483 



most important period of our earlier work was that immediately pre- 

 ceding this event, an examination of its consequences to the general 

 system of aquatic plant and animal life was an important part of 

 our object in recommencing systematic study. As the Illinois is a 

 rather peculiar member of the great Mississippi River system, it was 

 also much to be desired that comparative studies should be made on 

 the life of the more closely related companion streams; and as the 

 Illinois is economically one of the most productive rivers in the 

 United States, it was evidently time to study the subject of the con- 

 servation and possible increase of its values in the light of the knowl- 

 edge we had gained, and intended to gain, of its physical, chemical, 

 and biological conditions and requirements. 



The economic problem seemed especially urgent because of the 

 great changes in progress at the time in the environment of the river, 

 and the still greater changes impending, which were certain to affect 

 greatly and permanently its value for the purposes which it had 

 previously served. Reclamation projects, for the protection, drain- 

 age, and cultivation of its bottom-lands; manufacturing projects, 

 threatening various contaminations of its waters; canalization proj- 

 ect; and projects for the control of its flow in the interests of 

 transportation, were all being earnestly agitated, and some of them 

 were in course of active development. It is true that these changes 

 are both inevitable and desirable, in view of all the interests involved ; 

 but it becomes all the more imperative to learn as promptly as possible 

 what their effects have been and are likely to be, in order that prac- 

 tical correctives may be applied where necessary, to the end that a 

 modus livcndi may be found which will take all these interests into 

 full account, and make sure that nothing is needlessly sacrificed in 

 the course of the use and development of the stream. 



The reports of the work of the earlier period were largely on the 

 minute plant and animal life of the stream — its so-called plankton — 

 which forms a considerable part of the food of many kinds of fishes 

 and nearly all the food of the young of almost every kind; and the 

 plankton product of the waters of the Illinois under the new condi- 

 tions, as compared with those prevailing before the opening of the 

 sanitary canal, was one of the first topics to commend itself to us 

 for careful study. Involved in this subject of food production for 

 fishes, river mussels, and other useful aquatic animals, was the 

 economic effect of a great increase in the flow of the stream, the 

 rise in its levels, and the consequent expansion and longer contmuance 

 of its overflows, which there was some reason to suppose might so 

 increase the food supply and enlarge the breeding and feeding grounds 



