great. The largest count of any one form was ikS per liter and most of 

 the counts were much lower. Eddy's paper is based on surface collections 

 made near shore in the southern part of Lake Michigan, Diatoms were 

 predominant in the plankton at all times, and the same species were 

 always conspicuous. Comparison of recent collections with those made 

 forty years before showed essentially the same kind of plankton in both 

 periods. 



The most extensive study of the phytoplankton of the Great Lakes 

 was the one carried on in Lake Erie in 1928 and 1929 as reported by 

 Burkholder (1929a and an unpublished manuscript). In 1928 work was con- 

 fined to the area east of Long Point, but in 1929 all of the lake east 

 of Western Lake Erie was covered. Samples were taken by the pump method; 

 50 liters were pumped from the desired depth, emptied into a metal con- 

 tainer, and strained through a plankton net. Additional one liter 

 samples were run through a continuous-flow centrifuge to obtain the nan- 

 noplankton organisms. In later pages the results obtained will b e com- 

 pared with those obtained in the present investigation. 



Another recent study is that of Gottschall (1930) on the 

 plankton of the water supply at Erie, Pennsylvania, Finally, may be men- 

 tioned the work of Burkholder and Tressler (1932) on some bays at the 

 east end of Lake Ontario, Both of these reports will be considered 

 briefly later. 



Materials and methods 



This report is based entirely on samples of water from which the 

 plankton was removed by a Foerst continuous-flow electric centrifuge 

 like the smaller of the two described by Juday (1926), In 1929, l85 

 samples were taken, and these were grouped into 110 series, all samples 

 taken at a station on the same day constituting a series. At the 

 shallow stations, only single samples were taken. In 1930, 28? samples 

 in 115 series were taken. The stations visited were the regular 

 stations shown in Figure 1, and a few special ones which will be noted 

 in the text. 



Samples of water were taken from the lake with a Kemmerer- 

 Foerst water bottle similar to the one described by Birge (1922), The 

 size of the sample was commonly three liters, and was never less than 

 1,5 liters, the capacity of the bottle. In 1929, the routine procedure 

 was to take two samples at each of the deeper stations: one at the 

 surface and another about one meter above bottom. In 1930, samples at 



1U2 



