390 



and by the middle of September the water had practically dis- 

 appeared within its boundaries. 



The 7 collections average 4.59 cm.^ per m.'' — about double 

 the average production in the adjacent river, and in Quiver, 

 and Dogfish lakes on coincident dates. Individual collections 

 also exhibit in every case a greater plankton content in the 

 lake than in the river. This area in this season thus contrib- 

 utes to the enrichment of the channel waters, which its run-off 

 enters, and its contributions exceed those of the lakes on the 

 eastern side of the river. This higher production in this local- 

 ity is, I believe, a corollary of the greater impounding function 

 of Flag Lake, resulting from its freedom from tributary waters 

 of recent origin, from its somewhat sheltered location^ — which 

 checks the downward movement through its area of the gener- 

 al currents of overflow, and from the enrichment of its im- 

 pounded waters during this period by the decay of the abun- 

 dant vegetation of the previous season, which, for the reasons 

 just mentioned, is not extensively carried away by flood wa- 

 ters. 



The fact that production appears to be so much less in 1897 

 (4.59 cm.''' per m.^) than in the corresponding months of 1(S96 

 (11.21) may be due to several factors ; to the greater dilution 

 in the greater volume of overflow (cf. PI. XXXIII. and XXXIV.) 

 in the winter and spring floods of the latter year, to the greater 

 abundance in 1896 of decaying organic matter accumulated by 

 the vegetation of two preceding low-water seasons, and, possi- 

 bly, in a measure, to the infrequency of collections in 1897 and 

 the probable omission of the maxima of pulses of production 

 which would tend to raise the average. 



The similarity in the movement of production in this and 

 other localities will appear at once on comparison of PI. XXXIV. 

 with PI. XL, XXVIIL, and XXXII. The coincidence in the 

 direction of the changes is precise in all of the 7 instances in 

 the case of the river, in all but one for Quiver Lake, and in all 

 but two in the case of Dogfish Lake. This is a period of max- 

 imum overflow, when the individuality of these several locali- 



