MIDDLE EUROPE. 265 



He designates as meadows those communities of dense perennials in which 

 grasses play a dominant part, and further regards it as essential that the vege- 

 tation be mowed annually. Salt meadows are excluded. Without annual 

 cutting, meadows pass over into swamp or forest. He further points out that 

 cultivated meadows were known as early as the twelfth centiuy, and that 

 they have mostly arisen out of swamps, moor or forest, through the activity 

 of man. Furthermore, the meadow species themselves have come almost 

 wholly from the adjacent formation, especially from open woodland. 



Magnin (189S, 1894) has found that most of the lakes of the Jura consist of 

 the following zones, from the shore inland: 



(1) Phragmites to a depth of 1.5 m. and Sdrpus lacustris to a depth of 2 m.; 

 here belong also such floating plants as Potamogeton nutans, Nymphaea, and 

 Polygonum amphibium; (2) Nuphar luteum at 2 to 4 m. deep; (3) Potamo- 

 geton perfoliaius, P. lucens, Hipjmris, Myriophyllum, and Ceratophyllum at 

 4 to 6 m.; (4) Naias, Chara, Nitella, and mosses at 6 to 12 m. He points out 

 also that all lakes with similar beds show the same composition and structure 

 in their vegetation. 



Bargmann (1894) has studied the invasion on talus slopes in the northern 

 "Chalk Alps": 



The first invaders are lichens, but the chief pioneer is Thlaspi rotundifolium, 

 and in lower places Aethionema saxatile. Species of Galium next enter, and 

 then Alsine, Crepis, Leontodon, etc., together with a large nimiber of species 

 more sparsely represented. All of these bind the soil more and more, prevent 

 slipping, increase the humus, and prepare the way for Vacdnium, Erica, and 

 Rhododendron. 



Graebner (1895 : 500) has made a careful study of the origin of the heath 

 formation in northern Germany: 



He defines "true heath as an open land with important tree growth or a 

 closed grass covering." It is an area in which is present in quantity either 

 Calluna vulgaris or Erica tetralix, or at least one of the following: Myrica gale 

 Empetrum nigrum, Ledum palustre, Vacdnium vliginosum, or Ardostaphylus 

 uva-^rsi. In the development of the heath upon the Uttoral dunes, the strand 

 plants are replaced to some degree by annual sand-binders, Jasione, Eriophila 

 and Spergula, between which appear Aira, Arabis,^ Solidago, and Chrysari- 

 themum. In the protection of the individuals of these species develop colonies 

 of Hchens, Cladonia, Cetraria islandica, Baeomyces roseus, etc., and mosses 

 Bryum argenteum, Dia-anum scoparium, C&ratodon purpureas, etc., while here 

 and there spring up little plantlets of Calluna and Empetrum. During rainy 

 seasons a tenacious crust of algae, largely Cyanophyceae, covers the sand 

 everywhere; this crust serves to hold the sand particles together, and upon 

 dying produces the first humus. The rnosses also play an important part in 

 fixing the sand, inasmuch as many species, when more or less covered by the 

 blowing sand particles, send up new shoots, forming a tuft. The lichens 

 especially are humus builders. Finally, in a locality modified in the way 

 above, the seedUngs of flowering plants are able to maintain themselves in 

 large quantity. Calluna and Empetrum enter more and more abundantly 

 Jasione, Leucanthemum, and Solidago decrease in number, while Hypnum 

 schreberi spreads steadily and covers the moist places with a thick turf In a 

 similarly detailed fashion, Graebner has traced the development of the heath- 

 moor and, more generally, the modification of forest and heath-moor into 

 heath, as well as the changes exhibited by the latter, especially under culture 



