2 90 ECOLOGY [CH. 



ecology 1 . It is a matter of common knowledge that the land 

 flora suffers great changes in the passage from the lowlands to 

 the mountains, until an Alpine flora is reached, whose facies is 

 totally different from that of the plains below. The hydrophytes, 

 on the other hand, show singularly little change, though the 

 number of species diminishes rapidly as high altitudes are 

 approached. In Scotland, West 2 has pointed out that, if a high- 

 land loch is well sheltered and possesses a good shore and water 

 not too poor in mineral salts, its flora may scarcely be distin- 

 guishable from that of a lowland basin. In the Jura, to take a 

 Continental example, sixty lakes were investigated by Magnin 3 , 

 who showed that out of thirty species of hydrophytes, twenty- 

 four were common to all these basins, whose heights ranged 

 from 200 to 1000 metres above sea level. Tansley 4 , again, has 

 drawn attention to the fact that the plants recorded by Graebner 5 

 from sandy pools in the barren heaths of North Germany 

 Isoetes, Littorella, Lobelia, etc. are the same as those occurring 

 in Britain in mountain lochs, and suggests that this indicates 

 that the poverty in mineral salts, common to both types of 

 locality, has more influence than the actual altitude in deter- 

 mining the flora. 



In the Alps many aquatics reach considerable heights. In 

 the Upper Engadine 6 , Ranunculus trichophyllus has been found 

 at above 2500 metres, and a Potamogeton, a Callitriche and 

 Hippuris vulgaris at above 2000 metres. These plants have thus 

 an astonishing range of altitude, since they abound, on the 

 other hand, almost at sea level in the English fens. Outside 

 Europe, the same great range is also observed. In South 

 America near Chimborazo 7 , Myriophyllum, Lemna and Calli- 

 triche have been recorded at a height of above 2400 metres. The 



1 Overton, E. (1899) has shown that the data on this point given by 

 Schenck, H. (1885) have little value, since the altitudes which he names 

 are, in reality, much exceeded. 



2 West, G. (1908). 3 Magnin, A. (1893). 

 4 Tansley, A. G. (191 1). 5 Graebner, P. (1901). 

 6 Overton, E. (1899). 7 Spruce, R. (1908). 



