112 Lake Maxinkuckee, Physical and Biological Survey 



end of a slender stalk, attached to detritus ; insect larvse and larvse 

 casts, and a few small snails. On August 31, a fisherman re- 

 marked that the lake began "cleaning itself" four weeks ago and 

 that there was then a much thicker scum than at present. He said 

 neither he nor any of the residents had seen it act so ("clean it- 

 self") so early for 15 years. He remarked that fishes bite well 

 before and after the process of "cleaning" but not during that 

 time. 



Constitution, significance, etc., of plankton scum: — The plank- 

 ton scum of different lakes differs considerably in its elements. In 

 all lakes it is principally vegetable, such inert animal products as 

 exuviae of insect larvse and the statoblasts of bryozoa sometimes 

 being included in considerable quantities. It is best collected by 

 skimming or by simply holding the mouth of the collecting bottle 

 below the surface of the scum and allowing it to run in. Not pre- 

 cisely the same elements are obtained by drawing a towing net 

 through the scum, as many of the finer elements readily sieve 

 through, and Crustacea in the water near the scum, but not a part 

 of the scum, are captured. 



In Lake Maxinkuckee the principal elements of the plankton 

 scum are Lyngybya sestuarii, Anahsena flos-aquse, Botryococcus 

 braunii, Coelosphsen^im kuetzingianum, statoblasts of Plumatella, 

 and the staminate blossoms of Vallisneria. Occasionally Vorti- 

 cella was associated with the Anabsena, but this was only a tempo- 

 rary association. The most abundant element is Anabxna 

 flos-aqux; indeed, it is so predominant that the history of the 

 plankton scum is essentially the history of it. The plankton scum 

 of some of the surrounding lakes, such as the Twin Lakes north 

 of Hibbard, and Lake-of-the-Woods northeast of Plymouth, is also 

 Anabaena, but it is worthy of note that that of some of the neigh- 

 boring lakes is somewhat different. The principal plankton ele- 

 ments of Winona Lake appear to be Lyngbya xstuarii and Micro- 

 cystis xruginosa. Chapman Lake, Kosciusko County, and Bass 

 Lake, Knox County, have at times a scum composed of Rivularia 

 echinulata colonies. While in one of the Twin Lakes and in 

 Winona or Eagle Lake some of the quiet lagoons and adjacent parts 

 of the lake are so thickly overgrown with the little duckweed, 

 Wolffia, that this might properly be referred to as plankton scum. 

 In some of the lakes of the upper Mississippi, the principal plank- 

 ton scum element is Aphanizomenon flos-aquse, a species not yet 

 found in Lake Maxinkuckee. 



The character of the plankton scum varies of course with the 

 organisms composing it. And the characteristics of Anabssna and 



