158 PLANKTON OF WISCONSIN LAKES 



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CHAPTER VIII 



CHEMICAL ANALYSES OF VARIOUS ORGANISMS 



The purpose of this investigation was not only to obtain a general 

 idea of the quantity and of the chemical composition of the plankton 

 as a whole, but also to ascertain the chemical composition of the differ- 

 ent constituents of the plankton whenever they could be secured in a 

 pure or substantially pure state. Several plankton forms were obtained 

 in sufficient abundance and purity to warrant analyses of them and the 

 results of the analyses of these forms are shown in table 49 (p. 215). 

 Since the general problem of the total productivity of a lake was kept 

 in mind during this study, samples of the larger forms were secured 

 from time to time and the results of the analyses of these samples are 

 also given in table 49. 



The analyses of fifty-two samples are shown in this table, of which 

 thirty-four are results obtained on plankton organisms and eighteen 

 on non-plankton forms. Nineteen of the fifty-two samples represent 

 plant material and thirty-three animal material. 



Among the plants the Myxophyceae or blue-green algae are repre- 

 sented by Microcystis, Anabaena, Coelosphaerium, Aphanizomenon, and 

 Lyngbya; the Chlorophyceae or green algae include Ankistrodesmus, 

 Volvox, Spirogyra, and Cladophora, while the diatoms or Bacillariaceae 

 are represented by a sample containing both Fragilaria and Tabellaria. 

 All of these algae except Spirogyra and Cladophora are regular plank- 

 ton forms ; very rarely Spirogyra and Cladophora may be found in the 

 plankton but they are only accidental constituents. Samples of three 

 of the large aquatic plants which grow in the shallow water and which 

 represent the phanerogams, namely, Potamogeton, Vallisneria, and My- 

 riophyllum, have been analyzed. 



Of the thirty-three samples of animal material, nineteen represent 

 plankton Crustacea belonging to six genera ; the Copepoda include three 

 genera, namely, Diaptomus, Cylops, and Limnocalanus, and the Clado- 

 cera are represented by three species of Daphnia, by Holopedium, and 

 Leptodora. Besides the plankton forms of Crustacea two of the larger 

 forms of this group are represented, namely, a crayfish belonging to the 

 genus Cambarus and the amphipod Hyalella. The Oligochaeta are 

 worms belonging to the genera Limnodrilus and Tubifex, while the 

 Ilirudinea are represented by a sample containing two or three species 



