or Jun- 

 cetum. The Molinietum is followed by dry meadow dominated especially by 

 Bromus erectus. Scrub or woodland may also appear in the later sequence 

 when artificial factors do not prevent. 



Kurz (1912) has described the communities which appear where peat has 

 been dug: 



Conditions vary so greatly that the populations are much confused. The 

 youngest areas show the communities of MyriophyUum, Utricularia, Potamo- 

 geton, and Castalia, and of Phragmites, Carex stricta, C. rostrata, etc., and 

 Pseudocyperus. Such occur only where primary conditions have been rees- 

 tablished. Elsewhere are found Eriophorum, Sphagnum, and Rhynchospora 

 alba, with Drosera intermedia and Molinieta. He has given also a complete clas- 

 sification of the communities of the region, in which the general stages of the 

 water succession are indirectly though clearly indicated. 



