353 



exceptions of repeated vertical hauls ( Table V. ) in the winter 

 flood of 1895-96— from the beginning till May 22, 1896. After 

 this date all collections were made with the pump. 



This lake is a type of some other bottom-land waters, spring- 

 fed and rich in vegetation, and our collections suffice to show 

 the relation which these bear to production in the adjacent 

 channel waters. They also serve for comparison of production 

 with that in other backwaters less rich in vegetation, and since 

 the quantity of vegetation in Quiver Lake varied from year to 

 year they also throw some light on the effect of vegetation up- 

 on plankton production in a single area. 



PLANKTON PRODUCTION. 

 1894. 



(Table V., PI. XXV.) 



The 14 collections in this year average 1.08 cm. 3 per m. 3 to 

 2.49 cm. 3 in the Illinois. The maximum (3.50) falls on Septem- 

 ber 6. There is a striking resemblance in the planktograph of 

 Quiver Lake for this year (PI. XXV.) and that of the adjacent 

 channel (PI. VIII). The amplitude is generally less in the form- 

 er, but the direction of movement is the same in both. The 

 June production (monthly average) is low in both Quiver Lake 

 (.23) and the Illinois (.74); it rises in July (2.20 and 5.12); and 

 it declines in September (2.12 and 1.36) to a minimum of .80 and 

 .34, from which it recovers slightly in October (.95 and .61) to 

 fall again in November (.02 and .10) and December (.03 and 

 .10). The only exception to this parallelism in the movement 

 in production is seen in August, when in Quiver Lake produc- 

 tion drops to .74 but attains a seasonal maximum of 9.67 in the 

 river. Aside from the fact that this is the season of greatest 

 predominance of vegetation in the lake, owing both to growth 

 and to low river levels, there seems to be nothing in the en- 

 vironmental conditions to be correlated with this contrast. 



While as a whole for this year the contributions of Quiver 

 Lake (1.08 cm. 3 per m. 3 ), as shown by our data, only result in 



