372 



similar to that of the collections in Quiver Lake for this year, 

 the only exception to the coincidence of collections, actual or 

 approximate, being on December 29, when on account of rotten- 

 ness of the ice it was not possible to get the collecting outfit to 

 the station. 



The maximum production occurs in the vernal pulse in the 

 last fortnight of April, culminating at 20.35 cm. 3 per m. 3 on the 

 17th, though production is also large on the 24th (19.5). In Quiv- 

 er Lake this maximum is on the 24th (16.76), though production 

 is also large on the 17th (16.32). The maximum in channel 

 waters (9.39) is also on the 24th. These differences in the time 

 of the maxima may, I believe, be correlated directly with the 

 thermal factor. For example, in both Quiver and Dogfish lakes 

 the production is large and almost equal on the 17th and 24th, 

 but is greater in Dogfish Lake on the 17th and in Quiver Lake 

 on the 24th. This lag in the maximum is correlated with the 

 fact that surface temperatures in Quiver Lake on the 1 7th and 

 24th are respectively 3° and .8° lower than they are in Dogfish 

 Lake. On the 17th the latter is 8° warmer than the river. After 

 all allowances are made for the time of day at which tempera- 

 ture records are taken, it is still evident that the shallower waters 

 of Dogfish Lake would warm up more quickly than the spring- 

 fed waters of Quiver Lake or the deeper channel waters, and 

 we have found that the thermal increase favors the earlier rise 

 in plankton production. 



The coincidence of the dates of collection makes possible 

 a precise comparison of the production in the two lakes, and 

 facilitates the comparison with that of the river. A superposi- 

 tion of the planktographs of Dogfish and Quiver lakes and the 

 river (PI. XXXI., XXVII. , and X.) for this year emphasizes far 

 better than any description the most striking similarity at the 

 three stations of the movement of plankton production as shown 

 by the direction of the differences in plankton content in suc- 

 cessive collections. The correlation between production in 

 Quiver Lake and the river in this year — discussed in detail on 

 pages 357-360 — is paralleled in every important detail by the 



