77 



On the Vertical Distribution of the Plankton in 



Winona Lake. 



Glen WOOD Henry. 



During the summer of 1912, while studying at the Biological Station 

 of Indiana University, I undertook to make a quantitative determination 

 of the vertical distribution of the plankton in Winona I>ake. A study was 

 also made of the significant physical and chemical conditions associated 

 with it. The lake was mapped by A. A. Norris ('02). and some of its 

 physical features were considered by Juday ('Oo). 



Winona Lake is a small temperate lake of the deeper type. Its max- 

 imum length is 1.4 miles. Its maximum width is 1.2 miles and its maxi- 

 mum depth is 81 feet. It is large enough to present all of the usual plank- 

 ton problems and small enough to make their study at critical times easily 

 possible. All forms taken were determined, at least generic-ally, and their 

 abundance estimated. The exact quantitative work was limited to the 

 eleven genera and groups, Ceratiuni, Trihonenia, Aiiahacua, Diaptomus, 

 Fragilaiia, Microcystis, Lynghija. Cyclops, NatipUi, Cladocera. and Rotifcra. 

 The Cladocera were represented by the following forms: Daplnua hyalina, 

 Daplinia piilcr. Daplinia retrocurva, Chydorus. Bosinina. Pleuroxtis pro- 

 Gurratus. The following Rotifcra were identified: Anura'a coclilcaris, An- 

 uroea aculeata, Notholca lonyispina, Brachionus pala. and Hexarthra polyp- 

 tera. Weekly catches, July 11th to August 13th, were taken of the eleven 

 forms at ten levels, ranging from surface to 23 meters. The temperature, 

 also the amount of dissolved oxygen, carbon dioxide, and carbonates were 

 determined for the different depths. 



I desire to express my thanks to Dr. Will Scott, acting director of the 

 Station, for the many courtesies and helpful suggestions extended to me 

 :n the collection of the data for this paper. Scott Edwards made the 

 temperature observation and G. N. Hotter determined the dissolved gases. 

 To these gentlemen I am under obligation for permission to use these data. 



PHYSICAL CONDITIONS. 



Turbidity. 

 The turbidity of the lake was determined by means of a Seechi's disk. 

 The water was clearest on July 2-lth, when the disk disappeared at 4 m. 

 The minimum depth, 2.7 m., occurred several times during the summer. 



