ROOTED AQUATIC PLANTS IN LIMNOLOGY 



109 



no apparent drainage into them otlier than 

 that which enters by surface drainage from 

 the edges of their particular kettles, or from 

 meteoric sources. No outlet is present ex- 

 cept on rare occasions of high water. It 

 appears that the drainage lakes receive a 

 constant addition of mineral salts from 

 their inflowing streams and tend to have 

 harder water than the seepage lakes. 

 Chemical examinations have confirmed this. 

 The writer used this classification in a study 

 of the flora and its quantity in tlie lakes of 

 northern Wisconsin, but it soon became ap- 

 parent that a further division of the classi- 

 fication was needed. Having, apparently. 

 a natural division of lakes to begin with, 

 the most desirable things to know concern- 

 ing these lakes, then, were the stages 

 through which they passed in their mor- 

 phology. Hydrographic characters were 

 determined and the lakes were divided into 

 youthful, mature, and old age stages, after 

 the common practice of geologists. This 

 scheme is outlined in Fig. 1. AVhen ap- 



plied to ecological studies of the plants the 

 proposed scheme of lake development and 

 classification was found to be very useful. 

 Lakes fitting specific descriptions were 

 found to have certain assemblages of plant 

 species, and conversely when a lake flora 

 was listed by another worker it was found 

 possible to predict, with almost certainty, 

 the place occupied by the lake in the classi- 

 fication. The scheme outlined in Fig. 1 is 

 suggested only for northern Wisconsin, and 

 it will probably need modification or revi- 

 sion if applied to other regions. It is very 

 clear that before any classification of lakes 

 can be widely used in this country for the 

 rooted aquatic plants, a more intensive sur- 

 vey of the lakes of North America must be 

 made. 



The Hardness and Alkalinity of Lake 

 Waters 



The factors of hardness and alkalinity 

 have been widely used in studying the dis- 

 tribution of aquatic plants. Probably the 



Eiver througli swamp or 

 bog land. 



Bog land 



Fig. 1. Diagram of lake development in Northern "Wisconsin. 



