matter in a small pond. In general, the concentration was greater 

 with low level than with high level. He believed that concentration 

 was important in the periodicity of certain algae. Pearsall (1923) 

 cited some examples of diatom maxima coinciding with high water and 

 high concentration of salts. The spring maxima in Western Lake Erie 

 came at or near the times of highest lake level. In 1929> the highest 

 water was recorded for May, June, and in 1930, for April, However, 

 the autumn maxima of algae came at times of low lake level in both 

 years. Thus, the observed relation between lake level and diatom maxima 

 in Western Lake Erie cannot be said to support Pearsall's theory of 

 periodicity, but, on the other hand, the two seasons of observations 

 hardly constitute an adequate test. In both years the rainfall after 

 July was abnormal: a deficiency in August being followed by an excess 

 in September or October (Table 5)o It is possible that the excess 

 rainfall in early autumn brought in enough nutrient material to 

 support an unusual production of diatoms. 



It does not seem worth while to call attention to all of the 

 differences in distribution of the genera. Aside from the great 

 abundance of Rhizosolenia, and the absence of Amphora in 1930, the 

 principal differences are such as might be explsdhed by the difference 

 in the periods of time covered in the two years. 



Greens , Comparison of the seasonal distribution of the green 

 algae in 1929 and 1930 will be facilitated by reference to Fig. l6. As 

 shown later, the curves agree very closely with respect to actual abun- 

 dance, and time and degree of changes in abundance for comparable periods. 



The principal differences are in the earlier appearance of 

 large numbers and the earlier decline from the autximn maximum in 1930 

 as compared with 1929. Earlier appearance of large numbers in 1930 

 probably resulted from the higher water temperatures of that year, but 

 the reason for the earlier decline in autumn is not obvious. The data 

 suggest that the greens ordinarily persist a certain length of time, and 

 that earlier increase is balanced by earlier decline. 



The green algae reach their maximum abimdance in summer in most 

 of the lakes which have been studied (Steuer, 1910, p, 5U2), Some 

 writers have reported spring and fall maxima, for example, Tressler and 

 Domogalla (1931) in Lake Wingra. G. M. Smith (192h, page 110) stated 

 that large growths usually appear only in late spring or early summer. 

 In Western Lake Erie, greens were slightly more a bundant in May than in 

 April or June, 1930, but they were not conspicuous in the plankton 

 before July, West and West (1912) found that the greens were most abundant 

 in autumn in lakes of England and Scotland, and the same is true for 

 Western Lake Erie. In both years they reached a maximum in late 

 September, that is, at a time of declining water temperatures. The reason 



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