viii PBEFACE 



Wisconsin, who has had direct charge of all of the chemical work dur- 

 ing this investigation. He has made substantially all of the nitrogen 

 determinations, as well as many of the other organic analyses. Some 

 idea of the magnitude of the chemical work may be obtained from the 

 tables accompanying this report. The results given for nitrogen, ether 

 extract, pentosans, and crude fiber in these tables are based on 1,249 

 separate chemical determinations ; there are 425 quantitative results for 

 ash and 519 different determinations of inorganic constituents of the 

 ash. This represents a total of 2,193 separate determinations, many 

 of which were made in duplicate. In addition to this number, many 

 analyses were made which are not shown in the tables, such as ascer- 

 taining the quantity of nitrogen in the bowl water and in the filter 

 papers of the centrifuge as well as more complete analyses of the water 

 remaining in the bowl of the centrifuge at the end of a run ; the chem- 

 ical results presented in this bulletin, therefore, are based upon a total 

 of not less than 2,500 separate determinations, excluding the dupli- 

 cates. 



During the period covered by these studies Dr. Schuette has re- 

 ceived assistance in the chemical work from a number of individuals. 

 Mr. N. A. Bailey, Mr. Geo. M. Bishop, the late Mr. A. J. Duggan, Mr. 

 E. A. Hentzen, Mrs. Ethel Hoverson Miller, and Mr. G. G. Town may 

 be mentioned in this connection ; other persons have also given assist- 

 ance for varying periods of time. 



While engaged in this work Dr. Schuette analyzed some special 

 catches of plankton and his results were embodied in a paper which 

 appeared in the Transactions of the Wisconsin Academy of Sciences, 

 Arts, and Letters, Vol. XIX, 1918, pp. 594-613, under the title of A 

 biochemical study of the plankton of Lake Mendota". 



In the collection of plankton material Mr. W. S. Fusch, Mr. E. H. 

 Toole, and several other individuals rendered efficient assistance. 



The arduous task of counting the organisms in the net plankton 

 was done chiefly by Mrs. Henrietta Achtenberg Eyall and Miss Dorothy 

 von Toerne. The nannoplankton organisms were enumerated by C. 

 Juday. 



The junior author is responsible for the preparation of the tables 

 and diagrams and for the writing of the report, but the work was 

 reviewed in all stages by the senior author. 



The numerical results relating to the net plankton of Lake Mendota, 

 shown in figures 22 to 26 and discussed in the latter part of Chapter 

 II, are not presented in detail because they represent only a part of the 

 material of this character which has been secured during the past few 

 years. In the various investigations that have been made on Wiscon- 

 sin lakes since 1905, approximately 10,000 catches of net plankton have 



