February 10, 1905.] 



SCIENCE. 



233 



1885. 'The Oyster Beds of New York.' 

 Ihid., XIV. meeting', i). 85. 



1885. ' Keport of the Commissioner of 

 Fisheries of the State of New York in Charge 

 of Oyster Industry,' pp. 70. 



1886. Ihid., II. report, pp. 23. 



18S6. ' Report of the Commissioner of 

 Fisheries of the State of New York.' XIV. 

 report, p. 7. 



1887. Ihid., ' Oyster Industry.' III. re- 

 port, pp. 27. 



1887. Ihid., XV. report, pp. 17. 



1888. Ihid., XVI. report, pp. 30. 



1899. ' On the Spawning Season of the Eel.' 

 SciENf E, N. S., Vol. IX., p. 741. 



Basiiford Dean. 



Columbia University, 

 January 25. 1905. 



ILLINOIS RIVER PLANKTON. 



The Illinois State Laboratory of Natural 

 History has published, as Article II. of the 

 sixth volume of its Bulletin, a report on the 

 results of a virtually continuous study of the 

 minute plant and animal life, or plankton, of 

 the Illinois River and its tributary waters, 

 carried on for tive successive years by the staff 

 of the Illinois Biological Station. This makes 

 a volume of 534 pages, illustrated by 2 maps, 

 11 half-tone plates, and 37 full-page diagrams. 



Opening with an elaborate description of 

 the Illinois River and its drainage basin, this 

 report treats of the effect of variations of 

 temperature and peculiarities of chemical con- 

 dition on the life of the stream, and presents 

 at length and in detail a comparative study 

 of 630 plankton collections made from the 

 river at Havana, from one of its tributaries 

 which empties into it at that point, and from 

 five bottom-land lakes of various character 

 and variously related to the main stream. 

 These collections were so made, at regular 

 intervals, with identical apparatus, and by a 

 un form method, that they can be compared 

 with each other quantitatively, and may be 

 used as the basis of general conclusions con- 

 cerning the system of minute life in these 

 waters, from season to season and from year 

 to year. 



It appears from these studies that the 



plankton is distributed in the main stream 

 of the Illinois River about as evenly as it is 

 in the stationary waters of a lake, and that 

 generalizations based on an examination of a 

 small part of it are consequently as reliable 

 as those concerning that of a lake. The ratio 

 of the plankton of the river, year in and year 

 out, was 2.7 parts per million of the water in 

 the stream, and its total average amount mov- 

 ing down stream past any given point reached 

 the astounding aggregate of 75,000 tons per 

 annum, or 8.5 tons an hour. This is about 

 15 times the total weight of the fish taken 

 from the river in a year. 



The production of the plankton falls to its 

 minimum, as a rule, in January and Febru- 

 ary, and reaches its maximum in April, May, 

 and June. Floods, of course, dilute it, and 

 falling waters concentrate it, but, on the 

 other hand, a season of general high water 

 increases its total quantity, and a season of 

 general low water decreases it. Light and 

 heat favor its development, and it is conse- 

 quently more abundant, other things being 

 equal, in a season during which clear and 

 warm weather preponderates than in a cold 

 and cloudy one. The freezing of the river 

 does not seriously affect it, unless the ice-sheet 

 continues until the water becomes foul with 

 the gases of decay. The addition of sewage 

 to the river water greatly increases the pro- 

 duction of this minute life by increasing the 

 supply of available food, although an excessive 

 amount of sewage may render the water too 

 foul for it at the point of discharge. 



The production of plankton is less in short 

 streams with relatively swift current than in 

 long streams with slow current, and short 

 tributaries consequently tend to dilute the 

 plankton of the main stream. On the other 

 hand, the stagnant and relatively permanent 

 waters of shallow lakes bear a more abundant 

 plankton than the temporary waters of flow- 

 ing streams, and the outflow from such lakes 

 hence enriches the plankton of the river. 

 Parts of a stream with many small tributaries 

 will contain less plankton than those with 

 which numerous lakes are connected. 



The bottom-land lakes differ widely in the 

 amount of plankton which they contain, this 



