387 



sion of its effect in increasing the plankton of the channel can- 

 not be given. Similar marshy regions are found, along the course 

 of the river elsewhere, especially above higher bottoms which 

 have been built up across the flood-plain by tributaries such as 

 Spoon River, and such areas presumably share with Flag Lake 

 this contributory function in the maintenance of channel 

 plankton. 



In the discussion of production in Quiver and Dogfish lakes 

 I have called attention to the similarity in the movement in 

 production, these two lakes and in the river. In Flag Lake, 

 we are dealing with a very different environment ; bottom, 

 shores, vegetation, hydrographic relations, especially in the 

 matter of tributary waters, are all diverse. Indeed, the lake it- 

 self includes several distinct types of environment. It is inter- 

 esting to note that in so distinct a unit of environment as this 

 marsh we find so large a degree of similarity in the movement 

 of production as can be traced between its seasonal plankto- 

 graph and that of the river and of the lakes thus far examined. 

 It should, however, be stated that the similarity is less precise 

 here and is more evident in 1896 than in other years, though 

 this is probably in part due to the absence of sufficiently fre- 

 quent collections. 



The degree of similarity may be seen in the following com- 

 parisons. In 17 of the 27 possible comparisons between pro- 

 duction in Quiver and Flag lakes (PL XXVII. and XXXIII.) 

 the direction of the change in production coincides. Most of 

 the 10 exceptions are due to slight differences in the location of 

 apices of pulses, or occur at times of lowest water, that is, of most 

 pronounced local differentiation^as, for example, at the drop 

 in levels in May and again in July. The same number of excep- 

 tions similarly located occurs when production in Dogfish Lake 

 (PL XXXI.) is compared with that in Flag Lake (PL XXXIIL), 

 and there are 11 exceptions in the possible 27 in the case of 

 the river (cf. PL X. and XXXIIL). 



In general terms, the similarity consists in the rise in pro- 

 duction, probably obscured in Flag Lake by an overestimation 



