280. 



No. 



Time 





Vol. in cm.s 

 of catch 



Pl'nki I To- 



ton I Silt I tal 



Departure from 

 mean in per cent. 



Total 

 catch 



Plank- 

 ton 



~^ 75 ' 



- 68 



- 97 



- 93 



- 85 



- 90 



- 69 



- 85 

 +153 



- 25 

 +199 



+ 86 

 +107 

 + 34 

 +209 



+ 30 



+ 27 



- 83 



- 83 



1 ni. above Hardin.. 

 Kampsville Dam 



1 m. above C. A. bridg-e 



Florence 



Mauvaise Terres Cr'l 



Meredosia 



La Grange 



Beardstown 



Browning-. 



Holmes Landing- 



Havana 



Liverpool 



2 m. above Copperas 

 Creek 



Mackinaw Creek 



6 m. above Pekin 



7 m. above Peoria 



Chillicothe Park 



1 m. below Lacon 



Henry ... 



Hennepin . . 



Averag-e 



5:45-6:45 p. ni. 



6:45-7:45p. m. 



4:30-=':45 a. m. 



6:00-7:05 a. m. 



7:10-8:10 a. m. 



8:in-9:lSa. m. 

 10:00-11:00 a. m. 

 11:00-12:00 a. ra. 



2:45-3:45 p. m. 



3:45-4:45 p. m. 



6 15-7:30 p. m. 



4:20-5:20 a. m. 



5:25-6:30 a. m. 

 7:10-8:20 a. ra. 

 8:40-9:45 a. m, 

 ) 9:50-10:10 a.m. 

 ( 12-12:40 p. m. 

 12:50-1:50 p. m. 

 2:30-3:40 p. m. 

 4:00-4:55 p. m. 

 5:20-6:30 p. m. 



.10 

 .08 

 .OS 

 .03 

 .04 

 .04 



.04 



.04 



.05 



.051 



.05 i 

 .04 67.5 



.04 ' 68 

 .05 67 

 .06 67 



.71 I 2.23 I 2.941 -4- = 



An inspection of the data of this table at first gives little 

 comfort to one desiring to establish even an approximate uni- 

 formity in the distribution of the plankton along the length of 

 the stream. The average departure from the mean is ±57 per 

 cent, in the case of the total catch and ±89 per cent, in the esti- 

 mated plankton, with ranges respectively from— 85 to -f224, 

 a total of 309 per cent., and from —97 to +209, a total of 306 per 

 cent. This is greatly in excess of the figures above given from 

 the work of Reighard and of Apstein, and r/.s a irltoh the data 

 are so aberrant as apparently to disqualify them for scientific use. 



If, how^ever, we take into consideration the conditions un- 

 der which the collections were made, the aberrancy of this se- 

 ries loses its force. In addition to the errors introduced by the 

 slight clogging of the net and the uncertainty as to the precise 

 distance, there is an error of undetermined proportions caused 

 by the vertical movement of the planktonts and consequent 

 possibility of uneven distribution at the 18-in. level between 

 4:30 a. m. and 7:45 p. m. — the extremes of our time of collection. 



Furthermore, an examination of the planktographs in the 

 river and its backwaters for 1896 and 1898 (PI. X., XII., 

 XXVII., XXIX.,XXXI., XXXIII.) —in which years the collec- 



