420 



such as Thompson's and Quiver, this marked degree of resem- 

 blance is the more striking. 



A comparison of the course of production in Phelps Lake 

 (PL XL.) and Thompson's Lake (PI. XXXVII.) in 1896 reveals 

 14 agreements out of a possible 25, or 56 per cent. Of the 11 

 disagreements 3 fall in the period of few collections in the au- 

 tumn months, when Phelps Lake was reduced to shallow pools, 

 and 4 occur during the vernal pulse of April-May. A compar- 

 ison of the planktographs and thermographs of the two lakes 

 shows that in Phelps Lake the temperature is from 2° to 8° 

 higher than in Thompson's Lake for a period of six weeks dur- 

 ing the rise of the vernal pulse. Hence this culminates earlier 

 by a fortnight in the former, and in consequence a dislocation 

 of the course of production in the two lakes occurs in this peri- 

 od. The two planktographs are, however, strikingly alike in 

 the fact that in the interval between March 31 and June 1 

 there are three pulses of regularly decreasing amplitude in 

 both lakes. The similarity is thus greater than the percentage 

 indicates. 



A comparison of the course of production in Phelps and 

 Quiver lakes (PI. XL. and XXVII.) reveals 15 agreements out 

 of a possible 28, or 54 per cent. — but little more than chance de- 

 mands. In this case the environmental differences are greater, 

 the effect of spring water, vegetation, and flood invasion inter- 

 fering in Quiver Lake with the course of production. 



A comparison with Dogfish Lake, where the disturbing fac- 

 tors of spring water and flood invasion are less immediate in 

 their action, reveals a slightly greater degree of similarity — 16 

 out of 28, or 57 per cent. 



In the case of Flag Lake the agreement is still less, being 

 only 11 out of 24, or 46 per cent. It is a noticeable fact that 

 the disagreements are most numerous in Quiver, Dogfish, and 

 Flag lakes, all of which are rich in vegetation, and these disa- 

 greements occur in greatest proportion during the months of 

 May- August, when with changing river stages the proportional 

 occupation of these lakes by vegetation fluctuates greatly— 



