PREFACE 



The present bulletin is the third issued by the Wisconsin Survey 

 under the general title of "The Inland Lakes of Wisconsin". The 

 first bulletin of this series, No. XXII, was published in 1911. It was 

 based upon results obtained in a quantitative study of the dissolved 

 gases in about 150 lakes situated in different parts of the state ; mineral 

 and sanitary analyses of the waters of a few of these lakes vv^ere made 

 also. In addition to the chemical studies, temperature obesrvations 

 were made at different depths in the various lakes when the samples 

 for the determination gf the dissolved gases were secured. This in- 

 vestigation, therefore, comprised a general study of the thermal and 

 chemical conditions which existed in these lakes at different seasons of 

 the year, especially in the summer, together with a consideration of 

 the biological significance of these conditions. 



The second bulletin of the series. No. XXVII, was published in 1914. 

 It deals with the physiography, hydrography and morphometry of 54 

 lakes in southeastern Wisconsin, on which complete hydrographic sur- 

 veys have been made; it also contains data regarding 185 other lakes 

 in the state, chiefly their length, breadth, and maximum depth. 



The present report presents the results of quantitative and chemical 

 studies of the plankton of four Wisconsin lakes, by far the greater 

 part of the work being confined to Lake Mendota. Only a single 

 observation, in fact, was made on one of these lakes, namely Lake 

 Kegonsa. So far, these studies have not been extended to any other 

 lakes of the state because large samples of water had to be strained or 

 centrif uged in order to obtain enough plankton material for the chem- 

 ical analysis. This made it necessary to use large pumping and cen- 

 trifuging outfits which could not be readily transported from lake to 

 lake. In fact, a permanent lakeside laboratory had to be established 

 in order to carry on these studies. Recently, however, a portable type 

 of continuous acting centrifuge has been constructed and this instru- 

 ment can be used to ascertain the quantity of organic matter in the 

 plankton of many other lakes of the state. With this small machine, 

 enough plankton material may also be obtained for some chemical 

 determinations. 



The authors wish to acknowledge their great indebtedness to Dr. 

 H. A. Schuette, assistant professor of chemistry in the University of 



