Chap. Ill] 



FRESH-WATER VEGETATION 



8i5 



a remarkable diversity. Many species there are that occur in great 

 abundance in particular lakes, but that are quite absent or rare in other 

 lakes, as for instance, of Diatomaceae, Cyclotella bodanica (Fig. 500, d), C. 

 comta, van radiosa (Fig. 500, b) in Lake Constance and Lake Geneva. 



Fig. 500. Algae of the plankton of Lake Constance, a Fragilaria crotonensis, Kitt. b Cyclotella 

 comta, Kiitz., var. radiosa. c Asterionella gracillima, Grun. d Cyclotella bodanica, Eulenst. 

 e-g Botryococcus Braunii, Kiitz. After Kirchner. e magnified 140, others magnified 430. 



Gloeotrichia echinulata (Cyanophyceae) is confined to Lake Plon and a few 

 small neighbouring lakes in Holstein. In Lake Constance, the otherwise 

 very widespread phenomenon of ' red water ' that in its typical form is 

 produced by floating Oscillarieae, is wanting. It is not yet decided whether 



