Xi 
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IPHESEZV ALON GNA MICASUTEMENT. <<< 00. 0-00scesoncececqsosceescectsatocsencsescedesnscoses 254 
ren Peet s PLESCLV IM Bit W1d Gieese atee=anod-mun an veneseqaseeeetacncdemnnne satan eeanesovfae- 254 
Wers one ment DyyCentgtu pe pssteccntssserect ners ceeces seems pesenpeaeecer. cvevseceecscc 254 
Meth odhandve xtGn GOL MESA S Criscnt os /csensaoe-asetesanestessnr-etesaaeenteeseaeneccnee 255 
Comparison with gravity method................---cee-eeccreeeseeeeese ceceeeees eee 255 
Statistics of decrease in volume.... 255 
Factors determining decrease..............-..0.-.c0<+-rerss Upeeoncce sackoeeostes 256 
Composihion Oli AN ef OM cs cccsns cee) -loecteccses seen aeeave steve cer meee tet wedre yes: 256 
Ship aos-eren cspgeccuede 2e iontins sobsorc een oe Sou eeacceseeeeas Guo: nocbeneesce coeb Bsc be 257 
Comparisons with results of other investigators........0.ee-s0sceeeeeeee ners 257 
Formula for and computation of specific pressure... 257 
Effect upon plankton orgamnismis.............-.e+-eeceeseeceerees Garde eceererrtepeee= 258 
Priority in use of centrifuge for plankton measurement 
POEL EMER ENA A LIE Ll teenectans Orne acayManeeen snhesscanccrstsee cat anes =Kevor pera nue terse erowss ace e= 
sbercloprin piOuathe me lestnspresereces stesso carsccecnscr se: <caerteccne sense Se ESSE 
Correction by computed coefficient.... 
Computed coefficients of our nets.....-. .:.cseeeeeeeeeseee ee paps cnn eee ace 
Inadequacy of such means of COrrectiOn,.....-...c..s0-eeseeseeeseeeeseeeeeeees 
Determination of empirical coefficients........--.-..-:-eeeeeeeeeeeeneee ceeeeeees 263 
Progressive clogging of the drawn net........... SoChC SASS ase Rese eCCO TE 263 
Reasons for adoption of empirical coefficients.........-....... 22.00 0:seseeeees 264 
Volumetric Examination of Plankton of Channel and Backwaters,......... 265 
Plankton of Illinois River channel.......... Wiad cover ae Send at cones Certo etter entoae en tare 266 
Wescripbion on locality ok collection s..-.<. 20+ -c+--<20 <-receacrecrexecerescaseneenes 266 
Modifications of methods of collection at this station ...............0.e.eee00 267 
Chr onoloryiorColl lection: s<sscesc-sa serene saveer ccs sesoncidtewtoreresxeeeciees Wpancen- 268 
Local distribution of plankton and its relation to limit of error in the 
WING ENO ceveusnen cnr eeney demeeenswcwnnnccasunasaccontrsreccseectes sceveacconiseumnvencateds 269 
INGSUtSiOh Oler In VESH PC ALOLS anes: svcexcesvcctee=sre«sacctserecmacre-y sevastersas: 270 
Discussion of Reighard’s method of computation.....................0++ 271 
Problem stated for Illinois River............0::2::2s0eeseeceeees 272 
Longitudinal distribution of plankton in Illinois River.................- 273 
ilies toto nian GHOVed GhOAtseeccoresccuasecnererte concnecscoecerastine-sonanatas ates s 273 
Comparison with Apstein’s results in German lakes............... sere 2 7A 
MES TAEO DE HOACIN pe DOA ter wrest svena. tesee- toe ceostdacceviacasbieceu es oonaseeedcnaxee 
Comparisons and conclusions.... : 
Tests from chronological series..............s0ssees00e00es BELO -ecCeCDEER 
Test in traverse of river from Hennepin to mouth............0:0:-000+- 279 
Wie thro duet eal lec toners: taccnts an ssaneccecatoe-cacacaen see neatatce carers eo ece 279 
Conclusions as to distribution in river as a WhoOle.............eeeeeese00- 280 
Sources of error and disturbing factors -- 280 
pEirectiob hy@ropraphic cOnGitions.-.---¢-22-0-2<- ee-ce eae eaesceeccceeescn 281 
Distribution in minor units of environment... .........0.:00.ceseeeeeeees 281 
Transverse distribution of plankton in river................+. sesca ascaee 283 
Relation of shore to plankton.............s:sesseeseereeeee sisi ysteredee vate 283 
Plankton in cross-section of river at Station E.......... «+ 285 
arta tlonsyin plankton p@n tisesecns.<deccse-cnecenceccectesvacascamtscsssness 286 
Variations in plankton under one square meter........ -......ee.e000- 286 
