high counts and others c nsistently low count. Indirect evidence from a 

 comparison of seasonal distribution in the two years indicates that the lack 

 of uniformity was not such as to invalida:.e a determination of average abun- 

 dance for the area based on samples from several stations. 



The vertical distribution was essentially uniform. Differences in abun- 

 dance at different levels were found, but in general they were not large and 

 were not consistently of the same kind. That is, the greatest abundance may 

 be found near the surface at one time, and near the bottom at another time. 

 In general, samples taken at surface and bottom yielded about the same average 

 count as samples taken at four depths. 



Only in the Island Section was sampling continued long enough to trace 

 the seasonal changes in abundance clearly. Nothing is known of the abundance 

 in November, December, January, February, or March; the following summary is 

 based on a study of the remaining months of the year. Diatoms as a group had 

 tvro maxima, one in spring and another in autumn. In 1929 the spring maxiramn 

 came in early June; in 1930 in late May. Earlier appearance of the maximum 

 in 1930 probably resulted from earlier warming of the ^ater in that year as 

 compared with 1929. In autumn of 1929 the diatoms reached their greatest 

 abundance in late October, but may have continued to increase for some time 

 after the close of the sampling season. In 1930 only Stephanodiscus was 

 abundant in autumn. It seems probable that the diatoms as a group reached 

 their autumn maximum after the close of the sampling season in early October 

 of this year. Diatoms were more abundant in autumn than in spring 01 1929; 

 this may or may not have been the case in 1930. Greens had one maximum and 

 this came in autumn (late September in both years). Blue-greens had one maxi- 

 mum and this coincided with the maximum of greens. Groups other than diatoms, 

 greens, and blue-greens did not make important contributions to the abundance 

 of phytoplankton. 



In spring the phytoplankton was composed almost exclusively of diatoros. 

 In summer all f,roups were rare, although the diatoms were definitely dominant 

 in 1929. The autumn maximum was composed of large numbers of all three 

 t, roups. 



For comparable periods of time, the two years agreed closely with respect 

 to (1) average abundance of phytoplankton groups, (2) times of changes in 

 abundance, and (3) degree and direction of change. For the period late May - 

 early October, the two-year averages, stated in thousands of units per liter, 

 were as follows: diatoms, 90; greens 38; and blue-greens 58. The highest 

 avera,-e counts in period of two weeks (not necessarily the same period for 

 each group) were: diatoms, 26l; greesn, 128; and blue-greens, 203. The 

 lowest were: diatoms, li^; green 0.5; and blue-greens, 0.5. The highest average 

 count of all groups combined for a single period was 5UU, and the lowest 33. 



The genera of diatoms and blue-greens which made important contributions 

 to the plaknton were almost the same in both years, but there were about twice 

 as many important ^^enera of greens in 1930 as in 1929. 



