436 
PLANKTON PRODUCTION IN 1896.* 
Station Jan. Feb. | March |} Apr. | May June July 
Illinois "Rivers. esses oe —) .o1/—| 0.02/—| 0.07)+] 5.67}—| 1.30/—, 0.72/— 1.44 
Joe MSO hic MnGmenG mectrelli cl lorison|ioallacca nla mana tbollacesellealle cme Ns (Eee 
Omiver alka rrs- race i= .03|+] 1.75|+) 1.85 |+/12.12/—| 2.99/+] 1.26/— 0.30 
Dogfish Waker... 20 see +] .53/-+] 2.04)+| 3.43)/—|15.11/+] 9.63/+] 2.64)/— 0.91 
Bilao lake ive.(chsiere are tere +] .29'+] 3.06/+) 1.02 |+117.72/+]/51.93/—| 2.13]— 3-33 
Thompson’s Lake....... --| 2.51|/+] 2.58/+|10.26 |+)16.94/—|23.11/—| 4.92} -— 2.73 
Phelps Lake........-... j=! 1.89)+112.14|-+l19.20 |\+125.44! —|12.96|—! 2.90\-+ 9.03 
Mean of 
Station. Aug. Sept. Oct. Nov. Dec. | monthly 
averages 
Illinois River........... =| 112 )—-| 0 38 |—| 1.11 |—;  .02 [+]0.76 |—| 1.05 
Spoon’ Riverscrece- ace: —| ¢.018)—| 0.005|/+-]} 005 +005 002 0.007 
@Ouiverlake ses eecee +] 2.46 |—| 0.31 |+| 2.10 |+] .24 |+J0.92 |+] 2.19 
Dogfish Lake........... +| 3-91 |—| 1-63 |+) 5.58]—-| .26 |—|2.20 |+| 3.99 
Plapelbalcereeneerereeree +| 3-74 |—| 2-09 |—| 5-67 |—|] 4.37 |—|4.40 |—| 8.3: 
Thompson’s Lake....... 4.74 4.20 |—, 2.81 |—| 2.66 | —|2.56 |—| 6.67 
Phelps Lake............ eal Saciolllg all oacase — 23.04 |—| 32.00 |..]..... —| 14.74 
*The minus sign signifies below average and the plus sign above. 
While in 1895 production in the channel waters was both 
absolutely and relatively high, yielding the highest monthly 
mean (5.91 em.*) in our records, and exceeding production in 
the adjacent backwaters in 15 out of 27 monthly averages avail- 
able for comparison (see table on p. 432), in 1896 we find the op- 
posite extreme in production in these particulars. 
In the first place, the mean production as seen in the mean 
of the monthly averages, 1.05 cm.’ per m.*, or, in average of all 
collections, 1.16 em.’ (see table on p. 429), is the least observed 
in our years of record. This is 61 or 47 per cent., according 
as we base computations upon means of monthly averages or of 
all collections, below the mean production in the Illinois. This 
ensues from the catastrophic effect of recurrent floods which 
periodically flushed the channel (Pl. X.), sweeping away the 
plankton-rich contents of the stream and replacing them with 
barren silt-laden flood waters of recent origin. There are 6 
major and 5 minor flood culminations in this year, and most of 
them are marked by abruptness in rise, a factor which added to 
their destructive effects. The total movement in river levels 
in 1896 is only 45.7 ft. (see table p. 163), while that in 1895 is 
