this period of five ar.d a half months. Each month was divided into 

 two periods of roughly two weeks, and the counts from all stations 

 visited in each period were averaged together to determine the 

 abundance for that period. The second column in Table 5l gives the mean 

 of the dates on which samples were taken, and the third column indicates 

 the number of stations visited. Only eight stations were located in the 

 Island Section, so that numbers in excess of that indicate that certain 

 stations were visited twice during the period. The stations were as 

 follows: 18, 37A, 59A, 82, 1$8, 68, 7$, and 8F (Pig. 1), Originally it 

 was planned to visit each station at intervals of approximately two 

 weeks. For various reasons it was not possible to adhere to the plan 

 exactly. In late August and early Septeinber, only two stations were 

 visited in each period. Late June and early October also were poorly 

 represented. 



The most important groups were diatoms (Diatonieae), greens 

 (Chlorophyceae), and blue-greens (Myxophyceae) . The column headed 

 "Others" includes Heterokontaea, Chrysophyceae, Dinophyceae, and 

 Euglenineae. The results are shown graphically in Fig. 13. 



The diatoms were rather abundant at all times, but showed two 

 distinct periods of marked production. In late May the mean number of 

 diatoms in the Island Section was 39 thousand units per liter of lake 

 water. They increased rapidly and reached the spring maximum of 99 

 thousand units per liter in early June. The low point for the season 

 came in early July (26 thousand units); during late July and August 

 the counts were higher and rather constant. In early September the 

 diatoms increased rapidly to lUO thousand units, and continued on to 

 196 thousand in the last half of the month. There was no further in- 

 crease in early October, but in late October the number rose to 26l 

 thousand units, the high for the season. Whether this was the peak 

 for the year or whether they continued to multiply for some time must 

 remain a matter of conjecture. As far as the data go they indicate 

 two periods of abundance for 1929, a minor one in early June and a 

 major one in September and October. 



The green algae remained constant at about 6 thousand units per 

 liter from late May through early July. In late July and August they 

 increased gradually to 15 thousand units, but in early September in- 

 creased abruptly to 71 thousand, and reached a maximum of 128 thousand 

 in late September. Thereafter they declined and at the end of the 

 season they were 33 thousand units per liter. Thus the greens ex- 

 hibited only one period of abundance, which came in autumn. 



In the early part of the season the blue-green algae were 

 very rare, but in early August they increased rapidly to 23 thousand 

 units, and continued to increase to a maximum of 197 thousand units 

 in late September, In early October they dropped suddenly to 75 thousand 

 I units, and declined only slightly more in the remaining part of the month, 



' 1^9 



