28 PLANKTON OF WISCONSIN LAKES 



The autumnal increase began early in September and reached its 

 highest point on October 22-25, namely, 714.1 milligrams per cubic 

 meter, which was the maximum for the year. A marked decrease fol- 

 lowed in late October and in early November, while the sample of De- 

 cember 16-17 showed a secondary rise to 575.2 milligrams; the sample 

 for the following week, however, contained a distinctly smaller amount 

 of organic matter. 



This decrease continued during the month of January, . 1914, and 

 reached a minimum of 123.7 milligrams by the latter part of this 

 month. The February sample showed a similar amount, while that 

 for March 14-21 contained a larger quantity of organic matter, namely, 

 146.6 milligrams. The first sample obtained after the disappearance 

 of the ice in April showed a further increase and the organic matter 

 continued to rise until it reached 401.8 milligrams on May 5-9. The 

 amount then remained high until after a vernal maximum of 426.0 

 milligrams was reached on June 2-6. A decrease during the rest of 

 June brought the quantity down to 98.8 milligrams on June 30-July 2, 

 after which time the catches were discontinued. 



The series of net catches for 1916-17 (fig. 8) began on February 11, 

 1916, and continued until June 1, 1917. The sample obtained on the 

 former date contained 213.2 milligrams of organic matter per cubic 

 meter, while that of March 8, 1916, had only 172.1 milligrams and that 

 of April 15, 175.8 milligrams. The curve shows a small secondary peak 

 during the last week in April which is followed by a decline to 176.9 

 milligrams on May 8-10. It will be noted that the latter amount was 

 only a little larger than that of April 15. This was succeeded by the 

 regular vernal rise which reached 395.6 milligrams on May 18-19 and 

 a maximum of 418.1 milligrams on June 5-10. A rapid decline was 

 noted during the next two weeks, which was followed by a slight rise 

 during the last week in June ; after this a further decrease brought the 

 amount of organic matter in the net plankton down to the general 

 summer minimum during the second week in July. Between this date 

 and the third week in September the quantity of organic matter varied 

 between 73.3 milligrams and 134.5 milligrams. The smallest amount 

 was found in the sample obtained on August 22-25. The autumnal in- 

 crease began during the last week in September and, through a series 

 of secondary peaks, it rose to the maximum for the year, that is, 1,135.4 

 milligrams, on December 12, 1916. 



By January 18, 1917, the organic matter had fallen to 866.2 milli- 

 grams and by February 14 to 187.3 milligrams. It declined still further 

 during March and the first half of April, reaching a minimum of 92.4 

 milligrams on April 18. The latter was less than one-twelfth as much 

 as that of December 12, 1916. During the latter part of April, 1917, 



