Biological Survey — Erie-Niagara Watershed 63 



random counts was used and the number of organisms or colonies 

 per liter of lake water computed. 



Several interesting things were noted in making a comparison 

 of the "centrifuge" and "net" plankton results. It was dis- 

 covered that the so-called "nannoplankton" forms were compara- 

 tively scarce. Assembled data showed that for the most abund- 

 ant organisms occurring in both net and centrifuge catches there 

 was a difference in the computed results as to number per liter. 

 (3n an average the figures obtained from the centrifuge method 

 ran 3.9 times higher than the net catch figures. This may mean 

 that the net used was inefficient in straining. Also, it is pointed 

 out that the probable error involved in the random count method 

 of dealing with so small a sample as 1 liter is very great. 



Therefore, let it be stated that too much faith should not be 

 l)laced in the actual numbers obtained for the various kinds of 

 organisms. The value rather lies in recognizing that the data were 

 gathered by a standard method througout the investigation and as 

 such w^arrant certain comparisons and the deductions of certain 

 conclusions that are to follow. 



The Genera and Species of Microplankton.'^ — Isokontae. Of 

 the green algae, Sphaerocystis l^chroeteri was the most abundant 

 species in the lake. It occurred throughout the summer in compara- 

 tively large quantites and increased in number in September. In 

 early summer the colonies were compact and with large cells; as 

 the season advanced micro colonies became very abundant. Oocystis 

 was another very prevalent genus w^hich diminished somewhat in 

 midsummer and again increased in September. 0. elliptica and 

 0. crassa were the most common species. IStaiirastrum longiradia- 

 lum was the most common desmid found. Pediastrum was repre- 

 sented by three species: P. simplex^ P. duplex and P. Boryanum, 

 the last named being the most abundant, though at no time very 

 conspicuous. Other genera of green alg^ were never abundant and 

 were obtained only occasionally at the various stations. 



Ileterokant^. Botryococcus Braunii occurred in the surface 

 tows and less frequently at the bottom. It was never common in 

 the counts except at Station 09 on September 12, w^hen the number 

 reached 500 per liter. 



Chrysoi:)hyceae. Two species of Dino'bryon occurred in the 

 plankton, D. sfipitafum and D. diver gens. On September 1 the 

 number was at its maximum of 244 of the combined species per liter, 

 just six times the number for August 15. Malloynonas and Synura 

 were extremely rare in occurrence. 



Bacillariales. Diatoms formed a very considerable part of the 

 life in the lake. The most conspicuous genera were Asterionella, 

 Fragilaria, Melosira, Stei^hanodiscus and Tahellaria. Tahellaria 

 seemed to be the most prominent throughout the summer, increas- 

 ing to a maximum number of 882 per liter at station 05 on Septem- 



* For a comprehensive list of plankton algae of Lake Erie see "The Plankton 

 Algae of Lake Erie " by J. Snow, Bull, of U. S. Fish Commission, Vol. 22, 1902. 



