266 SUCCESSION IN EURASIA. 



The true heaths are (1) Calluna heath, (2) Erica tetralix heath, (3) Empetrum 

 heath, (4) heath-moor, (5) furze-heath, grass-heaths, (6) Molinia heath, 

 (7) Sieglingia heath, (8) dry-grass heath, forest-heath, (9) pine-heath, (10) de- 

 ciduous-wood heath. 



Meigen (1895) has studied the succession on fallow lands in Germany: 

 He finds that the weeds which first take possession are checked by new 

 invaders which completely replace them. New species continue to invade 

 until a characteristic community of Bupleurum falcatum is developed. This 

 seems to have a fairly constant composition and is formed chiefly out of the 

 original invaders, though in different ways. This is followed gradually by 

 shrubs and tall perennials which form the scrub, and this in its turn yields 

 finally to an open oak woodland. 



Meigen (1895) has also traced the development of vegetation on new soil 

 formed by repeated landslides from the mountaia-side: 



He found that the first colonists were Galiopsis angustifolia and Geranium 

 robertianum. These were followed chiefly by Cerastium arvense and Convolvuliis 

 arvends, and these were in turn invaded by Bupleurum falcatum and Brachy- 

 podium pinnatum, which persisted. The secondary plants in different places 

 were various, but the interesting fact was that this community, Bupleuretum 

 graminosum, was not followed by a scrub formation, but remained sharply 

 distinct from the surrounding forest. The same author (1896) found that, 

 in the vineyards of Saxony, which had been destroyed to exterminate the 

 Phylloxera, 73 per cent of the invaders of the first year were annual, 13 per cent 

 biennial ruderal plants, 13 per cent were perennials, while none were woody 

 plants. The changes of the second year consisted in the disappearance of 

 some of these, but especially in the entrance of new invaders. Of the former, 

 the annuals were the first to disappear, while of the latter, perennials were in 

 the majority. After 6 years, vegetation was still largely ruderal. 



Mannel (1896) has distinguished the moors of the Harz Mountains as 

 plateau-moors, slope-moors, and valley-moors: 



These vary greatly in extent, but especially in thickness, some being only 

 a few decimeters thick and others as thick as 25 m. The increase in thickness 

 as well as the horizontal extension and the formation of new moors can be 

 readily followed, owing to the fact that climate and soil cooperate. The 

 rainfall is abundant and the ground-water is retained in such fashion as to 

 favor a remarkable growth of swamp-grasses and mosses. Everywhere in the 

 forest, as well as upon the meadow and heath, develop moist seepage areas in 

 which the moss covering grows rapidly. The woodland vegetation is destroyed 

 and both forest and meadow moor change gradually into high moor. This 

 course of development is readily checked by the profile of the moor itself, in 

 which remains of birch, fir, willow, and hazel, as well as oak and beech, are to 

 be found. 



Schorler (1896) has studied the vegetation of polluted streams in Germany; 



In the case of the greatest pollution, flowering plants are entirely absent. 

 Those which can stand extreme pollution are Potamogeton, Ceratophyllum, and 

 Lemna. In the case of unpolluted portions of the stream, the number of 

 species of amphibious and aquatic plants is large, 7 and 12 respectively. In 

 polluted water these are decreased to 5 and 3 in the case of the Elster. In 

 portions of the Luppe polluted by factory water, the numbers are 4 and 5, 

 while pollution by sewage reduces the number of bank species to 3, namely, 

 Sparganium, Alisma, and Sagittaria. 



