170 Wisconsin Academy of Sciences, Arts, and Letters. 



torn to rest are ordinarily so colored that they are not easily dis- 

 tinguished from the mud. Frequently in littoral regions the 

 hottom is covered with a thick mat of Chara, which, in turn, 

 forms hiding places for enormous numbers of the invertebrates. 



The flora of the limnetic region can be, of course, only of 

 floating plants. Among these are an enormous number of dia- 

 toms. Chloroplnjceae are present in larger or smaller numbers 

 and sometimes large numbers of the Cyanophyceae. Generally 

 speaking, the limnetic flora is not sufficiently abundant to attract 

 attention, but on some lakes they are sometimes multiplied in 

 such quantity as not only to attract attention but even to excite 

 alarm. The surface of the lake has a thick coat of bright green, 

 and as this is cast up on the shore by the waves it forms 

 ridges which in their decay become very offensive. This phe- 

 nomenon has been known in England as ^^the breaking of the 

 meres," in Germany as the ^'WasserblUthe," and in this country 

 as the ^'working of the lakes." The appearance is sometimes as- 

 cribed to the seeds of littoral plants. Only a few species of 

 plants are concerned in this phenomenon, and the species differ 

 somewhat in different lakes. Certain diatoms may be present, 

 too, in sufficient numbers to produce an unpleasant "fishy" smell 

 in the water. This exaggerated gTOwth of the limnetic flora is 

 most pronounced in shallow or comparatively shallow lakes, and 

 is frequently a source of great annoyance to cities which get 

 their water supplies from such bodies. 



The limnetic fauna, as I liave said before in this address, has 

 but few kinds of animals, by far the most numerous and char- 

 acteristic being the Crustacea. These are beautiful, transparent, 

 and nearly colorless creatures. It is not true, as is sometimes 

 stated, that the limnetic fauna is entirely distinct from the lit- 

 toral. The general character of the limnetic animals is cer^ 

 tainly different, and distinctly different, from that of those 

 found in the littoral region, but many individuals are common 

 to both. It is true, however, that while there is hardly a radical 

 distinction between the two faunn:^, certain species are common 

 to the limnetic regions and only rarely found in the littoral, 

 while some that are everywhere in littoral collections are rarely 

 found in those taken in the open water. There is, of course, no 



