118 PLANKTON OF WISCONSIN LAKES 



Allowing 10.0 per cent for the ash of the organisms when the diatoms 

 were least abundant, the amount of ash coming from this source varied 

 from 80.0 milligrams to 200.0 milligrams per cubic meter of water in 

 1915 and from 83.0 milligrams to 228.0 milligrams in 1916. 



In 1915 the silt, as determined by difference (see p. 81), ranged 

 from 251.0 milligrams to 878.0 milligrams per cubic meter of water in 

 June and July. This represents somewhat more than a threefold varia- 

 tion ; the smallest amount was noted in sample No. 563 and the largest 

 in sample No. 583. In estimating the silt in the 1916 catches, the ash of 

 the bowl water has been regarded as 655.0 milligrams, just as in Lake 

 Mendota (p. 81). On this basis the amount of silt ranged from about 

 200.0 milligrams in sample No. 648 to 950.0 milligrams per cubic meter 

 of water in sample No. 696. Thus, all of the samples which have been 

 regarded as falling within the 10.0 per cent limit of ash in the organ- 

 isms, show less than one part of silt per million parts of water. Both 

 the minimum and maximum amounts of silt in Lake Monona are smaller 

 than those of Lake Mendota. 



Organisms of the Nannoplankton 



The centrifuge material from Lake Monona was made up largely of 

 the same kinds of organisms that were noted in Lake Mendota (p. 84). 

 The ciliates were represented by Vorticella, Halteria, and some uniden- 

 tified forms that were present in a few of the catches. The flagellates 

 consisted of Chlorochromonas, Cryptomonas, Euglena, a disc-like flagel- 

 late which was not identified, and, rarely, Peridinium. The monads 

 and the disc-shaped form were most abundant. The rhizopods were 

 represented by Amoeba and two unidentified forms belonging to this 

 group. 



Representatives of several genera of algae were noted, namely, An- 

 kistrodesmus, Aphanocapsa, Arthrospira, Closterium, Chroococcus, 

 Oocystis, Oscillatoria, Scenedesmus, Schroederia, and Sphaerocystis. 

 Small colonies and fragments of the algae belonging regularly to the net 

 plankton were more plentiful in this material than in the centrifuge 

 samples from Lake Mendota. The smaller colonies of Microcystis were 

 especially abundant in some of the samples obtained in 1915, while 

 fragments of the chains of Anabaena were numerous in some of the 

 catches both in 1915 and in 1916. The diatoms consisted of Cocconeis, 

 Navicula, Stephanodiscus, and a good many fragments of Melosira. 



In the centrifuge material secured in 1915, the most abundant forms 

 were the monads, the disc-shaped flagellate, Aphanocapsa delicatissima, 

 and Oscillatoria. The monads reached a maximum number of 819,200 

 per liter on July 13 and 409,600 individuals per liter were also noted on 

 August 31. The disc-shaped flagellate numbered 102,400 individuals 



