Februaky 16, 1900.] 



scieng:]:. 



255 



We may be sure, however, that these ques- 

 tions will be very slowly answered, since 

 they open the most complex questions of 

 lake life and those most diflScultof solution. 

 We know enough already to be confident 

 that general statements regarding the rela- 

 tion of littoral and limnetic regions are very 

 unsafe. It is true that lakes with steep banks 

 are plankton- poor, yet it does not follow that 

 lakes with large littoral areas are corre- 

 spondingly rich in plankton. It certainly 

 is not true that lakes are poor in plankton 

 in proportion to their depth, so that even 

 these most simple relations between the 

 shore regions and the deeper water require 

 careful and extended study in order that 

 any safe conclusions may be drawn. 



I have contented myself with pointing out 

 a few of the directions in which limnology 

 needs to move if the stock of facts which 

 limnologists are accumulating is to receive 

 an adequate interpretation. In order that 

 such a result may be reached in the 

 future, it is necessary for the student of 

 lakes to propose to himself definite ques- 

 tions and to work as definitely toward 

 their solution. The time has passed when 

 the publication of the limnetic species, or 

 even the quantitative determination of the 

 constituents of plankton can materially 

 further the advance of science. This work 

 was useful, chiefly in disclosing to us the 

 problems of limnology. These are now be- 

 fore us, in part at least, and the time has 

 come when the student of lakes must at- 

 tempt to answer some of them. 



E. A. BiBGE. 



University of Wisconsin. 



A PRELIMINARY ACCOUNT OF SOME OF THE 

 RESULTS OF THE PLANKTON WORK OF 

 THE ILLINOIS BIOLOGICAL STATION* 

 The Illinois River drains an area of 29,- 

 000 square miles, is over 500 miles in length, 

 * Abstract of address in opening discussion on 

 Methods and Results ot Limnological work at meet- 

 ing of Naturalists at Chicago, December 28, 1899. 



and has at low water a fall of but 31 feet in 

 the last 227 miles of its course. The low 

 gradient is due to the fact that, in a part of 

 its course at least, the present stream and 

 its bottom lands occupy the bed of an an- 

 cient outlet of Lake Michigan. The pres- 

 ent flood plain is but partially developed — 

 the bank height rarely exceeding 15 feet — 

 and overflows are frequent and extensive. 

 Floods rise from 16 to 24 feet above low 

 water levels, increasing the total extent of 

 water area to over 700 square miles. The 

 impounding action of the bottom lands, the 

 low gradient, and the backwater from the 

 Mississippi River combine to prolong the 

 flood period. The stream at low water is 

 from 500 to 1500 feet in width and three to 

 12 feet in depth, and by reason of the dams 

 forms a series of slackwater pools with aslug- 

 gish current of about one-half mile per hour. 

 The waters of the adjacent lagoons, bayous, 

 and lakes are also shoal and attain a high 

 temperature during the period of summer 

 heat. The water is rich in organic matter 

 being derived from the run-ofifand seepage of 

 fertile prairie soil and is further fertilized by 

 the sewage of a metropolis and of a score of 

 smaller cities along its banks, in addition 

 to the ofial of extensive cattle-yards and 

 large amounts of distillery wastes. Under 

 these conditions it is not surprising that 

 ammonia, nitrites and nitrates are present 

 in excessive quantities. The high tempera- 

 ture and the abundance of nutrition thus 

 favor the development of the aquatic flora 

 and in sequence that of the aquatic fauna. 

 Quantitative investigations of the plank- 

 ton have been carried on at somewhat regu- 

 lar and frequent intervals from June, 1894, 

 to April, 1899, in a series of representative 

 localities near Havana, 111.; (1) the main 

 stream ; (2) Spoon River, a typical tribu- 

 tary ; (3) Quiver Lake, rich in vegetation 

 much of the time and fed by spring water ; 

 (4) Thompson's Lake, a large (6x.5 

 miles) open lake, fed by the river and usu- 



