373 



sequence of the changes in Dogfish Lake. Indeed, the corre- 

 lation is, if anything, even closer, since the amplitude of the 

 plankton pulses is greater in Dogfish Lake than in Quiver Lake, 

 and the changes are here — as, for example, in August — the 

 more readily followed and compared with those of the river. 

 Since I have already compared in detail the production in 

 Quiver Lake and the river I shall not repeat the comparison of 

 these similar data from Dogfish, for the correlations are essen- 

 tially the same in both cases, and it will suffice simply to empha- 

 size the similarity of the course of production in the three local- 

 ities. 



The similarity between the production in the two lakes is, 

 however, even greater than that between either of them and 

 the river. This results from the greater similarity of the envi- 

 ronmental factors in the two lakes, with which the river con- 

 trasts in matters of sewage and current. The similarity of en- 

 vironmental factors lies in the amount and kind of vegetation, 

 the depth, the character of bottom and shores — excepting the 

 eastern margin of Quiver, the impounding function (modified, 

 however, in the case of Quiver Lake by the access of creek and 

 spring water), and the freedom from sewage. Under these cir- 

 cumstances it is not surprising that the details of the course of 

 production as well as its ensemble are so strikingly alike in the 

 two lakes. 



To be specific, the similarity in details of the course of pro- 

 duction in Quiver and Dogfish lakes lies in the fact that in the 

 31 coincident collections in these waters the plankton content 

 rises or falls in both at the same time in 23 out of the total num- 

 ber. The amplitude of the change is rarely equivalent, but its 

 direction is identical — referring, of course, to the fact of its being 

 an increase or decrease, and not to the particular angle which 

 the lines forming a planktograph might take. The 8 exceptions 

 to this similarity in the direction of movement in production 

 are shown in the following table, and may without exception be 

 correlated with differences in the environment. 



In this table the plankton contents of the two adjacent col- 



