186 



mining the seasonal and local production of plankton. The 

 primary source of the food of the plankton lies in the water 

 and in the gases and inorganic salts dissolved therein, the oxy- 

 gen, the carbon dioxid, the nitrates, and the phosphates being 

 usually regarded as of prime importance to the growth of chlo- 

 rophyll-bearing organisms. The phytoplankton, which utilizes 

 these inorganic materials, then becomes itself the food for the 

 zooplankton. These inorganic substances, the primary food 

 supply, are thus indices of the capacity of the water for the 

 production of plankton. 



With the inauguration of the work of the Biological Sta- 

 tion at Havana arrangements were made whereby collections 

 of water taken by the Station staff from the river and some 

 of the adjacent lakes were sent to the Chemical Department 

 of the University of Illinois, at Urbana, f or analysis. In 

 1895 the Chemical Survey of the waters of the state was es- 

 tablished at the University under the direction of Prof. A. W. 

 Palmer, and in September of that year regular shipments for 

 analysis from the Illinois River and from Quiver Lake were 

 made at intervals of one week, and in January of the following 

 year Spoon River was added to the collection points. These 

 collections were continued throughout the period of our oper- 

 ations at Havana. In September, 1897, collections were insti- 

 tuted in Thompson's Lake, and from that time on the samples 

 for chemical analysis were taken at the same time and place 

 as the plankton and, like that, by the plankton pump. After 

 the date above named a fortnightly interval corresponding 

 to the plankton interval was made between collections in 

 Quiver Lake, though the weekly interval was continued in Illi- 

 nois and Spoon rivers. August 16, 1896, a disastrous fire in the 

 chemistry building of the University destroyed many of the 

 records, and this fact accounts for the absence of data of the 

 analyses in the months of the year prior to the fire and for 

 some other gaps in the record. Special collections were made 

 during the last twenty months of our operations for the deter- 

 mination of the oxygen and carbon dioxid dissolved in surface 



