According to this interpretation. Lake Mendota would be 

 considered more productive than Western Lake Erie, even for the 

 period when the weight of organic matter in the plankton was the 

 same. The superiority of Lake Mendota as a producer of plankton is 

 indicated further by the fact that its spring and autumn maxima are 

 of similar magnitude, while in Western Lake Erie by far the most 

 plankton is produced in autumn, when the weight determinations were 

 made. Lake Mendota is the least productive of the Madison lakes, 

 but all of the others except Lake V5.ngra are markedly affected by 

 pollution, and Lake Mendota is probably the most nearly typical 

 eutrophic lake of the group. Another lake of this type is West 

 Okoboji Lake, Iowa, studied by Birge and Juday (1920), In early 

 August, 1919> this lake yielded only 526 milligrams per cubic 

 meter, which is less than one third of the amount in Lake Mendota 

 for a comparable period in 1915 and 19l6. West Okoboji is 

 probably much poorer in plankton than Western Lake Erie, 



It is certain that Western Lake Erie is poorer in plankton 

 than some of the soft-water lakes of northeastern Wisconsin, The 

 mean amount of organic matter in 8l lakes studied in July and 

 August, when the plankton should be low, was 2,020 milligrams per 

 cubic meter (Birge and Juday, 1927). This amount is only slightly 

 less than that of Western Lake Erie in autimn. Ten of the lakes were 

 very rich in plankton, with a mean of 5,5?0 milligrams; the mean 

 for the remaining 71 lakes was 1,530 milligrams. It is not unlikely 

 that Western Lake Erie would compare favorably with the average of 

 these 71 lakes. 



Green Lake, Wisconsin, is an example of the oligotrophic 

 type of lake. In 1921, the mean weight of dry organic matter for late 

 Septerrber - early October was approximately 658 milligrams per cubic 

 meter (Juday, 192U, Figures 1 and 2). In 1922, the corresponding 

 figure was approximately 1,100 giving a two year average of 880 milli- 

 grams per cubic meter for the period. The amoiont in Western Lake Erie 

 during a similar period was 2,200 milligrams, or 2,5 times as "much. 

 At no time from April through Noventoer did the amount in Green Lake 

 reach as high as 1,500 milligrams. Making allowance for the fact that 

 some of the dead plankton of Green Lake sinks to the bottom, there is 

 still a wide margin in favor of Western Lake Erie. Lake George, 

 New York, also of the oligotrophic type, is probably much like 

 Green Lake in the abundance of its plankton. In August, 1920, this 

 lake yielded 873 milligrams per cubic meter (Juday, 1922, pp. k^-hl) * 



178 



