438 



in the case of Quiver and Dogfish lakes (2.59 and 5.01 cni.^) when 

 we find for these lakes the highest mean annual production in 

 our years of records. In the case of Flag, Thompson's, and 

 Phelps lakes the annual mean falls below the average on the 

 basis of monthly averages, though the average of all collections 

 in Flag and Thompson's lakes is above the general average in 

 these lakes (see table on p. 429). The former basis of compari- 

 son is the better one, since it equalizes to some extent the ine- 

 quality in the distribution of collections. The plankton content 

 in backwaters in this year of recurrent fioods is thus increased 

 in some instances and but slightly reduced in others, with the 

 net result of predominantly higher plankton content than in 

 the current-swept channel, and a much greater total production. 



The effect of the run-off of the impounded backwaters 

 upon channel plankton may be seen in the river planktograph 

 for 1896 (PI. X.), where the March, June, August, October, and 

 November floods in each case reduce the plankton as they rise, 

 and are attended by a noticeable increase as levels fall again. 

 That other factors are involved may be seen in the rise in 

 plankton attending the rising flood of August, and in the de- 

 clines following the increases in plankton content in the midst 

 of rapid run-off in apparently favorable hydrographic condi- 

 tions in nearly every instance above cited. 



The effect of the midwinter flood following two years of 

 low water, which permitted the accumulation in bottom-land 

 forests, marshes, and backwaters of a great amount of vegetation? 

 may be traced in the large production in winter and early spring. 

 In the table on page 436 it will be noted that in the months of 

 February-April production is above the average in every back- 

 water in each month except in Dogfish Lake in April. More- 

 over, the largest records for this season of the year were ob- 

 tained in this year in Dogfish. Flag, and Phelps lakes in all 

 three months and in Quiver and Thompson's lakes in the first 

 two, that is, in a total of 13 out of the 15 monthly averages. 

 During the remainder of the year, from May to December, 

 production in the backwaters generally falls below the average 



