376 



waters rise in proportion. The readjustment which this ne- 

 cessitates so modifies production that its movement differs, 

 though the difference is slight and consequently the less sig- 

 nificant. 



On Aug. 15 and 29 we deal again with a phenomenon simi- 

 lar to that of May 21, namely, a pulse of large production in 

 Dogfish Lake with an accompanying one of lesser amplitude 

 in Quiver. The pulse in Dogfish was again later, apparently, 

 in reaching its culmination (on the 15th) than that in Quiver 

 (on the 7th), and its decline (93 per cent.) on the 22d more 

 complete than that which Quiver attains (63 percent.) on that 

 date from its maximum (4.36) on the 7th. The conditions in 

 Quiver Lake are further complicated by the fact that on the 

 15th river water was just beginning a temporary invasion at 

 the point of collection (see hydrograph, PI. XXXI. ). Save for 

 this invasion the similarity of movement might perhaps have 

 been preserved on the 15th. The abrupt and extreme decline 

 in Dogfish Lake on the 22d, however, with the resulting inter- 

 ruption of the similarity of movement on the 29th, is in some 

 way related to the excessive development of the 15th, which 

 may bring into operation again the factors above suggested in 

 connection with the like phenomenon in May. It seems not 

 improbable that the sharper localization in Dogfish Lake due 

 to absence of current and tributary waters and the presence of 

 these factors in Quiver tends to intensify environmental in- 

 fluences or inherent tendencies of the plankton in the one area, 

 and to minimize some if not all of them in the other, and that 

 this differentiating influence of these purely local factors is 

 fundamentally the cause of the dislocations and disturbances 

 of the otherwise similar movement in production in the two 

 lakes. These exceptions seem, however, to emphasize the es- 

 sential similarity in the production in the two areas, a similar- 

 ity founded on the common factors of the environment shared 

 equally by both, and on the identity, in the main, of the con- 

 stituent organisms of the plankton. 



The general hydrographic conditions of this year affect 



