492 



nel found in the lower end of the lake. This part of the lake 

 is shown in Plates XV. and XVI., which portray the conditions 

 as they appeared in 1894 and 1896 respectively. The upper end 

 of the lake and its western arm, Dogfish Lake, are shown in 

 Plates XVII. and XVIII., the latter having been photographed 

 in 1896, when the center of the lake was not so full of "moss" 

 as during the preceding year. The repeated floods of 1896 

 swept the lake of much of its vegetation, and during the three 

 following summers it never recovered the abundant flora which 

 it presented in 1895. In 1897 and 1898 there was also much 

 less vegetation than in 1895, though somewhat more than in 

 1896. The plankton production, as shown in Table V. and 

 graphically presented in Plates XXV.-XXIX., does not uni- 

 formly rise and fall as the vegetation decreases or increases. 

 The phenomenon of its fluctuations involves many other fac- 

 tors, among which the effect of vegetation may perhaps be de- 

 tected. The average production for the years of vegetation, 

 1.08 and .78 cm. 3 per m. 3 of water, is surpassed in 1896 (2.59) 

 and 1898 (2.44) but not in 1897 (.88). The marked increase in 1896 

 over the production of 1895 parallels the great change in vege- 

 tation, and is also accompanied by higher water, the average for 

 the year being over three feet above that of 1895. This differ- 

 ence in levels also tended to decrease the relative extent of the 

 vegetation in 1896. In Dogfish Lake also the contrast in vege- 

 tation in the two years, 1895 and 1896, is well marked, and the 

 average plankton production rises from 3.25 to 5.01 cm. 3 per m. 3 

 The omission of winter collections in 1895 makes the contrast 

 less striking. Allowing for this, it is probable that the plank- 

 ton production is practically doubled in the year of decreased 

 vegetation. This is approximately the ratio of increase in 

 Quiver Lake in 1896 and 1898. Other causes, such as current 

 and chemical conditions, doubtless share in producing this 

 change in the plankton, but it seems highly probable that the 

 reduction in vegetation caused a considerable part of this 

 doubling in the plankton production. A comparison of the 

 plankton production of the same body of water (Quiver and 



