323 



monia rose from a normal of less than 1 part per million in 

 October to 5.6 on the 28th — the maximum record for all the 

 analyses (Table X.). This is attended by slight increase in the 

 oxygen consumed and the albuminoid ammonia as well as in 

 the total organic nitrogen, all of which betoken the approach 

 of stagnation. This is reflected in the fall of the plankton pro- 

 duction to .03 cm. 3 per m. 3 on the 28th. The extermination of 

 the plankton did not approach that of Feb. 23, 1895, though 

 there was a marked decrease in the number of planktonts ex- 

 cepting only in stagnation ciliates. Temperatures during this 

 month were at the winter minimum of approximately 32°, with 

 only a slight increase to 36° with the rise of the second week. 

 The plankton of this December in average production (.56 

 cm. 3 ) falls below that of all other years with the exception of 

 the inadequately represented 1894. This relative falling off 

 results, it seems, from the near approach of stagnation, due to 

 sewage which the stable low water permitted under the ice- 

 sheet. 



As a whole, 1897 was a year of heavy plankton production 

 when measurements are stated in plankton per cubic meter 

 (3.69 cm. 3 if all collections are averaged ; 3.27 cm 3 ., mean of 

 monthly averages). If, however, we consider the slackened 

 current and reduced volume of the discharge of the stream, it 

 is evident that the total production may not be greatly, if at 

 all, increased during the low- water period of high plankton 

 content. The vernal production, judging from results in simi- 

 lar conditions in 1898, was possibly very large. It is evident 

 on comparison, that our isolated vernal catches do not ade- 

 quately represent the vernal production, and, furthermore, that 

 the vernal maximum may have exceeded that of the low- 

 water period in plankton content. Fuller representation in 

 this period would doubtless have raised the yearly average. 

 The high water, rapid current, and large discharge at this period 

 combine to make the production in these conditions relatively 

 very great, as compared, for example, with that of 1896, when 

 the impounding action of the reservoir backwaters was slight, 



