RECENT FRESHWATER INVESTIGATIONS 313 



presents the most general survey of plant life in the water. 

 He distinguishes by the vegetation three general types of water 

 basins, swamp, pond and lake; the swamp plants rise with 

 vegetative organs above and free from the surface of the water. 

 In the pond true submerged plants are wanting and only sub- 

 mersed plants with swimming leaves and submersed plants 

 with emersed leaves are normally present. To the single 

 plankton organism the term planktont is applied and among 

 the lake plants the author differentiates (1) the floating flora, or 

 phytoplankton with the eulimnetic species of the open water, 

 the bathy-limnetic forms, half floating, half inhabitants of the 

 littoral zone, and the tycho-limnetic plants, stray elements of 

 shore or bottom flora; (2) the swimming flora, pleuston, driven 

 about on the surface and with organs fitted to an aerial exist- 

 ence; (3), the bottom flora or phyto-benthos, bound to the sub- 

 stratum and consisting of flowering plants, Characeae, sessile 

 algae and mosses, epiphytic and endophytic algae, and fungi 

 and bacteria. Each individual body of water has its own char- 

 acteristic flora as is shown by comparison of a series of lakes. 

 A careful study of the plankton shows numerous adaptations 

 to the conditions of its existence. 



These general principles are repeated and emphasized by 

 examples in the general part of Schroter and Kirchner (96) 

 which deals with the flora of Lake Constance based upon about 

 five years of study. The special discussion of the algal flora 

 of the lake by the second author includes an account of charac- 

 teristic features and of the composition of each part of the 

 flora. There were found in the lake the very large number of 

 361 separate species. No quantitative investigations were 

 made on the plankton. Here also Bruyant (94) and Magnin 

 (95). 



Among the Cyanophyceae Strodtmann (95, 95a) and Klebahn 

 (96, 97) find in the so-called "red bodies " the cause of float- 

 ing. So long as these are present in sufficient numbers the 

 algae swim at the surface, when they are scanty or wanting 

 the algae sink slowly or rapidly to the bottom. The "red 



