THE LIFJ'] OF J^EVILS LAKE 75 



The sedges, which occasionally occur in the edge of the lake, 

 play an insignificant part in its life, and may accordingly be dis- 

 missed with brief mention. In 1916, however, as a result of the 

 abundant supply of fresh water thru the Mauvaise Coulee, Minne- 

 waukan Bay extended over a wide expanse of old lake floor, and 

 numerous sedges and rushes were found growing in its waters 

 (pl. 10). 



PROTOZOA 



The data on the Protozoa in Devils Lake are largely the result 

 of studies by Professor C. H. Edmondson, in 1914 and 1917. Some 

 data have, however, been taken from my own notes. 



As a result of his studies Edmondson (1920) found that: 

 "The protozoan fauna of the Devils Lake complex ... in many 

 respects, was such as one might expect in a fresh water lake of simi- 

 lar depth, j^et some very pronounced differences M^ere disclosed 

 . . . A most noticeable feature is the apparent total absence of 

 numerous forms universally found in fresh water. . . . 



"Experiments of a preliminarj^ character indicate that certain 

 protozoa having adjusted themselves to fresh water conditions are 

 not in all cases at least, readily adaptable to the waters of Devils 

 Lake." 



Just how large a part the Protozoa plaj' in the bionomics of 

 Devils Lake cannot be estimated. They are of relatively infrequent 

 occurrence in the plancton catches, and then mostly attached peri- 

 trichs, such as Cothurnia and Vorticella. Any collection of Ruppia, 

 however, after standing in the laboratory for a few days, contains 

 large numbers of Protozoa of several species, and it is this mate- 

 rial which is the chief source of Protozoa in the lake. No attempt 

 has been made to estimate the number of the Protozoa as a whole, 

 nor the relative abundance of the different species, except in ix 

 general way. 



Many of the forms are so minute as to escape thru the sand 

 filter in the Sedgwick-Rafter tube, and even if retained in the 

 preserved sample, they are so distorted as to prevent identification. 

 They are comparatively rare, so that the only way to obtain them 

 in considerable numbers for study is to allow a culture of ditch 

 grass and algae, or of ooze to stand in a culture .jar for several 

 days, when many of them develop in enormous numbers. In this 

 way it is possible to obtain them at any season, even in winter, 

 when they doubtless occur encysted in the ooze. 



The vitality of some of the Protozoa is quite remarkable. 

 Apart from the results of Professor Edmondson 's experiments, men- 

 tioned above, which show the ability of some species to withstand 

 sudden transfer from lake water to fresh, I have observed an 



