357 



year, as will be seen on a comparison of Plates X. and XXVII. 

 With a few exceptions which will be noted in the subsequent 

 discussion, the trend of the production is similar in the two bodies 

 of water to a most striking degree month by month throughout 

 the year. 



With rising temperatures in February-March, production 

 in the lake attains the unusual level of 1.75-1.85 cm.^ per m.^, 

 an amount not equaled at this season in this lake in any other 

 year, and exceeding by 88- and 26-fold the production in the 

 adjacent flood-swept stream (see table between pp. 342 and 343). 

 This greater production in the lake is due, it seems, to the fact 

 that Quiver Lake collections in these months represent the im- 

 pounded backwaters of the eastern bottom-lands forced through 

 the lake by the configuration of the eastern bluff (PI. 11. ). Slight 

 current and time for breeding permit in them a production not 

 possible in the silt-laden rapidly flowing channel waters with 

 which at our plankton station (PI. 11.) they are contiguous 

 during prevalent levels. The larger production in this year 

 may be attributed to the enrichment of the water by the great 

 mass of organic debris accumulated on the now submerged bot- 

 tom-lands during the two preceding years of low water. 



The vernal pulses in the two waters coincide in the posi- 

 tion of their limits and maxima though not in amplitude at 

 any time, as will be seen on comparing Tables III. and V. and 

 Plates X. and XXVII. The vernal development in the lake pro- 

 ceeds more rapidly, appears earlier, and attains a greater am- 

 plitude than it does in the river. Thus, on April 10 and 17 there 

 is present in Quiver Lake 3.29 and 16.32 cm,^ of plankton per 

 m.^ to 1.68 and 4.45 in the river. The rate of increase is 4.7 times 

 as rapid in the lake, and attains on the 17th a volume 3.7 times 

 as great as that in the river. The maximum (16.76) is almost 

 twice that in the river (9.39). The large development (16.32) on 

 the 17th indicates that the true maximum probably occurred a 

 few days earlier in the lake than in the river. A partial ex- 

 planation of this phenomenon, and also of the earlier and more 

 rapid rise in production, may be found in the somewhat higher 



