417 



the main representative of the plankton of the lake. Of the 67 

 collections, 32 were taken from water which in the deepest part 

 of the neighborhood of collections was less than 14 inches. 

 Owing to the roiling of the water caused by our movements, it 

 was necessary to dip from considerable areas in order to secure 

 the desired volume for straining. 



Since a separate report on these collections is being pre- 

 pared I shall only deal in this connection with those aspects of 

 the data most intimately connected with the phenomena of 

 the channel plankton. 



PLANKTON PRODUCTION. 



1894. 



(Table IX.) 



A single collection on June 8 yields a volume of 24.17 cm.^ 

 per m.^ an amount 7-fold that of the same season in 1896, al- 

 most equaled in 1897, and more than doubled in 1898. 



1896. 



(Table IX., PI. XL.) 



There are 29 collections in this year, extending from Jan. 

 8 to Nov. 17 — when only a few scattered pools remained. This 

 is the most fully represented year of our series in this lake. 

 The yearly average is 13.17 cm.' per m.% with a vernal maxi- 

 mum of 54.80 on Apr. 16, and an autumnal one of 51.60 on Oct. 

 15. This is the earliest vernal pulse recorded in our work, and 

 should be correlated with the early rise in temperature in these 

 shoal and protected waters. Thus, in Phelps Lake on Apr. 16 

 the surface temperature was 77° and the average for April 68.4° 

 to 71° (Apr. 17) and 62.6° (average) in Quiver Lake, and to 66.3° 

 (Apr. 17) and 63.2° in the Illinois River. This lake was thus 

 apparently 5° to 6° warmer on the average than these other 

 localities, and the vernal pulse is accordingly accelerated. 



Owing to the elevations of the lake and its outlet, run-off 

 from this area into channel waters practically ceases when 

 river levels fall below 8 ft. In 1896 there were but 114 days of 



