488 



Data are not available for a full comparison of the chemic- 

 al constituents of all the waters here under consideration. 

 No data whatever are available for Dogfish and Phelps lakes, 

 and only sanitary analyses for Quiver and Thompson's lakes. 

 These shed no light on the relative amounts of phosphates and 

 carbon dioxid in the water, both important elements in the 

 growth of plants. On the other hand, data for a comparison 

 of the ammonia and the nitrates are found in Tables XII. and 

 XIII. and Plates XLVIII. and XLIX. The nitrates, in so far 

 as they are concerned, — ^as shown in the accompanying table, 



CHEMICAL ANALYSES, SEPTEMBER, 1897, TO MARCH, iSgg. 

 AVERAGES OF ALL ANALYSES — PARTS PER MILLION. 



which gives the averages for coincident periods of examination 

 in 1897-1899, — offer no solution for the marked contrast in 

 plankton production which the waters in question exhibit, for 

 the amounts present differ but slightly in the two lakes. The 

 plottings in Plates XLVIII. and XLIX. show that the nitrates 

 run low during the period from June 1 to October 1, which is 

 approximately that of the maximum development of vegeta- 

 tion. The averages for this period are .244 and .222 respect- 

 ively for Thompson's and Quiver lakes in 1898. This is almost 

 identical in the two lakes, and may represent an unutilized 

 minimum of nitrates, the utilized portion supporting predomi- 

 nantly the phytoplankton in Thompson's Lake and the gross 

 vegetation in Quiver Lake. During the remainder of the year 

 the contrast between the two lakes in the matter of nitrates is 

 more marked, the average being .923 and .684 respectively. So 

 far as any contrast appears in the matter of nitrates the waters 

 of Quiver Lake are, if anything, a trifle richer than those of 

 Thompson's Lake. 



