eK ten by De Ay ends ‘ate ; iy = ¥ rt haat f Pees: ry iitom broek be ng oe tan of ‘a fo pee ba ti Wp i PECUN Te eo ey Wulf fk ¢ oe fi ie vice bag ri CT pl ALaal wee Ate Petr eg mie: s Prinidey ee isd oie hae é Ae Recta rat irae Se vn (M SNe vos may pe ois ca H ‘ai tf. See Nh oe LA, ‘Sn A, a tet *) cae 5 is We Dee by 1S wea at Bebe bd Hiei bets elt dag « a aaias 4a: pases aaeats AA tn 2 LAN Nee PA hi ches = oe icy: Aether bi Die a ton i a bonds Barents ul in tte ied rrr te pitt wing Ap Sa ra poe w fs fy i = i en iy) Per eet ate atta enti Agee i" (4 Sette Sb Sle ig ey ie Aad i gy nite At he ihe eo ie 8 ; Pi deg ne ei sae Ph # inde ip WiFi Tage tone ie J te ee faa, Be SH 94 ibe see fed ii Bens gts fs ie tantae pop 4 sess ied el isa ya cht dete: Pat bees s denuiesy ae pater eres vP ie ia ital EW Hottie Ps Wtarte vee fe dk RAbicerhe Fado bea fy Ltd ager fae iti oe ee oe) AY, riehi erp tay: ete Sa oe ety Se at rises eee fe Kagtordag isk ye bp ra Bi coarg ath one ea Liss i de incr Al ieee ’ ins bear aoe if forte S37 pitas Rabon cps mais ra ai Co's bremrenatet ees et (cid of ria tis i, she case Lee hang patria iepiiae age rmbt, ef if ae ie ie Pera areas Baie eae, : fee ak Oe a) a ind eos hats be = O4, Entre i) ae ya vaybinie Ta (for Eade. ee bo Wo Bien GA ye be Bm Ae ees pees He i poe Mth Ete etales rae os erg ee me os teal ee le ies ins Reve gigs iret} bets igh : Res ’ ah ge eA Re Me ais) chs ie to. 131295 pyr Lerin OF THE ILLINOIS STATE LABORATORY OF NATURAL HIS! One Urpana, Ivuinois, U. S. A. VOLUME “V4. 1901-1903 CONTRIBUTIONS TO THE NATURAL History SURVEY OF ILLINOIS, MADE UNDER THE DIRECTION OF S. A. FORBES GAZETTE PRESS CHAMPAIGN, ILLINOIS 1903 UNIVERSITY “OR TELINOIS BOARD OF TRUSTEES THE GOVERNOR OF ILLINOIS, BE EE De Psd Bey wees ccerarg sanbwatore fate otora oar ere nl waives. cad waka a veya een Springfield THE PRESIDENT OF THE STATE BOARD OF AGRICULTURE, NUE Se eC ie DIU SOUN Sc oycic's caiscareoaiyx sisiaicts cee Baye aan) Mee hererele Lawrenceville THE SUPERINTENDENT OF PUBLIC INSTRUCTION, ROE AON VNU SS: {cots stoi oreo Ps oes sein ame ee me sie oye oa dee eee Springfield PME eA SES Wik Yar OE Ure. ine x a 4 ue eb eho ele atte mraeagl) treteha Jaear eee Urbana LT D7] DM RG Dae 22 I Gel Ee ee ie eon ea mg Ucn rity Spring Grove ew oc Wer bh NIGH TINGA LB ii. cud 2. a cea ae ae ceaaeeens de eenam nai Chicago NIE BG NINH DY) B81 ell 4 O92) a ae eo eR are A Ser cep Sora nO re aacate Macomb SAVIN Are DOUG LIANR ID: vase crocs errata Sein erctereisy cisleisee cere sok aterinereheremornciotr= Springfield CAR 2 ba JA EGAN ID POR osc wise atarsns pe Seance hhc he ohare bamanye _. Belleville VVAITETS AUNTS TSS IVE CK TINGLE Vero rates sncsceiaiaicisens) ecsteyes chess eke oesst siitoce, svete orev aweaiaek fous Champaign EE ONIDAS: Hoe RRC Ke yc cadens pec newt hie en eee Mra com enegea Bloomington POE Esp h Ee WAAINS ahie re tearm a aia:kS me ekie end baa eta Coo Schate abate wean Taylorville ANDREW S. DRAPER, LL.D., PRESIDENT OF THE UNIVERSITY STATE LABORATORY OF NATURAL HISTORY SCIENTIPICG.£ STAE EE, s1003 STEPHEN A. FORBES, Pu.D., DIRECTOR CHARLES A. HART, SySTEMATIC ENTOMOLOGIST E. S. G. TITUS, M. S., FIELD ENTOMOLOGIST (to June 30) F. M. WEBSTER, M.S., ASSISTANT ON BIOLOGICAL SURVEY A. J. WOOLMAN, A. M., ASSISTANT ON .BIOLOGICAL SURVEY (to September 30) R. E. RICHARDSON, A. M., ASSISTANT ON BIOLOGICAL SURVEY E. P. TAYLOR, B.S., FIELD ENTOMOLOGIST (since September 30) CHARLOTTE M. PINKERTON, ArTIsT (to August 31) 3) Beats CONTENTS ARTICLE I. THE DRAGON-FLIES (ODONATA) OF ILLINOIS, WITH DESCRIPTIONS OF THE IMMATURE STAGES. PART I, PETALURIDA:, ZSCHNIDA, AND GOMPHIDA. BY JAMES G. NEEDHAM AND CHARLES A. HART INTRODUCTION sata (W] folie folies @ Fuel], enslwige) eye) e) a) =) els) \s-s acme Re Goaaskiaenaeuaaee crise cae Seaeaee one eae eee Jasssgertnes 210 (hemipsen spleakG cy anisqscss-sacenees dos Radel jaslencevion ste Geuiaedalstetsch ae eae tS aes 212 Comparison of plankton production with seasonal changes in nitrog- EGNOUSUSUDSEAN CES: -sncc2ac-s=cvacosBen a> on cee et ancacce sta snemsbenaan ss sence ner eases 213 With seasonal changes in nitrates............ eb tease laaceee Soeeckeeeseeece ey 20S The maximum-minimum cycle........ ae veudeee wecastesencanw as teeskica ae aeers 213 Relation to plankton maxima in the several localities................4. 214 With seasoualchanges tit W1EKiteS. \.2sc.s-ckesdss ences tenant seseeee ee 215 With seasonal changes in albuminoid ammonia and total organic IO ARO} *e( S10 Receipgcoc cdo COBB ECOOCUSCOGE BOOB SOCE CE iBoce-_opaas oBsne ston a eCRUGEEEaasoneD eae PAGE Intthe WlimoisiR vier, ., ccc. -cesscs! sees ne eter (ace andadesecupynseeemeanenase se aeke 216 In Spoon River........ a pas ssnsins eacarvieevadteavas avd sriesaiedeastecal tacearteriancae eee 217 Ty MOWIMED sale Gs save ercdevecivasiisoosnpavedtsanasjocesaeidiosdevesesnigecnc anctoeareeme 219 In hompsonis Wakel..v.ccs.-sess.cecactetsesessseduesseossssconeowarvee ae vee 219 Complenity of-the problemisss..0.ccscsccns.dease-d-mnsns? s-uane veupeeacesseenert 220 Lack of a common unit of measurement......0-5:---..sse-essons-ccosnesons 220 Chemical and plankton changes not proportional........s..:ssseeseeeee 221 Causes of absence of proportional correlation........cccesseeseeseeeees 222 Plankton only a part of the total organic nitrogen.............e006 222 Utilization of organic nitrogen by plankton........ neceseee: beeeeeeee 224 Observations on limnetic organisMS.....+-...05 essere senses aecescses 225 Cumulative character of growing plankton...... Siadhtee sosckosbeo 226 Some correlations between movements in nitrogenous substances 2nd pl aniston qoulSes 3 skeet: cpasweasiwlecvencsats Redux poemeawosee heme neeetce 226 With seasonal changes in free ammonia....... Saree ocecdees sche an Bice 227 Comparison of plankton production with seasonal changes in oxygen OHSU CG reences-patensmenen teasareetere tenets conta woetpenenseesne) ok Sees eee 228 Comparison of plankton production with senknme changes in chlorine ID Several localitesier +0555 cessucs sone) scans cwssesas ue ges ensoec ascent sane teanseee 228 Relation totsewagewt, Chica goretCsis.nccescesacssckt sect eeeesesateredes eee 230 Chemitcall amalySeGscccne. .tescoceasccotssncuenes nis (scsosssuaee Seceree ee eceneeeee 230 Bacteriological “exam a tlOMsssss0-ssccceanvdewtsesss.wasdnecesnee tee acdsee eee 231 PAL ERA AMAL ootececaraniasees scteactesdaadenuctlentecs sos secure tutes, meveeeneeneetene 231 Bridgepor ty te GraktGnscrsecscccwecssee-cecaseennshe. eeeasoneesenqehooseet penees 232 Seasonal changes in decay of sewage at Havama.ee.s...sssesceer severe 233 Complete mineral amplysis.ccavetavee-c-cwen to. pate a hnnceedtobis ce! Gaveae tats deme remmee: 234 Comparisons with other streamisy--t canes aac oWescansees 283 Plankton in cross-section of river at Station E.......<... c.0.s.+-2- eee 393 GOMECHONS Se Sie heels ote evar elare a thople miele ot oieie Oh ore ne SIN epee eon 305 Plankton production in Thompsonis*Lake, ...:.. <<. ~...sese- ee ee 396 JIS toy Ny ae ero Oar a ae oR err RL cd aries tc PPR PRUE Cha, A. BS 396 MTV EU BOG hatte ioie os svsre ie alio aye cusicye eiseraie etesaeleteheleis ereinue’s os 2%) «ib alelorereleieconmee 307 Contributory relations to channel waters...................5 398 Similanigvatonproductionjelsewhereeererr ere ees -eiec ee er 398 105 Uso LOE ee te teate a POAC EROS EE CRC CLG aceon AES c/CHERD ES Hoe AACN ac be 400 Fiydtogtapiic conditions. 2. . ves + <> 2 hem aeteuioetanietale 406 Contributory relations|to channel waters... .- 1... <0. deeb elke 407 Sicailarity to productionielsewhere:.. +--+ <)- ses ease eee are 408 Din BO ie Seoctee te GS lay wie aree ta aie saree Soe ka ned sal Shenae aN ore aee ner eR 409 SUNT A GY ool brace OA Percale vans. aiken Ako leet os oe eee ree 409 Relative)production 33 2a < ors. = Seige a sioiess & ovie te eles 410 Seasonal changes in relations of lake and river................ 410 Impound ine tunctionicic fe dees vies te nis > ae eee aise ie ae nee 413 Similarity tosproduction elsewhere: ...c .. cer. cee > eee ee eee 413 Phelps Wakes Station gh 2e secre nae!) co velelaete siete niche eierele ter aeetatel ser ees 414 Environmental mconditlonsrererseeiaceeseee cco noe Cee eee cer 414 GolleetionS:. 4 bee ane canies cease reeeneeter Atari ante sin: Ais can 416 Plankton prod Wetlon ty acciene see = eke 2 ries tate etait eee ee etree 417 DH RBGA SH 56a deaths aod oi cvale nae ree Gite eae ee een He else step aus eorstinns Oy Sener Are 417 | Fes 0:10 came ne Te eT eng cy a nt, Sarr os AMER A Sn ea Bete eA 417 Hydrographic iconditions.£< 1. oe ee ces sein tek seein 417 Relations to. channelsplanktonyacernce eee ee ree ee eee ee 418 Similarity to production elsewhere ssi... 2s). = ee eee 419 Nolen toloy SeemeI NG Acker Mote 5 cae aa ae me Mea GS- aa Ore me ahs oudo apo b.: 421 | Bote (o.6\s eee EER SAA Or Re Be He Nayp ty Ebi, seg aes so 42 Tin T8095. sha 3-0 ied wis Wate SRE ne He eas eis aL oie eens eee esters 426 Summatye 525. secs eee cee ee ae eer cece creer eoe ner Sone General comparisons of years and stations -.2....... <.ajcseas+ =< er 428 0), See ee RE re RAS Gi C.D sO NS CAR AGO S ox 430 1010) ee ae Seno 2 SPU Cr A dchaecrocr oats 54a oa ees Sg AS 431 SLE ii Cpe aA eRe ene cae nicin cpa ocdcuncoan oats barons, 96 OGRA 431 Effect of stable low-water at various stations.................... 431 CGomparisonkwithiother yearspeen cio eter eee eee eae 434 ’ XV PAGE ia. 6 0 ged hi ¢ rei Race eA oe eae eae Ae a ALT ABE ME PSANGEE Se ge Pm tic te 5 435 EANISEIES ys staat cca cune me eit otore"s PRN nai de em IAR as eer gue ssp hale ene taeda 435 PNifechomrecnirnentilOOdS sw. cela cree oe Hie eet rieron icici ela eites 436 Relation of production in channel and backwaters............... 437 Beet ob midi miter GOOG. 7.0: lant oak 2 oie ot Cateie eielcrntc ung wien aterere 438 TOG pe Re ere Nese ete tie vics Ciara oN @ auras ty aut hoe ee eee ern 441 SlapiSHICS eeryeas eens ers ale ts eie oc ousicnre cctaie pareve Pareter olor tee 441 Relationsyorebackwaters torchannelescne. sane eee aoe ee 442 Hitech prolonged: lOW Wath ...:../ss:scccjso1e tea Was Weta » iuele ee aes 442 Thole fovea OCS ROE EE ee EO Coe IO asY Oa SARE Sonica Ba: 444 SPAtiStICS's Sap yAbirstras Fast ea cid oo Sey eae Eee Een 444 ALemVvennial PUISE os 2, cea vast nie eee eee oe ey oe te Eee 446 Comparison of channel and: backwaters.. en 22220. oct as eee hee 447 1telov0) Stik eh Mea PAR RI RR An fn. Gi eh iets ingests Ae 449 SELLA O (Cie pares DiS ORs mn RRO on, OI RIA Rye AE A eel aphasia 449 Fiche winter=proG Wetlon o's2755 2'siys ed ae ern av ad oa RTS oe 449 Characterization of svears: dite 2 selas Sita pee te eee eta ee 450 Characterization of localities!.2 J50snees emacs See mernee ates eet. 451 Relation of environmental factors to productioni.(\. 6.4.25 .....0 ccs 454 Hydrographic conditions and plankton production.................. 454 Statement ofthe: proplemeiistceos ce eiatte saan at Tarai essences ayer 454 TEM CHOR ATCase tis ays cen seven acted amnrns Aas cieiane me methane mie emer 455 IB eCtrOl Ge pes oc on vas wey cao urs sae ous oo SS eee Bee ee ee 456 PALCCH OM APCIOR TNELWALET:: | cio aac/Jeis sath s oSaes Foren eax os lieres See 458 Waters @rnreCemt vor gy Ss hed: eit yar raya heeled oe ae eee 458 Dime requisite for development of plankton...; s.2../isi.6-2--.- 459 impounding function of hack waters: >. ~. .se.2 sess ssn eee es 460 Current andtratciof renewale sass ee eee eee ee eee 460 Directeliectioi- current eyaet toe eicielnct eases FOS eee 460 Effectofrate- ofonene wally v0.7 sess acters oe eee 461 Netetiecttoisnun-ofjandenenewaleeenee ens nena see eee 462 Pluctiationsiin. hydrographic. conditions... ...s54.. seen eee 463 Importance sniluviatile cnvironments:. 4 24.2245 ee eee 463 arise Of MeodSit sot ken. sara sch DLS loinc et tee Le eS ae 463 Eiector rising levels;on‘channel:. evan ous ee ee 463 Effect.of nisms levels im backwatersana. vsstss eos) bce eee 464 INecovery dnomiflood :) 22-51 .c4ki actors ae ad cn ee Pee ee 465 iesnit. oe deelming levels). 0. 4.0.0,.,snanuneela eaten ety ae: 465 Production and total movement in levels»... 4...-... 2.2.22 eee eee 466 High,and low-water periods;in channels). : J..02 ste danse outs 466 Levels and production in these periods during the year........ 467 SUDIMBARY Ns ote Goe eaten eA oa eh Bee i Sain he RDN 469 High andvlow:- water in, backwaters’ si. $.:'.00 oe hae ee 470 Effect of season in initial Stages: Ob slood=falll: 2545... 90608 2 erties 470 Remperature and: plankton production... .ta-0s 2ssaes soe aeeiet au ee 471 Contrast,of warm and’ cold seasons)y.,a0%.c:.440k felis ot te eee 471 Mhewernal. vise. in) temperatures +a. weno spaaha en dadeles eile enialae 472 Seasonal distribution of production and temperatures.............. 472 Xvi PAGE Hiectiot temperature uctvations on plankton... serie 474 inmiearly Sprite Of (1BO0.5. 6.ciemAaas vata ox le oe ee he etree ee eee 475 Indate autumnal 1807. s)42 76 aaa ee eek ee at ee oor emeniee 476 Exceptional high production at minimum temperatures.......... 476 Effect of autumnal decline-in tempetatures). -./.2. 42: sete Sees 477 itectolstemporanyleatapulSesmeperemereirs cites relates 477 Eftectiot theswinter 1¢e-Sheetis.meisece toe hee eee tenet 479 Lichtand plankton, productions. csaste sense case eee escent 480 . Imperection OL Galanccu.: ceee cee Reee eet ce coment Poth saa 480 _Production in periods of greater and less illumination.............. 480 Productionvinicleamanditurbidiwalens:e eee eee eoee eee ee eee Onene 481 Production invclear and cloudy “weather... 12 os oan oe ee 482 Vegetation and plankton productiony ys), sa. acdeesce ode e oe ease ects 483 Greater production in. vegetation-poor lakesis. 2. ..2+2...6-5-nne+ 4. 484 Comparison of monthly means of production in lakes rich and poor IMs VEPEetAtOMN Veen pease erAcer renee Ce oe eR COCR EO Ore 484 Seasonal changes in vegetation and in relative production....... 485 Combination of other factors with vegetation to depress production 486 Current and tributary waters st 0s. tener ee ee eee ees 487 Chemical conditions 25 Wyant ea ae oe eae ee ee 488 Corroborativie evidence from. Matanzas Lake-s {2.222377 ) ae 489 Production in Quiver and Dogfish lakes in years of much and little V.SMELALIOUy. vasrssaterererercerceierarete analaterete Ghee cts talk EA Rare no eee, eee 491 Depression of production during dominance of submerged veg- ClAMOM. Dee eee hice Peta ee ob Geile aeteteee om cn eres orca meee 493 Production in vegetation-rich waters of Flag Lake............... 494 Emergent vegetation asource of enrichment)... ---5--.4--4.4- 494 Struggle for existence between submerged flora and phytoplank- TOM sag cea wee eee emis Bala MEA Sein pelea else te eiboerer ey name eee tater 496 Chemical. conditions. in the two'types ofilakes..J2..-2-2 2... ose 497 Impoverishing effect of submerged vegetation.................. 499 Obstructivetetiectiof submerged veretations....4 ee en sae 499 Effect of vegetation on constitution of plankton........... ...... 500 Eifect.ol vegetation ion fish production. 12. ..1.4-< are eee nee eee 501 Experiment: sugpested iy. 2 sia .arnicc t= on sora arene eine Hemera 502 Internal factorsand planktonsproduction) 4a%74 44). se cere ene e ee 502 Nonmmnaliregimen of planktonsprod action: ss: % Sonne een seer tae 503 No seasonal regularity in amplitude of production.................... 504 Rank of different stations in production more stable................. 504 Degrees of'stability in ditterentwocalities.2: S32 sees ee ane ae 505 [sithere.a normal sequenceyims production's. -aeerer ese) eee ee eee 506 Direction of movement in mean monthly production............... 507 Predominant:seasonalichangespnidirection=. sees. eee eee 507 The cyclic movement of recurrenty pulses. ee ones cee eee 509 INecessityotbrieh intenvaliomcollectionse ee eee sree ener ene eer 509 Suggestions of cyclic phenomena in data of other investigators..... 509 Evidence iavourvrecords:2. ears Uete tec meerie RAeL oe ee ae eee 510 Xvil PAGE Affected by environmental factors........+--...eeeese eee eee cess 510 Approximation in time of pulses at different SPALIONS bertises parecer 510 Normal regimen in our waters one of recurrent pulses of varying am- plitudes PD ae Lae tar Ns sire Stat estriol grea tees aves edet ie) e.she Dyaehaas 511 Source and maintenance of potamoplankton.........-...-20+-+++ seers Sil i Deets) acpi Chic Wel pee CORR EAE ORGAO Onn nn irauinn trie Oo boc mdec hr ic 511 Relation of seepage waters...... 0... -- cece cece e eee eee e cece rec eees 512 Relation of tributary streams.............- 2s eee e eee e eee teen tenes 513 Examination of Quiver Creek ..........---. ese cece cere eee seee es 514 Goallection's atd~ method 257. 2. elects ae ener ners wes vic) ol= ieaiee nial 515 Constituents of Quiver Creek plankton............-.-.++ +++ -+e> 516 Comparison with plankton of river........-.+- sess eee eres eres 517 Quiver Creek a diluent of channel plankton......... ..--++++++5 518 Relative numbers of species in tributaries and river.............. 519 @henticali comaitionsS,. 2/0 favs ese eta eae otek sraial to tevae oni ocean 520 Examination of Spoon River........ 226-2202 ceee eee cece erst eeees 521 Comparison of chemical conditions in Spoon and Illinois rivers... 521 Resources of Spoon River adequate for large plankton......... 522 Lack of time for breeding a cause of barrenness...........----- 523 Comparison of quantitative plankton production in Spoon and iMiiaveNGaehiGcoade dusuccdoducdu paddomum eu baocKg bo DGeU Op ncaA 523 Errors resulting from leakage and silt.......-..+-4+s2e+eeeees 523 Statistics of production by monthly averages of all collections... 525 Ratio of production), «4.005.200 42 fees ele yee le cys nis a 526 Comparison of statistics of coincident catches...........++++++ 527 Cause of periods of relatively larger production in Spoon River. 528 Quantitative effect of access of tributary water formulated....... 529 Qualitative analysis of plankton of Spoon and Illinois rivers...... 530 Contrast in total population............+2-- esse eee eee ce eee 531 Relative development of different groupS......-.-.+-+-++++-++: 531 TN [oe Ree aio ney Ane E CO Sco ier Doe Saud eo aya uCOUC Ce hie 531 IDENto ea eae Eee Lbdn aero nsoo HOomEbcO DoCS worS DoNM Sado Gn dciC 532 Rizo pOda. ee alee an ceieees ceeokeisie olen eietenal ayn ire anos 533 Masticophorar.-22+ sh = cee cease segs cuts GOUT 534 [Dimov NONdCElnc nad-boao bone ouoe DODO DCO oaGS Ono 0OSt Seale eh gO hiss leap oton nt pe peep bo cososn>o apd GocudoduGosn0b0U06eG ¢ 536 Comparison of total number of specieS....--.. +++ ++++++rer++> 537 Comparison of seasonal routine.........---+--++- seer cert eree ees 537 Contrasts in autumnal plankton........--.. +++. eee eeer eee 538 Applicability of conclusions to Other StreamSes cetacean lel 539 Effect of tributaries upon channel plankton........-.+-+++2++++++5 539 Relation of backwaters to channel plankton......-.---.-++-++eeee0es 540 Complexity of the problem... 32.2... Seiivece 22s s cee e salen cele as 540 Impounding action of flood-plain........-. +++ ++seseeeeeereesste es 541 Amount of impounded water........----ssseee cress sete e eects eees 541 Duration of impounding...) 5-7... ale ye coats 542 Xvill PAGE Representative character or Gumdata. +: uae. “sie, etek eee 543 Predominantly higher production in backwaters................... 543° Causes of periods of low production in backwaters ................ 544 Summary of statistics of channel and backwater production........ 544 bidizenous planistonof- channels. \5, 3 ee h wee 2. 20 Ee Sahancan ees 545 Senne rasayana nes iar: pen eh alee eee aoe fib eee 546 SEotaleanuUale PROC UC TION: sae cece Meare «ea eie in tea Mtr Ker erniicer oy eka eee 547 Step Le AMT Alesse vo pO aia tors ks OYA: Secs ero pen APA Ghali Macdirsitine alte SER Oe 547 Jeter ag FOO ACO] Weal ha) ay MeN a-ring aR oth et Ma) Ry ee, ek eg 548 Vaniationginomyear:tomyear vig on ecco eae cc. tioenie ete ade oe eRe te we tas 548 Total annual loss of organic matter from Illinois River.............. 549 Determination of total production as affected by leakage through silk La Pee re RRO VATA er ie Get Sen re ine, Ain a wen ae i Pea Af 549 Volumetric determination by means of filter-paper catches.......... 549 Characterolsil tim These iCatchesy nm cence tec cieeae scien eee 550 Filter-paper catches not suited for volumetric work................ 550 Confirmation of my results by the work of Lohmann ............... 550 Methods of making filter-paper Catches J..(.\.\.4 a0: ss eee pee ne 551 Statisticalidatarof silksand hilter-papemieatcheses-. eee eeeere 552 FRAETOS jo 95) fps vw 2p eveseSoieyegateareset awe es ore ara) sy avs dats bays ahaa le lO Oe Nes eee 554 Sedsonal.chan ges imiravlOs Mm. : costes caenyeo che 4 uaa ee ae ae 555 Volumetric methods imperfect as a test of productivity.............. 556 Comparisonpwith other bodies! of waters... -.eseswic caste aes teeter 556 Absence.of-comparablesdatate. a5. osanscie Osc cee eie hs ae ar eer 557 Comparison, with Danube (Steuer);.....5).1-6 ao26: scsesae ns aes werk ee 557 Comparison with New England streams (Whipple).................. 557 Comparison with #ilbex(Schorler)....5,...c7 rt «a pseaeices 44 apie ae eee 558 Comparison with Oder (Zimmer and Schroeder)..... page site Lee Rate O @mission of comparisons with lakes. . 2.0). setae tee et ee eee 558 Does geographical position determine planktograph?................ 559 Comparison of maxioum production, sechuce . see wich eel er eae 559 Statisticalidatar. cwuieasceuiee ee ice Gise ctole tele ole ela a serene ee mee 560 Relative productivity of Illinois waters............ Besse a amen eae 9 0.0) Locationof seasonal maxima Goh cfu eine accent e be eee eee 561 COM OPBIC C OMSIACT ALON Sc stars eave. snc itn Pushers eioes oles ne ee LE eee 561 Llhinois Riverias‘asourceof wealltive 2 aur toc coll ca ce eeieene pee 561 Value for sport .andimecreationie).! 000 jill Guctpedop ca. ceshs tem cornea teens oreteaets 561 Avremnesourcces mowmutllizedutoradvantarie ener eee aan eee 562 Relation‘of plankton toMishenieswen. veh chou cer teem: beeen 563 ASifood ofhshesy path.» citcteascitn lake eels ob Chcstieeelae, mie es etemaoet: Messe 563 Importance of knowledge of plankton in scientific aquiculture........ 564 Comparison of annual product of fisheries and plankton............... 5605 Statistical -dataren joo sanccise ee elers om hole eect Olena een eReader rier 565 Correspondenceiain data. ras foie eite lars erste a piste eianele aie ot ichard site oun eeu 566 Annual wastage and fish) production). (6 ck reyripel rs tse reels tet rere 567 Suggestions for utilization of reSOUnGeS ii. je iierlr ial ere 567 CONCLUSIONS 31705 i tigh eae lee citen Gee Rieti cisbeie ahs Der rel eleyeees tate eet ey ee ies 569-574 o Oy) 1 2) AC ee ores eee a NES tale eitpc 4 Bo acinoris Moe Ge6H Rana o6 575-618 BIBLIOGRAPHY « & aie g cierto abs reels cla srtesatare anes ate a oleracea hee eer 619-624 EXPLANATION OF RU ADES aon mi iseriscie ree eee ieee teria itstter eer 625-628 ArticLE [—The Dragon-flies (Odonata) of Illinois, with Descriptions of the Immature Stages. Part I. Petaluride, A’sch- nide, and Gomphide. By Jamms G. NeEpHAM AND CHaRrLss A. Hart. INTRODUCTION. The present paper is the combined product of studies made by the authors upon the collections of the Illinois State Labo- ratory of Natural History, including those of the Biological Station at Havana, and by Professor Needham on his private collection. The state collections comprise the results of many years’ work in all parts of Illinois, including five successive years of field observation and collection at the Illinois Biolog- ical Station on the Illinois River at Havana; specimens ob- tained by Professor H. Garman from the Mississippi and related waters at Quincy, Ill. (Garman, ’90); a large series from the small lakes of northeastern Illinois; and collections made by Professor Forbes in Yellowstone Park and its vicinity (Forbes, 93) and from lakes Geneva and Delavan, Wis., under the au- spices of the U. 8. Fish Commission. Professor Needham’s pri- vate collection used in the preparation of this paper contains many [llnois and New York species, reared by him to the imago, and others contributed by correspondents, particularly by Mr. F. G. Schaupp in Texas, Mr. Adolph Hempel in Florida, and Mr. F. C. Willard in Arizona. The preparation of the in- troductory matter, biological discussions, and keys to the nymphs has devolved upon Mr. Hart, while the descriptive matter, with a few exceptions, was prepared by Professor Needham. We are indebted to Mr. C. C. Adams for abundant data on the occurrence of the imagos in Illinois derived from his large 1 2 private collection, and also for work on the keys to the genera of imagos. We are under special obligation to Dr. P. P. Calvert, of Philadelphia, for aid given Mr. Adams in the revision of keys and in the determination of doubtful species, and for notes on dragon-flies in [llinois made by Mr. Harry Walker at Belvi- dere, Mr. Shafer at Mt. Pulaski, and Mr. E. J. Kuegeman at Ravenswood and Edgewater. Data relating to collections in Ilhnois have been furnished us by Mr. Maurice Ricker, of Bur- lington, ia., and by W. E. Longley, and others, of the Entomo- logical Society of Chicago. Of the twenty-eight recognized Illinois species of the fami- hes of Anisoptera herein treated, we have here described the nymphs of twenty-four (six of them for the first time), repre- senting all our eleven genera. ‘To these have been added by Professor Needham descriptions of ten nymphs of extralimital species. Thirty-four nymphs are thus described in all, fourteen of them for the first time. Much careful study has been given to the preparation of the keys. In all cases the linear arrangement is according to the principles suggested by Comstock, the more generalized group or species being followed by the divergent ones in the order of the direction and amount of specialization. The de- scriptions of the nymphs are drawn up from full-grown exam- ples unless otherwise stated. he newly hatched insect quickly takes on the form and structure of the full-grown nymph, and may usually be recognized while still very young by the char- acteristic sculpture and armament of its species. ORDER ODONATA. The common dragon-flies of the suborder Anisoptera are familiar to every one, but the damsel-flies, constituting the sub- order Zygoptera, might not be recognized as also belonging to this order. These damsel-flies are small narrow-winged forms, which, like the butterflies, hold their wings back to back while at rest. The Odonata have no quiescent pupal state; the immature stages after the egg are collectively designated as the nymph. The latter is always aquatic. It has highly developed thoracic legs but no abdominal ones. Wing-pads appear at the third or fourth molt. There are no external gill structures except the three terminal appendages of the Zygop- tera. The abdomen of the nymph is slender among the Zygoptera, but in the ordinary dragon-flies (Anisoptera) it is rather short and broad. A very distinctive feature is the large and elongate labium, folded beneath the body like an arm, the “hand” of which, ending in a pair of claspers, covers the mouth or the entire face. The nymphs crawl rather slowly, often clumsily, but can dart some distance through the water like the crawfish, being propelled by the sudden ejection of the water in the rectal respiratory cavity. The Odonata and their near relatives the May-flies (Ephemerida), isolated remnants of former insect life, in gen- eral of primitive character although highly specialized along some lines, are probably among the oldest orders of winged insects. In younger groups the branching of the “family tree” of development may often be traced with some degree of satis- faction by a study of the primitive characters retained by still existing forms; but in the lapse of ages so many of the earlier lines of descent have been obliterated from the earth that in the Odonata only the upper parts of a few separated branches are traceable, their points of origin being involved in obscurity. In [lhnois the branch nearest the primitive stock is probably that of the “black-wings,” or Calopteryx, of our smaller streams, representing the Calopterygidw. Another branch (Agrionide), including the more common damsel -tlies, Agrion, Lestes, ete., 4 has a number of characters in common with the preced- ing, and the two constitute the suborder Zygoptera. In forms related to Calopteryx the three tracheated caudal sete of the May-flies seem to be represented by three shorter and thicker respiratory appendages, the laterals especially being more or less spike-like and triquetral. In the Agrionide these appendages are vertically flattened thin gill-plates. Quite a different development of the original type is found in the nymphs of the ordinary dragon-flies, the suborder Anisoptera. In these respiration is principally performed by internal rectal gills, and the three appendages, very short and subtriangular, are supplemented by two others, the five converging to protect the opening of the respiratory cavity. The five families constituting the Anisoptera—Petaluride, Ayschnide, Gomphide, Cordulegasteride, and Libellulide—are variously connected by common characters. It is worth not- ing that the obscure color, rough sculpture, and general habits of the Calopteryx nymph are also found in the more primitive forms of these families. The Petaluridw is probably the oldest of the five. It has not as yet been found in Illinois. In this family and the A’schnide the ovipositor is well devel- oped and oviposition is endophytic, as in all the Zygoptera. The Petaluride, jadging from Mr. Williamson’s observations (Williamson, ’01), breed in boggy or swampy spots, where the imagos may be found ovipositing. The nymph is re- markably synthetic in its characters and supplies a hitherto missing lnk in the evolution of the labium, being interme- diate in this respect between Aschnidew and Cordulegaster- ide, thus indicating a very primitive origin. In its form and antennal structure, on the other hand, it strongly approaches the Gomphide. In general, however, it is clearly most closely related to the A’schnide. The nymphs of the A’schnide are somewhat elongate, and climb on submerged branches, driftwood, roots, and smaller vegetation. The imagos are unusually large and high-flying, the eyes large, the wings much specialized, The nymphs of the third family, Gom- 5 phide, nearly all burrow in mud and sand. The imagos are usually of medium size, barred with green or yellow, the apical part of the abdomen often expanded to a greater or less extent. They are usually seen near water, but are not numer- ous as arule. The ovipositor is rudimentary or wanting and oviposition is exophytic, as in the remaining families. The eyes are small and widely separated, in which respect the fam- ily approaches the Zygoptera. The nymphs of the Aschnide and Gomphidw differ but slightly in the structure of the labium and gizzard, and both these organs are quite similar to the type found in the Zygoptera. The next family, Cordulegaster- ide, is of special interest. It has but few species, and examples are rarely seen in Illinois. While evidently related to the pre- ceding families in different ways, the nymphs are like those of the Libellulidw in having a spoon-shaped labium and a sym- metrically 4-toothed larval gizzard. The last family, Libellu- lide, comprises most of the commoner species. They are diversified in structure and habits, and may be grouped in three subfamilies. The first two of these (Synthemiine and Cordu- line) have a number of common features and have hitherto been classed as one, but the wing structure and nymphal characters of the Synthemiine, represented in Illinois by Ma- cromia and Didymops, seem to warrant its separation from the Corduliine. The greater part of the family belongs to the Li- belluline, which includes three general types, exemplified by Sympetrum (Diplax), Libellula, and Tramea. The grouping of these is based by Mr. Adams on the extent of development of the ovipositor. LITERATURE. A list of the more important papers, to which references are made, is appended to this paper. A brief summary of their contents may be given here. On the nymphs, the most important papers are by Hagen and Cabot, describing and figuring the nymphs of the Museum of Comparative Zoology, at Cambridge. Cabot’s first paper (72 ) 6 covered the Gomphide and Cordulegasteride, his second (’81) the A’schnide, and his third (’90) the Synthemiinw and Cor- duliine and also Tramea and Pantala. Hagen (’85) gave a greatly extended revision of the two families previously treated by Cabot (72). The large and abundant family Libellulide was not treated by them. Karsch(’93) gives descriptions, figures, and keys to West African nymphs. The characters assigned to the major groups in his keys are, as Dr. Calvert has pointed out, only locally or partially true. Lucas (’97, 97a) has described and figured a few English nymphs, and Roster (’86,’88 ), a num- ber of Italian Zygoptera. Beutenmiller (’90c) has given a bibhography of nymphal descriptions, excepting those in Cabot’s "90. Needham (97a, ’99) gives suggestions on collecting and rearing nymphs. Among the general works, Dr. P. P. Calvert’s admirable paper (’93) deserves first mention. It includes a complete and accurate summary of all the more important biological and anatomical details concerning dragon-flies and their nymphs, with generic keys for both. Descriptions are given of the species of the region about Philadelphia, among which are most of our commoner forms. The phylogeny of the dragon- flies in general, with especial reference to the structure of the gizzard, is discussed in a scholarly article by Dr. F. Ris (’97). The principal monograph of American species is in Hagen’s well known “Neuroptera of North America” (’61).. A num- ber of monographic papers have been published by Dr. Selys- Longschamps in Belgium. The best catalogue of species is that of Kirby (90). It contains several surprising changes in nomenclature, one of which—the use of A’shna in place of Gomphus—is fortunately not well founded. Banks (’92) has listed the American species, and given a key to the genera. From an economic point of view, especially as to their utility as destroyers of obnoxious Diptera, dragon-flies are treated in Lamborn’s collection of prize essays (90). The numerous published lists of Odonata in this country contain much valuable information as to the life history of our 7 species, dates of occurrence, and the like, and have been exten- sively used in the preparation of this paper. Such are those of the late Dr. Kellicott (95, 96, 97a); of Miss Wadsworth (’90) and Mr. Harvey (’9la) for Maine; of Calvert, Banks, and Van Duzee for New York; of Calvert for Virginia and the vicinity of Philadelphia ; of Williamson (’00) for Indiana ; and of Elrod for Iowa, and Banks for Kansas. The above localities are not far from our own latitude, and the data given are presumably quite close to the normal for [linois. Among L[hnois contributions to this subject we may men- tion the elaborate papers (’62, 63) of our pioneer entomologist, Mr. B. D. Walsh, who listed sixty species occurring about Rock Island, describing a number as new; a list of dragon-flies taken at Kensington, I[Il., by Mr. Jas. E. McDade (’92) ; and the treatment of the Odonata in Mr. H. Garman’s “Animals of the Waters of the Mississippi Bottoms near Quincy, IIL.” (’90). Eight nymphs are listed in the latter paper. The original specimens have been examined and determined as follows: His “4” is Gomphus externus; “8. Hpieschna heros” is Nasiwschna penta- cantha of this paper; “9” is Tramea lacerata; “10”, Epicordulia princeps; and “11”, Perithemis domitia. “12” is immature and not positively determined as yet. The others are correctly identified by him. LIFE HISTORY. Dragon-flies hibernate commonly as nymphs, less com- monly in the egg stage, and in one species as imago. Nymphs of the Anisoptera mostly transform to the imago in the early part of the season, especially from the latter part of May to the first of July in our latitude, the imagos scattering and becom- ing reduced in numbers by midsummer. Some species, particu- larly those of the Gomphide, have a very short period of emer- gence, large numbers transforming within a few days. Anaz, and perhaps some species of schna, has apparently two broods in a year. The adults appear very early in the season, and the young nymphs, feeding voraciously and actively, grow rap- re) idly, and have been known to produce imagos before the close of the same season. Tramea also seems to be two-brooded, emerging numerously both in spring and fall. On the other hand, the nymphs of the Gomphide probably require more than a year in which to mature, emerging in the second or third season after hatching. The one-year life cycle is, how- ever, the rule among the Libellulidew, which contains most of our commoner Anisoptera, the eggs laid during midsummer hatching in latesummer,and the nymphs maturing in time forthe general emergence the following season. In late August there is a Surprising number of very small nymphs,—tiny spider-like youngsters,—and even in September and October the prepon- derance of young nymphs is still manifest. As the period of maximum emergence of theirspecies approaches, usually in early summer, they mostly attain full size, and are at this time most readily seen and captured and apparently more abundant than in the fall, when they were small and easily overlooked. With regard to the Zygoptera, it is highly probable that there are a number of broods ina season, the processes of transformation and oviposition beginning as soon as the weather permits and con- tinuing industriously to the close of the season. In the species whose life cycle is apparently more than a year the nymphs are of two or three distinct sizes, the largest presumably being of the next brood to emerge. In species whose life cycle is completed within a year, the nymphs are fairly uniform in size, but there is, nevertheless, a sufficient extent of variation to cause a considerable number of strag- eling emergences during the season; and it therefore follows that, in general, nymphs of nearly all species of Odonata may be found throughout the entire season. Because of this fact it has not seemed worth while to give dates of the occurrence of nymphs. The accessible data concerning the imago period, on the other hand, is very fully given, thus indicating the hmits of the nymphal period also. Like many other immature aquatic forms, the ground color of the nymphs darkens greatly up to the close of each molting : 9 period. Immediately after molting they are very hght green- ish or grayish and their characteristic color-pattern is beauti- fully distinct, but they gradually darken and the coloration becomes more and more obscure until, as the time for the next molt approaches, it is almost entirely lost and the nymph be- comes uniformly dark and dingy. When grown, the nymphs seek the shore or some floating object and clamber up a little way on standing vegetation, logs, tree-trunks, sticks, bridge-piling, the sides of boats, or the lke, and, fixing their feet firmly, proceed to transform to the im- ago stage. Transformation mostly takes place very early in the day and is largely over with by nine o’clock, although scatter- ing emergences may occurat any time. The usual process will be fully described under Tramea lacerata. The adults scatter con- siderably, but a large number remain in the original vicinity, busily ovipositing for a new brood of nymphs. A short but undetermined period elapses before egg-laying begins. Oviposition is of two kinds, endophytic and exophytic. That of the groups with more slender nymphs, Zygoptera and Zéschnide, is endophytic. They have an elongated egg, which is inserted by means of an ovipositor into living or dead vege- table substances, either resting in water or at least moist. The female immerses the tip of her abdomen or enters the water completely. She usually succeeds in escaping safely from it, but is sometimes rescued by the male (Todd,’85). The oviposition of the groups with broader nymphs, Gomphide, Cordulegasteride, and Libellulide, is exophytic. Their eggs are shorter and oval, and are extruded in a gelatinous matrix. The female dips her abdomen in the water, usually during flight, releasing at each dip a number of eggs, which sink to the bottom or lodge on the vegetation. Sometimes, when too hotly pursued by males, she will alight on water moss or drit- wood and cast her eggs loose there. In the case of Leucorhinia this is apparently the usual method of oviposition. In some cases the eggs may be deposited on moist mud ( Diplar, Somat- ochlora) or affixed to the bank or to water plants. The female 10 of Celithemis is usually accompanied by the male, who helps her to escape when menaced by the open mouth of a hungry fish. Several hundred eggs are often laid by a single female. The period of incubation varies with the season and also independently of it. In midsummer, eggs of some species hatch in from six to ten days, while others, laid in autumn, do not hatch until the following spring. In the same lot of eggs the period of incubation may vary, even in midsummer, from a week to more than a month. The apparent abundance of nymph and imago is far from corresponding, the difference in some cases being quite surpris- ing. Of the nymph of Celithemis eponina, we have secured only a few examples; yet the imago is a familar sight everywhere about the Station. The species of Sympetrum are common and familiar dragon-flies; but we have obtained only a few of the nymphs. This genus probably breeds in swampy places, where the vegetation is so dense, the water so shallow, and the mud so deep as to make collecting very difficult. On the other hand, Epicordulia princeps is abundant and widely distributed as a nymph, but the imago is not commonly taken. Nymphs of Macromia, Progomphus, and Hagenius are not at all rare in streams; the imagos are considered very rare or almost unobtainable. In the Gomphide are numerous similar exam- ples. This discrepancy may be due either to the swift, high, or prolonged flight of the imago, or to the shortness of its life ; but in some cases it is almost inconceivable how the imagos can vanish so completely as they do. Walsh (’63, p. 239) makes some remarkable statements as to the relative proportion of the sexes in Gomphus. In some species he found four males to every female, and in another two or three females to each male, and he asserts that this is the case in freshly emerged material. Mr. Needham is of the opinion that in nymphs generally there is no notable excess of either sex, but that in the imago an excess of males may occur because of the destruction of the females by fishes in species the females of which oviposit unattended by the males. It is prob- 11 able that Walsh’s statements were based on insufficient data. The imagos usually keep near their nymphal home. The Zygoptera both fly and alight low, usually over water; the stronger Aschnide fly high and scatter more; while the other imagos are diversified in these respects, many species being taken both along streams and along borders of roads and fields at some distance from water. All dragon-flies are most active in hot, quiet, sunshiny weather. They cease flying by sunset, except a few of the ZEschnide, which may be seen in hot pursuit of small Diptera during the evening twilight. The history of the order as a whole in the vicinity of Havana, while under our observation, is interesting but some- what puzzling. In 1894 there was a great abundance of indi- viduals, in all stages. In 1895 the season’s collecting opened up well. Extremely low water prevailed, however, and in June the shallow waters became greatly heated by the sun, their recorded temperatures reaching as high as 96° Fahr. On one occasion, when the heat of the water was especially noticeable, a num- ber of dead nymphs were found floating about, along the west shore of Quiver Lake. Not many nymphs were seen in the usual situations at the close of this season, and from that time on through 1896, they were reduced to insignificant numbers. The low water of 1895, however, encouraged the development of spe- cies liking swampy situations, and there was consequently in 1896 an excessive development of Pachydiplax longipennis and species of Sympetrum. A shght rise took place in the spring of 1596 and the river became very foul. At the close of the year the drouth was broken, with a more extensive rise of the river, and the season of 1897 showed an increase in the number of nymphs. The winter and spring following brought much high water in the river, but the nymphs did not greatly increase In numbers. Kellicott has noted (’97a ; 97, p. 69) that in Ohio the warm rainy weather of April, 1896, following the drouth of 1894-95, caused emergence earler than usual, and the number appear- ing did not seem noticeably reduced by the drouth. 12 WATERS FROM WHICH COLLECTIONS WERE MADE. The nymphs in the State Laboratory collections were de- rived from a large variety of waters: from the broad Mississippi and Ohio, slow and majestic, but flowing more hurriedly at a few points—as at Rock Island and Golconda; from the bottom- land lakes of these streams, muddy and without much vegeta- tion; from the lower course of the [linois, broad, shallow, slow- flowing, with the bottoms more of mud than sand, the shores often margined with water vegetation ; from the broad and shallow bottom-land lakes along this river, some slightly deeper than others, but abounding in floating vegetation,—as Quiver, Thompson’s, and Dogfish lakes near Havana,—some shallower and swampy, as the great expanse of Flag Lake, and others changeable and temporary in character, as Phelps Lake ; from the smaller affluents of the rivers, usually flowing with an oc- casional descent over beds of mud, sand, and gravel ; from the small lakes which rest in the ancient glacial hollows to the west ef Lake Michigan in [llinois and Wisconsin, quite deep in places, permanent in character, usually well supplied with aquatic life of all kinds ; from the shallow ponds of similar origin scattered over the state, of all degrees of permanency ; and, lastly, from the rapid flowing rocky streams of Yellowstone Park. These waters present a great variety of situations, each with its char- acteristic forms, and it is interesting to note how each of these situations is occupied by a definite series of nymphs, in accord- ance with its particular character. NYMPHS INHABITING THE VARIOUS SITUATIONS. The nymphs may be roughly grouped in three divisions, according to the kind of situation preferred by them. The first includes groups having the endophytic habit of oviposition, Zygoptera and Aeschnide, as well as a few of the more agile members of the other families, such as Hagenius among the Gomphide, and Mesothemis, Celithemis, and Tramea among the Libellulide. The lighter-colored of these clamber among sub- merged vegetation, while the dark-colored forms (Calopteryg- 18 ide, Hagenius, and the lower 4schnide) inhabit driftwood and submerged roots and brush. The second division comprises the heavier nymphs of the Libellulide, which usually sprawl upon the bottom or climb over fallen rubbish; and the third con- sists of the remaining Gomphide, the Cordulegasteridw, and, to some extent, Libellula and its relatives, which occupy the mud or sand of the bottom. The species inhabiting submerged vegetation, constituting the first group, are of course most abundant in the quiet waters of slow streams, lakes, and ponds, where such growths have an opportunity to develop freely. The large and active nymphs of Tramea and Pantala appear to prefer the more exposed shores of large lakes and rivers. Mesothemis collocata is adapted for life in the high temperatures of water from the hot springs of the west. The Agrionide and Anax are common everywhere in bodies of water with vegetation, from the small- est pool to considerable lakes. The other “schnidw climb on dead sticks and driftwood where there is little vegetation and food is not abundant, as in the bottom-land lakes and sloughs of the larger streams with good current, or (Boyeria) in the deeper holes along small streams, where projecting roots catch the floating driftwood. Hagenius also lives amongst driftwood and dead leaves in streams. The Ca/opterygide thrive in little rapid-flowing sandy rivulets ike White Oak Run and Quiver Creek at Havana. In the second group, those living on the bottom, depth and current are important in determining the particular species likely to be found. Epicordulia likes the deeper waters, as of the Illinois River itself or its deeper lakes, or the bottoms of the small lakes of northeastern Illinois, finding there the molluscan diet it enjoys. On the other hand Sympetrum and Leucorhinia habit marshes and reedy shores, as well as shal- low weedy ponds and wet meadows. The “ Pumpkin Patch” at Havana, the shores of Fourth Lake in northeastern Illinois, and the swampy spots of the upland prairie, are situations of this character. Pachydiplax appears to like the deeper swamps 14 and ponds, such as Flag Lake at Havana. In the smaller streams, where the current is often rapid, such as the Mackinaw, the upper Sangamon, and the Little Wabash rivers, a number of very interesting forms find their home, especially the Synthemiine, Somatochlora and other Corduliine, and the species related to Libellula. Of the third group, which live 7» the mud or sand of the bottom, there may be found in the streams just enumerated other interesting material, especially Cordulegaster, Progomphus and Gomphus spiniceps. In this group the most definite selec- tion of situations prevails. Where rapid currents flow over rocky beds, as in the Mississippi at Rock Island, in the Mack- inaw at the “ Dells,” and in the streams of Yellowstone Park, is the chosen home of Diastatomma (Ophiogomphus). Where slow currents and a muddy bottom occur, as 1m many prairie streams and ditches, Plathemis and Libellula, covered with dirt, trail over the mud along the shores leaving a well-marked track, or lie concealed amongst fallen trash, the dorsally pro- jecting eyes of Plathemis enabling it to remain hidden and yet keep a sharp lookout. The nymphs of the Cordulegasteride conceal themselves in the sand beneath the eddies of streams or under the alluvial deposit in marshes, but do not burrow. Each scratches a hole for itself, and descends into it like a chicken into a dust bath, and, like the chicken, kicks the sand over its back, and does not rest until almost hidden, only the tops of its eyes, the tip of its treacherous labium, and the re- spiratory aperture at the end of its abdomen reaching the sur- face. The burrowers of the order are the members of the large and as a whole abundant genus Gomphus. These burrow shal- lowly along in the midst of abundant life, with the tip of the abdomen turned up for respiration. Some are lake or pond species, suchas graslinellus and pallidus. The former is com- mon in prairie ponds and in the small lakes near Chicago ; the latter in similar localities, and in open lakes near Havana, such as Matanzas and Clear lakes. Others choose the larger rivers, being most numerous in quiet corners where fine rubbish and 15 animal life accumulate. Such are notatus and fraternus ; while spiniceps prefers swifter flowing waters like Quiver Creek at Havana, or the upper Illinois River at Ottawa. In some species with which we have had but a limited experience further study may show a wider range of normal situations than that here assigned, but the preceding generali- zations should have a value to the student and collector, and may serve as a basis for a more exact account in future. The Llinois waters which afford the widest range of situa- tions and are most prolific in variety of dragon-fly nymphs are the small lakes of Lake county. Their shores are sometimes exposed, wave-washed, and rocky, and the life here found is remarkably like that of swift running water. Again, they are broad and marshy, and afford a home for Sympetrum. Out from shore we may find shallow waters with mats of aquatic vegetation, bare sandy surfaces, or, at great depths, a bottom of soft mud. As to numerical abundance I have seen nothing in Illinois that can compare with the multitudes of dragon-flies that issue in favorable seasons from the broad shallow lakes along the Illinois River. ODONATA OF THE VARIOUS WATERS IN ILLINOIS. Taking the subject from a different point of view, we may briefly summarize the odonate life of the Illinois waters as fol- lows. In the larger rivers, down to the size of the Mackinaw, in places where the water flows with considerable current over a rocky bottom, Diastatomma may be looked for; where mud or sand bottom and quieter waters prevail, Epicordulia and some species of Gomphus may be found. Other species of Gomphus occur in the bare muddy or sandy bottoms of the sloughs and bottom-land lakes. In tree-shaded waters, where driftwood and branches have gathered, or along muddy margins, especially amongst exposed roots, the lower Zschnidw may be looked for. In bottom-land lakes where vegetation is abundant, one may find Anax, Agrionidw, Mesothemis, Celithemis, Tramea, 16 and Pantala amongst the vegetation, the latter two especially on more exposed shores; and Tetragoneuria, Libellula, Epicordu- lia, and Leucorhinia on the bottom underneath. If the situation is inclined to be marshy, Pachydiplax, Perithemis, and Celi- themis will be scattered over the bottom; and the shallowest and most temporary waters or wet lands are the especial home of Sympetrum. In the smaller and quicker flowing streams, like the upper Mackinaw and Sangamon, quite a different series occurs: Ha- genius, clinging to stones and driftwood and amongst dead leaves; Boyeria and other dark 4schnide on submerged branches, roots, and sticks; Cordulegaster and the long-legged Macromia hidden at the bottom in sheltered eddies; Somato- chlora; and, finally, Progomphus, Dromogomphus, and certain species of Gomphus burrowing in the sandy bottom. In the prairie ponds and slow streams and ditches, Anar, Agrionide, and Mesothemis and other Libellulidw occur amongst vegetation, and Sympetrum in shallower parts, while Libellu/a and Plathe- mis will be found where there is more mud and less vegetation, as in ditches and tile ponds, resting at the lower ends of well- defined tracks. In streams of rapid flow, but not especially rocky or shaded, the Calopterygide are most likely to be found, the imagos fluttering along the banks. In the small northern glacial lakes of Illinois, a remarka- bly varied odonate life can be found. Among the vegetation and along shore, Agrionide, Anaxr, Tramea, Leucorhinia, Li- bellula, Tetragoneuria, Epicordulia, and Basieschna may be taken. Sympetrum has been found along the broader, shallow, reedy margins. On the sparsely grown flats, in somewhat deeper water, Gomphus graslinellus, spicatus, and pallidus oceur, and, especially where it is clayey, the Synthemiine—Didymops and Macromia—have been taken. On the other hand, Mesothemis, Pachydiplax, and Perithemis, elsewhere abundant, do not appear in our collections from these waters. As to the imagos, they are most hkely to be found along the shores of waters inhabited by their nymphs, though many 1 forms, such as some Agrionidw, most of the schnide, Libel- lula, Sympetrum, and Mesothemis scatter widely inland. Sym- petrum will bé seen about fields and lawns, and the schnide in the vicinity of houses. / FOOD RELATIONS. The nymphs are all predatory in habit. Most species remain in ambush, aided by coverings of sand, mud, silt, and algal growths, and by their own protective coloring, until their prey wanders within reach. Anar junius and a few others choose their prey. All capture it with a marvellously sudden extension of the labium, bringing it into the grasp of the for- midable lateral labial lobes. Almost all kinds of small aquatic animals appear on the bill of fare of the group as a whole. The Agrionide have a seeming preference for Hntomostraca and May-fly nymphs. The vegetation-inhabiting species have the most varied diet, including especially back-swimmers ( Notonecta) and water-boatmen (Corisa), small crustaceans, such as Asellus and Allorchestes, thin-shelled mollusks, like Physa, coleopterous and dipterous larvae, and even the younger or weaker members of their own order. Anar takes even the thicker-shelled univalves. like Amnicola. The deep-water E’pi- cordulia feeds principally on small mollusks, such as Amnicola and Physa, as well as on other life of the bottom. The sch- nidw, especially Anaxr, are most omnivorous creatures. The larger odonate nymphs eat very young fish, and in some cases appear to have caused a sweeping destruction of large numbers of them. On the other hand, the nymphs are apparently eaten prin- cipally by fishes and by one another; hence their need for hid- ing places in mud and sand or among matted vegetation. In the course of Professor Forbes’s studies of the food of fishes (88a, pp. 485, 524) he found odonate nymphs most abundant (twenty-five per cent.) in the food of the grass pickerel (Hsoxr vermiculatus), and forming ten to thirteen per cent. of the food of the crappie (Pomoxis annularis), the pirate perch ( Aphredoderus 18 sayanus),and the common perch (Perca flavescens). The latter is anabundant species in the small northeastern lakes of the state. Belostoma, Ranatra, Notonecta, and the like, according to Mrs. Aaron (Lamborn, ’90, p. 50), prey on young nymphs, and she also mentions a small red mite and a minute dipteron as parasitic on the eggs of Odonata. Mr. Needham (798) has recorded the finding of numbers of nymphs in the stomachs of herons, and he once found the intestine of a nymph parasitized by very large Gregarinide fully 1 mm. long. Emerging imagos while limp and pale are the easy prey of even their weakest enemies, and great decimation takes place among them at this time. Ants, spiders, robber-flies, frogs, and birds eat many of them. The full-fledged dragon-flies devour the small insect life of the air in vast quantities, especially gnats and mosquitoes, most of which probably developed in the waters previously inhabited by the dragon-fly nymphs. These seem to make little or no attack upon the larval stage of the gnats and mosquitoes, as if reserving them for their imago hfe. Dr. Lamborn, by offers of prizes, started an investigation to determine the practicability of artificially utilizing dragon-flies for the destruction of mos- quitoes and flies; but the evidence published (Lamborn ’90) indicates that these pests may be dealt with more effectively by direct measures, since the the attack of dragon-flies could not easily be controlled and directed, although in their own way and time they doubtless reduce the numbers of the pests very considerably. Mature dragon-fles do not usually suffer seriously from natural enemies. ‘hey are frequently found infested by small red mites. Some birds, such as the king-bird, possess sufficient alertness to capture them as regular articles of their food. It seems to be the weaker forms, such as Agrion, that suffer thus most extensively (Needham 798). The females while oviposit- ing are sometimes captured by fishes. COLLECTING AND REARING. A careful consideration of the statements and suggestions 19 in this article as to the various haunts and seasons of the dif- ferent nymphs and imagos, will give one a pretty good idea what species may be found in the waters near at hand. Nymphs of species inhabiting vegetation may be secured with a dip-net or rake. The dip-net is quite an essential article. The kind most in use at the Biological Station has a D-shaped ring made of heavy wire about a quarter of an inch thick, the two ends joined at the middle of the curve, the last three or four inches of the ends bent outward, welded together, and inserted into the handle, as in a hoe or rake. The net is of bobbinet, with a mesh about like that of mosquito-netting, or finer. Itis cut about four or five inches larger than the ring all around and gathered up to form a shallow bag without seams. This bag is edged with a band of strong cloth slightly larger than the ring and then sewed by this edge to the ring with good fine twine. The nymphs sprawling on the bottom are secured by vig- orous movements of the net close to the bottom, the currents produced sweeping them into the net. The burrowers are taken by scraping the surface layer of the bottom into the net or into a sieve, and then sifting or washing out the mud or sand, thus leaving only the nymphs and coarser rubbish. In deep-water collecting a dredge must be used. The swamp-inhabiting nymphs are easiest secured in the early morning as they come up for transformation. A pair of rubber boots is often very useful. The smaller imagos are easily taken, but the larger ones will often stimulate the activity and alertness of the collector to a considerable degree. If the air net be of light, strong, clean material, like bolting cloth, not too fine-meshed, the possibili- ties of capture will be greatly increased. The best time to col- lect dragon-flies is on cool, cloudy, or windy days. On one memorable occasion on the shore of Cedar Lake, just after a light rain, a heavier storm impending, the dragon-flies were found resting on weeds among the trees on the sloping shore, so sluggish that they were picked up by hand in large numbers. Eggs of the families which oviposit free in the water are 20 easily secured by capturing the ovipositing female and touch- ing her abdomen repeatedly to some water in a small dish, holding her only by the fore wings back to back, while those which oviposit in plants or soft wood may be watched and the stems or wood examined afterward. Experiments indicate that imagos will not voluntarily oviposit while in captivity. Formalin is not a good preservative for any of the larger insects. The best preservative is strong alcohol carefully heated in a water-bath. The hot alcohol penetrates more rap- idly than cold, arresting internal decomposition, and thus re- tains the beautiful but fugitive colors of the imago. The usual process of sterilizing and fixing the tissues by heating in water in a test-tube to the boiling point before transferring to alcohol is eminently satisfactory for aquatic forms as a rule, but in the Anisoptera this expands the air in the rectal gill-chamber and distorts the abdomen somewhat, while in the Agrionida, as in the Hphemeride, the flat external gill-plates are badly injured by inflation and gumming together. The slender and brittle abdomen of the imago breaks off very easily, and a bristle or fine non-corrosive wire should therefore be passed lengthwise through the body as far as the tip of the abdomen, but not so far as to project among the terminal appendages. A couple of insect pins, inserted lengthwise, one at each end of the body, are used by some. Specimens for the cabinet may be spread lke Lepidoptera. For shipment or exchange they are usually in- closed in soft papers folded diagonally. Rearing the nymphs is not usually difficult. They need plenty of clean water, something to crawl out on, and room to transform in. A pail or tub covered with mosquito-netting answers nicely. It must get plenty of sunshine, but notso much as to overheat the water. If the breeding-cage can be immersed in the water of the stream or lake where the nymphs live, suc- cess is almost assured. They may be fed bits of fresh meat or fish, insect larvee, flies, or the smaller aquatic Hemiptera. If meat is fed, it must be kept in motion before them, as they will refuse anything that does not seem to be alive. Mr. Needham 21 has reared Gomphus nymphs, which do not feed so readily as others, on earthworms. As they are more or less ready to eat each other, they must not be crowded. Anax is especially unprincipled in this respect, and Gomphus is fond of libellulids. Recently emerged lving imagos should be transferred, each with its cast skin (exuvia), to dry boxes for a short time, till their surfaces and wings gain firmness and their colors are matured. The imago and its exuvia should always be kept together. If the observer is able to keep a close watch on waters where nymphs occur, about the time of their emergence, and does not mind an early morning visit before breakfast for some larger species, he will be amply rewarded for his enterprise some day by discovering a large number in the midst of the processes of transformation, often of some species rarely taken on the wing and very desirable for exchange purposes. In all cases and by all means full notes of habits, food, flight, manner of oviposition, and the lke, should be carefully recorded. CHARACTERS USED IN CLASSIFICATION. The Nymph.—The most important recognition characters in the head of the nymph are derived from the labium, the an- tennz, and the form and sculpture of the upper surface. The latter is useful in the separation of species and genera. If the tip of the labium, or mask, which covers the mouth like a hand, be grasped and drawn forward, the labium will straighten out, and may be kept from springing back again. Like the arm, it consists of two joints, the submentum and mentum, the end of the latter broad, bearing a pair of broad flattened appendages, the lateral lobes of the labium. The mentum itself is called the median lobe. Kach of the lateral lobes bears outwardly, near its tip, a strong movable hook. In the Petaluridew, Avschnide, and Gomphide the labium is flat, and applied to the lower surface of the head; the lateral lobes are somewhat mandible-like, bearing a row of fine short teeth on the terminal edge in the Petaluride, and on the inner edge in the other two families 22 mentioned. In the Cordulegasteride and Libellulide the labium is spoon-shaped, covering the face, the lobes broad and sub- triangular, fitting closely against the median lobe and to each other. The teeth of the opposed terminal margins are, in the former family, large, acute, and interlocking, but in the latter they are rounded crenations, at most not higher than broad. These are tipped with short hairs, however, which when wet make them appear pointed. On the inner surface of each lat- eral lobe may be a row of several conspicuous sete, the lateral setw, and a similar row on each side of the middle of the median lobe—the mental sete. The antenne are usually small and cylindrical, 6- or 7-jointed, but are broad and flattened in. the Petaluride and Gomphide,and only 4-jointed in the latter family. The thorax and its appendages are not extensively used in the classification of the nymph. On each side of the prothorax, in the Aischnidw, are a pair of small tubercles, the supracoxal processes, best viewed in profile from above. They are fairly constant in form for each species. The tarsal joints are usually three in number, but in the Gomphide there are only two joints in the anterior and middle tarsi. The suture between the first two tarsal joints 1s oblique, making the basal joint much shorter above than below. The comparative length of these two joints, measured on the dorsal line, is a useful distinction in the Libellulide. Asthe suture between them is usually marked in darker color above, it is easily located. The wing-pads vary in size with the age of the nymph, being at first entirely want- ing. In the adult nymph four or five abdominal segments usu- ally remain exposed behind them. The two main groups of dragon-flies are quite unlike in the terminal appendages of the nymphal abdomen. In Zygoptera it ends in three large leaf-like gills, while in the An/soptera the last segment—the tenth abdominal—bears five small tapering appendages, which converge and form a valve closing the rectal opening. The middle one above is the superior appendage, the lower pair are the inferior appendages, and on each side of the superior appendage, above the inferiors, are the lateral append- 23 ages. ‘These are of considerable value in classification. The posterior lateral angles of some of the abdominal segments bear the lateral spines, sometimes very small but distinct, as in Li- bellula, rarely entirely wanting as in Mesothemis. There are also spines or teeth along the median line of the abdomen above, varying greatly in number and form, collectively known as the dorsal hooks. These and the lateral spines are extremely use- ful in separating species and subordinate groups. The dorsal hooks may be viewed in profile from one side, springing the abdomen down away from the wing-pads ; but when they are represented merely by teeth projecting backward on the hind margin and not elevated above the general level, as in Gom- phus, they are of course best viewed from above.’ The dorsal hooks are always absent on the first one or two abdominal seg- ments, beneath the wing-pads, and as their appearance on the posterior abdominal segments is of especial importance, it has usually been necessary to refer only to those on the exposed segments of the abdomen. The characters given can usually be applied to nymphs of any age except the very young ones. In case more or less of an antenna or leg is broken off during the hfe of a nymph, it may be imperfectly replaced, usually with one joint less than before and the relative size of the joints abnormal. A slight elevation on the under side of the abdomen, if near its base, indicates the male nymph ; if towards its tip, the fe- male. This may be easily observed in the common nymphs of Anax junius. In the A’schnide, the male nymph is also dis- tinguished by what seems to be a small median scale resting on the basal part of the superior appendage. —,. The Imago.—It is unnecessary here to describe in detail the external anatomy of the adult, but for the understanding of the keys a brief statement of the wing venation in the Ani- soptera is desirable. The fore and hind wings have essentially the same structure, modified to suit the difference in outline especially at the anal angle. The large number of adventitious minor longitudinal veins and cross-veins and cells are extremely 24 variable and unreliable, but the relative positions of the princi- pal veins and cross-veins are constant, and useful as distinguish- ing characters. On the front margin of the wing, near its apex, is a con- spicuous opaque cell, the stigma. The strong vein which runs along its inner side, extending the whole length of the wing, is the radius. This 1s intersected about midway of the wing by a vein (the nodal sector) which starts at the margin in-a notch of the costa called the nodus. Between the costal margin and the basal half of the radius is the swbcosta, extending as far as the nodal sector. On either side of the subcosta is a row of cells separated by short cross-veins, the antecubital cells and cross-veins. On either side of the radius, between the nodal sector and the apex of the wing, are similarly the postcubital cells and cross-veins. Behind the base of the radius is a large cell, the basilar space, bounded posteriorly by the cubitus and outwardly by a conspicuous cross-vein, the arculus. Near the middle of the arculus arise, jointly or separately, two longitudi- nal veins, the upper and lower sectors of the arculus. The up- per sector is the main stem of the median vein, the lower is its posterior branch. The bases of the media and the radius form one vein as far as the arculus. The anterior branch of the up- per sector is the principal sector. It also is intersected by the nodal sector. The next apparent branch of the upper sector, running parallel to and just behind the nodal sector, is really a branch of the radius, and should be called the radial sector. Two adventitious longitudinal veins, formed by the stringing together of cross-veins, are the apical sector, just behind the tip of the radius, and the supplementary sector, behind the radial sector. ae ee fo inte SSeS Snheheae + , for 1851-18 the horizontal lines indicate the averages for the years included. ERE [| LI | E fal LE is iz [| is ae Rw L in i bil Lil | is | EI al [| ie i ainfall of Illinois é Bel : a ne Es 2 a i e | el \ | iN ’ | ie ; : Pe ea el ea fe is Ps ai il sai ee ee eee att RAINFALL IN ILLINOIS 1651-1899 EEREEEREERER heal Sa2e08 & BERR ERB eee PS eV See soe oes Bee VT lee cit ae az ES a ial [ ua ie ae = & a | fe EEG fal fe ie a iS a a : ie i a present the depth in inches ; Hil ala re He |_| Bie i el ca = Pal a i: Ces fe = g I is a = The ordinants re The + and — signs indicate the location of the rainfall pulses attendant upon the sun-spot cycle. eee! es a e ens leS BEE a bal él Mt + Diagram showing the yearly variations in the average r Bureau. + Tae SZ PEREECEEEEE = Fig. A. 123 The average rainfall for the State of Illinois for a period of forty-nine years, from 1851 to 1899 inclusive, is 37.859 inches. Leverett (96) gives a tabulation of the records of the U. 8. Weather Bureau from stations within the state and on its bor- ders from 1851 to 1895 inclusive. The average for this period of forty-five years, was 37.85 inches per year. The averages for subsequent years, kindly furnished by Mr. M. E. Blystone, of the U. 8. Weather Bureau, increase this amount by 0.008 inches. The above diagram (Fig. A) shows the variations in the rainfall in the period above mentioned. The irregularity in the earlier years of observation may in part be due to the small number of stations from which records are available. In 1895 records were made at ninety-seven points within or adjacent to the state; in 1885, at twenty-seven ; in 1875, at twenty ; in 1865, at sixteen; and in 1851, at but five. The range of the annual averages is 24.8 inches, ranging from 54.1 inches in 1851 to 29.3 inches in 1894—a year of extreme drouth. Of the forty-nine records twenty-four lie above and twenty-five below the mean. An examination of this diagram of the rainfall of [h- nois shows that the period covered by our plankton collec- tions, 1894 to 1899 inclusive, was predominantly one of muini- mum rainfall. The average for the six years is 35.5 inches, or 2.3 inches below the general average. It includes one year, 1894, when the rainfall was only 29.3 inches, the lowest on record, while the remaining years with the single exception of 1898 are all more or less below the average. Omitting 1898, a year of excessive rainfall, 46.6 inches, the average for the re- maining years is only 33.2 inches, 4.4 inches below the general average. The reduction of overflow stages of the river conse- quent upon this lowered rainfall doubtless affected the plankton by the restriction of the breeding areas, the concentration of sewage, and the prolongation of the low-water period with its slackened current. Our collections thus, as a whole, are repre- sentative of a period of minimum rainfall and its attendant 124 low-water conditions. They are, however, fairly representative of the whole range of rainfall and river conditions, including, as they do, two years (1896 and 1897) which approximate the average rainfall, and a year of minimum (1894) and one of maximum (1898) rainfall. The periodicity of the rainfall of Illinois and adjoining states was noted by Leverett (96). There are alternating wet and dry periods of eleven years which correspond somewhat closely in duration to the sun-spot cycle as shown in Plate VI. There is, however, in the sun-spot cycle no recorded alternation of elevation and depression similar to that of the rainfall, the maximum of sun-spot occurrences appearing at intervals of eleven years while those of the rainfall appear in a twenty- two-year cycle. In the diagram this alternation is brought out by the horizontal lnes, which represent the average rainfall for periods of the eleven years included. ‘The first wet period within the time covered by the records of the Weather Bureau lies about 1853-1863, the average being 38.5 inches—only 0.59 inch above the general average, though this amount will be considerably increased if the period is shifted back to include one or two preceding years. These earlier records are, however, less reliable owing to the few places of observation. A dry period from 1864 to 1874 falls 2.96 inches below the general average, while the wet period of 1875 to 1855 rises 2.9 inches above it. The following dry period, 1856 to 1896, falls 3.05 inches below the general average, while the few years of the current wet period already yield an average above the general one. The average difference in rainfall between the wet and dry periods is about 6 inches. Our plankton collections are about equally divided between the closing years of the last dry period and the opening years of the current wet one. A second cycle or rhythm in the rainfall has been discov- ered by Sir Norman Lockyer and Dr. W. J. 8. Lockyer (’00 and 01) as a result of their study of the temperature changes in the sun, with their accompanying sun-spot phenomena, and the 125 rainfall in the region surrounding the Indian Ocean. They have found that the mean solar temperature is followed by a pulse of rainfall. These mean temperatures occur twice in each sun-spot cycle of eleven years, at intervals varying from four to seven years, and are accompanied by the crossing of the iron and “unknown” lines in the solar spectrum, These solar fluctuations in temperature produce atmospheric condi- tions, especially over large continental and oceanic areas, which result in rhythmic pulses of rainfall which have been traced by these authors in the rainfall of India and the snow upon the Himalayas, and in the rainfall of Batavia, Cape of Good Hope, Mauritius, and Cordova. They have also correlated them with the floods of the Nile and the famines in India. On Plate VI. is a diagram taken from Lockyer (01) which shows by curves the fluctuations of sun-spots (which in a general way coincide with solar-temperature changes), and of the iron and “unknown” lines. ‘To this has been added the plot of the rain- fall in [lhnois and the hydrograph of the Illinois River. As shown in the diagram the mean temperature (crossing of the iron and “unknown” lines) occurs twice in each sun-spot cycle, once on the rise in sun-spots (and temperature) (+ pulse), and once on the fall (—pulse). The location of the rainfall pulses of India and elsewhere accompanying these mean temperatures is indicated upon the diagram. A close correlation between these pulses of rainfall and the fluctuations in rainfall in Illinois and in the hydrograph of the Lhnois River is at once apparent on inspection of the dia- gram. The + pulses of 1892 and 1883, and the — pulse of 1876-77 are well defined, while that of 1888 is present though not so pronounced. Similar pulses of rainfall may also be detected at some- what similar intervals in the rainfall of Illinois in the period not covered by the Lockyers’ diagram, 1851-76. Thus + pulses may be located in 1872, 1862,and 1851, and — pulses in 1865 and 1855 or 1858. Another — pulse is probably to be seen in the heavy rainfall of of 1898, though according to the Lockyers’ dia- 126 gram no crossing of the iron and “unknown” lines had occurred though normally to be expected. These unusual solar condi- tions prevailing in 1897 to 1900 were accompanied by irregular- ities in the rainfall in India, and may perhaps also be reflected in the somewhat unusual irregularities in the rainfall records and hydrograph in Illinois during this period. The data avail- able for the discussion of the periodicity of rainfall are so lim- ited that only tentative values can be given to any conclusions upon the subject. The striking conformity of the Illinois data to the Lockyers’ cycle will perhaps justify this discussion. As might be expected, the variation in the rainfall for any given point of observation may far exceed that of the average for the whole state. Thus we find a record of 74.5 inches for Muscatine, Iowa, in 1851, while its lowest record is 25.6—a range of 50.9 inches. These extreme records are gen- erally due to local rains of considerable magnitude, which are often the cause of the sudden floods in the tributary streams of the [lhnois. The seasonal distribution of the rainfall for Illinois is shown in the following table taken from Leverett (96). Spring | Summer| Autumn | Winter | Annual | Cubic miles lin’ CHES. nner eee 10.2 Iyle2 9.0 ae 38.1 34.0 The distribution by months, expressed in percentages of the total, is as follows. r | 0 FON AR ae Ailes Aiea avAnie te sciene pie: x | 2 XII 6.2 | 6.7 7.0 8.2 | FO: || 02.2 go) No.0 g.0 8.5 | vi 6.0 The table shows a minimum in December with a gradual increase to a maximum in June, from which the decline is rapid, with only a shght interruption at the autumnal equinox. The tables given above apply to the state as a whole. An examination of the individual records shows that the south- ern part of the state has a somewhat greater rainfall than the 127 northern part. This is due to the greater precipitation during the winter months in the southern part, the rainfall during the remainder of the year being practically the same in all parts of the state. The Run-off—Highty per cent. of the Illinois River water- shed lies in two principal basins, each with peculiar climatic and topographical conditions. These basins meet at Havana, and consequently the conditions in the northern one constitute a prominent feature in the environment of the plankton at that point. As the two basins lie in different storm-tracks their rain-floods do not always coincide. The southern basin usually parts with its snow several days sooner in the spring, and more promptly, than the northern, since its latitude is more uniform, and, relatively, its floods are larger. The climatic conditions of the southern basin are manifest at Ha- vana principally in the backwater from floods in the lower river, which check the current and delay the run-off from the northern basin. The subject of fluctuations in the volume of water in the river is one of fundamental importance in our plankton work. With rising water comes a decided increase in the current and a rapid displacement of the sluggish waters teeming with mi- nute life by a turbid flood to a large extent devoid of life. With the overflow of the bottom-lands the subordinate lagoons, lakes, and marshes are for the time being obliterated from the landscape, and their peculiar fauna and flora mingled, merged, and swept away with the flood. With the decline of the flood, the unusual prolongation of which in the Illinois River has been already alluded to, a great variety of conditions of current, temperature, depth, light, and vegetation are afforded, the most of which favor the development and diversi- fication of the plankton. ‘The large amount of silt—composed of a wide variety of substances, from an impalpable earthy material to coarse sand and the comminuted debris of vegeta- tion—introduced by flood water presents a most perplexing problem in our quantitative plankton work, Aside from the 128 far-reaching effect that the turmoil of flood has upon the quantity and the distribution of the plankton, there are intro- duced other factors whose influence, though perhaps more subtle, is of no less importance. Such factors are changes in the chemical constituents dissolved in the water, in its temper- ature, in its transparency, and in the relative proportions of plant and animal life. - The run-off of the rainfall of the catchment-basin of the Illinois is influenced by a variety of conditions, all of which are more or less variable. These are the amount and distribu- tion of the rainfall, the slope, the perfection of drainage lines, the geological structure, the amount of vegetation, and the temperature. As has already been stated, the rainfall, amount- ing on an average to 37.858 inches, is distributed with consider- able uniformity—at least in the northern basin, with which we are most concerned. Purely local excesses and deficiencies of rainfall occurring within this area are rarely of sufficient pro- portions or duration to affect profoundly the customary regi- men of the stream as a whole. According to Leverett (96) the slope of the stream beds of the principal tributaries in the northern basin, the Des Plaines, Kankakee, Fox, and Vermilion rivers, 1s on an average in their lower courses several feet per mile, while in the lower two hundred and twenty-five miles of the Illinois itself the slope is only thirty feet or .13 foot per mile. In much of the state the principal streams have an average slope of about two feet per mile; and the small streams, of five to ten feet, excepting the head waters. In the main, therefore, the slope of the stream beds is such as to favor a very moderate run-off. The slope of the general surface is also very moderate. It ranges from ten to twenty feet per mile, being somewhat greater in the newer drift, where moraines are more abundant, than it is in the older drift of the southern basin. The steeper slopes of the newer drift are, however, counterbalanced by the much in- ferior development of drainage lines within its area. There are large tracts of land at the head waters of the Vermilion and 129 Kankakee in which natural drainage channels have not as yet been opened, a fact which has a tendency to further moderate the run-off in the northern basin. The newer drift which covers the northern basin presents a great variation in its structure and consequent effect upon drainage. In general it is less compact than the older drift and offers greater opportunity for the storage of ground water, especially wherever extensive deposits of sand and gravel occur. Storage in such deposits tends to equalize the run-off throughout the year. The basins of the several tributaries present marked peculiarities which influence their contributions to the flood waters of the main stream. The basin of the Des Plaines River is largely underlaid by impermeable rock upon which the drift is twenty to one hundred feet in thickness. The lower end of the watershed alone contains deposits capable of affording considerable ground storage, while the upper end abounds in lakes, bogs, and swamps, which also have a tendency to retard and equalize the flow ofthe run-off. In spite of these equalizing factors the floods of the Des Plaines assume large proportions and, owing to the extent in latitude of the basin, they are often prolonged. A considerable portion of the flood water, under conditions prior to the construction of the drainage canal, escaped over the Ogden dam and through the Ogden-Wentworth ditch and the Chicago River to Lake Michi- gan, following what seems to have been a former channel of the Des Plaines. Cooley (’$9) estimates that the discharge of the normal extreme flood at the junction of the river with the Kankakee is 12,000 cubic feet per second, and that this would be increased to 20,000 if all the water from the basin sought this outlet. This latter estimate is equivalent to the bank-full capacity of the Illinois River at Copperas Creek dam, seventeen miles above Havana. High-water level at the junction is 15.7 feet above low water. The flow at low water is insignificant, amounting in 1887 to less than 16 cubic feet per second for a period of five months. The variations in the Des Plaines thus 130 constitute a very important element in the fluctuations of the main stream, and its contributions of detritus are extensive. The basin of the Kankakee, occupying 5,146 square miles, lies in a single belt of latitude, extending 216 miles in an east and west direction. About 700 square miles of the lower part of the basin have a slope sufficient to afford a rapid run-off,and of the remainder fully one half is swamp and marsh, the other half being flat or slightly rolling, but capable of cultivation. The drift, except in the lower portion, is of considerable depth, and in much of the marshy region extensive deposits of sand are found. ‘The lower stream is also bordered by extensive sand deposits, and these afford a storage basin for the waters derived from the adjacent slopes. Cooley (’89) estimates the mean of the extreme flood-discharges of the Kankakee at its junction with the Des Plaines at 31,200 cubic feet per second, and the mean of the extreme low-water discharges at 500 cubic feet per second. Flood water at the mouth of the Kankakee has been known to reach sixteen feet above low-water level. Aside from the uniformity in latitude, the physical features of the Kankakee basin, under present conditions, favor a gradual run-off, with floods which rise slowly to a moderate height and continue for a considerable period. Owing to the storage facil- ities of the basin the stream maintains a relatively large flow even in periods of prolonged drouth. The Kankakee is thus an important factor in moderating the extremes of high and low water in the [llnois. Its contributions of silt are but shght. The northern part of the basin of the Fox River is similar to that of the Des Plaines, and acts as a storage reservoir; but the southern part, which is of greater extent, has steep slopes, and the rapidity of the run-off is thereby heightened. Leverett (’96) states that its flood waters reach a level of fifteen feet above the normal, and that the discharge, presumably at low water, is 526 cubic feet per second. Cooley (91) gives the discharge of the Fox in the flood of February, 1887, as 18,680 cubic feet per sec- ond. The conditions of its basin are such as to aggravate the fluctuations and to increase the amount of silt in the Illinois, 131 The Vermilion and Mackinaw rivers present common fea- tures of drainage. They both drain till plains of compact drift and have a comparatively rapid descent. The run-off is rapid, and floods are sudden and of extreme proportions. Owing to the absence of head-water marshes the flow in the period of low water is very shght. The steep slope, the rapid run-off, and the cultivation of practically the whole of their drainage basins render the amount of sediment carried by their flood waters very large. The minor streams, such as Bureau, Clear, Copperas, and Quiver creeks, and the rivulets which course down the bluffs from the adjacent uplands, differ from the streams last described only in the greater steepness of their slopes. This, added to their proximity to the main stream, makes their run-off very rapid. The clearing away of the forests and the cultivation of the hillsides also add to the debris which they carry. The varying contributions of these tributary streams com- bine to produce the fluctuations manifested in the main stream at the point where the plankton work of the Biological Station has been done. There are also other factors influencing the stage of the river at this point, notably the fluctuations of the larger tributaries below. as Spoon River and the Sangamon. Owing to the shght fall from Havana to the mouth of the river —only 20.4 feet*—the stage of the Mississippi River may mate- rially affect the gage-reading at Havana. High water in this latter streams prolongs the floods in the Illinois, or even turns the current up stream, as in 1844, when, as I am informed by Hon. J. M. Ruggles, of Havana, the up-stream current came within five miles of that place. The Volume Discharged.—Streams in fertile regions of the north-temperate zone usually discharge but little more than one cubic foot per second per square mile of watershed. ‘Thus the mean discharge of the Great Lakes is about 1) cubic feet *Based on Cooley’s figures in “ Lake and Gulf Waterway,’ Appendix I. Rolfe’s survey makes it 29 feet (Rolfe, ’94, p. 133), though other data in his possession make it 26.24 feet. 132 per square mile, while for some of the reservoir tributaries of the upper Mississippi, which include regions of less rainfall, it is estimated at about 0.75 cubie foot per mile. There have been as yet no adequate measurements of the flow of the Illinois River at its mouth, and no extended gagings at any point on its course aside from the observations made by the U. 8. Army Engineers at LaGrange, and a few isolated records and estimates at other points. The average flow of the river has been estimated by Cooley (97) to be under rather than over one cubic foot per second per square mile of watershed. Upon this basis it would be somewhat less than 29,000 cubic feet feet per second, or 915,- 170,400,000 cubic feet or 6.2 cubic miles per year. Measurements made in 1882 at Hannibal and at Grafton in the Mississippi River above and below the mouth of the Illinois indicate that the discharge of the Illinois River ranges from 11,000 to 89,000 cubie feet per second, with an average of 30,- 000 cubic feet. This is equivalent to a maximum run-off of nearly 3 second-feet per square mile, a minimum of 0.4, and an average of 1.1. In 1882, one of the wet-year series, the river was out of its banks during the greater part of the year owing to the heavy rainfall which, throughout the state as a whole, was 18 per cent. in excess of the average. A reduction of 18 per cent. from the average flow of 1882 leaves 24,600 cubic feet per second, or 0.902 of a second-foot per square mile, as an esti- mate of the mean annual flow of the Illinois River. Cooley’s estimate (97) of the average run-off of the upper 15,250 square miles of the basin, based upon the gage-readings at Copperas Creek for eleven years (1879-1889), is 10,500 cubic feet per second, or 0.688 second-foot per square mile. This is 25 per cent. below the above-given estimate, based on Greenleaf’s measurements at the mouth of the stream. Accepting these two estimates as approximately the average, and adopting the calculation for the river at Copperas Creek as applicable to Havana, eighteen miles below, we have the average run-off at our plankton station approximately 0.688 second-foot per square 133 mile, or 10,570 cubic feet per second—a total, for the year, of 333,963,832,000 cubie feet, or 2.27 cubic miles. The run-off in an ordinary year is equivalent to a trifle over eight inches of rainfall in the whole watershed, or 21% of the total rainfall for the year. Greenleaf (’85) states that the area of the entire catchment-basin of the Mississippi is 1,240,039 square miles, and that the average discharge per second is 675,000 cubic feet, or only .54 cubic foot per second per square mile. The Illinois, with one forty-third of the catchment-basin, thus contributes one twenty-third of the discharge. Greenleaf’s estimate of the discharge of the Illinois, even when reduced to 0.908 second- foot per square mile, places the stream in the category of the St. Lawrence River, whose discharge is shghtly in excess of one second-foot, rather than with the Mississippi River, whose total discharge is but about half that amount. The average dis- charge from the [linois is thus somewhat less than that of the Connecticut, of the Hudson, or of the Seine ; is about the same as that of the Delaware and of the Elbe; but is much lessthan that of the Loire and of the Po, and relatively less than that of many European streams. The maximum flood discharge of the Illinois has been vari- ously estimated. On the basis of normal basin ratios for streams of like chmatic conditions it should be equal to the two-thirds power of the area (A%), which would be about 123,000 cubie feet per second. The exceptional flood of May, 1892, the crest of which at Kampsville had a height of 22.8 feet above low water, was reported by the engineers of the Chicago Drainage Commission to have discharged only 94,760 cubic feet per second at the mouth of the river. Cooley (797), basing his estimate upon the discharge curves of the Mississippi at Hannibal and at Grafton, states that the maximum discharge seldom exceeds 70,000 to 80,000 cubic feet per second, and that a flood of 16 feet —a height which ordinary floods rarely exceed—would approx- imate only 55,000 cubic feet per second. The maximum dis- charge is thus considerably below what is to be expected, and the explanation hes in the delay in the run-off due to the im- 134 pounding action of the bottom-lands, a phenomenon which will be discussed later. This discharge occurs most often in March or April, or in June, and rarely, if ever, in the late summer or fall, from July to December. The minimum discharge of the Ulinois is, for a stream of its size, extremely small, indicating the impermeability of the strata of its basin and the slight contribution of ground water to its volume. According to Cooley (91) the discharge over the dam at Copperas Creek for a period of low water continuing for twenty days was less than 500 cubic feet per second, or 200 cubic feet less than the amount sent through the [lhnois and Michigan Canal by the operations of the Bridgeport pumping works. In conclusion Cooley says: “It is probable that since the Bridgeport pumps were erected, in 1883, over half the min- imum discharge above Havana has come from Lake Michigan, and one third of the minimum below the Sangamon. For the purposes of calculation, the normal low-water volume is taken at 600 cubic feet per second for the upper section of the river and at 1,200 cubic feet for the lower section.” The minimum discharge occurs most frequently in the late summer and early fallin August, September, and October,—and occasion- ally in the early winter months. THE REGIMEN OF THE ILLINOIS RIVER. Leverett (96) gives the following as the usual regimen of an Illinois stream: ‘During the winter, when the ground is frozen and precip- itation is comparatively light, the streams are low. In early spring the thawing of the ground and the greater precipitation lead to a spring freshet, when the streams are often bank-full, or even overflowing. This freshet usually occurs in March or early in April. For a few weeks after this freshet the streams are at a moderate stage, shghtly above the normal. This is followed by the ‘June rise,’ occasioned by the great rainfall which occurs in that month, when the streams often reach as high a stage as in the spring freshet. After the June rise the 135 streams usually drop to a low stage and remain low through the heated term, evaporation and absorption being so great as to dispose of nearly all the rainfall. In the autumn, about the autumnal equinox or a little later, heavy rains occur, which cause the streams:to become swollen for a few days, or even weeks, but which seldom cause them to overflow their banks. In some years these seasonal variations are shght, and the streams show but little change in volume, but such years are exceptional. The rainfall is seldom sufficient to cause freshets to last more than a few days. The moderate and low stages are estimated to generally cover ten months of the year, and occasionally eleven months.” In the Annual Reports of the Chief of Engineers of the U.S. Army for the years 1890 and following, Captain Marshall has published the readings of the river gages located at the govern- ment dams in the Illinois River. The readings at Copperas Creek, 16.8 miles above Havana, begin in 1879, and those at LaGrange, 42.7 miles below, in 1883. The dam at Copperas Creek was completed in 1877 and the one at LaGrange in 1889. On Plate VII. will be found hydrographs plotted from the daily readings at the gages below these dams from 1879 and 1883, re- spectively, to 1900. The heavy sinuous lines represent the fluctuations of the river, referred in the plot to the low-water level of 1879. The mean annual curve was plotted from the mean monthly readings at the above-named localities from 1879 and 1883, respectively, to 1900. Deficiencies in the records at the two points named have been supplied, by estimate, from records at nearest point of observation, in a few cases from our Havana records. A comparison of the hydrographs of the gages at Copperas Creek, Havana, and LaGrange reveals a close correspondence in the fluctuations, and suggests that these main movements are due to general rains or spring thaws coincident in the greater part of the drainage basin. The differences are of a minor character, and many of them are consequent upon local conditions of rainfall. On closer inspection the records at Cop- 136 peras Creek and LaGrange exhibit certain general differences which are not thus explained, but result from some more widely operative cause. Asa rule the extremes of high and low water are more pronounced at LaGrange than at Copperas Creek. This is apparent in the hydrographs of 1883, 1893, and 1896-98. “It is also expressed in the tabulation (Tables I. and Il.) of the ex- tremes of high and low water at Copperas Creek for twenty-one years (1879-1899) and at LaGrange for seventeen years (1583- 1899). The average range between highest and lowest water at Copperas Creek is 13.14 feet, at LaGrange 14.68 feet—an in- crease of 1.54 feet or 11.5%. In like manner the average of the total + and— movements per year of the river level at the upper dam is 50.5 feet to 59.15 feet at the lower one—an in- crease of 17.1% in the fluctuations of the stream at that point. The greater fluctuations probably result from the fact that in the lower basin, within which the lower dam lies, the rainfall is greater, the drainage lines better developed, and the run-off more rapid. The reservoir action of the Des Plaines, the Kan- kakee, and the pumps at Bridgeport are also less effective in regulating the flow of the stream at this point, owing to their distance and to the reduction in their relative contributions. The distance, by river, from Copperas Creek to Havana is 16.8 miles; from Havana to LaGrange is 42.7 miles—a total of 59.5 miles. The fall between the two dams is given by Cooley (91) as 8.5 feet at natural low water. Our plankton station thus hes in the upper and more evenly regulated portion of the LaGrange pool, and probably in the most stable portion of the river between Utica and its mouth. The dam at LaGrange is estimated by the engineers to raise the water 8 feet at LaGrange, 2.4 feet at Havana, and 2 feet at Copperas Creek. As has been stated on page 115, prolonged low water will lower the level at Havana to 2 feet or even less. At such times the river between the two dams is practically a slack-water pool, which responds quickly to flood water from any source. Two principal tributaries, Spoon River and the Sangamon, enter this pool from opposite sides of the river, the former $ mile above 137 Havana and the latter 22 miles below. During the summer season, when local rains occur, it sometimes happens that a storm is confined to the basin of a single tributary, especially as the Sangamon and Spoon rivers lie, according to Cooley (91), in different storm-tracks. In such cases the effect may be very evident at one gage, but be dissipated in large part be- fore it reaches the other. The progress down stream of floods which originate in the upper valley varies with the abruptness and extent of the rise and with the stage of water in the lower [llnois. As stated on page 117, it took 15 days for the crest of a flood to pass from Morris to the mouth of the Illinois, a distance of 259.2 miles. Compar- isons of the gage-readings at Copperas Creek and LaGrange show that the progress of the crest of the flood between the two dams is subject to great variations in duration. In some instances the culmination is reached upon the same day at both dams; 1n rare instances it is reached at LaGrange several days before it is at Copperas Creek, probably as a result of excessive flood water from the Sangamon. In the majority of cases, however, the maximum height is reached at the upper dam in from 2 to 3, or even as high as 7, days before it is at the lower dam. This delay is due to a variety of causes, of which one of the principal ones is the impounding action of the bottom-lands. FLOODS AND THE IMPOUNDING ACTION OF THE BOTTOM-LANDS. Owing to the shght development of its flood-plain, overflows occur at early stages of the rising river. The appended table, adapted from Cooley (91), gives data pertaining to bank height and bank-full capacity of the river at various points along its course. It will be noted that the bank-full capacity at Kampsville is 40,000 second-feet, only one third more than Greenleat’s (’85) estimate of the average discharge at that point. At Copperas Creek, on the other hand, the more moderate estimates of Cooley (91) place the average discharge at 10,500 cubic feet 138 per second, while the bank-full capacity is estimated at double this amount. In either case complete overflow stages appear more readily than they do in the majority of streams. The impounding action of the bottom-lands, on the other hand, begins with every rise of the river, for as the water rises large amounts are drawn off from the main stream by the adjacent lakes and bayous, many of which retain their connec- BANK-FULL CAPACITY OF LOWER ILLINOIS RIVER. Distance Bank Height Cubic feet Locality | from Utica (feet) per Remarks | (miles) Aye Range second Peru ae nee 6.2 10.4 87301) 18,000 —22,000' Measured in 1889. Varia- tion according as river is rising or falling Jaleniniyag Bae Bae 9.4 g—Il 20,000 —22,000|/Very tentative estimates from dam and prison Copperas Very tentative estimates (Creek .| 92.7 to 7) IZ—15 18,000—20,000| from dam and prison Havana Lee 109.5 10° 716 LaGrange . i D52e2 Tes 8—I5_ | 30,000 Measured in 1889 Kampsville.. 197.8 11.8 8—I5 | 40,000 Estimated from measure- ments in 1889 tion with the river even at the lowest stage. In the vicinity of Havana, for example (see Plate II.), Quiver, Thompson’s, and Matanzas lakes respond at all times to fluctuations in the river. Flag Lake is invaded at about the stage of 3 feet, and at 5 to 6 feet the water begins to overflow the bottom-lands between Flag and Thompson’s lakes. It is not, however, until the river has reached a stage of 8 to 9 feet that the water enters Phelps Lake. The wooded bottom-lands to the east of Flag Lake are not en- tirely submerged until the gage reads 12 feet, while those below Spoon River and adjacent to the main stream do not disappear until the water has reached 16 feet. Thus the impounding action of the bottoms is at its greatest as soon as the water reaches the condition of complete overflow, though it begins at the first stages of a rise above low water. In his discussion of this subject Cooley (91), speaking of 139 the inadequacy of the stream for the prompt removal of flood waters, says: “This lack of capacity, while it explains the wide and deep overflows, by no means implies that any large pro- portion of the volume moves down the valley for considerable distances except in the river bed. The dense timber and the vegetation in summer, the higher ground leading across from the bluffs along every tributary, the occasional approach of bluff, terrace, or ridge, the frequently returning sloughs from interior ponds and lakes, all forbid this. The bottoms are really storage grounds to impound the flood waters that arrive faster than the chanuel can carry them away, and they prolong the floods in some inverse ratio to the reduction of volume.” Observations made in the course of field work during the floods of 1896 to 1900 at Havana, lead me to suggest that there may often be developed a fair current outside of the channel of the main stream in such localities as Thompson’s, Flag, Quiver, and Phelps lakes (Plate II.), where a considerable reach of open territory lies in the general direction of the main cur- rent. Even in the wooded districts the current may not be wholly absent, though it is often very slight. The duration of the overflow in various parts of the valley illustrates the reservoir action of the bottom-lands. In the period from 1883 to 1889 the river was out of its banks at Morris 60 days, or 8.5 days per year; at Copperas Creek, for 444 days, or 63.5 days per year; at LaGrange, 526 days, or 75 days per year. I quote from Cooley (’91)the following discussion of this subject: “A better appreciation of the reservoir action, or equalizing effect, of overflows may be obtained by a consideration of the impounding area of the bottoms. An area of 704 square miles submerged to a uniform depth of four feet—this is a flood height of sixteen feet and not an unusual occurrence—represents 1.21 inches of water running off the entire watershed, and will sup- ply the river at the rate of 110,000 cubic feet at the mouth for 8.26 days, or at half this volume, which is an approximation to the true maximum discharge, for 16.52 days. An overflow of eight feet, or a flood of twenty feet, which is an extraordinary occurrence, represents 2.42 inches of water running off the 140 entire watershed, and will supply the river at the rate of 110,- 000 cubic feet for 16.52 days, or at half the volume for 33.04 days. * * * During flood stages the valley is a great lake of, say, 700 square miles, into which flood waters from above and from tributaries are precipitated, and from the lower end of which they run out more at leisure and in reduced and equalized volume.” When we remember that even in the average year over 21%, or more than 8 inches, of rainfall escapes by way of the river, that the greater portion of this run-off takes place at times of flood, and that the overflows are greatly prolonged in the lower river by the inadequacy of the channel to carry off the excess of water and by the imperfect development of the flood-plain consequent upon the past history of the valley, we realize how important, and at the same time how unique, a fac- tor is the retardation of the run-off in relation to our plankton operations. The past decade has witnessed the completion of a vast amount of surface and under-drainage throughout large areas in the watershed of the Ilhnois River. Extensive open ditches have been dredged through localities where the slope or other conditions do not favor the establishment and maintenance of natural channels. These have been supplemented by miles upon miles of tile drains, thus bringing under constant cultiva- tion hundreds of square miles of territory occupied in former years by pond, marsh, or meadow of the original prairie. Even in the rolling prairie the thousands of little ponds and marshes which formed the head waters of the various tributaries of the river have been blotted from the landscape by the tile drain. In addition to this the natural lines of drainage have been sup- plemented in a great many cases by under-drainage, in order to facilitate the run-off of the rainfall and the ground water, and thus bring the soil as soon as possible into condition for culti- vation. This work of drainage is to a great extent completed throughout a large part of the catchment area. The principal exception is the basin of the Kankakee River, but the drainage of even this has already been projected, 141 The outcome of this wide-spread interference with the established condition of natural drainage has given ground for the almost universal testimony that streams which in former years held a continuous flow throughout the summer no longer run in the dry season. The reservoirs at their head waters are emptied and the supply of ground water is early exhausted by the artificial drainage in their basin. There is also a consider- able concurrence of opinion that, in the smaller streams at least, the floods come more suddenly and rise to greater heights than they did in former years. The “wash” along the banks and consequently the amount of silt carried in suspension by the flood waters are thus increased. The presence of under-drainage undoubtedly facilitates the discharge of such water as reaches the drains, but this impetus is in large part counteracted by the greatly increased power of absorption of the soil when thus drained. Heavy rains upon a soil already surcharged with moisture may lead to even a greater run-off than the same rainfall upon the same territory rendered porous and capable of absorbing and retaining, for a short time at least, a large amount of moisture. From many points of view the subject of the effect of drain- age of the catchment-basin upon the flow of streams is one of interest and importance. For its adequate discussion records | of a long series of years of the stages of tributary streams and the river both before and after the installation of the drainage system are needed. With a view to throwing some light upon the possible effect of drainage upon the floods in the main river, and consequently upon the plankton, I have tabulated the fluctuations (in excess of .25 foot in 24 hours) in the river level at the lower gage at Copperas Creek for an earlier and a recent period, each of five years. The earliest authentic records which I have been able to secure begin with 1879. This antedates the completion of a considerable portion of the artificial drainage of the river basin. I have accordingly chosen the records of 1879-1883 inclusive for comparison with those of 1892-1896 inclusive. This choice is unfortunate in one respect, for the earlier series lies in a period of heavy rainfall and the later in- 142 cludes two years of unusual drouth. The fact that the earlier period is in a series of wet years and the later in one of dry years will, it seems, tend to obliterate whatever contrast may exist in the rate of the fluctuations. Thus the extent of the fluctuations is much greater in the earlier period and the dura- tion of high water is longer. The river was above the six-foot level during 1,028 days in the first period, as against 709 in the second; and it was above ten feet, that is ata stage of overflow, 645 days in the earlier period, and only 297 in the later one. The dam at LaGrange, completed in 1889, raises the water 2 feet on the lower gage at Copperas Creek at the low-water stage. Its effect at the stages above cited is not, however, according to Cooley, perceptible at the upper end of the pool. The results of the tabulation do not reveal any alarming changes in the flood habits of the river. There is, however, a well-defined increase in the rate of movement in the later period as compared with the earlier. The average daily movement (above .25 foot) is in the first period .416 foot, in the second period .492 foot,—an increase of 18%. The difference is still more marked when the comparison is made in the rate of rise alone. In the earlier period the rate of movement (in excess of .25 foot) was .4848 foot per day; in the later period it was 592 foot; an increase of 22%. The distribution of this increase through the year is somewhat irregular, and, owing to the in- sufficiency of the original data, is probably of slight significance. The greatest increase occurs, however, in the months of May, December, September, and March, all months in which floods prevail, or at least occur occasionally. As shown on previous pages the conformation of the valley is such as to induce a prolongation of the floods. The records and the hydrographs show that the decline from a rise is in most cases much less rapid than the approach of the flood. We find accordingly in the above table that the number of days of decline (at a rate exceeding .25 foot per day) is considerably less than those of rising waters, and that the rate of fall is also less than the rate of rise, being only .3185 and .387 foot, respec- tively, per day, in the two periods. 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So far, then, as the table goes, it indicates that there has been a moderate increase in the rapidity with which floods rise and a slight increase in the rate of their fall, as compared with the rate of their movements in a pores nontene period thirteen years ago. It is impossible from data at hand to determine whether or not the general drainage of the basin has shortened the period of high water and extended that of low water with a consider- able diminution of volume at low-water stage. The decade prior to 1896 seems to have witnessed such a change, as hydrographs on Plate VII.show. This diminution is the more marked when allowance is made at low-water stages for the 2 feet which the dam at LaGrange (completed October 12, 1889) is estimated to raise the water on the lower gage at Copperas Creek. The fact that the rainfall was deficient during this decade. doubtless MONTHLY MEANS OF GAGE-READINGS (IN FEET) BELOW COPPERAS CREEK DAM 1879-1899. (Basis of reference, low water of 1873 and 1879.) Year | Jan.| Feb. Men ee May June) July Aug.|Sept.|Oct.} Nov.| Dec. nee 1879 2.76 6.20] 8.66 10.80} 5.52) 2 66 4.53| 2.09] .30/1.03] 2.19] 5.24] 4.33 1880 9.88] 9.83] 9.65/10.15]12.39| 9.90] 7.48] 2.83] 2.90]2.32) 1.69] 1.58] 6.72 1881...) 1.48] 7.88/14.69'14.72|11.41| 9.01] 4.89] 2.04] 1.22|4.74]10.69/13.88] 8.05 1882... .|12.47| 9.61/13.87|12.43]12.91/14.65|11.64| 6.10] 4.06]3.29] 4.22! 5.08] 9.19 1883...| 6.58/10.01]14.95|12.60]11.85/11.57) 9-43, 5.83) 1.94|2.91] 8.48] 9.63] 8.82 1884 6.58]12.23]/13.54|13.55]10.57| 7.57) 6.41] 3.49] 2.82/7.89] 6.22] 6.91) 8.15 1885... .|13. 12/10. 31/12. 33]13.69]11.12) 7.34) 4.90] 5.04] 6.06/6.68/10.30] 9.07] 9.16 1886... |12.28|12.67/13.24/12.85|12.37| 8.87) 2.85) 1.78) 2.24|3.13| 2.01) 2.07) 7.32 1887...| 4.29]13.05]12.48] 7.77] 3.86] 2.40) 1.62] 1.40] 1.83/2.38] 2.09] 3.49] 4.72 1888,..| 6.48) 7.47/12.87|11.75| 7.81/10.18] 8.31] 4.05! 1.86]1.91] 2.85] 2.59! 6.51 1889...| 4.52] 3.84 18] 6.24| 3.88) 8.81| 8.80] 4.44] 1.30/2.47| 4.10} 6.03) 5.30 1890... 9.56] 9.31] 8.98|11.24/10.07|10. 46] 7.86] 3.17| 2.66)3.16] 3.32] 3.52} 6.92 1891...| 3.67] 4.08] 8.00]11.94] 9.23/.6.85] 4.73] 3-13] 2.41|1.93| 2.47] 4.24] 5.22 1892...| 4.58] 5.53] 6.88/11.44/16.46)14.52/13.41| 7.14] 3.31/2.83] 2.90] 3.77) 7.74 1893...| 3.87] 7.69|14.90|12.60/13.74|10.37| 4.93] 1.73] 1.67|2.42| 2.54] 3.33} 6.63 1894...| 3.92] -4.29] 9.24] 7.40] 7.29] 4.63] 2.32] 1.99] 4.43/2.96] 2.97] 3.41] 4.63 1895..-| 3-30] 3.51| 6.28! 5.41] 3.68] 1.88] 3.17] 2.43] 3.42/1.93] 2.20] 6.16) 3.61 1896... 10.65] 9.23] 9.79| 7.66] 7.35] 7.73] 4.38] 7-70] 4.66/6.37| 6.10] 5.64) 7.26 1897... /11.39|11.04/14.09/13.34] 9.52] 5.71] 6.19] 2.36] 1.81]/1.76] 2.42] 3.06] 6.86 1898 5.10] 9.31/13.25]14.69]11.49/11.49| 5.50) 3.52] 4.29/4.28] 7.79] 6.92] 8.11 1899...| 8.47] 7.28]/13.07|11.24| 7.86] 7.58] 4.05] 2.71] 2.24/2.54) 3.64] 4.56] 6.27 Means for 21 vears! 6.90] 8.20|11.34|11.11| 9.59] 8.29] 6.06] 3.571 2.82/3.271 4.38] 5.271 6.74 145 MONTHLY MEANS OF GAGE-READINGS (IN FEET) BELOW LAGRANGE DAM 1883-1899. (Basis of reference, low water of 1879.) Year | Jan.| Feb.| Mar.j/April] May | June] July | Aug. Sept.!Oct. Nov.| Dec. nee 1883)... 7. 41'11.36 16.71 12.77|12.18]13.04|10.34] 5.62] 1.67,2.52] 6.89] 8.81] 9.11 1884...| 6.09/13.04/14.17\14.92|11.22| 8.66] 6.42) 4.04] 2.74/7.62] 6.01] 6.70) 8.47 1885... |14.17|12.06/13.84/14.20]12.48] 7.99] 6.40] 4.72| 5.18)/5.69] 9.32] 8.15] 9.52 1886, . .|12.83/13.77/14.24113. 79 12577 G2 31) 22 79|| Tosalt P208|253) 2erz2.s2l) rar 1887...| 3.70|12.71 13.64| 7. 3G|- 3.75] 1.70) O.72| 0.23] 0.2410: 76] 0,83) 2.251 3.99 1888...| 6.25} 7.62] 9.87,12.01| g.02/10.78] 8.61] 3.93] 1.21/0.95| 1.79] 2.05] 6.17 1889*, .| 4.33! 3.59] 7-27| 5-78] 3-72] 9.48] 9.05) 4.00] 2.45/0.92| 3.75) 5.43] 4.98 1890... .|10.22] 9.41} 8.92|10.43] 9.39] 8.82) 6.83) 1.39] 1.11/1.58] 1.86] 1.92] 5.96 1SO1...|-2.21| 2.67| 6:06|10. 13) 00] 5. 18|| 3.56, 2. 16) '0.92/0.32) 1:23) 2.83) 3-86 1892...| 3.42! 4.84] 6.69 12.70/17. 16)15.97/14.39| 5.84 2.131129 1.69! 2.94] 7.42 1893...| 2.46] 8.31/15.44 13.74|15.87|12.00] 4.24] 0.68 0.34|1.28 1.09] 2.24] 6.45 1894...| 2.70] 4.19] 7.38) 6.28) 5.80] 3.24] 1.26) 0.57) 2.96/1.56] 1.73] 2.12] 3).30 1895...| 1.96] 2.70] 4.98] 4.05] 2.32] 0.73] 1.96] 1.55] 2.74/0.86] 1.02] 4.99] 2.49 1896... .|10.06) 8.64] 8.92; 6.61} 5.90) 7.09} 4.77| 7.59] 4.32|5.28] 5.20] 4.85] 6.60 1897. :|I11.50,10.95|14.50,15.49|10.28) 4.99] 5.65] 1.80] 0.98/0.86| 1.43] 1.93] 6.67 1898... 4.55| 9.09/13. 15/16. 33/12.74/12.85] 5.44] 3.29] 3-96/3.57] 6.75] 6.40] 8.14 1899...| 7.87| 7.87|13.79|11.58] 8.92) 8.93) 3.94] 2.28] 1.08/1.23] 2.45] 3.19] 8.09 Means for 17 years.! 6.57| 8.40]11.15/11.07| 9.56] 8.28] 5.67| 3.01| 2.11|2.28] 3.25] 4.07| 6.40 *Dam practically completed in November of this year. accounts for much of this change. Records during a period of abundant rainfall are necessary for an adequate discussion of the problem. The foregoing tables give the monthly means and monthly and yearly averages at the two dams for the period above named. In Tables I. and II. are to be found tabulations of the ex- tremes of low and high water, the range of movement, and the total of the + and — movements for each month in the periods covered by the records at the two dams. The appended table also gives some data pertaining to the major fluctuations at Copperas Creek. The rainfall statistics refer to the state as a whole and are taken from Leverett (’96). From the data presented in the hydrographs and these tabulations the variations and the average condition of the Illinois River may be determined, and some estimate made of the normal regimen of the stream. In general terms this is as follows: There is in each year a period of high water—that 1s, 146 FLUCTUATIONS AT COPPERAS CREEK. Months’. ° me OO AN Os oS tetra wnMN iS) fest Shea cg . Roan +0 Ss ee Zz [eSB OS ees - wonmtHOo oO rs eeces oe) [eo Rep cris or MAN] +tMK a. +tO0O O +0 vo +qOtA tA N 1 . AAAI AaOO BO Oo+r+agoag x eanann >, AN mum1n000 = MHuNnNONRM = ee Te aa or = eS Sah SDS o maoco + MO c 1O oO MUMiWM00 ae iinet ane hess > Ooo 4H Nm iS AO WMW+MN)O = INNO O00 ‘ _ =| or coo0own u tostAN tO = = Nuon Ot+H tIiMmO0 ~DO O DAABDDAOD 00 00 00 00 00 00 -_ = = Sete HIGHEST AND LOWEST WATER, RANGE, AND TOTAL MOVEMENT, BY MONTHS, OF RIVER LEVELS FROM GAGE-READINGS AT COPPERAS CREEK, 1894-95, AND AT HAVANA, 1896-1899. (Plane of reference, low water of 1873.) moon st + [pve eho | eiiaueet HAOQMnn es mb COEDS Bf SAA ellos te 12, naticd bed 7 TNs 5) Revo ge || so telee sshcs Re ATANO SOU | BES \ eat |Qmemesop | St EI Sw CATCH 1 o ShiENy || LOGIC Cs Sie co NnAOntst a jsamo’7T | PAGSLS > ADO FH + } et Cae Seg yoSIH | Sata svn H {ioneso Wy | tee or INaATwoOTOW 3B DSS Cesc a a Beet | Ee aR Uae Ss TS IN04 Ol | Ae ee Sar are Peso ede OHTA | eos dedio ) Bie ees) JHOMBAOW | indoor Tra Sen SASS) = esuey [inst or TAROAMSA < EMO'T | SF Sic Aa | SSesesece yoyo AL ROM wot ' 1 TROHNS JUSIIOAOW | rare CANES ea a aSURY | Gants “ © Ede Nesie alien Ss SOMO'T | Huger ads ' Laienthent Se] SSeS foie EEE ' MBO Ons: JUOMBAON | AF ciws al H PROMOS tT =| osuey, atenett a [aad = $S2EMO'T | aia Su ‘ aa Big | BMQVED ySoy ol FraddsS Juemeaoyy | SCeLNS.S s AAAS te, asury | DO4tSt 3 Santora 3 PSamMory nose vawinmo a ATO FOI a) Se SAS SOUSA | Hear 0 re 228585 TPIOK | DDHHDDODH an ih on hoe on holed JIMA OW | ADrONM | | wt i anttot bu iS) : Als italloh ole) H asuey | onsotud meee L k lnQut wer z yseMO'T | GU Saad i ' 2 ~ Seo & * sys | sdiascnost ic} ton oe oon on oe onl TESORO IES IGN09 190 JUITUBAOTN | Sr dncies - v 3 [oor ntt = eBUueY | ssascad ' = 5) : rOmMnone amo-yT | CHMSVS 2 POMOT | Gata s A 3 OQ rt Cyn CY a : z OYA | AGS ww PSEA RES _ | wemeaow | Sdaada x iar nHatS Fs IsUeY | soaewa a eeien Oms Cals = SOMO | Tawa 4) 4 oomnr+ oy sIA ANSMHat Parmooard JUSMIOIAOTN | Gato K 3 w {Stes 8B esse | adascasd 2 Toro eS Tiladtaca roatann ISOUDIA | Sai Sass {Leese » | ASMOAOW | tranosn 7) 2 [ROC ORO SON, b= asuey ATO nAOnn o rONorna ~ Le at ae aye’ 4 WSOMO'T | Gatada ® n & 00 SNH ISOUDIA | rusagaiwscs SOKO | ee yu Wj) adtara > | ein 1ESELO KOO TEN =O o 9SUEM | Gaiaiaid7 on 2 | wNocnaon P| 3S9MO'T | Gaiwinaia ae AMDOrS OUTTA | ig osus SoRnRe TPIK | ann nnD Sn onl on oe on ol from year to year in the S It is evident that the change conditions of the river environment are such that they must be taken into consideration in any study of the fluctuations of the plankton. A glance at the general hydrograph (PI. VII.) shows that the years of our plankton work at Havana practi- cally include the extremes of conditions in the river; no two , and both typical and aber- ~ Ne years present the same fluctuation 164 rant hydrographs are found. In the discussion which follows, the average or “normal” conditions and figures pertaining thereto are based upon the twenty-one years of record at Cop- peras Creek, eighteen miles above Havana. The year 1894 (Pl. VIII.) is typical in that the high- and low-water periods are normally located as to season and also in the presence of a March, June, and September rise. Both the extreme and average heights for the year, 10.4 and 4.63 feet respectively, are, however, much below the general aver- age (15.8 and 6.74 feet). The high-water period (above 8 feet) is shortened to three weeks, and the overflow stage is thus al- most eliminated. The concentration of the sewage in the nar- row limits of the channel during the early summer favors the greater development of the plankton. With the exception of the September rise the extreme low water continued without interruption for a period of eight months—till the last of Feb- ruary, 1895. These are conditions which cause the drying up of extensive backwater areas, and also the development of a large amount of aquatic vegetation in those lakes and marshes which remain—a circumstance which reduces their plankton, and their contribution, if there be any, to the river. The auton- omy of the river plankton is thus emphasized in such a year as this, which may be briefly characterized as one of predom- inant low water and unusually stable conditions. In 1895 (Plate IX.), another low-water year, we find, on the other hand, little that approaches the normal. There is, to be sure, a diminutive March rise and a sharp but very brief equinoctial one, with very low water in the autumnal period. The abnormal features are the failure of overflow, the long low stages,—almost ten months, with unusually low water in Feb- ruary and June,—the July rise, and the December overflow. The extreme low water of the year is apparent in the average, 3.61 feet, the lowest on record in twenty-one years. The low water in the winter combined with ice produced a stagnation fatal to the plankton, while the June minimum favored an un- usually large development for that season. The July, Septem- ber, and December rises flushed out the river. he low water 165 of this year, following that of the previous year and combined with the absence of overflows with rise and current sufficient to lift and carry away the vegetation, resulted in a very unus- ual growth of the aquatic flora in the lakes and even along the river margins. The conditions prevailing throughout the greater part of the year thus continued to favor the autonomy of the main stream noted in the previous year. In brief, the year may be characterized as one of extreme low water, with some minor and unusual fluctuations. The contrast with 1594 is best seen on comparison of the total movements of the two years, viz., 39.98 and 51.75 feet respectively. The year 1896 (Pl. X.) is one of still more unusual char- acter, since it presents a series of bimonthly rises culminating in step-like succession throughout the year. In none of these, however, save the initial one, is more than a very moderate stage of water reached. This results (Pl. VII.) in a reduction of the normal March flood, the isolation of the June flood in the hydrograph, and the submergence of the September rise between the abnormal rises of August and October. The gen- eral result of such a series of rises is to bring the average level for the year up to 6.98 feet (7.26 at Copperas Creek), 0.71 feet above the general average, though the rainfall for the year is slightly below normal. The increased average height does not, however, in this case carry with it the usual extension of the flood period. The river was above ten feet for less than a month and above eight feet only three months. The overflow stage was thus slight, and in addition it occurred in the first months of the year, during the winter minimum of the plankton, while during the spring months, when the normal overflow occurs, the river was ‘practically confined to its banks. The succession of minor floods and the slight increase in the average level does, however, greatly extend the reservoir action of the permanent backwaters. The repeated floods also had the effect of clearing out the vegetation in the river and lakes where some current develops, as, for, example, in Quiver Lake. This reduction in the amount of vegetation in the reservoir 166 waters is accompanied by a considerable increase in their plankton. This fact, combined with the increase in the vol- ume of their contributions due to higher levels, augments the relative importance of their share in the formation of the river plankton, tending to increase its quantity and variety. On the other hand, the repetition of floods, no less than eight of which may be found in the hydrograph, flushes the river so often that no concentration of sewage and marked maximum of plankton occur. The unusual extent of these movements is apparent when the total movement for the year, 50.7 feet, is compared with the totals of other years having about the same average height. For example, 1890 and 1897, with an average height of 6.9 feet, have a total movement of only 44.2 and 36.56 feet respectively. In brief, the year was one without extended overflow, with lower water than usual at the normal flood sea- son, with prolonged bank-full river and reservoir action of the permanent backwaters, and with more than the usual turmoil, In 1897 we find a hydrograph (Pl. XI.) which approaches the mean closely in its main features, and exhibits all the ex- pected movements excepting the equinoctial rise. The average height for the year, 6.90 (6.86 at Copperas Creek), is also near the general average (6.74). The year thus approximates the normal. The high-water period is of 141 days’ duration, al- most exactly the average (140), but it occurs somewhat earlier in the year and attains 16 feet—a little more than the usual height. The earlier decline renders more prominent the June rise, and gives an early start to the extreme and uninterrupted low water of the remaining five months of the year. The low- water period (155 days) is normally located but is somewhat in excess of the average (147), and it is also unusual in the fact that the extreme low-water level (1.7 feet since the completion of the dam at LaGrange) continued almost unchanged from the middle of August till the first of November. This was fol- lowed by the usual slight increase in water in the closing months of the year. The total movement of the year (43.1 feet) is considerable in view of the average height (6.9 feet), 167 but this was less disastrous to the plankton than usual since it was in the main due to the spring flood and not to minor changes when the stream was within its banks. This freedom from minor interruptions during the low-water period is some- what unusual, and resulted in a concentration of sewage ap- proaching stagnation and in a marked increase in the fall plank- ton. The overflow period, in which the reservoir action of the bottom-lands as a whole was operative, prevailed during the first tive months; the change to low water, during which the reservoir action of the more permanent and diversitied waters was in force, took place very rapidly; while the low-water stages, during which it is a minimum, were both pronounced and prolonged. These circumstances combine to emphasize in this year both the unity and the autonomy of the river. In brief, 1897 was a year of normally located but pronounced high and low water, of marked freedom from interruptions, and of unusually favorable conditions for the unity and autonomy of the plankton of the river and for the full development of its normal seasonal cycle. In 1898 (Pl. XII.) we find another year whose hydrograph approaches the normal in its main features. There is a well- defined period of high water followed by one of much inter- rupted low stage. The spring flood is normally located, con- tinues (above § feet) for 164 days, and culminates at 18 feet on April second. The extension of the flood period for 24 days beyond the normal is due largely to the “June” rise of unusual proportions, which culminated in the last of May at 13.8 feet, and covered a period of five or six weeks. The impounding action of the bottom-lands as a whole is thus shifted forward into the late spring and early summer, while the concentration of the overflow into the channel occurs in the early part of May and again in June, and the conditions of rainfall, season, and overflow combine to favor the production of a relatively large amount of plankton at these times. The decline is rapid in July to low-water stage, which continues but three weeks, the lowest record being 2.5 feet. This is followed by a series 168 of minor rises, which flush the river at short intervals during August and September, and a rise to bank height in November —fluctuations which favor the reservoir action of the perma- nent backwaters,and at the same time introduce much silt and interrupt and diversify the plankton cycle. Of all the years of our operations at Havana this was the one of highest average level—8.02 feet (8.11 at Copperas Creek)—and greatest move- ment (66.2 feet). The dilution of the sewage, the increased current and silt, and the flushings incident to such hydro- graphical conditions tend under most circumstances to de- crease the re/ative amount of the plankton, though doubtless they also tend to increase the total production of the stream. In brief, the year was a typical one of high water with much delayed run-off and interrupted low-water period. In 1899 (Pl. XIII.) we find another year conforming very closely to the normal hydrograph in its main outlines. Weare concerned only with the first three months, at the close of which occurs the maximum (14 feet) of the spring flood. The greater part of the rise occurs in a brief period at the close of February, and the declining waters or more stable conditions at other times reduce considerably the flushing and silt attend- ing most winter floods, such, for example, as that of the pre- ceding year. The decline in February also afforded a good op- portunity for the reservoir action of the permanent backwaters under midwinter conditions. Our collections of 1899 thus cover a period of winter flood of more than usual stability. The wide range of hydrographical conditions during the six years of our plankton work at Havana have afforded a unique and, up to this time, unexampled opportunity to follow the effect of flood and drouth, of changing season, and of yearly fluctuations upon the hfe in the waters of a stream, and to give to the conclusions here reached the confirmation which repeti- tion alone can bring. TEMPERATURES. The fluctuation in the temperature of the river water con- stitutes for the plankton one of the most marked evidences of 169 the chmatic changes of the recurring seasons. This factor in the environment of the plankton is thus an ever changing one, but at the same time it runs an annual cycle of the same gen- eral character year after year with ever present minor varia- tions of a seasonal or local origin. The extremes of tempera- ture in bodies of. water in this latitude are so divergent that they afford the basis for marked seasonal changes in both the constitution and the quantity of the plankton. Adaptations on the part of the organisms of the plankton to definite tempera- ture hmits thus occur. Records of the temperature of the air and of the surface and the bottom water have been taken regularly at all stations where quantitative plankton collections were made. These are recorded in Table I. The temperatures were taken with a Negretti-Zambra self-recording thermometer from 1894 till May 24,1895, after which time a Hick’s self-recording maximum-mini- mum thermometer was used. Under stable conditions no appre- ciable variation was noted in the reading of the thermometers, but at the times of sudden change, as in the mingling waters of a rising flood, readings would sometimes vary as much as four or tive degrees at one location and level. The temperature of the river water is influenced by a vari- ety of causes in addition to the immediate action of solar heat. The most prominent of these are the access of the tributary water from streams, springs, and impounding backwaters. The temperature of tributary streams, such as the Spoon River (Table LV.), is often, though not always, warmer in winter and colder in summer by several degrees than that of the main stream, as a result probably of the greater proportion of spring water and the greater nearness of the same to its subterranean source. A good illustration of this was to be seen along the eastern shore of Quiver Lake, where at low-water stages springs near the water’s margin kept up a continuous flow. The tem- perature of the water in summer was 54°, while in winter it fell only to 51°. The smaller tributary waters also respond more quickly to fluctuations of temperature than does the river 170 itself. In hike manner the backwaters, which are usually much shoaler than the river, are subject to greater changes, exhibit- ing in warm days greater extremes of heat, as high, for example, as 96° having been found in the margins of bottom-land ponds. On the other hand, the flood waters in the forests and marshes, where the vegetation protects the water from the direct rays of the sun, remain at lower temperatures than those of more open tracts. The lakes and bayous with aquatic vegetation also re- main cooler in their deeper waters, as, for example, Thompson’s Lake, where, among the Ceratophyllum, the temperature at the surface on the fifteenth day of July was 88.2°, while only six inches below, in the vegetation, it was 80°, the difference being due to the protection from sun and ane whieh the veg- etation afforded. Another factor tending to modify the temperature is the earth temperature, which in the very shallow waters of our environment becomes relatively important in both summer and winter. In the low temperature of winter this is heightened by the fact that most of the bottom of the backwaters is strewn with a mass of vegetation whose decay must produce some heat. This probably accounts for the higher bottom tempera- tures sometimes observed in winter (cf. Tables It. and VIII.) in Flag Lake, where such detritus was more abundant than in the river, where but little is found. For example, on February 26, 1897, the bottom temperature in Flag Lake was 36°, while in the river, with about the same surface temperature (52°) and greater depth, it was only 32.5°. This difference may also be due to the effect of the current in the river in mingling more quickly the surface and bottom waters and thus equalizing their temperatures more rapidly. The temperatures recorded in the Illinois River, Spoon River, and in Thompson’s, Quiver, Dogfish, Flag, and Phelps lakes are to be found in Tables III.-IX. respectively, and they appear on the plates with the hydrographs and plankton data of the re- spective years and stations. The extreme range of temperature observed by us in the river and its adjacent waters at Havana 171 was 32°-96°. The highest temperature recorded in the river was 89°, on the afternoon of August 3, 1897, and again, at the same time of day, July 26, 1898. The diurnal range in temperature is considerable at times, depending naturally upon that of the air. On August 3—5,1898, in connection with a test of the diurnal movements of the plankton and accompanying analysis of the gases dissolved in the water, the temperatures recorded indicate in the surface waters a range of 5.5°, with a maximum of 79.5° at 5:00 p. m, and a minimum of 74° at 2:00 a. m. The bottom water (depth 2.44 meters) showed a range of but 2°, from 74° at 8:00 a. m. to 76° at 11:00 a.m. The air temperatures on the days in ques- tion ranged from 83° at 5:00 p.m. to 58° at 5:00 a.m. A diur- nal variation of 5.5° in surface waters and 2° in bottom waters is thus indicated at this time. Other conditions will probably show a slightly greater range. MONTHLY AND YEARLY AVERAGES OF SURFACE TEMPERATURES, (894-1899, ILLINOIS RIVER. H > Year | Jan. | Feb.| Mar.|April| May |,June| July | Aug.|Sept.| Oct. | Nov.| Dec re > 1120). leeds el herria Helens | 2 Receeg a1OOr 25/82. 2583 5 l77re Su (Gor. ae BoM lumens IDO Si eas ee 2 BOs tet) 58 80 1790 ~=6|80.51|78.87 54.26 42.5 BT. Gull icerecee 1896... .|32.75/33-7 |39- 52/04. s4\72.7 |74-7 |80.7 |82 65.75/56 44 133-6 |56.66 1897-2005 | oe 38% 32.25/43.8 |60 60-3 75 _ |81.02/80.9 |77.07/65.1 |45.7 |33- .02 loses 1898... .]32-7 |32-12/43.3 |53.32/65.8 |78.8 |82.87/80. 56/71 .87/54.37/41 .42 32.98)55.84 1899. . - .|32.9 lid [Bott aters| tc tice vel[ t preic tl todnere Mwai Geallesees allies tetas We Beles eae ane c Monthly average|32.78/32. 73) 40.45/60. 46\68 27/77. 7581.03.81 . 49/74 .21 57.55|43.00 35 -22'57.08* *A verage of monthly averages. The temperature records are too isolated to plot complete thermographs of the river and its backwaters, though they do give a very fair idea of the seasonal fluctuations, especially in the later years, when they were more evenly distributed, and in the midsummer, when they were more numerous... They were usually taken between 7:00 a.m. and 5:00 p. m., and may be regarded as day temperatures. A comparison of the records in Table III., the plottings (Pl. VIII.—XIII.), and the above table, giving the monthly averages of surface temperatures of our records, shows the following seasonal routine in the river: 172 During the months of January and February there is a period of minimum temperature approaching 32°, averaging 32.75°, and rarely exceeding 34°. The constancy of the tem- perature at this season is probably due in large part to the equalizing effect of the ice which normally covers the stream, and especially its backwaters, at this season of the year. Dur- ing the early part of March the temperature rises, but the rate becomes more rapid in the last part of the month. The up- ward movement reaches 40° or 50°, in early springs, such as 1898, attaining the latter temperature. The average for the month rises to 40.45° and the fluctuations increase in extent. The rapid rise continues through April, attaining 60°-70°, and averaging 60.46°. The records for this month are somewhat meager for any comparisons. In May the season of maximum temperature 1s approached and occasionally reached, as in 1896, the average temperature from somewhat scanty records being then 68.27°. This month is one not only of marked rise but also of considerable fluctuation. The period of maximum tem- perature is in full swing in June, and continues through July and August and well over into September. The average rises from 77.75° in June to 81.49° in August, and falls to 74.21° in September owing to the decline which begins in the latter part of this month. This period of maximum summer heat is fairly well defined in the thermograph and continues at or near 80° approximately three months, from the middle of June to the middle or latter part of September. It is a time of consider- able fluctuation, most of the movements being within 10°, though the range for August in the five years of record was from 74.3° to 89°. These fluctuations combined with the di- urnal changes and the wind are effective in producing a con- siderable vertical circulation of the water. Following the summer maximum comes the fall decline, which begins late in September and is practically completed in November. ‘The greater part of the change takes place in October, the average decline in that month being 16.76°, while that in November is 14.55°. In some years, as 1897, the de- cline is a gradual one; in others, as 1895 and 1895, it is subject to some irregularities. With December the winter minimum returns, but with less persistence than in the months which follow, flood waters at this season bringing their higher tem- peratures. | The annual temperature cycle thus falls into four periods: one of minimum and quite constant temperatures, including December, January, and February, and a varying portion of March ; one of maximum and more fluctuating temperature, approaching 80° and extending, with some interruptions, from the early part of June till about the middle of September; and, separating these, the two shorter intervals of change. The period of increase in temperature, which is also one of rapid change and increase of the plankton, includes the latter part of March and the months of Apriland May. The period of de- cline, which is sometimes more abrupt than the spring rise, as in 1895, 1897, and 1898, extends from the latter part of Septem- ber until the end of November. This is also a period of change and of frequent but not universal diminution in the plankton. The average temperature for the years, as expressed approxi- mately in the table, is 57.08°. This point is passed about the middle of April and again about the middle of October with considerable regularity. Since, however, these dates both lie in periods of rapid change, the average temperatures are of much less duration than the more extreme ones. The existence of these well-defined periods of maximum, minimum, increase. and decline of temperatures affords the basis for corresponding seasonal changes in the minute life of the water as fundamental and extensive as those which affect the plant and animal life of terrestrial and aerial environment. This subject of the rela- tion between temperature and organisms of the plankton will be fully discussed in connection with the statistical study of their seasonal distribution. A comparison of the thermographs (Pl, VIII.-XIII.) of the different years and an inspection of the table on page 171, reveal but few significant annual differences. The spring rise 174 in temperature was somewhat delayed in 1896 and again in 1899, and the summer maximum was less pronounced in 1895 and 1897, though in compensation the summer heat was pro- longed into September in these years. The spring rise in 1896 and the autumn declines in 1895 and 1898 are rather more abrupt than usual. These annual differences extend and cur- tail the plankton periods characteristic of the seasons, or render their changes more abrupt. The difference between surface and bottom temperatures is, as arule, but shght. It is perforce usually lacking during the period of decline in the autumn, and at other seasons varies in amount with the air temperature, the wind, and other attendant circumstances. So long as the temperature is above the point of maximum density of water, 39.2°, the surface waters are the warmer by an amount ranging from a fraction of a degree to 5°, the latter occurring on still, hot days. With air temperature falling below that of the water the surface and bottom quickly come to have the same degree of heat. Below 39.2° the colder waters are at the surface, though at this season of the year there is usually much less contrast at different levels than in the warmer months. Temperature fluctuations, following those of the season and the day, occur inthe waters of this region toadegree not realized in the typical lake, whose deeper waters respond but slowly to the surface changes, and thus exercise an equalizing effect. Examples of this quick response are found in the unusually high temperature (82.3°) in both top and bottom waters of the river on May 13, 1896, while temperatures of five days later showed a drop to 71.2° in both regions. A decrease equal in suddenness and extent occurred in September, 1898. The surface layers of water, quickly affected by temperature changes, form relatively a very large part of the volume of the river and its backwaters, and thus instability of temperature becomes an important feature of the environment of the plankton of the river as contrasted with that of the lake. Changes of the ex- tent above noted must affect considerably both the movements and the multiplication of the plankton organisms. 175 The temperature conditions here described are those as- signed by Whipple (’98) to lakes of the temperate type and third order, those whose bottom temperatures are seldom very far from their surface temperatures, and in which there is con- siderable vertical circulation at all seasons when the surface is not frozen. Atno place in the region examined by us has a depth been found sufficient to permit the occurrence of a stratum of cold water at the bottom unaffected by the vertical circulation and warming process in the surface regions, such, for example, as has been found by Birge (’97) in Wisconsin lakes. This absence in the river environment of the “thermo- cline” and of summer and winter periods of stagnation in lower levels, marks another point of contrast between the river and some lakes as units of environment. The temperature conditions in the bodies of water adja- cent to the river do not differ to any considerable degree from those here discussed. The limited extent, greater amount of vegetation, shallower waters, or greater access of spring water in some of these will cause slight variations from the condi- tions found in the river. The ice conditions attending the winter minimum are of profound biological significance, since they produce important alterations in the winter routine. As a result of the presence of an ice sheet on a body of water, the temperatures become more constant, the mingling of waters due to winds ceases, the usual processes of aeration are interrupted, and the propor- tions and amounts of the gases dissolved in the water may be very much altered, the degree of the change depending upon conditions such as the completeness with which the surface is sealed by the ice, the amount of sewage, the relative abundance of plant and animal life, the duration of the ice, and the exist- ence of currents. So faras our observations goat Havana, the stage of stagnation attended by the destruction of the animal life which is sometimes found in small lakes is rarely realized in this environment. Several reasons may be assigned, the principal one being being the instability of river levels in the 176 winter season, which prevents the culmination of stagnation conditions. Again many of the backwaters are rich in vegeta- tion, and some of them are spring fed at the margins which thus remain open even in the coldest weather. The river itself rarely closes over entirely, air-holes remaining where the cur- rent is rapid. Thus, below the mouth of Spoon River (PI. II.) a large area was usually free from ice even when the river was closed above this point. The currents due to tributary waters, as in Quiver Lake, and to changes in level, as in all impound- ing waters, also tend to prevent stagnation conditions. In spite, however, of these favoring circumstances one catastrophe of this nature did occur in the years of our work at Havana. In the winter of 1894-95 prolonged low water and heavy ice upon the river and lakes combined to render the conditions unfavorable to hfe in the river, and to some extent in Quiver Lake. Conditions in other localities at this time were not observed. The practical extinction of the plankton and the death of large numbers of fish attended this period of stagnation. The duration of the ice at the various stations in the sev- eral years is indicated at the bottom of the diagrams which give the hydrographs and plankton data of the several stations by black lines of a thickness proportional to the ice. The occurrence of ice in the different years at Havana has varied considerably. No records were made in 1894-95, but from other sources, river stages and weather reports, it seems probable that the river closed in the last days of December, and that the ice continued until the rise of February 25, a period of almost 60 days. In the winter of 1895-96 there was but little ice, the river and backwaters being partially closed only for the first fortnight in January. In 1896-97 the river did not close until after the rise in the early part of January, the ice remaining about one month, going out with the rise of Febru- ary. The lakes, on the other hand, were closed toa large ex- tent throughout December, and again, to varying extents, dur- ing January and a part of February, the current due to high water keeping portions free from ice at times. 177 In 1897-98 the lakes closed the last days of November and opened again on December 12, freezing again December 17, and not clearing entirely until February 14. Rising water continued from January 10, so that stagnation conditions did not ensue. The river also closed partially early in December, opening and closing again with the lakes. The first ice went out with the rise on January 11. The river closed again Jan- uary 27, and the ice went out February 9 and 10. Again on February 21 ice was present, and for several days following. In 1898-99 ice again formed early in December and par- tially closed the river during the month, going out about the 27th and reappearing on the 30th, This went out gradually January 17-24, and the river froze over again on the 26th and remained closed fora month. Thin ice formed March 5, re- maining only three days. The lakes closed early in December, the ice never entirely disappearing until the middle of March, Partial breaking up occurred at the times of breaking up of the river ice. These partial openings and the changes in level were sufficient to prevent a period of stagnation. OTHER METEOROLOGICAL FACTORS, As indicated in Tables III.—IX., at each plankton collection observations of the direction and force of the wind, with its effect upon surface conditions and on the state of the sky, were recorded, The relation of these factors to the plankton may not seem intimate or apparent. They have more bearing on the subject of vertical movements of the plankton, data upon which will be found in the study of the surface and bottom col- lections made with each of the vertical collections which form the basis of the present paper. The surface waters affected by the intensity of the sunlight and the movements caused by the wind form relatively so large a part of the environment of the river plankton that these factors are much more widely opera- tive here than in the lakes, where the surface stratum thus affected is relatively small. 178 The wind conditions on the river and the lakes adjacent to it—which are generally elongated in the direction of the main stream (Pl. I].)—are somewhat peculiar. Owing, it may be, to the configuration of the river valley, or perhaps still more to the bordering forest of the contiguous bottom-lands, the pre- vailing direction of the wind is either up or down the river or lake, especially during the summer season. The effect of an up-stream wind is greatly to increase the disturbance of the surface when wind and current are thus opposed. These winds, when prolonged and violent, decidedly affect the levels of the different parts of the lakes, and, for example, in Thompson’s Lake (Pl. II.) determine at low-water levels whether the lake shall discharge its waters into the river or itself receive an access of river water. Owing to the mobile condition of the abundant bottom deposits, at low stages the winds also add very much to the silt in suspension in the water, and thus hin- der the penetration of light. The effect of varying sky conditions hes primarily in their re- lation to the temperature of the water, but is due in a less degree to the influence of light upon the multiplication of chlorophyll- bearing organisms—the primal food supply of the plankton— and upon the movements of these and other plankton organisms. The abundant silt in suspension in waters of the river and most of the adjacent lakes doubtless hinders the penetration of the sunlight, but modifies to a much shghter extent its effect upon temperatures. Wind and sky conditions combine to favor or prevent the appearance of the “water-bloom.” This is a char- acteristic green scum which coats the surface of the river, and occasionally of the lakes, on still, warm days in midsummer. On cloudy or windy days the minute organisms ( Huglena, Chlam- ydomonus, ete.) which form the bloom do not rise to the sur- face. The conditions of wind and sky are thus important fac- tors in the economy of limnetic hfe and, by reason of their rel- atively greater effectiveness in the river and its adjacent waters as contrasted with the typical lake, add to the elements of instability in the fluviatile environment. 179 TURBIDITY. Records of the turbidity were made (Tables ITI.—IX.) in gen- eral descriptive terms during the first two years of our work at Havana. After April 29, 1896, the turbidity was tested by means of a white plate of semi-porcelain, 10 cm. square. The depth at which this square disappeared from view was recorded in centimeters as a measurement of turbidity. Although the method is somewhat primitive and subject to some variations with the conditions of sky and daylight, it is still sufficiently accurate for the purposes of the present paper. The disc method has not as yet been correlated with the platinum-wire method, the diaphanometer method, or the silica-standard method of Whipple and Jackson (’00), and comparisons with these are consequently excluded. As might be expected in the river environment, when floods occur the turbidity is often extreme, and is exceedingly varia- ble according to the locality and the river levels. (Cf. Tables Ill.-IX.) The extreme range of our records extends from 1.3 em., in a Spoon River flood, to 260 cm., in Quiver Lake, under the ice. In the river (Table III.) the great majority, about two thirds, of the records lie between 20 and 50 cm., while the ex- treme range is from 2 cm., in the flood of May, 1897, to 115 cm., in the declining waters of July, 1896. The clearer waters ap- pear, as a rule, with declining floods and stable low stages, especially under the ice. With the inception of floods the most turbid water is found, which gradually clears even while the rise continues. The river varies in clearness according to the instability of the river levels, as will be seen on comparison of the turbidity in 1896 and 1897, the latter year being more stable and having relatively fewer records of a marked turbidity. The turbidity of the river is due to both plankton and silt, the latter being as varied as the character of its tributaries, with the added contamination from the cities along its banks. In Spoon River (Table IV.) the extremes are even more marked than in the main stream, varying from 1.3 cm., in flood 180 conditions, to 165 cm.at low water under the ice. The turbidity here is almost entirely due to silt, that at flood being largely composed of earth and clay, giving a black or yellow tinge to the water. The amount of comminuted vegetable debris found in the waters is considerable. In Thompson’s Lake (Table VIII.) the turbidity is not so frequently marked by the extremes seen in the other bodies of water examined, the range being from 115 cm. in the declining waters of May, 1896, to 6 cm. in invading floods, and again in the late autumn of 1897, when high winds roiled the shallow waters. As a general rule the turbidity of this lake is somewhat less than that of the river, but as great or greater than that of other backwaters. This turbidity is often due in part to the heavy planktons occurring here, and also to the floccu- lent debris loosened from vegetation and stirred up from the mobile bottom by fish and the waves. Very little silt enters the lake except at times of inundation, especially with back- water from Spoon River. Owing to its origin the silt in this locality is usually of finer, more flocculent material than that found elsewhere. In Quiver Lake (Table V.) the extremes are much more marked than in any other locality, ranging from 3,5 em., in flood water from the river, to 260 cm, on June 5, 1896, in clear impounded water. In winter, under the ice, the bottom was vis- ible on December 8, 1896, in 260 em. of water. A great deal of variation in turbidity occurs in this lake. In years of low water, as 1894 and 1895, when vegetation is abundant, the turbidity is ' very slight, the bottom being visible much of the time, In the three succeeding years the lake was free from vegetation, and the turbidity was considerably increased as a result largely of the increase in the plankton. The sources of the silt in this body of water are varied; occasional freshets in Quiver Creek, which enters the upper end of the lake (PI. II.), invading floods from the river, and debris from vegetation and the bottom put in suspension by the wind, current, or movements of fish,—all contribute their share to the pollution of the otherwise clear water of this lake. 181 In Dogfish Lake (Table VI.) the conditions are essentially those of Quiver Lake, of which it is an arm. The principal difference lies in the fact that flood water entering Quiver Lake at low stages never moves as far up as our station in Dog- fish Lake (Pl. II.). Floods from Quiver Creek also merely back up the clear water in Dogfish Lake without themselves invad- ing that territory. The only flood silt entering this region is, consequently, that which comes with general inundations. In Flag Lake (Table VII.) the conditions at inundation are similar to those of other impounding backwaters. The great amount of vegetation found here adds to both the vegetable and the flocculent debris which roil the water whenever this is disturbed by waves or the movements of fish. Turbidity is but rarely caused by plankton here, with the exception of the few instances when diatoms or Oscillaria became very abun- dant. The water is thus usually clear, the bottom being commonly visible in the small spaces left free of vegetation, even at a depth of 215 cm. In Phelps Lake (Table IX.) the silt conditions are peculiar. The high level at which the lake les and the intervening stretch of bottom-lands (PI. II.) combine to keep out all silt- laden flood-waters except those that enter by a now abandoned channel from Spoon River or from the main stream at times of their maximum floods. At other times the silt consists prin- cipally of particles of bark and dust from the adjacent forests, or of fragments of loam from the bottom, which is here unusually stable. The comparative freedom from vegetation removes a large element common in the silt of the other lakes. The turbid- ity, however, is very marked in this lake, falling in many cases below 20 cm., and in the majority of instances is largely due to the very abundant plankton characteristic of its waters during the greater part of the summer. Movements of fish and water- fowl add considerably to the silt in suspension in this lake at some seasons of the year. The color of the water has not been made a subject of special inquiry. In general the turbidity gives it a grayish cast 182 that varies to yellowish or blackish tints with silt of clay or loam origin. When diatoms are abundant a brownish tinge is very evident, and with Oscil/aria rising in quantity, as 1t does in some semi-stagnant waters in late summer, a blackish tint becomes pronounced. In midsummer and early fall, when water-blooms rise, we find varying tints of green according to the kind and quantity of chlorophyll-bearing organisms present. The turbidity, as above suggested, is due to a great variety of factors, one of the most important of which is the plankton itself. Indeed, under some conditions turbidity be- comes a token by which the relative abundance of the plank- ton may be estimated. The presence in our plankton of vast numbers of the most minute planktonts, such as the flagel- lates, renders this relation of plankton and turbidity more prominent in our waters than it is in waters where such organ- isms are less abundant. The turbidity otherwise is due to non-living solid matter in suspension. This is brought in by tributary streams, and is torn loose from the shores and bottom by the current of the river, the movements of fish, the wash from steamboats, and the constant sweeping of the river channel by fishermen’s seines during the open season at stages when seining is possible in this place. The dust from prairies and forests brought by winds; the waste from factories, distilleries, glucose-works, and cattle-yards; and the sewage ofa score of cities along the banks, —all make additions to the burden of the water. Microscopical examination of the plankton has revealed the diverse character and origin of the silt which accompanies it. Fine fragments of quartz, bits of mollusk shells, small pieces of coal or ashes, minute particles of loam or clay, and the fecal pellets of aquatic organisms—especially of mollusks and of insect larvee—constitute the heavier element of the silt. To this is added a variable but ever considerable quantity of exceedingly fine sediment of earthy or clayey origin, some of which remains long in suspension. ‘The coarser and lighter silt consists largely of comminuted vegetation, both terrestrial 183 and aquatic, minute bits of leaves, stems, bark, and wood, with the characteristic grain refuse from distilleries and glucose- works and the offal from the cattle-yards at Pekin and Peoria. At all seasons of the year and in all waters the scales of Lepi- doptera and the pollen of coniferous trees are of common oc- currence. Mingled with this material, especially when aquatic vegetation is present, is a very light flocculent material con- sisting, in part at least, of the zodgloee of bacteria. It isin the midst of debris of this varied composition that the plankton lives, and it is in collections consisting to a greater or less ex- tent of silt material that the river plankton must be studied, its species determined, and its individuals enumerated. In collections made with the silk net the greater part of the fine silt passes through the meshes with the water. In filter-paper catches some of it adheres to the paper, and the finer flood silts will even pass through hard-pressed filter paper in small quantities. With silt of so varied a character it is practically impossible to establish and continue any standard of measurement or estimate which affords a satisfactory basis for the determination of the relative amounts of silt and plank- ton present in the collections. After considerable experience in the examination of our collections I have endeavored to estimate the amount of silt present in them as they appear in the Rafter counting-cell. The distribution of the material in the cell and the conditions of examination are such as to favor a uniform standard of estimation. On the other hand, the estimates are purely personal, without any volumet- ric check, and are thus only comparable with each other. This method seems to be the only solution at present available for this perplexing problem. These estimates are given in Tables III.-IX., together with computations, based thereon, of the amount of both plankton and silt per cubic meter. These figures form the basis of the diagrams in Plates VIII.-XIII. and XXII-XLII. As will be seen in the tables, the per cent. of silt varies from a mere trace to almost the entire catch, changing with the river conditions as previously, stated. 184 A still more accurate determination of the total amount of solids in suspension in the river, both silt and plankton, is afforded by the catches made by the Berkefeld army filter, data concerning which will be found in Table XV. This filter removes all of the suspended solids and permits their complete removal from its surface, but adds a small portion of its own substance to the catch. After the first few catches with this filter the wear becomes somewhat uniform and is thus dis- tributed. On computing the loss from the filtering sur- face by wear, and quadrupling this volume to allow for its less compact condition, we find that it constitutes less than five per cent. of the catches washed from its surface. The true amount of solids is thus about five per cent. less than the figures cited in the tables and in the following discussion. The amount of water strained in making these catches was usually 5 liters, while the tables give the computed amount per cubic meter. The amount of solids was measured by our usual method of measuring plankton, that is, by condensation in a centrifuge. In this treatment it usually attains the consistency of soft mud. For the river the amount ranges from 148 cu. em. (per cubic meter), indeclining water under the ice in December, to 5,416 cu. em., in the incipient stages of the winter flood of February 28, 1899. The average amount of the weekly catches for 1898 is 592.2 cu.cm. per cubic meter, which for an average flow of 24.600 cubie feet of water per second (see page 132) means a discharge of 14.57 cu. ft. of solids per second, or, 459,794,232 cubic feet (1,801,990 cubic meters) per year, or 16,472 cu. ft. (46.64 cu. meters) per square mile of the catchment-basin of the river. The average amount, per cubic meter of water, of solids taken at fortnightly intervals in 1898 in Quiver Lake was only 378 cu. cm., a fair index of the greater clearness of its waters. In Thompson’s Lake similar collections average 557 cu. cm., in- dicating waters somewhat clearer than the river. In Phelps Lake the average amount is large, 1,572 cu. cm., due in no small 185 degree to the very abundant and minute plankton organisms. In Spoon River the average of the monthly collections is 1,746 cu. cm., three times aS much as the main stream carries. The heavy floods and rapid current of this tributary are responsible for this large amount of earthy solids in suspension. In this matter of silt and turbidity the river as a unit of environment stands in sharp contrast to the lake. Deposition of solids and clear water are normal to the environment of the lake, while solids in suspension and marked turbidity are the rule with river waters. Owing to their varied occurrence these elements, silt and turbidity, also add to the instability of fluviatile, as contrasted with lacustrine, conditions. Siltand turbidity are usually attendant upon floods, so that their unmodified effect upon the plankton is not easily deter- mined. Some inferences and observations regarding the rela- tion of these factors to the economy of the plankton may, how- ever, be made. The silt affects the plankton indirectly by hastening the solution of nutrient substances from the organic detritus that forms a considerable portion of the unstable de- posits which accumulate in shoal and in sheltered parts of the stream. It hinders the penetration of light, thus checking the development of the chlorophyll-bearing organisms while favor- ing the multiplication of bacteria and hastening the decay of organic matter in suspension. It also seems probable that it produces a deleterious effect upon the E’ntomostraca by ad- hering to the hairs which clothe their various appendages, thus hampering their movements and causing them to sink to the bottom. Accessions of flood water are frequently followed by an increase in the relative number of moribund and dead Entomostraca, especially of the Copepoda. CHEMICAL CONDITIONS. The food supply is the most fundamental feature in the environment of the plankton. Its abundance or scarcity de- termines to a large degree the growth and reproduction of or- ganisms, and its fluctuations are important factors in deter- 186 mining the seasonal and local production of plankton. The primary source of the food of the plankton lies in the water and in the gases and inorganic salts dissolved therein, the oxy- gen, the carbon dioxid, the nitrates, and the phosphates being usually regarded as of prime importance to the growth of chlo- rophyll-bearing organisms. The phytoplankton, which utilizes these inorganic materials, then becomes itself the food for the zooplankton. These inorganic substances, the primary food supply, are thus indices of the capacity of the water for the production of plankton. With the inauguration of the work of the Biological Sta- tion at Havana arrangements were made whereby collections of water taken by the Station staff from the river and some of the adjacent lakes were sent to the Chemical Department of the University of Illinois, at Urbana, for analysis. In 1895 the Chemical Survey of the waters of the state was es- tablished at the University under the direction of Prof. A. W. Palmer, and in September of that year regular shipments for analysis from the [llinois River and from Quiver Lake were made at intervals of one week, and in January of the following year Spoon River was added to the collection points. These collections were continued throughout the period of our oper- ations at Havana. In September, 1897, collections were insti- tuted in Thompson’s Lake, and from that time on the samples for chemical analysis were taken at the same time and place as the plankton and, hke that, by the plankton pump. After the date above named a fortnightly interval corresponding to the plankton interval was made between collections in Quiver Lake, though the weekly interval was continued in I]h- nois and Spoon rivers. August 16, 1896, a disastrous fire in the chemistry building of the University destroyed many of the records, and this fact accounts for the absence of data of the analyses in the months of the year prior to the fire and for some other gaps in the record. Special collections were made during the last twenty months of our operations for the deter- mination of the oxygen and carbon dioxid dissolved in surface 187 and bottom waters, but determinations of these dissolved gases made by Professor Palmer immediately upon collection in the field, yielded results which throw some doubt upon the value of those made on samples which were shipped for analysis at the laboratory of the Chemical Survey. Twenty-four to forty-eight hours elapsed between the time of collection and that of anal- ysis, and during this time changes no doubt took place in the gases dissolved in the samples, so that the results of the analy- ses give no trustworthy basis for a statement of the amount of dissolved oxygen and carbon dioxid in the water at the time of collection. I am indebted to Professor Palmer not only for the data of the chemical analyses which he has furnished me from the records of the Chemical Survey, but also for many other cour- tesies in connection with this subject. COMPARISON OF CHEMICAL CONDITIONS AND PLANKTON AT THE DIF- FERENT STATIONS. In Tables X.-XIII. will be found data from the chemical analyses of the waters of [Illinois and Spoon rivers and Quiver and Thompson’s lakes, together with plankton data of the same or contiguous dates. The most important of the determinations, those of chlorine, oxygen consumed, free and albuminoid am- monia, organic nitrogen, nitrates and nitrites, as well as the plankton, are graphically shown in Plates X LIIL.—L. CHEMICAL ANALYSES OF WATER FROM PLANKTON STATIONS. AVERAGES OF ALL ANALYSES. PARTS PER MILLION, Residue on Evaporation Nitrogen a 7s = z | o — v s cy 2. * L Loss on oie atoll Eh < = iia) Ignition s | Ammonia} 2 ¢ be oO | aaa ae = hl eee Sy os e 5 | = ama x ale Locality od 31 9 eh ay Il S| pA a“ = S 2 “) 2 2 = = (oe) n 2 ae Dam g es alo] o Spee Oia |e eal ee kes FS Bl Gugsaaly: Gal selL gale lae| Boel eisai e aS Nie S a IS ca a Si Sy ey ae be SE ian) foal Q D Z Sl) 2 a Sr ie) 88) |] er |) 4S 14 4 mo Illinois River. .... 188| 367. See 61.4 32.8] 25.1/21.6]10.4] .86 | .46 1.03).147/1.58} 1.91 2.00 Spoon River ....... 137/522.3}167.1'274.3 41.9} 24.4) 3.8]14.1] .245 | .604 |1.292].039}1.01 388 .969 Quiver Lake .... 50/268 .9/248.2] 25.1 27.5] 25.6] 4.8] 5.9] .165 | .251 61|.023} .66} 1.62 62 ‘Thompson’s Lake 40|326.4/282.9! 44.6 36.5! 28.3!16.3]11.9! .422 | .546 | 1.05'.048) .64) 6.68 1.00 * Plankton and silt averages are for collections coincident with or contiguous to collections of water samples. The foregoing table gives the number of samples analyzed from each locality and the averages of the different substances 188 determined for each. Since the samples were collected at in- tervals throughout the year, the averages may be regarded as presenting in succinct form the chemical characteristics of the stations examined, and they may therefore serve as a basis for a comparison of the relative fertility of the localities. The residue upon evaporation, which comprises the solid matters left upon evaporating the water and drying the residue, includes both organic and inorganic substances. The inorganic constituents are salts, and comprise mainly compounds of lime, magnesia, soda, potash, iron and alumina with chlorine and with carbonic, sulphuric, nitric, and silicic acids. In this residue lie both the mineral constituents of the food of the phytoplank- ton and the undecayed organic matter found in the water. Not all of the constituents of the residue are equally utilized as food by the phytoplankton, so that the quantity of the residue gives a basis only fora very rough estimate of the fertility of the different waters. Some significance, however, attaches to the marked differences shown in the table. The differences in total residue in Ihnois and Spoon rivers (867.5 and 522.3) and Quiver and Thompson’s lakes (268.9 and 326.4) show no particular correlation with those of the average plankton production of these waters for corresponding periods (1.91, 0.384, 1.62, and 6.68 cm.? per m.°, as shown in Tables X.- XIII.). The amounts and relative proportions of the dissolved and suspended residue in these localities show some relation to the plankton production. The residue in suspension is not, in its present form at least, available for plant food. Its occurrence in the four localities is almost directly correlated with the rela- tive turbidity of the water Spoon River has from four to eleven times as much suspended matter (274.3) as the other localities, and this consists largely of clayey material with considerable fine quartz, neither of which contributes any considerable source of nutrition to the phytoplankton. The suspended ma- terial in the other locations at times of flood partakes of the character of that in Spoon River. At other times it contains a considerable proportion of debris of plant or animal origin 189 including the plankton itself. The current of the river is doubt- less responsible for the excess (61.4) which its waters carry above that in the lakes (25.1 and 44.6). The greater amount in Thompson’s Lake (44.6) may be due to two sources, its ereater dependence on the river for its water supply and the greater disturbances in its waters due to fish and to waves. The fact that the total catches of the plankton net (3.91, 1.35, 2.24, and 7.68) do not on the average more nearly approximate in their ratios to each other the ratios of the chemical resi- dues (61.4, 274.8, 25.1, and 44.6) is due to the great leakage of the finer suspended particles through the silk, especially in Spoon and [llinois river waters. The residue in solution contains the available supply of mineral salts for the phytoplankton as well as some organic materials which become sources of plant food, and its distribu- tion in the four localities is correlated with the plankton pro- duction in the direction of the differences, though not in their quantity. Thus Spoon River with the least dissolved residue (167.1) has the least plankton production (.384), and Quiver Lake has likewise less residue (248.2) and less plankton (1.62) than Thompson’s Lake (282.9 and 6.68). The [llnois River ex- ceeds all of the localities in its dissolved residue (304.1), which may be attributed to the fact that the water is “older,” afford- ing greater time for solution, and that it is the recipient of considerable sewage and industrial wastes which add to its burden of substances in solution. The small amount in Spoon River may be attributed to the fact that it is largely uncon- taminated surface water of recent origin. The greater amounts in the two lakes (248.2 and 282.9) are due in part at least to their dependence upon the river, which in the case of Quiver Lake is slight during the summer season. In so far as the total res- idue held in solution is an index of fertility, the data indicate that the river itself carries the greatest store of food (304.1); Thompson’s Lake, somewhat less (282.9); Quiver Lake, still less (248.2); and Spoon River, least of all (167.1). On this basis and in the light of the production of Thompson’s Lake it would 190 seem that the river water might under more favorable condi- tions develop a more abundant plankton. These favorable conditions are to be found in the quiet backwaters of river-fed lakes, where time for breeding is afforded. The loss which the residues of total solids suffer upon igni- tion (heating to redness) includes the organic matters which are burned away and such constituents of the mineral matters as are volatile or are decomposed by heat into volatile sub- stances. In stream waters the suspended portion of this mate- rial may be a rough index of the quantity of plankton and silt of organic origin, all of which on decay add to the water sub- stances available for plant food. From the data in the table it may be ascertained that the four localities yield respectively, in the order of the the table, 7.7, 17.5, 1.9, and 8.2 parts per million of such material. The excess in Spoon River (17.7) is_ doubtless due to silt of organic origin, while the plankton pre- sumably forms a larger proportion in Thompson’s Lake and in the Illinois River. The poverty alike of plankton and of silt in Quiver Lake is reflected in the small amount (1.9) lost on igni- tion in its waters. The loss, on ignition, of substances held in solution shows no differences at all commensurate with the relative production of plankton, though the trend of the differ- ences is similar in three instances of the four. The chlorine is contained in surface waters in combination with various basic elements, but chiefly in the form of common salt. Its principal source is animal matter, sewage, or drain- age from refuse animal matter. In our river and lake waters it is largely an index of their relative contamination with sew- age from cities within the drainage basin. Since its combina- tions are not utilized by plantsas foodinany considerable quan- tity, at least as compared with other constituents of the sew- age, such as the nitrates, the chlorine becomes the best crite- rion of the amount of sewage andthus of the principal adventi- tious fertilizer which the waters examined by us contain. The differences in the four localities are striking and significant. The average chlorine in the Illinois River (21.6) is more than 191 five times as great as that in Spoon River (3.8), while that in Thompson’s Lake is more than three times the amount in Quiver Lake. The large amount of chlorine in the Illinois and in Thompson’s Lake—which draws its water supply mainly from the river—is due to contamination by the sewage of Chi- cago, Peoria, and other cities within the drainage basin. Quiver Lake receives water from the river only during flood periods, when the sewage is diluted, and at other seasons it contains more nearly the chlorine of the uncontaminated prairie stream. Its chlorine thus averages low (3.8). That of Spoon Riverruns higher (4.8), in part because of backwater from the main stream to the point of collection. The sewage systems discharging into this stream are few and but slightly developed, and its chlorine is correspondingly low. While it is true that the chlorine is not a precise measure of the amount of sewage or of the adventitious fertilizing material received by a stream, it is nevertheless significant that ratios of chlorine and plankton production not only trend in the same direction but are quanti- tatively somewhat similar when lake is compared with lake and stream with stream. Thus in Quiver and Thompson’s lakes the ratio of their chlorine content is 1 to 3.4 while that of the plankton production is 1 to 4.2. The corresponding ratios in Spoon and [llinois rivers are | to 5.7 and 1 to 5. An increase in chlorine due to sewage or animal wastes seems thus to be accompanied by a proportionate increase in the plankton pro- duced. It is safe to infer that it is one of the factors producing the increase, but,as shown elsewhere in this paper, other fac- tors, such as vegetation and current, are also potent in produc- ing the contrasts in plankton production above noted. The oxygen consumed in oxidizing the organic matters af-° fords an additional index of the quantity of these substances present in the water, but since all kinds of organic matter are not oxidized in the analysis it does not yield a criterion of the total quantity of organic matter. A comparison of the oxygen consumed in the four localities yields results very sim- ilar to those obtained by a comparison of loss on ignition, ex- 192 cept in the case of Quiver Lake, where the oxygen consumed (5.9) is proportionately very much lower than the loss on igni- tion (27.5). The amount of oxygen consumed is greatest in Spoon River (14.1), and may be attributed largely to the detri- tus of organic origin which the stream carries, or to the prod- ucts of its decay held in solution. It may also be due in part to the organic material of the water-bloom (Huglena) which es- capes the silk of the plankton net. There is, however, no in- crease in the oxygen consumed in the season of the water-bloom which can be considered commensurate with its development. Nitrogen is an essential constituent of protoplasm and of many of its products. It is taken up by plants in the form of nitrates and free ammonia, and there is increasing evidence that it may be utilized, especially by the lower plants, in more complex combinations, such as the amido-compounds. Since the other principal constituents of protoplasm—carbon, hydro- gen, and oxygen—are present in inexhaustible quantity in the air, water, and carbon dioxid, and since the nitrogen available for plant food is practically limited to that contained in the above-named compounds, the nitrogen in combination in any given body of water becomes par excellence an index of its fer- tility. These compounds exist in living plants and animals, in their wastes, and in the products of their decay. They enter stream and lake waters in various ways: in the debris of veg- etable and animal origin washed into the stream, especially by flood waters ; in leachings from such matters drawn from the soil in seepage and spring waters ; and, especially (in the [h- nois River) in the sewage and industrial wastes of Chicago, Peoria, and other cities within the drainage basin. In the lake and stream waters these nitrogenous compounds are found in solution in the water, in the sediment and debris of organic or- igin in suspension, in the zo6- and phytoplankton, and in the macroscopic aquatic plants and in the larger animals—such as fish, mollusks, insects, and crustaceans. The chemical anal- yses show only those nitrogenous compounds in solution, in silt, and in plankton, while that stored in the larger plants and 193 animals is not determined. Since the silt is undergoing decay, and since the individuals of the plankton are short-lived and rapidly release their nitrogenous compounds into the water by waste and decay, the determinations of nitrogen in its various forms in the analyses represent both the present fertility and that in immediate prospect. The contributions from the ma- croscopic plants and animals not included in the samples analyzed constitute an undetermined element in the sum total of the nitrogenous matter available for the sustenance of the phytoplankton. The relative amounts of nitrogen in theseveral stages of decomposition are shown in the determinations of total organic nitrogen, of nitrogen as albuminoid and free am- monia, and of nitrites and nitrates. The total organic nitrogen wnecludes all nitrogen that is in combination with carbon (together with other elements) in the tissues of living plants and animals and in many of the waste products of the latter. It is also present in organic matter in the early stages of decay, and is accordingly found in organic debris and sewage of stream and lake waters. It is accord- ingly an index of the quantity of organic matter which in its present form is not available for plant food (with the possible exception of certain amido-compounds) but is destined to be- come available by decay. It thus indicates the potential fer- tility of the water. The differences in the amount of total organic nitrogen present in the four localities are not in each case correlated with the actual plankton production. Spoon River, which contains the least plankton, has the greatest amount (1.292) of organic nitrogen. The absence of any ex- cessive contamination by sewage in this stream combined with the paucity in plankton, makes it apparent that this mat- ter is probably in the organic detritus of the silt, which is pres- ent in an unusual amount in this stream. The close resem- blance of the Illinois River and Thompson’s Lake in the matter of total organic nitrogen (1.03 and and 1.05) is explained by the dependence of the latter upon the river for its water supply, and by the excess of sewage in the former and of plankton in 194 the latter. The small amount in Quiver Lake is attributable to its greater independence of the river, to the paucity of its plankton, and to the sandy nature of its drainage basin and consequent share of spring water in its water supply. It is noticeable that the large amount of submerged vegetation in this lake does not contribute any great amount of organic nitrogen to the water at any season of the year. The nitrogen as albuminoid ammonia is included in the to- tal organic nitrogen, and exhibits almost identical relative amounts in the four localities, though actual quantities are only half as great. It represents the nitrogenous materials which have not undergone decomposition. The nitrogen as “ free” ammonia represents the ammonia contained in the water in free or saline condition. Itis a prod- uct of the decomposition of organic matter in the first stages of oxidation, and its quantity is an indication of the amount of such matter present in the water in a partially decomposed state. It is abundant where sewage occurs, and together with the chlorine affords evidence of the degree of contamination. The occurrences of free ammonia in the four localities (.86, 245, .165, and .422) are not in most instances in the same ra- tios as those of the chlorine (21.6, 3.8, 4.8, and 16.8) or of the plankton (1.91, .384, 1.62, and 6.68). The excess (two to five times as much) of decaying organic matter in the river as com- pared with the other situations is apparent, and is doubtless due to the concentration of sewage in its channel and to the more recent access of the sewage there as compared with that in the reservoir backwaters, as, for example, in Thompson’s Lake. The early stages of decay are in consequence more active in the river. The free ammonia is high in both the river (.86) and Thompson’s Lake (.422) but lower in Spoon River (.245), where the organic material in suspension is considerable, as indicated by the loss on ignition, the albuminoid ammonia, and the organic nitrogen and oxygen consumed. The decay of this matter and the accompanying release of free ammonia has not been attained as yet in a part at least of the silt in Spoon River to the same 195 degree that it has in the older river and lake waters. Its bur- den of silt thus adds to the sources of fertility of the main stream and of the reservoir backwaters at times of flood. The small amount of free ammonia in Quiver Lake (.165) is corre- lated with the small amounts of the substances above named in its waters and the sandy nature of its drainage basin. The differences in the two streams in the quantity of free ammonia (.86 and .245) have the same trend as the differences in plank- ton production (1.91 and .384), but they are not commensurate quantitatively, owing apparently to the more recent origin of the water in Spoon River. In the lakes the free ammonia (.165 and .422) and plankton (1.62 and 6.68) exhibit a similar trend and a like absence of quantitative differences in the plankton commensurate with the free ammonia available for support of the plankton. The effect of the relative food supply is thus apparent in the trend of the differences, and the operation of other factors is suggested by the quantitative contrast. The factors in Quiver Lake tending to reduce the plankton below the amount that the food supply would make possible are to be found in the passage of tributary waters through the lake and in the excessive aquatic vegetation. It is noticeable that the considerable amount of submerged vegetation in Quiver Lake does not seem to effect any appreciable increase in the free ammonia. The abundance of free ammonia in the Illinois River would seem to afford a basis for a greater development of the phytoplankton than it attains under the conditions in that stream. The time for breeding which is afforded in the backwaters is one factor involved in this contrast. The nitrites constitute a second intermediate stage in the oxidation of nitrogenous substances into inorganic products. Their presence indicates organic matter in the final stages of decay, and that decompositions due to the vital processes of living organisms are under way. The nitrites exhibit a distri- bution in the four localities which in the trend of the differ- ences is similar to that of the free ammonia. The ratio of the free ammonia in Spoon River to that in the Illinois is 1 to 3.4, 196 while that of the nitrite content of the two streams is | to 3.7. The ratios in the two lakes, Quiver and Thompson’s, are 1 to 2.6 and 1 to 2.1 respectively. Spoon River and Quiver Lake are thus poorer in nitrites than Illinois River and Thompson’s Lake. The same contrasts are to be found in their production of plankton, though the differences in the amounts produced are greater than those in this source of fertility. The amount of nitrites (.045) in Thompson’s Lake is quite low when the large plankton production in this lake (6.68) is contrasted with the much smaller amounts (1.91, .854, and 1.62) in the other local- ities, where the nitrites are but a little less or even greater (.147, .039, and .023). Either the nitrites are an inadequate measure of the potential fertility of the water, or the other waters named might, in the environment of Thompson’s Lake, support a more abundant plankton. The nitrates are the final products of the oxidation of ni- trogenous matters, in which the nitrogen returns to imorganic compounds and is once more in a form most available for util- ization as food for the phytoplankton or other aquatic plants. The quantity of these compounds is a prime index of the im- mediate fertility of the water, and becomes a basis for future growth of the phytoplankton and other aquatic plants. The amounts of nitrates present in the waters of the four localities are very different, and at first glance exhibit httle correlation either with the other forms of nitrogen present in the water or with the quantity of plankton produced. It should be noted in this connection that the nitrates, more completely perhaps than any other form of nitrogen, are utilized by the chloro- phyll-bearing organisms as food, and if taken up by the phyto- plankton the nitrogen appears in the subsequent analysis as organic nitrogen. If, however, the phytoplankton or the zo6- plankton feeding upon it is utilized by some macroscopic animal, —as, for example, by Polyodon, or by the Unionide which cover the river bottom in places,—it is removed from the field of analysis, excepting only in such animal wastes as are returned to the water by the feeding organism. If it is utilized by the 197 grosser forms of submerged aquatic vegetation, it is likewise effectually removed from the field of analysis until again released by the decomposition of this vegetation. The nitro- gen aS ammonia in organic compounds, or as nitrites, is either entirely unavailable for plants or, with the probable exception of the free ammonia and the amido-compounds, is less availa- ble than the nitrates. These other forms consequently more fully represent the potential fertility of the water than the ni- trates do, for the latter indicate mainly the wnutilized portion of the nitrogenous plant food immediately available. In the light of the foregoing conditions more significance attaches to the distribution of nitrates and plankton in the four localities. The excess in the river (1.58) over that in the tributary waters of Spoon River (1.01) and Quiver Lake (.66) may be due in part to the greater age of the waters of the main stream and the opportunity thus afforded for the completion of the processes of decomposition of organic substances delivered to the main stream by tributaries above the point of examination. When the quantity of nitrates in the river is compared with the or- ganic nitrogen, free ammonia, nitrites,and nitrates in Spoon River or Quiver Lake, it becomes apparent that the tributary waters of this stream still act as a diluent of the river water. The source of this excess in the main stream is to be found in the sewage and industrial wastes of Chicago and Peoria. The unutilized nitrates are two and a half times as great in the river (1.58) as in Thompson’s Lake (.64). In so far as the ni- trates are concerned, both Spoon River and the Illinois might support a much more abundant plankton than they now pro- duce (1.91 and .384) if the conditions permitted. Thompson’s Lake, drawing its water from these sources, does maintain a greater production (6.68) and exhibits a great reduction in the amount of nitrates (.64), the unutilized residium being less in this lake than in any of the other localities. The increase in the amount of plankton in Thompson’s Lake over that in the river (3.5 times as much) is roughly proportional to the decrease in nitrates in the lake as compared with the river (.4 as much). 198 The similarity of the residual nitrates in the two lakes is strik- ing (.66 and .64), and it bears no apparent relation to their plankton production (1.62 and 6.68). The excess of other forms of nitrogen in Thompson’s Lake (roughly twice that in Quiver) would seem to indicate either that the decomposing nitroge- nous substances are utilized before they reach the form of ni- trates, or that they are abstracted from the water so promptly that they do not accumulate above a certain residual minimum which is apparent during the growing period of the phyto- plankton and of the coarser forms of aquatic vegetation. (See Plates XLIX. and L.) It is evident that the nitrates in the two lakes (.66 and .64) cannot adequately represent the nitrogenous resources of the two bodies of water; neither can they furnish any reliable clue to their actual productiveness in plankton. Other factors of the environment are equally or even more potent. The number of analyses and of plankton catches is so great (188 and 156 from Illinois River and 40 of each from Thomp- son’s Lake), and they are so distributed through the year, that the inference is justified that the nitrates shown by chemical analysis in the water of a lake or stream, especially during the growing period of vegetation, afford no reliable basis for judg- ment as to its plankton production. The sewage received by the Illinois River bears an 1mpor- tant relation to the chemical condition of its water and thus to the plankton which it produces. No measurements are made by boards of public works of the amount of sewage which mu- nicipal systems discharge into the various streams which unite to form the Illinois River. Two sources of information are, however, available which throw some light on the extent of sewage pollution arising from these sources. They are the population of the cities in question and the pumpage of their water-works. Municipal engineers are accustomed to estimate the sewage discharged from a city with well-established sewage and water systems as approximately equivalent to the pump- age of the latter. I have accordingly prepared a table which includes practically all of the cities provided with these works 199 in 1897, and states the pumpage in gallons per day, the popula- tion, and pertinent data concerning the systems in discussion. The population is that reported by the census of 1890, and the figures for 1897 would show a considerable increase owing to the rapid growth of the urban population in the vicinity of Chicago during the past decade. The second part of the table includes the smaller cities with water-works but without de- veloped sewage systems. These do not contribute to the stream POPULATION AND PUMPAGE IN CITIES WITH SEWAGE SYSTEMS. Daily Pumpage City Population in 1890 in. gall Remarks. Lllinots Aurora 19,688 1,338,570 |Combined sewage system Chicago 849,850 520,275,109 | Population 1,099,850,from which 250,000 was de- ducted for area of City draining directly into Lake Michigan. Pump- age is that at Bridge- port. Elgin 17,823 1,143,488 |Combined sewage system Hinsdale 1,584 124,000 Joliet 23,264 2,500,000 |Part separate, part com- bined systems. Kankakee 9,025 1,200,000 LaGrange 2,314 223,609 |Combined sewage system La Salle 95855 1,503,835 Lemont — ooo |Population not given in 1890 apart from that of township. Mendota 3,542 205,479 |Separate sewage system. Ottawa 9,985 511,000 |Sewage system incompl't. Pekin 6,347 750,000 ,; “ Peoria 41,024 5,000,000 Peru 5,550 216,183 |Sewage system incompl't. Pontiac 2,784 750,000 |Pumpage estimate re- duced from 2,000,000 gal. Streator 11,414 2,000,000 Utica 1,094 720,000 |Water supply from ar- tesian wells. Watseka 2,017 150,000 |Pumpage estimated. Wheaton 1,622 70,000 |Sewage system incomp!'t. Wisconsin Waukesha 6,321 500,000 |Separate sewage system. Indiana La Porte 7,126 747,788 Total 1,032,229 540,529,061 Total pumpage, 442.17 cu. ft. per sec. a EE Es ed a ee eee 200 waters a volume of sewage equal to the pumpage, though their imperfectly developed systems of drainage, combined with the surface run-off, carry some sewage to the stream. POPULATION AND PUMPAGE IN CITIES WITHOUT SEWAGE SYSTEMS. City Population in 1890 Sane ee Remarks. Lllinots : Batavia 3,543 2,500 1,500— 3,500 gallons. Braidwood 4,641 5,500 1,000— 10,000 a Chenoa 1,226 20,000 Delavan 1,176 50,000 Dundee 2,073 70,000 Earlville 1,058 25,500 Elmwood 1,548 19,000 7,000—31,000 gallons, El Paso 1,353 27,500 25,000—30,000 +“ Fairbury 2,324 71,500 53,000—90,000_ “ Forrest 1,021 8,442 Geneva 1,692 40,000 Pumpage estimated. Lacon 1,649 15,000 Lexington 1,187 60,000 Lockport 2,449 44,500 Minonk 2,316 109,689 Momence 1,635 250,000 Morris 3,653 54,795 Plano 1,825 31,500 Princeton 3,396 650,000 Spring Valley 3,837 5 5,000 Washington 1,301 100,000 Wenona 1,053 23,000 21,000—25,000 gallons. West Chicago 1,506 20,000 Total 47,562 1,753,426 Total pumpage, 2.8 cu. ft. per sec. The principal sources of the sewage contributed to the Illinois River above Havana are Chicago, Peoria, and the smaller cities within the drainage basin. The amounts contributed by each are approximately 520,275,109, 5,000,000, and 16,007,378 gallons respectively per day. The total amount of 542,282,487 gallons per day or 838.7 cubic feet per second is about 8 per cent. of the average flow of the river at Havana and exceeds by 40 per cent. the estimated low-water flow at Cop- peras Creek dam, eighteen miles above our plankton station. In 1890 the population of the two larger cities and the total of the remaining smaller ones was respectively 849,850, 41,024, and 188,817, a total of 1,079,691, 250,009 having been deducted 201 from the population of Chicago, as before stated, because of the tact that the drainage of certain districts did not enter the I]li- nois River. It is apparent that Chicago, with a population four times and a pumpage twenty-five times as great as that of the remaining territory, is the principal source of sewage, over- shadowing all others by its magnitude. The sewage of Chicago during the period of our operations was mainly discharged into Chicago River, a tributary of Lake Michigan. An area of 50.63 square miles lying within the city limits and having in 1897, according to estimates kindly fur- nished us by the engineering department of the Sanitary Dis- trict,a population of 250,000 to 300,000, drains directly into Lake Michigan. The water supply of Chicago is drawn directly from the lake,and to decrease its pollution by sewage, pumping works were established at Bridgeport which raised the fouled water of Chicago River into the [llinois and Michigan Canal, which emp- ties into the Illinois River at La Salle. At low-water stages the pumpage of Bridgeport prevented the discharge of a considerable amount of the sewage into the lake, reversing at times the direc- tion of the current in the river. During floods the pumps were powerless to prevent the discharge of large amounts of sewage into the lake. Under the conditions prevailing during the years of our operations a considerable portion of the sewage of Chicago thus found its way into the Illinois River. This sewage included a large amount of industrial wastes, especially from the Union stock-yards and slaughter-houses connected therewith. The average daily pumpage of the city water-works in 1897 in Chicago was 265,530,910 gallons—an amount 50 per cent. less than the pumpage at Bridgeport. The amount discharged into the Illinois and Michigan Canal thus represents a somewhat di- luted sewage as compared with that from other sources. Chemi- cal examinations of the canal water indicate (see Palmer, ’97) that the maximum period of decomposition of the sewage passed before the water entered the river. The location of the crest of this wave varied with the temperature, ranging from Lock- port to Morris. Bacteriological determinations (see Jordan ’00) 202 also indicate a somewhat similar wave of bacterial develop- ment, which is to be correlated with the wave of nitrification detected by the chemical analyses. By the time the sewage of Chicago entered the Illinois River at La Salle it was thus al- ready in the advanced stages of decay and available for the sup- port of the phytoplankton or other vegetation, if, indeed, it was not already used to some extent by these agencies. The progressive nitrification of the sewage in the canal is shown by the average nitrates found by Palmer (96) at Lockport (.84), Morris (1.44), and La Salle (2.51 parts per million ). The average at Havana, about one hundred miles below La Salle,in the same year, was only 2.34 with the added amount from Peoria’s con- tribution. At Kampsville, about 190 miles from La Salle, the amount falls to 1.39. The sewage of Chicago under conditions prior to the open- ing of the drainage canal in 1899 thus enters largely into the sources of fertility of the river water. It reaches the maximum of decomposition before mingling with the channel waters at La Salle, and is reinforced by the sewage and wastes of Peoria. The products of decomposition ( nitrates ) continue in dimin- ishing quantity, diluted by tributary streams—as, for example, by Spoon River, where the average amount of nitrates (1.01 ) is somewhat less than that of the river at that point (1.58, for 1894-99 )—and utilized by the developing phytoplankton and other aquatic vegetation. Entering practically at the head- waters of the Illinois, it becomes one of the most potent fac- tors in the maintenance of the abundant plankton found in the river and its backwaters. The sewage of Peoria, as represented by the pumpage of the water-works, is but a small fraction of the total amount re- ceived, being less than one per cent. if industrial waters are included. For two reasons its effect upon the plankton in the river at Havana is proportionally much greater than the fig- ures indicate. The firstis the proximity of Peoria, it being 55.7 miles above Havana. The maximum stages of decomposition are usually passed, even in the coldest weather, before the sew- 203 age reaches our plankton station, so that its fertilizing effect upon the water has been operative for some time. ‘T'he second reason lies in the fact that large industrial plants with private water supplies—such as the distilleries and cattle-feeding yards connected therewith and the glucose factory—discharge im- mense amounts of organic wastes directly into the river. As many as thirty thousand head of cattle are often on hand at one time in these feeding-yards, and the refuse from the feed- ing-pens is flushed into the stream or piled at the river’s edge till a rising flood carries it away in huge floating islands. The contributions from these sources at Peoria and Pekin are con- siderable. The comminuted vegetable debris of the silt owes its origin to this source in some degree, and it shares also in producing a wave of bacterial development (Jordan, *00), of putrefaction (Palmer, 97), and of the rapidly developing plank- ton organisms whose crest lies between Peoria and Havana. The contributions of sewage from the smaller cities in the drainage basin above Havana are relatively so small, so scat- tered, and so mingled with tributary. waters in many cases be- fore they enter the river, that no localized effect upon the plankton of the stream can be traced. The direct conveyance into drainage channels of so large an amount of animal wastes as occurs in sewage diverts from the soil and adds to the water an unusual, and, owing to the narrow confines of our streams, a proportionately great, source of fertility. In these particulars, together with its unusual ex- tent of impounding backwaters, its low gradient, and its im- mediate access to markets, the Illinois River offers a magnifi- cent field for the development of a scientific aquiculture. CHEMICAL CONDITIONS AND PLANKTON PRODUCTION. A summary of the chemical conditions as related to the production of plankton in the four localities, Illinois and Spoon rivers and Quiver and Thompson’s lakes, yields some evidence of correlation, and also some points of difference which indi- cate the operation of other factors than nutrition in determin- ing the production of plankton. The following table—giving 204 the sum total of the averages of the nitrogenous matters (free ammonia, organic nitrogen, nitrites, and nitrates) and also the average plankton production—sets forth in brief the relative fertility and production of the four localities. Sum of averages of Locality. nitrogenous matters —parts per million. Average plankton— cm.* per m.? Hilineis iverson -.:% 3.617 1.91 Spoon Raver see. «20 2.586 384 Ouiver vlLiakersyss cos: 1.456 1.62 Thompson’s Lake.... 2.160 6.68 There is more nitrogenous matter in the streams than in the lakes, but also less plankton. Nutrition for the plankton is present, but time for breeding, owing to the more recent or- igin of stream waters, has not been afforded there, while in the lakes, which have somewhat of a reservoir function, there is time for growth of the plankton, and the store of food is de- pleted as compared with that in the river. It is also evident that there are unutilized stores of food in the rivers affording a basis for further development of the plankton. The Illinois River exhibits the greatest fertility (total nitrogenous matters 3,617), owing largely to sewage and in- dustrial wastes. These matters cause the high chlorine (21.6) and the large amount of free ammonia (.86) and organic nitro- gen (1.08), while the abundant solids in solution (304.1) and the nitrites (.147) and nitrates (1.58) show how large a part has reached the last stage of decomposition. The unutilized prod- ucts of decomposition are without exception in the data here discussed greater in the waters of the channel than in the trib- utary or impounded reservoir waters. In Spoon River the solids in suspension are highest (274.3) and those in solution least (167.1), a condition due to the re- cent origin of its water and to the large amount of silt which it carries. The organic origin of some of this silt is shown by the large loss on ignition (41.9), the oxygen consumed (14.1), the albuminoid ammonia (.604), and the total organic nitrogen 205 (1.292), all of which are in excess in its waters. The freedom from sewage is evidenced by the low chlorine (3.8), while the considerable amounts of free ammonia (.245), mtrites (.039), and nitrates (1.01), indicate organic decomposition in progress or completed. In the absence of any considerable contamina- tion by sewage it seems probable that these substances have their origin in the organic silt and the soil waters of the very fertile catchment-basin of the stream. The water of Spoon River, in so far as the nitrogenous substances (2.586) are con- cerned, could support a much more abundant plankton than it produces (.3884). Asin the case of the main stream, the ex- planation of the slight production les in the recent origin of the tributary water. Impound Spoon River water in Thomp- son’s Lake, and it produces an abundant plankton. In food resources Quiver Lake is the poorest locality of the four (1.456, total of nitrogenous substances), having 40 per cent, of the amount of the nitrogenous substances in the Illinois, 56 per cent. of that in Spoon River, and 67 per cent. of that in Thompson’s Lake. The suspended solids (268.9), the loss on ignition (27.5),and the oxygen consumed (5.9), are least here as a result of slight access of silt-laden waters. The chlorine is low (4.8), and would be much lower if contaminations from river water at overflow could be eliminated; and corroborative evi- dence of the slight contamination of the waters of this lake by sewage is seen in the amounts of free (.165) and albuminoid (.251) ammonia, of organic nitrogen (.61) and nitrites (.025), all of which exhibit minimum averages in this lake. Organic mat- ter in decay is less abundant here than in the other localities, being, for example, about 50 per cent. less than in Thompson’s Lake. The final products of decay, the nitrates, are greater (.66) than the amounts of organic matter would lead us to ex- pect, and are probably due in large part to soil waters from the drainage basin. In the light of the production of Thompson’s Lake (6.68) the small amount of plankton produced in Quiver Lake (1.62) finds no adequate explanation in a reduction of 33 per cent. in the total nitrogenous substances. Flushing by tribu- 206 tary water and abundance of submerged non-rooted vegetation are the more potent factors in the failure of the plankton de- velopment in Quiver Lake. In most particulars the averages of the analyses of water from Thompson’s Lake approach those of the river water, from which it draws its main supply. There are less solids in sus- pension (282.9) than in the river as a result of sedimentation, and less in solution (44.6)—probably the effect of the small amount of creek water, or of the utilization by the plankton and vegetation of substances held in solution. The loss on ig- nition (86.5), oxygen consumed (11.9), albuminoid ammonia (.546), and organic nitrogen (1.05), all run higher than in the river as a result of the greater amount of plankton. The de- creased amounts of free ammonia (.422) and of nitrites (.048) as compared with those in the river (.86 and .147) would seem to indicate less decomposition here, while the small amount of nitrates (.64)—the least of all the averages—suggests utiliza- tion of these matters by the plankton, which here reaches a greater development than in any of the other localities under present consideration. SEASONAL CHANGES IN CHEMICAL CONDITIONS AND PLANKTON. The data concerning these changes are given in Tables X— XIII., and they are presented graphically in Plates XLIII-— L. They afford evidence for the following general conclusions: There is a major seasonal movement in the chemical con- ditions which can be traced in the analyses for each year and each locality. There are, in addition to this wide-spread and recurrent cycle of changes, many abrupt and often considerable fluctuations due to floods, while others are of minor importance and apparently of local origin. The various nitrogenous sub- stances to a considerable extent fluctuate together. The quan- titative fluctuations in the plankton show no intimate and im- mediate correlation with those of any substance determined in the analyses. Certain relations of the plankton to the quantity of nitrogenous substances are however indicated, but precise quantitative correlations cannot be established. The operation 207 of other factors is evident, chemical conditions alone offering no satisfactory clue to causes of many of the fluctuations in the amount of plankton. The cycle of seasonal fluctuations in chemical conditions is best seen in years of more normal hydrograph, such as that of 1898, and it is more regular in the backwaters, such as Quiv- er and Thompson’s lakes, than it is in tributaries such as Spoon River, or in the [lhnois itself. In the streams the floods produce irregularities which either do not enter the reservoir backwaters or reach them only in diminished volume. The varying degree of contamination by sewage in the different lo- calities and in different seasons in the same locality adds an- other element which diversifies the seasonal changes and makes it more difficult to detect the common features which the fluc- tuations exhibit in all the localities. The cycle of seasonal fluctuations (see Pl. XLII.-L.) in the chemical conditions is, in the most general terms, an in- crease in the nitrogenous compounds during the colder months and a decrease during the warmer ones. The maximum period usually appears in October and continues until the following summer, declining in May and June to the summer minimum, which in the following October and November rises again to the winter maximum. ‘This fluctuation is somewhat similar to that found in soil waters. This coincidence suggests the oper- ation of fundamentally similar causes back of the common phe- nomenon. These maximum and minimum pulses in the [llinois River in 1896 (Pl. XLII.) are most evident in the nitrates and free ammonia, though traces of their influence can be detected in the curve of the albuminoid ammonia. The suppression of this spring flood and the recurrence of four minor but unusual floods during the summer and fall are probably the cause of the nonconformity of some of the substances to these pulses and of the irregularity which they all exhibit in this year. In 1897 (Pl. XLIV.) the curve of the nitrates again exhib- its these pulses, but they are not apparent elsewhere unless it 208 be in the free ammonia. The prolonged and unbroken low water from August to the end of the year, and the consequent concentration of the sewage in the river and the marked de- velopment of the water-bloom during this period, seem to have obliterated the minimum pulse in all but the nitrates. The marked rise in chlorine and free ammonia gives some idea of the unusual degree of concentration of the sewage. In 1898 and the first three months of 1899 (Pl. XLV.) these pulses are much more evident, being traceable in the nitrates, albuminoid ammonia, organic nitrogen, and oxygen consumed. The marked depression of the free ammonia during the flood season in a measure modifies its conformity to these pulses. A relation of these maximum and minimum pulses to the erowth of the plankton is suggested by the chronology of the chemical (especially that of nitrates) and the plankton curves. The spring maximum of plankton production, which normally occurs in the last of April and the first of May, comes toward the close of a long period of high content of nitrogenous mat- ters. It is followed by or is coincident with the decline in these substances. With the decline in plankton production in late autumn the nitrogenous substances again increase (PI. XLUI-XLV.). During the low water of 1897, when the mid- summer minimum of nitrogenous substances was overshadowed by the concentration of the sewage, we also find a marked in- crease in plankton production as contrasted with that of cor- responding seasons of 1896 and 1895. The warm season is pre- sumably one of more rapid nitrification, the heat favoring the more rapid decomposition of the organic matter in water, but excepting instances of great sewage concentration, as in the late summer of 1897, we do not find an increase or an accumu- lation of the products of such decay in the water during the warm season. Indeed, the opposite seems to be the tendency. The explanation of this phenomenon lies, it seems, in the rapid utilization of the nitrogenous products of decay by the nitro- gen-consuming organisms of the water. In open water these are the chlorophyll-bearing organisms of the plankton. In 209 lakes rich in vegetation the grosser forms of aquatic vegetation draw heavily upon these resources. The accumulations of de- cay in winter and the increased products of decomposition in summer are all largely and promptly transformed again into organized matter, leaving only an unutilized residual mini- mum which represents an equilibrium of the processes of growth and decay in progress in summer waters. The seasonal distribution of floods may also enter as a determining factor in the problem. The coincidence of the spring plankton maximum and the decline of nitrogenous matters in the river water has its par- allel in the decline of nitrates in soil waters with the pulse of spring vegetation. In both cases the decline in nitrogenous matters seems to be due to utilization by growing vegetation, by chlorophyll-bearing organisms. These maximum and minimum pulses of nitrogenous mat- ters may also be traced in the analyses of samples from Spoon River. In 1896-97 (PL XLVI.) the nitrates exhibit most clearly the fluctuations in question. Traces of their presence can be detected in the plottings of the organic nitrogen, albuminoid and free ammonia, and oxygen consumed, though in all these cases the effect of flood waters is also evident and cannot be eliminated from the problem. Invasion of Illinois River water is also apparent in October of the low-water period of 1897, be- ing shown especially by the chlorine curve. In 1898 and the first three months of 1899 both the cold weather maxima and the warm weather minimum are more sharply defined and appear in all the substances above enumer- ated. The plankton of Spoon River, with the exception of that of the low-water period of 1897, is too insignificant to make much of a showing even when plotted upon a scale tenfold that used for other stations (see explanation of Pl. XLVI.); nevertheless we still find here the same midsummer reduction in nitrogenous substances which has just been explained as the result of the utilization of such matters by the phytoplankton. 210 In spite of this seeming contradiction, | believe the explana- tion still holds in the case of Spoon River. The minimum peri- od occurs during the time of low water, when the principal source of the flow in the stream is ground water which has already been robbed of its nitrates to some extent by terrestrial vegetation. Again, the plankton production of Spoon River, judging from the development of the water-bloom (Huglena), consists largely of chlorophyll-bearing organisms, which also rob the water of its nitrogenous substances. The period of de- velopment of the water-bloom covers the months of summer and early autumn, thus coinciding with the period of depressed nitrates. It is quite certain that the collections of the silk net fail completely to represent the quantity of those minute or- ganisms which compose the water-bloom, and thus give no adequate clue to the amount of nitrogen-consuming organisms present in these or other waters. The reduction in nitrates in this stream during summer months is not, however, as great in quantity as it is in the Illinois River (cf. Pl. XLV.and XLVIL.). The excess of sewage in the latter creates a greater winter maximum, thus permitting a greater range in reduction to the residual minimum of midsummer, which is about the same in both streams. But little correlation between the chemical conditions of Spoon River and its plankton production can be established beyond the reduction in nitrates in the plank- ton maximum of the autumn of 1897 at a time of abnor- mal low-water. Under normal conditions the plankton curve (silk-net catches) exhibits no movement correlated with or commensurate with the changes in chemical conditions. Flood and current afford here no time sufficient for the expression of the chemical factors. In Quiver Lake the maximum and minimum periods ap- pear with distinctness and affect all of the substances in ques- tion. This is partly the result of the diminished effect of floods in this reservoir area, and also of the delimitation of the lake as a separate unit of environment with the cessation of overflow. During the flood period (see Pl. III. and hydro- 211 graphs on Pl. XLVIII. and X LIX.) the lake receives in addition to the drainage of its own catchment-basin some access of flood waters from the bottom-lands above and from the adja- cent river. The water along the eastern shore, even in flood conditions, is “ lake” rather than river water, as a comparison of the plottings of the analyses of water from the two sources clearly demonstrates. Our collections of plankton and water samples were taken within or near this belt of lake water, in which contamination by flood waters was not usually noticea- ble. Compare in this connection the chlorine curve of the river and lake (Pl. XLV. and XLIX.). To some shght extent, then, the analyses pertain to two sources: to the waters of overflow, largely belonging to the colder months and period of the maximum of nitrogenous substances; and to the waters of a spring-fed lake, delimited during the period of low water and of the minimum of nitrogenous substances. The data at hand do not cover low-water conditions during a “maximum’”’ period, which might give evidence of a seasonal cycle in chemical conditions in this lake independent of the river overflow. From conditions elsewhere it seems probable that such a cycle does occur here also, though the overflow and probable contamina- tion may serve here to heighten somewhat the contrast be- tween the maximum and minimum periods of the seasonal cycle. . In the autumn months of 1896 and 1897 covered by the analyses, the rise in nitrates only is indicated (Pl. XLVIII.), the summer minimum continuing through the low-water period of autumn. In 1898 and the first three months of 1899 (Pl. XLIX.) the period of maximum, November to May, is well distinguished from that of the minimum, May to November, and not only in the nitrates but to some extent also in all of the other substan- ces, appearing most clearly in the free and albuminoid ammonia and the organic nitrogen. As in the Illinois River, so here also the sprmg maximum of the plankton (Pl. XLIX.) comes at the close of the period 212 of maximum of nitrogenous substances in the water and is fol- lowed by a period of depression in these substances, and in this case by a much more marked fall in the amount of plankton, which does not again rise until the return of the nitrogenous substances in the autumn. The unutilized minimum of nitrates during the summer season is but a trifle less than that in the river (cf. Pl. XLV. and XUIX.), but the fact that all the other forms of nitrogenous matters are not only low but are lower than in the river throws some light on the shght devel- opment of the plankton here as compared with that in the river during this period of the summer minimum of nitroge- nous substances. While the small amount of plankton seems inadequate to explain the marked reduction in the various ni- trogenous substances, it may be that the more permanent veg- etation, the submerged aquatic flora of this lake, is an import- ant factor in the reducing process. In its seasonal production the plankton of Quiver Lake shows a general correlation with the movement of the chemical changes, though all of its fluc- tuations are not commensurate with the fluctuations of the ni- trogenous materials. The operation of other factors—such as the submerged aquatic flora and replacement by tributary wa- ters—must be called in to throw light on all the plankton changes in this lake. In Thompson’s Lake the seasonal cycle of periods of maxi- mum and minimum amounts of nitrogenous matters is almost as well defined as it is in Quiver Lake. The plottings of the analyses (Pl. L.) from September, 1897, to March, 1899, include two periods of winter maximum and one of summer minimum, all of which are well defined, and affect not only the nitrates butalso the organic nitrogen, the albuminoid and free ammonia, and the oxygen consumed. The diminished effect of floods and of unusual flushes of sewage in this reservoir backwater is evident in the greater regularity of its seasonal curves of nitrogenous substances as contrasted with those of the river. Its close dependence upon the river for its water supply is shown by the similarity of its chlorine curve to that of the 215 river. Therise in chlorine during the minimum period, July to November, indicates the entrance into this lake of sewage- laden waters of the river during this period, but it brings with it no corresponding increase in the residual nitrogenous sub- stances. The depression of the nitrates, and possibly of the other forms of nitrogen, may be referred here as elsewhere to their utilization by the phytoplankton and submerged vegetation of the lake during their period of growth. Asin the Illinois River and Quiver Lake, the spring maximum of the plankton appears at the close of the maximum of nitrogenous substances and is followed by their minimum period. The autumn maximum appears, at least in 1897, somewhat before any marked in- crease in the residual nitrates, though in both this year and the following one it extends into the period of rising ni- trates. A general correlation thus exists between the seasonal production of plankton and the seasonal fluctuations of ni- trogenous substances. The seasonal fluctuation of the several nitrogenous substances exhibits some interrelations with the changes in the plankton, and especially with the accession of flood waters, and some variations from the general maximum-minimum cycle above discussed which call for brief notice. The nitrates, the final products of decomposition, exhibit the maximum-minimum cycle most clearly, as, for example, in Pl. XLV.,XLIX., and L. The fluctuations which affect the other substances appear here in diminished prominence, as may best be seen by comparing the plottings of Spoon River (Pl. XLVI. and XLVII.) with those of Thompson’s Lake (Pl. L.). The close of the maximum period of nitrates is usually later than that of the free ammonia (PI. L.), and extends for a varying distance into the period of growth of vegetation. This growth in our latitude becomes marked in the last days of April and the first of May, and continues, in some plants at least, until the frosts of October. The nitrates do not reach minimum levels, how- ever, (see Pl. XLV.—L.) until late in June. In like manner the close of the minimum period is frequently delayed beyond the 214 limits of the growing period of vegetation into November or even December. This seeming inertia in the seasonal move- ment of the nitrates seems to be due on the one hand to the gradual utilization of the accumulations of the winter and con- tributions of the spring floods by the spring plankton ; and on the other, to the slow accumulations of the autumn and to utilization by the autumn plankton, which, as in Thompson’s Lake in 1897, often attains a considerable development. A somewhat intimate connection between the nitrates and the plankton maxima can be detected in many instances in the diagrams. When the plankton increases, the nitrates often exhibit ‘a depression, the extent of which, however, is not always proportionate to the change in the plankton. This absence of any constant ratio between the apparent changes in these two factors indicates the operation of other factors, one doubtless due to defects in the quantitative plankton method, and another due to changes in the component organisms of the plankton. In the [lhnois River in 1895-96 (Pl. XLII.) the plankton maxima of April and October are accompanied by a marked fall in nitrates; on the other hand, those of November, June, and August appear with rising nitrates, the last two accompanying floods. ‘The depressions in nitrates in October, December, Feb- ruary, June, July, and September are not in any case associ- ated with arise in the plankton, though often with the initial stages of the flood. In 1897 (Pl. XLIV.) the April-May, July, September, and October maxima are all associated with de- pressions of the nitrates. The February and March depressions of nitrates occur with floods, while in November and Decem- ber no correlation is apparent. In 1898-99 (Pl. XLV.) the effect of the May, June, and July maxima can scarcely be detected in the nitrate curve, while those of December and March pro- duce corresponding depressions. In this diagram neither plank- ton nor nitrates show marked changes after July. In Spoon River the development of plankton is apparently so shght and the nitrates are relatively so abundant that no 215 correlation between the respective fluctuations is apparent in the data except in the fall of 1897, when an unusual minimum of nitrates appeared in conjunction with an unusual develop- ment of plankton (PI. XLVI.). Decrease in nitrates often at- tends the initial stages of flood independently of plankton development, as in December, 1896 (Pl. XLVI.). Some nitrate increases, as in the autumn of 1896 (Pl. XLVI.), appear with the crests of floods, especially those of the gradual type. Other fluctuations in the nitrates—and they are often considerable— show no correlation with available data In Quiver Lake in 1898-99 (Pl. XLIX.) the plankton maxima of April-May, June, and December all occur when nitrates de- crease. The tendency of nitrates to increase and then fall again with the crest of the flood is apparent in January, March, May, November, January, and March. In Thompson’s Lake in 1897-99 (Pl. L.) practically all of the maxima are attended by a greater or less diminution of the nitrates. This appears in October, November, December, April- May, June, July, August,and December. The effect of floods in decreasing the nitrates in their initial stages and subse- quently increasing them is slightly indicated in January, Feb- ruary, November, and February. The nitrites exhibit a tendency in the Illinois River to ex- cess during the low-water period of midsummer (Pl. XLIII.— XLYV.), averaging about .8 to .4 parts per million to .1 during the remainder of the year. This excess was prolonged into November in 1897 with the low-water period of that year. It seems thus to attend the concentration of sewage in the river. No constant correlation of movement between the nitrites and plankton can be detected. In a few instances, however, plank- ton maxima coincide with marked decrease in nitrites, as, for example, in the river in September and October, 1897 (PI. XLIV.), and the spring maximum precedes the rise in nitrites in each year. The changes in the nitrites show no constant correlation with those of other forms of nitrogen, though at 216 times they exhibit indications of a common movement with the nitrates or the free ammonia. In Spoon River (Pl. XLVI. and XLVI.) the summer rise in nitrites is not apparent except in the low water of 1897. The decay of organic matter is thus less active during this season in tributary water than it is in the main stream. In contrast with the summer, the winter exhibits somewhat more nitrites, but these are not markedly different in amount from those in the main stream at that season. The only correlation between the nitrites and the plankton of this stream appears in 1897 from May to December, when plankton maxima are uniformly attended by decrease in nitrites. As elsewhere, they present no constant relation to the fluctuations of other forms of nitrogen. In Quiver Lake (Pl. XLVIII. and XLIX.) the nitrites have their maximum during the colder months and the flood period. A marked depression of nitrites appears with the May maxi- mum of the plankton in 1898 (Pl. XLVIIL.). In Thompson’s Lake (Pl. L.) the changes in the nitrites are slight, irregular, and without apparent correlation either with other nitrogenous substances or with the plankton. Like the nitrates, the nitrites are not greatly and immediately affected by the accession of flood waters, and they run lower in the reservoir backwaters than in the main stream. The albuminoid ammonia and the total organic nitrogen fluctuate together so closely (see Pl. XLIX.) that it seems un- necessary to distinguish between them in this discussion. The seasonal fluctuations in these substances in the [lnois River (Pl. XLUI-XLV.) are not marked, as a result apparently of the somewhat uniform accession of sewage. The dilution of the sewage consequent upon overflow is to some extent offset by the large accessions of these substances, which as silt and leachings accompany flood waters. A slight increase attends concentration in the low water of 1897 (Pl. XLIV.), and a slight decrease comes with the period of overflow of the same year. Similar movements are less evident in the other years 217 (Pl. XLIII. and XLV.). The effect of sudden floods, presuma- bly those of tributaries but a short distance above Havana, appears in February, 1896 (Pl. XLIII.), and in 1899 (Pl. XLV.) as a twelve- and two-fold increase respectively, which is re- markably abrupt and is followed in both cases by a quick but somewhat more gradual return to the previous condition. Owing to the complexity alike of the substances included in these items of the analysis and of the plankton itself, no uniform correlation of these factors can be discovered. ‘T'wo different and in a certain sense opposite tendencies can be de- tected in the relationship of the movements of the plankton to those of the substances under discussion. During the winter season and the period of excess of nitrates, plankton pulses are attended by increase in the albuninoid ammonia and organic nitrogen. This appears in the Illinois with the pulses of April, 1896 (Pl. XLIII.), and December, 1898 (Pl. XLV.). During the warmer months, when most of the plankton pulses occur, the opposite tendency is seen in the movement of these substances. They tend to decrease at times of plankton pulses, as may be seen in August and October, 1896 (Pl. XLIII), in May, July, September, and October, 1897 (Pl. XLIV.), and in June, 1598 (Pl. XLV.). With the pulses of December, 1895 (Pl. XLIT.), and May, 1898 (Pl. XLV.), no marked effect in either direction is apparent. In Spoon River any seasonal movement of the albuminoid ammonia and organic nitrogen is quite thoroughly masked by the disturbances due to floods. In 1898 (Pl. XLVII.) these substances are a trifle lower in the warmer months than in the colder, a condition which may result from the prevalence of floods in the latter season. In 1897 (Pl. XLVI.) they increase during the warm season and period of low water attending a development of the plankton unusual in the water of this stream. The effect of flood upon the quantity of these substances in the water of this stream is well defined, and seems to throw light upon the relation which flood waters bear to the plankton 218 of the main stream. Not all of the floods which flush this tributary appear with corresponding prominence in the hydro- graph of the main river, which is the one plotted upon all the diagrams pertaining to Spoon River. In many instances they coincide. All instances in the chemical diagrams (Pl. XLVI. and XLVII.) of abrupt, steeple-like eminences in the curves of albuminoid ammonia and organic nitrogen (and also of oxygen consumed) are due to sudden floods, and appear most promi- nently when the date of collection of the water sample coin- cides with the initial stages of the flood. This is well shown in September, 189% (Pl. XLVII.). Not all of the samples from flood waters were collected at times which afford evidence for the enriching effect of the initial stages of these tributary flushes. The relative amount of these and other forms of nitrogen which floods bring to the river is well shown in this flood of September, 1898 (Table XI. and Pl. XLVII.). On August 80 the amounts of albuminoid ammonia (.32) and organic nitrogen (.6) are normal for that season of the year. With the flood of the first week of September these amounts increase more than tenfold (being 3.6 and 8.32 respectively ), falling again a week later to the normal (.2 and .48). A large part of this matter is in suspension. For example, in the flood of May, 1898 (Pl. XLVII.), about 86 per cent. of the albuminoid ammonia (2.32) and 90 per cent. of the organic nitrogen (5.46) was 1n suspension. It is not plankton, neither is it to any large extent sewage, which the tributary floods of Spoon River bring to the [hnois as organic nitrogen, but largely organic debris not yet decayed. The sewage-laden river habitually carries much less of these substances than these tributary flood waters laden with this organic debris from fertile prairies. The latter thus become very important agents in maintaining the fertility of the river water. The effect of these periodic additions of nitroge- nous substances by tributary floods upon the plankton of the river will be discussed in another connection. A decrease in these nitrogenous substances attends the two 219 plankton pulses of 1897 (Pl. XLVI.) in the warm months of May and September, but the increases noted with the pulses of plankton in the winter in the [llnois River are not apparent in the case of the pulses of February and December in this stream, though no decrease appears as in the summer months. In Quiver Lake in 1898-99 (Pl. XLVIII.) a seasonal move- ment in the albuminoid ammonia and the organic nitrogen is evident, though it seems to accompany the access of sewage- contaminated waters of overflow, as appears on comparison with the chlorine curve. This seasonal movement is evident as a depression of the curves during the warm and low-water months, and as an elevation during the colder months of the flood period. As in Illinois and Spoon rivers, the plankton pulses in Quiver Lake of the warm period, in May and June, are attended by a temporary decrease in these nitrogenous sub- stances. A still more marked decrease in both albuminoid ammonia and organic nitrogen attends the winter pulse of plankton in February, 1899, while that of the preceding De- cember appears with an upward movement of the organic nitrogen and a downward one in the albuminoid ammonia. The correlation between the movement of albuminoid am- monia and organic nitrogen and of the plankton is thus in this instance (predominantly, at least) similar to that noted else- where in the warmer months. The very slight ripples in the plankton curve in July, August,and September attend minor increases in these nitrogenous substances, a feature noted else- where in colder months. In Thompson’s Lake (PI. L.) the albuminoid ammonia, the organic nitrogen, andthe plankton are all more abundant and ex- hibit greater fluctuations than they do in Quiver Lake. These conform in a general way to the tendencies noted in other localities. The amounts present during the colder months, October to May, are a trifle greater than in the intervening warmer period. There is also a temporary decrease in those nitrogenous matters attending plankton pulses in the warm months. This appears with the pulses of June, July, and 220 August-September, 1898. A temporary /ncrease appears with plankton pulses in eo/d months, as in December-January and February, 1899. Some exceptions to these general tendencies appear here asin Quiver Lake; such, for example, as that in the low water of the autumn of 1897, when the great plankton pulse of October-November attends an unusual wave of both the albuminoid ammonia and the total organic nitrogen. Temporary decrease in the former appears with the crest of this plankton pulse, and again in the pulse of December, along with an ‘crease in organic nitrogen. The spring maximum of April-May, 1898, comes with a rising wave of both substances, whose crest coincides with the fall in the plankton. It is evident from the data here presented that the fluctu- ations in the volume of the plankton, as determined by the methods employed by us, show some intricate correlations with the changes in the quantity of albuminoid ammonia and organic nitrogen. The massing together of all organic matters, both living and dead, indigenous and adventitious, in the de- termination of these two substances, and the composite nature of the plankton itself, including both the synthetic phytoplank- tonts, and the analytic zoéplanktonts, alike combine to conceal the relationship which exists between the succession of living forms in the plankton and the flux of nitrogenous matters in suspension and solution therein. Furthermore, the plankton is not the only assemblage of organisms concerned in this flux of matter; the bottom fauna, the fishes and other aquatic ver- tebrates, and aquatic fauna of the grosser sort, all share in effecting the changes here manifest. We lack a common unit of measurement in terms of which we can express the values alike of the chemical analyses and of the volumetric and the statistical determinations of the plankton. Precise comparisons, for example, of the changes in the organic nitrogen with the cubic centimeters of plankton and the number of diatoms cannot be made. The direction of the changes in these several elements can, however, be noted, 221 and its interpretation, in many cases at least, becomes probable, if not, indeed, certain. In the first place it may be noted that the fluctuations of the plankton are not paralleled by proportionately great move- ments in the total nitrogenous substances in the water which enter largely into their composition. For example, the spring maximum of the plankton is accompanied by no such wave in thesesubstances. Indeed,aslightrippleof depression seems to be the only concomitant fluctuation. Even granting a large mar- gin because of the absence of a common unit of measurement, it remains apparent that the fluctuations of the substances in question and of the plankton are not proportional. A single illustration, found in the spring maximum in Quiver Lake in 1898 (Pl. XLIX.), will suffice to make this point clear. The following table, drawn from Table XIII., gives the amounts of plankton and of the several forms of nitrogen present before QUIVER LAKE. Date Free Albuminoid| Organic Ree ats ¢ 1898 Ammonia | Ammonia Nitrogen Nitittes’ |) Nitrates | Plankton April V9.2 ss." .046 44 1.01 .033 65 103 Miay 3st Seu .0g2 132 .82 .022 a5 | 42.14 Day g aI Be sear ccs sve 05 .48 .98 O15 4 ee Per cent. of Change. April 19 to ; ; UIE ee, Se ea +100 sored, | —Ig | TOOTS | — 46 +3991 (April 19), during (May 3), and after (May 11) the plankton wave, and the extent of the change, in per cent., of the amount present on the 19th which each exhibits. The plankton rises from 1.08 cm.* per m.* to 42.14, falling subsequently to 4.70 and 1.97. This is an increase of 3991 per cent. No one of the ni- trogenous substances in the table exhibits a change exceeding 100 per cent.,and the average change is only 45 percent. In this case the change in plankton is eighty-eight times as great as that in the average of all forms of nitrogen, assuming, of course, that the units of measurement are comparable, 222 Three causes may be assigned in explanation of the absence of proportional correlation in the flux of these nitrogenous sub- stances and of the plankton, all of which are operative, but in varying effectiveness at different times and under different conditions. In the first place, the plankton itself constitutes but a part of the total organic nitrogen; how small a one the data at hand do not determine. Barring out error arising from the death of the plankton and from the solution of the products of its decay which might take place during the interval between the collection and analysis of the sample, we find in the relative amounts of albuminoid ammonia and total organic nitrogen in solution and in suspension respectively some evi- denceasto the possible limits of the proportionate amount which the plankton and silt together form of the total nitrogenous substances. The average amount (Table X.) of albuminoid ammonia in solution and in suspension from July 6, 1897, to March 28,1899, is .355 and .151 parts per million respectively. Plankton and silt together thus constitute about one third of the total albuminoid ammonia in the Illinois River. The rela- tive amounts of dissolved and suspended albuminoid ammoniaat the weekly intervals of analysis fluctuate according to access of flood waters and increase in the plankton. The former is the more potent factor. Usually the amount in suspension is from one third to one half that in solution, rarely equaling or surpas- singit, as in the flood of February, 1898, when it rose to .4 as compared with .28in solution. The plankton pulse of April-May, 1898, accompanies a rise in total albuminoid ammonia from .4 to .6—an increase of 50 per cent. The increase lies almost entirely in the suspended form, which rises from a previous level of .04 to .08, to .08 to .20, that is, it is more than doubled. The volumetric increase in the plankton is, however, over thirty-five-fold. Thus, under the most favorable conditions, receding flood, little silt, and plankton maximum, the increase in suspended albuminoid ammonia attending a thirty-five-fold increase inthe plankton constitutes but 33 per cent. of the total 223 amount present. During the long-extended periods of plank- ton minimum it is apparent that the plankton must constitute a very much smaller part of the total amount of albuminoid ammonia in the water. That much of the albuminoid ammonia may be in the silt is shown especially in the table (Table XI.) and diagrams (PI. XLVI. and XLVII.) of Spoon River at times of flood. In such waters there is practically no plankton—as will be shown else where from the examination of our plankton collections in that stream—although the amount of albuminoid ammonia is often very great. The average amounts of total organic nitrogen (Table X. ) in solution and in suspension during this same period are .69 and .34 parts per million respectively. The latter (.384), which represents plankton and silt, thus constitutes about one third of the total amount (1.03) of organic nitrogen in the water. The proportion of this fraction which the plankton may consti- tute under the most favorable conditions may be inferred from the increase in the suspended organic nitrogen which attends the spring pulse of 1898(Pl. XL.). This rises from a previous level of .12-.16 parts per million to .24-.64, the latter with the de- cline of the plankton, and at its maximum (.64) it constitutes 46 per cent. of the total amount of organic nitrogen in the water. On May 3, when the plankton is at its maximum, the suspended organic nitrogen is but .24, or .25 per cent. of the total. During the periods of plankton minimum the propor- tion which the plankton forms of the total organic nitrogen must be very much less than at times of plankton maximum, since the amount in suspension shows no decrease at all pro- portional to the fall in the amount of plankton. Here also floods are quite as potent as plankton in causing marked in- crease in the amount of total organic nitrogen in suspension, as will be seen on comparison of the curves of this matter with the hydrographs on Plates X LITI.—L. It is thus evident that the plankton does not form, even under most favorable conditions, any large part of the total 224 organic nitrogen—certainly less than 50 per cent. and on the average much less than 33 per cent., which figures represent the total organic nitrogen, both plankton and silt, in suspen- sion. The fluctuations of the organic nitrogen contained in the plankton are thus masked by the predominance of the dis- solved form, and by the undetermined quantity of nitrogen- containing silt. A second cause for the lack of proportional correlation between the movement in these nitrogenous substances and the plankton may lie in the utilization by the plankton itself of some forms of nitrogen included within the range of sub- stances reported in the analyses as albuminoid ammonia and total organic nitrogen. For example, some organisms of the phytoplankton may utilize as food such forms of organic nitro- gen in solution in the water as the amido-compounds and the humus acids. It may be that some of the animal wastes are turned into the more highly organized nitrogen of the phyto- plankton without passing through complete oxidation and a return to the inorganic nitric acid and nitrates. If this be the case the flux of nitrogenous matters may he quite within the range of substances here discussed, and the movements in nitrogen incident to these changes will consequently produce no pulses in the common curves of these substances. When, however, the inorganic nitrogen enters largely into the ebb and flow of the nitrogen of the plankton, the possibility of a correlated movement of plankton and organic nitrogen be- comes apparent, though proportionate pulses in the two remain improbable so long as the organic but non-living nitrogen con- tributes also to the flux of matter involved in the plankton changes. That the phytoplankton, as other low forms of vegetation, may thus utilize organic nitrogen in some of its forms as food, has been rendered probable by the experimental work of Loew. (96), Bokorny (’97), Maxwell (96), and Zumstein (99). The work of the latter is especially in point in this connection, since his experiments deal directly with a genus, Huglena, which 225 furnishes a large part of our phytoplankton of midsummer and the bulk ofthe water-bloom. The experiments of this author have shown conclusively that this chlorophyll-bearing organism is usually autotrophic (holophytic) in the light and in the ab- sence of abundant organic nitrogenous matters in solution, and under these conditions its chromatophores are a bright green. When organic nitrogenous matters in solution are abundant the organism becomes mixotrophic (half saprophytic) even in the light, and its chromatophores may become paler. In the dark it becomes colorless, and depends entirely (saprophytic) upon the dissolved organic nitrogen for its growth and multi- plication. The waters of the Illinois River and its backwaters are unusually turbid, thus excluding more than the usual amount of light. The plankton of this environment is rich in species and individuals of flagellates, alge, and diatoms, many of which exhibit this tendency to become paler. This I have noticed repeatedly in the examination of the living plankton, and to some extent in material preserved in formalin-alcohol. It has occurred in the several species of Huglena, viz., viridis, sanguinea, deses, acus, spirogyra, and gracilis. 1 have noted it also to a very marked degree in Chlamydomonas, Carteria, Trachelomonas, and Lepocinclis. It has been less pronounced in the Peridinide, in Mallomonas, and Dinobryon. Among the diatoms the most striking instances occur among the typical lim- netic forms, such as Synedra, Melosira, and Asterionella. Inthe hghtof Zumstein’s results, and in view of the chemical data exhib- iting an absence of proportional correlation between the move- ments of the organic nitrogen and the fluctuations in the volume of the plankton, and of the frequent occurrence in our waters of colorless individuals of chlorophyll-bearing species, it seems that we are justified in assuming that the flux of nitrogenous matter involved in the plankton changes lies to some appreci- able and as yet undetermined extent within the range of sub- stances included within the dissolved and suspended nitroge- nous matter of the water. 226 A third reason for the absence of proportional correlation between the movements of the organic nitrogen and the fluc- tuations of the plankton hes in the cumulative nature of the latter as contrasted with the non-cumulative character of changes in the chemical substances at whose expense it. increases. Growth and reproduction of organisms is funda- mental in the plankton pulses, and there is nothing comparable to either of these in the chemical changes of non-living matter. It remains only to discuss the correlations that do appear between the albuminoid ammonia and total organic nitrogen, on the one hand, and the plankton, on the other. The two diverse tendencies noted in the preceding pages, the one for the plankton pulses of warm months to coincide with a decrease in these nitrogenous matters, and the other for the pulses of cold months to coincide with an increase in these substances, or at least in the organic nitrogen, will be fully accounted for only when the changes in the different elements included under these common designations, the dissolved por- tion, the silt, and the plankton, shall be differentiated,and when the changes in the different kinds of organic nitrogen shall be separately unraveled, and, furthermore, when the fluctuations of the synthetic (phytoplankton) and analytic (zoéplankton) portions of the plankton can be separately expressed in terms of acommon unit. It is evident that the available chemical analyses and volumetric and statistical determinations of the plankton do not afford such comprehensive data. The incom- plete data at hand throw some hght, however, upon the nature of the correlation, and suggest the probable explanation for the two divergent tendencies noted and the numerous excep- tions thereto. As has been previously shown, plankton pulses are usually coincident, or nearly so, with an upward or a downward move- ment in the nitrogenous substances, organic and inorganic. The upward movements of the albuminoid ammonia and organic nitrogen and the downward movement in the nitrates 227 occur most frequently when the diatoms are most rapidly mul- tiplying. As will be shown later, these seasons occur in the colder months, and often precede the summer pulses of plank- ton whose crests are predominantly of the animal plankton. The upward movement of the organic nitrogen and the down- ward movement of nitrates is thus due in large part to the synthetic action of these organisms. The major plankton pulses, which are as a rule predominantly animal in their com- position, usually occur in the warmer months With their cul- mination there is always a great decrease in their food supply (the phytoplankton) and analytic processes thus predominate, . and the decay of the products of animal metabolism results in a decrease in the total organic nitrogen and leads to a recovery of the nitrates. This interplay of the synthetic and analytic processes of the phyto- and zoéplankton, is, I believe, the basis of the coincidence in the fluctuations of the plankton and of the nitrogenous contents of the water. Further reference will be made to the subject, and data illustrating it will be cited in connection with the discussion of the seasonal changes of the plankton. The seasonal changes in free ammonia seem to be due to the effect of floods and temperature upon the processes of decay, and reveal but minor correlations with plankton changes. A marked increase with rising flood waters is appar- ent in Spoon River (Pl. XLVI. and XLVI.) and occasionally in the [linois, as, for example, in February, 1896 (Pl. XLIIT.). Prolonged high water, on the other hand, tends to lower the free ammonia (Pl. XLIV.). The stagnation in the sewage- laden river when it is covered with ice at low-water stages appears in the elevenfold increase in free ammonia under the ice in December, 1897 (Pl. XLIV.). The fluctuations are also much more marked in the rivers (Pl. XLIII.—XLVII.) than in the lakes (Pl. XLVIII-L.), owing to the diminished and equalized effects of flood and sewage in the reservoir back- waters. There are repeated instances where the plankton pulses coincide with decreases in the free ammonia followed 228 by a recovery upon the decline of the plankton. T[llustrations of this may be seen in the April-May pulse in Thompson’s Lake (Pl. L.), where a decline of fifty per cent. accompanies a nine- fold increase in the plankton. The April pulse of 1896 in the Illinois (Pl. XLIIT.) coincides with a still more pronounced decline in the free ammonia. Upward movement of both plankton and free ammonia appears occasionally, as in the Illinois in September, 1897 (Pl. XLIV.), though a downward movement of the free ammonia attends the plankton pulse of the subsequent month. The free ammonia thus exhibits some evidence that it enters into the flux of nitrogenous matter involved in the rise and fall of the plankton. It decreases when the synthetic activities predominate in the plankton, and some, at least, of its increases coincide with periods of predominantly animal (analytic) plankton. The changes in the oxygen consumed coincide very nearly with those in the organic nitrogen and albuminoid ammonia both in direction and amount, and thus bear much the same relation to the plankton changes. The changes in the chlorine are of especial interest, not be- cause of their direct relation to the plankton, but on account of the fact that they indicate, perhaps better than any other ele- ment in the analysis, the relative contamination by and con- centration of the sewage in the different localities at different seasons of the year. In the Illinois River (Pl. XLII.—XLV.) the chlorine usually fluctuates in a direction opposite to that of the hydrograph, running low during high water and rising with the return of low water. Some exceptions appear, as in the rising flood of December, 1895, and the declining flood of June, 1896, the former apparently due to the flushing of sewers by initial flood water, and the latter to an irregularity for which no natural cause appears. The marked irregularity of the chlorine in the Ilhnois, indicating a corresponding instability in access of sew- age, with its additions of matter helpful or deleterious to the plankton, adds to the environment of the potamoplankton a 229 further factor of uncertainty not present, to alike degree at least, in the reservoir waters of the lake. That natural waters in this locality are not subject to the presence of chlorine (sewage) in such excess or in such fluctu- ating amounts appears on contrast of the chlorine curves of Spoon River (Pl. XLVI. and XLVII.) with those of the Illinois (Pl. XLUI-XLV.). In the former, barring a few instances of apparent contamination by river water (October, 1897, January and February, 1899), the chlorine runs uniformly low through- out the year, dropping but a trifle with rising floods. In Quiver Lake (Pl. XLVIII. and XLIX.) the chlorine similarly runs low during the period of individuality of the lake, that is, of low water. The increase in chlorine comes only at times of invasion of flood water from the river or the bottom-lands above, as, for example, in November and Deceme ber, 1898 (Pl. XLIX.). The periods of fertilization of this lake by sewage thus depend upon floods, and occur at times of greatest dilution. In Thompson’s Lake (Pl. L.) the chlorine (sewage) content exhibits the same general tendencies found in the river, from which its water supply is derived. The chlorine content runs high during low water and drops with the rise of the flood. The abrupt and numerous fluctuations of the chlorine of the river do not, however, appear in the lake, being diminished and equalized by its greater permanency. Even under these favor- able conditions it is difficult to find any constant or well- defined correlation between the chlorine pulses and those of the plankton. It may be that the fertilizing elements of the sew- age which the chlorine is regarded as representing have already been exhausted, so that the chlorine curve no longer represents a commensurate fluctuation in the fertility. In a few cases, as, for example, in December, 1897, and in January and September, 1898 (Pl. L.), a sight correlation in the chlorine and plankton curves appears, though the only relation between the two may he in the effect of changing river levels upon both, a declining 230 flood (as in September) concentrating the sewage and at the same time favoring the development of the plankton. That the sewage of Chicago is quite thoroughly rotted out before it enters the Illinois at La Salle, and that the contribu- tions from Peoria are also well advanced in decay before they reach Havana have been demonstrated by the chemical and bacteriological examinations made at the instigation of the Sanitary District of Chicago apropos to the opening of the drainage canal. The full results of this work have not as yet been published, but from the data published by Prof. A. W. Palmer (’97) from the analyses of the Chemical Survey and from the preliminary report of Jordan (’00) upon the bac- teriological examination it is evident that the nitrogenous matters of the Chicago sewage were in process of rapid oxida- tion in the upper reaches of the Illinois and Michigan canal near Lockport; that this process was largely completed before the canal waters entered the river at La Salle; and that the Pe- oria pulse of sewage is, during the summer months at least, well decayed before it reaches Havana, though in colder weather, when decay is less rapid, the sewage is not so well oxidized and the bacteria are more abundant than during the summer at this point. The following table, which has been made up from the averages in Palmer, ’97, exhibits to some extent these facts in tabular form. The increase in nitrates and decrease in free ammonia unite in indicating the extent to which decay has progressed. Total ‘Total Albu- | Total . Free riled ; : Station. below, (gaate, Hage. os) Cie | aap (pei One| eae Chicago. NEN nia : oration. tion nia. | trogen WOCKPOrt)..cs0-s-c5 2-5-2: 29 438.6 20.5 24. -092 417 84 -019 95 Morris, (222 s.cccsn 57 359.4 23.4 29.7 | 3.55 -709 1.44 149 1.72 Wjalisalllles io seePesecesee eect 95 372.3 23.03 19.6 971 -612 1.26 255 2.51 PGOr ase ee eee 158 376.7 21. 41.8 252 . 516 1.06 209 2.59 Maivalitia' snes 5 eee 199 355.3 21.2 15.4 -63 455 1.06 135 2.35 Kampsville® .............. 288 352.1 22.4 13.4 -261 .508 1.17 062 1.39 *Average July 23—Dec. 29, 1896. The influence of the sewage of Peoria upon conditions at Havana, owing to temperature changes, is not uniform 231 throughout the year, and it may be that some of the seasonal fluctuations in the chemical substances which have been dis- cussed in the preceding pages, and some of those in the plank- ton also, depend in some measure upon this changing effect of temperature upon the sewage. The following table, taken from Jordan (700), gives the seasonal changes in numbers of colonies of bacteria from May BACTERIOLOGICAL EXAMINATION OF ILLINOIS RIVER AT HAVANA. mete Locating Sere i | "Temperature No. of colonies per cm’, 1899 Gon river, in feet , | lhe an | Havana Pekin May gar... 2. 13.6 8.7 21 4,500 542,000 pamies (6: si. it 9.3 26 18,450 129,000 i capa 13.5 8.8 25 15,900 205,000 ZOVE Rae 12a 75 26 2,500 225,000 (1) ROSA 14.9 5.2 25 4,500 2,030,000 (2) saliva G5). ss 14.7 4.7 26 2,400 52,000 (3) 2s aes 2348 4.1 26 7,300 1,435,000 IQ)ng ater 36. 4.9 27 5,700 470,000 (4) DOs a: 31, 4.8 30 850 980,000 (5) JNO SO eee 27.5 4.1 26 1,550 g85,000 (6) 2B a sae 34. s 26 goo 10,000 (7) BO) ea 39. 22 29 9,800 30,000 (8) BEDts OKs 0: 40. 2.4 29 1,900 650,000 (g) ils canoe 46, 2.5 22 1,500 310,000 (10) BOL as ves ace 3.5 14 3,400 240,000 (I!) POTS BIS 49. oy 16 3,700 120,000 (12) OCH HWA. 52 2: 14.5 2,500 500,000 (13) Melee oerate 59. 32 16. 6,600 430,000 (14) WORE ee 58. 3.2 17 8,800 Zsopone 60.5 3. 12. 3,900 30,000 (15) WO Wee eM ici acier 63. a5 9. 7,000 150,000: (16) ere oer ee sis 37 10. 3,300 30,000 2D ae 47.5 4.4 ite 128,000 1,650,000 QO nm stk 43. 4. 6. 41,600 380,000 (17) DEG Oi a6 35 an Sel De 85,000 | 140,000 (18) BO) p81 35 4.8 Ii | 66,800 5,000 (1) June 21. (2) June 27. (3) July 6. (4) July 18. (5) July 25. (6) Aug. Sh) M7) ae 22. (8) Aug. 29. (9) Sept. 5. (10) Sept. 12. (11) Sept. 18. (12) Sept. 26. (13) Met 3) (14) Oct-10. (15) Oct.’31- (16) Nov. 7. (17) Nov. 30. (18) Dec. 5. 30, 1899, till the end of the year at Havana, and at Pekin, thirty-two miles above. The decline from the larger numbers in June to a fairly well-maintained minimum during midsum- mer at Havana is very evident, as is also the rise as the tem- perature lowersinthe autumn. Both the period of time andthe 232 reach of the river in which the bacterial action and attendant decay of the sewage ensues, are lengthened as the temperature falls, and we find in consequence an increase in the bacteria in the river water passing Havana which approximates fortyfold. The pulse in bacteria due to the sewage of Peoria which is found at Pekin during the summer, reaches Havana also, thirty- two miles below, as temperatures fall in the autumn. The averages of the number of colonies of bacteria found in the canal and river water at points from Bridgeport to Graf- ton during the period of analyses given in the first table are to be found in the following table, also taken from Jordan (00). CHLORINE AND BACTERIA—DES PLAINES AND ILLINOIS RIVERS, BRIDGEPORT TO GRAFTON. Distance from | Chlorine (pts. | Number of col- Collecting Stations Bree epot per million) | onies per cm.’ NG WE DOM: sank 5 tec orem etre fe) 119.2 1,245,000 MOCK DOTA cancers Sateen eee eek 2 724 650,000 (our AEN RAY Baty OCR om te 33 104.8 486,000 OLAS ai eoe tele es Sikctoere bre cE ENS 57 68.1 439,000 Ottawa ioc. is.aveis sc presen oe oes riers 81 58.5 27,400 [ea Salles a. agaaas ep cere iie ne eene 95 46.1 16,300 PL EMIYe hotsc aie cs easton tee aie lereters 123 44.2 11,200 AV OTY VALE sous cis ate ene mgn seit 159 40.9 3,660 Wresley;Gity scour eceeeG seee 165 40.9 758,000 IP Gk eo ee os eo eee ioe 175 38.4 492,600 PlaWviana a Aiare ehsicusoaree ses orleans 199 36.2 16,800 Beardstowis..:% 52+ a: sere «eee 231 29.3 14,000 Kampsyallect. 2h sinsecrersceren erect 288 22.9 4,800 Gratton gs seis nu hie ae cone eee 319 18.3 10,200 The chlorine content at the several points also appears in the table, and exhibits a steady decline from Chicago to the Mississippi River with a brief pause at Peoria. This decline expresses approximately the dilution which on an average the sewage undergoes during the low-water period. The flood season of the spring was not included in the period of analysis. From Ottawa to the mouth of the Illinois, as indicated by the chlorine, this dilution is about one third. The decrease in number of bacteria, while it may not coin- cide strictly with the completion of processes of decay still 233 gives in general a suggestive index to the extent to which oxidation of the sewage has proceeded. When the facts of both tables are taken into consideration it becomes evident that the sewage of Chicago has been thor- oughly decayed, and its fertilizing capacity presumably to some considerable extent utilized in the development of the plank- ton, before the water reaches Havana. The sewage of Peoria likewise, during the summer months, is well oxidized by the time the sluggish current of low water brings it to Havana, thus adding new resources for the increase or rehabilitation of the plankton. During the colder months the process of decay is not so fully completed owing to the lowering of the temper- ature and the increased current attending the higher water which often prevails at that season. In the winter the initial effect of the sewage upon the plankton may be witnessed, par- tially at least, at Havana. At all seasons the plankton of the channel waters passing Havana is the resultant of two succeed- ing pulses of fertilizing additions to the normal constituents of stream waters. It represents during the warmer months pre- dominantly the later phases of the cycles of organisms, which multiply and sueceed each other with considerable rapidity after the enrichment of the water. In this important particu- lar the plankton at this point in the stream differs from that of the lake, where the whole sequence of changes may be accomplished in one locality. The fact that a relatively small proportion of the tributary waters enters the stream .between La Salle and Havana makes it possible for these chemical changes to take place, and for the plankton cycles to run their courses with less interruption and disturbance than in other parts of the stream. The enrichment of the Illinois River and its backwaters by the sewage of Chicago and Peoria has been utilized thus to some considerable extent before the waters reach Havana. The chemical products of its oxidation have been converted into aquatic vegetation and phytoplankton, and some of the latter in turn into zoéplankton. The development of new 234 cycles of limnetic organisms at this middle reach of the river comes accordingly to depend to a great extent, not upon the primary contributions of the sewage, but upon secondary or even later conversions of the nitrogenous matters originally contributed. The decay of the vegetation of the backwaters and bottom-lands, and the wastes and decay of the plankton itself and of the other organisms dependent upon it, come to be to a greater extent the immediate sources of support of the locally developed plankton. COMPLETE MINERAL ANALYSES. Three complete mineral analyses of the water of the Illinois River have been made by the Chemical Survey under the direction of Professor Palmer, the samples for which were collected by us at Havana. These appear in the accompany- ing table. ANALYSES OF MINERAL MATTERS CONTAINED IN SAMPLES COLLECTED FROM ILLINOIS RIVER AT HAVANA, ILLINOIS. PARTS PER MILLION. [Nowe Iand2,| Oct. 31 and | June15, | 1897 Nov. 1, 1898 1900 (Orso) Ea Aareees Reiey sere oct Sei Aa ene sid 0.0 trace 0.0 Potassium phosphate ~ (KyPO4g.055.)... 2... 0.0 2.4 0.0 Potassium nitrate KONO es f2 cs see oc 5.05 2.4 6. Potassium nitrite KINO aS eet: 6.06 0.0 0.0 Potassium chloride KOiT eee nee ace 3.72 4.4 2.2 Sodium chloride NaC a see eats 100.85 44.2 21.4 Sodium sulphate NaeSOlre sue sere 1772 27.5 20.1 Ammonium sulphate (QMelaSOVss ndeo oc 6.21 10.2 22 Magnesium sulphate MeSOn wo. a. s: 31.02 33.4 35.5 Magnesium carbonate MgCOs........... 74.01 TaeB 69.7 Calcium carbonate CaCO ase weeeeer 137.79 150.3 267.5 Iron carbonate BeCOs nc semen: ele? ae 6.6 Alumina AlsOe eee aiiese seas 8.95 ey hic Manganese oxide MinOe neato ies 0.0 0.0 Ong Silica SIO eee neces 26.07 31.6 27.6 Total gccccecte stevaverete oe a en On ee oe 420.65 385.7 466.5 The analysis in 1897 was made in a period of prolonged low water, the effect of which appears in the large amount of sodium chloride, indicating the concentration of sewage, while the presence of potassium nitrite suggests the active decay of 235 sewage or the products of animal metabolism, such as might occur with the abundant plankton of that autumn (PI. XII.). The analysis of 1898 was made toward the close of a con- siderable rise, and it shows the effects of dilution of sewage in the lessened sodium chloride. The analysis of 1900 was made in a high-water period, and exhibits even a greater dilu- tion of sewage, as shown in the chlorine and ammonia salts. These analyses indicate an abundance of all the salts upon which plant life depends for its growth, and complete the demonstration of a chemical basis for the development in abundant phytoplankton. COMPARISONS WITH OTHER STREAMS. So far as I am aware this is the only instance in which opportunity has been offered for a comparison of the chemical conditions in stream waters and the plankton fluctuations coin- cident with them. Steuer (’01), who worked upon the plank- ton of the Danube, near Vienna, in 1898-99, cites averages of chemical analyses made in 1878. These analyses indicate that the Danube at that time was barren in comparison with the Illinois River. The average organic matter in solution as shown by the oxygen consumed was only 5.6 parts per million in the Danube to 43.4 (in 1898) in the Illinois River, while the chlorine was but 2.4 to 12.40. The conditions of analysis differ, so that the nitrogen content of the two streams cannot be compared, though the indications are that the nitrogen com- pounds are low in the Danube as compared with the Illinois River. The silica and carbonates are also lower in the former than in the latter stream. The poverty of the plankton of the Danube which Steuer describes, seems thus to be correlated with a deficient food supply, and the rich plankton of the Illi- nois with a more abundant one. In general terms, a chemical analysis of stream and lake waters throws some light on the productive capacity of the water. This appears in a comparison of the chemical condi- tions and plankton production of Quiver and Thompson’s lakes. 236 With less nitrogen we may expect to find less plankton. The contrast of [lhnois and Spoon rivers shows the same tendency, though the difference in the chemical conditions in the streams is less than that in the lakes, while the contrast in plankton production is much greater. Likewise in seasonal changes, the ereatest developments of the plankton—the spring maxima— appear at the close of a period of high nitrogen content. On the other hand, precise comparisons and correlations cannot be maintained, in part because of the operation of other factors,—such as temperature and vegetation,—and in part be- cause of the fundamental difference between chemical and biological phenomena. The fertility of a body of water must be judged, not by chemical analyses only, but in conjunction with other phenomena which condition growth and reproduc- tion. Itis also evident that isolated chemical analyses throw as little hght upon the fertility of a body of water as isolated plankton examinations do upon its productiveness. The routine of seasonal changes must be discovered in both before trust- worthy data for estimation of fertility can be obtained. VEGETATION. The aquatic environment at Havana impresses the visiting biologist who for the first time traverses its river, lakes, and marshes, as one of exceedingly abundant vegetation, indeed al- most tropic inits luxuriance. The aquatic flora of the ponds, lakes, and streams of New England, of the Middle States, and of the north central region is, as a rule, but sparse in comparison with that which here constantly meets hiseyes. He will note the entire absence of beds of Chara and patches of Nitel/a, and will find the Potamogetons fewer both in species and numbers: The shore-loving Juncacee, Cyperacee, and Hquisetums are also less in evidence, for here the shore itself is a shifting region, lacking the permanence which these plants demand. On the other hand he will find acres upon acres of “moss,” as the fish- ermen call it—a dense mat of mingled Ceratophyllum and Hlodea choking many of the lakes from shore to shore, and rendering 237 travel by boat a tedious and laborious process. Beds of lotus (Nelumbo lutea) and patches of Azolla will suggest warmer climes, while the fields of rushes (Scirpus fluviatilis), and patch- es of water-lilies (Nymphea reniformis), arrowleaf (Sagittaria variabilis), and pickerel-weed (Pontederia cordata) will recall familiar scenes in northern waters. The carpets of Lemnacee will be surprising, and the gigantic growths of the semiaquatic Polygonums will furnish evidence of the fertility of their en- vironment. Both the nature and the quantity of the vegetation varies in the different localities whose plankton has been the subject of investigation by us, and in the same locality the conditions may change at different seasons and from year to year, low water in the early summer favoring its growth, and summer floods and fishermen’s seines uprooting and sweeping it away. The following list includes only the most common and most important members of the aquatic flora, with brief notes on their habitat and frequency. Ranunculus multifidus Pursh. Found occasionally in quiet waters in shoal regions with soft alluvial bottom. Caltha palustris L. Rare, along springy shores. Nelumbo lutea Pers. Forming large patches in the more open vegetation in the permanent backwaters on very soft allu- vial bottom. Usually at some distance from shore and in quiet waters. Nymphea reniformis D.C. Common in the more open regions of the permanent backwaters in quiet regions, and along channels on alluvial bottom. — Cardamine rhomboidea D. C. Rare, along springy margins. Cardamine hirsuta L. Occasional, along alluvial margins. Nasturtium sessiliflorum Nutt.. Rare, along wet sandy mar- gins. fasturtium palustre D.C. Common, in shallow water along alluvial shores. Proserpinaca palustris L, Rare, along shady shores perma- nently fed by springs, 238 Angelica atropurpurea L. Oceasional, along margins. Sium cicutefolium Gmelin. Occasional, in swamp margins near bluffs on alluvial bottoms. Cicuta maculata L. Common, in places with the preceding. Cicuta bulbifera L. Occasional in margins of swamps. Utricularia vulgaris L. Rare in quiet backwaters, in the more open places with alluvial ooze and underlying sand and springs. Polygonum amphibium L. Common in shoal water, in places, in the flooded bottoms and along margins of permanent backwaters. Habitat usually dry at low water. Stems often attaining a length of fifteen to twenty feet. Ceratophyllum demersum L. Abundanteverywhere in shoal and deeper waters, often above low-water levels, and at times even encroaching upon channels where currents are main- tained. It grows in patches and dense masses, sometimes choking the smaller lakes from shore to shore. It occurs us- ually on bottom of soft alluvium, which in some places forms but a thin film above the hard sand beneath. It reaches the surface in early summer, and grows throughout the warm sea- son unless swept away by floods or seines. These agencies, combined with wind and decay, remove much of the summer’s erowth in the autumn. Large areas of bottom growth survive the accidents of the colder season and, together with the de- tached terminal buds, provide for the rapid recovery of the water meadows of Ceratophyllum in the following spring. Though essentially an immersed floating plant, this species has its lower stems fixed in the soft ooze of the bottom upon which they rest, and it thus becomes almost as firmly “rooted” as do the Potamogetons and similar plants. ‘This species consti- tutes the greater mass of the aquatic vegetation of the larger impounding and permanent backwaters. It is known in local parlance as “moss,” though this designation is not always con- fined to this plant. No true aquatic mosses have been found in this bottom-land region. This Ceratophyllwm forms by far the greater part of the aquatic vegetation in this locality. 239 Elodea canadensis Michx. Common on alluvial bottom with Ceratophyllum, especially in quiet waters, but not reaching the surface so generally. It is widely distributed and is next in abundance to the preceding species, though forming a very much smaller proportion of the total vegetation. Vallisneria spiralis L. Rare; found only in channels with currents, as at the mouth of Quiver Creek. Pontederia cordata L. Common along open places, such as the channels at the head of Quiver Lake and the outlet of Flag Lake, on both alluvial and sandy bottoms. Heteranthera graminea Vahl.. Creeping along margins of lakes and the river, usually on alluvium. Juncus acuminatus Michx. Common in shoal water along sandy shores. Typha latifolia L. Occasional patches found in the swamps and sloughs of the permanent backwaters. Sparganium eurycarpum Engelm. Frequent in the margins of lakes and sloughs along channels on sandy and alluvial bot- toms. Spirodela polyrrhiza Schleid. Everywhere in quiet waters, forming in places dense mats upon the surface. Often drifted by wind or current in great windrows along shore. Very com- mon in open water, usually but not always on the surface. Often taken in the plankton with other species of the family. Lemna trisulea L. Locally abundant in the more open veg- etation of the backwaters in quiet bays and nooks in both sur- face and deeper waters. Not generally distributed, and less abundant than other members of the family. Lemna minor L. Associated with Spirodela but much less abundant. Wolffia columbiana Karsten. In surface and deeper waters in both river and backwaters among vegetation and in open water. Frequently taken in the plankton. 240 Wolffia braziliensis Weddell. With the preceding but less abundant.* 7 Sagittaria variabilis Kngelm. Abundant in shallow water along margins of lakes and swamps and in protected nooks along the river. On both alluvial and sandy bottoms, and often forming well-defined belts of vegetation. Triglochin palustris L. Occasionally found in marshes on alluvium. Potamogeton natans L. Widely distributed along margins of lakes, sloughs, and the river, in both quiet and flowing water, often occupying the open spaces in the littoral vegetation and among Ceratophyllum and Elodea. Potamogeton pusillus L. Rare, in open water of larger lakes. Potamogeton pectinatus L. Rare, in lakes and in river near channels where there is considerable current. Naias flexilis var. robusta Morong. Frequent along shores of lakes and river in shallow water on alluvium. Dulichium spathaceum Pers. Occasionally found along allu- vial shores of quiet backwaters. } Eleocharis palustris R. Br. Very common, forming patches of considerable extent along low sandy shores and in the mar- gins of Swamps. Eleocharis intermedia Schultes. Occasional in the mar- gins of lakes and swamps. Eleocharis tenuis Schultes. In shallow water in margins of swamps. Not common. *According to some criteria all of our representatives of the Lemnacee might be considered as part of the plankton. This is especially true of Wodffia, which is found in open water at all levels. Wind and current have much to do with its distribution, but, it has, nevertheless, a limnetic habit, comparable with that of many organisms of the plankton. Its general distribution and its small size afford further reason for regarding it as a part of the plankton of our locality. It was therefore not removed before measurement of the plankton. There are but few instances in our collections where it becomes a disturbing factor by reason of its predominance. The other members of the family are much larger and are more irregular in their distribution, and thus tend to distort the quantitative relations of the more typical plankton. For these practical reasons it seemed best to remove all specimens of these species from our catches before measurement. 241 Eleocharis acicularis R. Br. Common in shallow water on ° alluvial and sandy bottoms. Scirpus pungens Vahl. Common along sandy margins. Scirpus lacustris L. Lake and swamp margins; common on both sandy and alluvial bottom. Scirpus smithii Gray. Occasional along sandy shores. Scirpus fluviatilis Gray. Very abundant in bottom-land swamps on alluvial bottom. Forming great tracts, to the ex- clusion of other plants, and contributing largely to the decay- ing vegetation of the backwaters. Scirpus atrovirens Muhl. Common, in marshy borders. Rhynchospora alba Vahl. Rare, along sandy margins of backwaters in shallow water. Zizania aquatica L. Forming meadows of considerable ex- tent in margins of lakes and more open swamps in the backwaters. Equisetum limosum L. Sparingly present along springy margins of sandy shores. Azolla caroliniana Willd. This brilliant little eryptogam is locally abundant in warm sheltered regions of the back- waters in early summer. It is found principally in the dense mats of drifted Spirodela, where it forms bright red rosettes, the clusters sometimes forming an area several square feet in extent. The filamentous alge, principally Spirogyra and Zygnema, becomes very abundant in shallow waters in spring and early summer as the bottom-lands emerge from the receding flood. As the shores of the more permanent bodies of water are left bare, there remains upon them, half supported by the semi- aquatic vegetation, a thick felted mat of fading green, the strength and consistency of which are sufficient to justify the local name of “blanket moss.” Its rapid decay in warm shal- low water contributes immediately to the support of the plank- ton. VEGETATION AT THE SEVERAL STATIONS. Illinois River (Station E).—The following statements con- cerning the vegetation of the river are based upon many obser- 242 vations about Havana, and upon the conditions observed during a trip made in May, 1899, by the courtesy of the Illinois State Fish Commission, upon the steamer “Reindeer,” from the mouth, at Grafton, to Hennepin, 211 miles above. Asa rule, the river is quite free from vegetation. ‘There is, to be sure, in the upper part of Peoria Lake, which is merely an expanse of the river (Pl. 1.), an extensive area which is permanently occupied by aquatic plants. A similar expansion known as Havana Lake (Pl. IL.) is also at times abundantly supphed with vegetation in its shoaler and quieter portions. There are also springy shores, usually of gravel or sand, located where the channel encroaches upon a bluff upon which a permanent littoral veg- etation is maintained regardless of river levels. Generally, however, the water reaches the steep or sloping bank of black alluvium without any fringe of green. There are scattered Lemnacee—principally Spirodela polyrrhiza and Lemna minor, with Wolfia braziliensis and columbiana—floating with the cur- rent from spring till late in the fall. Patches of “moss” con- sisting of Ceratophyllum demersum are also floated into the chan- nel from flooded backwaters, or loosened by fishermen’s seines and then carried by the current from backwaters or the shores of the river into the channel. On some protected shores where the current is shght the arrowleaf (Sagittaria variabilis) main- tains a foothold—as on the eastshore, just above the “towhead”’ (PL IL.). A small patch of Potamogeton pectinatus also remains year after year in the river in the rapid currents that rush through Quiver cut-off (Pl. II.). Such instances of permanent vegetation are, however, of rare occurrence, and form but insig- nificant factors in the immediate environment of the river plankton. A temporary fringe of vegetation has appeared along the river margins when relatively low-water stages prevailed in the spring and were maintained without marked floods until sum- mer, as in 1894 and 1895. This littoral growth is not composed, however, of the permanent littoral flora, such as the arrowleaf, the Polygonums, and the rushes, but is like that found in deeper 248 and more permanent backwaters. It consists, in the main, of Ceratophyllum with some Naias and Elodea. Scattered sprays of Potamogeton natans lie in the more open places, and the Lem- nacee multiply in the more sheltered nooks, while the yellow- flowered Heteranthera abounds at the water’s edge and creeps out upon the black mud at the margin. This fringe of vegetation continues until it is stranded on the shore by the recession of the water, washed away by sudden floods which lift it from its slight foothold upon the unstable bottom, or pulled out upon shore or floated down stream by tishermen’s seines. Thus, of the heavy fringe present in June, 1895, only a trace was left by September of that year. In the four years following, the river levels were such that no vegetation of consequence appeared along the shores of the river at any season of the year. Even at the time of its maximum development this littoral belt of vegetation did not often exceed ten meters in width. It is thus a relatively small, as well as an inconstant, factor in the environment of the plankton of the river itself. The current carries the plankton-laden water through its tangled growth, and sessile animals, such as Hydra and the Bryozoa, find in it an abundant food supply. These and other organisms which find a retreat in the shelter of the vegetation are from time to time carried into the channel by the current and serve to diver- sify the plankton. On still, warm days Hydra habitually aban- dons its sessile mode of life and adopts a limnetic habit, often attaching itself to the surface film of water. Owing to the changes in levels and to other reasons above cited the vegetation of the river, where it occurs, does not con- tinue until autumn, and is absent during the ice blockade of the winter. In this respect the river environment is in strong contrast with that of most of the backwaters, in which the veg- etation, though reduced, persists throughout this period. This absence of winter vegetation in the river is one of the condi- tions favoring the stagnation which sometimes occurs, as in 1899, in the Illinois. Spoon River (Station M)—Spoon River, throughout the 244 bottom-land region at least, is free from vegetation—a condi- tion which prevails throughout the greater part of our prairie streams. Quiver Lake (Station C). Pl. XV.-XVII.—The vegetation is a very important and much more constant factor in the environ- ment of Quiver Lake than it is in that of theriver. In its max- imum development reached in the summers of 1894 and 1895 it fills (Pl. XV.) the lake from shore to shore with a closely matted growth, the only open places being an interrupted and_ tor- tuous channel through which the waters of Quiver Creek (PI. II.) make their way to the river. The vegetation in the body of the lake consists in the main of Ceratophyllum, with an admix- ture of Klodea and Potamogeton toward the margins. Along the eastern shore, and toward the upper end of the lake where springy shores and sandy bottom are to be found, the vegeta- tion partakes more of the permanent littoral character. Here rushes, sedges, arrowleaf, and the aquatic Cruciferw and Um- bellifere appear among the Potamogetons and other floating plants. In the northern area, especially along its western shore, where more alluvium is found, water-lilies, pickerel-weed, and the lotus abound, and the Potamogetons are more abundant (PI. XVII). The “wild celery” (Vallisneria spiralis) is sparingly pres- ent in the channel of the eastern arm of the lake, while in the tributary bottom-lands above are aquatic meadows of wild rice and other water-loving grasses, rushes, and sedges. In years of higher water (Pl. X VI.), such as the four follow- ing 1895, the vegetation differs from that of low-water years more in quantity than in kind. The main body of the lake and a considerable portion of both arms are freed to a greater or less extent from their vegetation, a border of varying width remaining near the shores, and scattered clumps dotting the lake here and there in the broad stretches of open water. Dogfish Lake (Station L). Pl. XVIII.—This lake shares the flora of Quiver Lake, of which it is but the northwestern arm. Its vegetation is somewhat denser, having no channels travers- ing its matted growth. A fringe of marsh flora along its north- 245 eastern border and the encroachments of the semiaquatic bot- tom-land plants but slightly vary the uniformity of the vegeta- tion, which at low-water stages fills the greater part of the lake. In such lakes as Dogfish and Quiver the vegetation by reason of its predominance exerts a profound influence upon the quantity and the constitution of the plankton. Its fluctua- tions in quantity with the change of the seasons and the inva- sion of flood water are attended by marked readjustments of the plankton. Phelps Lake (Station F’). Pl. XX1.—Phelps Lake was prac- tically free from vegetation throughout the period of our plank- ton collections. The drying up of the lake in 1894 and its ecul- tivation in 1895 destroyed whatever foothold the aquatic veg- etation had obtained. In the following years the ingress of the aquatic flora become increasingly evident, though the alluvium in the bed of the lake, hardened by the drouth, gave but scant foothold to marsh-loving plants, especially to the perennial species or to those with well-developed roots. Each spring saw here a remarkable development of “blanket moss,” a mat of algee, principally Spirogyra, Zygnema, and Cladophora. In the period of midsummer stagnation a dark green film of Oscillaria coated the bottom or rose to the surface in scattered masses. The fringe of button-bush (Cephalanthus occidentalis) and: willows (Salix nigra and S. longifolia) at the edge of the sur- rounding forest gave shelter to a few semiaquatic Composite and rushes, and beyond these there were scattered clumps of Pota- mogeton natans and Nais flexilis var. robusta, which found a place even in the first year in which the water reentered the lake. In 1899 the margin occupied by these plants had increased in width, and arrowleaf and lotus were represented by a few isolated plants, while the ubiquitous Ceratophyllum had made its first appearance in the lake. Aside from the alge, the aquatic flora formed but a small part of the environment of the plank- ton in this body of water. Thompson’s Lake (Station G). Pl. XX.—This lake combines in one area almost the whole range in the development of the 246 aquatic flora characteristic of the backwaters of the Illinois River bottoms. The regions occupied by aquatic vegetation (Pl. II.) are of considerable extent even at low-water stages, and increase rapidly in area at higher river levels. The diver- sity of the aquatic flora is most pronounced at the moderate stages of water (3 to 6 feet above low water) which often pre- vail after the decline of the spring flood during early summer. A characteristic littoral flora is found along the firm san- dy margin of the eastern side, and ona few points of similar soil which project from the western bluffs to the lake. Jun- cacee and the shore-loving grasses and sedges abound here, and as the shores emerge the bottom-land Composite and Polygo- mums encroach upon their domain. In other regions the slope is more gradual and the shore line, as the water recedes, moves over wide stretches of alluvial soil, often of slight con- sistency, to a considerable depth. Here the vegetation is more luxuriant, and Polygonum amphibium, the arrowleaf, and the water-lily vie with the big river rush (Scirpus fluviatilis) for a foothold in these regions, exposed only at lowest levels and never baked hard by the midsummer’s drouth. At higher levels is found a varied mixture of semiaquatic and upland genera, such as Lippia, Bidens, and Polygonum, with coarse grasses and sedges. Inside of this varied littoral zone is found a permanent flora of almost equal diversity. Along sandy shores we find a belt of more or less open vegetation con- sisting largely of Potamogeton natans, Elodea, Nais, and a few Juncacee, with scattered lihes and lotus. At the southern end of the lake there is an area over a mile in length occupied mainly by Scirpus lacustris, great beds of lotus and water-lily, and mats of Lemnacee. A narrow belt with less of the Scirpus is found along the alluvial margins of the western shore, and scattered patches occupy the shoals that connect the northern end of the lake with the swamps that le to the northward. In the deeper waters Ceratophyllum takes possession in some regions to the practical exclusion of all other species save a few Potamogetons and some scattered Hlodea. The region in which 247 this species prevails lies in the southern third of the lake and along its sides for a distance of several hundred feet from shore, and again at the northern end for a distance of three quarters of a mile from the outlet. During low-water years scattered clumps of Ceratophyllum and Potamogeton were found as far north as the middle of the lake. Thus, at all seasons about half of the lake—often two thirds of it—is open water with scarcely a trace of fixed vegetation. The seasonal changes in the vegetation of this lake are very marked. In midwinter, during the ice blockade, which contin- ues much longer upon the lakes than upon the river, the vege- tation is not much in evidence. At low stages dead rushes rise above the ice in a few places, but give little hint of the great mass of broken and more or less comminuted vegetable debris which covers the bottom in those portions with vegeta- tion of a semi-littoral character. This debris is of great extent, and in the absence of current and buoyancy is notcarriedaway, but remains to enrich the waters and the unstable ooze upon which it lies. Most of the vegetation in this belt is dormant at this period, little trace of green appearing on the half-buried root-stalks and rhizomes of the perennial species belonging to this zone. In the deeper water, on the other hand, a consider- able quantity of Ceratophyllum, with some Hlodea, remains upon the bottom throughout the winter, keeping its folhage beneath the ice. This isan important factor in preserving the equilib- rium inthe gaseous contents of the water, and thus in the main- tenance of the winter plankton. With the rise in temperature in spring the vegetation starts into growth which the spring floods to a large degree conceal. This growth and the decline in river levels combine to make its appearance at the surface or its emergence above it some- what sudden. The greatest growth takes place during the months of May and June, and is in large part attained by the close of the latter month. The changes subsequent to this pe- riod which are incident to growth are but slight, and have but little effect upon the ‘‘waterscape.” 248 Late summer and early autumn see the decay of much of the more succulent vegetation, such as the water-lilies and lotus, the arrowleaf, the Potamogetons, and some of the Elodea and Ceratophyllum, while the emergent and more resistant rushes, sedges, and grasses yield more slowly and later to the accidents of flood and ice. and do not reach the late stages of decay until the following spring. The vegetation of Thompson’s Lake is subject to consid- erable fluctuations, due to other than seasonal changes. These are variations in river level, the seining of fishermen, and the movements caused by flood, wind, and ice. The changes in level, owing to the very gentle slope of most of the shore of this lake, greatly contract the littoral zone as the spring flood recedes, and restore more or less of it with each recurrent rise—changes which facilitate the decay of whatever vegetation of the submerged type develops in this zone. The location of the lake with its long axis in the direction (S. W. to N. E.) of the prevailing winds, gives a force to the waves suffi- cient at times to tear isolated patches of “moss” from their slight hold on the unstable bottom and drive them toward the northern end of the lake. This is an important factor in keep- ing the greater part of the lake free from vegetation. The vegetation of 'Thompson’s Lake is thus a considerable factor in the environment of the plankton. It furnishes a con- siderable quantity of decaying organic matter in fall and spring, both being periods of marked plankton development. At high and moderate stages of water, when a gentle current passes through the lake, its influence must be generally diffused. At low-water stages, when the current is cut off, its effect 1s much more local. At such times no open channel is maintained through the vegetation at the northern end of the lake (PI. IL.) to the outlet, as in the case of Quiver Lake. The movements in the lake attending change in level tend to mingle the plank- ton of regions full of vegetation with that of the open lake or vice versa, thus tending to diversification. There still remains at all times a large tract of open water in which for considera- 249 ble periods of time the vegetation forms no appreciable part of the environment of the plankton. It was in this region that the most of our collections were made, and they may therefore be regarded as in the main typical of vegetation-free waters of our locality. Flag Lake (Station K). Pl, X1X.—In vegetation this is the richest by far of all the bodies of water examined by us. It is the type of a permanent marsh, filled from shore to shore by a rank growth of plants (Pl. XTX.), with little or no development of channels or current, anda bottom of ooze with great quanti- ties of decaying vegetation. The wide expanse of this marsh (over 1,200 acres) and the varied character of its borders afford opportunity for great diversity in its vegetation. Its margins are not sharply defined, and the vegetation in such regions varies greatly according to the locality, and in the same local- ity according to the present and previous stages of water. Thus in the autumn of low-water years the Composite, Polygonums, and grasses of the dry and higher bottoms attain a rapid and rank growth in regions where Sagittaria and Lemna held sway in the spring. A greater part of this marsh is occupied by a dense growth of the river rush (Scirpus fluviatilis) to the exclu- sion of almost all other aquatic species of any size. Here and there irregular areas of considerable extent are filled with scat- tered Scirpus, water-lilies, and the lotus, together with great quantities of the Lemnaceew (Pl. XIX.). Near the center of the marsh there existed throughout the years of our examination two irregular spaces of open water of several acres in ex- tent, more or less encroached upon by a surrounding belt of Ceratophyllum. Whenever access was possible our collections were made in these open places. The vegetation of this marsh, by reason of its omnipres- ence, its great volume, and its periods of growth and decay, isa factor of great importance in the environment of its plankton, The nourishment taken up by the submerged and more succu- lent vegetation is released again by decay in the autumn, and thus favors the development of the autumnal plankton. The 250 emergent vegetation, which reaches a great development here, adds its contributions to the enrichment of the marsh waters with the return of flood conditions and temperatures facilitat- ing decay—conditions prevailing in the spring at the time of plankton maximum. The growth of vegetation in the spring, and the choking up of the lake which attends its transforma- tion into a marsh seem, on the other hand, to introduce condi- tions of nutrition and light inimical to the development of the plankton. PLANT ZONES. The classification of the aquatic vegetation of our locality and its divisions into definite zones or belts is made difficult by the fluctuating character of the environment. The average range in river level is almost fourteen feet, and with the changes in level go advance, recession, or even obliteration of the shore-line in a large part of the territory included in our field of operations. Drouth and untimely flood also bring wide- spread catastrophe to the aquatic vegetation. The depth, even if it was constant, is insufficient to provide for any extreme differentiation of plant zones, while its inconstancy obliterates any which may gain a partial development. The greatest depths, <8 meters, occur temporarily in maximum floods in Spoon and Illinois rivers. The depth at such times over areas of vegeta- tion in the backwaters rarely exceeds 5-6 meters, while during the period of spring growth itis usually less than 3-4 meters and in large areas less than one. The whole area of vegetation thus lies within the depth assigned by Magnin (’93) to the lit- toral zone. Under these conditions the origin and mainte- nance of permanent zones of vegetation is far less possible in this fluviatile environment than it is in the more stable condi- tions of the typical lake. An attempt to classify our water meadows according to the scheme adopted by Magnin (’93) for lakes in the Jura, and by Pieters (94) for Lake St. Clair cannot succeed in our fluviatile environment. The zone of deep and colder water character- 251 ized by Chara—called the Characetum—is entirely absent in our locality. The zone characterized by pond weeds—Potamoge- tonetum—may perhaps be found in the great areas of immersed vegetation, principally Ceratophyllum, which occur in Quiver and Thompson’s lakes. The few Potamogetons found in our locality occur in this zone, though they are not confined to it. The depths in which this zone is here found are much less than in Lake St. Clair, in the lacustrine environment. The ‘“Nu- pharetum” may be represented in the lotus beds of Quiver, Thompson’s, and Flag lakes; but these do not show a zonal arrangement, and merge variously with littoral and Ceratophyl- lum regions. The littoral zone, which, according to the authors above quoted, extends from the shore line to a depth of 3 me- ters, is confined in our waters to a much shoaler region, and, as elsewhere, is characterized by Scirpus, the sedges, Polygonum amphibium, Nymphea, and Potamogeton natans. Almost all of Flag Lake, the northern and southern ends of 'Thompson’s Lake, and the northern and eastern margins of Quiver Lake belong to this zone. A classification more applicable to our locality is that of Pieters (’01), who recognizes in Lake Erie two regions,—one including all submerged forms and those with floating leaves, the other all the remaining species with emersed leaves and growing with roots and parts of the stem in the water.” These regions of immersed and emergent flora are often recogni- zable in our locality. To the latter belong the greater part of Flag Lake, a considerable portion of Quiver Lake along the eastern and northern shore, and the two ends and the margin of Thompson’s Lake; to the former, the body of Quiver and Dogfish lakes, a small area in Flag, and a large area at either end of Thompson’s Lake. It is this zone which constitutes the ereat plant factor in the environment of the plankton of our waters, and it consists almost entirely of Ceratophyllum. The effect of vegetation upon the production will be discussed in another connection. It is evident that our investigations afford a unique oppor- 252 tunity for examining the effect which vegetation (the word is used in the sense of the coarse aquatic growth as distin- guished from the microscopic phytoplankton) has upon the quantity and kind of plankton in bodies of water the remain- ing factors of whose environment are for the greater part com- mon. 253 QUANTITATIVE INVESTIGATION OF THE PLANKTON. GENERAL CONSIDERATIONS. The purpose of this investigation was the determination, by measurement, of the quantity of minute organisms develop- ing in the water at intervals throughout the year, and by this means to trace the seasonal fluctuations in production, and the relation of quantitative changes to constant and fluctuat- ing factors of the environment, to flood and drouth, to chemi- cal conditions, to the ice blockade, and to vegetation; and to contrast production in waters of the main and tributary streams, In impounding backwaters and the channel, and in bottom-land lakes and the main stream. METHOD OF COLLECTION. The method used in determining the quantity of plankton was based upon that devised by Hensen (’57) and modified by Apstein (96) for use in fresh water. The changes and modifi- cations which were made to adapt the method to use in our situation and to correct some of its errors have been described in detail by me elsewhere (97); I shall, therefore, only briefly refer to a few phases of the subject of special pertinence or interest in this connection. The changes in method during the progress of the work are indicated in Tables II].-IX. From June, 1894, to May 20, 1896, the plankton was collected by means of the silk net, made after Apstein’s smaller model (see Apstein °96) of No. 20 silk bolting-cloth of Keller’s manufacture. This net was drawn through the water at a uniform rate of one half meter per second for a distance of thirty meters. As shown in the tables referred to, most of the hauls were made by the ob- lique-haul method devised by Prof. Frank Smith, in which the net was drawn along an oblique rope from bottom to surface across channel in the river, and across the current, where cur- rent existed, at our other stations of collection, except in 254 a few instances when conditions of ice or vegetation necessi- tated a temporary modification of the direction. Collections subsequent to May 20, 1896, were made by means of the plankton pump, a known volume of water being strained through the silk net. The water strained was taken in such a way as to represent a vertical column of equal di- mensions from bottom to top. This was accomphshed by low- ering the inlet of the hose from the intake of the pump to the bottom, or as near it as we could go without fouling the water by disturbing the unstable deposits, and raising it to the sur- face during the progress of the pumping. ‘To secure a_ perfect column it is necessary to begin raising the hose with the first strokes that deliver water to the net, and to arrive at the sur- face long enough before the required amount is pumped to allow surface water to reach the net. With a fixed hose length and a known capacity of pump, this is easily deter- mined by experiment. The volume strained varied with the contents of the water. Asa rule, one fourth ofa cubic meter was strained. When plankton was scanty and silt hght the quantity was doubled, and occasionally in excessive plankton or unusual silt but half this volume was strained. Variations of minor importance in the methods here noted will be men- tioned in connection with the discussion of the plankton at the several stations. These variations are such as were ne- cessitated by difficulty of access with collecting apparatus, or by the exigencies of flood, ice, and current PRESERVATION AND MEASUREMENT. During the first three years the plankton was killed and preserved in strong alcohol. In subsequent years 70 per cent. alcohol to which formalin had been added to the grade of 2 per cent. was used, and proved to be a better preservative than the strong alcohol. The quantity of plankton present in the catch was deter- mined by compression in a Purdy centrifuge for two minutes 255 at the rate of 1,000 revolutions per minute, resulting in an appli- cation of 1,420,484 dynes. All records and discussions in this paper are based upon this method of measurement. It brings about a considerable reduction in the volume of plankton as compared with that recorded by the usual method of allowing the plankton to settle in the Eggert color-tubes for twenty-four or forty-eight hours and condense by gravity only. I have de- termined the amount of this reduction in measurement of all planktons collected by us up to June 6, 1896. There are two hundred and forty-three of these catches, and they represent the full seasonal and local range in quantity and quality, cov- ering, as they do, a period of two years and all the localities with which we have dealt. The actual quantity of plankton handled in these tests ranges from .025 to 10.25 cubic centi- meters (centrifuge measurement), and 143 of the 243 catches he between .25 and 2. cubic centimeters. The average decrease in volume when determined by the centrifuge as compared with that by the gravity method in these 243 cases was 49.5 per cent. As shown in the following table, the decrease ranges from 8 per cent. to 76 per cent. In 21 cases itis just 50 per cent., in 111 cases it is below this, and in 111 above. TABLE SHOWING DISTRIBUTION ACCORDING TO PERCENTAGE OF DECREASE OF 243 CATCHES MEASURED BY GRAVITY AND CENTRIFUGE METHODS, Per No. Per No. Per No. Per No. Per No. cent. of cent. | of cent. of cent. of cent. of lost | catches lost catches lost | catches lost | catches lost | catches 76 I 62 | 4 52 4 2 3 32 3 75 I 61 5 51 5 41 2 31 I 74 2 60 5 50 21 40 4 29 5 Zen Ae i 59 9 49 8 39 I 27 I 69 I 58 9 48 II 38 7 26 I 67 4 57 10 47 10 37 5 25 I 66 4 56 | 5 46 7 36 4 22 I 65 3 55 12 45 9 35 4 21 I 64 5 54 | 7 44 6 34 4 13 I 63 3 53 II 43 9 33 I 8 I 256 The factors determining the decrease are the proportions of silt and plankton and the character of each. When floccu- lent debris is abundant, or when filamentous diatoms or alge, Copepoda, or the Cladocera with long antenne are present in numbers, the decrease upon centrifuging is greater. When the silt is earthy or contains considerable quartz, and when the plankton consists of Protozoa such as Synura, or Rotifera such as Syncheta, or Cladocera such as Chydorus or Bosmina the de- crease is less. The amount of plankton placed in the tubes of the centrifuge also slightly affects the ratio of decrease in vol- ume. For example, one of our largest planktons, measuring 11.15 em.’ by the gravity method, fell but 8 per cent. when cen- trifuged in a single tube. When divided among three tubes the decrease became 14 per cent. This was a plankton largely composed of Chydorus and Bosmina. Another large plankton, measuring 11.85 em.’ by the gravity method, fell to 7.6 cm. upon centrifuging in a single tube—a loss of 56 per cent. This con- sisted very largely of Synuwra. As other large catches decreased as much as 50, or even 60, per cent., it is clear that large vol- umes do not necessarily yield only shght decreases. The instances in which the decrease exceeded 70 per cent. are 5in number. Of these, 3 contained Melosira or Fragillaria, 1 was rich in Osec/laria, and 2 contained considerable floccu- lent debris from aquatic vegetation. All of the 12 whose de- crease was less than 80 per cent. occur in April and May, when Chydorus and Bosmina are at their maximum and constitute a large, if not the greater, part of the plankton. In a few in- stances these catches which showed shght reduction in volume contained Hydra, insect larvee, and other adventitious forms from surrounding vegetation. Both extremes contain numerous instances in which the plankton catch is made up of typical plankton organisms, and consequently the range in the decreases here recorded ts normal Jor the range in planktons occurring in our waters throughout the year. Itistherefore reasonable to assume that the centrifuged vol- umes here reported for plankton in the Illinois must, onthe average, 257 be doubled for comparison with volumes reported in similar regions elsewhere and measured by the gravity method. The silt in our catches and the predominance of rotifers at times will tend, I believe, to render the decrease on centrifug- ing somewhat less in the case of our planktons, on the average, than that found in lake planktons where filamentous diatoms and Copepoda abound more generally. Ward and Graybill (’00) find that the decrease ranges from 60 per cent. to 70 per cent. and averages slightly less than two thirds. Juday (’97) finds that the decrease amounts on the average to 80 per cent. Both of these records deal only with a small number of midsummer planktons, while our records cover the.whole round of sea- sonal changes. This may be an element which tends to increase the range of the decrease shown in our results. The gravity work in our experiments was done in tubes identical in pattern with those used by Ward and Graybill (00), and the time for settling was the same. Juday (’97) gives no account of his gravity method. ‘ne centrifuges which we have severally used are only approximately of the same pattern, and they have not been used in exactly the same way by any two of us. We may compute the specific pressure in dynes per square centimeter ata given distance from the axis of rotation accord- (nea ing to the formula ° : in which 6 is the density } of the contents of the tube; », the angular velocity in ra- dians per second; 7 the distance in centimeters from the axis of rotation to the bottom of the tube; and 7, the dis- tance from the axis to the top of the fluid. For deusity I have used the specific gravity of water, since the extractions from the plankton considerably increase the specific gravity the alcohol in varying degrees in which the plankton was preserved. ‘ Be A i |e, : : The formula for » is —z5—, in which » is the number of revolutions per minute. 258 On this basis the pressure in dynes in our use of the centri- fuge, where there were 1,000 revolutions per minute with dis- tances of 16.7, and 4.5 em. to bottom of tube and top of lquid respectively, was 1,420,484. Professor Ward writes me that these distances 7 and 7; in the Bausch & Lomb machine he used were 14 and 5 cm. respectively, which witha density of 1 and 80 turns of the crank, equaling 1,840 rotations of the axis (on the manufacturer’s authority that the machine is geared to give 23 rotations of the axis to one of the crank), gives 2,774,- 897 dynes. Mr. Juday (’97) states that the pressure in his cen- trifuge was 391,680 dynes, but he writes me that the density used was the difference between that of alcohol and dried plankton, amounting to only .2 and .25. Reducing his caleu- lations to our basis in so far only as the matter of density is concerned, we find the dynes to be from 1,958,400 to 1,566,720. A further difference between our methods hes in the fact that in our use the pressure was exerted fwo minutes, and but one minute in that of the other investigators. The practical differences may not really be so great as the figures indicate because of the asymptotic character of the curve of reducing volume as the pressure continues or is in- creased. It it desirable that some standard unit of measure- ment be agreed upon for purposes of comparison. The use of the centrifuge in the many measurements here recorded has only confirmed the views expressed by me (97) regarding its utility, greater accuracy, and convenience for volumetric plankton work. Material which has been properly preserved has not sufferedin the compression. All of the enu- meration work to be reported in the second part of this paper has been done upon plankton which has been centrifuged at least once and in some cases six times. I have not detected any mutilation or distortion of the constituent organisms unless it be of Leptodora hyalina, an elongated and delicate cladoceran, and several other organisms of great delicacy of organization. These are often crumpled as a result either of the compres- sion or manipulation of the plankton, but the crumpling rarely 259 interferes with identification of the species or determination of sex or breeding condition. The statement made by me (’97, p. 20) that “this is, I be- heve, the first appleation of the centrifugal machine to quan- titative plankton work” requires modification. In Kraemer’s account of Samoan plankton (97) he describes a traveler’s centrifuge for use on shipboard for measurement of plankton, and I infer from his text that this machine was in use by him in 1893-95 in Samoan waters, though I find no explheit statement to that effect. If this be true, his use antedates ours, which did not pass the experimental stage until January, 1896. In any case the measurements he publishes (’97) were made by the centrifuge. The following statement made by Ward and Graybill (00), — “Juday (’97) was apparently the first to publish an account of the use of the centrifuge for this pur- pose. Both Dr. Kofoid and I had, however, experimented indepen- dently for more than a year before that, and had written to var- ious investigators regarding the advantage of such aninstru- ment,’—requires notice in this connection, since the question has been raised by these writers as to the priority in publication of the use of the centrifuge for plankton measurement, and the facts are incorrectly given. The date of Juday’s paper is subse- quent to May 28, 1897,* for the volume containing the paper contains the records of the field meeting of the Indiana Acad- emy held on that date. The date of publication of my ac- count of the centrifuge was March 10, 1897, and it was also mentioned by Professor Forbes (’96) in the biennial report of our Station operations. This report was again issued January 24, 1897, in separate form, and distributed to plankton investi- gators generally. The date of publication of Kraemer’s work is ‘Ende Januar oder Anfang Februar 1897; genauer kénnen wir das Datum leider nicht augeben,” according to informa- tion received by me from the publishers Lipsius and Tischer, of Kiel, Germany. The empty honor of first publication thus probably belongs to us, and certainly not to Juday as Ward *In a letter Mr. Juday informs me that his paper was published in August, 1897, 260. and Graybill state. The real credit for first centrifuging plank- ton belongs evidently to Kraemer. In view of the statement above quoted it may be well to add that our experimental use of the centrifuge was begun in the autumn of 1896. It was at once adopted, and our plankton thus far collected was meas- ured by it at that time. The measurements made are those used in the present paper. Our experiments with and adop- tion of the centrifuge were independent of and without knowl- edge of similar work elsewhere. SILT ESTIMATION In Tables II1-IX. the amount of the actual catch of the plankton net will be found, and in subsequent columns the estimated percentage of silt, and computed volumes of silt, plankton, and total catch are given in cubic centimeters per cubic meter of water. In all our discussions of the plankton the amounts used are those of plankton only, unless otherwise stated, that is, of the total catch /ess the estimated amount of silt, and they are always quoted in terms of cubic centimeters per cubic meter of water. The determination of the amount of silt has been of ne- cessity a matter of personal estimation, and involves a source of error of uncertain extent. The estimates have been made large- ly by myself, with some aid from Mr. R. E. Richardson, and no effort has been spared to maintain a uniform standard of esti- mation so as to distribute, as far as possible, the error incident to the process. Accordingly the estimates were revised and cor- related after the qualitative and numerical analysis of the col- lections at Station EK, and they consequently rest upon a com- parative basis upon the examination of the catch as it appears in the Rafter cell.* In the case of the collections from the Illinois River only, they have been controlledin some degree by the re- sults of the numerical analysis. The estimates of silt were made *Closer study of the quantitative and qualitative data since the above was written leads me to suspect that in some cases the silt estimates are too high, especially where there is much light flocculent debris, which occupies considerable space in the Rafter cell but may be compressed considerably in the centrifuge. 261 without reference to, and in most cases prior to, the prepara- tion of tables and plots of seasonal distribution. Estimates made by others, not accustomed to judging the plankton, re- veal a wide divergence in percentages, and independent esti- mates which I have made of the same material on different oc- casions show some divergence, though, as a rule, quite within the probable error of plankton method. The silt estimation does not, I believe, essentially vitiate any of the conclusions drawn in this discussion of quantitative results, and in no way enters into the qualitative analysis. THE CLOGGING OF THE NET. The collections made with the silk net drawn from the bottom to the surface of the water in vertical or oblique hauls are all diminished in volume to some extent by the resistance of the silk to the rapid passage of the water. As a result of this, the net pushes aside some of the water in the column which it is supposed to traverse. As its meshes clog with the accu- mulating catch the amount pushed aside is increased progres- sively during the haul. The actual catch of the net is there- fore only a portion of the total contents of the column of water, whose length is that of the haul and diameter that of the mouth of the net. The volume of plankton actually present in this column can be computed if we can determine the factor of correction. Hensen (’87 and ’95) has sought by experiment with filtered water to determine the mathematical formula which will give this correction for a net of known silk and di- mensions drawn at given velocities. This factor he calls the ‘coefficient of the net.” Reighard (94) attempted to de- termine the coefficient of -his net by using a miniature model in water in which Lobelia seeds had been placed, but ultimately adopted the formula of Hensen. It was necessary that in our final computation of the volume of plankton we should make some correction in all catches of the drawn net for this loss due to the pushing aside of the water. Since our net was constructed after the Hensen-Apstein model it was possible to apply the mathematical method of 262 Hensen (795). This coefficient—computed for us by Instruc- tor W. C. Brenke, of the University of Illinois—is 1.320 or ‘1.303, according to the area of the silk in the bucket of the net, for the velocity of one-half meter per second, which we uniformly employed. Our net has an area of 81.72 square centimeters in the opening; of 1,847.5 and 22.66 square cen- timeters respectively in filtering cone and windows of the bucket; and its coefficient is 1.32. With a disk of silk clamped to the lower end of the net,—a method used prior to the adop- tion of my detachable bucket,—the area of the silk of the buck- et falls to 15.2 and the coefficient is accordingly reduced to 1.303. A second net frame which we used, with an opening two millimeters less in diameter, has a coefficient of 1.318. Apstein’s (96) net has an opening of 92 square centimeters, a filtering cone of 1,730, and the silk of the bucket measures 62 square centimeters. The coefficient of his net is computed to be 1.39. Observations on the operation of the net in the field through the seasonal changes of the plankton led me to _ be- heve that a uniform coefhicient, and, moreover, one founded on the operation of the net in filtered water, would not ade- quately correct the error, since it takes no account of the sea- sonal changes in the quantity and kind of plankton, and does not recognize the effect of the progressive clogging of the net by the catch, or the change of the net with use. Upon the adoption of the pumping method cf collection a number of tests were made for the comparison of the amount of plankton taken by the drawn net and that by the pump and filtering net along parallel courses of thirty meters—our usual haul. The results amply justified my belief that the coefti- cient fluctuates with the conditions above named as well as with the condition of the net. We therefore sought by this empirical method to determine the coefficient under a variety of conditions representative of our environment. ‘These tests were not carried beyond this point, since we had adopted the pumping method for the later and major part of our work. ed he i . gt ‘ a | s) 4 i i» “> : a Pe = : i: a i 4 P ee 7 f os ‘ Rh 7. ; f a 4 Ax i at i aim boda; Mu. pull Nariman} mn ie Hf : {i | ‘eee J pranks NATE Ne x ey a ae A white i \; "is a) OR : r : e . q is ee de i | ma Wh a A } , ¥ ne ‘s { H hi ‘ S| ARs ips si ih MO ag a 1 hace.) TRO | | We } eee cial eal oie be | De seu i efi a ac nin Re a iz fia. Nest) SAD. a vo ial ai toe Y} pit sa hy i thy paid \ i af Onin tes | ye ‘Qe Tt Peet | Gad he PA Gp x ip ah ; {hemp aa Sat | a & Var | : <¥ OVE Ria f Ppl ye ~ j O51 Paice) rains 2 AK Ao a y ond. Hy ® “a H : evo het OAT, uf] ie | OR Mc haa } ‘a Pon. en t \ : “i ‘ a4 , ' TS ne eatin’ i ar AN eee embers © RUIN sR ile nein n ; ! 1) GOL FY aXe 4 Voge) Gab. tf | } } | ied it NE a dkihah tend } A a ieee ; CAP 1 L pawnhpemen ies vsieid emabortaves Du oasis on at | Settee aE -— > x - — — | wibor |) Miblodiineo om) to | u i ; ee spi ii sel | Set Dy | Mera: | \ } i h ‘ hee { rca ia | i. Whole ich ona AD ta \ ! . 7 | 0) y | PAY | | a ie : he tio. % | : cd) Ff AA TE a, aR Hae : OR BA 4 eee VN: SRR RA) Aleman Aik Nn ae hy al cu.cm. 263 In this method the question of coefficient is entirely eliminated. The results of these tests are given in the preceding table. The variation in the coefficient with different seasons, lo- calities, and planktons is apparent upon the first glance at the table. The greater straining capacity of a new net as com- pared with one which had been used for some time may be seen in the tests made June 16,and July 9, 11, and 21, 1896. The new net—the silk in which had been shrunken by washing and pressing several times prior to use—catches at least 50 per cent. more than the old one which had done service since February 25. The rise in the coefficient as the net progressively clogs by plankton is demonstrated by the tests of October 14, 1899, and July 27, 1897. The latter test is graphically presented in the accompanying figure. 5S -_- - pI 20 is 10 J O =m. Fic. B.—Catches of plankton made on 30-meter haul by drawn net and pump The upper, continuous line represents the pump catch; the middle, dotted line the catch of the net measured by the settling method; the lower, heavy line the same measured by the centrifuge. Length of haul Net Locality, etc. Illinois River Dec. 30} Illinois River June 16) Quiver Lake 30 m, |— July 9 | Matanzas Lake July 11/Thompson’s Lake} 30 m. July 21)Thompson’s Lake} 30 m. Aug. 28} Illinois River | 30m. lane | Mmmm un Vw MIN Pam 3 20 cm. below | 30 m. surface 15 m, Oct, 14 | 4} ——-———-— €| 40cm. below | 30 m. 2 surface 15 m. ) a Haul OAL N | Exuw fo Ww 1.750 +325 mere: 625 410 .520 -550 .675 1.375 8 5 5m.|] 5 5 5 IG Whe) 5 5 ism.| 5 July 27/Thompson's Lake 2om.| 5 ae 5 25m. | 5 .725 |2. 1.050 .950 -950 .720 -879 475 | 2.717 4.750 .850 [oe] -750 ‘850 365 [1-300 | 3.562 1.225 1.125 050 Gravity Method—24 hrs. Net fPeeae (Coefiicient 2.615 3.617 3.036 1.360 2.073 1.635 2.227 -961 1.667 .642 1.175 1.175 804 .976 .881 1.242 1.005 Ped 1.627 1.281 1.434 yi 1.367 2.103 1.656 2.373 3.107 2.690 —___ Centrifuge Net [Fae Coefficient « Adem am Ss PN . 3 Enumeration—I m.* water Plankton. Ea Net | Pump hap -acags 3 Some silt. Sy#ura and Copepoda. 2.868 | a Egat | 1.533 | 4.375 243,181 | 2.041 119,150 | Much silt. Syazura, Syncheta, and Copepoda, .140 | .285 2.143 | 141,490 | 458,057 3.468 | Small amount of flocculent debris. Polymixic 080 | .350 -090 | ,310 115 | ie . 180 .230 280 | .255| 1.071 | 195,990] 439,054]. 2.448 2 ad 1.667 16,840 ! .300 1.304 ] 180,410 | 489,708 2.604 ; 84,160 1507 5.819 | plankton. Many nauplii. xéomostraca, Rhi- 2°69 114/830 4 / = 4.3 sopoda, Rotifera, diatoms,and Protophyta present. 566,216 2.971 Small amount of debris. Polymixic plankton, .180 : 540 | 3.000 96,891 | 421,175 | 4.347 | Entomostraca, Rotifera, Rhizopoda, Protophyta, -200 | | 2.100 117,898 Polymixic plankton. Xofifera, Entomostraca Protozoa,and Protophyta. 239,744 | 2.034 -495 | mew .848 | 261,961 | .....-. 915 -180 | goo | 2.222 | 133,559 | 438,108 | 3.280 Entomostraca somewhat more abundant than in 591 | 237,643 | ....... 1.844 the preceding test. Plankton polymixic. 100 | ae 183,595 Tee Much silt and debris. Polymixic plankton. Ay- ie ia 4.144 | “2s¢raca, Syncheta, Protophyta, BOOZ ilh cies oe,ee 3.600 ; : 160,932 | 310,470 : .075 Wersy WORE AON i. «56 1.968 .095 ABO) LAB RIOI I cicero e'sr0 2.090 110 G2) tea ose lrses sc 2.025 -OgI OC WE TEE. ZOS AIP cs cies « 2.000 | Very little debris. Polymixic plankton. Roéifera, —— ee -—| ———- --- |---| especially Synch@eta, Protozoa, Entomostraca, -150 | meee 283 | 146,418] ....... 2.120 | Profophyta, and diatoms. Largely small forms. -055 yi EM ere 3 ee Sd VP ae 1.455 .100 AZ) N TSTO2A iirc eos « 1.720 075 .567 | 166,917 | ....... 1.860 .077 -552 | 179,630 | ....... 1.738 ea el [at he a ee .800 2.100 2.625 2,071,984 7,755,061 3.740 .700 | 2-490 1.500 | 1,830,862 | 275 ’ 3 a -118 | vonotonic plankton. Principally Syncheta, a nes 1,563,763 | ..... Ba a few Synura, nauplii, Brachionus, and Codonella. Serine 1,387,151 batch a petees 105 1.468] 593,311 | ..... 1.706 . 100 1.542 | 364,135] ..... 2.780 103° 1.503 BIO TAS Veins os P16 iia 135 [sree] 2.284] 3921461 ..... | 2.981 130 | oe Sear atG.063°| -..... 133. aaa 2.327 403,608 Bone. are 2 508 180 | Sens Z. a “275,11 ee he oe 696 PET | Way a ia'e 3.696 . 165 | aifos BAR AOD ce kc 2.930 ‘ “ @ G61 | 310,236| ..... 3.299 eal amount of flocculent debris. _Pglymixi a . oo Plankton. Lepsodo>p-. Ve. nae paella 2.565 | S597 ces ue 3-995 }| and Fogle Diaries, » Mugen, 2.936] 294,670] ..... 3-746 2.740 | 274019] ..... 3.867 195 3.952] 223,065| ..... | 4.538. 135 5.710 shai Por 2 pee O| 105 1).... | 4-672 | ro4.sag | 2222 5.203 -230 | .925 4.022 | 224,932 j1,012,1 "7 i daceeaad .260 | . 3-558 | 198,195 at Fi oe 235 3-936 | 209,654] ..... 4.868 +275 3-3 mp “Bi Dae 5-151 256 3. vt eee 5.343 -700 | 203,712 | ..... 4.969 | ea ot oe as ee ey i er ne 264 The coefficient has been computed in each case on the ba- sis of measurements by the gravity method, by the centrifuge, and by enumeration of all the larger and quantitatively more important constituents of the catch. An examination of the table will indicate that the relation and direction of the dif- ferences of the various coefficients do not materially differ by the three methods. Theresults by the enumeration method give the largest coefficient—probably as a result of the elimina- tion of the silt factor in some instances, and possibly by reason of the large margin of error involved in the method. It is evident from the table that an average of a number of catches, not only by the net but also with the pump, should be used if empirical coefficients are to be established with ac- curacy. It is probable that the low coefficients seen in a few instances result from insufficient pump catches, or from some error in paralleling the catches. Since the coefficient problem was eliminated in our later work by the use of the pump, fur- ther efforts to establish empirical coefficients were abandoned for lack of time to carrv on more elaborate tests. Three alternatives were thus before us. First, to adopt the coefficient computed according to Hensen’s formula, and use this one factor, 1.32, for all catches irrespective of the age of the net and of seasonal, local, quantitative, and qualitative differences in the catch. This method Apstein (96) and other European planktologists have adopted. Reighard (’94), Ward (95), and Juday (’97) have also followed this plan, but in each case they were dealing only with catches taken in midsummer from the same or similar bodies of water, and the resulting error thus introduced was much less than would result from the adoption of a uniform coefficient for our varied catches. Furthermore, we had the evidence of the probable extent of this errror which the pumping method afforded. A second alternative was to ignore the coefficient question entirely ; but this involves even greater distortion of the prob- able seasonal and local fluctuations in the plankton. A third method, and the one finally adopted, was that of 265 assigning an empirical coefficient to each catch. This coeffi- cient was decided upon after analysis or inspection of the plank- ton, and in view of its quantity and constituent organisms, the amount and nature of the silt, and the age of the net, the basis of estimation in each case being the coefficient test by the pumping method whose conditions most nearly approached those of the catch in question. These coefficients were decided upon without knowledge of or reference to the effect which they might have upon the theoretical questions arising from the analysis of the quantitative results, and prior to the organ- ization and analysis of the volumetric data. Obviously this latter method involves both possible and probable error in estimation of similarities and differences in the catches examined and in maintaining throughout a uniform standard. Nevertheless, for plankton catches as varied as those with which we deal, it is probable that this method involves less distortion of volumetric results than the omission of the coeffi- cient factor or the adoption of a uniform factor for all catches irrespective of the fluctuations in this factor as revealed by our field tests. Accordingly all of the volumes of catches by the drawn net, of plankton, silt, and total catch per cubic meter recorded prior to May 20, 1896, in Tables III.—-IX. have been computed with this coefficient as one of the factors, the actual factor employed being given in the tables in each case. The results of my efforts (see Kofoid, 97a) to find an ade- quate correction for the loss by leakage through the silk by the use of hard-pressed filter paper and the Berkefeld army filter will be discussed in another connection. The volumetric data of the plankton at the seven stations (see Pl. II.) at which periodical collections were made, name- ly, the river channel (E), Spoon River (M), Quiver Lake (C), Dogfish Lake (L), Flag Lake (K), Thompson’s Lake (G), and Phelps Lake (F) will now be discussed, and the general ques- tions arising from the investigation as a whole will then be treated. The chronological series of collections at these seven 266 stations included in this discussion number in all 648, distrib- uted as follows: Illinois River 235, Spoon River 36, Quiver Lake 115, Dogfish Lake 48, Flag Lake 44, Thompson’s Lake 99, and Phelps Lake 67. ILLINOIS RIVER CHANNEL, STATION E. (Table III.; Pl. 1, V., VIIL—XIIL.) DESCRIPTION OF LOCALITY OF COLLECTION, The collections were made two and a quarter miles above the city of Havana, a short distance above the outlet of Quiver Lake (Pl. II.), at a point where the river was about 500 feet in width at low water and about 600 feet from crest to crest of the banks, which are here fringed by willows (Salix nigra and S. longifolia) on both sides. The eastern shore is a nar- row spit, 6 to 8 feet above low water, separating the river from Quiver Lake. The western bank is higher, 8 to 10 feet, and is covered by bottom-land forest. This is also a spit or “towhead”’ between the river and Seeb’s Lake. At low water (Pl. IV.) the eastern bank is exposed asa gentle declivity of 25 to 40 feet, while the western one is much wider—a belt, 50 to 75 feet in width, of soft black mud with gaping cracks (Pl. V.). A short distance from the low-water shore-line the bank shelves some- what abruptly to the bottom, which with the exception of a shght ridge near the center of the channel extends in an un- broken level from side to side of the stream. The depth at low water for a width of over 400 feet is 8 to 9 feet. To the north- ward the river deepens slightly, while towards the mouth of Spoon River it shoals to 6 feet, and below it to less than 5 feet. The banks are of black alluvium, hardened in the upper levels by exposure at low water, but al- ways soft and treacherous near the low-water line. The bot- tom in the channel is firm, being a compact bed of heavy blu- ish mud mingled with sand and the shells of Unionidae, which form in many places continuous beds of large area. A slight curve in the river above our plankton station shifts the current at that point towards the eastern shore, but at the 267 point of collection the run of driftwood in the stream exhibited no marked difference in current in the channel for an extent of fully 400 feet. Approximately uniform conditions thus pre- vail over a considerable extent of the river channel at this point. At high water (PI. III.) the banks are submerged, but aside from increased rapidity and some lateral extension there is no noticeable difference in the conditions of the current. MODIFICATIONS OF METHODS AT THIS STATION. Collections made by the oblique-haul method were always taken on the western side of the stream, across the current from a point in deep water, the surface end of the haul being completed in shoaler water. At times of high water it was necessary, both on account of the strength of the current and the depth, to shift the apparatus still more towards the shore, and, finally, in the flood of December, 1895, to abandon the method and substitute temporarily a series of four to six vertical hauls, amounting to about 30 meters—the usual dis- tance of the oblique haul. These were made in midstream from a floating or anchored boat, and were continued from De- cember 27, 1895, to May 20, 1896. After the adoption of the pumping method on the latter date the boat or launch was at first allowed to drift with the current while the collection was made. Owing to frequent difficulty caused by the drifting of the boat into shallow water by the wind before the catch was completed, we finally adopted the plan of anchoring the boat or launch in or near the mid-channel while the collections were being made. During the winter season, owing to air-holes and weak places caused by the irregular melting of the ice upon the low- er surface, the ice on the river channel was rarely firm enough to permit safe transit of our plankton outfit, whose total weight was over 800 pounds. Steel runners were placed upon the bottom of the boat, and by the aid of ice hooks it was pos- sible to run over or to break one’s way through thin or rotten ice to the mid-channel station, where open stretches of 268 water were not infrequently found. In a few instances, owing to roughness and rottenness of the ice, it was not possible to reach the point up-stream where the collections were usually made, and in such instances the catch was taken nearer Ha- vana but always above the mouth of Spoon River (PI. I.). Even when the ice was running at the time of break-up, it was possible by floating in rifts of the floes to secure a catch of the channel plankton. Thus in all seasons our catches at this station are typical of the channel plankton. CHRONOLOGY OF COLLECTIONS. As shown in Table IIT., the collections at this station cover the period from June 12, 1894, to March 28, 1899, in which time catches were made on 235 different days, 10, 50, 76, 34, 52, and 13, respectively, for the several years included. The interval between collections in 1894 (Pl. VIII.) ranges from 14 to 34 days. In the first half of 1895 (Pl. IX.) they were few and irregular, but four being taken, while in the second half of that year 46 were taken at intervals of one to twelve days, the interval varying with flood conditions, since an attempt was made to follow closely the effect of changing river levels upon the quantity of plankton. The December flood of this year was followed at intervals not exceeding five days until Februa- ry 10 of the following year (Pl. X.). From this time till April 24 the intervals average about seven days, in no case, however, exceeding eleven. From this date till the end of August, 49 col- lections were made at intervals of one to seven days, following thus closely the fluctuations attendant upon the two recurrent floods of that season (Pl. X.). The field station at Havana was then closed, and until it was reopened in the following July fortnightly or monthly trips were made to Havana for collec- tions (Pl. XI.). From this time until the suspension of opera- tions March 28, 1899, the collections—with the exception of a few extras and two delays due to sickness—were made at regu- lar weekly intervals (Pl. XII., XIII.). Thus, in one or another of the years in question all months but October, November, 269 February, March, and April have been covered by collections at intervals of five days or less, and from July 14, 1897, to March 28, 1899, a period of nearly twenty-one months, the series of regular weekly collections is almost unbroken. The following table gives the distribution of the collections by months in the several years. DISTRIBUTION OF COLLECTIONS BY MONTHS. Year ee |e ie) 2 ee acl jae) oone fa ea etal bea ee RE elie Meinl eal en |= 1894 272 I 2 I I 1) 10 1895 I 2 De Nes Ab p YO4H ER Me Se i ae SO 1896 Op ae Be Side 2G) iBank RB Neat Ne ators er eran leas 1897 ZEEE a Peay Wl bel cA aS age Slee Amnee SOSH Uh Se [ye Ma As ee Neds We ee eG Wi Ae Aa a Sis is Shi ine 1899 Baliye ae 13 otal Woy LS | TS 2. | rs | 26. 30" abel 27 re Wi e16) | Zones The distribution by months is such that a fair basis is formed for the determination of the seasonal fluctuations, since every month is represented by a considerable number of collections. The larger numbers in the summer months re- sult from the fact that the field station was always open dur- ing this season. The total number, 235, is more than twice that made at any other station in our field of operations, and affords the most complete and longest series in our collections. It is fitting that in this our most variable station the interval between collections should be least. The total period covered by our collections here is a little over fifty-seven months, and the average interval between collections 7.4 days. I know of no series of quantitative plankton collections, in any waters, of equal range or time, variety of season, and brevity of interval. THE LOCAL DISTRIBUTION OF THE PLANKTON AND ITS RELATION TO THE LIMIT OF ERROR IN THE METHOD. The investigator of plankton problems is constantly con- fronted by the question of the extent of the error resulting 270 from the assumption that a collection at a single place is rep- resentative of a larger area—an assumption necessary if any wide significance is to attach to the analysis of plankton data. It has been a matter of observation that the quantities of plank- ton taken at different places in a body of water, or even within very narrow hmits, are not equal in volume under similar methods of collection. Thus, Apstein (96) in eighty catches in German lakes finds the average deviation from the means to be 5.52 per cent. when the plankton is computed per square meter of surface. Of the eighty catches 68 or 85 per cent. ex- hibit a departure of less than 10 per cent. from the mean, and only four have a departure in excess of 15 per cent. ‘These de- partures are derived from averages of comparable collections on various dates and in several different lakes in groups of only two to five, evidently from mid-lake waters, and hardly afford suf- ficient data for an analysis of the conditions of distribution in any given lake or inatypical lake, since on account of their small number they do not throw any light onthe effect of shore, tribu- tary waters, vegetation, currents, or other factors of the environ- ment. They indicate, however, the probable error of +5.52 per cent. in mid-lake collections, and seem hardly sufficient to sub- stantiate fully the more general conclusion that “das Plankton sehr gleichmassig in einern Seebecken vertheilt ist.”” Reighard (94) finds in the case of twenty-nine hauls that his results “agree very well with that of Apstein.” Of his twenty-nine hauls, 26, or 90 per cent., have a “percentage of difference from the average” which is less than 20. These percentages yield, I find, an average of 9.7 per cent. to Apstein’s 5.52 per cent. Reighard does not, however, compute his “percentage of dif- ference from the average” in the same manner as Apstein deter- mines the ‘““Abweichung von Mittel,” the former using the vol- ume of each catch as the basis for the determination of the per- centage of difference from the average, while the latter employs the average of the two or more catches for this base. Obviously this slightly increases one half of Reighard’s percent- ages and decreases the other half, though it does not materi- 271 ally affect the average of all of them. Apstein’s method of stating the + error in terms of departure from the mean is, it . seems to me, to be preferred to the “percentages of difference” which Reighard uses. In all instances but one Reighard averages but two collec- tions, made at some one of fourteen points of collection in Lake St. Clair. His percentages of difference, therefore, refer only to these individual points of collection and not to the lake as a whole. His collections were all made within an interval of ten days, and it is probable that the results can be used to deter- mine the departure from the mean in the lake as a whole. This he has not done, though he concludes from these percent- ages of differences of the pazrs of collections that ‘‘the plankton is distributed over Lake St. Clair with great uniformity.” In the case of Apstein’s data the sets of collections are scattered over several seasons and represent a number of lakes, and range in number from two to five in each test. It is obvious that conclusions as to the uniformity of distri- bution of the plankton in the lake as a whole should be based upon a comparison of all catches with their average, and are best expressed in terms of departure from their mean, employ- ing the mean as a base and expressing the deviation in percent- ages whose average will constitute the mathematical expres- sion of the variation in distribution or the + error of the method. For reasons above stated, this method cannot be applied to Ap- stein’s data as a whole, though it is the one he uses for indi- vidual lakes or tests. Applying this method to the data of Reighard’s (’94, p. 33) table, asin the accompanying tabulation, I find that the aver- age departure from the mean is 31.8 per cent., with a range of -+111.5 to—57.5,—a total of 169 per cent,—on the basis of the amount of plankton per square meter of surface ;and +28.8 with arange of +91.3 to —-55.4,—a total of 146.7 per cent.,— ona basis of plankton per cubic meter of water—a deviation much greater than that expressed by Reighard’s method. This deviation is much greater than that found by Apstein (796), and it re- 272 sults in large part, doubtless, from the greater number of catches averaged, and from the fact that they represent a num- ber of more widely separated points in a larger body of water, DISTRIBUTION OF PLANKTON IN LAKE ST. CLAIR. | Plankton per sq. m. of surface| Plankton per m.° of water i nee Volume in Departure from} Volumein {Departure from Oo. meters 3 . i 3 Rake cm. mean in pel Gu cm. mean in per Ct. IIlQ 5.00 7.19 —29.4 1.44 —55-4 II 5.00 13.38 oles 2.68 —17.0 II1e 5.54 - 15.27 +49 .9 2.76 —14.6 Ill 5.54 21.55 “111.5 3.89 +20.4 IVQ 2.50 5.02 —50.7 2.01 —37.8 IV 250 5.02 —50.7 2.01 —37..8 VQ 5.26 14.40 +41.2 2.74 5.2 V 5.26 19.04 +86.8 3.62 +12.1 VIQ 4.70 10.93 =-7.2 2e20 —29.1 Vi 4.70 14.69 +44 .2 3.08 —4.7 Vile i 7 4.32 S575 3.69 +14.2 vil Ig 107/ 4.32 = S7/o5 3.69 14.2 VIIIQ 4.44 11.99 +17.1 2.70 —16.4 Vill 4.44 V2, SAS 31.1 3.01 —6.8 IXQ 4.28 10.88 +6.8 2.54 SPAS IX 4.28 10.22 +0.3 2.39 —26.0 XQ 1.50 6223 38.5 wens +28.5 xX 1.50 6.2 —38.8 Ags +28.5 XIIIQ DPN 10.59 =|=3'.9 4.79 +48.3 XIII 2e2T 8.76 —14.0 3.97 +22.9 XIVQ 2.89 10.41 +2.2 3.60 +-11.4 XIV 2.89 9.56 —6.2 Busi +2.5 XVQ oly) 9.29 —8.8 1.80 —44.2 XV 5.17 12.50 +22.6 Be42 2551 XVIQ 4.55 8.65 15-1 I.gO =41.2 XVI 4.55 10.61 +4.1 238 —27.8 XVIIIQ 12 7.09 —30.4 5.56 +72.8 OV OR Site 27: 6.13 —39.8 4.83 +49.5 XVIII 127, 7.85 —22.9 6.18 +o91.3 Av 10.19 SECM Ate} 2.23 +28.8 Range -FIII.5 to —57.5 =-O1.3/t0 —55-4 in which currents, vegetation, shore, and bottom are important factors environing its plankton. This large variation in the distribution of the plankton in lakes naturally raises the question whether there is in the channel of a running stream, for example the Illinois River, a plankton whose uniformity of distribution is such that a collec- tion made ata given place and time may be considered as a fair 273 sample of the contents of the water in contiguous parts of the stream, or of the plankton present in the water passing a given point of the stream for any considerable length of time. Will not the conditions pertaining to fluviatile life cause such local variations in the plankton and such changes in it from day to day that chronological series of isolated collections will reveal only erratic and meaningless fluctuations, without significance for the analysis of the factors of the environment and incapa- ble of revealing an orderly regimen of aquatic life? In other words, is the river a unit of environment sufficiently compact to yield, by the plankton method, data of scientific value com- parable with those derived from other bodies of water, types of which we find in the sea and the lakes ? As contrasted with the lake, the river as a unit of environ- ment. presents a constant and excessive predominance of the longitudinal over the transverse axis. This feature, combined with the fact that in a river the relative shore development is much greater than it is inthe lake, makes it necessary to discuss the longitudinal and transverse distribution of the plankton in the stream separately. LONGITUDINAL DISTRIBUTION. With a view to testing this question ofthe local longitudinal distribution of the plankton in the Illinois River, I made a series of ten catches in immediate succession from a boat anchored at our usual station in mid-channel on October 29, 1896. This was at a time of a considerable autumnal development of Sy- nura and Syncheta, and the quantity of plankton present (see Table III.) was sufficient (Pl. X.) to allow room for considera- ble fluctuation and to minimize the error attributable to meas- urement. In the following table the volume of the centrifuged plank- ton per m.3 and the deviations from the mean in volume and in percentages of the mean are given. : The similarity in the amounts of these successive catches is shown in the fact that the average departure from the mean catch is only +3.58 per cent. and the total range ofthe mits of 274 departure only 14.1 per cent. I know of no test of similar ex- tent elsewhere with which this may be compared, but its range is well within the limits of the records of repeated catches in TEN CONSECUTIVE CATCHES FROM ANCHORED BOAT. N _Vol. of catch cry Departure from average RB: in Bue perm. ( Invohime aa In percentage I 3.20 + .07 +2.2 2 3.24 + .11 3.4 5 3.04 — .09 —2.9 4 3.40 See +8 6 5 3.06 = CY = HS 6 3.20 + .07 sine i 2.04 ee ae Cs = 5-5 8 3.20 =O, 2.2 9 2.94 = eto 5.5 10 3.10 — .03 —1, Average 2513 + .112 +3.58 Greatest + + .27 +8.6 Greatest — =) ale = 5,5 DEPARTURES FROM MEAN CATCH COMPUTED FROM HAULS FROM EQUAL DEPTH IN GERMAN LAKES BY APSTEIN (96, pp. 56-57). Ap- No. | Average catch | Average depar- | Limits of depar- Total stein’s of : ture from mean | tures of percent- | range of No. hauls In cm.® in per cent. ages. departure 23 b-d 3 4.66 Dee) — (2:4 t0 -- 13 6.4 26 a-C 3 5.5 Gar = 9.1 “ or 18,2 27 a-e 5 4.1 7.8 —14.6 “ +15.9 30.5 28 a,b 2 4.5 Tite ce #8 ates 1 at D2 a2 30 a,b 2 9.12 tag! salen Oo eran meat ess) 2.6 32 a-c 3 13-2 4.3 — 5.3% + 6.1 11.4 33 a,b 2 26.3 6.4 — 6:7 “ + 6.7 1353 33 d,e 2 15.5 3.2 — 3.2 “ + 3.2 6.4 34 a,b 2 Ws 8.8 — 8.8 “ + 8.8 17AO 37 a-c 3 2.43 8.6 — 7.4 “ +13.2 20.6 41 a,b 2 1.5 13.3 SSNs ae 26.7 43 a-c 3 1.93 19.5 — 17.1 “* —29.5 46.6 46 a,b 2 2. Oo. O. O. 65 a,e 2 3-3 7-7 may AA Nomar be 15.4 Ge) Eo) 2 255 O. O. O. 45 a,b 2 1.2 8.3 833“) 8:3 16.7 47 b,c 2 ry O. OF O. 63 a,g 2 r23 Zo — 2.5)" + 2.5 Se 68 a,b 2 0.1 O. Oo. O. 69 a,b 2 --O.I O. OF O. 70 a,b 2 0.16 O. O. Oo. 24 a-c 3 I. oO. oO, oO. 83 a-c 3 1.13 3.8 — 2.7% + 6.1 8.8 275 smaller number in waters of European lakes. For example, Apstein (96) records 23 instances of ‘hauls on the same date from equal depths and evidently in every case within distances between catches Jess than that represented in the extremes of our test. The number of hauls did not, however, in any of his tests exzeed four. Ihave compiled or computed from Apstein’s table (pp. 56-57) the average and limits of departure from the mean in these 23 cases. In 12 of the 23 the average de- parture exceeds 3.58 per cent.—the average departure in our test, in which there were from two and a half to five times the number of hauls. In 10 of the 11 instances in which the departure from the mean in Apstein’s records falls below +3.58, only two hauls were averaged. The total range of the limits of departure also exceeds that found in our test in 8 of the 23 cases. In the light of Apstein’s results and considering the larger number of catches averaged in our test, and also the considera- ble length of the channel that it covers, it seems beyond rea- sonable doubt that single catches of the plankton inthe channel of the Illinois at our station of collection afford as trustworthy a basis for the analysis of plankton problems as do similar catches made in a lake. The margin of error thus introduced is no greater, if indeed so great, as that appearing in investiga- tions in such waters. Since these catches were made from an anchored boat, the water from which the plankton was taken was distributed over a considerable length of the stream. The test was made between 7:30 and 9:30 a.m. The river stood at 5.1 ft. above low water and was falling rapidly, so that the current was noted at the time as unusually swift, probably approaching two miles an hour in mid-channel at this point. At this rate the collections represent plankton taken at ten intervals from a body of water about three miles in length. This areal distribution is compar- able with, if it does not exceed, the limits of widest distribu- tion of catches in Apstein’s tests, but it is much less than that of Reighard’s, which lay within an area of about ten by thirty miles. 276 A series of ten consecutive hauls made on the afternoon of August 21, 1896, from a floating boat between the bend in the river above the plankton station and the towhead below it (PI. II.) throws some light on the questions of local distribution and of variation in catches from a limited area. Owing to the wind it was not possible to float with the current, and the apparatus also served to impede the boat. The river stood at 7.1 ft. above low water and was falling slowly, so that the current was not so strong as when the ten were made from the anchored boat. The test occupied about eighty minutes, and the boat drifted about a mile, so that the body of water actually passing it, from which the plankton was taken, was less than half a mile in length. Considerable dislodged vegetation and some cattle- yard debris were floating at the time, causing more than the usual inequality in the distribution of the silt which these elements introduce into the plankton. The catches ranged in centrifuged volume from .4 to .575 cm.3, averag- ing .48, and showing an average of divergence of 11.2 per cent. from the mean, with limits of +19.9 and --16.6—a total of 36.5 per cent. The divergence in this test is greater than that from the anchored boat, owing in part to the floating debris, and in part, probably, to the fact that the wind drifted the boat across fully three quarters of the channel. These divergences, both in average and limits, fall within the figures of parallel catches in lake waters quoted above from Apstein (96) and computed from Reighard (94). The fact that the range of variation on the whole is greater than the average run of Apstein’s results is doubtless due in part to the larger number of catches included in my test. These two tests thus indicate that the plankton of the main channel waters of the Illinois at the point where our col- lections are made, is distributed quite as evenly as that in lakes thus far examined from this point of view, and in consequence single collections may be utilized for the study of plankton problems with no greater error for the potamoplankton than for the hmnoplankton. The divergence from the mean will upon 277 the average, in all probability, fall within +10 per cent. Our chronological series of collections affords a few instan- ces of catches under somewhat stable conditions of river levels and temperature, and at intervals so short that they may be utilized as tests of local distribution within certain larger limits of error, since the utilization of such data introduces the er- rors resulting from changes of chemical conditions due to rot- ting of sewage, and from growth, reproduction, and destruction of the plankton in the interim between collections. The follow- ing tabulated instances (p. 278) from Table III. and Plates X. and XI. may be cited as throwing light on this question of local distribution along the length of the stream. The fourteen groups of collections were selected with refer- ence to stability of conditions, therefore in falling or low water and in periods of relatively even temperatures. Inspection of the tables and plates above referred to will show that the selection has not been made so as to eliminate wide varia- tions, and it may therefore be regarded as fairly typical. The periods included, range from 2 to 15 days in extent, and upon estimated rates of current the several tests include plank- tons taken at intervals in reaches of channel water from 24 to 252 miles in length. The average departures from the mean, range from +0 to +29.8, and yieldagrand average of +14.1. In view of greater number of catches averaged and extended time element involved, these results compare very favorably with those derived from Reighard’s data and Apstein’s results. The probable error resulting from variations in the longitu- dinal distribution under stable conditions seems to be less than +15 per cent. An inspection of Table III. and Plates X.—XIII. will show that in the case of invading flood waters the departures from the mean of catches at similar intervals would be considerably greater than the averages above computed. Also, thatin case of plankton pulses in stable conditions—for example in Sep- tember and October, 1897—collections at weekly intervals may exhibit departures in excess of +50 per cent. Itis evident, how- 278 LOCAL DISTRIBUTION OF PLANKTON IN RIVER AS SHOWN BY CHRONOLOGICAL CATCHES. Th nPEStio i sti- a De) Ay T'Ir’ge mated face Temp | Stage Catch | parture depart.| of limit No. SRN ate BA ISHBE Date a of per from |inper | in per group | cur- m.° mean in| ct. of | ct. of rent | miles |__| percent,|mean | mean per cent,|mean | mean 5 J Wee 75-5 | 5.38 EO Wi I BF 4 uly 29 : : 5 2233 2 tae! 1 | 77.8 | 4.20 74 —22.3 | =22-3| 44.6 2 5 36 J Aug. 5 | 79. 3-13 -95 fe) ce (ae 2.63 95 re) e a 33 36 Aug. 12] 82.5 2.40 5-94 —1.2 ; STNG) ogee Ml 2ea5 6.08 4ty\2 |= 22 2.4 ‘ Aug. ys 78 2.35 7.87 ee 4 4 “ 20) 79. 2.7 4-32 —10.5 ; yo) 291 80. 2.58 3.92 ae +24.3) 74-5 Veep teas) Wallet f7Ary 2.65 5.08 4.1 Sept) 172g y 5.70 1.48 +22.3 e We 6.85 1.16 + 4.1 108 ca an he 88 86 | —28.9 |+17-6| 51.2 5 75 7 5 9 9 | 72.5 145.98 | 0-48. | eeaeg PoE egy 4.25 1.06 ie Sept.12| 78. 3.90 2.92 +2 1 © PEAY 75s5. i) 3-30 3-49 +43 6 6 115 1G) 7405 4] 3-20 1.9L ai +29.8] 91-3 Seis es cr Cina ene WAL 1.19 = 48.3 Uae 3.20 1.98 —13.9 { Sept: 2347655 02-75 Noe y/ +15.1 7 25 24 ' ‘ 25| 72.5 | 2.63 1.05 —11.8 |+130.4| 26.9 aa as eras 3.2 1.14 L433 1896 ) Jan. 6 | 32.2 | 12.20 51 eee 8 Ap 252 cB ts Bz EOS 1-20 20 ; Se ORE 32.3 |11.40 | 1.02 ite £25 78.7 ty ie a3 2.4 | 10.80 83 =a ; Jan. 15 37-f 10.40 ue —0.2 WS) 2.18) 32. 9.50 1.01 —I1.7 9 2 720 ON ee ag |) 33. 8.60 2.36 OF en +10.8| 26.8 bi 30 ear g | e810 2.18 N68 § Mar. 9| 37-1 | 10.20 4.96 Se 10 2 720° 8) IZ 35.8 Sle OeyOr lh 5:08 |) 1358) Se oro MamisnG i SE ZANT AOL, 8.80 5.80 sO oS Apr. 24 | 71.8 | 6.90 | 17.07 ages II I 24 i Te 67.5 6.90 10.91 — 0.5 0.5 I Apr. 2 79 7.10 9-03 +28.1 12 I 48 {Mae Fl Geis i! o.to | goo |) ag ese anaae { Aug Is, | 7o- 7-40 2.32 + 1.1 13 75 HOB ats) | RON aeve, 7-50 2.72 +18.8 |+12.8] 38.4 fi) ER onal Aas FalO 1.84 = 10.6 Aug. 26 | 77 6.50 1.44 — 7.7 ae 6 43.4 : i S20 7 4e cl osee 1.68 St Aoi a iA Av._| | | | | | [14.1] 37-4 279 ever, that in all tests extending over many days other factors than variation in local distribution come in to modify the re- sults. LONGITUDINAL DISTRIBUTION FROM THE MOUTH TO HENNEPIN. By courtesy of the Illinois State Fish Commission I made on May 18-21, 1899; a trip on their steamer “Reindeer” from the mouth of the Illinois to Hennepin, about 205 miles from the mouth, making ichthyological collections for the State Survey. Incidentally plankton collections were also taken continuously from a short distance above the mouth to Henne- pin—in all, 21 collections. Of these, 19 will be utilized in the following comparison, the first being omitted because of uncer- tainty as to the distance, and one other because of loss of the collection. The catch was made by means of a 1} in. iron pipe carried from the guards of the boat to a depth of 18 in. below the surface of the water. The intake was redueed to { in. and turned toward the prow of the vessel, so that, while moving, a continuous stream of water was discharged into the plankton net, immersed in a barrel on deck. In this fashion a con- tinuous stream from the level of the intake was filtered. The contents of the net were removed approximately every ten miles of transit, and its clogging to the point of resistance pre- vented by shaking it down whenever necessary, thus minimiz- ing, in part at least, this source of error. The following table gives the data concerning these catches and the measurements and silt estimations,* together with my computations of the de- partures of the total catches from their mean and of the esti- mated planktons. The distances between points of collection were not deter- mined with great accuracy, since we had no log, and maps give no clue to the not infrequently tortuous steamboat channels. The distances are therefore approximations based on the expe- rience of the pilot and engineer in charge of the boat. *By the generous permission of Professor Forbes, centrifuge measurements and silt estimations have been kindly furnished tome by Mr. R. E. Richardson, who is preparing for publication in this Bulletin « detailed report upon these collections. PS Vol. in cm. Departure from | a) | Be 2 of catch mean in per cent. No. | Location | Time ma Were betes — - -— A le sio 8 |Prnk| Mos Total Plank- |" g|@ ton | Silt] tal catch ton 1 |lm.above Hardin... 5:45-6:45 p.m. | .10|) 72 | 60 | .18 -26 44 — 85 — 2 |Kampsville Dam___.... 6:45-7:45p. m. .08 | 71 | 80 | .23 -91 | 1.14 — 61 — 68 3 jim. above C. A. bridge} 4:30-7:45 a. m. -08 | 69 | 90 | lost 4 Ai orences 6:00-7:05\a..m- 103) |) 68) || 99° | 202) |\>'3p" "2334 — 21 — 97 5 jMauvaise Terres Cr’k| 7:10-8:10 a. m. .04 | 68 | 98 | .05 |2.36 | 2.41 — 18 — 93 6G Meredosia: 22.22 8:10-9:15 a. m. 2045/69") 95.) 1 2 15e 512.26 — 23 — 85 7 |La Grange ........ ....... |10:00-11:00 a. m. 04) Of 0% | 2i2t 42:28 — 24 =) 8 |Beardstown ...... ...-- |11:00-12:00'a. m. | .04 88 | .22 | 1.61 | 1.83 — 38 — 69 O PBrowiine:.. 7. 2:45-3:45 p. m. .05 95 1245" | 2:26 — 23 — 85 10 |Holmes Landing | 3:45-4:45 p. m 05} 10 1.80 .20 | 2.00 — 32 +153 lien av attals oo een 6 15-7:30 p. m 05} 80 | .53 |2.13 | 2.66 — 10 — 25 IQ WLiverpool, 4 eas 4:20-5:20 a. m 04 67.5} 50 2.12 |2.12 | 4.24 + 44 erloe 13 |2 m. above Copperas Creek 22 =e ee 5:25-6:30 a.m. | .04!' 68] 80 1.32 15.29 | 6.61 +125 + 86 14 |Mackinaw Creek. ..| 7:10-8:20 a. m. -05{ 67 | 70 |1.47 |3.42 | 4.89 + 66 +107 15 |6m. above Pekin __ | 8:40-9:45 a. m, .06 | 67 | 90 95 |8.59 | 9.54 +224 + 16 |7 m. above Peoria...| } Cute 08 | 67 | 60 |2.19 |3.29 |5.48| + 86 +209 17 |Chillicothe Park ____. 12:50-1:50 p. m. | .12| 66 | 15 | .92 16 | 1.08 = (2) + 30 18 j1m. below Lacon .....! 2:30-3:40 p.m. | .15] 66 | 20 | .88 22 | 1.10 — 62 + 27 LOM Henry eo eee See _| 4:00-4:55 p. m. 201 66 | 88 | .12 90 | 1.02 = (il — 83 20 |\Hennepin . =) 15220-6:30p.1m. | 20] 66 | 95 || 12. 1eie0 eaaalh i= ar aes Average “71 | 2.23 | 2.94 +57 | E89 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 + 224, 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 as a whole the data are so aberrant as apparently to disqualify them for scientific use. If, however, 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 shght 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 1$-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 (Pl. X., XIL., XXVIT., XXIX.,.XXXI., XX XIII.) —in which years the collec- 281 tions were sufficiently frequent to trace the movement in plank- ton production—shows that this season of the year is wont to be a period of rapid change in plankton content. Thus, in the river in 1896 on May 13-18 the plankton fell from 3.56 to .86, or 76 per cent., in stable hydrographic conditions. A similar phenome- non may be involved in the fluctuations in plankton content found in this transit of the river. The time intervening between the first and last collections was a little over two days. To this must be added the consideration that the collections represent a strip more than 200 miles in length, since we were traveling against the current, and, furthermore, that we have to deal with the volumetric changes in plankton content, as it passes down stream, due to growth and decay. Allof these influences areapparently butshghtin comparison with the effect of certain environmental factors which are local- ly dominant within certain sections of the river. We can distin- guish on the days of collection four sections or minor units of en- vironment dominated by different factors. The frst three col- lections made in the lower river lie in a region of comparatively clear water free from flood invasion. Unfortunately the third collection was lost, but the remaining two exhibit a departure in the case of the estimated plankton of +12 percent. and of +44 per cent. in the total catches. The next six collections, covering a stretch of 60 miles, from Florence to Browning, were all taken in a section of the river invaded by flood water of recent origin and poor in plankton, as was evident from the increased tur- bidity, the large amount of drift floating, and the discharge from tributary streams—principally on the right bank. In such conditions the amount of plankton (estimated) is small, and its variations form proportionately large percentages of its mean, the average departure being +51 per cent., with a range from —79 to +127—a total of 206 per cent. If, however, simply the total catch is taken, the average departure is+5 per cent., witha range of —18to +8—a total of 26 percent. In view of theextent of the river included in this section—60 miles—and the uneven distribution of the flood contributions, it is not surprising that 282 we should find such irregularity in the (estimated) plankton. We now come to the section of the river dominated by the Peoria-Pekin pulse of sewage, including 70 miles of channel— from Holmes Landing to Peoria. The flood waters are still in evidence, but in reduced volume, and there is marked increase in the plankton content. The average departure from the mean plankton is +82 per cent., with arange of —64 to +48—a total of 112 per cent. In the case of the total catches the average de- parture from the mean is +36 per cent., with a range of —60 and +89—a total of 149 per cent. The upper section of the river, above Peoria, a stretch of 40 miles, was less disturbed by flood conditions, there being only slight local invasions. This region is within the sphere of influence of Chicago sewage, and not receiving any large tributaries, we might expect but do not find conditions some- what equalized here. The average departure from the mean plankton is + 76, with a range of —76 to +80 per cent.—a total of 156 per cent. The average departure of the total catch is +34 per cent., with a range of —27 to + 66 per cent.—a total of 93 per cent. These departures will be much reduced if we break this section into an upper and lower region of two collections each, the percentages falling from +34 to +2 and +0 for plankton, and to +1 and +89 per cent. for the total catch for the two sections, each of which represents 20 miles approximately. The average departures from the mean plankton in the four sections are respectively +12,+51,+382, and +76 per cent., yielding a grand average of —43 per cent.; while the corre- sponding average departures for the total catches are +44, +5, +36, and +34, with agrand average of +29.7 per cent. These four subordinate units of environment represent longitudinal extensions of 20, 60, 70, and 40 miles. The area included in Reighard’s Lake St. Clair collections has a length of 32 miles and a maximum width of 54, and the average departure from their mean (computed by similar methods for all localities ) is + 28.8 per cent. Similar methods of computation thus yield for Lake St. Clair and these sections of the Illinois River almost an identical + error of distribution. 283 In the light of these volumetric data the conclusion is pat- ent that plankton data from fluviatile environment contain on the average a distribution error which approximates that in plankton data from limnetic areas of similar extent selected with reference to unity of environment as determined by local factors. It should be noted in this connection that the conditions | prevailing when this plankton traverse of the [llinois River was made, were most adverse to an equalized plankton in the fol- lowing particulars. It was at a time of rapid seasonal change in plankton during the decline of the vernal pulse, and it was at a time of intercalation of flood water of local and recent ori- gin, whose poverty in plankton is brought into contrast with the larger content of the run-off of impounded backwaters else- where. Finally, the river stage, which was 9 feet at Kamps- ville and 6.9 at La Grange, was such that the equalizing effect of general overflow on plankton content in impounded back- waters had ceased and local differences were emphasized, while at the same time their discharge continued in considerable volume. All of these factors, the last two of which are more impor- tant in the river than in the lake, tend to diversify the plankton content in the river at this season. It is reasonable to suppose that under other conditions—such as general overflow, the more stable features which attend falling levels above or below 3-7 feet, or in prolonged low water—we should find the uni- formity of distribution of the plankton more pronounced than it was on May 18-21, 1899, barring, however, the effect caused by sewage contamination, which at all stages and seasons is the most potent factor in the environment of the plankton of the Illinois River. TRANSVERSE DISTRIBUTION AND RELATION OF SHORE TO PLANKTON, The shore is a factor of great importance in the aquatic environment. It is here that land and water come into most intimate relation; seepage and drainage waters enter here; vegetation gains its foothold, affects the gaseous contents of 284 the water, and contributes by its decay to the nutrition of aquatic organisms; rise and fall of temperature are more pro- found here in shoal surface waters; light pervades more com- pletely; and currents are less rapid. Itis in many respects a less stable region than the central waters which it bounds, and it may, indeed, be regarded as a separate unit of environment, in contrast with mid-lake or channel waters. The effect of the shore-line upon the distribution of the plankton in the lake has not entered into the data referred to in the previous section, for in the investigations of both Ap- stein (796) and Reighard (94) along-shore collections were not made, and, moreover, the shore-line is less important relatively in the lake as compared with the stream. For example, the absolute development of the shore-line in Lake St. Clair—de- termined by the method of Seligo (90) (—shore-line divided by square root of area) is given by Reighard (94) as 9.23. In the Illinois River at high water, from Utica to the mouth it is ap- proximately 17.1, and at low water 78.3, omitting all the con- necting lakes and bayous, computing the area on the basis of the average of the low-water widths given on page 110, and ig- noring sinuosities exceeding that of the channel. The relative development (absolute development divided by absolute devel- opment in a circle in which 7=1) in Lake St. Clair is 2.607, in the [linois River at highest water, 4.83, and at low water, 22.1. These figures serve to show in a general way the exceed- ing importance of the shore-line in the environment of the po- tamoplankton. Owing to the great sinuosities of the shore- line as rising waters invade the bottom-land, these figures are probably very much smaller than actual measurement would make them. It is probable that the relative shore develop- ment in the Illinois is ten times that of Lake St. Clair, and fif- teen times that cf most lakes. Added to the diversifying action and predominance of the shore-line in the river, there is the tendency of its tributary waters, especially of the smaller lateral feeders, to follow their shore for some distance. ‘he absence of great sinuosity in the 285 Illinois as compared with other streams, as shown by th © slight ratio of development of the stream (see p. 102), tends to prevent the rapid mingling of channel and marginal waters, and thus gives cumulative effect to their differential charac - ters. In order to trace the quantitative effect of the shore and determine the variation in transverse distribution, | made two series of ten collections each along a transverse line, the first at our usual plankton station and the second below the mouth of Spoon River (see Pl. II.). The results of the first-named test, made August 26, 1896, are given in the following table, to- gether with conditions of distance from shore, depth, tempera- tures, and turbidity. The river at this time stood at 6.5 feet above low water, and had a width at the station of 150 meters. PLANKTON IN CROSS-SECTION OF RIVER AT STATION E. . b Tempera- Centrifuge Enumeration Omitting Omitting Srila tlhe ee aa method method Nos. 1,9, 10] Nos. 1, 8, 9, 10 - Es iS : DES Se Woeel So eer ie | —______ 2 & ie = ie 2a 2 | ae De- Per m.3 |Under 1 sq. m. - aS - af a | ee gf @ | Sur-| Bot- | 329 oan ture pose ture Re. me o 13a| 2 |face [tom |4 o'3| cm.3 | from Plank | from ean S $a Q he pa ) ager SDE SEE ena Vol-| ture | Vol ture a a m.3 in) == fa in = ss bu = mie in = | per ct perc per ct 1 10 | 1.68 | 82 77 | .33 | 2.00 127.5 | 143,800 31.8 3.36 2 | 37.5) 3:96 | 78] a7 | 133 | 1.34) 145 | an0-000 it 0.8 11.34 —22.1 et 25.2 3 sh We) re Gi |i |) Tee |) Ses 95,600 STP tie Soo 6.54 | — 7.9 4 85 | 4.88 | 77.5] 77 | .45 1,52 | —93:2 || 110200 SEO) 1952) |= 1186 im leon s Sy] 95 4.27 | 75) 77 | 45° | 144) | ipo. Lois Iniag |Zxe3 | eas | cota 6) let '-4049 m5: |/ 77 aoe) 25a.) cents 93,100 |—14.7 |2.36 |437.2 | 9.53 | +342 d _ ce 77.5 ie ab 2.40 | +53.1 | 112,500 + 3.1 |2.40 |439.5 7.63 | + 7.5 : 77.5| 77.5] .40 1.64 }+ 4.8 | 110,300 Heth led ae ui 9 135 1.22 1.75) 77.5) .38 1.04 | —33.9 109,900 a 0.7 i Ha 10 | 146 | 0.56 | 77.75] 77.6] .30 .60 | —61.7 96,200 Sah [ .34] Average | 1.57 | + 37.21 109,120 | 7.8 11.72] 21.9! 740 | £154 The collections were made with the pump, one fourth of a cubic meter of water taken from bottom to surface being strained in each catch. The variation in the catches is much greater in the cross- section than in limited longitudinal tests, in accord with the greater contrast in environmental conditions. The marked decline near the western shore may be due to the marginal belt of vegetation then present along that side of the river, and 286 the increase in the initial collection at the east shore is caused in part by the greater abundance of Wolffia drifted there by the prevailing wind. It is obvious that for comparison with lake collections these shore catches should be excluded, for the former are rarely taken so near shore. Furthermore, all our chronological series on which this paper is based were taken in mid-channel, far from the shore belt,.and in excluding those marginal collections but one sixth to one third of the total width of the stream isremoved from the test. After all al- lowances are made, it is obvious that quantitative differences in the plankton are much greater in a single transverse trav- erse of the stream than they were found to be in a longitudi- nal test extending over approximately thirty times the width of the stream. Indeed, it is to be expected that differences arising from the effect of the shores and of tributary waters would be carried by the current far down the stream. On the basis of volume per m.* the probable error of distribution 1s + 27.23, with a range of —61.7 to +53.1, and a total between limits of 114.89—all within these limits of variation in -Reig- hard’s data from Lake St. Clair, but exceeding, somewhat. the more limited data of Apstein. If we omit the three inshore collections, Nos. 1, 9, and 10, the probable error of distribution falls still lower,— to +21.9 per cent., with a range of —22.1 to + 39.5, a total of 61.6 per cent. between limits. If we take the amount of plankton under one square me- ter as the basis of comparison the results will be much more di- vergent, owing to the greater relative difference in depth in my locations and to the introduction of variation due to verti- cal distribution of the plankton. In Apstein’s tests the great- est departure from the mean depth in no case exceeds 10. per- cent., and with but four exceptions his 31 tests are in water from 15 to 45 meters in depth, where differences in depth are of less importance than in shoaler water., In Reighard’s se-- ries the greatest departure from the mean depth i is 66.9 per cent., the range being from 1.17 to.5.54 meters. . In my test the range, is from .56 to 4.88 m.,, the greatest depar ture being 81. ) per centeg, 287 and my inshore collections were all probably very much nearer the shore than any of his were made. It is therefore legiti- mate to omit these inshore collections in comparisons based on amounts under one square meter. Accordingly, if we omit Nos. 1, 8, 9, and 10, the probable error of distribution becomes +15.4 per cent., with a range of —25.2 to +34.2, a total of 59.4 per cent. between limits. This is far within the limits of error which Reighard’s St. Clair data yield. Since his catches include two at depths of 1.17 m., we may include all of my catches except No. 10, in which case the probable error of dis- tribution rises to +388 per cent., with a range of —77.1 to + 71.7, a total of 148.8 per cent., Reighard’s data yielding on this same basis of computation +31.8 per cent., —957.5 to +111.5, and 169 per cent. The greater average + error of distribution in my river test when these lateral collections are included is manifestly an expression of the effect of shore—an element not so pronounced in Reighard’s tests. On this basis the limits and total range still remain less in the river test than in the lake. From the data of transverse distribution in the Illinois River it isapparently demonstrated that, on the whole, the dis- tribution is no more variable than it is in Lake St. Clair; and if we eliminate marginal collections and consider only channel waters, that is the middle two-thirds beyond 20 meters from shore, the variation falls considerably within the margin of er- ror found in the lake, being in the six centrally located col- lections +15.4 per cent. on computations per square meter of surface, and +24 per cent. for the same on the basis of plank- ton per cubic meter. The variation was also tested by counting the planktonts in the catch, with the resulting error in distribution of +7.5 per cent. for all ten catches, with limits of —14.7 and +31.8—a total of 46.5 per cent. The cross-section made below the mouth of Spoon River September 30, 1897, contains ten collections made at equal dis- tances, about 12 meters apart, and the first and last this same 288 distance from the east and west shores respectively. As will be seen in Plate XI., this was made after nine weeks of uninter- rupted low water, when the river had been standing at 2 ft. for some time. The catches were made between 2 and 4 o'clock p.m. There was no vegetation in the river at this point in this season, though both Havana Lake and Quiver Chute, to the north (PI. II.), contained a small amount. The discharge from Quiver Creek and Lake makes its way along the eastern margin of the river, while that of Spoon River un- der these hydrographic conditions hugs the western shore. The effect is seen in the turbidity records, the clearer water be- ing on the eastern side and the more turbid on the western. The following table gives the data of collection. There was almost no silt in the catch, and the silt estimates are therefore omitted. PLANKTON IN CROSS-SECTION OF ILLINOIS RIVER BELOW MOUTH OF SPOON RIVER. = Departure from mean Num-| Temperature ae Plankton per Plankton under J in per cent. Derot (F.) Depth | depth m.3, in cm.3 1sq. meter (omitting Nos. land 2) 2 in m. | (in m.! | ee Boa Sen pets tse flash ee Bash ba Wee fae mean |Perm.® | Usderd aN ay visi : sq. m. veo fom SS ne in per cent. eee birt per cent. ae | 71.5 70 -66 Be i5) 2.40 —60 1.58 —83 2 ales 70 1.06 33 3.88 —35 4.11 —57 3 70.5 70 1.42 35 5.40 —10 7.67 —20 —20 —32, 4 | 70.5 7 1.58 .30 6.32 | +5 9.99 + 4 6 =P 5 70.3 70 1.58 31 5.60 — 7 8.85 — 8 = iz —22, 6 70.5 70 1.68 -25 7.64 +27 12.84 +34 +14 +14 uv |) Os 70 1:83 n eee 8.20 | +37 15 00 +56 +22 +33 8 70.5 70 1.88 22, 7.40 +23 13.91 +45 | 10 +23 9 71 70.5 1.83 -20 6.84 +14 12.52 +30 se +11 10 71.2 71 1.52 ike 6.28 = 5 9.55 —1 — 6 —15 ENG aE | 6.00 |+-22.3 ([ot60) ae Saas sere ee The results of this test are confirmatory of the thesis here maintained, namely, that the distribution of the plankton in a stream does not differ in the main from that thus far observed in lakes in the matter of variations in the plankton content (volumetric) in different localities. The average + depar- tures from the mean volume, computed per m.* and under 1 sq. m., in these ten catches are 22.3 and 33.8 respectively, as compared with 31.8 and 28.8 for Lake St. Clair and 5.52 for the German lakes examined by Apstein. 289 The hydrographic conditions and the location of the test in the stream are responsible for a large percentage of this va- riation. ‘Though the low-water levels cut off and reduce the diversifying action of impounding backwaters, the slight cur- rent minimizes the equalization due to mingling by the flow of the water in the channel, and, most of all, the location of the test just below the outlets of Quiver Lake and Spoon Riv- er (Pl. II.) involves the full effect of the diluent action of their relatively poorer waters. In Spoon River, on the day of the test, 3.12 cm.’ of plankton per m.* of water was found (Table IV.), while in Quiver Lake on October 1 there was only 07 em. per m.* (Table V.). The discharge from Quiver Lake is reinforced by the seepage from springs along the eastern shore,and these diluents are probably the cause, to some extent, of the low plankton content in the two collections nearest the eastern shore—2.4 and 3.88 em.’ to an average of 6. for the ten collections. The effect of Spoon River isseen in the much smaller decline in the inshore collection on that side of the river. Combined with the diluent action of these plankton- poor tributaries may also be the effect of shoal water and the horizontal stratification of the plankton. If we eliminate from the test the two collections made in the marginal belt of spring-fed waters, 24 meters wide along the eastern shore, the departures from the mean fall from + 22.3 and +33.8 to £12.1 and +20.2. These latter figures more truthfully represent the variation in distribution of plankton in channel waters including four fifths of the width of the stream—a lateral extension far beyond the range in that direction of the mid-channel collections of our chronological series which form the basis of the conclusions of the present paper. The data concerning the local distribution of the plankton in the Illinois River in longitudinal and transverse directions presented in the preceding pages may be summarized as fol- lows: The average + departure from the mean longitudinal distribution in consecutive catches at the same point in the 290 stream is 3.58 per cent; from a floating boat, 11.2 per cent.; at intervals of 1—7 days for periods of 2 to 5 days in the more stable hydrographic conditions, 14.1 per cent.; and in the stream as a whole for 200 miles of its course, 57 (total catch) or 89 per cent. (plankton estimated). If, however, we break up the 200 miles into four sections representing sub- ordinate units of environment, each dominated by some local factor, the + departures from the mean are 12, 51, 32, and 76 per cent. respectively for estimated plankton (1. e. after silt deduction), or 44, 5, 36, and 34 per cent. for the total catches, the averages for the two methods being + 483 and + 29.7 per cent. The average departure from the mean catch in two trans- verse series of 10 catches each is + 27.2 or + 22.3 on the basis of plankton content perm.’ If we eliminate the shallow-wa- ter shore collections, the departures fall to + 21.9 and +12.1, or on the basis of volumes under | sq. m.,to + 15.4 and + 20.2. The departure from the mean number of planktonts is only + 7.8 for the whole cross-section. These results are in the main within the + error of distri- bution of the plankton in lakes arrived at by similar methods of computation. The plankton method may therefore be applied to the quantitative investigation of the life of a stream as legitimately as to that of alake. The laws of the horizontal distribution of the plankton are in this respect essentially the same in both types of aquatic environment. Whether or not a fundamental source of error as large as this—probably the greatest of all the errors in the method as we have used it—vitiates the utilization of such data for scien- tific conclusions must be to some extent a matter of opinion. The extent to which it renders conclusions tentative must de- pend upon the distribution of the error, the extent of the data, and the method of their utilization. Personally I may say that close study of the at first sight aberrant data upon which this paper is founded, has led me to attach less significance to this source of error than I was at first inclined to do. Readers 291 of the paper will, I believe, find that in the main the conclu- sions arrived at rest on a body of confirmatory data so large as to counterbalance to some extent the probability of vitiating error from this source. The distribution of the error is, more- over, continuous throughout the whole series of data, with, however, some probability of variation with the stability of the hydrographic conditions. Finally, the conclusions to be drawn in subsequent pages rest upon data which to a large extent rise above the level of the error resulting from the irregularity of distribution. PLANKTON PRODUCTION. 1894 (Table III., Pl. VIII.) Ten collections were made by the oblique-haul method in this year between June 12 and December 15. The volumes of plankton, silt, and total catch per cubic meter average 2.49, .28, and 2.77 cm.’ respectively. The maximum catch, 10.18 cm.’ per m.* (plankton, 9.67; silt, .51) was taken Aug. 15,and the min- imum, .25 em.’ (plankton, .10; silt, .15), on Nov. 11. The series of ten catches form a somewhat regular curve, rising during July and August, and declining, most rapidly in September, toa minimum in October-December. A comparison of the record of 1894 (Pl. VIII.) with that of other years (Pl. [X.-XII.). as shown in the accompanying table of averages (p. 292), and with the conditions of temperature and hydrograph, will serve to throw light on the significance of the plankton volumes of this first year of our collections. As shown on pages 168 and 164, this wasa year of normally located high and low water, with March, May, and September rises all so reduced as almost to eliminate overflow stages and to prolong low-water stages, resulting in the low average height of 4.63 ft. above low water. Our collections all fall in the sta- ble period, broken only by the September rise. They therefore afford no data on the spring maximum of plankton production, 292 *SUOI}99][09 ‘ON [2I0.L *SUO!9aT[09 IT FO} ‘soSvIOAR A[TYIUOM JOx 61°z | | | Ay DLNZ 1Z°0, |9g°0| |od:1| |oS*z| Iggt| |€z'y) jez-Z g0'9 6S"; | 4z-o cag €1z‘o | x AV , gz‘o | |1g°0S | g1°0 | 66, Gig | conceals 66°0)5 Gz‘olt Ipz-ol |69°0|$ |16'ob |gS-olh |g6°E |S jo€s1\h job tS | Eo |p j Se bee ol El ale Biol elle cielo tla izle e NS Zby 2iz| 2 Z2\o <|Z|\'0 x ee le Sal ei a lS ales Pik. ela aie Rs ee elas | TPA ge oe 2 Siig £18 ly Siais S/sia Sis £/3\5 H/8ia > jsis® (sia |3) B= 8\5&\8| = | Ayewuins potas 99 | ‘3dag | ‘sny ct | oun{ Ae | qudy | yore 4 | ‘uel ‘66g1-F6g1—aaLondad LIIS—UAAIN SIONITII NI NOLMYNV1d JO NOILONGOUd ATHLNOW 293 revealing only a single midsummer pulse, culminating in the August maximum ina period of maximum heat and lowest water. In the light of collections of later years in this and other localities it seems probable that collections at more frequent intervals would have yielded a curve of greater irregularity, with other fluctuations than the single one apparent in the present record. It seems probable from the records of 1896 (Pl. X.) and 1898 (Pl. XII.) that the small average (0.74) in June is due to the fact that the dates of collection fall in a period of deeline from an April-May pulse, hastened by the rise in May and per- haps reduced in volume by the relatively small contributions of impounded backwaters resulting from the depression of the spring flood. It may also be that the collection of June 29 ex- hibits the flushing, depleting effect of the rise of the preceding ten days. It will be noted that the collection of June 12 lies about four weeks after the crest of the May rise—a location which is attended in 1896, 1897, and 1898 (Pl. X.—XIIL.) by a decline to a minimum after a pulse of plankton development. The hydrographic conditions of July in 1894—decline of flood to low-water levels—are approximately realized with va- rying stages of river and rates of decline in all the other years but 1895 (Pl. IX.-XII.). In 1894 they attend a tenfold in- crease in the plankton during this month. The movement of production is in the same direction approximately in July in 1896, 1897, and 1898, though its development is less in 1896 and 1898, and data are lacking for its progress in 1597. In 1894, and to a varying extent in other years, this rise attends among other factors the restriction of contributions from impounding backwaters and the differentiation of what might be called channel plankton proper. The July production in 1894 aver- ages 5.12 cm.’ per m.’—the largest, with the exception of that for 1895, of any year, and a fact to be correlated with the un- usually stable conditions then prevalent. In August of this year the single collection forms the apex of the season’s production, reaching 9.67 cm.’ per m.°—an 294 amount not surpassed for this month in any subsequent year. It may also be correlated with the continuance of stable con- ditions. The nearest approach to this amount is found in 1897 (9.45 cm.*, Table III.), likewise in stable conditions. It is not im- possible that there is more than one culmination in the months of June and July, collections being at too great intervals to suggest the direction of the movement in production. The flood of September attends a decline of the plankton to a minimum of .34 on the 17th in the fluctuations in level on the crest of the flood (Pl. VIII.). Similardirection of movement in production may be traced in 1895, 1896, and 1898. This decline in production attends the beginning of theautumnal de- cline in temperature, 10°-15° of which occur within this month. The hydrographic conditions during the remainder of the year are exceedingly stable, there being a gradual rise of only .5 ft. from the middle of October until the middle of December. Beyond the insignificant rise in the October catch no movement in production is evident. A comparison of these scanty data with the curves of production in these months in 1895 and 1897, both with low-water autumns, makes it evident that collections in 1894 were too infrequent to serve as a basis for any conclu- sions as to the average autumnal production in this year, and raises the query as to whether considerable fluctuations of pulse-like character might not have run their course in the in- tervals between our collections. The higher averages in Octo- ber-December in other years supports this suggestion. It is evident that the monthly interval of plankton collection is too infrequent to afford usable or significant data. The average of the ten collections in 1894 is 2.49 cm.*, and that of the seven monthly averages 2.53 cm.’ Thisis larger than the averages for a similar period in 1896 and 1898 (.99 and 1.09 respectively), both years of disturbed autumnal hydrograph. It is much less than that of the last seven months of 1895 (7.15). If, however, the exceptionally large collections of June-July be omitted in this year, its average (of monthly means) falls to 2.05. In the main, the hydrographic conditions in 1894 and 295 1895 in the last five months are somewhat alike, and their plankton production is somewhat similar (ef. Pl. VIII. and X.). In 1897, however, the uninterrupted and prolonged low water yields a much larger production of plankton (3.56 for the last seven months). | Though incomplete, the evidence in a general way indi- cates that 1894, in the period included in the collections, was a year of abundant plankton production, approximating 2.5 cm.* per m.° of water. 1895. (Table III.; Pl. 1X., XLII, LI.) Of the 50 collections of this year but 4 were made in the first six months. This was particularly unfortunate, for the spring was one of exceptionally low water, and the collections are so in- frequent as to give only the faintest clue to the curve of plank- ton production in this important period. All of the collections were made by the oblique-haul or repeated vertical-haul method. Omitting the very unusual catch of June 19, the mean volumes of plankton, silt, and total catch per cubic meter are respective- ly 2.12, 1.88,and 4.01 em.* As an average, the proportion of silt in the catches is thus quite low—a fact explained by the absence of considerable floods during the period of most frequent col- lections. As is shown on pages 164 and 165, this wasa year of unusu- ally low water, the mean annual stage of the river being 3.61 ft. The spring rise did not bring the river to much more than min- imum bank height, and there was no June rise. Aside from a few minor meteoric rises to less than 6 ft. in July and Septem- ber the low-water period was unbroken until the December flood culminating at 12.6 ft. at the close of the year A glance at Plate IX. will indicate that the collections suffice to trace the production during the last six months,—a low-water period with minor rises,—and to follow somewhat closely the effect of these hydrographic changes upon the volume of the plankton. The isolated collection of Feb. 23, made beneath 37 cm. of ice at the close of a period (Pl. IX.) of ice blockade of approx- 296 imately two months’ duration, reveals an almost complete ex- termination of the plankton, the amount given in the table,. 01 em.*, being only an expression for an amount beyond the reach of our methods of measurement. As shown in Plates VIII. and IX., there was prolonged and quite stable low water from Oct. 15, 1894, till the flood of the last week of February of the following year which carried away the ice. The concentration of sewage under such conditions was shown by the stench of the water, by the departure of fish into tributary backwaters, and by the death of many not escaping. Unfortunately no chemical analyses of river water at this season are now availa- ble, and the chemical conditions can only be inferred from those in later years at times of briefer ice blockade, higher water, and presumably less contamination. For example, in January, 1898, following the low water of 1897, we find under ice of three weeks’ duration (Pl. XI, XII.,and XLIV., XLV.) great excess of freeammonia and chlorine, and high albuminoid ammonia, organic nitrogen, and oxygen consumed—all, in- dices of contamination. The ice sheet upon a contaminated stream must also profoundly affect the equilibrium of oxygen and carbon dioxide dissolved in the water, and thus directly influence the life of all constituents ofthe plankton. It is there- fore not surprising that these unusual conditions should ex- terminate all but the most resistant members of the plankton. The catch consisted almost entirely of flocculent debris (zo- ogloee?) with a few minute filaments of bluish green alga of uncertain affinities, while the usual plankton was represented by only 43 individuals, representing 14 + species, as follows. Protozoa: Diffugia sp. (deformed?).......... ] Episigiis sp., neddsauneacy & eee 3 Carchesium lachmanni, head....... i! Ciliate, indeterminate............ 1 Hehozoan “02 Vs ae a eo ] 297 Rotifera: Brachionus dorcas, female......... 1 Rotifer tardws, temiale:i.3) 20. 5--4- 9 Polyarthra platyptera, female...... 2 Polyarthra platyptera, female with TG OOO Munchen error 1 Indeterminate rotifer sp........... 1 Entomostraca: Cyclops bicuspidatus, female, young, dead or moribund..... il GU CHO MS Ay OUMIP ie 3 yin, ld reset cho iss 2 Cyclops, Maples aise cael ce = 4 Canthocamptus, nauplil...........- 4 Chydorus glob0sus. a... 50+ 5es2. 7 - 1 Miscellaneous: Riahdocols tas.6h act ws ae 1 WDCKO! COU Cee mate Se is es peice 2 indeterminate 0604... oot fi GGA. it ete ae 43 In towings made at the time of the quantitative collec- tions Mr. Hempel found an individual each of Pterodina patina and Notholca acuminata. The list includes representatives of the prominent winter planktonts excluding alge and diatoms. The effect of the sewage contamination is observed in the reduced numbers both of individuals and species, in the moribund condition of Difflugia, Carchesium, Epistylis, Brachionus, and Cyclops, and in the fact that apparently the only breeding forms, with the exception of the Cyclops, were the ubiquitous and_ perennial Polyarthra and the muck-loving Canthocamptus, and possibly the slime-dwelling Rotifer tardus. This incident affords a striking illustration of the catas- trophic effect of the ice blockade upon the life of sewage-fed streams in whose waters the products of decay are concen- trated by the exclusion of the air by the ice sheet. The absence of collections in March prevents any tracing 298 of the initial stages of the rise in vernal production indicated in later years, especially in 1896 and 1898. The two April collections average 3.18 cm.*°—about 37 per cent. below the mean for this month in the three subsequent years. An inspection of the vernal plankton curves for this and subsequent years at this and other stations (Pl. [X.—XIL, XXVI.-XXXIV., XXX VI.-XLII.) reveals the presence of a ver- nal volumetric pulse* of plankton, which, as a rule, marks the maximum period of production in the year, and follows imme- diately upon the vernal rise in temperature. In 1895 our collections were too infrequent to detect the location and extent of this vernal pulse. In other years, as seen in the plates to which reference is made above, the best- defined vernal pulses appear in the closing days of April and the first week of May. From the character of the best delineat- ed vernal pulses—e. g. those of 1896 and 1898 (Pl. X. and XII.) —it is probable that the apex or crest of the pulse is narrow, that is, the maximum development lasts but a few days. If this be the case, our two collections in April may miss entirely the period of culmination. The second collection, upon the 29th, would appear to be located at the probable season (tem- perature?) to detect the maximum development. If this be the case the vernal development of 1895 is much reduced, and might be correlated with the suppression of overflow stages and con- sequent reduction of contributions from the impounded back- waters. ‘I'wo facts lead me to think that two well-developed vernal maxima may have been present in 1895. First, a com- parison of the vernal pulses of 1896 (Pl. X.) and 1898 (Pl. XII.) indicates that the pulse of the former year culminates about *IT use the term plankton “pulse” to designate the phenomenon of a periodic in- crease of the plankton volumetrically, as a whole, from a minimum to a maximum, followed by a decline to another minimum, the rise and fall being more or less gradual, and the data forming when plotted a more or less symmetrical curve, re- sembling that known as the “probability of error” curve. A typical example of this phenomenon and resulting curve is seen in the case of the April-May plankton of 1898 (Pl. XII.). The term may also be applied to a periodic increase in individual members of the plankton similar in its graphic delineation to that of volumetric changes. The pulses will be designated by the months in which the major part of their course is run. 299 April 24 and that of the latter about May 3. The temperature curves of 1896 pass 60° about sixteen days before they reach that point in 1898. This may be the cause of the earlier cul- mination of the vernal pulse in 1896. Now in 1895 there is a suggestion in the temperature curve of an early spring, and the suggestion is borne out by the records of the U. 8. Weather Bureau for central Illinois. The normal mean temperature for Illinois as a whole in April is 51.8°. In 1896 it was 54.8°. In this case we might expect to find an earlier vernal pulse culminating, as in 1896, before the end of April, so that our col- lection of the 29th would fall upon its decline rather than upon its apex. I use the term vernal maxima advisedly, for I am inclined to the view that the period from April 29 to June 19 witnessed a remarkable development of the plankton. The reasons for this view are found, first, in the fact that the catch of June 19 contains many Moina micrura, numerous males and epphippial females being among them, whose presence suggests the close of a period of rapid multiplication by parthenogenesis. The catch of June 19, though large, may thus represent the decline of a still larger population. In the second place, the qualitative collections made witha tow-net in the river in the in- terim between the quantitative collections of April 29 and June 19 indicate an exceedingly abundant plankton rich in Moina. From the available data in 1895 and the course of the ver- nal production in other years it may be inferred with some de- gree of possibility, if not indeed of probability, that the vernal production in this year was accelerated by the early spring, and that a pulse appeared prior to April 29, and that this was followed in May-June by another pulse of much larger propor- tions and longer duration, a part of which (probably the decline) is detected in catches of June 19and July 6. Of the occurrence of this latter and larger pulse there is little doubt, though the data are not available for its location and delineation. The unusual and prolonged low water of these spring months thus seems to result in a marked increase in the plank- ton content. The causes which lead to this are not far to seek. 300 The decreased volume of water causes a relative concentration of the sewage and consequent increase in fertility of the chan- nel water over that of the usual high water of this season. Lower levels insure more rapid rise in temperature, and the slackened current affords more time for the breeding of the plankton. The occurrence of Moina micrura, a lover of foul water, is in itself an index of the character of the stream in this low-water spring. The contributions of the impounded backwaters to the stream during this April-June period (see Pl. [X.), owing to the small areas submerged, are reduced in volume so that both the relative and actual share which they have in the formation of the channel plankton is probably less than in years of normal spring flood. Nevertheless, as seen in Plate XXXVI., such waters as Thompson’s Lake tend by their run-off to enrich and increase the channel plankton. The month of July (PI. [X.) witnesses the rapid decline of the second vernal pulse from 29.68 cm.’ on the 6th to6.5 on the 23d and .33 on the 29th—a fall of 98 per cent. in 23 days. The last stages in this decline were hastened by the rise of 3 ft. in the third week of July, the flushing and destructive action of the flood waters continuing until the close of the month. In this and subsequent years I shall call attention—when- ever the interval between collections is brief enough to afford adequate data—-to the phenomenon of recurrent pulses of plankton production. [am led to make this emphasis by ob- serving in the numerical analysis of these catches recur- rent pulses in most if not all of the more abundant species, pulses, moreover, which exhibit a degree of concurrence in many species which I beheve to be expressed in the faintly traceable volumetric pulses which run like waves, erratic in amplitude but more regular in interval, through the seeming vagaries of the volumetric data. I shall therefore treat the volumetric data from this point of view, endeavoring to discov- er evidence of cyche production wherever it exists, and seek- ing to correlate this phenomenon with the more patent fac- tors of the environment. 301 Considering, then, the data from July to the end of the year in 1895 (Pl. [X.), we find that the month closes at a min- imum of .33 em.’—the end of a pulse of uncertain limits and the beginning of the next, which culminates in the third week of August. This August pulse is followed by one of less ampli- tude and duration, culminating about three weeks later, by one of slight amplitude in October, culminating at an interval of about four weeks, by one of greater amplitude in November, after an interval of about five weeks, and by one in December, al- so of considerable amplitude, at an interval of about four weeks. The fluctuations of some of the component groups of organ- isms are shown in Plate LI., and considerable correspondence inthe volumetricand statistical pulses will be apparent on com- parison. | The August pulse has a duration of 39 days,—trom July 29 to Sept. 9,—and a maximum amplitude of 7.63 cm.* on August 24. The mean of the pulse,* that is the line upon which the center of gravity of the polygon formed by connecting the ordi- nants lies, falls upon August 22. This pulse occurs in a period of somewhat stable low water, and its decline from the maxi- mum of 7.63 reaches 2.07 on Sept. 4 and occurs without the assistance of flood waters. On Sept. 5 a sudden minor flood, due to local rains, flushes the stream and completes the deple- tion of the plankton to .69 on the 7th. The August average for 1895, 4.03 em.*, is higher than that of any other year excepting 1894, in which but a single collection was taken, which may not be representative of the whole month. Freedom from ris- ing flood waters in 1895 is doubtless one cause conducing to this high average of production. The enriching effect of the minor flood which culminated in the closing days of July may also contribute to this end. The absence of rises in May and June would also tend to increase the contributions of organic material to the stream by this July flood as compared with *The mean was computed by multiplying the volume of each catch in the pulse (ordinant) by the number of days from preceding minimum to date of collection (abscissa) and dividing the sums of the products by the sum of the catches in the pulse, the quotient being the abscissa of the mean. 302 floods which followed normal spring rises. The correspond- ence of the August pulse of plankton with a heat wave of 10° amplitude is well shown in Plate [X. Similar correspondences may be detected in some instances elsewhere in the plankton and temperature curves, but neither the completeness of our temperature data nor the corroborative evidence is sufficient to lend much support to a causal nexus between the phenomena. The September pulse has a duration of 25 days,—from Sept. 7 to Oct. 2,—and a maximum amplitude of 3.25 em.’ on the 14th. Its mean falls on the 17th, 26 days after that of the August pulse. This isa month of considerable hydrographic disturb- ance, the rises of the 6th, 17th, and 27th causing almost twice as much movement (8.75 ft.) in river levels (see Table I.) as is found in other years of our operations. ‘These accessions of flood water in each instance attend a fall in temperature of 5° to 8°, though that on the 27th is combined with normal autum- nal decline. None of the three is sufficient to cause overflow, and each is of but few days’ duration. Their effect upon plank- ton production is, however, considerable. In the first place, the immediate result of the invasion of flood water is an in- stant decline in the plankton, as shown by the change from 2.07 on the 4th to .69 on the 7th, the flood in this case acceler- ating and perhaps continuing the normal decline of the August pulse. So also the little rise of the 17th checks the rising curve of production, the fall being from 3.25 cm.’ on the 14th to .59 em. on the 18th. The rise of the 27th evidently occurs towards the minimum of a declining plankton pulse, and the fall from 1.03 em.’ on the 25th to .87 cm.’ on Oct. 2 is of less extent. The location of these floods in the pulse is such that if my conjec- tures as to their reducing effect be true they cause a shifting of the apex of the curve and of the location of the mean to the left of their probable position had not the floods occurred. In technical phraseology the mode of the curve of this pulse ex- hibits left-handed skewness. In the second place, the general effect of these recurrent rises is a reduction in total production the extent of which can only be conjectured. It seems proba- 303 ble that the rise of the 17th is responsible for the suppression of a rising pulse whose culmination had not yet been reached. The slight recovery in the following week is indicative of the upward tendency in production thus interrupted. That con- tinued low water in this month may attend great plankton production is seen in the records of 1897, when the monthly average (see table on page 292) is 8.83 cm.’ to 1.52 em.’ in 1895. On the other hand, in 1896 and 1898 the disturbed conditions, with higher water and more current, are accompanied by much reduced production, averaging only .38 and .69 cm.’ The last week in September witnesses the first stages of marked decline in temperature from the well-sustained summer heat of 75°-85°. The decline reaches 68° at the end of the month. This phenomenon combined with the last flood to ac- celerate and complete the decline of the September pulse which had already appeared prior to the last flood. . The October pulse has a duration of 29 days,—from the 2d to the 80th,—and a maximum amplitude of .76 cm.’ on the 11th and 15th, following a rise in nitrates and attending in- creased sewage contamination (PI. XLIII.). Its mean falls on the 18th, 31 days after that of the preceding pulse. This isa month of stable low water approaching minimum levels, the total movement in the pulse period at Havana being only 1.03 ft. The temperature in this period falls from 61° to 45°, and this taken in connection with the fall of 11.5° in the preceding week brings to bear upon the plankton production of this month the cumulative effect of a decline of 27.5° and the results of the low temperature of 45°. The consequence is that the summer planktonts are killed off or reduced in numbers, and the winter planktonts have not as yet had time or temperature to reach any considerable development. The plankton produc- tion is therefore low ; so low, indeed, that its pulse-like char- acter is largely a matter of conjecture in the volumetric data (cf. statistical data on Pl. LI.). Phenomena of like character are to be detected at corresponding periods of autumnal decline in temperature in September-October, 1896 ; in October-Novem- 304 ber, 1897; and in October, 1898. The effect of this autumnal decline of temperature may also be traced in monthly averages of production in the table on page 292. Rapid decline in tem- perature is thus immediately followed by rapid decline in pro- duction in the channel plankton. Such correlation in decline of temperature and plankton cannot, however, be found as a general phenomenon in the bottom-land lakes (cf. Pl. XXX— XLII.) and a causal nexus between the two declines must there- fore be of hmited operation and at the best highly conjectural. The operation of other factors than that of direct temperature is probable. The monthly mean of production for October in 1895 is .57 em.’, approaching that of 1894 (.61) and 1898 (.24). In 1896 and 1897 it is much higher (1.11 and 5.95 respectively), an earlier decline of temperature in 1896 (Pl, X.) and a later one in 1897 seeming to shift accordingly the attending declne in plankton, so that the September (.388) and November (1.) aver- ages respectively more nearly represent the October averages of 1895. The November pulse has a duration of 35 days,—from Oct. 30 to Dec. 4,—with a maximum amplitude of 4.37 em.* on Nov. 27. Its mean falls on the 22d, 36 days after that of the pre- ceding pulse. This is also a month of continued stable low water, with a shght rise of .75 ft., due to the checking of evap- oration and to autumnal rains: Thetotal movementis only .99 ft. at Havana. Temperatures during the first three weeks are somewhat stable for this season of the year, exhibiting a range of only 5.8°—from 48.5° to 48.2°. The last week, however, ex- hibits a fall of 10.2°, to minimum winter temperatures and the beginning of the ice blockade. Under these stable conditions the plankton production in November rises to a level approach- ing that of midsummer of the current year, its apex (4.37) fall- ing 44 per cent. short of the August apex (7.63), and its aver- age (3.02) 25 per cent. short of the August average (4.03). Both volumetric (Pl. 1X.) and statistical data (Pl. LI.) demon- strate the rapid multiplication of the plankton in these stable 305 conditions, and the result is a pulse of considerable amplitude, moreover, one not attained in any other year in channel plank- ton; a fact whose significance is apparent when we find (PI. VIII—XII.) that no other year combines to the same extent stability of hydrographic and thermal factors. The relative production in different years (see table on p. 292) bears upon the point in question, the monthly mean (3.02) being from 150 to 3 times as great as that reported for other years. The chem- ical conditions attending this remarkable plankton production (Pl. XLII.) are those following increased sewage contamina- tion, namely, a rise in nitrates, free ammonia, and chlorine. The December pulse has a duration of 21 days,—from De- cember 4 to 25,—the limits being taken from the statistical data (Pl. LI.), which are based only on catches at intervals of 5 to 7 days. Its maximum amplitude (2.60) occurs on the 20th, and its mean falls on the 16th, 24 days after that of the preceding pulse. The first 18 days of the month are relatively stable, with a movement in levels of only 1.05 ft. and stable minimum temperatures under the ice sheet. During this period a shght- ly developed pulse begins its course (cf. also Pl. LI.), but its apex does not rise much above the level of previous produc- tion. It is noteworthy that this takes place beneath the ice sheet which covered the upper river during the fortnight pre- ceding the flood. It isin this month that the contamination noted in November reaches its maximum (PI. XLIII.), at least as shown by nitrates and free ammonia. The chemical condi- tions thus favor a continuance of the productive activity of the previous month. On the 19th heavy general rains started a flood of unusual magnitude which continued to rise, culmina- ting at 12.6 ft. at the end of the month. This raised the temper- ature about 9°, brought in an immense load of silt, flushed out the plankton, and increased the rate of the current so as to greatly reduce the time for breeding. The first two days of rising water did not materially change the quantity of plank- ton per m.°, indicating a considerable rise in production had not the flood occurred. By the 25th, however, the flood waters had 306 swept away all but a vestige of the rich plankton of the earlier weeks. The amount remaining was so small that its quantita- tive changes were swamped in the errors of the volumetric method and silt estimation. The large amount of silt carried in this and subsequent floods of the winter is due to the fact that bottom-lands and fields covered with a rich vegetation were now submerged for the first time in two years (Pl. VII.), and vast quantities of debris from this region and tributary streams now entered channel waters. In comparison with other years December in 1895 is, in spite of its fortnight of flood; the most productive December recorded (see table on p. 292), averaging 1.14 cm’ to .76 in 1896, .96 in 1897, and .99 in 1898. It shares the large development of the preceding month, and with it presents the most marked late autumnal development in channel waters, though falling far below the production of some of the permanent backwaters in thisand other years in this season. The unusually stable hydrographic conditions in the river doubtless contribute in large measure to this exceptional development. That low tem- peratures alone do not prevent the development of a large win- ter plankton is apparent from this December development of 2.6 cm.* per m.* and 11.1 cm.’ per square meter at temperatures but little above 32°. The year 1895 as a whole may be summed up as one of mid- winter stagnation followed by excessive spring and early sum- mer development of the channel plankton, of midsummer and equinoctial floods, which check development at that season, of stable autumnal conditions and exceptional production in late autumn, and of catastrophic reduction by flood to a minimum. As a whole the year was one of exceptionally heavy production when expressed in terms of plankton per cubic meter. This is seen in the high average—3.22 em.’ of all catches, 5.31 cm.’ of monthly averages. When total production is considered it may be that the decreased volume of water at the time of the maxi- mum in the low water of June will at least counterbalance the excess per cubic meter, and that the total production will not 307 exceed, if indeed equal, that of years of more normal hydro- raph. eee 1896. (Tables III., X.; PI. X., LI.) There were 76 collections made in this year, of which 69 are prior to Sept. land are, moreover, at intervals brief enough to enable us to trace the curve of plankton production with some degree of accuracy. In the last four months the fort- nightly interval is too great to permit more than conjecture as to the probable course of the plankton curve. The collections prior to May 22 were all the result of com- bining 4 to 9 repeated vertical hauls of the net. Subsequent to that date they were made with the plankton pump. This, as is shown on page 165, was a year marked by recurrent floods, which bring the average height for the year up to 6.98 ft. ina year of less than average rainfall. This is almost twice the average height (3.61) of the preceding year. Since the flood did not in most cases reach bank height, the overflows were not extensive and did not occur during periods of large plank- ton production (Pl. X.). The distribution of the collections with reference to the floods is such that we have again in this year the opportunity to test the effect of the access of flood wa- ter upon the curve of plankton production at all seasons of the year but the autumn months. Inthis year the vernal rise in temperature occurred abruptly in the middle of April, and the autumn decline began quite early but progressed slowly. Summer temperatures were also lowered somewhat by access of flood water. The plankton of January, February, and March (Pl. X.) forms so small a portion of the total catches that its quantita- tive changes are swamped by the probable error of silt estima- tion, and are apparently of such shght extent that their signifi- cance cannot be detected. The amount of silt carried is very large, doubling or trebling in quantity on rising floods, and reaching a maximum of 14.77 cm.’ per m.’ on the crest of the March freshet. Norecurrent pulses appear in the volumetric 308 data, though the statistical data (Pl. LI.) indicate the recur- rence of three such pulses in this period. The volumetric: production is very small throughout this whole period, rising above an estimated amount of .01 em.’ per m.* in only 7 of the 18 catches, and not exceeding .13 in any of them. This results in monthly averages of .01, .02, and .07 re- spectively for the three months (see table on p. 292). These are lower than those of any other years excepting only that afforded by thesingle collection of February, 1895. The cause of this slight production is, | believe, the high water and increased current resulting therefrom, which does not afford to the channel plank- ton the time requisite for breeding a more abundant plankton. Some corroboration of this view may be found in the fact that the February collections in the high water of 1897(PIl. XI.) lhke- wise yielded minute quantities of plankton (average .04 cm.* per in.”), while the channel waters of 1898 (Pl. XII.) in January and the early part of February, and of January—March, 1899 (Pl. XIII.), produced at stages below that of overflow (8 ft.) a more abundant plankton—.07 to 1.15 cm.’ per m.* of water. High water with accompanying rapid current is thus deleteri- ous to plankton production in channel waters, in midwinter at least. It is noteworthy that this minimum production occurs in the presence of nitrates in great excess, in fact in quantities larger than those recorded at any other period of our records. (ef. Pl. XLII-XLV.). It is not therefore for lack of nitrates and other products of decay that the plankton fails to develop. The data of the collections in the latter part of March in- dicate a rising production as levels fall and temperature rises. The direction of movement is upward, though the quantity at- tained in this month is not great. The interval of collections and the quantities of plankton obtained from March to September enable us to trace with some probability the course of the recurrent plankton pulses of this season. The April pulse has a duration of 32 days,—from March 30 to May 1,—with a maximum amplitude of 9.39 cm.* on the 24th. 309 Its mean falls onthe 23d. Thisis the vernal pulse, often the lar- gest of the year, this distinction being attained in 1896. It rises in 25 days from a minimum of .18 cm.’ on March 30 to a max- imum of 9.39 on the 24th—an average daily increase of .37 em.*? This pulse, as elsewhere, follows immediately upon the vernal rise in temperature, which in this spring reaches 72° on the day of the maximum of the pulse and passes from 46° to 66° a week prior to it. The maximum thus lies a fortnight after the most rapid vernal rise in temperature begins. It attends a sharp decline in nitrates and free ammonia, and its maximum coin- cides (Pl. XLIII.) with that in the organic nitrogen. It also occurs in a period of apparently stable hydrographic condi- tions, the total movement in April in this year being only 1.4 ft. less than in any other year. This stability is more appar- ent than real. The decline of the March flood (Pl. X.) was checked, and slight rises resulted from spring rains which brought large quantities of silt into the stream, so that move- ment in river levels is not in this instance a sufficient index of hydrographic stability. The result was apparently the sup- pression to some extent of the vernal pulse (cf. on this point 1896 and 1898, Pl. X.and XII.). The amplitude of this vernal pulse (9.39) is less than that of 1898 (35.68)—the only other year in which our collections are frequent enough to lo- cate and delineate this pulse with sufficient accuracy. This may be due to the operation of one or more of the following factors. First, to the spring rains above referred to, at the time of the apparent maximum of the pulse, which flush it out and dilute it, and to some extent destroy the plankton. In the second place, there was no general overflow at this season, and plankton bred in the less current-swept, impounded backwaters is not entering the channel to the usual extent at this period of the year (cf. Pl. X. and XIL.). Again, the periods of standstills in levels and those of rise check the outflow from impounding areas or turn channel water into the bottom-lands, conditions which obtained in 19 of the 30 days in April. Lastly, there is some possibility that 310 the days of maximum production were not touched in our col- lections. The meteoric character of the vernal pulse of 1898 in channel waters (Pl. XII.) is indicative of such a possibility. If a greater production than that recorded did occur, it prob- ably fell between the 17th and 24th—a period of non-interfer- ence by flood and of rising production. The location of the apparent maximum in this year is sig- nificant. This was an early spring, the average of the surface temperatures in April in 1896 (see p. 171) being from 4° to® 11° higher than that in any other April represented in our records. The temperature of 70° degrees is attained almost a full month earlier in 1896 than in 1898 (ef. Pl. X.and XI.). The maximum production was recorded in 1898 on May 8; in 1896, on April 24, nine days earlier, and it may have antedated even this. Karly spring thus affects the life in water much as it does that upon land. Vegetation bursts into leaf and insects mul- tiply in field and forest in proportion to vernal rise in tempera- ture; so in lakes and streams, in like response, thealge multiply with meteoric rapidity, and the animal planktonts dependent on them follow in their wake. In 1896 the early vernal rise in temperature deflects the maximum of the vernal pulse to an earlier date by virtue of this response on the part of aquatic life to the environing factor. The average production in April in 1896 (5.67) exceeds that in any other year of our records, in large part, it seems, because of the early spring and the deflection into that month of the maximum production, which in other years passed un- detected or fell in the following month in consequence of la- ter vernal rise in temperature, as in 1598. The May pulse has a duration of 31 days,—from the Ist to June 1,—with a maximum amplitude of 3.56 em.’ on the 13th. Its mean falls on the 15th, 22 days after that of the preceding pulse. There is in this month considerable hydrographic dis- turbance—a total movement of 7.5 ft., consisting of a fall of 3.1 ft. followed by a rise of 4.4. The maximum production oc- ce urs during the decline in the earlier weeks, which is practi- 311 cally the run-off of the April rains which checked the fall of the March flood (PI. X.). This is also a period of rising tem- perature, a rise of 12° (to 82°) attending the decline of river levels and the rising plankton production. The rising plank- ton pulse is, however, flushed out by the entrance of flood waters in the closing fortnight of the month. The plankton falls at once from 3.56 em.’ on the 18th to .86 on the 18th with the first stages of the flood, and the fluctuations during the period of rise are erratic, suggestions of recovery and decline appearing in the data. These vagaries may be due to the dis- tribution of local storms, which contributed largely to this somewhat slow rise in river levels. The general effect of the flood seems to be to depress the production and thus to deflect the apex or node and the mean of the curve of production to the left, that is, toan earlier date. The flushing effect of the floods of May, 1896, is apparently greater than that in 1898, as shown by the plankton production. The flood of 1896 did not exceed bank height. Its diluent action is thus concentrated in channel waters. In 1898 the floods occur in overflow stages and are thus diffused over a large area. The chemical conditions show but little relation to plank- ton movement in this month. The maximum production fol- lows immediately upon a rise in nitrates, nitrites, and free am- monia, and coincides with a shght decline in the two first named. The decline in production during the rising flood takes place along with considerable increase in nitrates and nitrites. The average production in May, 1896 (1.80 cm.*), 1s less than that of the following years (see table on p. 292), since it does not contain the vernal maximum, and also because it 1s reduced by flood action. The June pulse is not well differentiated in the volumetric data, and its delimitation here becomes largely a matter of conjecture though it stands out more clearly in the statistic- al results (Pl. LI.). If we follow the latter the pulse termi- nates, at least so far as the chlorophyll-bearing organisms are 312 concerned, in the last week of June. If, on the other hand, we delimit the pulse here as heretofore by minimum volumes, we shall find its later limit to be July 6, giving it a total duration from June 1, of 35 days. Its greatest amplitude, 1.68 cm.’, oc- curs on the 11th, and its mean on the 14th—29 days after that of the preceding pulse. With the exception of the first three days this was a month of continuously falling river levels. The large proportion of silt in the catches and the fluctuations in the temperatures in the first ten days of the month suggest flood water of recent origin. Nevertheless, the maximum pro- duction of the pulse appears at the close of this disturbed peri- od,a slight decline with httle subsequent fluctuation in pro- duction marking the remainder of the pulse. The average production in June, 1896 (.72 em.*) is low in comparison with that of 1898 (3.96), the only other year in which the June production is sufficiently represented in our records. In both of these years there was rapid and prolonged decline from previous flood, but in 1896 the proportion of con- tributions from impounded backwaters was much less than in 1898. Greater time for breeding plankton is thus afforded as a whole in 1898, and greater production follows. The maxi- mum production coincides with the maximum of nitrates (Pl. XLITI.), though it attends a depression in nitrites and free ammonia. The general low production of this month occurs in the presence of an unusual quantity of nitrates, so that one at least of the important elements for production was not lacking. The July pulse has a duration of 19 days,—from the 6th to the 25th,—with a maximum amplitude of 2.24 cm*. on the 20th. Its mean also falls on the 20th—86 days after that of the pre- ceding pulse. This isa month of considerable hydrographic disturbance, the total movement in levels being 7.7 ft.—a_ fall from 5.2 to 2.5 followed by an interrupted rise to 7.3. The pulse hes in the middle of this period and falls under the in- fluence of both fall and rise. During the period of decline the recovery of the plankton from its minimum of .26 on July 6 318 progresses irregularly to a shght maximum of 2.24 on the 20th during a very rapid rise caused by a Spoon River flood (Pl. Il.) which, while not invading the stream above its mouth to any great extent, held back the water from the upper river. The greater part of the rise in the latter part of the month was due to the access of water below the plankton station or in re- mote headwaters, and is thus a reflection of the rise in the lower river or distant tributaries. The freedom from silt apparent in the catches bears testimony to this fact. The pulse reaches its culmination and declines in this rising flood. The average production for July in 1896 (1.44 em.*) is less than that in any other year save 1898, and that, too, in what seem to be favorable hydrographic conditions. The sharp de- cline in nitrates (Pl. XLII.) from 2.8 to .4 parts per million may be a factor in the small production. The August pulse has a duration of 27 days,—from July 25 to August 21,— with a maximum amplitude of 3.90 cm.* on July 30. Its mean falls on the 5th, 16 days after that of the preceding pulse. This was predominantly a month of falling levels. The culmination of the rise at 8.6 in the first six days is followed by a steady decline reaching 5.8 on the 31st, broken only by the shght interruption in the middle of the month. The total movement is 3.7 ft., and the total at Copperas Creek (4.60) is somewhat above the average (4.06). The disastrous effect of the local floods at the culmination of the rise which flushed out the rising plankton pulse is apparent in the de- cline from 3.90 em.’ on July 80 to .40 on Aug. 1, and in the in- troduction and continuance of a considerable volume of silt. The rapid recovery of the plankton is seen in the rise from a minimum of .26, .48, and .82 on Aug. 3-5, to 1.08, 2.40, and 2.60 on Aug. 6-8. These data suggest the intercalation of barren flood waters of recent and local origin in the course of channel waters bearing a much more abundant plankton, and the apparent result is a cleft in the otherwise somewhat sym- metrical curve of production of this August pulse. It also re- sults in an apparent shifting of the node and means of the 314 curve to the left, giving a left-handed skewness to the curve. Aside from this depression due to flood there is a general de- cline in production as levels fall, the pulse closing on the 21st with a minimum of .28 ¢m.* This decline in production is at- tended by a steady rise in nitrates, organic nitrogen, and free ammonia (Pl. XLIII.), and thus in the presence of increasing nutriment, as well as growing hydrographic stability—that is lower river levels. The two summitsof production in this pulse coincide with temperature pulses. The plankton and tempera- ture pulses are alike set off by flood waters, and the causal nexus may lie between plankton and flood rather than between plankton and temperature. The location of the flood also has the effect of lowermg the average production of the month to 1.12 cm.s—the lowest average on record, excepting only 1898 (.91), also a year of much disturbance. From this point the remaining collections of 1896 are too infrequent to delineate or even to suggest recurrent volumetric pulses. They are also insufficient to adequately trace the results of hydrographic changes. Diminished production at the time of rapid decline of temperature is apparent late in September. Increased production follows declining flood and stable tem- peratures and a downward movement of nitrates (Pl. XLII.) in October, and the phenomenon is apparently again repeated in December, though the volumes do not equal those of the preceding year. As a whole, 1896 was a year of but shght plankton produc- tion, averaging only 1.16 (average of all catches) or 1.05 (aver- age of monthly averages) cm.* perm.’ This is only a half or a third that of other years in our records (see table on p. 292). The silt, on the other hand, is more abundant than in any other year, averaging 2.55 cm. per m.* to .28, .72, 1.91, and 2.11 re- spectively for 1894, 1895, 1897, and 1898. The total movement in levels for this year at Copperas Creek is 53.16 ft., an excess of that in all other years but 1898 of 4 to over 40 per cent. (Ta- ble I.). From this fact,and from the evidence accumulated in the detailed discussion, it is apparent that the oft-recurrent 315 floods of this year are responsible in large degree not only for the increased silt but also for the reduced production of plank- ton. The floods of this year were not only more numerous, but they were also more effective as reducing factors, since they rarely reached stages of considerable overflow, So long as the flood does not exceed bank height its flushing action is concen- trated in channel waters, and impounded backwaters do not contribute so largely to channel plankton, nor are they so im- mediately connected with the channel on account of the bank development along the stream. The floods of 1896 were of such a character that they continually flushed the channel without at any time, except midwinter, forming any large body of impounded water in which the plankton had time to reach any marked development. Although there was a plankton in the backwaters—e. g. Thompson’s and Phelps lakes—which was more abundant than that in the channel (see Pl. XX XVII. and XL.), contributions from such areas to the channel plankton are relatively small owing to their shght connection with the stream in this year. As shown in Table X., the average amount of nitrates in 1896 is 2.34 parts per million; in 1897, 1.66; and in 1898, only.81. The smallest production of plankton observed in the years coy- ered by our data has thus taken place in water richest in ni- trates. Other forms of nitrogen than the nitrates vary in the same general direction with these. It seems probable that ni- trates, or available nitrogen generally if not, indeed, nutrition as a whole, are less dominant in determining plankton produc- tion in our waters than other environing factors, as, for exam- ple, in this instance, hydrographic conditions, or, more specific- ally, current in its relation to time for breeding. 1897. (Tables Til X= Pl xt, XLIV., Lil.) There were 34 collections in this year, of which 6 were madeat intervals of abouta month from Februaryto July, and the remainder at approximately weekly intervals, or less, during . 316 the remainder of the year. All of the collections were made with the plankton pump. ‘This was a year of high winter floods, a normal March rise, a belated June rise, but prolonged low water throughout late summer and autumn. The collections afford a good opportunity to observe the result of prolonged low water and a late autumn. From February to July the collections are too infrequent to enable us to trace the curve of plankton production or de- tect any cyclic movement. Of the two collections in February the first was made under the ice sheet and yielded little plank- ton or silt. The second, made while the ice was going out, contained much more silt—the result of the rising flood. Both were very poor in plankton (.03 and .05 respectively), but neither showed the least evidence of stagnation conditions such as obtained in 1895. This was due to the larger volume of wa- ter and the swifter current and greater dilution of sewage, as well as to the briefer ice blockade and the direct connection of channel waters with the vegetation-rich bottom-land lakes and forests when the ice was full of air-holes, so that the equilibrium of gases inthe water did not undergo so violent a disturbance as in 1895. In the March collection there is evidence of the increas- ing production as vernal temperatures approach. The col- lections of April and May were both made on the decline of the March flood, and both he at temperatures between 60° and 70°. This spring presented ideal conditions for a very large plankton production, namely, uninterrupted decline, with run-off of impounded backwaters in which the plankton had had abundant time to breed. Neither of our vernal collections shows any large production, though that of April hes in the period in which the vernal maximum may be expected. It is not improbable that a maximum occurred but was not detected. The June collection lies in the midst of turbulent flood waters, as the great proportion of silt (26.33 cm.* per m.*) indicates. From this point until the close of our operations in March, 1899, the weekly interval of collection was adopted, and the 317 data accordingly afford opportunity to trace the cyclic move- ment in production in this period. The July pulse has a duration of 32 days,—from June 28 to July 30.—with a maximum amplitude of 8.16 cm.’ per m.’ on the 14th. Its mean falls on the 20th. This was a month of falling river levels with slight interruptions by local rains, of rising temperature and of falling nitrates, but of increasing sewage contamination (Pl. XLIV.) as shown by the rising chlo- rine and oxygen consumed. The pulse presents a very sud- den drop in production from 6.40 ¢m.* on the 16th to .92 cm.’ on the 21st, followed by an immediate recovery to 6.91 on the 23d. I amataloss fora satisfactory explanation of this fluc- tuation. There is no change in levels at Havana (see page 160) which suggests flood, though there is a slight increase in turbidity (Table III.) and was a rise of .1 ft. at Copperas Creek on the 20th which does not appear in the Havana gage readings. The chemical analysis of the sample taken on the 21st (Table X.and Pl. XLIV.) contains evidence of some dis- turbance in conditions. There isa sharp decline in nitrates, nitrites, and oxygen consumed, with a check in the rising chlorine, while free and albuminoid ammonia and total or- ganic nitrogen move upwards. Had the oxygen consumed risen and the free ammonia fallen, all indices would point to- ward access of recent storm water carrying silt into the stream and locally diluting the plankton, though not materially af- fecting the hydrograph. In any event the fluctuation in pro- duction is correlated with a localized disturbance in chemical conditions suggesting in some particulars restricted access of recent storm waters. The average production for this month (4.69) is higher than in any other year excepting 1894 and 1895, due it seems to the somewhat stable conditions of continued decline in lev- els, with slight overflow sufficiently prolonged (3 weeks at 6 ft.) to afford time for breeding plankton in the waters of overflow, though apparently similar floods in 1896 resulted in much light- er production (Pl. X.). The main difference in hydrographic 318 conditions between the summer floods of 1896 and those of 1897 les in the fact that in the latter year a great spring flood preceded the summer floods. This, it seems, might occasion the difference in summer production apparent on comparison of these two years. The slowly receding spring overflow of 1897 seeded the submerged territory with cysts, spores, and rest- ing stages of the planktonts which afford the basis for rapid production upon the next flood invasion. In 1896 the summer floods follow a period of two years in which there had been no prolonged overflow in a period of marked plankton production. The overflowed lands were thus not recently seeded, and pro- duction was longer in gaining headway in 1896 and did not at- tain the same amplitude. It is to be noted that this pulse arisesin declining nitrates and falls away as the temperature rises. The August pulse does not reveal itself plainly in the vol- umetric data, though it stands out more clearly in the statis- tical curves (Pl. LII.). Adopting these as a clue to its limits, the pulse has a duration of 25 days—from the 30th of July to Aug. 24. The volumetric data would apparently terminate it on the 17th and limit it to 18 days. Its greatest amplitude is 2.02 cm.* per m.*, attained on both the 3d and 10th. Accepting the shorter interval, the mean falls on the 10th, 21 days after that of the former pulse, while with the longer interval it is on the 14th—24 days after the preceding mean. This is a month of remarkably uniform production, the departure from the mean in no case exceeding 26 per cent. It is accompanied by stable hydrographic conditions, the total movement being 2.2 ft., most of which occurred in the first week. After a heat pulse in the first week the temperature conditions were also stable, while in the chemical conditions there is but slight change. The chlorine increases as the sewage contamination rises with decline in levels. The absence of any marked max- imum in this month is evidently due to the fact that the ani- mal plankton which forms the greater part of the volumetric pulses has not greatly fluctuated as a whole. The occasion for 319 this may be detected in the slight wave of the chlorophyll- bearing organisms (PI. LII.), which in comparison with the wave of July and September is indeed diminutive. There is, however, nothing in the chemical data to explain this suppres- sion of the pulse of the chlorophyll-bearing organisms. The average production for this month as a whole, 3.65 em.’, is large, though not so great as that of 1894 (9.67) or 1895 (4.03), both, ike 1897, with stable conditions. It 1s, however, greatly in excess of the production in 1896 (1.12) and 1898 (.91), when August floods flushed out the stream. The September pulse, on the other hand, is very well de- fined. It has a duration of 35 (28) days,—from Aug. 17 (24?) to Sept. 21,—and a maximum amplitude of 19.80 cm.* per m.* on the 14th. Its mean falls on the 9th (10th), 80 (27) days after that of the preceding pulse. As a whole, this is a month of great stability. The total movement of the hydrograph is only .4 ft.—the smallest monthly movement recorded at Ha- vana during the years of our operations, and but rarely sur- passed in many years at Copperas Creek (Table I.). Most of this movement—Sept. 3-10—was due to the flash-boards placed upon the LaGrange dam. The chemical conditions also are in the main remarkably uniform, the only aberrant movement being the constant upward tendency of the chlorine (Pl. LIT.)— an index of the increasing proportion of sewage in the stream. There is, however, no proportional increase in the various forms of nitrogen, though they all exhibit a shght upward movement. The temperature is sustained at summer heat (80°+) till the middle of the month, dropping 10° in the third week. The plankton, however, exhibits considerable fluctuation, rising to a maximum of 19.80 cm*. per m.* on the 14th, and fall- ing again to 8. on the 21st, at the rate of 2.4 cm.’ per day. This is the maximum record for this year, though, it may be, not equaling the undetected vernal maximum. It is also the lar- gest volume recorded inany year after the first week in July. Contributing causes for this exceptional development are to be found in the stable conditions and concentration of fertilizing 320 materials attending low water. This is the month of greatest production in 1897, and also the one of lowest unutilized ni- trates, the latter not exceeding 1 part per million during the month. It isin the rising chlorine (Pl. XLIV.) that we have a suggestion of the degree to which sewage has made contribu- tion to the stream. The unutilized nitrates do not of course afford a measure of its quantity. The October pulse has a duration of 42 days,—from Sept. 21 to Nov. 2,—with a maximum amplitude of 12.92 cm.* per m.* on the 5th. Its mean also falls on the 5th, 26 (25) days after that of the preceding pulse. This extended volumetric pulse is found to include within its limits two of the pulses of chlorophyll- bearing organisms (cf. Pl. LII.),one culminating Sept. 29 and the other Oct. 19. The month was one of continued hydro- graphic stability. The total movement in levels was only .d ft., due mainly to the check in evaporation resulting from decline in temperatures. The temperatures in this month average about 64.5°, which is 6° to 8° higher than the average in other years of our records. The difference between the extremes is only 17° as compared with 23° in 1896 and 27° in 1898. The autumnal decline in this year has come later and progressed less rapidly, at least till the last ten days of the month (PI. XL), than is usuallythecase. Thecurve of the October, as well as that of the September, pulse is delimited on either side by declines in temperature. The chemical conditions in this month (Pl. XLIV.) are less stable than in September. The nitrates and nitrites move in- versely with the plankton,and both chlorine and free ammonia ascend rapidly to unusual heights, suggesting the presence of sewage in which decay had not yet progressed as far as was wont during warmer weather. This is doubtless the result of the Peoria sewage pulse, which as winter approaches extends down stream toward Havana, and under the stable low-water conditions of 1897 appears in exaggerated form. In view of the stable conditions, excessive fertilization by sewage, and abnormally high temperatures, it is not surprising 321 that the production in this year exhibits a monthly average (5.95 em.*) 5 to 25 times (see table on p. 292) that found in the same month in other years. The decline at the close of this pulse to .06 cm.’ on Nov. 2 reaches the lowest pointrecorded after the midwinter-flood con- ditions of the previous February. ‘This decline is abrupt and complete, and is followed by a recovery in production of ap- parently normal proportions. The prime cause may lie in the cyclic growth and reproduction of the planktonts in which an “internal” factor may be dominant, or it may be due to the operation of one or more external factors in the environment or to the combined action of internal and external factors. What external factors can be cited to “explain” this abrupt decline in production in the midst of these apparently stable conditions? In the first place, the minimum record (.06 cm.°) was made when the autumnal decline had reached 54° (a little below the yearly average), and after a decline of 25°+ from the summer heat of 80°+. The cumulative effect of this change in temperature is suggested, and similar declines in pro- duction during or towards the close of the autumnal decline in temperature in other years may be cited in corroboration of this conjecture. The recovery in production inthis year in the face of the cumulative effect of further decline may not weaken the force of this conjecture, since it occurs at a time of change in the con- stituent organisms of the plankton. This minimum of produc- tion is, then, a period of readjustment between summer and winter conditions. Again, in the chemical conditions the pulse of the nitrites (Pl. XLIV.) and chlorine, and the steady rise in free ammonia may indicate conditions which compelled a readjustment of the fluviatile population and resulted ina temporary decline in production. It is not, however, a simple matter to find corroborative instances in the records. It may be that we have in this marked decline at the close of this pulse an instance of combination of the internal (cyclic) factor on the part of the constituent organisms and several depress- ing agencies in the environment, whose united effect is this almost complete but temporary suppression in production, 322 The November pulse has a duration of 21 days,—from Nov. 2 to 23,—with a maximum amplitude of 1.86 cm.* per m.* on the 15th. Its mean falls on the 16th, 42 days after that of the preceding pulse. The lmit between this and the December pulse is not well defined in the volumetric data, and any treat- ment from the cyclic standpoint seems arbitrary. The end of the pulse might as well be regarded as Dec. 7,1n which case its duration is 85 days and its mean falls on the 21st, 47 days after the preceding one. The conditions during this month are not so stable as during September and October. The autumn rains, though slight, cause a meyement in levels of 2.1 ft. and intro- duce considerable silt into the stream. These are insufficient to flush out the river or to materially reduce the sewage con- tamination. There is some decline in chlorine (Pl. XLIV.) and considerable in nitrites, but the free ammonia continues to rise rapidly, indicating much organic material in process of decay. The nitrates also show much increase. The temperature de- cline to the winter minimum is completed. The production rises, however, in these conditions from .06 to 1.86, and continues ata fair volume for this time of the year throughout the last half of the month, bringing the monthly average up to 1. cm. per m.*—an amount surpassed only by the heavy production of 1895 (3.02 cm.’ Seetable on p. 292). This is also a year of sta- ble November hydrograph. It may be noted that the maximum accompanies a pulse of nitrates and a check in the falling tem- perature , and that the decline on Dec. 7 attends a drop to the minimum beneath the forming ice. The December pulse has a duration of 21 days,—from the 7th to the 28th,—with its greatest amplitude of 1.22 cm.* per m.° on the 14th, and its mean on the 16th—380 (25) days after that of the preceding one. This is likewise a month of stable hydro- graphic conditions, the total movement in levels being only 1.1 ft. The ice-sheet covered the river during most of the month (Pl. XI), with a slight break with rising levels in the second week. This closing of the river conduced to stagnation, as is shown by the chemical conditions (Pl. XLIV.). The free am- 325 monia rose from a normal of less than 1 part per million in October to 5.6 on the 28th—the maximum record for all the analyses (Table X.). This is attended by slight increase in the oxygen consumed and the albuminoid ammonia as well as in the total organic nitrogen, all of which betoken the approach of stagnation. This is reflected in the fall of the plankton pro- duction to .03 em.’ per m.* on the 28th. The extermination of the plankton did not approach that of Feb. 23, 1895, though there was a marked decrease in the number of planktonts ex- cepting only in stagnation ciliates. ‘Temperatures during this month were at the winter minimum of approximately 32°, with only a slight increase to 36° with the rise of the second week. The plankton of this December in average production (.56 em.*) falls below that of all other years with the exception of the inadequately represented 1594. This relative falling off results, it seems, from the near approach of stagnation, due to sewage which the stable low water permitted under the ice- sheet. As a whole, 1897 was a year of heavy plankton production when measurements are stated in plankton per cubic meter (8.69 cm. if all collections are averaged ; 3.27 cm’*., mean of monthly averages). If, however, we consider the slackened current and reduced volume of the discharge of the stream, it is evident that the fota/ production may not be greatly, if at all, increased during the low-water period of high plankton content. The vernal production, judging from results in simi- lar conditions in 1898, was possibly very large. It is evident on comparison, that our isolated vernal catches do not ade- quately represent the vernal production, and, furthermore, that the vernal maximum may have exceeded that of the low- water period in plankton content. Fuller representation in this period would doubtless have raised the yearly average. The high water, rapid current, and large dischargeat this period combine to make the production in these conditions relatively very great, as compared, for example, with that of 1896, when the impounding action of the reservoir backwaters was slight, 324 current and discharge reduced, and plankton content below the normal. The effect of prolonged low water, with its attendant stability, is shown in increased plankton content, and in the increased contamination by sewage, which under the ice results ultimately in stagnation and great reduction of production. 1898. (ables si Xx -sRls ear Ves elie) As shown on page 167, this is a year of normally located spring floods of considerable amplitude followed by a disturbed summer and a considerable autumnal rise. It accordingly af- fords our best opportunity for tracing the vernal movement of production in flood conditions, and also another chance to note the effect of floods at times of reduced flow of the stream. Both vernal and autumnal changes in temperature came on gradually, and chemical conditions were free from catastrophic fluctuations. The collections of this year number 52, all at weekly intervals excepting only in January, when the regular interval is slightly varied. They are without exception pump collections. The interval between collections is so brief that the cyclic movement can be traced, as a rule, and this point of view will continue to control the discussion, though in this year the suppression of production by floods increases the ele- ment of conjecture in this method of treatment. The January pulse has a duration of 28 days,—from Dee. 28 to Jan. 25,—with a maximum amplitude of .81 em.’ per m.* on the 21st. Its mean falls on the 22d, 37 days after that of the preceding pulse, This isa period of stagnation followed by a small flood which carried off the ice-sheet. = = vee wee eee ee an eg A er en I OLLIE A A LL A A be” c Ie < 32 - . ~ te ae ’ ~ * - hs Stl SC ol. sedate + = oe Sty P >. fret i 4s Ow = “ <= > = ¢ e C i at e: ieee > 2s "i a I S : | a = 66 &f 4D ~ —~wAaD ~ & & i & > - ; é - Fi - naa > are le mi ia le

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Rie aE” Coe re? ed Re se ana . a o- cay et we A ie sag § ee ng Md aD ie View Lf *: ." . : . a) aa ; : - : wat wor yueyd | aseiay | sayoiws ON | = mao : oo0oo0oono ° 9OmMOoON Oo st+oamHoo : Ronmsd : uo}yurd | aseloay | sayoivo ‘on >MORN : *OWOOm . uo} yue|d aSviday sayo}eo ‘ON uo}yued asrisay 11.46 | 44 48 4.22 1.70 |1I5 465| 35 2.19 |235 2.71 Sayoieo ‘ON rey O on ‘ ~ pope Heme | LaSaen she! 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DOORS Pegs + l< |< | < | | < |< <|as = 42,12 = Aynt | jsnsny Jaquiajdag | 19q0190 | JoquwisAoNn | Jlaquis.0q om a wm | Saude ON oonoon| | ooxnnoNn Oonm ena | | oot+HANO ootnao| mownao | vo eh 8 ox is | : : : | ~ Refs} o| nioan le 2 aa oe 3: 381s amor > eels (8 SN8 1S = nN | SAF ea) — FOTO N QSPIDA Cae is Be . Oe ine ge Sei 4 Oe ety ee ces a TS) a ee a er Pel Eo Pc ge be . finon ile S Vv | 4 + 7a i$ | an QHor 4 | LO stun = ago:|w Ra A Gi fa A j| seysqwo on | OOH OH OonnaA oonnan| | oxmnno| | onmnmo Hate ao s 6 I me mm F | : : tuo: aagaaan: S\\2 5! uo}yue]d ways ONO | ee Bas FF DASRa IS (2Sms 1S S=SAi/Al SSsas: 3 | 27 & al SAPIOAG ih ea liaie lh ess Pet rope ied ee > 20000 0 | "Q.0 ON + aonw |g SoS S fe : Shs ee S ae sayoje2 "ON | OO 000 oonNOO ooo | oomHO0O oOnH00 oomHOO =] one > > . s 5 || 4 ; ; Fi 2 ea ° elias) wormed | 228 ee) eS ee ee: :)a| iige i eee ZAw aBelIAy . : ne =e . . Cp ee eo eile is . ee a whe . . = a a te <= . 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SS SS ES EE eee ~ = ee ON «pce ~ ou ele awl Pe Re aey 1). oe eNO _ m tO N oo -|eo a ee SR Da Ss | aBviaAYy :0 :60|0| cso0o00|o ee : sll Sez SW cael Ma AC NSE : = ; :| 4 DB LOO LONON | | ON ON OOD, | < > a c | Auenue{ Arenaqe 7 your | judy | AeW | aunf tions Av. of monthly averages 343 (Table IV.), with a maximum of .032 on August 25. The . amounts reported are all very small, and the significance of their differences is questionable. The following correlations with environmental conditions may be noted. There is little plankton (.004) in the turbid (8 em.) flood water of August 18 ; there is more (.032) in the clearer water (380 cm.) of August 25. The production following the rapid decline of temperature in September falls to a minimum (.002) as it does in the channel waters (.53 and .23), and like the latter rises again (.008) late in October, after a month of somewhat stable temperatures (Pl. XXII.). The December production (.002 and .001), how- ever, Shows no rise corresponding to that in the main stream. The average production in Spoon River for the five months in 1896 in which collections were made there is only .007 cm. per m.*, while that in the main stream is 97 times as great, the production there exceeding that in the tributary from 4-fold to 380-fold in each month (see table between pp. 342 and 343). Spoon River water is thus throughout this season a diluent of the channel plankton. The chemical conditions during this period reveal unutil- ized nitrates averaging 1.2 parts per million in Spoon River to 1.15 in the Illinois. Other forms of nitrogen are somewhat more abundant in the main stream. There is, however, plenty of food for the plankton in the tributary, and other causes than poverty of nutrition must be cited to explain its paucity of plankton. 1897. (Tables. 1V., X15; Pl XXVIIL, XLVI) There are 13 collections in this year, at intervals of two to six weeks. They average 1.257 cm.’ per m.’, and have a maximum of 7.296 on September 11. The conditions attending the unusual plankton production in Illinois River channel waters in this year affect Spoon River also in much the same manner. The vernal overflow mingled impounded backwaters 344 to some extent with the channel water of Spoon River, and the prolonged drouth of the autumn cut down the run-off and re- duced the stream to a series of slack-water pools, in which, owing to the reduction in current, there was time enough for an abundant plankton to develop. The explanation of the contrast between the plankton con- tent of this stream on February 38 (.002) and 26 (.092) is to be found in the hydrographic conditions. The tributary shares the rise in production seen in channel waters (.03 to .05). The rising flood of the 26th forces the impounded backwaters away from the channel, and in their downward movement some of them get into Spoon River channel in the overflowed bottom- lands above the point at which our collection was made. Thompson’s Lake waters contained considerable plankton (.39) at this season, and it seems probable that some of its richer waters may have entered and (PI. II.) enriched Spoon River channel plankton at this stage of river. Under such circum- stances we find the tributary with a richer plankton (.092) than the storm-filled channel (.05)—an exceptional occurrence in the history of the two streams. The very slight production (.007) on March 22 is due to the fact that Spoon River itself at this time was rising rapidly, turbid (2 ¢m.) with silt, and invading rather than receiving contributions from the impounded back- waters through which it rushed to the channel. The collection of April 27 was also in flood waters (turbidity 5 em., silt 4.75 em.*), which are in part responsible for the check in the flood decline at that time (Pl. XXIII.). This held back contribu- tions from connecting and impounded backwaters, and the plankton content is low (.048), while that in the main stream (5.11) shows no such flood reduction. In the collection of May 25 (.44) we find the tributary waters as well as the main channel exhibiting a vernal rise in production, though its amplitude is 13-fold greater in the latter. The lower river level (8 ft.) then prevalent precludes the possibility of any considerable contri- butions from impounding areas, though accessions in small vol- ume are not improbable, On June 28 the silt-laden storm-water 345 in the Illinois River channel (turbidity, 2 em., silt, 26.33 em.*) contains but .27 cm.’ per m.* of plankton, but the vernal pro- duction in the tributary does not suffer so marked a decline, remaining at .25 em.’, so that its diluent action on this occasion was shght. As in the main stream, so also in the tributary there is a dropin production in August (.056) toabouta fourth that in June-July. From this time throughout the remainder of the year the production in Spoon River is considerable, exceeding that in the main stream, however, only in the last two months of the year. The production rises on Aug. 26 to 1.248 and on Sept. 11 to the unprecedented record of 7.296 em.*, while that in the main stream is only 2.77 on Aug. 24, and on Sept. 7 and 14 is 8.47 and 19.80 respectively, On the 2lstand 29th of September production in the Illinois falls again to 3.00 and 4.04 cm- re- spectively, while in Spoon River on the 80th it is only 2.96, production in the tributary thus remaining below that in the channel throughout this period. The low chlorine in Spoon River at this time (3 to 4 parts per million. See Table XI.) as compared with the main stream (21-50 parts) indicates that the Spoon River water is not contaminated by channel water, and that we are dealing with an indigenous plankton. None of our collections falls in the period in October (PI. XLVI.) in which chlorine in Spoon River rises temporarily. The three collections of November-December, 1.351, 1.99, and O99 cm.”, are respectively 22.5, 1.6, and 20 times as great as the production in the main stream at the same time. The month- ly averages for this period are 1. and .56 for the Illinois, and 1.671 and .599 cm.’ for Spoon River, so that the excess in the latter is apparently not more than 50 per cent. Under these conditions the tributary stream enriches the plankton of the channel instead of diluting it, but its discharge is slight. Hydrographic, thermal, and ice conditions are similar in the two streams, and we find the main difference in the chem- ical conditions. Aside from evidences of sewage contamina- tion in the last weeks of October, the Spoon River records 346 (Pl. XLVI, Table XI.) show somewhat uniform conditions in strong contrast with the instability in these particulars in the Illinois. With greater stability Spoon River apparently pro- duces a more abundant plankton in this low-water autumn. The exceptional production in this autumn stands in strong contrast with the poverty of this tributary in the same months in 1896 and 1898. As seen in the table between pp. 342 and 348, the maximum monthly production in the low water of 1897, as recorded in monthly averages, is from 285 to to 5,130 times greater than that in any month in this season in the other two years. A comparison of the data in Table XI. for the three years in question and of their plottings on Plates XLVI. and XLVII. will show the great similarity in the chem- ical conditions which accompanies this remarkable inequality in production. The accompanying table summarizes the data concerning nitrogenous contents of the water and the plank- ton. NITROGENOUS SUBSTANCES AND PLANKTON, 1896-1898. MONTHLY AVERA GES—PARTS PER MILLION. November December Y <= S oo ~ — a) tes | oo i S = oe o§|m2| & | § ao (28) Se \oSelb Seana See ees = ‘ a Ee ee ares = a So OR Ne hee Ae Oe ee 1866) si eeaeotee .005 | .84 FOrg ime) sore .OI 52 11 eOosm|akes .002 LOO7 eoaicctone sie ore 052 | .76 | .008 -§6|1.671 | 622] £687) 005) || 63 | .599 FOOS stains Soe 02 597 2h 3069 5o|-OO1 | ).084|. <85>| 2015) | 3354) 008 Other factors than these chemical conditions are thus re- sponsible for the great differences in production in these three years. Low water, slight or imperceptible current, and conse- quent time for breeding in the latter part of 1897 are the most probable factors in causing the high production of that sea- son, while in other years the recent origin of the tributary wa- ter, from rains or springs, precludes any considerable produc- tion in water otherwise capable of supporting an abundant plankton, as is shown by the production in 1897. As a whole, Spoon River plankton in 1897 reflects the same 347 relation to environmental factors that was found in the case of the Illinois. This is seen in the increased winter produc- tion, in the vernal rise, in the decline after the vernal pulse, and in the unusual autumnal development. The tributary stream, with but four exceptions, was acting as a diluent of channel plankton at each examination of its plankton content. These four exceptions—on Feb. 26, Nov. 2 and 30, and Dec. 28— are due in the first instance to channel flood, and in the last three cases to exceptionally low water in the tributary and less stable chemical conditionsin the channel. In the four years in which Spoon River was examined they are the only exceptions to the general rule that these tributary waters are dilu- ents of the channel plankton. The average production for 1897 (1.257 cm.’) is 180 times that recorded in the last half of 1896, and 438 times that for 1898—as a result of the low-water con- ditions discussed above. 1898-1899. (Tables IV., XI. ; Pl. XXIV., XLVIL) There are 14 collections at intervals of four or five weeks in the 15 months included in this period, and they fairly rep- resent the contributions of this tributary ina year of consider- able flood and repeated access of storm water. In 1598 there is but a trace of plankton in the January (.017) and February (.016) collections, while that in the March collection (.124) isthe maximum for the year. At this time the spring flood is nearly at its height (16.5 ft.), and the watersofSpoon River are in quite free connection with the general overflow that spreads over the surrounding bottom-lands. On the day of the Spoon River collection there was .43 em.’ of plankton in the [hnois and .79 the week prior in Thompson’s Lake, three miles above Spoon River (Pl. II.). There is thus three and a half times as much plankton in the main stream and six times as much in Thomp- son’s Lake. With its maximum burden of plankton, the trib- utary is still a diluent, and its plankton content at this time is probably in large part derived from the run-off of the contigu- 348 ous impounding backwaters. No Spoon River collection falls in the week of the vernal maximum (see Pl. XII.), but the col- lections of May (.023), June (.096), and July (.036), all exhibit a considerable rise above the usual level of production, and all, moreover, were made during the run-off of the spring flood and receive slight contributions from impounded waters. It is in the direction of the movement in production that the tributary and mainstream are alikeatthisseason. In the amplitude of the curve of production the difference is very great, production be- ing respectively 491-, 41-, and 16-fold greater in the latter in the three months named. Throughout the remainder of the year 1898 plankton pro- duction inSpoon River is at a minimum, there being but the merest trace of hving organisms in the catch. None of these catches was taken in rising flood water (Pl. XXIV.), though they all show the results of the flushing action of the frequent floods which wash out with rapid current whatever plankton may have developed in the tributary, and at the same time af- ford little opportunity for its replenishment. The relative ab- sence of backwater feeders in the tributary stream at this stage of river levels serves also to emphasize the poverty in production of the tributary. The average for 1898 (.029 cm.* per m.°) is exceeded over 73-fold by the yearly average of the Illinois (2.13). The tribu- tary waters are at all times—at least in so far as the data go— diluents of the channel plankton, reaching their lowest ratio, .124 to .58, in March, when they share most in impounded back- waters of the main stream, and at the same time are at the max- imum of their own reservoir action. This meager production occurs in waters almost as rich in nitrates (av., .67 parts per million) as the main stream (.809), and, save on rising floods (Pl. XLVII.), in normal chemical con- ditions. The potent environmental factor is rather to be found in the recent origin of the tributary waters than in any availa- ble chemical data. In the three months’ collections of 1899 we find that the low 349 level of production continues under the ice, which remains on the stream for about three months (Pl. XXIV.). There is con- siderable fluctuation (Pl. XLVII.) in the organic nitrogen, free ammonia, and oxygen consumed, most if not all of which are traceable to the access of storm waters rather than to any con- siderable degree of stagnation. The catches are all full of silt, though the turbidity of the stream is not great under the ice in January and February. The silt at such times is mainly com- minuted vegetation brought in by the storm waters. There is a slight rise in the plankton production in March (.026), when the river stands at 12.9 ft. and the plankton-rich waters of Thompson’s Lake (see Table V.) are brought into connection slightly with Spoon River by overflow. During these three months the production in the tributary is but a small fraction—never more than a tenth—of that in the main stream. It continues to be a diluent of the channel plankton. SUMMARY. The average plankton in all of the Spoon River collections is .465 cm.? per m.? of water. In the Illinoisit is 2.19, or over 4.7 times as much. If we omit the low-water period, Aug. 26 to the end of 1897, and compare only the remaining collections between Aug. 18, 1896, and the close of operations, the ratio of production in the two streams becomes .044 to 2.19, or 1 to 50. As has been repeatedly pointed out in the preceding discussion, this contrast in production is not explainable on any difference in available chemical data. The tributary waters are fertile enough to yield a large production. The explanation is rather to be sought in the hydrographic conditions, in the recent ori- gin, from rains or springs, of the tributary water, and in the more rapid current, and consequently the less time for breeding a plankton in the tributary environment. That this is the proba- ble explanation is borne out by the large production in the only period of prolonged low water in the tributary in the fall of 1897, when time for the growth of the plankton was afforded in the slack waters of the tributary. 350 The immediate effect of the access of the tributary waters of the stream is as a whole diluent upon the plankton content of the Illinois. A mixture of equal volumes of each would re- sult in a reduction in the [lhnois to 1.33 em.’ per m.* from 2.19 —a falling off of 39 per cent., or even of 49 per cent. if we omit the low-water period of 1897. If we consider the areas of the drainage basins as an index of the relative volumes of water carried by the two streams, and determine the effect of Spoon River contributions, we find the net result, based on the aver- ages of our collections, to be a decline in plankton content in the linois from 2.19 em.’ per m.’ to 2.00—a decline of 9 per cent. If the low-water period of 1897 is omitted, the decline is even greater, namely, from 2.19 to 1.96—a fall of 11 per cent. in the plankton content as an immediate result of the contri- butions of this tributary. Spoon River thus exerts in the econ- omy of the [lhnois an immediate diluent function upon its pro- duction, which, qualitatively, is approximately 10 per cent. STATION C, QUIVER LAKE. (Tables V., X11. ; PLAIL, IV., XV=XVIL, KXV-AKXIX, XLVIG SEES) ENVIRONMENTAL CONDITIONS. This lake les on the right bank of the Illinois (PI. II.), ex- tending parallel to the river for a distance of three miles, in- cluding Quiver Chute. This is the lower end of the lake, which is separated from the Illinois River only by a low mud bank submerged at levels of 4 ft. and crossed just below our plankton station in the main stream by two “cut-offs” which bring a va- rying volume of river water into the chute, the amount de- pending upon the relative levels on the two sides of the spit. The close connection of the lake and river makes the former responsive to all changes in level in the latter at all stages of water. This lower spit extends northward as a low bank 5 to 40 rods in width and generally less than 6 to 8 feet above low- water mark, lying between the lake and river. This is covered with low willows and, to the northward, with heavy forest (PI. 301. IV., XV., XVI.). The northern end of the lake is Y-shaped, and the western arm is known locally as Dogfish Lake. The lake from Quiver Creek to its mouth near Spoon River is about 3 miles long, and does not exceed a quarter of a mile in width at any point. The lake proper, that is, above the chutes and excluding the western arm, contains at low water about 230 acres (93 hectares), but approaches 500 acres if these contiguous bodies of water be included. As levels rise, its area increases rapidly, and at 6 to 8 ft. the demarcation between river and lake is obliterated, and extensive areas to the north- ward (Pl. II.) come into connection with it, while at higher levels it quite loses its identity as a separate area (PI. III.) ex- cept as the tree tops and its clearer waters serve to differentiate it from contiguous channel waters. Its depth at low water (river levels about 2 ft. above low water of 1873) is throughout most of its area less than 2 ft., and in the deepest parts, at the narrows above the chutes, it does not exceed 4 ft. The bottom is of hard sand and bluish clay covered gener- ally by a soft alluvial ooze of 1 to 2 or more feet in depth. Its eastern bank is a sloping sandy bluff (Pl. XV.), which abounds in clear springs of cold water, occurring the whole length of the lake and contributing nota little to its water supply. The western bank is of black alluvium, and the ooze along its mar- gin of considerable depth. The eastern arm of the lake receives Quiver Creek, a tributary draining 220 sq. miles of sandy upland and ‘“‘second bottom.” The vegetation, described on page 244, in low-water condi- tions frequently chokes the channel, which extends from the mouth of Quiver Creek in a tortuous course through the vege- tation along the western shore of the eastern arm towards the point between this and Dogfish Lake, and thence in an equally crooked and shifting course towards the mouth. It was in this channel in low water, and in its neighbor- hood at times of high water, that our plankton station was lo- eated (Pl. II). It is simply a shifting path through the vegeta- tion, and is not generally marked by deeper waters than adja- 302 cent regions. It was only a few meters in width, and in 1894 and 1895 it was frequently necessary to clear it of encroaching vegetation in order to make feasible the 30-meter oblique haul. In high water and generally in years subsequent to 1895 it was only necessary to avoid with drawn net or pump the clumps of Ceratophyllum which still dotted the bottom in this neighbor- hood. The point of collection thus lay at all seasons towards the narrowing end of the lake and in the path of the current maintained by Quiver Creek and the marginal springs. At times of high water it was in the direct path of the downward current of impounded backwaters thrust towards the channel by the encroaching eastern bluff (PI. IT.). At times of flood the invading river waters extend for some distance, even to the middle of the lake, crowding the clearer lake waters to the eastern side. When the western bank was not submerged the backwaters entering by way of the chutes sometimes reached the plankton station. Our collections were always made in evident lake water unless otherwise stated (Table V.). The access of creek and spring water, the extensive areas of dense vegetation, and the shoal waters, which at all levels form the greater part of the area of this lake, all combine to make the temperature conditions subject to great local varia- tion, and to diversify the fauna and flora indigenous or adven- titious in the plankton of this body of water. COLLECTIONS, Our chronological series in this lake includes 115 collections, extending from June 6, 1894, to March 28, 1899. The collec- tions in the several years number 14, 18, 31, 24, 26, and 7 re- spectively. Their distribution by months is shown in the table between pages 342 and 348. In the earlier years the interval of collection was somewhat irregular, though with 6 exceptions every month is represented. From July, 1897, collections were made at least every fortnight and on the same day as at the other stations. The oblique-haul method was used—with a few 399 exceptions of repeated vertical hauls (Table V.) in the winter flood of 1895-96—from the beginning till May 22, 1896. After this date all collections were made with the pump. This lake is a type of some other bottom-land waters, spring- fed and rich in vegetation, and our collections suffice to show the relation which these bear to production in the adjacent channel waters. They alsoserve for comparison of production with that in other backwaters less rich in vegetation, and since the quantity of vegetation in Quiver Lake varied from year to year they also throw some light on the effect of vegetation up- on plankton production in a single area. PLANKTON PRODUCTION. 1894. (Table V., Pl. XXV.) The 14 collections in this year average 1.08 cm.’ per m.’* to 2.49 cm.? in the Illinois. The maximum (3.50) falls on Septem- ber 6. There isa striking resemblance in the planktograph of Quiver Lake for this year (Pl. XXV.) and that of the adjacent channel (Pl. VIII). The amplitude is generally less in the form- er, but the direction of movement is the samein both. The June production (monthly average) is low in both Quiver Lake (.28) andthe [llinois (.74); it rises in July (2.20 and 5.12); and it declines in September (2.12 and 1.36) toa minimum of .80 and 84, from which it recovers slightly in October (.95 and .61) to fall again in November (.02 and .10) and December (.03 and 10). The only exception to this parallelism in the movement in production is seen in August, when in Quiver Lake produc- tion drops to .74 but attains a seasonal maximum of 9.67 in the river. Aside from the fact that this is the season of greatest predominance of vegetation in the lake, owing both to growth and to low river levels, there seems to be nothing in the en- vironmental conditions to be correlated with this contrast. While as a whole for this year the contributions of Quiver Lake (1.08 cm.’ per m.*), as shown by our data, only result in 304 an immediate dilution of the channel plankton of the Illinois, there is a season when its plankton content exceeds that of the river. The average of the collections in September-Novem- ber in Quiver Lake exceed by 70 per cent. the average of those in the Illinois. This is the season when some autumnal decay of vegetation takes place, and this vegetation-rich lake has a larger plankton production than the river waters which it thus enriches. 1895. (Table Vo3 Pl. SCV I Xie) There are 13 collections in this year, with an average of .78 cm.” per m.* as compared with 3.22 in the Illinois. The maxi- mum of 4.57 occurs on April 29, being but 1.26, or 22 per cent. less than the corresponding vernal maximum in the adjacent, but—owing to river levels in this season—non-contiguous, river. The similarity in the movement of production between this lake and the river noted in the previous year can be traced in 1895 in but two instances,—in the rise to the vernal maximum and in the increased production in December (cf. Pl. XX VI. and IX.). Outside of these periods there is no resemblance between the planktographs of the two waters. From July to November inclusive the low level of production is broken only by two pulses, both of which attend a rise in river levels with increase in the impounding function of the lake. These changes in level shift the loosely attached vegetation, and are often followed by death and decay of masses of aquatic growths. The slight rise in the last week in August (Pl. X XVI.) caused an invasion of muddy river water into the lower end of the lake. Decay of the vegetation and death of many fish, clams, and other ani- mals ensued in the invaded area. The flood early in Septem- ber (Pl. XX VI.) came largely from up-river rainfall, and the lake waters, enriched by invasion, were impounded with result- ing increase in the plankton. It was not apparent that either of the large collections were made in invading waters, and I infer that the plankton was indigenous and not adventitious, 309 though the invasion resulted in the enrichment of the lake by the decay of vegetation and dead animals. It may also have “seeded” the lake with organisms whose subsequent multipli- cation caused these temporary increases in production. These same floods are attended by depressions in production in the main stream, so that these two pulses in Quiver Lake lie in these depressions, intercalated between summits of the curve of production in channel water (cf. Pl. [X.and XXVI.). The inference is suggested that the run-off of this plankton-breeding impounded water of Quiver Lake and similar reservoirs else- where may have contributed to the increased production in channel waters following the flood. The plankton content of Quiver Lake water on July 26 (.71) and Sept. 6 (1.57) thus exceeds that in the river on July 28 and Sept, 6 (.68 and .99), and its contributions to the stream, if any were made, serve to enrich the channel plankton. In three other cases the lake production exceeds that of the river; on Feb. 23 (lake, .03, river, .01), April 9 (1.42 and .52), and Dec. 28 (.29 and .01). In the first instance there was stagnation under the long continued ice-sheet in both river and lake, as wasshown by the great mortality of fish in the latter. The plankton, how- ever, did not reach the degree of extermination in lake water that it did in the channel, since there was less sewage, more veg- etation, and access of spring water. In the April instance the silt burden of the channel waters (4.67 em.*, Pl. LX.) is much greater than that in the lake (1.43), and suggests the intercalation of storm water in the former, resulting in the slight rise in levels (Pl. 1X.) and the lessened plankton content of the channel waters as compared with those of the less dis- turbed lake. The great contrast on December 28 is also due to the flushing action of the great winter flood which depleted the channel plankton but increased the impounding function, and therefore breeding capacity and productivity, of the lake. Each of the three instances of greater production in lake than in river waters occurs with rising river levels, when the rising river checks the relative outflow from the lake or otherwise 3906 increases itsimpounding function. Whatever run-off from lake to channel occurs under such conditions will result in a shght enrichment of the plankton content of the channel waters with which the tributary mingles. At all other seasons of this year our collections indicate that the immediate result of the aecess of Quiver Lake waters to the river is a reduction in plankton content of the main stream, on an average for the year for equal volumes of tributary and channel waters, of 38 per cent.; or if the relative volumes of each based on areas of drainage basins are considered, the plankton content of the channel is reduced to 3.19 cm.* per m.’—a decline of about 1 per cent. This was a year of maximum development of vegetation in Quiver Lake. The low water of this and the preceding year and the absence of floods adequate to flush the lake of its loosely attached vegetation permitted an unusual and enor- mous growth of Ceratophyllum and other aquatic plants, which | choked the lake from shore to shore and from Quiver Creek far down the chute towards its mouth (Pl. XV.). The very slight plankton production in its waters during the summer is due, I believe, to this predominance of vegetation. The rise in pro- duction when river levels rose in July and September (PI. XXVI.) attends, among other factors favorable to production already discussed, a reduction in the relative abundance of vegetation. 1896. (Table V., Pl. XXVIL.) There are 31 collections in this year, with an average of 9.59 cm.* per m.’ as compared with 1.16 in the Illinois. The maximum of 16.76 em.2 oecurs on April 24, exceeding by 7.37 cm.', or 78 per cent., the production in the adjacent river on that day. The similarity in the movement of plankton production in Quiver Lake and the Illinois noted as generally present in 1894 and but slightly so in 1895 is quite apparent throughout this 307 year, as will be seen on a comparison of Plates X. and X XVII. With a few exceptions which will be noted in the subsequent discussion, the trend of the production is similar in the two bodies of water to a most striking degree month by month throughout the year. With rising temperatures in February-March, production in the lake attains the unusual level of 1.75-1.85 cm.’ per m.', an amount not equaled at this season in this lake in any other year, and exceeding by 88- and 26-fold the production in the adjacent flood-swept stream (see table between pp. 342 and 343). This greater production in the lake is due, it seems, to the fact that Quiver Lake collections in these months represent the im- pounded backwaters of the eastern bottom-lands forced through the lake by the configuration of the eastern bluff (PI. II.). Sight current and time for breeding permit in them a production not possible in the silt-laden rapidly flowing channel waters with which at our plankton station (PI. Il.) they are contiguous during prevalent levels. The larger production in this year may be attributed to the enrichment of the water by the great mass of organic debris accumulated on the now submerged bot- tom-lands during the two preceding years of low water. The vernal pulses in the two waters coincide in the posi- tion of their limits and maxima though not in amplitude at any time, as will be seen on comparing Tables III. and V. and Plates X. and XXVII. The vernal development in the lake pro- ceeds more rapidly, appears earlier, and attains a greater am- plitude than it does in the river. Thus, on April 10 and 17 there is present in Quiver Lake 3.29 and 16.32 cm.* of plankton per m.* to 1.68 and 4.45 in the river. The rate of increase is 4.7 times as rapid in the lake, and attains on the 17th a volume 3.7 times as great as thatinthe river. The maximum (16.76) is almost twice that in the river (9.39). The large development (16.52) on the 17th indicates that the true maximum probably occurred a few days earlier in the lake than in the river. A partial ex- planation of this phenomenon, and also of the earlier and more rapid rise in production, may be found in the somewhat higher 358 temperatures in the shoaler and clearer impounded waters which are drained off through Quiver Lake. The temperatures of surface waters in the lake from February up to the time of the maximum are from 1° to 15° higher than in the river, as will be seen on comparison of the thermographs on Plates X. and XX VII. The May pulse in Quiver Lake attains 8.14 cm.*,—more than twice the amplitude of that in the river, 3.56,—while the aver- age production for the month in the lake (2.99) exhibits a sim- ilar ratio to that of the river (1.30). The very sudden decline from 8.14 on the 8th to .51 on the 16th attends a decline of about 2 ft. in river levels at a stage which cuts off the lake from large impounding areas to the north, and also, at this season of the year, brings the submerged flora to the surface. These two factors combine in effecting this sudden drop in production in the lake before it appears in the stream (cf. Pl. X. and XXVIL.). The flood which wipes out the rising June pulse in the river (Pl. X.) increases the impounding area and relative occupation of the lake water by vegetation and permits a pulse of some amplitude (2.60) to develop in the lake, while only a belated and slight development appears in the contiguous river. As levels fall in July and impounding areas are again cut off and vegetation anew occupies a relatively larger proportion of the lake, production declines to so slight an amplitude that a July pulse can hardly be traced (Pl. XXVII.), and the average monthly production in the lake falls to a fifth of that in the stream, whose plankton content it had in previous months of the year exceeded. With the riseof the August flood, production again assumes a pulse-like character, lagging throughout its development a few days behind that in the adjacent stream (ef. Pl. X. and XXVII.), and lacking in the lake the cleft in the apex of the curve caused in the river production by the flushing action of local floods. The seven collections during the remainder of the year ex- hibit a similar direction of movement in production in every 309 instance but two, Oct. 14 and 29. In the first of these, silt-laden flood waters in the river, but not in the lake, interrupt the par- allelism. In the second instance the production of the lake de- clines and that of the river rises—again as a result of the prior flood conditions, as will appear on a comparison of the sequele of the June and August floods in the two bodies of water. In these, as also in the October flood, there are indications that the rising plankton pulse common to both is temporarily suppressed in the river and continues undisturbed and reaches an earlier culmination in the lake, but only a delayed one of slight ampl- tude in the stream. The average production in the lake in the last four months of the year exceeds that in the river by 52 per cent. and in five of the seven collections. The comparison of production in Quiver Lake and the [lli- nois River in 1896 is very instructive in several important par- ticulars. In the first place, both the relative and absolute pro- ductivity of the lake has increased, rising from 1.08 and .78 em.* in 1894 and 1895 to 2.59, an increase of two- to three-fold. The ratio of productivity in the lake to that in the river in 1894 was 1 to 2.3; in 1895, 1 to 4.1; while in 1896 it falls to 1 to .45. The low average in the river is, as has been shown, the result of the repeated flushing by storm waters. The increase in the lake is due to the higher levels and increased impounding function, and to the actual and relative decrease in its vegetation. The combined result of the operation of these factors is thatin this year the lake waters cease to be diluents of the channel plank- ton and become sources of enrichment. Considering the areas of their respective drainage basins, and basing calculations on the yearly averages, the net result of the contributions of Quiv- er Lake is a rise in the plankton content of channel waters from 1.16 em.’ per m.* to 1.18—an increase of a little less than 2 per cent. Not only was the average production in the lake (2.59) greater than that in the stream (1.16), but individual collec- tious upon coincident or approximate dates exhibit the same 360 relation in 22 out of 31 instances, and 4 of the 9 exceptions fall in the period of low water in July,during predominance of veg- etation in the lake. The monthly averages in the lake also exceed those in the stream in all months but July and Sep- tember. Higher levels, increased impounding function, and decrease in vegetation thus favor plankton production in Quiv- er Lake, and tend to raise it from a diluent toa source of imme- diate enrichment. In this connection it should be noted that the increased production of this year (2.59) still falls below that of the river in 1894 and 1897, and, as seen in the table on p. 292, below the general average of the river production (2.71); and also that the higher river levels of this year tend to lower the proportion which the tributary spring and creek waters form of the total volume of Quiver Lake. A second significant fact brought out by the comparison is rendered patent by the frequency in this year of the coilections in Quiver Lake. The weekly interval from April to Septem- ber (Table V.) makes it possible to trace somewhat fully the movement of production, and demonstrates in Quiver Lake a pulse-like movement in production similar to that previously de- scribed in the Illinois River, and one, moreover, which exhibits a very striking coincidence of developmental succession. A superpo- sition of Plate XXVII. upon Plate X. will make this demon- stration apparent. There are exceptions, but these, as shown in the preceding discussion, are in most, if not all, instances to be correlated with local environmental factors confined to one or the other body of water. The return to parallelism with the cessation of the peculiar factor incident to the interruption serves still further to emphasize the significance of this simi- larity. The key to the parallelism must he in fundamental factors common to the plankton of both areas or to their envi- ronment. 361 1897. (Tables V., XIII.; Pl. XXVIII, XLVIII.) There are 24 collections in this year, with an average of 0.88 cm.* per m.® as compared with 3.69 in the river, and a max- tmum of 13.38 on April 27—more than twofold the production in the river (5.11) on that day. The collections of the first six months of this year are so infrequent that the course of production is but slightly indicat- ed. In February the production in the impounded waters of the winter flood in Quiver Lake (.19) is nearly fivefold that in the current-swept channel (.04), while in March there is little differ- ence (.34 and .38) in their plankton content. The collection of April 27 probably falls near the presumably common vernal max- imum and in the midst of the decline of the spring flood. Since Quiver Lake at the stage of river (11.6 ft.) then prevalent contains the run-off of the impounded backwaters to the north, it is not surprising that its plankton content (13.38) 1s more than double that of the river (5.11). The similarity in the movement of production thus far seen in this year is interrupted on May 25 by the decline in the lake to 1.29, while the river rises to 5.62. The decline in the lake may be attributed to the great reduction in impounding area due to the decline in levels to 8 ft., and to the gain in proportion in the lake of the contri- butions of creek and spring water and of the area occupied by the now rapidly appearing vegetation. The silt-bearing flood of June in the river yields less (.27) than the lake waters (1.26) impounded by the rise of the river. In the last six months of the year the collections are of sufficient frequency to enable us to trace somewhat the move- ment in production. This period is marked by a great depres- sion in plankton content as compared with that of the same season in the previous year, the average for each being 1.06 and .23. The parallelism in the movement of production can still be traced inthe slight tendency in Quiver Lake to increased production in July, September, and November at times of pulses 362 in the channel plankton. The amplitude attained in the lake is, however, but slight. The explanation of this marked decrease in production in this year as compared with that of 1896 lies, I believe, in the hydrographic conditions of the two years. In 1896 (Pl. XX VIL.) the average height of the river for the period August-Decem- ber is 5.89 ft., while in 1897 it is only 2.47 ft. The impounding action of the lake was at its minimum, and there was present in it in these months of 1897 only abouta third the quantity of water that it contained in the corresponding season of 1896, and this consequently gave to vegetation in 1897 a relatively greater predominance in the lake, and also made possible a more frequent renewal of lake water by the contributions from the creek and tributary springs, thus cutting down the time for breeding. Both of these factors tend to limit plankton produc- tion. We find, accordingly, that the lake produces on an av- erage from August to December but .1 cm.’ per m.* to 4.0 in the adjacent river, that is, only a fortieth of the plankton content of the stream. The contrast between the lake and the river in this year is heightened by the fact that owing to low water and increased fertilization by sewage the production in the river is much greater than usual. A comparison of Plates XI. and XXVIII. will reveal the fact that in only 5 instances out of 24 in 1897 does Quiver Lake contain more plankton than the river. Theseinstances in Feb- ruary and April attend impounding action of the lake when it is not differentiated from overflowed bottom-lands as a separ- ate unit of environment, while those of June 28 and July 21 are caused by the flushing of channel waters by floods from which the lake is exempt. As a whole for this year, the net result of the contributions from Quiver Lake is a dilution of the channel plankton with which it mingles. Basing calculations upon the yearly aver- ages and areas of the drainage basins, the quantitative effect would be a decline in the plankton content of channel waters from 3.69 to 3.65, or a loss of 1.1 per cent. 363 The lake waters in October-December contain (Table XIIL., Pl. XLVIII.) but a fraction—from a third to a tenth—of the nitrogenous matter that is found in the channel. This is an index of the relative poverty of Quiver Lake waters when isolated as a separate unit of environment and dependent upon creek and spring waters, mainly of seepage origin, for its supply. This relative poverty, combined with the factors be- fore discussed, lies at the basis of the relatively small plankton production in this body of water in this year. 1898. (Tables) Vi, 201l, Pl Xe ELS) There are 26 collections in this year at fortnightly inter- vals, with an average of 2.44 cm.? as compared with 2.13 in the river, and a maximum of 42.14 on May 8 coincidently with the vernal maximum in the channel (PI. XII.), which, however, falls 6.46 em.*, or 15 per cent., short of that in the lake. The parallelism in the movement of production noted to a varying extent in prior years may be traced also in 1898. The most striking coincidence is the agreement in the location and relative development of the vernal pulse, and further resem- blance may be seen in the June pulse and the December rise in production. The small quantities of plankton in the lake at other seasons and the fortnightly interval of collection render the correspondences less obvious though perhaps not less sig- nificant. During the low water of January and in the subsequent flood (Pl. XXIX.) there is little plankton in the lake (.02) as compared with the river (.45—see table between pp. 342 and 343), though an increase with a rise in levels and development of the reservoir function of the lake might have been expected. There is, therefore, no January-February rise in the lake cor- responding to that in the river unless the increase from .003 Jan. 11 to .04 Jan. 25 be held to be significant. The February flood, which depletes the plankton of the channel, 1s accom- panied by arise to .58 on the 22d in the lake coincidently with 364 a slight but not equal rise (.10) in channel production. The March pulse in the river, with a maximum amplitude of .77 on the 22d, is attended by almost equal production in the lake (.67). The vernal pulse rises with like abruptness at both stations, increasing from April 1 to May 3 from 1.03 to 42.14 in the lake, and from 1.12 to 35.68 in the river. The decline of this pulse is much more abrupt in the lake, falling from 42.14 on the 3d to 4.7 on the 11th—a decrease of 89 per cent. in 8 days, while the decline in the stream is from 35.68 to 10.31, or 71 per cent., in 7 days. ‘The more abrupt change in the lake plankton is due to the fact that the decline in levels of 1. ft. in the interim be- tween the two collections compared, is at the critical point ap- proaching bank height, when the bottom-lands to the north of Quiver Lake are beginning to emerge and cut off and divert some of the run-off of the impounded backwaters which at higher levels make their way tothe channel through Quiver Lake (PI. I1.). There is a very sight July pulse in the lake on the 19th coincident with the July maximum in the river. Inthe early part of August there is another maximum in the river, but no parallel developement in the lake, owing possibly to the low water then attained and the resulting dominance of vegetation and tributary waters—conditions not incident to these levels in hke degree in channel waters. The rise at the close of August and again in September, and the low level and slight change in production in October found in channel waters are all to be traced coincidently, or approximately so, in the less complete records of the lake production. The silt-laden flood waters which cause rising levels in No- vember deplete the channel plankton (.25), increase the im- pounding function of the lake, and lead to greater production (.73) in the latter. There are coincident culminations in river and lake on Dec. 6, but the interval of collection in the lake does not permit Comparison in case of the river maximum of Dec. 20. The large December production (1.74), six to eleven times that of July (.16), August (.22), September (.33), or Oc- tober (.28) is noteworthy. 365 There is thus a striking similarity in production in the river and lake in 1898, not only in the larger movements, such as the vernal pulse, the low level of midsummer, and the De- cember rise, but also in the minor details which differentiate movements at shorter intervals, suggesting in some cases, and demonstrating in others, the presence of coincident recurrent pulses of production with approximately similar locations but, it may often be, with more widely differing amplitudes. A part of this similarity is doubtless due to the fact that in 1898 for fully five months of the year, when the river was at 8 ft. or above, the lake was not, superficially at least, differen- tiated from the general bottom-land environment, and there- fore shares more extensively the course of production elsewhere than it does when its emerging boundaries delimit it as a sep- arate unit of environment. The similarity is not, however, con- fined to this period of aquatic continuity, but appears also in the season of delimitation, when local factors are relatively more potent. It is also true that even in the period of conti- nuity the environmental factors peculiar to the lake continue, though submerged or invaded,—as, for example, the chemical conditions, which even in flood periods exhibit a certain auton- omy in the lake, as will be seen on comparison of Plates XLV. and XLIX.,—to exercise some differentiating influence, which, in the presence of the apparent tendency towards similarity of movement in production, still produces modifications sufficient to stamp the seasonal planktograph with a characteristic facies, thus differentiating it from other localities. The average production for the year is 2.44 em.’ per m.* as compared with 2.13 in the river, so that as a whole in this year the outflow from this lake enriches the channel plankton. On the basis of yearly averages and drainage areas the net result is an increase from 2.18 to 2.14, arise of lessthan .5 per cent. A more detailed analysis of the data reveals the fact that in 7 of the 12 months, in January, April, and June—October, the river ex- ceeds the lake in production. As will be seen on Pl. XXIX., the remaining months are those of high river levels, when the im- 366 pounding action of the lake is most operative and its localiza- tion least pronounced. The largest production, in May and June, occurs when on declining flood the flow of impounded bottom-land waters from the north is greatest through the lake. If we omit from both records the months of May and June, we find that the averages of the remaining monthly averages (see table between pp. 342 and 343) are.91 and .50 respec- tively for the river andthe lake. Thus for ten months of the year the plankton content of the latter is but five ninths of that of channel waters, and during this period the immediate result of the access of the run-off from Quiver Lake will be a dilution and diminution of the plankton content of channel waters, due, it seems, to the relatively more recent origin, from storm and seepage waters, of these tributary contributions, and to the greater prevalence of vegetation in the lake. Another factor operative in the diminished production of the lake is relative poverty in nitrogenous substances. For example, the average nitrates (cf. Tables X.and XIII.) for the year in river and lake are respectively .809 and .68; the nitrites, .121 and .029; the or- ganic nitrogen, .92 and .569; the albuminoid ammonia, .431 and .275; and the free ammonia, .95 and .138. The unutilized ni- trogenous substances in the lake are, however, of sufficient pro- portions to indicate the possibility of the support of a larger volume of plankton if greater time for breeding were allowed. 1899. (Tables: V.,. XUL: PIXXX, DIX) The 7 collections in January-March average .67 cm.’ per m.* as compared with .41 inthe river. Asin the previous year, the direction of movement in production is similar in the two regions. For example, the January pulse in both culminates on the 17th and that of February on the 14th and the 21st, while the March production is at low levels in both, and the apex of the pulse is not apparent in the lake records. The invasion of some channel flood water with the March rise and its speedy elimination may be traced in the chemical records (Pl. X LIX.) 367 The production in the lake during this period is greater than that in the river at all times of coincident examination excepting March 14 (.14 and .35). The average production in the lake (.67 cm.*) is 63 per cent. greater than that in the river (.41 cm.). This percentage of increased production is a meas- ure, or an index, of the impounding or reservoir action of the lake under the hydrographic conditions of these months. The immediate result of the access of Quiver Lake waters to the channel will be a rise in its plankton content from .41 cm.’ per m.* to .414—an increase of 1 per cent. . The summary of the interrelations of production in this lake and the river will be made in conjunction with that of Dog- fish Lake, which is only an arm of Quiver Lake. DOGFISH LAKE. (Gable Vi-= Pl XVI, XXX, OX IE) ENVIRONMENTAL CONDITIONS, This so-called lake is only the westerm arm of Quiver Lake (Pl. II.), separated from the eastern by Quiver Point, a low marshy spit covered with rushes and willows and lying but a few feet above low-water mark. It is of elliptical form, about three quarters of a mile long and one third of a mile wide, contains about 150 acres at low water, and as levels rise it ex- tends northward and eastward over the low bottoms towards Mud Lake and Cartwright Slough, but it is only at highest levels that very much of a current makes its way down through this lake. As levels rise above 8 ft. the intervening ridge sep- arating this lake from the river is gradually submerged, and channel waters invade more or less of the lake. It affords the natural channel for the run-off of the backwaters impounded in several square miles of bottom-land marsh and forest through the swale (Pl. II.) which extends towards Mud Lake. Its shores are everywhere low and marshy, of black alluvi- um, and a soft black ooze of similar origin covers the bottom of the entire lake. In only a limited area towards the east- 368 ern side can a substratum of harder sandy clay be reached be- neath two or more feet of this deposit. With the exception of a narrow fringe along the eastern side, the vegetation lacks the lilies, rushes, sedges, and other emergent plants which charac- terize the eastern shore and northern end of Quiver Lake proper (Pl. XVII). It consists (Pl. X VIII.) almost exclusively of Cer- atophyllum, E'lodea, and Potamogetons, which, in the low water of 1895, represented in the plate, filled the lake from center to periphery. Irregular openings in this dense growth appear oc- casionally in the area, and are modified by the shifting of the lightly attached vegetation, by wind, and by flood water. Except at high water and during the rapid run-off of im- pounded backwaters no appreciable current traverses this area. It receives no immediate contributions of spring or creek water along its margins, but depends entirely upon backwater from Quiver Lake or flood invasions for its supply. The examination of the plankton content of its waters ac- cordingly affords an opportunity to test the effect of this im- pounding factor, and also serves to throw some further light on the effect of vegetation on plankton development in impounded waters. COLLECTIONS. The collections in this lake cover a period of two years— from April 29, 1895, to June 28, 1897 (Table VL). They num- ber 48, and are distributed in much the same manner as those in Quiver Lake in the same period. The collections of 1895 and those of 1896 through May 8 were all made by the oblique-haul method with the single exception of that in the flood of Feb. 27, which was one of repeated vertical hauls. The collection of May 19, 1896, was made in the midst of rapidly growing veg- etation by dipping from surface waters, which then afforded no area suitable for an oblique haul. The oblique hauls were made for the most part near the center of the lake in a channel freed from vegetation a day prior to the collection. From May 21, 1897, all collections were made by the plankton pump in open stretches of water amid the vegetation. 369 In 1895 the lake was choked with vegetation which the winter flood largely removed and the recurrent floods of the following year reduced somewhat in extent, while higher levels lowered its relative occupation of lake waters. PLANKTON PRODUCTION. 1895. (Table VL, Pl. XXX.) There were 12 collections in this year, from April to De- cember, averaging 3.25 cm.’ per m2 The average of the monthly averages (see table between pp. 342 and 348) is 3.3 cm.* to .74 and 6.65—similar averages for the same period in Quiver Lake and the Illinois River. The maximum collection was made Dec. 19—a very unusual date for such production. A superposition of the planktographs of the river and Quiver and Dogfish lakes for this year brings out some in- structive similarities and differences in the movement of pro- duetion. The vernal pulse of April 29, in so far as the data reveal it, is quite similar in all three localities, reaching its greatest development in Dogfish Lake (8.20), where im- pounding action is greatest, and being greater in the river (5.83) than in Quiver Lake (4.57), where, owing to low levels, the proportion of water of recent creek or spring origin is greater than in the channel of the adjacent river. The June-July pulse may be found in all three localities, but it is belated and much smaller in the lake waters. This pulse in Dogfish Lake (4.59 em.’ per m.*) is less than a sixth of that in the river (80.42), where, in the semi-stagnant sewage- polluted channel waters of unusually low levels, Moina and other Cladocera caused the unusual production. Between the April and June-July pulses the river levels fell 2 ft., to mini- mum stages (Pl. XXX.), so that the proportion of creek and spring water in Quiver Lake is probably more than doubled at the later date. This may account in large part for the very low production in Quiver Lake (.02) on July 8, while on July 5 370 the contiguous but impounded and current-free waters of Dog- fish Lake contain 229 times as much plankton. The increased production following the September flood is apparent in all three localities, but reaches its highest level (4.65) in Dogfish Lake, the region where the impounding factor is greatest, while the least increase and quickest decline is in Quiver Lake, where tributary waters of recent origin are in greatest proportion. The low production in October is com- mon to the three localities, reaching a slightly lower level in the lakes (.13 and .52) than in the river (.57). The consider- able increase in production in November-December attains the highest level in Dogfish Lake (5.01 and 10.57), exceeding by 100- and 17-fold that in Quiver Lake (.05 and .63), and that in the river (4.37 and 2.60) by 1.2- and 4-fold. Here also the effect of the quieter impounding waters of Dogfish Lake is apparent in this relatively greaterdevelopment. The large plankton content on Dec. 19 (10.57) seems to be due to a combination of several favoring environmental factors. This collection was made after a steady but slight rise lasting for over five weeks, fol- lowed by ten days of gentle decline in levels and contracting margins of the lake. The steady rise to levels which intro- duced no run-off currents through the lake established the im- pounding function to its fullest, and invaded a considerable stretch of margins rich in dead and decaying vegetation. There is also at this season of the year less growth and more decay of the Hlodea and Ceratophyllum which abound in the lake. The collection was taken when the December flood had just be- gun to rise (about 2.6 feet) and with the combined action of wind and waves which attended the storm then raging had torn loose the vegetation and dislodged many of the smaller Crustacea and insect larve which find shelter in it. There were at the time 572 AJllorchestes per m.* adventitious in the plankton. A part of this large production is thus adventitious owing to disturbed hydrographic conditions. Nevertheless, there still remains after such contributions are deducted a con- siderable plankton of normal constitution (mainly Cladocera), 371 in amount certainly much in excess of the production at that: time in Quiver Lake (.63) or the river (1.74). This large pro- duction in this locality is then, it seems, to be attributed to im- pounding and decaying vegetation combined with accession of adventitious planktonts. The average monthly production (3.3) in this lake is on the whole less than half that in the river (6.65) for the same period, and it exceeds by over fourfold that in Quiver Lake (.74), through which all its run-off passes to reach the river. Since the com- parison of the two lakes is based on coincident collections, these amounts may serve as a quantitative statement of the effect of the environmental differences. As vegetation is much the same in both lakes the difference in production must be attributed to some other factor presenting a difference which may be corre- lated with that in production. Such a factor is found in the impounding action, which is at a maximum in Dogfish Lake and is relatively much less in Quiver Lake at the point of our collections, where creek and spring water of recent origin cause a more rapid displacement of the contents of the lake and car- ry away the products of decay of vegetation before the plank- ton can reach the degree of development that it does in the more stable waters of Dogfish Lake. The run-off from this lake in this year would thus tend to enrich Quiver Lake, though not on an average of sufficient pro- duction to enrich the river even if it could reach it without mingling with that of Quiver Lake. However, owing to the fact that this lake receives no tributary creek or spring water, and except at high levels has no bottom-land current through it, we must infer that its run-off is confined—excepting only at stages of general overflow—almost wholly to stages of falling water. During rising levels and in fairly stable conditions its contribu- tions to Quiver Lake, and thus to the river, are practically n7/. 1896. (Table VI., Pl. XXXI.) There are 80 collections in this year, with a distribution 372 similar to that of the collections in Quiver Lake for this year, the only exception to the coincidence of collections, actual or approximate, being on December 29, when on account of rotten- ness of the ice it was not possible to get the collecting outfit to the station. The maximum production occurs in the vernal pulse in the last fortnight of April, culminating at 20.35¢m.* per m.* on the 17th, though production is also large on the 24th (19.5). In Quivy- er Lake this maximum is on the 24th (16.76), though production is also large on the 17th (16.32). The maximum in channel waters (9:39) is also on the 24th. These differences in the time of the maxima may, I believe, be correlated directly with the thermal factor. For example, in both Quiver and Dogfish lakes the production is large and almost equal on the 17th and 24th, but is greater in Dogfish Lake on the 17th and in Quiver Lake on the 24th. This lag in the maximum is correlated with the fact that surface temperatures in Quiver Lake on the J 7th and 24th are respectively 3° and .8° lower than they are in Dogfish Lake. On the 17th the latter is 8° warmer than the river. After all allowances are made for the time of day at which tempera- ture records are taken, it isstill evident that the shallower waters of Dogfish Lake would warm up more quickly thar the spring- fed waters of Quiver Lake or the deeper channel waters, and we have found that the thermal increase favors the earlier rise in plankton production. The coincidence of the dates of collection makes possible a precise comparison of the production in the two lakes, and facilitates the comparison with that of the river. A superposi- tion of the planktographs of Dogfish and Quiver lakes and the river (Pl. XXXI., XXVII., and X.) for this year emphasizes far better than any description the most striking similarity at the three stations of the movement of plankton production as shown by the direction of the differences in plankton content in suc- cessive collections. The correlation between production in Quiver Lake and the river in this year—discussed in detail on pages 357-360—is paralleled in every important detail by the 373 sequence of the changes in Dogfish Lake. Indeed, the corre- lation is, if anything, even closer, since the amplitude of the plankton pulses is greater in Dogfish Lake than in Quiver Lake, and the changes are here—as, for example, in August—the more readily followed and compared with those of the river. Since I have already compared in detail the production in Quiver Lake and the river I shall not repeat the comparison of these similar data from Dogfish, for the correlations are essen- tially the same in both cases, and it will suffice simply to empha- size the similarity of the course of production in the three local- ities. ; The similarity between the production in the two lakes is, however, even greater than that between either of them and the river. This results from the greater similarity of the envi- ronmental factors inthe two lakes, with which the river con- trasts in matters of sewage and current. The similarity of en- vironmental factors lies in the amount and kind of vegetation, the depth, the character of bottom and shores—excepting the eastern margin of Quiver, the impounding function (modified, however, in the case of Quiver Lake by the access of creek and spring water), and the freedom from sewage. Under these cir- cumstances it 1s not surprising that the details of the course of production as well as its ensemble are so strikingly alike in the two lakes. To be specific, the similarity in details of the course of pro- duction in Quiver and Dogfish lakes lies in the fact that in the 31 coincident collections in these waters the plankton content rises or falls in both at the same time in 28 out of the total num- ber. The amplitude of the change is rarely equivalent, but its direction 1s identical—referring, of course, to the fact of its being an increase or decrease, and not to the particular angle which the lines forming a planktograph might take. The 8 exceptions to this similarity in the direction of movement in production are shown in the following table, and may without exception be correlated with differences in the environment. In this table the plankton contents of the two adjacent col- 374 lections determining the direction of the change in production are given under the date of the later collection, and the posi- tion of the entries also indicates the direction of the change. VARIATIONS IN THE MOVEMENT OF PRODUCTION IN DOGFISH AND QUIVER LAKES, 1896. Apr. 24 | May 8 |May 16-19} May 21-22) July 3 | Aug. 15 | Aug. 29 | Sept. 16 20.35 to 13.39 to 18.40 18.40 to 1.58 11.25 1.18 3.06 Dogtish Wake. 19.50 13.06 | 13.06 to 36} 1.14 to | 3.88to | .75to | 1.18 to 16.76 8.14 8.14 to 99 .68 to 4.36 to 1.60 to -72 to Quiver Lake._..___... 16.32 to 4.24 to

  • a > Sous ra) g m g pets S) es - fal, w = bo |2 ¥V 2) > oO Oo V/s - g/ 2] 8/2) 2/4) 2) 2\s4) 2 le 5\e52 = s a < in © |2@ 2) Cs Illinois River.. 213) - -23| .27| 4.50] 6.08 7.22 4.23| 3.88 2.56) 1.70) 88) 71) Qe Thomp. Lake..|3.79 | 1.27) 2.96]14.49|29.59|10.66) 4.74| 6.19] 5.37|10.64] 6.39! 3.08} 8.26 Ratio niccciec: 22 PSES"}) WG: | SEE EZ RG STS) PSE enG| keae | WeON | ahe7 aeees | 1:3 Average height a | of river in {t..17.77 | 7.89112.34!10.02! 9.18! 6.19! 4.36! 2.26! 3.78! 3.44! 4.26! 4.97 The average height of the river for the years represented in the several monthly grand averages is also given in the above table, and exhibits some relations to the relative plankton pro- duction in Thompson’s Lake and the Illinois River, which, however, are so combined with other factors—such as seasonal temperature changes, the period of dominance of vegetation, and qualitative seasonal changes in the plankton itself—as not to be readily analyzed. We find in January—May a period of high levels and low temperatures, of flood invasion everywhere— but most potent in channel waters, a period in which production in thelake is from 3-to 18-foldthatin the river and averages 8.4, 411 This is the time of greatest contrast, and also the time of highest levels (averaging 9.44 ft.) and therefore of continuous and largest run-off. It is also the season of largest plankton production, averaging 10.42 cm.’ per m.*,—S.4 times that in channel waters,—and is accordingly the period of greatest en- richment of the channel plankton by the run-off from the lake. The factors operative in producing this result are the high levels, with resulting increase in the impounded waters of the lake at a season of rising temperatures favorable to plankton production and to the enrichment of the waters by decay of the vegetation of the previous year’s growth. In June-September we have a period of falling levels, maximum temperatures, lowest water, and growth predominat- ing over decay in the aquatic vegetation, which is relatively more abundant in the lake than in the river. It is therefore the season of greatest predominance of local environmental factors, and of run-off reduced to minimum volume and fre- quently interrupted. It is also the season of least plankton production, averaging 6.74 cm.’ per m.’—only 1.54-fold that in channel waters. The midsummer season is therefore one of least enrichment of channel plankton, as a result of both the decreased and interrupted run-off and the decrease in the relative production in the lake. This latter feature results both from the decline in production in the lake and the low-water condi- tions in the river, where increased fertilization by sewage and slackened current tend to raise its level of production at this season. Other factors tending to bring about the conditions of production prevalent in this season are possibly the greater relative exhaustion of the fertility in lake waters during the mid- summer and low water, as indicated in our chemical analyses bythe generally lower level of the various forms of nitrogen in the lake than in the river. (Cf.on this point Plates XLV. and L.) This greater relative exhaustion maybe attributed in part only to reduced interchange of river and lake waters at low levels and consequent reduction in influx of sewage from the channel, and tothe utilization of some of the constituents which support 412 the phytoplankton by the rapidly growing aquatic vegetation. These factors are not, however, potent enough to overcome the effect of impounding and consequent time for breeding which prevail in the lake more than in the river, and thus to lower the plankton production in the lake below that in the channel. In October-December we find another season marked by rising water but not high levels, in fact, averaging only 4.22 ft.—a level insufficient to provide for any current through the lake or any considerable discharge in periods of decline. It is thus a season of slight and interrupted run-off. It is, however, a period of increased production, reaching 10.64 in October, declining to 3.08 in December, with an average of 6.70—a trifle below that of the midsummer period. Its relation to channel production changes decidedly, rising from a ratio of | to 1.54 in midsummer to 1 to 5. This five-fold greater plankton con- tent in Thompson’s Lake makes whatever run-off occurs of con- siderable enriching effect upon channel plankton, though pre- vailing low levels and large proportion of rising levels tend to reduce the actual volume contributed in this season. The fac- tors operative in increasing the relative production in lake waters in this season are the influx of sewage-laden river water, and the decay of some of the succulent vegetation of the lake and its re-submerged margins at a season of plank- ton pulses of an amplitude increasing by virtue of other fac- tors, internal or external. Rising levels also bring about an increase in current in the channel, while marked changes in the bacteriological and chemical condition of channel, waters attend this and the fall in temperature. The com- bined effect of these factors, as shown by a comparison of the records of 1897 (Pl. XI.)—when low levels continued and the autumnal decline in temperature was late—with those of other years, is to depress production in channel waters more than it falls in the lake. This fact, together with the increase in the impounding function of the latter as levels rise, suffices to bring about the increased relative production in lake waters in the closing months of the year. 413 Thompson’s Lake and presumably other bottom-land wa- ters of similar character, by virtue of their impounding fune- tion, are reservoirs in which flood waters are stored for a great- er or less time, permitting the development in general at all seasons of the year of a plankton exceeding in volume from 1+-fold to 18- fold that coincidentally developed in channel waters of the adjacent river. The run-off from this and like areas elsewhere thus serves to enrich and maintain the river plankton proper. The slightly developed tflood-plain of the [lli- nois and the consequent considerable area of such bottom-land waters—which equalize the floods, prolong the run-off, and favor the production of an abundant plankton in the impounded areas —become, accordingly, factors of great importance in causing the richness, abundance, variety, and long continuance of the unusual plankton production of the [Illinois River. The similarity in the course of plankton production in Thompson’s Lake aud elsewhere in our field of operations is shown in the following tabular sammary, which giyes the num- ber of instances of agreement and disagreement in the direc- tion of the changes in production in the four localities. SIMILARITY IN DIRECTION OF CHANGE IN PRODUCTION IN THOMPSON’S LAKE AND AT OTHER STATIONS. [llinois River|Quiver Lake|Dogfish Lake] Flag Lake | Total we | 82 les) 28 [ees] 2s [22s] Ss |x oe] 2g leks or Sie ¥ or BI ae seal (uiaioa Sura He Abs] oe Awe] oe Pe] Se As] Oe [Awe ESOS eae eeiaee 9 4 7 5 9 3 2 I 27 13 LEO Oya es aes 18 8 12 13 18 8 16 9 64 33 LOG Patera are ierens 14 4 ite) 3 5 I 5 2 34 15 ISOS ey eens Px 4 22 Be Alle elects fe ne ame Red Wc 3 o 43 7 NOOO teres 3 4 a dik OM |Begeteco| he che ene beeen leretceee 8 Metals. seus 12 Gsuuie24 54 33 32 12 23 12. | ia | St This gives a grand total of 174 instances of similar direc- tion of change in production out of a possible 255, or 68 per cent., for the 5 years included. It is noticeable that the years differ considerably in the degree of agreement detected, the latter years of fuller records exhibiting fullest agreement. They are 414 also years of higher water, of greater uniformity of environment —because of greater extent of open water, of greater interchange of water in overflow stages, and therefore of greater agreement in the course of plankton production. The similarity in the course of plankton production in different bodies of water is in a large measure a function of the similarity of their environ- ment and the resemblance of their planktons in the matter of constituent organisms. STATION F, PHELPS LAKE. (Table LX. oPle XX, Lx) ENVIRONMENTAL CONDITIONS. This body of water lies on the western side of the river about a mile below the city of Havana, in the elevated bottom-lands below the mouth of Spoon River. It trends northeast and southwest for a distance of seven eighths of a mile, has a width of 40J-690 feet, and a total area of 50-60 acres. Its bottom les about 6.5 feet above low-water mark, and the greatest depth re- corded in it at high water at the point of collection was only 10 ft. It is but slightly deeper toward the lower end. Its out- letis by a tortuous slough choked with driftwood, which runs for two fifths of a mile ina southerly direction to the river. The elevation of the bottom of this slough at its entrance to the river is 8-9 ft. above low-water mark, so that all run-off from the river drained hy this slough ceases when it drains to this level, and it is not reinvaded by floods below this elevation. When the river falls below the level of the outlet and the lake drains as fully as the outlet permits, there still remain about 1.5 ft. of water from which no further run-off occurs. The vol- ume is then slowly reduced by evaporation or increased by sum- mer rains. The lake is not fed by springs or tributaries of any sort be- yond seepage from the level alluvial bottoms in which it lies, and which nowhere in the vicinity rise more than 10 feet above its bottom and generally very much less than this distance. At river stages of 11 ft. and above, backwater from Spoon River 415 makes its way through a now abandoned channel to the lake and thence out to the river through the slough. Below this level, the current of the gentle run-off of the great tract of adja- cent impounded backwaters with which this lake has then but a slight connection is the only movement in the area. The surrounding bottoms are heavily wooded for a narrow margin along the lake, though the forest gives way to cultivated fields on both sides within a short distance. Its bottoms and shores are of a rich black alluvium, which in low-water seasons such as 1895 becomes the soil of a cultivated field. The vegetation of this area is unique among our plankton stations in its character and relation to the plankton. In 1894 there was little vegetation present, and whatever aquatic growth had gained a foothold was eradicated by the dry au- tumn and by the cultivation of the soil in 1895. In 1896-1899 the occupation of the lake by water was more continuous, and Potamogetons, Naias,and even Nelumbo, gained a slight foothold along the margins. ‘The principal vegetation was a dense mat of filamentous green algwe, such as Spirogyra and Zygnema, which covered the margins for a considerable distance into the lake. During the heated term of midsummer a dense felt of Oscillaria covered the bottom of the lake everywhere at times. These algw were present during most of the summer, though most abundant in spring, and by their continuous and prompt decay they release into the lake waters a volume of nitrogenous and other substances which are utilized by the phytoplankton. The cumulative action of the longer-lived aquatic phanerogams in withdrawing from the lake large stores of food which are again released in the ensuing autumn or spring by the decay of the season’s growth, is thus quite absent from this body of wa- ter. The rapidly growing and rapidly decaying alge permit a repeated flux of nitrogenous and other substances utilized by the plankton as food in the course of a single season. This fac- tor, combined with the complete impounding function of this lake below river levels of 8 to 9 feet and the absence of tributary and spring water, is, I believe, the secret of the unusual plank- ton production in this area. 416 The absence of coarse vegetation, the sheltered situation in ariftin a dense forest, and the shallowness of the whole lake during much of the summer, permit an unusual range of diurnal temperature-changes falling but a few degrees short of the diurnal range in the air. The records (Table [X.) fre- quently contain readings of 90° to 95° in the summer season. This lake swarmed with the fry of various native fishes and the introduced German carp, all of which make great roads upon the vernal plankton. It was also the favorite haunt of many fish-loving water-fowl. This abundant animal life served in turn to enrich the lake waters with its nitrogenous wastes, at once available for utilization by the phytoplankton. There are thus many chains of food relations in this lake, in most of which, if not, indeed, in all, the plankton forms many lhnks. COLLECTIONS. There is a total of 67 collections from this lake ; 1 only in 1894, 29 in 1896, 9 in 1897, 22 in 1898, and 6 in 1899. The single collection in 1894 was made by the oblique-haul method. The absence of collections in 1895 is accounted for by the fact that there was no water in the lake in that year. In 1896-1899 collections were made in various ways according to the conditions of access to the lake and the depth of the water. Owing to rafts of driftwood, access at any season through the slough is prevented. At high flood-levels, when ice did not prevent, it was possible to enter the lake by boat with our plankton pump and usual collecting apparatus. At all other seasons access by boat was impossible, and apparatus had to be carried across fields and through dense under- brush to the lake, and collections made by wading out into the lake or from a staging carried out from the shore for some dis- tance over the water. There are accordingly but 9 pump col- lections. The remaining 57 were all made by dipping water from the surface and pouring it through the plankton net. Most of the collections represent, therefore, surface waters, but owing to the exceedingly shoal water they are, nevertheless, in 417 the main representative of the plankton of the lake. Of the 67 collections, 32 were taken from water which in the deepest part of the neighborhood of collections was less than 14 inches. Owing to the roiling of the water caused by our movements, it was necessary to dip from considerable areas in order to secure the desired volume for straining. Since a separate report on these collections is being pre- pared I shall only deal in this connection with those aspects of the data most intimately connected with the phenomena of the channel plankton. PLANKTON PRODUCTION. 1894. (Table IX.) A single collection on June 8 yields a volume of 24.17 cm.* per m.°, an amount 7-fold that of the same season in 1896, al- most equaled in 1897, and more than doubled in 1898. 1896. (Table 1X., Pl. XL.) There are 29 collections in this year, extending from Jan. 8 to Nov. 1?7—when only a few scattered pools remained. This is the most fully represented year of our series in this lake. The yearly average is 13.17 cm.’ per m.*, with a vernal maxi- mum of 54.80 on Apr. 16, and an autumnal one of 51.60 on Oct. 15. This is the earliest vernal pulse recorded in our work, and should be correlated with the early rise in temperature in these shoal and protected waters. Thus, in Phelps Lake on Apr. 16 the surface temperature was 77° and the average for April 65.4° to 71° (Apr. 17) and 62.6° (average) in Quiver Lake, and to 66.3° (Apr. 17) and 63.2° in the Illinois River. This lake was thus apparently 5° to 6° warmer on the average than these other localities, and the vernal pulse is accordingly accelerated. Owing to the elevations of the lake and its outlet, run-off from this area into channel waters practically ceases when river levels fall below 8 ft. In 1896 there were but 114 days of 418 stages above 8 ft., 90 from Jan. 1 to Mar. 30, and 14 and 10 re- spectively in the floods of May-June, and August. Of the 114 days there were 28 of levels above 10 ft., when, owing to run-off from Spoon River, a current passes through the lake to the river regardless, as a rule, of rising or falling water. In addi- tion there were 483 days of falling water when a run-off might be expected, making a total of only 71 days in this year in which there was any run-off to channel waters from this lake. The remaining 45 days of levels above 8 ft. were times of sta- tionary (20) or rising (23) water, when discharge from Phelps Lake was diminished or cut off. Of the 71 days of discharge, 61 fall in the winter, in Janua- ry-March, and 5 each in Juneand August, at times of depres- sion in production (Pl. XL.). Nevertheless, the plankton con- tent in Phelps Lake at all of these times greatly exceeds that in channel waters. The ratio of Illinois River and Phelps Lake plankton in Jannary is 1 to 189,in February, 1 to 607, in March, 1 to 274, in the June flood, 1 to 4,and in the August rise, | to 7. These latter ratios are somewhat exceeded by those of the av- erage production for the year, 1.16 to 13.17 cm.*, or 1 to 11. During the months of little or no discharge, April-December, production in the lake as shown in monthly averages is 4- to 1600-fold greater in Phelps than in the Illinois, the latter figure being reached in November and the other months averaging only 11-fold. Thus, this lake contributed to the enrichment of channel plankton for a relatively brief part of the year, and at all times produced a plankton greatly in excess of that in channel wa- ters. The sharp contrast between the poverty of channel wa- tersand the wealth of this lake is due to the impounding fune- tion in the latter, and to the repeated flushings by storm waters of recent origin in the former. Full time for the normal utili- zation of the resources for growth of the plankton is permitted in the lake but not realized in the constantly replaced river water. This is the only year in which collections were made in 419 Phelps Lake at weekly intervals for any length of time. Such intervals extend from the end of March to the last of August, and since similar series were made elsewhere we have an excep- tional basis for comparison of the course of production in the several localities. A comparison of the planktographs of the river and Phelps Lake (Pl. X. and XL.) reveals certain general similarities. These are expressed in the three major fluctuations of the year, the vernal, midsummer, and autumnal rises in production, which, in the main, have coincident limits, but very divergent ampli- tudes, in the two bodies of water. The absence of the sudden | diluent action of flood waters is noticeable in Phelps Lake rec- ords, though declines in plankton content coincide with the flood invasions of both June and August. The absence of col- lections in September in Phelps Lake at the time of the decline in plankton content between the midsummer and autumnal rises is due. to the very low stage of water in the lake, per- mitting no collection. Replenishment by autumn rains is followed by the large development in October (51.6 cm.’). Not only is this general similarity between the movement in plankton production in Phelps Lake and the Ilhnois River traceable in 1896, but there is a more detailed agreement in the changes in the direction of movement in production in coinci- dent or approximate collections. This is most clearly seen in the months of April to August, when collections are of sufficient frequency to trace with some certainty the course of produc- tion. During these five months there are 16 agreements in the direction of the change out of a possible 20—a total of 80 per cent.—between Phelps Lake and the [linois River. In the year as a whole the agreements number 19, or 68 per cent., out of a possible 28. Two of the exceptions in April-May are due to the dislocation of ‘the vernal pulses in consequence of the higher temperatures in the lake above noted. When we take into con- sideration the marked differences in the local environment of the plankton in these two localities and the considerable inde- pendence of this lake as contrasted with other reservoir lakes, 420 such as Thompson’s and Quiver, this marked degree of resem- blance is the more striking. A comparison of the course of production in Phelps Lake (Pl. XL.) and Thompson’s Lake (Pl. XX XVII.) in 1896 reveals 14 agreements out of a possible 25, or 56 per cent. Of the 11 disagreements 3 fallin the period of few collections in the au- tumn months, when Phelps Lake was reduced to shallow pools, and 4 occur during the vernal pulse of April-May. A compar- ison of the planktographs and thermographs of the two lakes shows that in Phelps Lake the temperature is from 2° to 8° higher than in Thompson’s Lake for a period of six weeks dur- ing the rise of the vernal pulse. Hence this culminates earlier by a fortnight in the former, and in consequence a dislocation of the course of production in the two lakes occurs in this peri- od. The two planktographs are, however, strikingly alike in the fact that in the interval between March 31 and June 1 there are three pulses of regularly decreasing amplitude in both lakes. The similarity is thus greater than the percentage indicates. A comparison of the course of production in Phelps and Quiver lakes (Pl. XL. and XXVII.) reveals 15 agreements out of a possible 28, or 54 per cent.—but little more than chance de- mands. In this case the environmental differences are greater, the effect of spring water, vegetation, and flood invasion inter- fering in Quiver Lake with the course of production. A comparison with Dogfish Lake, where the disturbing fae- tors of spring water and flood invasion are less immediate in their action, reveals a slightly greater degree of similarity—16 out of 28, or 57 per cent. In the case of Flag Lake the agreement is still less, being only 11 out of 24, or 46 per cent. It is a noticeable fact that the disagreements are Most numerous in Quiver; Dogfish, and Flag lakes, all of which are rich in vegetation, and these disa- greements occur in greatest proportion during the months of May—August, when with changing river stages the proportional occupation of these lakes by vegetation fluctuates greatly— 421 a variable factor from which Phelps Lake is to a large extent exempt. The degree of agreements, as a whole, in production between Phelps Lake and other localities is seen in a total of 84 instances out of a possible 141, or 60 per cent. 1897. (Table IX., Pl. XLI.) There are only 9 collections in this year, at approximately monthly intervals with the exception of the last collections, when the interval was somewhat reduced. Collections cease in August, when the water entirely disappeared from the lake. The average plankton content for the year is 10 cm.’ per m.’, the lowest annual average in which summer collections are in- cluded in this lake. The vernal pulse was not detected, if pres- ent, and the maximum record, 29.94 cm.*, was on Aug. 26, the date of the last collection. The hydrographic conditions were such (Pl. XLI.) that a current from the flooded bottom-lands about Spoon River passed through the lake uninterruptedly from Jan. 7 to May 18, and the run-off of impounded waters continued until the 25th, a total of 139 days. Throughout the period covered by our few collections they indicate that the plankton content of this area exceeded that in channel waters by from 1.6- to 11-fold with the single exception of Apr. 27, when the lake had 4.26 em.’ to 5.11 in the channel. During the 139 days of run-off the production in the lake scarcely exceeds 5- fold that in the channel, but when discharge ceases the content rises to 10- to 11-fold that in the river—a phenomenon which illustrates the equalizing effect of general overflow on the one hand, and the effect of impounding in increasing production on the other. The run-off from this lake in 1897 thus predominantly served to enrich channel plankton. The fact that produc- tion in Phelps Lake falls below that of the channel on Apr. 27, when a vernal pulse might be expected of an amplitude greater in backwaters than in channel,—as indeed it is in Thompson’s (PI. XXXVIIL.), Quiver (Pl. XXVIIL), Dogfish (XXXII), and 422 Flag (XX XIV.) lakes by 50 to 150 per cent.,—is to be attributed to the diluent effect of invading flood-waters from Spoon River, whose plankton content on Apr. 27 was only .05 em.* per m.° The entrance of these flood waters, indicated by the check in the decline of the hydrograph (Pl. XLI.), was noticeable at the station on the day of collection, and is the cause of the increased turbidity in Phelps Lake on that day (Table IX.). The similarity in the movement of production in Phelps Lake in 1897 to that in the other bodies of water examined by us, is very close. In the case of the Illinois River, 8 out 9 pos- sible instances, or 89 per cent., are in agreement; in Thomp- son’s Lake 7 out of 9, or 78 per cent.; in Flag Lake all in- stances are in agreement; in Quiver Lake 6 out of 9, or 67 per cent.; andin Dogfish Lake 4 out of 6, or 67 per cent. As a whole, 32 out of 40, or 80 per cent., of the changes in the direction of production in Phelps Lake accompany similar changes in di- rection in these other localities. All of the 8 exceptions to this agreement occur at levels below 8 ft., when local environments are more potent, and 5 of the 8 are found in Quiver and Dogfish lakes, where vegetation and access of tributary waters become proportionately more or less potent as levels fall or rise in May to August, when the 5 exceptions occur. This unusual degree of agreement in 1897 must be attrib- uted in large part to the hydrographic conditions in the period of comparison. For almost 5 months of the year levels were above 8 ft., when fluctuations have relatively but a slight effect on the various environments. Above this level the several lo- calities are more or less submerged in the general overflow, and all share alike in the wide stretches of open water in which some current exists, and the commingling to an increasing extent, as levels rise, equalizes and obliterates local differences in pro- duction. The first 4 collections of this year were made under such conditions, and agree without exception in the course of production. The remaining 5 were taken at stages below 8 ft., in the very midst of the season of local diversification, and the proportion of agreements falls from 100 to 60 per cent., and is 425 greatest in the most differentiated localities, Quiver and Dog- fish lakes. It might also have been expected in Flag Lake (PI. XXXIV.) if examination had continued there beyond the mid- dle of July. It would seem, accordingly, that similarity in the course of plankton production in different localities is to a large extent a function of the community of environmental factors, and possibly also of the similarity of the constituent organisms. 1898. (Table, TX., Pi ELT) There are 22 collections in this year, at fortnightly inter- vals, in March—-December. The average production for the year is the unsurpassed amount of 44.08 em.’ per m.*, with a maxi- mum, also unsurpassed in our records, of 224.48 on Aug. 25. An unusually high level of production is also maintained from Aug. 9 to Dee. 13, averaging 63.54 cm.*, and falling below 30 in but two instances. Water re-entered Phelps Lake with the flood of February, river stages passing 8 ft. on the 12th and 10 ft. on the 20th. From this latter date until June 28, with the exception of 4 days in May, levels continued above 10 ft., so that a continued current of overflow from the bottom-lands to the north passed through the lake to the river. Declining river stages continued from June 28, passing 8 ft. July 9, thus permitting a run-off for a total of 138 days from the lake to the river in the period of spring and summer floods. To this must be added 7 days of de- clining levels above 8 ft. in the November-December rise, mak- ing a total of 145 days of contributions to channel waters from this lake. This is the most extended period of contribution in the years of our operations, and is a result of the unusually high and prolonged floods which brought the average height of the river up to 8.02 ft., almost bank height, for the year. The plankton content of Phelps Lake waters in the 10 col- lections made during the period of discharge above noted, is in excess of that in the channel in 7 instances by from 1.4- to 15- fold 424 and averages 7.3. In three instances, March 3 and 1, (.01 and .02), March 29 (.20 and .48), and April 26 (10.72 and 15.81) the lake contains less than the river. All of these instances fall at “times of high levels, exceeding 11 ft., when Spoon River floods invade this territory, and this deficiency in Phelps Lake is doubt- less due to their diluent effect. Since ourstation for collections was located in the upper end of the lake (Pl. II.), the full effect of the flood would be detected at this point, but would be di- minished by mingling with the lake waters and the adjacent impounded backwaters before it joined the channel. The first of these exceptions, on March 3, isnot accompanied by increased turbidity (.45) in the lake (Table [X.), but the other two, March 29 and April 26, are attended by a marked rise in turbidity (.05 and .16). During this period of maximum spring flood in March and April, owing doubtless to this dduent action of Spoon River, the run-off from this area, as indicated by plankton content at the upper end of the lake, dilutes, or but slightly enriches, the channel plankton. This appears in the monthy averages (table following p. 342), which for March are .33 cm.’ for the river and but .25 for the lake. In April they are 4.4 and 5.6 respectively. In later months, during the declines of the spring flood, and owing to absence of the flushing action of Spoon River floods and to the rise in impounding function with decline in levels and delimitation of the lake, we find a rapid rise in the relative plankton content in lake waters. The production in coincident collections is greater in the lake than in the river by 3- to 15- fold, and the monthly averages for lake and river respectively rise to 40.44 cm.’ per m.*? and 11.30 in May; to 27.67 and 3.96 in June; and to 6.97 and .58 in July; that is, the production is from 3+- to 12- fold greater at this season in the lake than in the river. During the run-off in these months this lake and its contributing adjacent bottom-lands serve to increase, in some unknown ratio dependent on their relative volumes, the plankton content of the channel waters with which they mingle. Although the frequency of the plankton collections is in- 425 sufficient to trace with accuracy the course of production in Phelps Lake in this year, they yield many suggestions of recur- rent pulses of production similar in duration, though of greater amplitude, to those more clearly defined in channel waters. A comparison of Plates XII. and XLII. will indicate the presence of pulses of production in both localities, culminating in the ma- jority of instances at approximately monthly intervals. There are eight such culminations in Phelps Lake visible in the rec- ords of March—December, culminating in March, May, June, July, August, September, November, and December. In spite of the disparity in the records in this lake and the river, the similarity in the location of the pulses in the two localities is apparent in all of the above months but August and November —hboth of which are months of unusual hydrographic disturb- ances in channel waters. A detailed comparison in the movement in production in this lake and the adjacent river shows agreement in the direc- tion of movement in 14 out of 21 possible instances,or 67 percent., 5 of the 7 exceptions falling in the hydrographic disturbances in August-September and November. Inthe case of Quiver and Thompson’s lakesthe problem of comparison is made difficult be- cause the fortnightly collections in Phelps Lake and these local- ities are not upon coincident, but alternate, weeks, and makes the the similarity or difference probable rather than precise. A comparison shows 16 agreements out of a possible 20, or 80 per cent., in the case of Thompson’s Lake, and 17 out of 20, or 85 per cent., in the case of Quiver Lake. Both of these lakes are af- fected by hydrographic changes at lower levels which do not disturb Phelps Lake, and we find that 6 of the 7 exceptions oc- cur in the period of floods at low levels. As a whole the move- ments in production in the lake in 1898 agree with those else- where in 47 out of 61 possible instances, or in 77 per cent. Jn view of the fact that the recordscover also the low-water period this is a notable degree of agreement, and is to be attributed to the unusually high average level for the year and to the equalizing effect of high water. This factor is not, however, in 426 immediate operation during the last half of the year in so far as Phelps Lake is concerned, and other factors common to the whole environment or inherent in the common plankton must be responsible for the similarity in this period. 1899. (Table IX., Pl. XLII) There are but 6 collections in this year,—in January—March, at fortnightly intervals. The hydrographic conditions are such that the lake is cut off from the river for 34 days during the 3 months, and of the remaining time there were only 32 days of stages above 10 ft.in which currents passed through the lake to the river, and 7 of falling stages at levels below 10 and above 8 ft., when the run-off continued, making a total of 39 days of contribution to channel waters. These times of contribution in January and March (PI. XLII.) are also times of high plank- ton production for that season of the year. ‘Thus the plank- ton content in Phelps Lake on Jan. 24 is 8.47 cm.’ per m.’ to .03 in channel waters. The run-off from the lake at that time is thus 286-fold richer in plankton than the water it joins, Again, in March, it is 3- to 9-fold greater. The monthly aver- ages of production are (see table following p. 342) from 6- to 26-fold greater in the lake than in the river. This lake thus serves, even in winter conditions and under a thick and long- persisting coat of ice, as a rich breeding ground for plankton whose run-off enriches the channel plankton. ‘This is due to its impounding function, which results in high production, as, for example, during the decline of the January flood (Pl. XLITL.). Proof of this is seen in the sudden decline in production (from 9.3 cm.* on Feb. 7 to .1 on the 21st) when flood waters from Spoon River were scouring out the lake beneath the ice. The movement in production in these months in Phelps Lake bears little resemblance to that elsewhere, agreeing with changes in channel production (Pl. XIII.) in only 1 out of 6 possible instances, and in 3 and 2 respectively out of 6 in the case of Quiver and Thompson’s lakes. This exceptional disa- 427 greement may perhaps be due to the changes elsewhere, inci- dent to rising winter floods. SUMMARY. Phelps Lake is the richest in plankton of all the localities examined by us, averaging 19.65 cm.* per m.*, the mean of all collections, or 22.35 em.*, the mean of the monthly averages. This is 8- fold the production in the river and more than twice that in any other impounding area examined. We find, how- ever, that the lake does not contribute to the river at levels be- low 8 ft., and is therefore cut off for a considerable part of the time. In the years 1894-1899 inclusive, the days of run-off were 14, 0, 71, 1389, 145, and 86 days respectively, or an average of 76 days. Asarule the plankton content of the lake waters during periods of run-off exceeds that in the channel in varying degrees, and the lake by virtue of the impounding function serves to increase the plankton content of channel waters. The exceptions fall mainly at levels above 10 ft., when the diluent action of Spoon River floods affects the production in the lake. The high records of production which indicate the great rela- tive and absolute fertility of this body of water are in the main found during summer and autumn months, when there is no discharge and the impounding function is at its maximum. This is confirmatory evidence of the effect of impounding when the disturbing factor of tributary water is absent and coarse vegetation is of little extent. Owing to its small area, its early separation from the channel, and its relation to Spoon River at high levels, the total contributions from this area are relatively small as compared with those from Thompson’s and Flag lakes, and at times from Quiver Lake, and its relative fertility during months of run-off, as compared with these localities, is wont to rise above their level of production, especially at stages be- tween 8 and 10 ft., when run-off is shght and impounding function dominant. Illustrations of this will be found in the monthly averages of 1897 and 1898 in April-June, the sea- son of greatest run-off, when 4 of the 6 monthly averages 498 are considerably larger in Phelps Lake than in the other lo- calities. The course of production in this lake, as has been shown, is predominantly like that in the other localities. It frequent- ly has similarly located pulses, though their amplitude, es- pecially in late summer and autumn, is often much great- er than elsewhere. Moreover, in the majority of instances the direction of the changes in production in coincident or approx- imate collections is also similar to that elsewhere. In a total of 260 possible instances there is agreement in 169, or 65 per cent. This excess of agreement over the demands of chance, combined with its recurrence in successive years and its occur- rence in the case of different localities, is confirmatory of the view that it is the result of the operation of common factors of the environment. The predominance of the disagreements at times of greatest local differentiation or disturbance, as in low water in summer or in rising floods, lends further support to the suggestion. GENERAL COMPARISONS OF YEARS AND STATIONS. It is my purpose to summarize in the following pages the results set forth in detail with respect to the individual locali- ties in the several years, and to make the comparisons and draw the conclusions which follow from such a summary regarding the relative production in these different years and localities and the factors operative in modifying production. The following table gives forthe various localities the yearly averages of plankton, silt, and total catch, and the number of collections in each year. ee a Av. of all collections No. of Station Year collections ee Plankton} Silt | Total = 1894 Porta 2553 2.49 .28 2.77. ia: F 1895 50 5-91 eee Wea be | Himois Maver... .20- 1896 56 1.05 ¥.16 | 2.55 | 3.95 1897 34 3.28 3.09) | 1.91 1/560 1898 52 2.03 Pe MSY |) Deis |e rian 1899 Iie kl -42 41 O41 235 Grandiavies sinc tee nee cris: Pag ts Z1Gh 70) 163-08 Votal-ssene en: 235 ee 9 ee 1007 11) "3407 |) 1-36 3 1897 13 .983 Be257) Pe L732 a3 SPCOnMRAVehe aaeis esi 1898 se 029 “029 796 83 1899 3 oll SOLE) 2.206 | 2:23 Grand anges ace Cn enon 256 405 939 | 1.41 Motally cesta se 36 Wei a 1894 14 .gO E. O00 |e balg. (32°25 ne 13 65 78 70 | 1.48 : 189 31 2.19 2.59 20 | 2.79 Ouiiver: bake tes, aa. 1807 24 6 ag 62 | 1.50 1898 26 1.96 2.44 4o | 2.85 1899 7 66 67 AY NST Grandiave.nck a5)| sce cette sso 175 1.70 520), 2e22 Motaleeacsce te 115 1895 12 3.30 3-25 | 2.15 | 5.40 Doghsh Wake vec. sas 1896 30 3.99 5.01 Se babe 1897 6 2.65 223 2.45 Grandiav.. cee cle ceaee 3.10 4.22 88 | 5.10 Total®. fesse 48 1895 4 25 66 20245 3.45 ae 189 27 pes 13253) | 145, [to Flag alkenes: cits 1897 7 5.34 4.59 .69 5.28 1898 6 Bead e2e0ay \r4ia30\} 71s Gran dlaven seas heeer eearaee @:23. } 11.46 |) 1.90))/19596 Mota sige ate sae 44 | wis 1894 5 8.89 S209) || 2523) |iai2 1895 14 1231 Q207) Nlendd ened ) 1896 27 6.67 g .00 22a |On22 Thompson's Lake.... 1897 18 10.41 10:43. | 1-28 |v 1898 25 5.06 5.71 79 | 6.50 1899 7 Tes Ea 2, (Te 53 Grangay cal \Asor cites Wess 8.26 7.94 86 | 8.79 Motaltencesseder 96 1894 I 24.17 24.17 |trace |24.17 1896 29 14.74 13.17 -77 |13.94 BhelpsiMakereereeee. 1897 9 9.15 10.00 54 |10.53 1898 22 37.34 36.31 | 7.76 |44.08 | 1899 6 3.74 3-74 -29 | 4.03 Eran diay: 342. all’ sestearoae oh 22.35 19.65 | 2.95 |22.60 Mota ar rinse ci 67 *Grand average of all monthly averages, not of annual averages. {Grand average of all collections, not of annual averages. 430 1894. (OBL VEE PXOXK Vig Vy) Only three stations were established in this year: the Ili- nois River Station, with 10 collections ; Quiver Lake, with 14; and Thompson’s Lake, with 5. The appended table gives the production in monthly averages of plankton per m.* for the seasons covered by the collections. PLANKTON PRODUCTION IN 1894.* Mean of Station June July | Aug: | Sept-| Oct: | Nov. Dec; monthly averages Illinois River... |—| .74|/+ 5.12} +19.67/—|1.36/—| .61 |—|.10 |—| .10 !—! 2.53 Quiver Lake...|—| .23|+| 2.20/—] .74]+/2.12/+] .95 02 |= |," oan \aeoe Thomp. Lake.. !|+]24.92'4+ 10.74|/—|1.08/+'6 4o}|..|.....].. Peet 1.29 + 8.89 *The minus sign signifies below average and the plus sign above. It is evident from comparisons with records in years of fre- quent collections, for example, in 1898, that the interval of col- lection is too great in 1894 to give a satisfactory basis for a dis- cussion of production. As far as they go the data indicate a level of production below the average of our records. In the river and in Quiver and Thompson’s lakes the monthly aver- ages in 1894 are below the general averages for the respective months in 5 out of 7, 4 out of 7, and 2 out of 5 months respec- tively, a total of 11 out of 19. The mean of the monthly aver- ages in 1894 for the river, 2.53 em.* per m.*, is 7 per cent. below the mean of all monthly averages in 1894-1899, and that of Quiver Lake is 49 per cent. below its mean. Thompson’s Lake, on the other hand, with 8.89 em.’*, presents an excess of 8 per cent. The low level of production in the river and Quiver Lake is attributable to the absence of overflow in June with its ac- companiment of run-off of impounded and plankton-rich wa- ters, to flushing action of the repeated rises in September, and to the relative dominance of coarse vegetation in the lake and, to some extent, in the river. The larger production in Thomp- son’s Lake is attributable to freedom from the flushing action of floods in the prevalent low water and to the relatively stable 431 hydrographic conditions. It is noticeable that production in the river is on the average 7- fold greater in July-August (Pl. VIII.), during stable low water, when current is slackened and impounding most prolonged, than in June and September, when high levels and flushing by floods occur. The low level of production in the river in October-Decem- ber is exceptional. Similar hydrographic conditions in 1897 Pl. XI.) yield a 5- to 10- fold greater production. It is not im- probable that the monthly collections of 1894 may be interca- lated in the depressions between plankton pulses of greater vol- ume, and thus inadequately represent the real production. Pro- duction in Quiver Lake in the months represented in our rec- ords in 1894 exceeded that in channel waters only in September- October, when a slight run-off occurred, and that in Thomp- son’s Lakein June, July, September, and December, but a run- off of any consequence occurred only in June and for a week each in July and September. Apparently the channel plank- ton in this year was largely independent and indigenous in origin, deriving but little enrichment from impounding back- waters, and not infrequently diluted by their contributions. 1895. (BIE, XOCVL., SOX OIL, SOV EE) To the river, represented by 50 collections, Quiver Lake, by 15, and Thompson’s Lake, by 14, there are added this year, Dogfish Lake, represented by 12, and Flag Lake, by 4 collections in late autumn—a total of 93. The table on page 482 gives the monthly distribution of production in the several localities, and indicates their relation to the general averages. This is a year of lowest levels, averaging only 3.61 ft. above low water, and also one of high plankton content. On the basis of means of monthly averages, the average content in the river, 5.91 cm.’ per m.’, is the largest recorded, exceeding the average of all monthly averages, 2.71, by 118 per cent., and being sec- ond in the list if we base comparisons on the average of all col- lections. This high content in river waters must be attributed 432 to stable hydrographic conditions, abrupt changes being limited to less than 8 weeks in the year (Pl. [X.), and to low water and consequent slackening in the channel with increase of time PLANKTON PRODUCTION IN 1895.* Station Feb. Apr. May | June July Aug. HMlimoissRivieraasteaceee bee ieeeie cee —|] 0.01/-—| 3.18}..}.....)+130.42/+] 9.33/+] 4.03 @utver hake. Ape. oe dices Seteie bere || CeOBI || SsC9) [5 a|looccullelle soca) —|| @.39//=|| ©.25 apes hice state Queer merce oc dlinele es | 8.20]..].....|—] 0.12/+] 2.99]--] 1.11 Flag Lake... es Saeed Sethauall) SERGs. elllaya lfadtetete ll awed] eve ternal ees resent Thompson’s Lake...............-|.-|....+-+|28.201-+-|61.44|—| 9.42I-+| 4.831—| 3.09 Mean of Station | Sept. Oet Nov. Dec. monthly Averages TtinGis Rivers Vee wetcwe ce. “eee =|. 1.52 || -O. 57. (| S62 iol lenlA sear OwiversGake sw ae tee ey Sell Ce Nl Ose) |! OOH ||| O24 ||| OS Dogfish. Cake .....05-06.6-2e2-05 | 305) |—t O.§2 |sa) gor Io) 5.92 Ie geste [oy ios Bie ie Seemarand ane BA, Selon Lab) eens +] 57.76 |+] 14.40 4] 4.82 |4] 25.66 Thompson's kake sl. peeks —| 3.58 —| 3.15 I—| 5.07 '—| 1.00 I+] 13.31 *The minus sign signifies below average and the plus sign above. for the breeding of the plankton. The larger amounts of plank- ton were found only during stable conditions, and floods inva- riably depleted the volume of the plankton. These periods of stable conditions occur in summer and late autumn, and we find the plankton content at such times 8- to 30- fold that in contiguous flood conditions. In the river the monthly produc- tion exceeds the monthly average for our records in 5 out of the 9 months represented, the exceptions being February, when stagnation under the ice prevailed, April, a vernal period of low water without overflow, September, a month of repeated floods, and October, when an unusually early decline in temper- ature occurs. The stable conditions which attend low water thus favor the increase in the plankton content per m.*, though by reason of the lower levels and slackened current the total volume pro- duced in the stream asa whole must be greatly diminished by such hydrographic conditions. The results of this low-water year upon production in Quiv- er Lake (Pl. XXX.) are as a whole diametrically opposite to those in the river. Here in the lake, production falls below 433 the average, the mean of the monthly averages (.65 em.*) being 63 per cent. below that of all monthly averages of Quiver Lake, and but a ninth of the production in adjacent channel waters. The cause of this very marked contrast is to be found in the relative dominance of tributary waters of recent origin and of coarse aquatic vegetation in the lake,—a dominance increas- ing as levels fall_—and accordingly we find in this year of low- est levels the least annual production (see table on p. 429). Production is not only low on the average but also lower than the average in every month of record save September, when it rises 22 percent. above the mean content for that month. This is a month of higher river levels,and a similar tendency to in- creased production is to be found in the August flood (PIX XVI.). In Dogfish Lake, production in this year averages for the 8 months represented 3.3 cm.’ per m.’—44 percent: less than that in the adjacent channel waters and 408 per cent. more than that in Quiver Lake. This is 4 per cent. more than the average monthly content, and 18 per cent. less than production in the same months of the following year. The deficiency below channel production may be attributed to the effect of vegeta- tion, and the excess over that in the contiguous waters of Quiver Lake to the absence of access of tributary waters of re- cent origin. Production is above the average for 4 of the 8 months, the exceptions being April, June, August, and October. The absence of overflow is apparently the cause of the suppres- sion of the vernal pulses in April and June, and the dominance of vegetation may be responsible for the low production in August and October, both low-water months. The months of plankton content exceeding the monthly average are 4; July and September—months of flood, and consequently of impound- ing and greater extent of vegetation-free water—and Novem- ber and December—times of lessened growth on the part of the aquatic vegetation, of rising levels, and of some decay of organic matters from the summer’s growth. Causes of hke nature are the basis for the large production iu Flag Lake in the late autumn months, when in October-No 434 vember the production is 10- to 8- fold the average, and in De- cember 9 per cent. above the mean for that month. In Thompson’s Lake the mean of the monthly averages, 13.31 em. per m,’ is 61 per cent. in excess of the mean of all the months of our records, though but 3 of the 9 months repre- sented in the records of 1895 are above the average. The first two of these, April and May, owe their predominance to a ver- nal pulse of unusual volume, andthe small number of collections gives these months abnormally high averages, while the large production in July may be attributed to the enrichment of the lake in this year by an invasion of plankton-rich river water from the channel (Pl. XXXVI.). The deficiency shown in the records of the remaining 6 months, falling from 10 to 70 per cent. below the averages of our records for these months, finds its possible explanation in the relatively greater dominance of vegetation in the lake in this season, due to two successive years of low water and the prevailing low levels. Collections in this year were, moreover, taken near the margin of the veg- etation belt of the lake. Production in this, the second, year of low water, and the lowest in our term of operations in all the backwater plankton stations but Quiver Lake, is above the average in the year as a whole, though falling below it in 57 per cent. of the time rep- resented, The apparent suppression of the vernal pulse in the river and in Quiver and Dogtish lakes may be attributed to the ab- sence of spring overflow and the consequent elimination of vast impounding and breeding areas normally present at this season, and also to the direct delivery of tributary water to the chan- nel and increased relative diluent action of the slight April rise (Pl. IX.) in both the river and Quiver Lake. The low levels also serve to bring the vegetation of the two lakes named into early dominance, and the relative occupancy is also increased by the second year of low water and no removal of the accumu- lated growth by flood action. Thompson’s Lake, on the other hand, owing to its great extent of open water, is less affected 435 by the low levels, the cutting off of breeding backwaters, and the relative occupancy by vegetation, and consequently a ver- nal pulse of unusual dimensions reaches a culmination in its area. The June-July pulse of the river, abnormal in its location and relative size and apparently without equivalent elsewhere, is due to the unusual development of a stagnation plankton in the sewage-laden river in a period when rising temperatures hasten the decay of its unusual load of organic matter. The causes above enumerated render this the year of great- est fertility, in so far as our records reveal production, in the river and in Thompson’s and Flag lakes, the next to the greatest in Dogfish Lake, and the least in Quiver Lake. The low levels preclude any extensive impounding of flood waters and, moreover, the period of run-off is of shght extent. The rise in plankton content (PI. IX.) in the river following the April, July, and September floods is suggestive of the effect of impounding, the plankton content (cf. Pl. XXVI., XXX., and XXXVI.) being generally greater in the discharging backwaters examined than in the recipient channel during these run-offs. At all other seasons in our records for this year there is scant opportunity for enrichment by tributary backwaters, and but httle suggestion of it. 1896. (PIX XOX, XVII XO) XE XV Ee: This is the most fully represented year in our series in the number of stations examined. There are 76 collections in the Illinois, 9 in Spoon River, and 31, 30, 27, 27, and 29 respectively in Quiver, Dogtish, Flag, Thompson’s, and Phelps lakes—a total of 229. It was a year of higher levels, averaging 6.98 ft. above low water,—almost twice the record of the preceding year,—and witnessed a series of recurrent floods approaching or surpassing bank height of the stream. The accompanying table gives a summary of the data of production, 456 PLANKTON PRODUCTION IN 1896.* Station Jan: || Feb. | Mareh | Aipr.9 |) May June | July PilinoiswRiverseeeeeeeeee —] .O1]/—| 0.02!|—| 0.07 |+| 5.67/—| 1.30|—' 0.72 BS ey | Spoon Riversscsen< once |enes Pelt roa loe Oe ee Fees esa ty ct ley, Goat Quiver Lake............|-- .03/+] 1.75|/+| 1.85 |+)12.12}/—| 2.99/-++] 1.26;— 0.30 Dopish Ulake.t 222.0020: +} .53/4-| 2.04)+] 3.43)—|15.11/+] 9.63/+-| 2.64/— 0.91 IRIEVOM ILA eiaoaadon soto +} .29+] 3.064] 1.02 |+]17.72/+\51.93]/—| 2.13/— 3-33 Thompson’s Lake....... —-| 2.51/+] 2.58)+ |10.26|+|16.94|—|23.11|—| 4.92] -— 2.73 Rhelpspllakereceseeeece |—l 1.89, +112. 14|+]19.20 +125 .44! —|12.96}/—! 2.90,-+ 9.03 Mean of Station. Aug. Sept. Oct. | Nov. Dec. | monthly averages illinois, River. .2.220.2.. = [08 82 |= [9938 |S) Par Sheet ieeyon aimeees SOOM IRIE e500 bone sees —| ¢.0i8}—) 0.005|/-++ 005)—| .005)—] .002/—| 0.007 Quiver Dake, 22. occ +| 2.46 |—| 0.31 |+) 2.10 |+] .24 |+]0.92 [+] 2-19 Dots Lakes. cso oe 89h |=] Ne 631s p 5250 26 |—|2.20 |+] 3.99 Filagn Moakce ancpceckens ates oe tr) 3-74 2-99 = 5-07 |—| 4-37 |= \4dO 1a Onae Thompson’s Lake....... —| 4.74 |—| 4.20 |—, 2.81 |—| 2.66 | —|2.56 |—| 6.67 Phelps lalve..c0 iene.c oe ==|| 810) || oollsccoce —‘' 23.ce4 |—| 32.00 |..1.....]—1 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. 452), 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, inaverage of all collections, 1.16 cm.* (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 437 o1.9 ft. It is not so much the extent of movement in levels as it is distribution which produces this depression in production. Repetition of floods at relatively brief intervals is the cause of low production in channel waters in 1896. Not only is the mean production in the river below normal, but all of the monthly averages are likewise from 97 to 35 per cent. below their averages except those of April and December, which are 23 and 7 per cent. above. Hydrographic conditions in these two months of higher production are such as to favor in- crease in plankton, since in both cases there is a period of 6-8 weeks of slowly declining levels with little or no interruption in which a more abundant plankton becomes established. The relation of production in the channel and the back- waters in 1896 is also very different from that in 1895. While in 1895, owing to low levels in general and to the prolongation of rising levels, the backwaters were contributing but a shght and interrupted run-off to the channel, and production, as shown in monthly averages, was in the case of backwaters examined predominantly lower than in the channel, we find in 1896, owing to higher levels, that there is more impounding, and, owing to the slow declines, a larger continuance of it and more run-off to the channel. There are, for example, 157 days of falling levels above 6 ft. distributed through 10 months, while impound- ing and run-off continues for 90 days more at lower levels and in decreased volume. Not only are backwaters thus contribut- ing to the channel for a much longer period in 1896, but their plankton content is predominantly higher than that in the channel. An examination of the relative production (see table on p. 436) reveals but 3 out of the 58 monthly averages of pro- duction in backwaters, excluding Spoon River, which are less than coincident production in the channel. These are for Dogtish and Quiver lakes in July, and forthelatter in September—both months of lowest water, and consequent predominance of creek and spring water in Quiver and of vegetation in both lakes. This relatively greater production in the backwaters is not due to increased absolute production as compared with 1895 except 458 in the case of Quiver and Dogfish lakes (2.59 and 5.01 em.*) when we find for these lakes the highest mean annual production in our years of records. In the case of Flag, Thompson’s, and Phelps lakes the annual mean falls below the average on the basis of monthly averages, though the average of all collections in Flag and Thompson’s lakes is above the general average in these lakes (see table on p. 429). The former basis of compari- son is the better one, since it equalizes to some extent the ine- quality in the distribution of collections. The plankton content in backwaters in this year of recurrent floods is thus increased in some instances and but slightly reduced in others, with the net result of predominantly higher plankton content than in the current-swept channel, and a much greater total production. The effect of the run-off of the impounded backwaters upon channel plankton may be seen in the river planktograph for 1596 (Pl. X.), where the March, June, August, October, and November floods in each case reduce the plankton as they rise, and are attended by a noticeable increase as levels fall again. That other factors are involved may be seen in the rise in plankton attending the rising flood of August, and in the de- clines following the increases in plankton content in the midst of rapid run-off in apparently favorable hydrographic condi- tions in nearly every instance above cited. The effect of the midwinter flood following two years of low water, which permitted the accumulation in bottom-land forests, marshes,and backwaters of a great amount of vegetation, may be traced in the /arge production in winter and early spring. In the table on page 436 it will be noted that in the months of February—April production is above the average in every back- water in each month except in Dogfish Lake in April. More- over, the largest records for this season of the year were ob- tained in this year in Dogfish, Flag, and Phelps lakes in all three months and in Quiver and Thompson’s lakes in the first two, that is, in a total of 13 out of the 15 monthly averages. During the remainder of the year, from May to December, production in the backwaters generally falls below the average 459 production for those months in the several localities. Out of the 51 monthly averages in this period (see table on p. 436) 37 are below the mean, and of the 14 above, 9 occur in Dogfish and Quiver lakes, where reduction in vegetation. increases the pro- duction. The cause of this sharp contrast in the relative pro- duction in the two parts of the year, is to be found in the hy- drographic conditions which affect the nutrition of the plank- ton. The rank vegetation which filled the forests, marshes, and margins of the lakes during the two years of low water was submerged by December flood, and by this early submer- gence and subsequent decay increased the production in winter months. This early consumption of the products of decay and the relatively early run-off of the spring flood combined to make vernal production relatively low in 1896. A comparison of the planktographs of the 6 localities (see plates named at the head of this section) will indicate the suppression of the April-May, or vernal, pulse in every locality but Phelps Lake. No plausible explanation for its occurrence here when it is not found elsewhere is apparent. Subsequent floods by their brief duration and frequent repetition tend to impoverish the back- waters by the removal of vegetation and organic debris, and by the run-off of nutrition in solution or suspension and of the de- veloping plankton. In more stable conditions or floods of longer duration, when the backwaters are impounded for longer times, —largely by the restraining action of high water in the Missis- sippi,—decay is longer continued, and there is more opportunity for the utilization of its products by a plankton not removed quickly by the rapid run-off of the flood. A comparison of the different regions even in this one year bears out this inference. Spoon River, scoured by repeated floods and swept by constant and relatively rapid current, con- tains only an insignificant amount (.007 cm.’ per m.*) of plank- ton. Quiver and Dogfish lakes, rid to some extent of the accu- mulated growing vegetation and enriched by dead vegetation in their submerged borders, yield in this year the largest an- nual mean of monthly averages (2.19 and 3.99) in our records. 440 In these lakes at levels prevalent in this year the impounding or reservoir function is at its height. The higher levels reduce the relative proportion of creek and spring water, and the ab- sence of extreme high water cuts off to large extent the cur- rent of general overflow through the lakes. Accordingly, pro- duction here in the year as a whole exceeds the mean of all monthly averages by 25 (Quiver) and 26 (Dogfish) per cent., and exceeds the mean of the respective monthly averages in 8 and 7 of the 12 months. In the case of Thompson’s Lake, on the other hand, the hydrographic conditions are such that its pre- dominantly reservoir function is interfered with as each recur- rent flood passes the level of 6 ft. and starts the current of channel water in at the northern, and out at the southern, end of the lake (PI. II.). Accordingly production in this lake falls below the average of all monthly averages by 24 per cent., and the individual monthly means are likewise deficient in 9 of the 12 cases. In Flag Lake the production (8.31 or 13.83 em.’ per m.*) is 10 per cent. below the mean of all monthly averages, or 21 per cent. above that of all collections, and exceeds the means of the monthly averages in 6 of the 12 months. The accumulated vegetation in and about this lake, and the moderate levels which develop the reservoir function of the area without per- mitting any current of overflow through it tend to keep up the level of production. It is in considerable excess of that in sub- sequent years, but falls below that of the exceptional condi- tions of the preceding autumn, discussed on page 385. The moderate levels free Phelps Lake from currents of overflow and increase its impounding function, and we find here, accordingly, the largest production recorded in any of the backwaters in this year. The fact that the production (14.74 cm.° per m.°) falls 84 per cent. below the mean of all monthly averages for the lake and is deficientin 6 of the 12 months, may perhaps be due in part to the fact that in the previous year the lake had been a cultivated corn field and had not therefore been seeded by the spores and winter eggs of planktonts left on the 44] drying up of the lake. In September the lake did temporarily dry up only to be re-entered by the October flood, in which an unusual plankton (51.6 cm.*) at once developed. 1897. CRIS XT OCT XC VALE XO, MEX XIV, SEVIS, STE ) This year is represented by 34 collections in the Illinois, and 138 in Spoon River, and by 24, 6, 7, 18, and 9, in Quiver, Dogtish, Flag, Thompson’s, and Phelps lakes. It was a year of protracted winter and spring flood, a late June rise, and pro- longed low water in summer and autumn. The data of compar- ative production are given in the accompanying table. PLANKTON PRODUCTION IN 1897.* Station | Feb. | March | April | May | June | July | Illinois River........ All .o4 {+/ .38 [2 Beary |= 5rooe | 27 ee 4.69 Spoon River. 7... |, 2047 || / 0074/2 .048;-+| .440; + | el Se ae miveriGake sc. cases: Fail iets he seat +)13.38 }|—| 1.29 |+/ 1.26 |+ 89 Dogfish Lake ....... 2 -15 |—| .48 ie 8.18 le 1 GASH 22 AS alee lag eaker fee! SS) ae i 8.55 |—\10.61 |+] 4.87 | 4] 7.13 Thompson’s Lake... |—, .27 |—| .65 | —|10.38 |—| 7.88 ;—| 3.59 |—| 3.31 PhelpsRakes2..:.:.. = <19 | --| 1.44 | —| 4.26 |—|22.58 |—| .42 |+] 9.49 = | | | | | Mean of Station Aug. | Sept. | Oct. | Nov. | Dec. monthly - averages Illinois Rivers: 272: —| 3.65 |-+! 8.83 |+] 5.95 | +] 1.00 |— .56 |-+| 3.28 Spoon River...-..0.. felt! 6524) al Bo D3t tos anee cn +] 2.671}-+, .559] +) 1.225 OuiverFakesnaeraee —| .21 |—| .16 |; =| .04 |=] .09 } —, .007/} —| 1.71 Dogtish Wakes 2... alleen eats | FEIN esters | Riba se | fall eooe | : ; weeahs —| 2.65 CpG AK Gr sorcerer Syl bsyrovots consol | cave | Snes Sysueses |e eel ietencr sores Peel tevez scorn ker ereeceirene —| 5.34 Thompson’s Lake ... +)19.40 +/to.01 | +/35.35 | +/16.67 |+ 6.98 |+]10.4t Phelps lakes ae. scsi 12 ora Obes | Weel mecre ete eles on ek J rice oe —| 9.15 *The minus sign signifies below average and the plus sign above. The infrequency of collections in January-June and the suspension of work in Dogfish, Flag, and Phelps lakes before the year ended, render general comparisons with other years of less value because of insufficient data. The annual channel production, 3.28 em.’ per m,*,—the mean of monthly averages,—or 3.69, the average of all collections, is 21 or 68 per cent, respectively above the means, and 6 of the 11 442 months represented also exhibit a plankton content above the average. The causes of this large production are to be found mainly in the prolonged low water, slackened current, and sew- age contamination of the last half of the year. No large ver- nal pulse appears in the records of the river or its backwaters. It was either intercalated between collections, and thus escaped detection, or the early winter flood, as in the previous year, by its washing away sources of nutrition prior to the season and temperature of greatest plankton development, tended to depress production below normal at this season. It was to be expected, however, that a large plankton development took place in the stable conditions attending the three months of declining levels which followed (Pl. XI.) the crest of the spring flood. If such a development took place it would tend to raise still higher the level of production established by our records for this year. The relation which the backwaters bear to channel produc- tion in 1897 is correlated with the hydrographic conditions. In January—June, a period of continued high water, the plankton content in the backwaters exceeds that in the channel in 22 of the 30 monthly averages (see table on p. 441), or, omitting Spoon River, which does not properly belong in the category of back- waters, in 21 out of 25. This was a period of extensive and long-continued impound- ing and of high levels, and, in the last three months (Pl. XI.), of rapid decline and therefore of speedy run-off and rapid cur- rent in channel waters, factors which favor the breeding of the plankton in the reservoir regions and cut down the time for its development in the channel, in which barren tributary waters of recent origin and plankton-rich backwaters impounded in the more or less current-free areas for a greater or less length of time, depending upon the direction and rate of change in river levels, are mingled in varying proportions. In the low-water period, July-December, stability of hydro- graphic conditions continues throughout, while the extreme low levels maintained for so long a time make the channel wa- 443 ters very largely independent of backwaters and tributaries by reason of cutting off of communication in some cases and ces- sation of run-off in others. Along with this independence goes increased fertility by virtue of greater relative contamination by sewage and longer time for breeding by reason of the slack- ened current. Asa result, production in channel waters reach- es in July-November, 1897, a level unsurpassed in our records, rising above the monthly means of all years (see table fol- lowing page 342) 11 per cent. in July, 245 per cent. in Sep- tember, 250 per cent. in October, and 14 per cent. in Novem- ber, but falling behind by 6 per cent. in August. As a result of this increased development of plankton in the channel the pro- duction in backwaters becomes relatively less with respect to the channel production than in.times of high water. Thus in July-December, backwater plankton exceeds that in the chan- nel in only 10 out of 19 monthly averages, or, omitting Spoon River, in 8 out of 15—-a marked change from the excess in the preceding six months, 21 out of 25. This is the only season in all our records in which the plank- ton content of Spoon River rises above the barren level of .1 cm. per m.’, or less. The production now rises to a level ap- proximating, and in November—-December exceeding, that in the channel asa result of the practical absence of current and consequent increase in the reservoir function of the stream. The course of production this year in the various backwa- ters is in most instances strikingly similar to that in the chan- nel in its major outlines. Thus in all of them (Pl. XXVIII, XXXII, XXXIV., XXXVIII., and XLI.) production rises grad- ually from the midwinter minimum to an unusually low ver- nal pulse in April-May and declines again in June-July. At this point collections were suspended in Dogfish and Flag lakes. Production in channel waters rises again in August and con- tinues at high levels till November, and in hike manner and with even greater amplitude in Thompson’s Lake (Pl. XXX- VIII.), while a similar movement is initiated in Phelps Lake (Pl. XLI.), only to be stopped by the drying up of the lake in 444 September. Quiver Lake, however (Pl. XXVIII.), pursues a different course, production there dropping to a level rarely exceeding .5 cm.’ for the remainder of the year. This results from the greater relative volume of spring and creek water in this lake. The discharge from Quiver Creek and the marginal springs continued with relatively much less diminution through the autumnal drouth than that from Spoon River, with the result of making this lake far less productive of plankton at this season than Spoon River (ef. Pl. XXIII. and XXVIII.). 1898. (PL XI, XXIV., XXTK MXGXIV, AXKTXS XLT) This year is represented by 52 collections in the [lhnois and 11 in Spoon River, and by 26, 6, 25, and 22. respectively in Quiver, Flag, Thompson’s, and Phelps lakes. It was a year of normally located and fully developed spring floods, followed by low water in summer much disturbed by minor floods, with a subsequent autumnal rise of unusual proportions. This re- sulted in the highest average river levels in our years of opera- tion, 8.02 ft.—a level almost equaling bank height. The accompanying table gives the data of comparative production of the different localities in this year. PLANKTON PRODUCTION IN 1898.* Station Jan. | Feb. | March | April : May | June | July HWE IRM |B) ols || .27 |+| .33 |—| 4.40]+ 11.30 | —| 3.96 | — 58 Spoon River|;+] .017,;—| .o16)-+] .124]..]..... =" 5023), ||| 2090)//==)) 2036 Ouiverakes| 02) 2 |store eS a 16.27 | +] 2.23 |— 16 lle Ieee ll sal) poate lire eecteuspceeell leael ieperctieren: pot pe a a Misterenere ta | eacl|meetee =|, §36 Thom, Ls. || 7iz2el lh 6a lezen al Seal oetog sions 2.08 PhelpsLake|..| ..... eee Se el eal lao aa) || alae tere eee | | Mean of Station Avge’ 4 Sept Oct. Nov. Dec. monthly | | averages Illinois River....... — .o1 |—| .69 |—| .24 |—| .25 |+] .99 | —| 2.03 SPOON River. t.2.25. |= a _ ae => 001) —|' cor |||) Sool) — | ee2 Oulverdakera ae — .22 | 23 }+ 73, ,+] 1.74 | +] 1.969 laps alkene ee = .03 ses 3 ie oe eters sal ence Ben ice =| 5.3} Thompson’s Lake.. | —| 2.63 | —| 2.66 1.25 |—| 1.17 | +] 3.58 | —| 5.06 Phelps Lake....... +1139.85 | 147.25 __ | +132. 31 |-+15.14 | +]21.96 | 137.34 * The minus s sign signifies below average and the plus sign above. 445 The average production in the Illinois for the year is 2.03 em.’ per m.*, or 2.13 cm.’ if the average of all collections is taken instead of the mean of monthly averages. This is 25 per cent: below the mean of monthly averages, or 3 per cent. below that of all collections. This depression in production is due to the disturbed and irregular hydrographic conditions which throughout most of the year left insufficient time for the plank- ton to breed. As shown by the + and — signs in the table, production in channel waters is below the average in 7 of the 12 months, and 4 of the 7 deficiencies fall continuously in the disturbed period of August-November. The decline below the average produc- tion in this disturbed period ranges from 72 to 86 per cent. The other 5 months of deficient production are April, June, and Ju- ly—4, 45, and 86 per cent. below their averages. The April defi- cit is due to the delay in the vernal pulse, while those of June and July are due, possibly, to the after effects of the high ver- nal pulse of May. Production in excess of the average is found in January-March, during the unusually slow rise of the spring flood, in which the catastrophic effect alike of the sudden and higher floods and of stagnation under ice in low water is eliminated. Production is also high, by 86 per cent. in May, as a result of the delayed culmination of the vernal pulse —the largest one, moreover, found in our records in channel waters. It isalso high by 40 per cent. in December, when declining levels (Pl. XII.) afford the stability necessary for the breeding of the plankton. Production in Spoon River, as might be expected in a year of much flood water, falls to a barren level exceeding .1 cm.’ in but a single instance, in March (.124), when waters of general overflow mingle with those of the tributary to a considerable extent. Production in the backwaters in 1898 again bears a striking resemblance, throughout, to the course it presents in the chan- nel. The higher levels conduce to greater unity in the envi- ronment, and to greater interchange between many localities, 446 and the plankton accordingly foliows similar lines of develop- ment. This is noticeably prominent in the planktographs of the river and Quiver and Thompson’s lakes, as will be seen by a comparison of Plates XII., XXIX., and XXXIX. The princi- pal features of the common course of production are the coinci- dence of the May and June pulses, the subsequent low level of development throughout the summer and early autumn, and the December rise. These three bodies of water were submerged in the common flood of overflow in February—June, and the succeeding minor flushes of summer and autumn caused re- current ingress and egress of water from and to the channel. The similarity in the course of production in these three local- ities and the lessened differences in the amplitude of produc- tion in this year are in no small measure the consequence of this equalizing action of this interchange due to floods. Phelps Lake (Pl. XLII.) is the only one of our backwaters which diverges from this marked agreement, and its divergen- ces are increased by its intimate connection with Spoon River during high levels and its isolation during the remainder of the year. The vernal pulse of this year is noticeable for its amplitude, its meteroric appearance and disappearance, and its coinci- dence in different localities. It follows a prolonged period of extreme overflow, and a very gradual and somewhat tardy rise in vernal temperatures. It appears, moreover, at levels of 10— 11 ft., just when great stretches of bottom-lands are contribut- ing their last run-off to the channel. The submergence of the bottom-lands did not occur until late in February in this year, so that the period of vernal increase in the plankton was not preceded by a long interval of flood, as in 1896 and 1897, which might carry away in suspension or solution those organic sub- stances in the vast amount of vegetable detritus which covered the bottom-land as a result of the low water of the preceding autumn, and which may have been utilized by the plankton in this extraordinary vernal development as a result of the juxta- position of flood and vernal growing season. 447 The comparison of backwater and channel production in 1898 is in some contrast with that in 1897. In 1897, omitting Spoon River, production in backwaters exceeded that in the channel in 29 of 40 monthly averages, or in 73 per cent., while in 1898 the excess occurs only in 26 of 37, or in 67 per cent. The excess, moreover, is frequently of less amplitude in the lat- ter year, as is seen in the relation of the means of the monthly averages of backwaters and channel in the two years. Thus in 1897 production in Thompson’s Lake (10.41) was 217 per cent. in excess of that in the channel (3.28), while in 1898 (5.06 and 2.03) the excess was only 149 per cent. In Phelps Lake, on the other hand, production rose to the unparalleled height of 37.34, the mean of the monthly averages, 67 per cent. above the mean of all monthly averages, and fourfold that in the previous year, when the last 4 months were cut off by the drying up of the lake. Production in Quiver Lake in this year is 1.96 cm.*, mean of monthly averages, or 2.44, average of all collections—12 per cent. and 44 per cent. above the mean respectively of all years. This larger production is due to the excessive production in the vernal pulses in May and June and to the high levels of pro- duction in November and December, rising 138, 78, 217, and 176 per cent. above the average respectively for these months. The hydrographic conditions in these months in Quiver Lake are favorable to increased production. The May and June pulses are at levels (11 ft.) when impounded run-off from slightly submerged bottom-lands to the north was rapidly draining to the channel through the lake. In November and December there was at least double the usual volume of water in the lake, due to a 34 per cent. increase in river levels, with a considera- ble reduction in the proportion of tributary water and increase in the impounding function. In the remaining 8 months of the year, then, average production is 79 per cent. below the general average for those months in Quiver Lake. This very considerable depression in production falls in the main in the period of greatest hydrographic disturbance. This body of water, owing to its frequent invasion by channel waters and to 448 its own influx of tributary water from Quiver Creek, is the most liable of all the backwaters examined by us to hydrographic disturbance. It is therefore not surprising that in this year of extreme disturbance we should find marked depression for a long period in this lake. The total movement in levels in 1898 is 67.2 ft. (see table p. 163), 44 per cent. above the average. Of this, 50.8 ft. fall in the 8 months of depressed production, that is, 76 per cent. of the movement occurs in 67 per cent. of the time. To this relative excess of fluctuation in levels, and proba- bly to large access of local flood and spring water, we must at- tribute the low production in Quiver Lake in these months. Thompson’s Lake has an average production of 5.06 cm.’, or, if all collections are averaged, 5.71 cm.*, 39 and 28 per cent. below the respective averages for all years (see table, p. 429). Not only is the general average below normal, but all of the monthly averages, save only those of January (7.22) and De- cember (3.58), are likewise deficient by from 2 to 88 per cent. The large January production is the largest plankton content in this month in any year or locality, and accompanies an invasion and impounding of sewage-laden river waters in the lake (ef, Pl XV. sand i: ), The cause of the low production throughout the remainder of the year is again to be found in the hydrographic conditions. During 8 months of the year (at levelsabove 6 ft., see Pl. XX XIX.) the lake is swept by a gentle current entering at the northern end and discharging to the channel at the lower. There is, thus, in this year more than the usual run-off, not only of or- ganic matters in solution and suspension, received with the waters of ingress, but also those developed in its impounded waters or about its shores. This tends to impoverish the waters, and interferes with the accumulation and flux of or- ganic matter in the plankton which manifested itself in such amplitude in the low water of the preceding year (Pl. XXX- VIIIL.). Toa much less extent than in Quiver Lake is the de- pressing effect of flood waters seen in the broader expanse of this body of water. While in the former the production in 449 months of flood disturbance falls 79 per cent. below the mean for that season, we find in the 10 months of depression in Thompson’s Lake a falling off of only 46 per cent. The differ- ence is due to the greater proportion of creek and spring water of recent origin in the former, and to the greater reservoir ca- pacity and consequent longer impounding, as a rule, of the sewage-laden channel waters which predominate in the latter backwater. Production in Phelps Lake is 37.34 em.’ per m.*, or, if all collections are averaged, 36.31—67 or 84 per cent. above the means for all years. In keeping with these facts we find that the monthly averages equal or exceed the means for their months in 7 of the 10 months of record, the greatest excess oc- curring during the period of complete isolation of the lake. 1899. (PETIT 5. XC | POC, OX ELT.) This year is represented by 13 collections in the Illinois and 3 in Spoon River, and by 7 each in Quiver and Thompson’s lakes and 6 in Phelps Lake, all in the first three months of the year. This was a period of a slow rise of the river in January to bank height, with an equally slow decline in the next month followed by an abrupt and well-sustained March flood. ‘The data of comparative production are brought together in the following table. PLANKTON PRODUCTION IN 1899. Mean of Station Jan. Feb. | March | monthly | averages KbinGistRiversvawe oa etn ence ose mee —| .18 |+) .81 |-+) .28 |+] .42* SPOON WRN Tes xt ay Ry iecraacie sols) oe Sere yet i—| .005;/*| .oor;—| .026)—| .or1 Ouivenibakes eae eos tnc ko ee |+) .77 |+]} 1.05 |—| .15 ;+] .66 MBhompsomis eaKer on. h..s a creer Cerra mite —| 1.64 |+] 1.59 |—| .21 | —| 1.15 BEL PS takes rchates Sc A Aciireeonis ees =f=1, 4109" ||) 4670) | al Oe soled *The + and — signs for this column refer to the relation of these averages to the mean of all January-March collections; otherwise they are used as heretofore. The average production in these winter months in the river is .42 cm.’ per m.*, or, if all collections are averaged, .41 cm.° 450) This is the largest production for this period of the year in our records, exceeding the average, .24 cm.*, by 75 per cent. and ap- proximating or exceeding the monthly average in each instance. The cause is to be found in the relatively stable conditions at a level sufficient to prevent sewage stagnation beneath the ice- sheet which covered the stream prior to the March flood. Spoon River continued to discharge barren waters (av. .011 em.*), while the backwaters, with the exception of Quiver and Thompson’s lakes in March, produced a more abundant plank- ton than the channel. Quiver Lake produces .66 cm.’,—an ex- cess of 20 per cent. above the usual production for this season,— and in the first two months has 2- to 3- fold the usual plankton content as a result of the moderate levels which make the lake a reservoir without greatly increasing its current. When, how- ever, the general current of overflow passes through it with the March flood, production drops to one fifth of the mean for that month. In Thompson’s Lake the mean production is 1.15 em.’, 56 per cent. below the mean production for these months. It also falls below in January and March, when hydrographic con- ditions are such (Pl. XX XIX.) that channel water is diverted through it, and rises above the mean by 25 per cent. in Febru- ary, when the run-off is diminished by falling levels. In Phelps Lake the mean production, 3.74 em.*, is 23 per cent. below the mean for these months. This lowered production, which also falls below the mean in the last two months, is due, in part at least, to the invasion of Spoon River water with the higher levels. The various years of our operations may be briefly charac- terized as follows. 1894. O. | a | OQ | a, | O | a, | B(s8| 6/88] 8 |s8| 8 | 88) § | 8s) gee B 1A Eas Et) ea ft | A | A Sn ie TSG) Se 2h «a eeaig Yin ita asell Sa Oe Le | eceie Soe Te a SRT eco eee eee 80.25] 0.74 WOR eer ssrl oes oe 32 OVO ER tanya ane 8 BuilO|eeeseacte (eae 80. 30.42 1896/32.75 | 0.01] 33.7 | 0.02) 39.52} 0.07] 64.54) 5§.67| 72.7 | 1.30] 74.7 | 0.72 POOP lciee sch eee 2.25] 0.04] 43.8 | 0.38] 60 SE 0623-4) a5 <021- 75 0.27 1898|32.7 -45| 32.12] 0.27] 43.3 | 0.33] 53.32] 4.40) 65.8 | 11.30] 78.8] 3.96 1899132.9 | 0.18] 32 Coro A Mes ea a 90 +3) ee a Pee ers (Riana ollaans Hi olleticothallomte ot July | August | September October November | December b > | | Gc. | oben ee ce | a a. | os Gc. | ose) g |es) 8 jae) seit 8 es wee Ee | a ow tH a fe | ae a Ay fH Ou in Thompson’s Lake, 29 per cent. The difference would be in- creased if the aberrant data of the late autumn of 1897 were removed from the records. Low temperatures thus tend to depress production in both channel and backwaters, and high temperatures to increase it. The minimum production of the year occurs in the river, and with few exceptions in the backwaters, in January-Febru- ary, the two months of minimum temperature. With the period of rising temperatures in March—May there comes gen- erally at all of the stations a rapid rise in plankton production, culminating in the vernal pulse in the last days of April or the first of May at about 60°-70°. The effect of this is seen in the generally high average production in April and May in both channel and backwaters. With the establishment of the sum- mer period of maximum temperatures, which includes the months of June-September with the exception of a few days 473 of rising and falling temperatures at the beginning and close of the season, there comes, as a rule, a decline in production from that of the vernal season. In channel waters this amounts to 16 per cent. of vernal production, or, omitting the single aberrant datum of June 1895, to 44 per cent. In the backwa- ters, owing to the combination with various local factors, such as tributary waters and vegetation, the change from vernal pro- duction in midsummer varies greatly in different localities. Thus, in Quiver Lake, where vegetation and the proportion of tributary waters is increased in summer, the decline in that season amounts to 87 per cent., while in Dogfish Lake, where veg- etation alone is the main disturbing factor, the decline is 74 per cent. of the vernal production, as seen in the April-May aver- ages. In Flag Lake, where also vegetation enters as a disturb- ing factor, the decline is 80 per cent. In Thompson’s Lake, where disturbing local factors are less in evidence, it is but 69 per cent. In Phelps Lake, in contrast with all the other localities, pro- duction during the period of maximum heat exceeds that in the vernal season by 68 per cent. Thus the period of maximum heat in most localities attends a depression in production, but the exception in Phelps Lake is so striking as to preclude any conclusion that summer heat is necessarily inimical to large production, or that it is of necessity the most potent of the co- operating factors. The omission of the averages for August and September in 1898 from the Phelps Lake data would make the average production in the period of maximum heat 33 per cent. below that of the vernal months, and bring this locality into agreement with the other stations as to the depressing effect of summer heat in plankton production. It should be emphasized in this connection that these conclusions apply to catches of the silk net only, that the summer temperatures of our waters approximate 80° on the average and frequently rise above it,andthat temperature is only one of the factors involved. Following the period of maximum summer heat is that of decline in October-November—including also a part of Sep- tember, or even December in some seasons—to the winter min- 474 imum. In general, this is a period of declining plankton in channel waters, where production in these two months falls 71 per cent. below that in the preceding four months of maximum heat, and in Quiver Lake, where it falls 48 percent. below. On the other hand, in the rest of the backwaters there is a shght in- crease in these two months as compared with the production in the period of maximum heat. In Dogfish, Flag, Thompson’s and Phelps lakes the October-November increase in percent- ages over the average summer production in each of these sev- eral localities is 35, 362, 26, and 11 per cent. respectively. In view of these divergent tendencies in production under similar temperature conditions it is evident that other factors are operative, or at least more potent, in controlling autumnal pro- duction. The October production is as a rule higher than that of November, and suggests a tendency towards an autumnal pulse comparable with the vernal pulse but of lesser amplitude. The vernal pulse occurs in rising temperatures of 60°-70°, and this autumnal one in falling temperatures of 60°—50°. The month of December does not on the average quite at- tain the minimum winter temperature, though in some years, as in 1897 and 1898, it approached closely to it. Neither does the plankton production drop to so low a level on the average or in individual years in channel waters as during the two colder months which follow. In general the same relation ex- ists in the backwaters, though exceptions occur—principally in Thompson’s Lake. Thus, in a large way, temperature plays an important part in controlling plankton production. Additional proof of its potency is to be found in the correlations between production and exceptional divergences from the normal course of tem- perature changes, such, for example, as early or late vernal rise or autumnal decline. The accompanying table (p. 475), kindly furnished by Mr. W.G. Burns, Section Director for Illinois of the U. S. Weather Bureau, gives the vernal air temperatures for 1896-1898, and permits a comparison with the course of plankton production. 475 MONTHLY MEANS OF VERNAL TEMPERATURES FOR ILLINOIS AND OF PLANKTON PRODUCTION—CM.® PER M?®, 1896 1897 1898 Temper- Temper- Temper- ature |Plankton| ature |Plankton| ature’ | Plankton (Fahr.) (Fahr.) (Fahr.) North section... 31.9 34.4 39.0 Central section. 36.4 AI.1 44.4 March . |South’rn section 40.6 07 46.8 .38 48.7 33 State, average.. 35.6 39.5 43.4 Normale sr 37-6 | 37.6 37.6 North section. . 55-3 Ay e2 46.9 Central section 59-9 51.3 50.5 April ..|South’rn section; - 63.6 | 5.67 55.0 5.11 53.0 4.40 State, average.) 59.0 | 50.4 49.6 Normale ef-s 51.8 | 51.8 51.8 North section.. 67.2 S7ials 59.1 Central section. 70.6 59.7 63.0 May...|South’rn section} 71.7 1.30 62.1 5.62 66.8 II.30 State, average..| 69.5 59.3 62.2 Normale ss. 61.8 61.8 61.8 The most notable instances of correlation between deflec- tions of temperature and plankton production are to be seen in the early spring of 1896 and the late autumn of 1897. These correlations have already been noted in connection with the discussion of production in the river and the several back- waters. The mean temperatures of the air here given corrob- orate our conclusions based on the relatively scanty data of water temperatures delineated in the thermographs of the plates accompanying this paper. Thus, the spring of 1896 was 2° be- low normal in the state as a whole in March, but was 7.2° above normal in April, and 9.4° above the mean for 1898. Mean plankton production is also higher in April in 1596 than in any other year. Indeed, in this month the descending scale of mean temperatures in 1896-1898 is accompanied by a similar scale of decreasing mean production of plankton, and, as has been noted in the discussions of the course of production in the river and backwaters, the vernal pulse of 1896 is from 10-14 days earlier than in 1898, when, as this table of mean tempera- tures shows, the April mean of air temperatures was 9°—10° below that of 1896. 476 So also in 1897, the means of our records of water tempera- tures for September, October, and November of that year are 2.9°, 7.6°, and 2.7° above the average of the monthly means for all years. This maintenance of high temperatures into the pe- riod of normal autumnal decline is apparently one of the fac- tors tending to make production in these months of this year greatly exceed that of the same season in other years. In chan- nel waters in these months of 1897 (see table following p. 542) production is from 135 to 250 per cent. above the mean of all years, and often 10- to 20-fold that in other years. In Thompson’s Lake the excess in 1897 is even greater, ranging from 87 to 235 per cent. of the mean of all years, and from 1.6 to 28 times that in the same months in other years. The higher temperatures do not suffice, however, in the case of Quiver Lake, to overcome the other factors tending to depress production there in these months, and we must conclude that, although all-pervading and potent, temperature is nevertheless not always pre-emi- nent among the environing factors of the plankton. We thus find that ina general way, in conjunction with other factors, rising temperatures tend to increase, and falling to decrease, plankton production, and that in the same locality the warmer months generally yield more plankton than the colder ones. On the other hand, minimum temperatures when once established are not of themselves inimical to a considera- ble plankton production. Evidence of this is to be found in the not infrequently increased production in December over that of several months preceding. ‘This is perhaps most notice- able in the records of 1898. Thus in channel waters the am- plitude of the December pulse (PI. XII.) exceeds that of all other months since the last of June, and the December maxi- mum in Phelps Lake (43.14) exceeds in amplitude all other pro- duction in our records for 1898 in all other localities save only the single apex of the vernal pulse (51.89) in Thompson’s Lake. It is, however, only about one fifth of the August maximum (224.48, Pl. XLII.) in Phelps Lake itself, so that the depressing effect of lower temperatures is still apparent if we limit com- parisons to a single locality. 477 The effect of the autumnal decline, and, in general, of low- ered temperatures, in depressing production is apparent in not a few instances in ourrecords. It can be seen in the October- November thermographs and curves of plankton production of channel waters in 1894-1898. and in those of Quiver Lake for the same years; is much less apparent in Thompson’s Lake, especially in 1897, even when temperatures have fallen; and is often but feebly developed in Dogfish and Flag lakes in 1895-1897, while in Phelps Lake in 1896 and 1898 there are pulses of considerable magnitude (51.6, and 99.86) in this period of decline of temperature. The minima demarking these pulses are, however, of less than the usual amplitude. This depressing effect is thus traceable in all localities, but is bet- ter developed in stream than in lake waters, appearing most clearly in the channel and Quiver Lake, where, at this season of the year, tributary waters are present in considerable propor- tion. Our water temperatures and the records of the United States Weather Bureau at Havana and elsewhere in our lo- cality reveal many instances of heat pulses at various seasons of the year. There is little regularity in their duration or amplitude. When plotted from the means of the tri-daily readings of the air temperatures at Havana they do not ex- hibit delimitations as well defined as those, for example, of a fully observed plankton pulse. Their amplitude, except in winter months, rarely exceeds 20° between extremes, and their duration is usually less than a fortnight between minima. That these fluctuations affect the course of plankton production can- not be doubted. A detailed comparison of the course of produc- tion in 1896 and the thermograph of that year will show that, predominantly, vises of temperature attend or precede rising pro- duction, while declines in heat are often correlated with de- creased production. This may be largely coincidence, or, in some cases, the common effect of cooler, barren flood-waters, especially in the case of the records of channel production. A close comparison, however, of the planktograph in Phelps 478 9681 $b 8 hb st "BURARTT 1B Sainjesadua} sre Ajiep-143 jo sydeisousay ]—'Dd ‘914 | oT 09 BL ‘Bog 479 Lake—where flood factors are largely excluded—and the ther- mograph (air) for 1896 will serve to suggest the possibility of a causal nexus between the two phenomena of fluctuations in heat and some of the movements in plankton production. The many exceptions to any close correlation emphasize, however, the fact that heat is only one of the many factors involved in the problem, and also indicate the necessity for much fuller plankton data, with closer interval and the proper quantitative representation of the minute forms now lost by leakage through the silk, for any adequate discussion of the problem. The present data serve only to suggest the problem for investiga- tion. The effect of the ice-sheet upon the course of plankton pro- duction is apparent in a number of instances in our records. The most noticeable case was the extermination of the plank- ton in the channel in February, 1895, by the ice-sheet of two months’ duration; but this catastrophe was not repeated else- where in our records in this or other years. Indeed, owing to the fact that the period of the ice blockade is usually one of lower levels and more stable conditions, we find generally that production under the ice, even at minimum temperatures, rises above prior or subsequent levels. An inspection of the plates, especially those of 1898, will show repeated instances of this phenomenon in both channel and backwaters. One of the most striking phenomena in all our records is this winter pro- duction under the ice-sheet in 1898-1899, a production which in the river attained an amplitude in December (.99) not equaled since June, and in February (.81) one surpassed only by the August (.91) and December means. In Quiver Lake likewise, the December (1.74), January (.77), and February (1.05) means are all considerably in excess of the June-Novem- ber production, the average of the winter months (1.19) being over threefold greater than that of the warmer months (.33) named. In Thompson’s Lake also the midwinter production in this season was large, reaching an average of 1.94 for the winter months above named, and only 1.96 for the five preceding 480 months, while the amplitude of the December and January pulses was surpassed but once from June to December. Con- ditions under the ice at minimum temperatures were thus in these years and localities quite as favorabie to the quantita- tive development of the plankton as were the conditions prey- alent in summer and autumn. As a whole, then, temperature changes bear an important relation to the course of plankton production, but at times they are not more potent than other factors. An abundant plankton may develop at any temperature within the normal seasonal range provided other factors favor it, but generally the ampli- tude is less in lower or in falling temperatures, and greater in higher or in rising ones. The relations here discussed between the volume of plank- ton and temperature depend primarily upon adaptations of particular species to temperature—a subject which will be dis- cussed in another connection. LIGHT AND PLANKTON PRODUCTION, There are at hand no adequate data on this subject, and it is, moreover, complicated with the thermal and other forms of solar energy and with the problem of turbidity in the water itself. No detailed comparison is afforded by the data, espe- cially since the more minute forms are not adequately repre- sented by the catches of the silk net, and it is largely these synthetic organisms, chlorophyll-bearing alge and flagellates, which are most dependent upon light for their growth and re- production. Our data alike of hght and plankton are thus deficient. Nevertheless, in the chain of relations, the catch of the silk net—largely of animal plankton—is, at most, but a few links removed from these synthetic organisms, and it must therefore in some measure reflect their quantitative fluctua- tions. Our data suggest a few inferences concerning the rela- tion of light and plankton production. The period of greatest illumination les between March 20 and September 22, and owing to the proximity of these dates 481 to the ends of the months it will be possible, for the purpose of utilizing our data in monthly totals and means, to divide the year into two periods, April-September and October—March, of greater and less illumination respectively. The contrast in illumination is further heightened by the fact—derived from the following table of cloudy days—that the number (at Havana, 159) of cloudy days between the vernal and autumnal equi- noxes is only about one half that (311) between the autumnal and vernal. On the average, the season of greatest hght is also the season of greatest production. Thus, in the channel waters average monthly production in April-September (4.76) is seven- fold that in October—March (.67), and in the backwaters, such as Quiver, Thompson’s, and Phelps lakes, it is respectively 5-, 2.2-, and 1.6-fold greater. The records of individual years in all of the localities will be found to exhibit a similar relation- ship. We may infer, accordingly, that the increased lhght be- tween the vernal and autumnal equinoxes tends to increase production, and that the decreased amount in the remainder of the year tends to lower it. It operates, of course, in conjunc- tion with other factors, and our records contain not a few in- stances where production in the period of less illumination ex- ceeds that in the period of greater light. For example, on December 20, 1898, in the minimum illumination of the year and under an ice-sheet 21 em. thick, which still further reduced the light, the plankton production in Thompson’s Lake reached an amplitude (2.58) exceeding that on June 21 (2.47) in the same lake in maximum illumination,an amplitude, moreover, sur- passed but once from June to October. Other factors are thus, at times, at least, more potent than light in controlling production. A phenomenon of like import exists in the conditions of illumination and production in Quiver and Thompson’s lakes. Both lakes are of approximately the same depth, but the former, especially in low-water conditions, has remarkably clear water, the bottom being generally visible, while the latter is always more turbid, and light penetrates the water far less completely. Nevertheless, the lake, with most illumination, 482 yields least plankton. The factors of vegetation of the coarser sort and of tributary waters serve here to modify and overbal- ance light as a controlling factor in production. From the data of the U. 8S. Weather Bureau at Springfield, Mr. W. G. Burns, Section Director, has kindly furnished me the records of the number of cloudy days per month in 1894-1899 observed at Peoria, Havana, and Springfield. These are given in the accompanying table. The records for Havana have also been plotted on Plates VII]—XIII. in the uppermost row of squares. NUMBER OF CLOUDY DAYS. Sales o|.|o| 5 BS |S|SICl Ele olm|Slelelele| sla oct Lee Sor (tes bo} Vv Per) (b) o ° S | eee ee Se Sle te | = eo Nene oo eae i a Ea ESM on |= 1894 | 13) 13, 8| 12| 19) 51 o| 7| 9) 94 ral 15/133] 5 1895, | 00) 271 73/0 2) ol 7 A eal ree elton a Springheld cs: Aree a-.o8 a 12) 16) 8) 9} 9) 7), 2 12| 97) tel asi ized 1897 | 16] 15' 20] 17} 4! ro] 5] 2] 3] 4} 12) 21/127] 3 FOO8 | 12) 12) 16) 43] TEES 8i 10] 15 12|126} 1 1899 | 16] 14, 21] 12] 17; 7] 13] 7 6| 8] 16! 10/147] 6 Total | 82] 73, 92] 75] 62] 45| 44) 30] 42| 47| 841 91|767 1894. 7} 8: <7) Gl \ealial voles él io] 7| 61] 1 1895 || 6) 3 to! oO} 3h al al 93 ay 2 13) 13743 Hayanarice cek othe ee 1896; 7} OF 4! 3) 5} 6 4} 2| 11) 3] 10] 9g! 70] 2 1897 | 10] 10) 17] 13) 61 6 o| 4 2] 4 12) 15) gol 6 1898) |, 11 Tol v1) Gl 8) 4 §3l 18) 2G Si Ponies 1899 | 7| 6 16) 4) 5) 3) 5| 3) 3] 6] 10] 7| 75] 4 Total | 48} 43) 65] 41) 31} 23] 16] 23] 25] 37] 60] 58!470]... 1894 IT} 9} 6] 8) 9] ‘ol 3) Si 8) <6) a2) aaesien 1895 | 10} 8! ro} 8] 4] 5] 6) 5] 4] 2! 18] 10} 99} 2 REOKIAT Recent te acs ree 2200 17] 10) 8) 3) 6 8) 6} 2) ro) ro} 16) 14}1I0) 4 1897 13) 14) 18) 16) 951) (6 eal) 4 Bi) 3ih rs | ate agiies 1898 15| 14, 14} 10) 13 ©}, AA tsi) A Co} er 13/126 6 1899 | 12} 12) 16) 10, 8] 2] 5) 5] 6| 6) 13) 41106) 3 Total! 781 6 | 72! 55' 45! 27| 23! 29! 35! 43! 851 78646)... The variations in the relative cloudiness in the three local- ities in many months and in the total number of cloudy days in the several years in the three localities render any correla- tion with production largely conjectural and close comparisons 483 impossible. That the reduction in light due to clouds does in a measure affect production might be inferred from the August —October records in 1896 and 1898. In the two years named, cloudy days and production in August are 2 and 8, and 1.12 and .91 cm.’ per m.’ respectively ; in September they are 11 and 2, -and .38 and .69; and in October 8 and 16, and 1.11 and .24. Hy- drographic conditions are not remarkably different in the two years, and while their differences in this respect are doubtless potent, causing differences in production, it still seems prob- able that the fluctuations in light are also operative. In any event in these three months the mean production runs higher in the year of fewer cloudy days and lower in the year of less sunshine. Similar relations will be found to exist generally in the production of the backwaters for these months (see table following p. 342). The statistical data of the synthetic organisms to be discussed in Part IL. of this paper still further serve to demonstrate the correlation of light and plankton pro- duction. The necessity of hght for the process of photosynthe- sis on the part of the phytoplankton places this factor at the very beginning of the chain of relations whose later links are the larger animals of the zoéplankton which constitute the greater proportion of the volume of the catch of the silk net— the basis of the present discussion. VEGETATION AND PLANKTON PRODUCTION, It is evident that our investigations afford a unique oppor- tunity of determining the effect of vegetation (the word being here used to refer to the coarser aquatic growth as distin- guished from the microscopic phytoplankton) upon the course of plankton production with reference to both its volume and constitution. The conclusions to be drawn from our observations with reference to volumetric production, already suggested in the detailed discussion of production, will be summarized and dis- cussed here, though some of the data upon which they rest lie outside the scope of the present paper. 484 l. Other things being equal, bodies of fresh water free from vegetation (submerged macro-flora) produce more plank- ton than those rich in such vegetation.* Thus, the amount of plankton produced (as indicated by the averages of all of our collections in the several localities examined) in our open waters is from two to eleven times as great as it is m our lakes” closed by vegetation. As shown in the table on page 429, the average planktons in Thompson’s and Phelps lakes are 7.94 and and 19.65 em.’ perm.’ respectively, while in Quiver and Dogfish lakes the quantity is only 1.70 and 4.22. Flag Lake, with an average of 11.46 cm.’, is an interesting exception to this con- trast which will be discussed in another connection. The con- trast 1s even more striking if the averages of the monthly averages for all the years.are made the basis of comparison, as in the following table and diagram. COMPARISON OF PLANKTON PRODUCTION IN VEGETATION-POOR AND VEGETATION-RICH WATERS. Vegetation-poor Vegetation-rich Month Sc ee eal elon TiShien Thompson’s|ln, 1.7.3. Ratio Quiver Lake| D°8ts sampson's |Phelps Lake JaANWATY 323 frag caleniahiewr 547] 53 3.79 BE20 1:9 HCDIMALY fa: cccinsme pei or .67 1.10 1:27 5.68 1:4 Manchina ae masa nee si 1.96 2.96 5.68 1:3 April ec crac aneiete cine ere 7.26 10.50 14.49 L177, BI sls Maly acnio se tetceise Senne 6.85 5.79 29.59 25.33 1:4 UNE Wieee crc erie 1.25 Wn Zs 10.66 II.40 1:7 ULVnsscvacieis: sarneteenrrsee 78 1.95 4.74 8.50 1:5 ATUP UST .te sarcenictermocen te Bi Zab 6.19 58.12 1:20 September se 2525 cc deve S/H 2.39 5.37 47.25 Lw7, Octoberssocnscoeees seen .69 3.05 10.64 27.68 1:10 November: :o..020h0ne 23 2.64 6.39 41.57 1:17 December. .-ceceeecteoee 63 3.76 3.08 21.096 1:6 Gr’d av. of monthly av.. ays 3.16 8.26 22.35 1:6 On this basis, the waters full of aquatic vegetation pro- duce throughout the whole year less plankton than waters free from such growths. Relatively few exceptions to this rela- * This relation of vegetation to the plankton may be formulated as follows: The amount of plankton produced by bodies of fresh water is, other things being equal, in some inverse ratio proportional to the amount of its gross aquatic vegeta- tion of the submerged sort. 485 ! ! ' 1 i ae he re pe = = Ad. iy es Fic. D.—Seasonal distribution of plankton production in vegetation-poor and vegetation-rich waters, based on the averages of the monthly averages for all years of collection. Quiver Lake, tion will be found in the individual collections recorded in Tables V. and IX. and VI. and VIL, or in the monthly averages of the table following page 342. This striking contrast is still more enhanced by the statement of the monthly ratios of pro- ductivity in waters rich and poor in vegetation. These range from | to 1.5 in April to 1 to 20 in August. The. fluctuations in the ratio are of themselves very significant. During the period from February to July inclusive the ratio is at its lowest, ranging from | to 1.5 to 1 to 7. Excepting only the month of July, this is the period of high water, in which the vegetation, if present, occupies a much smaller proportion of the volume of the lake, and is therefore to a proportionate degree restricted in its effect upon the plankton. Under such flood conditions these several localities are more or less merged in the general 456 overflowed district, and are to a varying degree traversed by waters from the bottom-lands above and adjacent to them, and the purely local factors of their environment, such as vegeta- tion, thus become less potent. Again, it is not until the latter part of this period that the vegetation attains the development which continues throughout the remainder of the summer. The relative barrenness (in plankton) of the vegetation-rich waters is thus least striking when the vegetation is least in evidence. During the period from August to November inclusive the ratios are very much higher, rising to 1 to 16 or 20. This is the low-water period, when the vegetation in the vegetation-rich lakes isat its maximum development both in quantity and in the relative volume of the lake occupied by it. It is also at such times that these several bodies of water are more distinct units of environment, with their local factors no longer merged by flood conditions. The relative barrenness of the vegetation- rich waters is thus greatest when the vegetation is at its maxi- mum development and is most emphasized as a factor in the environment. The conclusion from this comparison of the mean production of plankton in vegetation-rich and in vegetation-poor waters in our locality is thus inevitable that vegetation (in the usual sense of the word) is inimical to the development of an abundant plankton. It may also be said that the contrast would be considerably heightened if it were possible to elimi- nate from all the collections on which this comparison is based the adventitious organisms—such as small insect larve, mol- lusks, oligochetes, Hydra, ete., which form a considerable vol- ume of many of our catches in the vegetation-rich waters. On the other hand, it must be maintained that the vegeta- tion is only one of the factors concerned in the phenomenon pre- sented by this contrast. It is quite probable that other fac- tors, especially the current, tributary waters, and the chemic- al constituents of the water, affect the problem in hand. Dur- ing high water both Thompson’s Lake and the Dogfish-Quiver region are traversed by a considerable current from the bottom- 487 lands above. The elevated deposits of Spoon River and the consequent crowding of the channel of the river to the east bluff at Havana force all of the water of overflow (at stages below about 16 feet) to seek the main channel. The configura- tion of the low-lying bottoms above is such (see Pl. II.) that the lakes in question form natural channels for the movement of a large body of impounded water. This movement is well marked at stages above eight feet. So far as I am able to judge from field observations, the current conditions in Thompson’s Lake and the Dogtish-Quiver area are not greatly different. The current continues in both lakes as levels fall to six feet, at which level Thompson’s Lake loses its connection with the river through the “cut road” (PI. II.), and movements in it at lower levels are confined to those due to ingress and egress of water through the slough, and are consequently inconsider- able. On the other hand, Quiver Lake continues to be traversed by the discharge from Quiver Creek, and our collections were usually made in the channel in the vegetation. In Dogfish Lake at low stages there is no current traversing the lake. Phelps Lake hes at so high a level that only the floods exceed- ing eleven feet bring it into connection with the general cur- rent of overflow, which in this case generally comes from Spoon River. Below this level the only movement in its water is the gentle one due to the receding flood. So far, then, as the current is concerned, it is a common though not equally distributed factor at high-water stages in all areas compared, while at low water it is an important feature in the environ- ment in Quiver Lake but is practically absent in the other three localities. This fact undoubtedly accounts in part for the barrenness of the waters of Quiver Lake (1.53 cm.’ per m.’, or only .55 for the average of low-water periods—i. e. below 5 ft.) as compared with those of Dogfish (4.22), Thompson’s (8.13) and Phelps (19.44) lakes. This current does not, however, traverse or appreciably affect the waters of Dogfish Lake, and their bar- renness still remains for contrast with the productiveness of the vegetation-poor waters of Thompson’s and Phelps lakes. 485 Data are not available for a full comparison of the chemic- al constituents of all the waters here under consideration. No data whatever are available for Dogfish and Phelps lakes, and only sanitary analyses for Quiver and Thompson’s lakes. These shed no light on the relative amounts of phosphates and carbon dioxid in the water, both important elements in the growth of plants. On the other hand, data for a comparison of the ammonia and the nitrates are found in Tables XII. and XIII. and Plates XLVIII. and XLIX. The nitrates, in so far as they are concerned,—as shown in the accompanying table, CHEMICAL ANALYSES, SEPTEMBER, 1897, TO MARCH, I8g9. AVERAGES OF ALL ANALYSES——PARTS PER MILLION. Thompson’s Lake |Quiver Lake MreeammOonlaacnceeecre ecicieeicieleciee oe mene .422 .199 Albuminord ammonutlalssn2 .sccise 42 oh as salve lees: .546 .293 INGTITES 22 tear ycce eis eer ceca cosa Sabin eeeioae .048 .023 INGtrAtSS ee irae cee cena rare eerie otoein rere ree eee .640 .708 which gives the averages for coincident periods of examination in 1897-1899,—offer no solution for the marked contrast in plankton production which the waters in question exhibit, for the amounts present differ but slightly in the two lakes. The plottings in Plates XLVIII. and XLIX. show that the nitrates run low during the period from June 1 to October 1, which is approximately that of the maximum development of vegeta- tion. The averages for this period are .244 and .222 respect- ively for Thompson’s and Quiver lakes in 1898. This is almost identical in the two lakes, and may represent an unutilized minimum of nitrates, the utilized portion supporting predomi- nantly the phytoplankton in Thompson’s ‘Lake and the gross vegetation in Quiver Lake. During the remainder of the year the contrast between the two lakes in the matter of nitrates is more marked, the average being .923 and .684 respectively. So far as any contrast appears in the matter of nitrates the waters of Quiver Lake are, if anything, a ‘trifle richer than those of Thompson’s Lake. 489 It is different, however, in the matter of nitrites, which are about twice as abundant in Thompson’s Lake as in Quiver, and the same ratio also holds approximately for the free and al- buminoid ammonia. . These are all substances indicating or- ganic matters in the process of decay, or available for decay and thus for plant nutrition. These data show clearly that in these particulars the waters of Thompson’s Lake are much richer than those of Quiver, and this difference is undoubtedly one of the factors on which the contrast in plankton produc- tion depends. The more abundant plankton of the former lake may itself be one of the sources contributing to the or- ganic decay here indicated. This contrast in the chemical constituents in part at least follows from the sources from which the waters in the two lakes are derived. River water impounded from receding floods and more or less charged with sewage and industrial wastes constitutes the principal source of the water in Thomp- son’s Lake. Spring and creek waters replace this very slowly, and every rise in the river introduces a new supply of richly fertilized water which at levels above six feet trav- erses the whole lake. Quiver Lake is subject to like invasions, but its more abundant supply of creek and spring water coun- teracts their influence to some extent and soon replaces their contributions. A consideration of these other factors, current and chem- ical constituents, makes it probable that they also are efficient in causing the contrast in plankton productivity in the two lakes. How much of this contrast is due to vegetation and how much to their agency is a matter upon which conclusive evidence is needed. Experiment in the field may yield con- clusions that will be final. Some evidence corroborative of my contention that the vegetation of Quiver Lake is inimical to the development of its plankton is afforded from two sources; (1) the examination of Matanzas Lake, and (2) the comparison of the plankton pro- duction of Quiver Lakein yearsof abundant and scant vegetation. 490 Matanzas Lake (PI. II.) more than any other body of water in our field of operations resembles Quiver Lake in the various factors of its environment,only upon a somewhat smaller scale. Like Quiver Lake it has free communication with the river at all levels, is subject to the same conditions of invasion and submergence, has an eastern sandy and springy shore with lit- toral vegetation, a western one of alluvium, and, between, a bottom changing from sand to mud. The depth and bottom configuration are very similar, and there is a supply of creek and spring water roughly proportionate to the size of the lake. The two lakes are thus strikingly alike save only in the matter of vegetation. The vegetation in Matanzas Lake is confined to a narrow belt of the littoral zone along the greater part of the eastern margin and to a little Ceratophyllum adjacent to it and fringing the western shore in places. Less than 5 per cent. of its area is thus occupied. Quiver Lake, on the other hand, has at all times a more abundant flora, which even in the years of its least development holds possession of not less than 30 per cent. of its area. Under these circumstances a comparison of the production of the two lakes should throw some lght upon the effect of vegetation upon the development of the plankton. No chronological series of collections has been made by us in Matanzas Lake. A few isolated collections have indicated that it is rich in plankton, and two thorough tests of the local distribution of the plankton, made in 1896, afford a basis for comparison with Quiver Lake at that time. Fifteen collections with the plankton pump were made in various parts of Matan- zas Lake on July 9, and twenty-five, similarly distributed, on August 14. The averages of the plankton per m.’ of water in these collections and the amounts found in Dogfish and Quiver lakes on the days following (July 10 and August 15) are given in the accompanying table (p. 491). Averages for the months of July and August in the several years are also given for Quiv- er and Dogfish lakes. The production of plankton in Matanzas Lake on the dates 49] PLANKTON PRODUCTION IN MATANZAS LAKE COMPARED WITH THAT IN QUIVER AND DOGFISH LAKES. Date Matanzas Lake Ouiver Lake |posice ane) RN ei sce een folg Se Bes ee Be ake ae Beeld cena tna es Stake teeta, o Teale ea We me oUt 1 co a = PR eae emess ae Berra ee Te oar age een Secale oe wi Cltiae gee AF ee ae a imma eh Re cg eS ee Dy eee rae 0 ae ely ee ae of collection above indicated is approximately twice that of Quiver and Dogfish lakes, where vegetation was at that time somewhat more abundant. In 1896 Quiver Lake was freer from vegetation than at any other time in the period of our opera- tions, and the contrast between the production of the two lakes appears greater if we consider other years or the average for all collections in the months named, On the latter basis the ratio rises to 3 to 1 for July and 8 to 1 for August in the comparison of Matanzas and Quiver lakes. In the case of Dog- fish Lake the contrast is less striking, but still evident. Ma- tanzas Lake, similar in its environment to Quiver Lake save in the matter of vegetation, thus produces a more abundant plank- ton, and we may infer that the vegetation of the latter is in- imical to the development of plankton in its waters, A second line of evidence bearing upon the question under discussion is to be found in the production in Quiver Lake itself under different conditions of vegetation. In 1594, and still more in 1895, owing to low water in early summer, vegetation was very abundant in Quiver Lake. The growth of Cerato- phylum and Elodea choked its waters from shore to shore and from bottom to surface except in a narrow poorly defined chan- 492 nel found in the lower end of the lake. This part of the lake is shown in Plates XV. and XVI., which portray the conditions as they appeared in 1894 and 1896 respectively. The upper end of the lake and its western arm, Dogfish Lake, are shown in Plates XVII. and XVIIT., the latter having been photographed in 1896, when the center of the lake was not so full of “moss” as during the preceding year. The repeated floods of 1896 swept the lake of much of its vegetation, and during the three following summers it never recovered the abundant flora which it presented in 1895. In 1897 and 1898 there was also much less vegetation than in 1895, though somewhat more than in 1896. The plankton production, as shown in Table V. and graphically presented in Plates XXV.-XXIX., does not uni- formly rise and fall as the vegetation decreases or increases. The phenomenon of its fluctuations involves many other fac- tors, among which the effect of vegetation may perhaps be de- tected. The average production for the years of vegetation, 1.08 and .78 cm.’ per m.* of water, is surpassed in 1896 (2.59) and 1898 (2.44) but notin 1897 (.88). The marked increase in 1896 over the production of 1895 parallels the great change in vege- tation, and is also accompanied by higher water, theaverage for the year being over three feet above that of 1895. This differ- ence in levels also tended to decrease the relative extent of the vegetation in 1896. In Dogfish Lake also the contrast in vege- tation in the two years, 1895 and 1896, is well marked, and the average plankton production rises from 3.25 to 5.01 em.’ per m.* The omission of winter collections in 1895 makes the contrast less striking. Allowing for this, it is probable that the plank- ton production is practically doubled in the year of decreased vegetation... This is approximately the ratio of increase in Quiver Lake in 1596 and 1898. Other causes, such as current and chemical conditions, doubtless share in producing this change in the plankton, but it seems highly probable that the reduction in vegetation caused a considerable part of this doubling in the plankton production. A comparison of the plankton production of the same body of water (Quiver and 495 Dogfish lakes) in different years thus shows that more plank- ton is produced in years of little, than in years of much, vege- tation, and tends to confirm the view that abundant submerged vegetation is inimical to the production of plankton. An inspection of the planktographs in Plates VITI.—XIII. and XXV.—XLIT. shows the frequent occurrence of an autumn maximum, often well defined. In the planktographs of Quiver and Dogfish lakes, this autumn maximum is usually depressed or missing. The spring maximum occurs, as a rule, while the lake is full of water from the general overflow, and it is therefore not purely a local phenomenon. The midsummer and autumn plankton, on the other hand, is entirely a local product, and the depression of the autumn maximum must be due to local influences. in 1896, in both Quiver and Dogfish lakes the autumn maximum occurs in two or three sharply marked prominences, that of October 14 (3.52 and 6.60) being a Melosira-Syncheta assemblage, typical for the autumn season. This was a year in which there was little vegetation and high (for autumn) water, the vegetation being, consequently, at a minimum as a factor environing the plankton. In other years this autumn maximum (see Tables VI. and VII.) is less evident. In 1894 the apparent maximum on September 5-6 is almost wholly due to the development of Oscillaria at a time of local stagnation consequent upon backwater. In 1895 there was in Quiver Lake a maximum on September 6 (1.57), due in part to au- tumnal plankton and in part to adventitious organisms. Dogfish Lake exhibits a somewhat larger maximum (4.65) on Septem- ber 17, which is mainly normal in its components. The No- vember-December maximum of 1895 in this lake is wholly due to adventitious organisms, and may be disregarded in this con- nection. At their best, these maxima in vegetation-rich years are but one half to one third the magnitude of those of 1896, a vegetation-poor year. In Quiver Lake in 1897 and 1898 the autumn maximum is again depressed almost beyond discern- ing. Although vegetation was not abundant in the lake in these two years, the period of the autumn maximum was one 494 of prolonged low water in both years, so that whatever vegeta- tion was present occupied relatively a large proportion of the area and volume of the lake, especially as contrasted with the conditions in 1896. The available data thus indicate that veg- etation is inimical to the production of plankton, as shown not only in the general averages but also in these maxima, which may be regarded as the expression par excellence of the produc- tive capacity of the lake. There still remains for consideration, with reference to the effect of vegetation upon plankton production, the result of our examination of Flag Lake. As before stated, this is a marsh choked with a rank semiaquatic growth whose extent, abundance, and relative occupation of the area of the lake equals or exceeds that in any other body of water examined by us. If our thesis that vegetation is inimical to the production of plankton be true, we might expect to find here, of all places, barren waters. ‘This is not, however, the case; for,as shown in the table of comparison of plankton production on page 429, Flag Lake is very productive (11.46 em.’ per m.*), being ex- ceeded only by Phelps Lake (19.65). The only indication that vegetation is in the least inimical to the plankton in the lake is suggested in Plate XX XIII. The amount of plankton present from May 15 to October 1, the erowing period of vegetation, is only 2.87 em.’ per m.*, while in spring and late autumn (April 1 to May 15 and October 1 to December 30) it is 32.89. In Phelps Lake, which, save for vege- tation, is much like Flag Lake, the plankton during the period of dominance of vegetation in 1896 averages 7.64, and in 1898 52.43 em.’, 3 to 18 times as much as in the vegetation-rich waters of Flag Lake, In the character of the vegetation in Flag Lake lies, I be- lieve, the explanation of its fertility in plankton. Two kinds are predominant, neither of which is present in like abundance in Quiver Lake. These are (1) succulent vegetation, such as Sagittaria, Pontederia, Nymphea, and Nelumbo, which die down and undergo considerable decay in the early fall, and (2) the 495 emergent vegetation, principally Scirpus, which, on account of its growth and structure, does not reach an advanced stage of decay until ice and winter floods have broken it down. With rising spring temperature it yields to decay and releases a great store of nitrogen which the phytoplankton can utilize. Both of these types of vegetation are rooted in the humus and allu- vial deposits of the lake,and both are to some degree emergent. They thus draw their supply of food (dissolved salts and gases) largely from soil waters and the air, and less from the supply in solution in the water of the lake. The submerged and non- rooting vegetation (Ceratophyllum and Klodea) is not abundant in Flag Lake, so that the food supply in the lake waters is not drawn upon to any great extent by the aquatic vegetation, and it thus becomes available for the phytoplankton, which, in turn, supports the zodplankton. The products of decay of the succulent and emergent vegetation, on the other hand, are in large part released directly into the lake waters, and at times (fall and spring) when the plankton reaches its greatest devel- opment.in this region. Owing to its character and to the pro- tected situation of the lake the vegetation is never swept away by floods, nor is the lake traversed by any marked current as are both Thompson’s and Quiver lakes. The fertilizing effect of the decaying vegetation is thus more localized in this region than in the other bodies of water examined by us. The data from Flag Lake thus throw hght upon the effect of emergent and rooted vegetation—which is typically of the littoral type—upon the plankton. They indicate that this kind of vegetation favors the development of the plankton by add- ing to the food materials in the water, while at the same time it does not to a large degree compete with the phytoplankton in the consumption of the food thus released by its decay. In 1896 a series of examinations of the local distribution of the plankton in Quiver, Matanzas, and Thompson’s lakes was made by the pumping method, and since the collections were made in the areas of vegetation as well as in the open water they might also be examined to determine, if possible, the effect 496 of vegetation on the distribution of the plankton. Only the quan- titative data are at present available, and the results are con- flicting. In some cases the plankton is greater in the vegeta- tion than in the adjacent open water; in others the reverse is true. These examinations were made at times of unstable river levels, and the movements of water consequent thereupon make any satisfactory analysis difficult. The general conclu- sion that lakes full of vegetation (Quiver) are everywhere poor in plankton, while those relatively free from it (Thomp- son’s and Matanzas) support generally a more abundant plank- ton is in all cases upheld by these examinations. This poverty of the plankton in vegetation-rich lakes was one of the surprises of our investigations, and, so far as I have been able to ascertain, it contradicts the general expectation among observers of aquatic life. It has its parallel in the pau- city of life in tropical forests and among the pines and red- woods of the Sierras. It is fundamentally a problem of nutri- tion, and inheres in the utilization of the available food supply by a single type, or a few types, of plants which do not them- selves in turn afford support for an abundant or varied animal life. Wherever the depth of the water, the currents, the winds, or other factors, prevent the development of a submerged aquatic flora, the nutrient materials for plant growth—the oxy- gen, the carbon dioxid, the nitrates, phosphates, sulphates, and carbonates dissolved in the water—are utilized by the phyto- plankton, which, in turn, supports the zoéplankton. The en- tire production of such a lake takes the form of plankton and, in turn, of those larger species, insect larvee, mollusks, and fish, which are directly or indirectly supported by it. When, on the other hand, the conditions are such that a submerged non- rooted aquatic flora obtains possession of a lake,—as, for exam- ple, Ceratophyllum and Elodea in Quiver Lake,—these nutrient materials are appropriated by it to the great reduction, even practical exclusion, of the phytoplankton. In the struggle which must ensue between the phytoplankton and the sub- 497 merged aquatic flora for the possession of a body of water capable of supporting either, the greater duration and perma- nence of the larger plants which constitute the submerged flora must in the long run inure to the advantage of the latter, hence they predominate over the phytoplankton wherever other conditions favor their appearance. This coarse sub- merged vegetation cannot in its living condition be utilized by the minute organisms of the zodplankton, and only such as feed upon it in decay can find sustenance in the vegetation-rich lake. The absence of an abundant phytoplankton and of the greater part of the zobplankton may thus be accounted for in waters rich in submerged and non-rooted vegetation. The total production of such a body of water consists mainly of a large amount of coarse aquatic vegetation, which but few ani- mals can utilize in its living condition as food, and a much re- duced plankton, largely of animal constituents, together with such larger and often attached species as find food in these elements. Some light on the relation of vegetation and plankton to certain of the chemical constituents of the food of the aquatic flora can be gained from a comparison of Plates XLV., XLIX., and L., and Tables X., XII., and XIII., which show the results of analyses in 1898. The appended table also gives the average AVERAGE OF ALL ANALYSES—PARTS PER MILLION. Station Free Ammonia | Nitrates June 1 to Octo-| Remainder ane 1 to Octo-| Remainder | ber 1, 1898 of year ber 1, 1898 of year Thompson’s Lake...... | .154 .457 244 .684 yoni IWFIKS 555565 0006 | .02¢ 199 22D .923 HMinvors Ravetee snare cere | . 566 .786 .297 1.036 amounts of free ammonia and nitrates in Illinois River and in Quiver and Thompson’s lakes in the period from June 1 to Oc- tober 1 and in the remainder of the year—two periods which approximately represent the times of maximum and minimum of chlorophyll-bearing organisms. 498 A comparison of these two lakes indicates more nitrates in Quiver than in Thompson’s (.68 to .53 parts per million)—a phenomenon which may be explained by the proximity of the former to the river and the greater invasion by its richer (.81) wa- ters. In the matter of free ammonia Thompson’s Lake is much the richer (.3852 to .138 parts per million), though it falls con- siderably below the river (.95) in this particular. The striking feature of the diagrams and tables is the marked reduction in nitrates and free ammonia during the period of growth, from June 1 to October 1, in both lakes as contrasted with that of quiescence, from October 1 to June 1. The former period is one of higher temperature and less flood water, thus favoring the process of decay and the concentration of its products. The marked decrease in both the free ammonia and nitrates during this period may be explained by the utilization of these prod- ucts of decay by the chlorophyll-bearing organisms, which presumably are much in excess of those of the colder period. In Thompson’s Lake the phytoplankton would be the principal consumer, while in Quiver Lake submerged vegetation assumes this role. The uniformity in the nitrates throughout this period, and the reduction to a similar amount (about .2 parts per mil- lion) in both lakes are significant of some sort of an equi- librium between the supply furnished by decay and its utiliza- tion in the growth of plants. This phenomenon of reduction of nitrates to a summer equilibrium is to some extent manifest in the analysis of soil waters (see Palmer, ’97), and may in like manner be attributed to utilization of the nitrates by vegetation. At first thought the volume of submerged vegetation seems large in comparison with that of the phytoplankton, which it replaces; but when the permanence and persistence of the con- stituent cells of Ceratophyllum are contrasted with the many generations of the alge and diatoms of the plankton which arise during a season’s growth, the difference is less evident. Furthermore, a much greater proportion of the cells of the phytoplankton contribute directly to the growth of the animal hfe of the lake. 499 The submerged vegetation—such as that found in Quiver Lake—affects the conditions of nutrition in other ways than those above indicated. The absence of roots and the slight hold which its lowermost stems can obtain upon the soft bot- tom facilitate its removal by floods and seines, and the nutri- ment stored in its tissues is thus taken from the lake, and its waters are impoverished to that extent. Again, both Cerato- phyllum and Elodea are perennial, continuing beneath the ice from year to year and never wholly yielding to decay. The lit- toral vegetation of Flag Lake, with its large annual growth and well-marked periods of decay in autumn and spring, contrib- utes more generously to the enrichment of the water. Thus, while robbing the water of its food material, the submerged vegetation often fails to make equivalent returns. The submerged vegetation also interferes with the free operation of certain other factors which affect the plankton of open water. It shuts out the sunlight, and effectually modi- fies the temperature thereby. Thus, on a midsummer day the water in Thompson’s Lake rarely shows a difference of more than three degrees (Fahr.) between surface and bottom in two meters of water. In the vegetation, on the other hand, the temperature contrast is much greater and within much narrower limits. On July 15, 1897, when surface waters were at 88.2°, the temperature was but 80° at 15 cm. below. The diurnal range of temperature is thus much less in vegetation than in open waters. The growing portion of the submerged vegetation is usually at or near the surface, while the deeper portions are older and often moribund. This vegetation thereby enjoys the full benefit of the sunlight, so essential to the growth of chlorophyll-bearing plants, while its occupation of the water —especially at the surface—shuts out the light to a consid- erable degree from the more open deeper waters, and in this way adds another effective barrier to the growth of the phyto- plankton in surrounding water. The dense growths of the Ceratophyllum also interfere with the movements of the water,and thus tend to establish and 500 maintain local units of environment within a body of water. Lakes full of vegetation, like Quiver Lake, exhibit greater variations in the local distribution of the plankton than are found in open ones, such as Thompson’s Lake. Greater differ- ences in the component organisms also appear. ‘The vegeta- tion thus acts as a barrier, isolating differing assemblages of organisms. Thus, in Quiver Lake in one instance local aggre- gations or swarms of Volvox, of Copepoda, of Oscillaria, and of Melosira were detected in the examination of the local dis- tribution of its plankton. To this isolation by the vegetation may also be attributed the considerable irregularity in the sea- sonal fluctuations of the amount of plankton, which is some- what more evident in the planktographs of Flag Lake (PI. XXXII. and XXXIV.) and Dogfish Lake (Pl. XX X.-X XXII.) than in those of other stations. Such fluctuations, for ex- ample, as those in May, 1896, in Flag Lake, when the plankton fell from 203.52 em.’ to 0.72 in 18 days, or the fluctuations in Dogfish Lake in 1895, which do not seem to be correlated with any fluctuating feature of the environment, may be referred in part to the isolation resulting from vegetation and the modifi- cations of food supply and reproduction consequent upon it. The maximum-minimum contrast in Flag Lake was due to an excessive local development of Bosmina followed by its sudden disappearance. The cycle of changes in the succession of life are thus accentuated, and run a more rapid course in the midst of vegetation than they do in the larger unit of environment, the open water, where minor differences are quickly merged by the turmoil of current and waves. The plankton catches made in vegetation-rich lakes usually contain a larger proportion of littoral and bottom-loving spe- cies than those from open water. There are the Rhizopoda— often those with the heavier shells—the attached diatoms, cili- ates, and rotifers, together with many bdelloid and Ploiman rotifers not found in open water, the aquatic insects, both adult and larval,the oligochetes, the smaller mollusks, Hya/el/a, and Hydra. They materially increase the volume of the 501 catches recorded in the tables, and show in the plates of the plankton of Quiver, Dogfish, and Flag lakes. The sessile or- ganisms above named, with the Bryozoa, which often occur on Ceratophyllum, avail themselves of the plankton as food. Hydra, especially, increases when the plankton is more abundant. In Quiver Lake on May 8, 1896, Hydra was taken in plankton at the rate of over five thousand per m.’ of water. ‘These organ- isms which find a substratum and shelter on the aquatic veg- etation must have some important effect on the plankton, and their presence is doubtless one of the minor factors in the suppression of the plankton in lakes rich in submerged vege- tation. The economic aspects of the question of vegetation in bodies of water arise from the relation which it bears to the production of marketable fish. Quiver and Thompson’s lakes are both seined by local fishermen, and their relative produc- tivity as fishing grounds may be expressed in the market value of the leaseholds of the fishing privilege. Quiver Lake is so blocked with vegetation that clearing it for seining is at times an expensive operation, and this has a tendency to lower its market value. Thompson’s Lake, on the other hand, is less accessible, and some clearing out of the littoral belt of vege- tation is always necessary before seining, the operating ex- penses being thus somewhat increased. For years the lease- hold of Quiver Lake has been purchased for a merely nominal sum, not exceeding $100, and it has often lacked a purchaser. Thompson’s Lake, on the other hand, has been, in recent years at least, an object of increasing value, and brings over ten times this amount fora portion of the lake only. Thompson’s Lake has an area of about 1,200 acres, while Quiver has only 230. Their market values are thus out of proportion to their re- spective areas. Capt. J. A. Schulte, of Havana, whose knowl- edge of the fishing industry in the Illinois River is extensive and accurate, estimates that in the same area Thompson’s Lake will produce five times as much fish as Quiver, and production of fish thus stands in somewhat the same ratio as the average 502 plankton production (1.75 and 8.26 cm.’ per m.*). The produc- tivity of the lake full of submerged vegetation, is, it seems, less than that of one free from it, whether measured in cubic centi- meters of plankton or returns for marketable fish. The data here presented concerning the inimical effect of submerged non-rooted vegetation upon the plankton suggest an interesting subject for field or laboratory experiment. In- deed, experimental proof is desirable for the generalization here advanced. How far it will find support in the examina- tion of other localities remains to be seen, for no investigation bearing upon the question seems to have been made elsewhere. It should be noted that it is not maintained that all vegetation is inimical to the development of the plankton, but only such as successfully competes with the phytoplankton for the availa- ble plant food, and thus brings by its decay no additional sources for plant nutrition into the water. These conditions are approximately realized where the submerged non-rooted type of vegetation prevails. Where, however, by reason of the local conditions or the nature of the constituent plants, the aquatic vegetation adds by its decay to the fertility of the water owing to its utilization of sources of food in the soil and the air not available to the phytoplankton, we may expect to find the development of the plankton fostered by such vege- tation. These conditions are realized wherever rooted, and especially emergent, vegetation prevails and contributes by its decay to the enrichment of the water. A belt of littoral vege- tation of this sort may thus be of considerable effect in main- taining the plankton in a body of water. INTERNAL FACTORS AND PLANKTON PRODUCTION. Under this head attention will be called to certain phases of plankton production with which in the present state of our knowledge no environmental factors stand in apparent corre- lation. From this point of view, which lays emphasis upon the reacting organism rather than upon the stimulating environ- ment, most of the relations and adaptations of the plankton to 003 environmental factors might be treated under this head. But this has not been my method nor is it now my purpose to adopt it. The phenomena of growth and reproduction of the con- stituent organisms of the plankton, on the other hand, owing to our ignorance of their controlling factors, can at present be treated only under this head. The volumetric data in them- selves contain little evidence bearing directly upon the prob- lem, but in the light of the statistical results the fluctuations in the plankton become dependent upon fluctuations in the rate of growth, and especially in that of the reproduction of its constituent organisms. These fluctuations are often concur- rent, or, at most, shortly consequent, in many species at the same time and in several different localities, and give rise to the coincident volumetric pulses to which’ attention has so often been called in the preceding pages. Somewhat regular alternations of growth and rest, of fission and spore formation, or of parthenogenesis and sexual reproduction, are funda- mentally the basis of the cyclic movement in production. The amplitudes, and to some extent the location and duration of the pulses, are plainly affected by the various factors of the envi- ronment discussed in preceding pages—by hght, temperature, vegetation, tributary water, various hydrographic factors, and by food supply, and, possibly, also, by chemical conditions not directly concerned in nutrition, but the available data fail com- pletely to afford any satisfactory environmental factor or group of factors which stands in correlation, even remotely obvious, with this cyclic movement in production. IJ therefore class this periodic growth, these seruwal cycles which cause volumetric pulses, under the head of internal factors. The element of periodicity in itself does not seem to be consequent upon any known external factor. NORMAL REGIMEN OF PLANKTON PRODUCTION. The records of plankton production in the Illinois River, its tributaries, and backwaters, contained in this paper raise 504 the question whether there is in this fluviatile environment a normal regimen of production. Is, there in the course of pro- duction an orderly sequence, of any sort, of sufficient stability and of sufficient frequency in occurrence in SUCCESSIVE years to justifiy its designation as anormal regimen? A cursory inspection of the planktographs in the plates, of the data in the plankton tables, and of the table of monthly means following page 342 reveals at once an apparent state of chaos that accords well with the instability of most of the en- vironmental factors of the plankton, notably the hydrographic. For example, the production in the same month in different years or in the different localities examined by us is exceeding- ly variable. Taking at random the month of August, we find that the mean production for this month in the years of exam- ination ranges in the channel from .91 to 9.67; in Spoon River from .002 to .652; in Quiver Lake from .22 to 2.46; in Dogfish Lake from 1.11 to 3.91; in Flag Lake from .03 to 3.74; in Thompson’s Lake from 1.08 to 19.40; and in Phelps Lake from 8.80 to 189.85 cm.* per m.*; and, furthermore, that the extreme range in these means—.002 to 139.85— is found coincidentally in the same year, 1898 (see table following p. 342). This does not afford a very satisfactory basis for predicting the probable August production in cubic centimeters of plankton in any of these localities. It is evident that there is httle regularity in the actual amplitude of production in a given season and locality in successive years. If the problem be approached from the standpoint of rela- tive production in different localities at the same time, or in the same locality at different times, more semblance of order is traceable, though not equally so in all localities or in all months of the year. The relative rank of each locality in mean monthly production, as seen in the table following page 342, is tabulated below. For example, in the case of the Illinois River in the total of 51 monthly means there were 5, 6, 16, 12, 4,10, and 1, instances when its production attained first to sev- enth rank respectively among the seven or less localities repre- 505 RANK IN PLANKTON PRODUCTION. Ror Illinois | Spoon | Quiver | Dogfish Flag ee Phelps ; son’s River River Lake Lake Lake Pate Lake Tisrcseireieotere ese 5 fe) 4 2 4 12 28 Bi Meike oa ciciete's 6 I 2 Z II 27, 4 Brace sapnek 16 I 14 fe) I 38 I AE eS art ent aes 12 I 14 8 5 3 I Reon eae nesid vo 4 12 15 2 2 oO I Oa oe asians 10 5 4 fo) fe) fo) I Ti Mele evsish aletad I 8 (o) fo) oO fe) oO Oth. .j2e sees 51 | 28 | 53 24 23 51 36 Average rank 3.9 | 5.6 4 3.3 2.6 2 i ee sented in the months concerned. An examination of this table shows that in relative production (see table following p. 342) the localities tend to arrange themselves in a sequence which is represented by the average rank. As shown in the above table, this is as follows: Phelps Lake (1.5), Thompson’s Lake (2.), Flag Lake (2.6), Dogfish Lake (3.8), Illinois River (3.9), Quiver Lake (4.), Spoon River (5.6). This is essentially the sequence in relative production represented by the averages of all collec- tions and of the monthly means (see table following p. 342), except that Flag and Thompson’s lakes are transposed. From the points of view either of average rank or of average produc- tion the relations of production in the 7 localities examined by us are, it appears, essentially similar. A considerable measure of stability in this respect may therefore be expected. If we inquire if these relations in production expressed in terms of rank are equally constant for all localities and at all seasons, we find that there are departures from the average in all localities, and that different localities show different de- grees of stability of relative production varying to some extent with the season. This appears in a comparison of the ranks of Phelps Lake and the Illinois River in the table above given. In the case of Phelps Lake (average rank, 1.5) 382 of the 36 months rank first or second, while in the Illinois (average rank, 3.9) but 28 of the 51 rank third and fourth. Obviously the divergences from the expected rank in production are greater 506 in the river than in Phelps Lake. A further inspection of the table indicates that Phelps and Thompson’s lakes and Spoon River exhibit the most stable relations in productive rank. It is in these bodies of water that we have found environment- al conditions most uniform. In Flag, Quiver, and Dogfish lakes the divergences in rank are much greater, and it is in these localities that conditions of high and low water and of vegetation afford sharpest contrasts. In the Illinois River itself, where hydrographic fluctuations are most immediately effective, we find apparently the widest divergences in produc- tive rank. Even in these instances of greatest divergence the tendency towards a certain rank in production in each locality is sufficiently evident to warrant the statement that in the main the relative rank in production in the several localities examined by us is well established and generally maintained. Still more pertinent to the question of the existence of a normal regimen in production is the question of sequence in the course of production in successive years and in different localities in the same year. Dothe planktographs form curves which may be superposed in successive years in the same lo- cality or in different localities in the same year? A single glance at the plates which accompany this paper will suffice to reveal the chaotic complex of lines which such a superposi- tion would produce. There is no such unity or similarity if we base the comparisons on the actual volumetric production. If, on the other hand, we disregard coincidence in amplitude of the curve and consider mainly the direction of the changes, sim- ilarity becomes increasingly apparent. It rarely approaches to the condition of complete parallelism, however, owing to the great variety in the amplitude of production in various years and localities. If the data in the table following page 342 be analyzed with reference simply to the upward or downward movement in mean production from month to month and year to year in the various localities, we find certain tendencies appearing which may afford a basis for predicting the probable course of pro- 507 duction to a shght degree in the localities examined and in the region asa whole. The following table exhibits the instances of upward and downward movement in the monthly means for each locality for each month of the year. DIRECTION IN MOVEMENT OF MEAN MONTHLY PRODUCTION. Station Jan. | Feb. Mar. Apr. May Sune | July Aug. sept| Oct. | Nov. | Dec. |: | = = Re = a) ie 1: = E s = [Bac ealostn eg ele es ele tals tele emo. eloekalece iA DA PIA PA PA PA PA a PIA PA PA RIA Illinois River... aiiw Merrow $103 woes 2 4.852 | owe: Spoon Riwer.- +...) -.22-- | ee 2d Ie 2 1 ie 4 “cal a jE baesil baal a ie dl aN) | alee Oniver Wakes > = Qe st Omeed een 3 Os | De i QURS 4 eee 2 eee 3 4. 7 ES ee] | oa Dogfish Lake ............. Tice hence rete ee Suara elt | hos 2 Wlardhakess 2 1 2 OW easel! oe OF | 0. A PAU Mere r || ila si lieal 1 OR at 22 Olea Thompson’s Lake Dee ll Sie | ieee he 1 3 4 <0) 55-7 OF Qeta Qe Soe |p Seco eek eee Phelps lakers =. | HeeAl), Wi | W244) Due 3 fees Des EO) bye 2) te 22h tO ae tO ee ae AO taller ee ee 11 3, OmelsS 6...16 1.19, 8 1115... Wyle. 9 12.12 12 S12 138 lS oO el This table, combined with the plottings of the averages of the monthly means at each station, shown in Fig. E (p. 508), indicates the following course in production which predominates in our records. Production falls in January, begins to rise in February, continues to increase in March, but only to a shght extent though more generally. In April the increase is prac- tically universal and more extensive than in any other month of the year. In May the increase continues in the majority of instances (11 out of 19), and more frequently (65 per cent.) in the backwaters than in tributaries (50 per cent.). In either June or July there is a decline to a lower level of production in all localities. There is, however, considerable diversity in this matter in the several years and localities (partially as a result of imperfect records). This appears in the ratios of downward and upward movementin June (15 to 7) and in July (14 to 9). In the months of August and September there is a tendency towards a higher level of production in some ofthe backwaters, though on the whole the instances of rising and falling produc- tion are equal in number. In October and November produc- Uv + rae Z Lees PARA AhAh~wolLal EAT d erie: ‘ 2 : : F a es Ve EU: SEP 4 AUG. OcT, Fic. E.—Planktographs of all stations, plotted from averages of monthly means. 509 tion again drops to a low level, and this movement appears in 60-70 per cent. of the instances in each month. In December the decline in production is checked, and in a few cases the upward tendency reappears, only to give way again in most cases to the January minimum. There is thus a general seasonal regimen apparent in the totals of all localities, and an approximately parallel seasonal routine for each of the localities, the degree of approximation varying with the locality and the season. Butthis regimen can be outlined only inthe most general terms, and is everywhere subject to divergences that frequently reduce it well nigh to a semblance of chaos—a condition arising from the instability of this aquatic environment. The course of production above outlined considers only the movement of the average monthly production, and consequently deals only with the larger and more general seasonal move- ments. It masks almost completely the minor fluctuations, and especially obliterates all consideration of the phenomenon of pulses discussed in the treatment of the course of produc- tion in the several localities. It is inthis matter of pulses, or,in other words, in the cyclic movement in plankton production, thatthe nearest approach to a normal regimen appears in our volumetric data. I have shown that wherever our collections were made at intervals of a week, or less, this movement is generally distinctly traceable. In the backwaters, where collections were usually less frequent, the cyche character of planktographs is still apparent, even in fortnightly collections. This phenomenon is therefore, it seems, a constant feature of the movement in plankton production in our waters as it appears in the purely volumetric data. Sug- gestions of the occurrence of a similar movement in the plank- ton of other waters may be found occasionally in the data of other investigators, but nowhere, to my knowledge, is there at present a chronological series of collections of sufficient dura- tion and brief enough interval of collection for comparison with the data presented in this paper. The main basis for the 510 emphasis laid upon the subject in connection with my discus- sion of the volumetric data will be found in the statistical data of Part II. of this paper. In this connection it may be noted that the statistical data of other investigators lend some sup- port to the probability that this cyche movement in the plank- ton will be found to occur in other localities as well as in those examined by us. Instances suggesting this occurrence may be found in the statistical data of Amberg (’00), Steuer (’01), and the more recent work of Cohn (703). This cyclic movement consists in the repetition of rise and decline in production—a repetition broken in our records only by the imperfection of our data. Wherever collections are of sufficient frequency it is possible to trace it—sometimes, how- ever, only with the aid of statistical data—continuously through all the vicissitudes of changing seasons, of summer heat and winter’s ice, of the vernal rise and autumnal decline in tem- perature, and of high and low water. Moreover, it appears in all of our localities whenever collections have been made with a weekly, or even fortnightly, interval. These pulses vary in duration from 2 to 7 weeks, though the majority occur in limits of 3 to 5. Their amplitudes vary greatly, and are plainly influenced by various environmental factors. Their limits are also frequently modified by these factors, though the evidence is not clear that any of the envi- ronmental factors we have discussed are correlated directly with the cyche movement itself. In the discussion of production in the backwaters the uni- versal approximation in time of these pulses in the various localities, or even their precise coincidence in many instances, was recorded. The cause of this tendency toward uniformity in the direction of movement in production in these various localities at the same time is not apparent from the data at hand. Contributory to it are the facts of a plankton largely composed of the same species of planktonts, of a connection and commingling of waters in all of the localities in flood con- ditions, and of the operation of environmental factors com- mon to all of the localities. 511 The normal regimen is accordingly not delineated by a planktograph of marked definiteness in its course, but is one formed by a sequence of recurring pulses of approximately a month’s duration and varying amplitudes, low in winter floods, rising with the temperature to a vernal maximum of consider- able magnitude, often, but not always, dechning during the summer months, frequently rising again in late summer or au- tumn, and in some localities and years to an extent exceeding that of the vernal season, and falling with autumn tempera- tures but increasing in stable winter conditions after the min- imum winter temperature is reached,—such is the general reg- imen of plankton production in the Illinois River and its back- waters. If this cyclic movement in production be characteristic of the plankton generally, fresh water and even marine, it must follow that scattered and irregular collections, or those at in- tervals exceeding a week or at most a fortnight, may fail en- tirely to give an adequate representation of the course of pro- duction or relative fertility of a body of water. Chronological series throughout the whole seasonal range of climatic condi- tions and at close intervals—of one week or less—are neces- sary for any accurate delineation of production and fertility of water by the plankton method. SOURCE AND MAINTENANCE OF THE POTAMOPLANKTON, The existence of a very characteristic and abundant plank- ton in the Illinois River at once raised the question as to its source and maintenance. We find at Havana a stream which year in and year out carries by a burden of life, microscopic as to its individuals, to be sure, but in the aggregate a volume of surprising extent. This stream of life exhibits a routine of seasonal changes in constitution and quantity which neither flood, the ice of winter, nor the drouth of summer wholly inter- rupts. It recurs year after year with a regularity which stands in strong contrast with the fluctuations of the environment. Although the water in the stream is subject to continuous re- 512 newal,—the channel from Utica to the mouth discharging in from 5 to 25 days, according to the rate of the current,—the plankton is continuously maintained, and the seasonal routine is run in the face of this continuous renewal of the water. Furthermore, the plankton product of the stream is discharged at the mouth of the river practically in its entirety, for the or- ganisms of the plankton cannot maintain their place in the stream against the current. The only organisms of the pota- moplankton which remain, are those used as food by fishes and other animals which are not carried away by the current, and such as may be lodged—usually in encysted, and thus heavier, condition—along the bottom or banks of the stream. At times of flood the receding waters leave some of the plankton side- tracked in the reservoir backwaters—in the lakes, lagoons, bayous, and marshes of the bottom-lands. As river levels fall it may be slowly drawn off into the channel of the stream, or cut off from connection with the river. This continual dis- charge of the plankton, never to return, makes the problem of the maintenance of the potamoplankton, quantitatively at least, very different from that of the maintenance of the plank- ton in a lake. Three suggestions arise in explanation of the perennial character of the plankton of the river: (1) The plankton en- ters with the tributary waters, in which case the problem is only removed a step; (2) it is autonomous, developing in the stream while the waters are in transit, in which case the solu- tion liesin the river andits environment; or (3) thetwo elements, contribution and autonomy, are combined, in which case the share of each will appear on a comparison of the plankton of the river and of its tributary streams and backwaters. The water in the channel of the river comes from three sources ; from springs and seepage along the banks, from the impounded backwaters of the bottom-lands, and from tributary streams. RELATION OF SEEPAGE WATERS. The contribution from springs and from seepage are incon- 513 siderable in comparison with that from the other sources. Wherever the river encroaches upon the bluffs, as, for instance, below Havana, seepage areas of some extent and springs of some size are to be found. Such banks, however, in immediate contact with the main stream itself, are of very limited extent. Furthermore, their contributions to the plankton are relatively still smaller. These springy banks abound in life—planarians, amphipods, isopods, oligochetes, and rhizopods, mainly limic- olous species, which rarely leave their habitat to enter the river with the spring water. Such springy banks, exposed to midsummer’s heat during low water, do at times teem with species common in the plankton. For example, a bank of this sort on the levee at Havana was covered with a brownish scum composed principally of Synedra acus, a diatom abundant in the plankton at cooler seasons of the year. The temperature of spring waters along the bluffs in midsummer is about 60°. Elsewhere in the warmer waters of this springy shore are to be found patches of green and red scum, where Huglena viridis and FE. sanguinea were abundant, both species being common in the plankton at that time. Tiny rills of cool water traverse the oozy bank and carry stray individuals of these various species into the river, but their clear waters are poor in com- parison with the brown water of the stream which they join, turbid with plankton. Their contributions are thus insignifi- cant in amount and, while adding a trifle to its diversity, their main action is that of diluents of the potamoplankton. RELATION OF TRIBUTARY STREAMS TO CHANNEL PLANKTON. The relation of tributary streams to the potamoplankton in the channel of the Illinois is a much simpler problem than that presented by the backwaters. ‘Their contributions enter the river in well-defined channels, and the areas of their respective basins are an index to the quantity of water they bring to the river. Their share in the formation of the potamoplankton can thus be more readily tested and estimated. Under conditions prior to the opening of the Chicago drainage canal the river 514 received at Utica, the upper end of the basin under considera- tion in this paper, the drainage of 10,365 square miles of catch- ment-basin, over one third of the total basin of the stream, to which was added at La Salle, a few miles below, the water from the Illinois and Michigan Canal containing the sewage from the Chicago River. A large volume of water, richly fertilized, is thus provided for the reception of tributary streams, no one of which, with the exception of the Sangamon, has more than one ninth of the drainage basin above the point of its union with the river. The Sangamon has at its mouth a basin one fourth as large as that of the river above. This presence of a considerable initial volume and the distribution of tribu- tary waters in relatively small streams at intervals along the course are conditions which favor the mingling of the constit- uent waters of the stream and tend to maintain the uniformity of the plankton in the main channel. The tributary waters, with a few minor exceptions, such as Quiver Creek, enter the main channel directly. The elevated deposits built up across the bottoms by their agency confine their floods within their banks except during the maximum stages of overflow, when they contribute directly to the back- waters, but even under these conditions a strong current 1s stil maintained along their customary channels directly to the main channel of the river. Their contributions are thus, as a rule, carried directly to the river and mingle with it without any period of impounding, and their effect upon the plankton is direct and immediate. Two tributaries, Spoon River and Quiver Creek, were availa- ble for examination at Havana, in both of which collections were made by us which throw considerable light upon the character and quantity of their plankton contributions. QUIVER CREEK. In Quiver Creek we have a small tributary with a basin of only 220 square miles, largely of alluvial second bottom with more sand and less heavy loam and clay than the adjacent 515 prairies. Its waters are discharged into the upper end of the eastern arm of Quiver Lake, and are impounded for a varying length of time before reaching the river. No channel defined by the configuration of the bottom traverses the lake, and since its area is relatively large in comparison with the discharge of Quiver Creek, the tributary waters are subject to considerable impounding when the lake is free from vegetation. When, however, vegetation is abundant, a fairly well-defined channel, through which the discharged waters make their way with per- ceptible movement, is kept open through the matted growths. The impounding period is thus reduced for the channel water under such conditions. Collections were made in Quiver Creek, near Topeka, II1., above McHarry’s mill-pond, from September 1, 1896, to April 20, 1897, at intervals of ten days, by Mr. W. R. Deverman, who kindly volunteered this service for the Station. : Navicula spp....+..-.- yO ee eet eee eaenem Saceeecee Zeccatueees ocala ol eceteoa || been sea ee ee ees Wee eee bee are eset | 0100) INitS7ZCHialSipinmoOideSsot eee eerste ea |e ee oe 2 De ae OSE eens 4 Pleurosigma angulatum.................... 4 OMe Veeeeeer eeaceeta CN eens | earac ee 4 14 Surirella ovata......... -....-- 0 Splendidas sce. eee SyMledta vaAChS 2. erm ser enene oe Acmeetne see eeeae ee fltiassees SP eee) Ne Pee ee eee Unidentified phe ese pee eee mene see eel hes os 2, Rhizopoda—totals . RSE ny eee eee Basa 86 10 INC ER TSE, ee once, | Ret ocneccetl| pened eeeeron Bi | Beet lee a 4) sli ct ete] eee discoides._______. aoscabioseses spores duces tadlabes yore eee a oan _ 1 lo ' io) N _ oo e > No) On fs - nN as nay Ww es w Co; : nN N _ + Ww Wit aS ee peecbsckence sesveciace=o 2 Centropyxis aculeata.. Ae eee 2 2 ecornis ..... Bes OUR A ES a eee 8 Cy phoderia ampulla. eet: eee Nee | ea Pee Ae PI saa 2 oft NHANN No hn ae ~ ho = > +e 2 fr Difflugia acuminata............-..... ene 160/225 Sees 6 4 Cees : 2 EN lib aye cya) yh le eae adesecece) aaaues| [eaere nee: Be eel [epee eal lecomcsoee Roe ahr leet eee Pua Oe 2 COTSEDIC tas Nees yee oe eee eral pate be LS So eee ete ee| ee | eeeen es Zid | ba eees Slobwlosay cise ence) eee ee eee 54 8 32 14 18 10 6 10 BSS 0 ee ee en ee eer espera (eee eerenerel Rect PA) een ot) eee ai | se LE SROVEVEN Gye baes See) teteactgackosaros-t wetoertecees Pill esetsos 2 Trinema enchelys 1s ee eee ON a 2 4 4 2 2 i | ee Mastigophora—totals.... eee se 2! 2 AQ Wiese oe] ee eee : Bid oriciayele pants sss eg eee eel neal S| Hapen asad bcsocee 2 foe sae teeeee ae ec eeress 2 Pacts tore iCatid area nse eer eeereee | eee Be Li Seas enlace | gee | Coc ee Sy titina stivellalc 2 - eee ee ee ee ee Woes ee 46) 3) ssS2eccbs ene. | Eaeeemcaal|| eee Trachelomonas B lispida: na) ee ee ye) ewe Bal fe Pees pl EAS F Unidentified - . Rotifera—totals_. ae Cathypuna tana es Goltirisiobtisis snes ne nee Conochilus sp. bes = TOURED Spey oes -5-sorte coon Sopeeee Cespspecees: cscne: 4 | Beet oe Miaistig OCencays presets cee se eee eee eee | ees : shieeee he Metopidia|solidiiss:. ee 979 |e oa a oes Bis |i saean alee PSS, | eo Bg spat Notholea jugosa.. Se ereceeseeee peat | osgessoce| |esd-enen|| moses | laeereeast a setha [ssect5| leas od [7 2 Philodina megalotrocha.. Rae ee sae eree | eee eee IY | \Seeeaize | poeereee | eter Roe Yel mh RTO Gt he Ye eae Cee ee Peele BE Pr epee) (nem peed leoeee eon eeeaeemenl preaees| ares P| | peor ee ee bi we io3) _ on nN on— > ANNAN NFOODNNNNNN adn Lb! n nN > fe on eee Sy, _ q Bs Oe oD i=} o Ne, Eh: @ a > nN nN nN — PROULLOH: CL G'S) case oes ccee ts ce ncae nee eeee eecan eal] Ceaeeeetm | epereeeceal cee eee pees eaee | eee ure eee cmar 4 Entomostraca—totals --....._.. ae Pea eee Ss Cyclops serrulatus Be ates eanteres || aceeen IN ENT oy DS eee e et enter cee etn emeneeceeedad| (6 conted|[ece abe Soi emotes ||eoe curl cesesoee | ee een Ostracod.. seoph cette use coreee Genk Uae | eee Romeo PAE Voeheganesi| peepee nee ace be be) | SSE Miscellaneous—totals._ oe ee a Meee Re oe eer eee 12 Wocuates ah Chironomuswatiya screen eee |e ees 1 6 I ere Wmnidentified insect. --—--; 2.s.-cone- eee ence De AUR 5 a re meee | a Insect egg.- ae eR ke ee ed | eae 2 14 24») eesoncerh| [aceacesce 2 2 22 Unidentified egg... Sseresece Oy ee ee (eee ee reste oe 8 Dy MV asew Gee | Re eee 10 Wnidentitied: i330. oe eee eee (Fi PEAS Sree 2 Seated PEMD | por Slee ease 8 22| 16| 19 63 781 | 126, 261 | 2497 | 6323 oa nN =" NAN CHOUNNNFNFENND nN = on ned ies) ( w mo oO fon MotalmtinibeniOh Ss peClessy sess sess neat 32 18 33 29 Total number of individuals..................0.. | 794 | 238 | 875 | 751 *Estimated. tEggs only. 517 in the predominance of the diatoms, the Rhizopoda, and Chiron- omus larve, and in the character of the few rotifers present. It is also evidenced by the erratic distribution and often small numbers of many of the species occurring in the creek waters. There is little evidence in the data of marked seasonal changes. The diminished number, both of species and individ- uals, in the winter and spring months is due in part to the flood conditions prevailing at that time. The disappearance of the desmids in the colder months is apparent, as is also the decline in the diatoms, the effect of which is heightened by the greater proportion of dead and moribund individuals in the winter months. There is also some slight evidence in the ta- ble of a spring increase in March and April and of a late au- tumn maximum in November. From conditions observed in Spoon River and Quiver Lake during the summer months not included in the period of our Quiver Creek collections it seems probable that the plankton of this stream at that season of the year is more diversified by the addition of flagellates and rotifers. The flow of the stream is, however, much reduced at this sea- son, and its contributions correspondingly small in quantity. The inter-relations of this creek plankton are very patent. The diatoms are the predominant members, having one third of the species and nine tenths of the individuals. The rhizo- pods include one fifth of all the species and almost two thirds of the animal individuals. We have here a rich diatom flora supporting a rhizopod fauna. The remainder of the species, about one half, belongs to diverse groups and is numerically, at least, an insignificant element in the plankton assemblage, constituting but 4 per cent. of the total population. A comparison of the plankton here delineated with that of the river at the same seasons of the year leads to the follow- ing conclusions: 1. The creek organisms all occur in the river plankton. 2. The facies of the river plankton is quite different from that of the creek in that it has a greater abundance and variety of organisms, a greater proportion of limnetic species, and a 518 much greater proportion of limnetic individuals, with a cor- responding decrease in the relative numbers of the littoral in- dividuals. This is very apparent throughout the whole season covered by the collections. Thus in autumn months, when Melosira, Synura, the ciliates, Syncheta, and various Brachi- onide characterize the potamoplankton, we find them but sparingly represented, or, as in the case of Syncheta and the cilates, wholly absent from the creek plankton. So, also,in the winter months Brachionus dorcas and Cyclops bicuspidatus, so characteristic of the river plankton, form no part of the popula- tion of the creek. The perennial and abundant Polyartha playtyptera was at no time found in the creek. That limnetic species are not wholly absent from the creek is shown by the presence of Melosira, Synura, Notholea jugosa, Hudorina, and Trachelomonas, but their occurrences are isolated and their numbers few. The creek is thus not a center of distribution for such planktonts as these, their presence and numbers in the river being practically independent of their appearance in the tributary. The abundance of diatoms in the creek waters suggests that these may find centers of distribution here. Most of the species, however, are quite as abundant in the river, with the exception of the Surirellas. These are present in small num- bers in the potamoplankton, and are often moribund. 3. The creek waters act as diluents of the potamoplank- ton. The character of the Quiver Creek plankton and the quantitative studies on Quiver Lake support this view. The contribution of Quiver Creek to the potamoplankton is thus largely of littoral species and of small quantity, and its effect is that of a diluent of the potamoplankton. The following table, which gives the relative number of species in the plankton of [linois and Spoon rivers and Quiver Creek, demonstrates the small number of species found in the creek, and the monotony of its composition as shown in the pre- dominance of the Rhizopoda and the diatoms. The relative pau- city of the Mastigophora in its fauna may be due in part to the 519 RELATIVE NUMBER OF SPECIES IN THE PLANKTON OF QUIVER CREEK AND SPOON AND ILLINOIS RIVERS. Quiver Spoon Illinois Group Creek River River Allpae totals): oii.) we wd ide sin ghts esr « ay | 25 34 74 SEMA PUY CEE 2) tre septa usa et ae I 4 Il in OTOP MY Cl de ew aoe ceive me oie cs I Il 30 Bacillanacedwey. csc cere ee 20 14 25 Con puppataes ati vaoe oes eels wee Mee ees 3 5 8 Protozoa —totals “ees Oe ne ee ee 18 63 154 - SUM ZOIO A), Liars ea )arn'e rate ps oe este Pee oe sie 13 17 30 Eleligz@aet cat ch. ccktaeeone ae eT eeRiee fo) fe) 4 WASEPOPHOLAS ¢alirau is. teenie ne ee Se 5 28 62 Ciliataa ee Pelee ccs Seno ae ae O 16 55 SIGlOniae teehee es chee Oe fo) 2 | 5 Rotitera— totals: t/sa73 Geko ainm nce one II 44 107 RMI ZO ale sts cr. hoatessv ta wate theta ere eee I I 6 BdeWotdaieen Aec5c, one see eee 3 4 6 IRotrmay se eycks cote os oe cere ee 7 39 95 Grustacea— totallst scsi aes a eee 2 13 49 COPE POM as cio: .5 16 cis o.ctata 270) ote sha eee I 5 17 Clade lasses so8 ceived alaende meee fo) i 26 Ostracodat.- 6 viene Ree I I 3 OtheriGnustaceay sas en ee eee fe) O 3 Miscellaneous—totals:....* .0.o.c.ctaue tree ray 4 16 45 INSEE ELATVEE s ...+<- 2 .86 .165 | Albuminoid ammonia .... .60 .48 25 Nitrogen as< Total organic.:........... We2 1.03 61 WNMERIEES 2 heer anata sida os .039 .147 .023 WWINMERATES 55. St A's; a veeetein eae I.o1 1.58 .66 *Data from Tables X., XI., and XIII. 522 It is noticeable that Spoon River carries the largest amount of matter in suspension, both absolutely and relatively, as shown by the high total residue on evaporation (522.8 to 367.5 and 268.9) and by the smallest amount of the residue in solu- tion (167.1 to 304.1 and 248.2). This is further shown by the fact that the solids removed by the army filter in Spoon River average 1,755 cubic centimeters per cubic meter to only 592 in the same year in the Illinois. The large amount of organic matter undecayed and undissolved, and therefore not available for the support of the plankton, is partially indicated by the high oxygen consumed (14.1 to 10.4 and 5.9), the high albumi- noid ammonia (.60 to .48 and .25), and the high total organic nitrogen (1.29 to 1.03 and .61), when considered in conjunction with the small amount of residue in solution. On the other hand, the waters of Spoon River are quite deficient in forms of nitrogen more available for the phytoplankton, the free am- monia (.24), nitrites (.039), and nitrates (1.01) being in each case less than in the Illinois (.86, .147, and 1.58), while the chlorine (3.8), an index of sewage contamination, is less than a fifth of that in the channel (21.6). Spoon River has therefore great resources, in so far as or- ganic matters and the products of their decay are concerned, for the support of the plankton. Not all of the matter is in solution for immediate utilization, but there is still sufficient for a large plankton development, time for which has not been allowed in the tributary stream. The immediate effect of the access of the contributions of Spoon River to the channel is, in the average, a dilution of its inorganic nitrogen per m.’ of water, which is in some unknown measure made good by the contributions of silt, in part of organic origin. The net result is, of course, a large addition to the tota/ resources of the chan- nel waters available for the present and future development of the plankton. The amount of nitrogen in its several forms which Spoon River carries is not small as rivers go, for this stream drains a plain unsurpassed in fertility by any other part of the catch- 525 ment-basin of the Illinois. It also receives a moderate amount of sewage from the cities of Lewistown and Canton, and the drainage from a considerable number of towns. Its diluent effect upon the plankton of the Illinois is thus not due to the poverty of its own waters but rather to the excessive fertility of the main stream, a fertility resulting from the sewage and industrial wastes received by that stream from the cities of Chicago and Peoria. The contrast in fertility as indicated by the analyses tabu- lated above is not as great as the differences in the plankton production of the two streams. The ratio of nitrates which perhaps most fully expresses their relative fertility is 1.01 to 1.58, while the ratio of the plankton production as expressed in the average of the monthly means of the catches by the silk-net method is 0.256 to 2.71. The failure of Spoon River to develop amore abundant plankton is thus apparently due to some other cause than the lack of nutritive elements in the water for the support of the plankton. The development of a considerable volume of plankton in it at times of low water and slack current makes patent the probability that the lack of time for breeding is at least one of the important factors in the relative paucity of the plankton of this tributary stream. QUANTITATIVE COMPARISON. A comparison of the quantities of plankton taken by means of the silk net in the two streams affords a fair contrast of their relative productivity. Certain sources of error are, how- ever, present in the data of comparison, and as they are not equally distributed in the case of both streams they invalidate to some undetermined extent precise comparisons. These sources are the leakage of the plankton through the silk and the presence of silt. The plankton escaping through the silk is largely made up of the Mastigophora and small diatoms and algw, and they are found alike in both streams. The presence of a more abundant plankton in the Illinois and the somewhat flocculent nature of much of its silt tend to induce more per- 524 fect filtration and to check slightly the leakage of small organisms through the silk. In Spoon River, on the other hand, the plankton is scant and the silt mainly of fine loam and clay in suspension, so that the silk net rarely clogs and the escape of small planktonts is but shghtly impeded. This loss by leakage is far more significant in the case of Spoon River than it is in the Illinois, for the escaping plankton con- stitutes a relatively larger proportion of Spoon River’s total product than an equally large or even greater loss would form of the total product of the Illinois. Again, the quantity of silt is both relatively and absolutely much greater in the waters of Spoon River than it is in the [llnois, and it is of a different nature. This greatly increases the difficulty of maintaining any uniformity of standard in the estimation of the silt con- tent of the plankton catches in the two streams. These sources of error, although considerable, do not, however, invalidate the conclusions here drawn regarding the relative productivity of the two streams. They are still patent within any reasonable limit of error. The plankton of Spoon River is very much less than that of the Illinois. The average amount present in a cubic meter of water in Spoon River, as shown by the average of the amounts in thirty-six collections made between August 18, 1896, and March 7, 1899, is .465 cubic centimeters. ‘This average amount is reduced to 0.191 cubic centimeters if the two collec- tions of September 11 and 30,1897, are omitted. This average is still more reduced if we omit the collections from the last of August, 1897, to the close of the year—a period of exceptional and prolonged low water. ‘The omission of these four months lowers the average to 0.044 cm. per m.* of water, an amount which more truly represents the normal contributions of the tributary to the main stream in years of rainfall normal both in quantity and distribution. The average plankton content of a cubic meter of [linois River water, as shown by the average of 255 collections made between June 12, 1894, and March 28, 1899, is 2.19 cubie centi- 525 COMPARISON OF MONTHLY MEANS OF PLANKTON PRODUCTION IN ILLINOIS AND SPOON RIVERS, BASED ON ALL CATCHES.* January | February March | April | May | June eat 5 mentee (necbulioes cetera lisede | eerie Be eh Nee I eter tly ae lhe ey Ee eceen kw w(eo g = 2) pus ° pais fo) ats 2) = 2) : ° Ss fe) = fo) = e) = fe) = fe) = fe) om ey as (oe (et ale om rs a. = a a, ee ie eae oe adel Palle’ nN | Kot y. ul wl lee en ENIS rirdl ihe alm bkc A cal iaicr oar lies Lo eaerel ieraats Glee in ol enon OZ AR acts TOO See alleys cell eae sees OVO ctiace oe csltoctasrs FAIS tepoees taal erst ees ees BOA Del iene Soo OO ooace O-02|eere OOfloccoc Orie sarees Was llliceumes ON727 ener TOOY Pde dial ade 0.040.047] 0.380.007] 5.11] 0.048] 5.62/0.440} 0.27 | 0.250 1898 0.45 |0.017 0.27|0.016 OoRVOo) Astellosecac II. 30|0.023] 3.96 | 0.096 1899 [0.18 |0.005 0.810.001 OX ZSOVO26| alan A wee le See setae eal oars as oltre Monthly av.'o.213/0.0111 0.23'0.021! 0.27'0.052! 4.59! 0.048! 6.08!0.232! 7.22 | 0.173 July August |September| October | November |} December Bee cl aisle |) gals (ue Mee ligeeia lar e Bue, uleotgn Renn lnieepe kes a | es eS m e a = = m | 2a) (e) ats fo} a ° as e) — e) = fo} = ° = ° = je) = o) = e)} = 9 a | Sia aS a. om a. = a, ai joa ae | 2 | a Nn A) T8G4) 502 1.0 oa QVWOVAls ono ¢ Desolace: @QOilecooc ObltGloococ Op Ol secoue LSQ5. (9533 enaet MeCBileoaoc Gel lesa eae (lei v/|paesi ceric Be O02 eres Talal [eerie TooO) |Esaa lyse. I.12|0.018| 0.38]0.005| 1.11] 0.005] 0.02/0.005] 0.76 | 0.002 USQ7 =, (14:60 la-roeie 3).65/0.652)/ 8.9315. 130|5).95\|(s «aa I.00|1.671| 0.56 | 0.599 1898 = [0.58 |0.036} 0.91/0.002} 0.69/0.002} 0.24} 0.001} 0.25|0.001| 0.99 | 0.001 1309 ea Iced In Bec |roe callow. 6 valbocballbopeallad olddl tae rcn soa ealloeeedl Bnecoote aon ctc Monthly av.!4.23 0.036! 3.88l0.2241 2.56l1.712 1.701 0.003! 0.8810.559 0.71 | 0.201 *Amountsin this table are cubic centimeters of plankton per cubic meter of water after subtracting from the total catch the estimated amount of silt. meters. This is 4.7 times as much as the average of all the Spoon River collections—l1.5 times, if we omit the two exceptional collections of September 11 and 30, 1897, and 44 times, if we exclude the low-water period of the autumn of 1897 from both averages. This latter ratio, 1 to 44, represents the relative plankton content of the two streams except during periods of prolonged and extreme low water. Even in such low-water periods the waters of the tributary are less pro- ductive than those of the main stream. For example, the aver- ages of the monthly averages of production for July—October, inclusive, in the two streams are respectively 2.89 and 5.78 cm.° 526 of plankton per m.* In Novemberand December, however, the mean production in the tributary, for the only time in our rec- ords, exceeds by 67 and 7 per cent. the production in the chan- nel. On the average, however, production in the tributary, even in most favorable conditions, is less than in the main stream, and the contributions of the tributary continue to be generally a diluent of the channel plankton. If the means of the monthly averages are compared, the ratio, when all collections are included, between production in Spoon and Illinois rivers rises from 1 to 4.7 to 1 to 10.6. This ratio, which eliminates somewhat of the error resulting from differences in the number of collections in the two streams, probably represents more nearly the actual ratio of production in the two streams derivable from our data. In the table which follows, the catches in the two streams upon coimcident—approximately so in five instances—dates only are averaged. This reduces the number of catches in the Illinois River from 285 to 33, modifies some of the monthly averages, and changes the ratios of production in the Illinois and Spoon rivers, based on means of the monthly averages, from | to 10.6 to 1 to 9.9, but does not otherwise materially alter the relationship of production in tributary and channel waters as determined on the basis of all collections. If the silt is not eliminated by estimation the average amount of the silk-net catch in the two streams is respectively 1.41 and 3.98 cubic centimeters per cubic meter. The change in the ratio is due to the greater proportion of silt carried by Spoon River. In the table of plankton comparisons following page 342, the averages of the amount of plankton per cubic meter of water in the two streams is given by months for the years of our operations. Decimals to three places are not here indica- tive of great accuracy of measurement, They result from ef- forts to represent the small proportion which the plankton forms of the silt-laden catches from Spoon River. -Considera- ble differences in these small quantities in this table and else- 527 where in Spoon River tables have little significance save as they express relative quantities in catches of chronological sequence. Thus, in this table differences in successive months have more significance than those in the same month of differ- ent years. COMPARISON OF MONTHLY MEANS OF PLANKTON PRODUCTION IN ILLINOIS AND SPOON RIVERS, BASED ON COINCIDENT CATCHES.* January | February | March April | May | June sc a el gt (Palo a al fe <= a= a = oo Male peri eee] vee meaezi bE galego] (ead PS ae feat a ane (e) wale ° as fo) pas ° as o) —s ° = (e} _— ° _ e) — ° — 2) — te) = oh |) = a. = ey || = a. oa ans 2. 0) N on ROY S| eels (ee MSQOe sles Al kove: = cleal zecmsacmell Meteetere [lame tcl Pox gees IP eseeye [Ie ehsienare letra eee Peep cy let ca a US OW ANn Lette a) Peete 0.040|0.047| 0.380!0.007|5.119]0.048} 5 .620/0.440]/0.270] 0.250 1898 |0.470.0.017|0.100|0.016] 0.430)/0.124].....|..... 10. 310/0.023|5.280| 0.096 1899 10..22010.Ga5|0.. 11010. Col! GO, 540|0,026|",. (e) 2AS 2) = (o} gad e) = 2) = ° = ° — fe) = ° = 2 = Ba. a. = ey a = ies a an | | # ee: ma Vs) Nn TOQO"! lar leee 0.68 |o.004| 0.380/0.005|1. 105|0.005| 0.020.0.005/0.765| 0.002 LSG 71 ulcers 2302 5/0 ) “0216 22,795 d ie. easily 1000 II 110 99.90 | 109.89 vlan sOLLd 22,799 e Steele 1000 08 80 99.80 | 79.84 .16 | 0.04 22,802 d |15, XI. | 1000 12 120 99-95 | 119.94 .06 | 0.10 22.5040 GS 22 eee 1000 20 200 99.99 | 199.98 OZ) ||) On22 22-807 Gi |(2O yee le 1000 o4 40 95.00 | 38.00 ZOO | PLOa75 22,809 d 65 Exe 1000 03 30 93.00 27.90 2.10 1.26 22-01% © 113; 204. | 1000 04 40 85.00 | 33.00 7.00 | 0O.OI 22 OTA) | T5eae UL 1000 03 30 65 00) 19250)|| i1e-50" eG.56 22,816 d | 20, XII 1000 04 40 85.00 | 34.00 6.00! 1.98 22,819 d | 27, XII 1000 02 20 75.00) )i (E560 5.00} 1:06 A Vera Pensa ee ecco ae ne eerie shots 5.64 2513 5d4 FILTER-PAPER CATCHES, ILLINOIS RIVER—Continued. Bit cs} 3 ioe Z bo pel a6 os 22 e Se |) 8 | 88 Vee eae al ee o& 4 S's =, | Go. | Su sven asa 2 A SS s So | spo os oe i og n 5 © na fa Oo = 8 Oa < BH Hoa fe = 1899 22827 at 3; I 1000 04 40 82.00 | 32.80 7 20n\Oree 22,826 d | Io, I 1000 025 25 8€.00 | 21.40 3.60 | O15 22,828 d | 17, I 1000 05 50 95.50 | 47.75 2.25 | 0.50 22,831 d | 24, I 1000 045 45 99.00 | 44.55 7450 O.05 22,033000)| 3, I 1000 04 40 99.00 | 39.60 740))|) (0505 22636,0) | 7, OE 1000 05 So 98.00 | 49.00 3456.0) |} (sith Z22,04tad) | t4,0 EI 1000 05 50 90.00 | 45.00 Le, el Mie Be 5 22b4G dpi, = il 1000 05 50 60:00 | 30:00 |, .20.00) 4 1.92 22,0470) )-28,.. 11 500 41 820 99.99 | 819.92 ,08.)| 0,07 22,850 d | 7, III 500 .20 400 99.90 | 399.60 .40 | 0.54 22,853 d | 14, III 1000 16 160 99-90 | 159.84 TOM) O35 22,856 d | 21, III. | 1000 28 230 99.80 | 229.58 A2) || Os21 22,858 d | 28, III. | 1000 04 40 99.80 | 39.92 -08. | 0-0 PAVIETAC ESAs Sot: ee tek eee EAP EOC enn Bue | 0.41 undetermined extent invalidated by the errors above noted, I wish to call attention to the fact that they may still serve to indicate in some degree the extent of the leakage and its sea- sonal distribution—conclusions which are in some measure corroborated by the results of enumeration. The ratios of the volumetric determinations of the plankton by the silk and fil- ter-paper methods in August—-December, 1896, in 1897, in 1898, and in January-March, 1899, as shown by the averages, are respectively 1 to 4.1, 1 to 3.6, 1 to 2.6, and 1 to 7.7, or, averaging all collections, 1 to 3.38. If these figures approach the actual loss by leakage it becomes a matter of some volumetric importance. An examination of the table reveals the fact that in a third of the cases the estimated plankton in the filter catch is exceed- ed by that of the silk net. It will be seen that most of these cases occur in instances of small plankton, where the tendency, above noted, to overestimate the silt is most effective in caus- ing this apparent deficiency. In all cases the total filter catch greatly exceeds the total silk catch per m.’ (cf. Table III. and the one under discussion). In general the preponderance of the filter catches is greatest in the warm season of May—September, the growing period of 50 vegetation, in which green flagellates and small alge and dia- toms are most abundant numerically, and, therefore, quanti- tatively. Moreover, in 46 of the 105 instances the movement in production, as shown in the rise and fall of the plankton taken by the filter-paper and silk net, is in the same direction, though amplitudes reached are rarely proportionate. The co- incidence is most marked when the catches of the silk net re- veal changes in production of considerable magnitude, as, for example, during the rise and fall of the vernal pulse in 1897 and in 1898, and during the winter changes of 1898-99. There are suggestions in these records of vernal pulses of considerable magnitude, of a large midsummer production, and of a great development in the low water of 1897, when an enormous growth of Chlamydomonas turned the river to a livid green, and contributed to the maximum filter-paper record of 119 cm.’ per m.*, 14-fold the coincident catch (8.47) of the silk net. There is also, even in these erratic data of the filter-paper catches, some evidence of the pulse-like character of the production of these minute organisms which form the greater part of the catch. This appears often to be coincident with the cycle movement in the volumetric data of the silk net, and may best be seen in the records of the winter of 1898-99. The enumer- ation confirms beyond all question the existence of these recur- rent pulses, dimly suggested in these volumetric records. The spring and summer plankton which leaks through the silk is largely made up of small alge, flagellates, and diatoms, with some ciliates, principally Codonella, and rhizopods. The winter plankton thus lost is largely composed of broken colonies of Synura, together with many predatory and elusive [nfusoria, largely representatives of the Holotricha, which multiply abun- dantly with the autumnal increase in bacteria. It can be apparent to no one more than to the writer that such data as these are unsatisfactory in determining the pre- cise volumetric extent of the leakage through the silk. That this leakage is, however, beyond all question considerable must become evident to any one who actually works over collections 556 made by some finer filter than that of the silk net. The work in this line which I have done since the publication of my tests of the leakage through the silk net (Kofoid, ’97b) has only confirmed my opinion as additional data, volumetric and enu- merative, have accumulated. The corroboration of the cor- rectness of my eriticisms on this point by the recent work of Lohmann (708) on marine plankton adds to the testimony against the Hensen plankton-method as a complete quantitative test of the productivity of water. The criticisms which Brandt (99), Reighard (798), and Ward (799) have passed upon my con- clusions in this respect have not stood the test of actual inves- tigation, in so far as the work of Lohmann (’03) and Volk (01 and ’03) and my own investigations, as given in the preceding pages, are concerned. ‘To my mind, owing to si/t contamination, no purely volumetric test is sufficient to solve adequately the problem of productivity of water. It may be possible by pure cultures and measurements of many individuals to establish unit values for the various planktonts, so that volumetric de- terminations can be made from enumerative data, and to sup- plement these by chemical analyses, so that chemical values in proteids, silica, etc., can be in like manner approximated with sufficient accuracy for scientific purposes. This may seem chi- merical at a distance, and it raises at once the question as to the utility of so great an undertaking. Something of the sort is, however, necessary if quantitative plankton investigations are to cease being merely desultory and disconnected and be- come joined in a substantial structure which comparative sci- ence alone can rear. The development of a scientific aquicul- ture demands some standard of this kind as a basis for its per- manent success. COMPARISON WITH OTHER BODIES OF WATER. Comparisons of the quantitative production in the Illinois River with that in other localities are obviously of value only when based on similar or approximately similar data. Asa result of our operations upon the Illinois and its backwaters we 557 are able to compute the mean annual production on the basis of 235 observations extending over a period of five years. At present writing no series of observations of like, or even approx- imately hike, extent has been published concerning any other body of water. Comparisons upon this basis are therefore not possible. The scientific or economic value of comparisons upon other bases than the mean annual production or the full seasonal course of production cannot be great, unless it be for coinci- dent seasons. Furthermore, data of production without com- parable environmental data lose much of their significance. The volumetric determination of the plankton of streams elsewhere has not been carried on to any considerable extent. Steuer (701), in his paper upon the entomostracan fauna of the backwaters of the Danube at Vienna, gives a brief list of organ- isms observed in the plankton of the Danube itself, but no vol- umetric determinations. Huis conclusion regarding the potamo- plankton—a term whose very validity he contests—is: “Das elnzige wichtige Ergebniss der ‘ Potamoplanktonforschung’ scheint mir bis jetzt die Feststellung der grossen Armuth un- serer fliessenden Gewasser an Mikroérganismen zu sein.” It isin a similar vein that Whipple (99) notes the paucity of plankton organisms in rivers, resulting presumably from santi- tary examinations of streams of New England. ‘The results of our investigation upon the [llinois River place limitations on these conclusions. It is a question of time and nutrition and the absence of deleterious industrial wastes. Given ordinary stream water free from poisonous industrial wastes and _ suffi- cient time for breeding, a typical plankton may be expected, it seems, In every river, especially the larger ones, and in the lower reaches of those of the smaller type. Steuer’s volumetric work on the two backwaters of the Danube, covering, it seems, nineteen collections in a period of fifteen months, from June, 1898, to August, 1899, indicates a planktograph somewhat similar to our backwater plankto- graphs in that he finds a vernal pulse in May and a midsum- 558 mer rise in August. No trace, however, of the phenomenon of recurrent volumetric pulses-so prominent in our fuller records —appears in his infrequent data. His statement, “Den ganzen Winter hindurch ist hier constant das Planktonvolumen unmess- bar gering” (italics are his) has no counterpart in winter pro- duction in our backwaters. The plankton of the Elbe and its backwaters has been in- vestigated by Schorler (’00), but no volumetric determinations were made of its channel plankton because of the difficulties occasioned by the current and by detritus in suspension. The quantity of plankton per m.* in three of the backwaters was de- termined in twelve instances in April-October. There are in the data suggestions of a May-June maximum and of one in August, and the quantities are generally higher than the aver- ages in our backwaters, though the greatest amount, 146 cm.’ per m.*, falls below the highest of our records. The channel plankton of the Elbe was found generally to contain fewer species and individuals than its contiguous backwaters. The plankton of the Oder has been examined by Zimmer and Schréder (’99), but no volumetric determinations were made. Regarding the quantitative conditions, Zimmer makes the general statement that these are influenced by tempera- ture. The quantity in December-February is very small, rises in March, and again, to a greater degree, in May, but attains the maximum for the year in August, declining rapidly after the middle of September, and reaching the winter minimum in December. A comparison of the seasonal course of production of plankton in the various lakes that have been explored in re- cent years, with those of our several stations, does not promise any profitable results, since most of the quantitative work is limited in seasons, or has been made at such long intervals as —in the light of our results—to raise some question as to the representative value of such collections for comparison. In addition to this, the very great divergence in the annual plank- tographs of such localities as have been examined, including 559 our own, raises a doubt as to the value of any conclusions de- rivable from such data. Steuer (’01) has suggested that the geographical position of the bodies of water in a large measure determines the character of the planktograph. I should pre- fer rather to put the emphasis upon temperature, which is not everywhere merely a matter of latitude, and also to insist upon the dominance of purely local conditions over those more gener- ally operative, such, for example, as temperature, in determin- ing the amplitude of the movements of the planktograph and the general position of seasonal maxima. Illustrations in sup- port of this view can be found in our own records—for example, in Phelps and Quiver lakes. These are bodies of water within three miles of each other, and with quite similar temperatures, yet their planktographs are in some years quite as different as any of those whose difference Steuer seeks to explain by lati- tudinal positions. Furthermore, the ‘“Sommerschlaf” which he predicates as probable in tropical waters is least of all evi- dent in Phelps Lake, the warmest of all our localities, where temperatures during midsummer approximate those of the tropics. More chronological series of collections at brief in- tervals, not exceeding a fortnight, from many localities are needed before general conclusions of permanent value concern- ing the seasonal course of plankton production will be possible. The maximum production has been used by some writers as a asis of comparison of plankton production in different bodies of water. It doubtless has a slight value in suggesting the relative productivity of waters, though it would seem that an annual average of weekly or fortnightly collections would be very much more accurate. Difficulty attends these com- parisons when deep and shallow waters are brought into con- trast. If the volume of plankton under one square meter is made the basis the shallow waters are at a disadvantage, while if the amount per m.° is made the basis the more barren deeper strata reduce the average plankton content of deep waters to a relatively small figure. Since, however, all strata, at least of most bodies of fresh water, are productive of plankton, it 560 seems best to express the production of a body of water in vol- ume per cubic meter. I have therefore used this basis through- out my paper,and employ it in the following table of compara- tive production in some of the representative bodies of water thus far reported. RELATIVE PLANKTON PRODUCTION BASED UPON MAXIMUM RECORD. Depth | Plankton—in cm.' Locality Investigator Date —in l meters | Per sq. |Per cu. me- meter ter. HilimorsiRaweryereeeeeer Kofoid 3, Vs 1808! o5.8 413.89] 71.36 SPOORV RIVED ecne «rent bs ii, IDS, usop| Aan 60.11 14.59 Quiver Lake wise 2.355. 4 3, | V, 1808!" 4.2 353-98] 84.28 Doomsh Wakes csis ge ccc. i 17, IW, uetols|| oir 102.16] 40.70 laeaealke eres. setee octets Pp V, 1896} 1.64 | 667.55) 407.04 Thompson’s Lake..... 7 I, Win Its] Lt sis 184.32 122.88 | Phelps vake wc. arcnok us 23, VIII, 1898 a2 89.79! 448.96 ) wa, WAND, usis{e}} ir 1439.5*| 684.* Turkey Makes eee Juday, (97) 12, Velie 1896 ae $36.0 135 5* Lake St. Clair..........|Reighard, (’94) 17, AXSSo3) 437 G flag. 17.05 Lake Michigan.........|Ward, (’95) 1, VIII, 1894) 107-8>), 176.29 1.64 Danube, backwaters...|Steuer, (’or) ? V, 1898 3? 36 1122.. Elbe, backwaters...... Schorler, (’99) 20, V, 1898] 3-4 | 438-584] 146 GardaySee nise.. vance Garbini, (’95) — == 50 62 1,21 Jillepits) hers Saami sia oe sero Zacharias, (’96)| 10, VIII, 1895} 4o 862 21.55 PIGRer SCG 4.c.Aaene eee Apstein, ('96) Gy IDSC iibtopl} 97 1242 720i Dobersdorfer See...... Apstein, (96) A) xXersol|iero ss 4242} 218.05 INAvVern (See. s-aceee os Huitfeldt-Kaas, (98) ? Ti 520 74.29 Sognsvandet See....... Huitfeldt-Kaas, (798) 30(?), VI, ? |shallow 240 a Waterneverstorfer See.)_Lemmermann, (798) 1898) 2 70 Bite (ac Lemans... cen. me Jung, (99) 18, VI, 1695) * 120 Iol.9 0.85 Vierwaldstatter See....|Burckhardt, | (oob) ? ? 150. — Neuenburger See...... Fuhrmann, ('00), 27, V, 1899 4o 91.3 2.24 KatzeniSees.44: sion Amberg, ('00) 14, <1, 1898; 5 9,2 1.24 SLblveVeIe SS oodassao se Seligo, (’oo) 9, VIII, 1898 23 2340 IOI .79 *Reduced to settling method of measurement by multiplying by 5. See Juday (’97). +All records for our stations reduced to settling method of measurement by multi- plying by 2. See page 256. A comparison of this maximum production in these various localities, upon the basis either of plankton per square or cubic meter, ranks our localities (barring Spoon River) among the more fertile regions. If the content per cubic meter be the ba- 561 sis, production in Phelps and Flag lakes exceeds that reported in any other body of water save only from the shoaler part of Turkey Lake (Juday, 97). This greater production in Turkey Lake disappears if centrifuge measurements are employed in both planktons, the ratios being 203.52 and 224.48 cm.’ for Flag and Phelps lakes to 156.8 and 27.1 cm.’ for Turkey Lake. The ten- dency on the part of this maximum production in all of the lo- ealities to fall in either the April-May period or in that of August-September is apparent, though in some cases, as, for example, those of Lakes Michigan and St.Clair, and Turkey Lake, the hmitation of collections to a few weeks in midsum- mer precludes the possibility of a vernal pulse appearing in their records. 562 Economic CONSIDERATIONS. The Ilhnois River and its backwaters, under present con- ditions, contribute annually to the wealth of the state over 10,- 000,000 pounds of marketable fish and 15,000 dozen turtles, with a wholesale market value of about $375,000. This amount will be very considerably increased if to this sum be added the in- crease due to retailers’ profits, to the unmarketed catch of local fishermen and visiting sportsmen, and to the annual har- vest of migrant water-fowl which are shot in great numbers for local use as well as for shipment to distant markets. Fish from the Illinois River find their way into the local. markets and are shipped by the car-load from the principal fish- ing centers, such as Peoria, Havana, and Beardstown, to Chi- cago, St. Louis, and New York City. The remarkable increase in the catch of the introduced German carp from practically nothing in 1894 to 5,890,200 pounds in 1901 is one of the fac- tors which assures the economic value of the fishing industry in this stream. These fish find a ready sale among the foreign population of our great cities, and hold the market without fear of rivalry by any of our cheaper native food fishes. In addition to these economic phases of the fishing industry of the Illinois River there are other considerations which arise from its value to the state at large as a field for sport and rec- reation. This cannot be estimated in dollars and cents. The backwaters and marshes teem with migrant water-fowl in autumn and spring, and the spring-fed lakes are the home of large-mouthed black bass (Micropterus pallidus), while the crop- pies, the striped bass, the white perch, and the various sunfish, to say nothing of the catfish and bullpouts, provide no mean sport for the less fastidious angler. Are these present resources of the stream economically utilized under existing conditions? How may they be best con- served? What developments are possible which will tend to in- crease the production of this stream and multiply the numbers of those who resort to it for recreation and sport? Does the investigation reported in this paper have any bearing upon 563 these problems? These are questions which continually occur to one familiar with this locality, observant of the operations of fishermen, and cognizant of some of the seasonal flux of life and matter in this water world of which fish are but a part. The plankton is an integral part of the chain of food rela- tions which extends from the water, with the gases, salts, and products of decay dissolved therein, on the one hand, to the fish and other vertebrates of commercial importance upon the other hand. The water, the carbon dioxid dissolved therein, the nitrogenous matters, and various salts in solution are util- ized either by the grosser aquatic vegetation or by the micro- scopic phytoplankton. In the former case the growing plants are rarely utilized directly as food by any aquatic animals. A possible exception to this statement is found in the case of the turtles. Fishermen are accustomed to feed these animals, when penned up for the market, upon “moss” or Ceratophyllum, though it may be that the insect larvee and mollusks found in the vegetation constitute the more important elements of the food. It is only when this growth of vegetation decays that it releases into the water the elements which conduce to its fertility. The phytoplankton, on the other hand, multiples very rap- idly and is immediately available for the support of the micro- scopic animals of the zoéplankton, and this, and to some ex- tent also the phytoplankton itself, is the immediate food of most young fish upon hatching and the customary food of some adult fishes,—such as Polyodon (Forbes, 88, and Kofoid, 99) and many minnows.—of the bivalve mollusks, and of many other or- ganisms of sessile habit. The plankton is thus the prime source of food of fishes and of many other organisms utilized by fish as food. The chain of food relations, for example, between the food elements of the water and the black bass is in the main a short one, with the plankton as the principal link. Pro- fessor Forbes (’80) has shown that 86 per cent. of the food of the game fish consists of other fishes, principally Dorosoma with 564 perch and minnows. In its youngest stages the black bass was found to be a plankton (Hntomostraca) feeder, and later chang- ing to a fish diet. It is interesting to note that its principal fish food, young Dorosoma, is itself in its younger stages a plankton feeder, secondarily adopting a limophagous habit. The bottom slime thus eaten by the growing and adult Doro- soma is a food largely because it contains so many organisms normal or adventitious tothe plankton. Thus at all seasons the plankton forms an important link in the chain of food relations leading to the black bass. The buffalo-fishes and the German carp are likewise to a large degree dependent for food upon the plankton in early stages of growth, and, lke Dorosoma, subsequently adopt the limophagous feeding habit. The organisms of the plankton thus at all times enter largely into the sources of their food supply. The contents of the digestive tracts of these impor- tant food fishes examined by me at Meredosia during the spring months of 1899 were found uniformly to contain com- minuted vegetable debris, which constitutes the greater part of the unstable ooze or slime which abounds in the backwaters of the river, and, associated with this, many H’ntomostraca, rotifers, rhizopods, and unicellular or colonial alge, belonging to species common in the plankton at that season of the year. The mori- bund, the spore-forming, the egg-laden organisms of the plank- ton sink to the deeper strata, and together with the normal denizens of the bottom slime, which are everywhere adventi- tious in our plankton, form the food of these fishes of greatest commercial importance. A very striking instance of the adaptation of the breeding seasons of fishes to food conditions is found in their nice ad- justment, for the most part, to the seasonal course of plankton production in our waters. Most of our minnows, the dogfish and gar, the Catostomide, the carp, Dorosoma, and the Etheosto- mide spawn in central Illinois during April and the first of May, while the bass, the sunfishes, and many of the Siluride follow in May. This brings the maximum number of young fish, re- 565 cently hatched and generally plankton feeders, just at the sea- son of the vernal plankton pulse, which is often the maximum production of the year. It may well be that the abrupt dimi- nution of plankton following the May and June pulses is accel- erated to a large degree by the plankton-feeding habits of the fry of these fishes. The plankton thus enters directly into the food of most young fishes and of some important adult fishes, and indirectly it is the primal source of food of most fishes. A knowledge of its local and seasonal distribution and of the environmental conditions which favor or impede its development is fundamen- tal to any scientific utilization of the present resources of this stream or any future development of resources now unproductive. The data at hand afford an opportunity of comparing the plankton production and the annual output of marketed fish. The reports of the Illinois River Fisherman’s Association for 1894-1898 give the following statistics based upon estimates and partial records of leading men engaged in the fisheries. They are not exact records, but the error involved is no greater than that in the plankton data. PLANKTON AND FISHERIES. 3 |Total plankton discharged—in Total number , } 3 ee of pounds of Average plankton content in cm.’ per m. fish marketed | [pn channel | In backwaters | Total cubic meters 1894 8,276,227 2.53 4.40 6.93 455757 1895 8,588,000 5-91 10.76 16.67 83,340 1896 7,252,011 1.05 7.18 onZ3 28,629 1897 9,703,298 3-51 5.85 9.36 94,605 1898 10,647,466 2.03 12.42 14.45 63,596 Aver’ge 8,933,560 BG 8.42 Hah 5 163) 67,750 Hydrographic conditions control to some extent the rela- tive possibilities and efficiency of fishing methods, and this adds to the difficulties of comparison. While the relative and absolute amounts of plankton do not determine the number of marketable fish taken in any year, they do indicate in a measure the available primal food supply, and this is a factor in determining the growth, and 566 — therefore the weight, of the marketed catch. Some correspond- ence in plankton and the products of the fisheries might there- fore be expected, though on account of the complexity of the problem and the limitations of our data it is difficult to demon- strate it In every case. ; In 1894, when our data indicate a plankton production be- low the average in channel, in backwaters, in their sum, and in the estimated discharge, we find the total production of mar- ketable fish also below the average (for 1894-1898). In 1895 our collections indicate an increase, approximating 50 per cent. in plankton production as exhibited by each of the methods tabulated, and there is also an increase in the product of the fisheries, though it amounts to only about 4 per cent. The direction of the change in production is the same in all cases. In 1896 plankton production falls in channel, in backwaters, in their sum, and in total] discharge, the decline in all but the back- waters being greater than the increase from 1894 to 1895, and we find, accordingly, that the decline in the product of the fish- eries is also greater than its antecedent rise to the level attain- ed in 1895. In 1897 plankton production again rises in the channel, in the sum of channel and backwaters, and in total discharge, but not in the backwaters. This apparent decline in backwater production may be due to the elimination from our data, for a part of the year, of Phelps, Flag, and Dogfish lakes, thus giving undue weight to the depressing effect of the Quiver Lake data. The fact that in Thompson’s Lake plankton pro- duction rises from 6.67 in 1896 to 10.41 im 1897 is an indication that plankton production in the open backwaters in 1897 rose above the level of that of 1896. In correspondence with the increased plankton production in channel, and total discharge, we find the product of the fisheries rising from 7,252,811 pounds in 1896 to 9,703,298 in 1897—a change not exceeded in any other year of the records. In 1898 the product of the fisheries continues to increase, reaching 10,647,466 pounds, but plankton production rises only in the backwaters and in the sum of chan- nel and backwaters, falling in channel and total discharge. 567 There is thus, in general, a correspondence between plank- ton production and the product of the fisheries in that the di- rection of movement in both is usually the same, They rise or fall together. If we compare the changes of the product of the fisheries with those of the sum of plankton production in chan- nel and backwaters, as given in the table on page 565, we see that the direction of the change is the same in both from year to year in every instance in 1894-1898. If similar comparisons are made of the product of the fisheries and plankton produc- tion in channel or backwaters alone, or in total discharge, we find that in three cases out of four the direction of the change is the same in both. It is also’ generally true that years in which plankton production is below the average are also ones in which the product of the fisheries falls below the mean. Plankton production at Havana, provided a similar plank- ton content 1s maintained until the run-off reaches the mouth of the river, would result in an average discharge of 67,750 cubic meters of plankton, equivalent in weight to somewhat more than 149,050,000 pounds, or 15 times the annual produc- tion of fish. To this wastage of organic matter, which in great part is permanently lost to the drainage basin of the Illinois, should be added the unutilized nitrogen and other food elements in suspension and solution which escape with the run-off, es- pecially of flood waters (see Table X.). How shall this waste be prevented and the plankton be turned into marketable fish? ‘The problem is a complex one, but the results of this investigation should contribute towards its solution. The first step will be to impound the richly fer- tilized flood waters and thus to afford time for the utilization _ of their food elements by the developing plankton, which by various chains of food relations is joined to marketable fish. An illustration of the productive possibilities of impounded Spoon River floods is seen in Phelps Lake, our richest plankton station, and also the home of great numbers of young fish. Thompson’s Lake, another impounding backwater, not only breeds an abundant plankton but contributes no insignificant $ 568 portion of the 1,000,000 to 1,500,000 pounds of fish marketed annually at Havana. The development in recent years of extensive systems of levees in the bottoms of the Ilhnois River for the purpose of protecting farm lands from untimely floods increases the impor- tance of, and necessity for, the reservoir backwaters. In con- nection with these systems it might be feasible from an engi- neering point of view, and perhaps even profitable from the commercial standpoint, to convert some of the adjacent low- lying marshes, swamps, bayous, and lakes into reservoirs in which invading and richly fertilized storm waters might be impounded and retained as river levels fall. The increased vol- ume of water thus provided should—in the light of our results —yield an abundant plankton, and support a large fish popula- tion. Under present conditions of abundance of most of our valuable food fishes in the Illinois, stocking such reservoirs is relatively a simple matter. If properly protected from es- cape at high water, such an area once stocked with the now rapidly disappearing Polyodon, whose roe is much sought for the manufacture of caviar, might become a very profitable in- vestment. As a basis for further development of the fishing industry it seems desirable that public and private waters should be more accurately defined, and that fishing privileges for market purposes in the former should be matters of license or franchise to responsible parties, so that legislation concerning methods and seasons of fishing could be more easily controlled. With the ever increasing industrial development in the drainage ba- sin of the Illinois River, especially in Chicago and the minor cities along its banks, there is great danger that industrial wastes will so accumulate in the river waters that not only the plankton but also the fish and other animal inhabitants will be driven out or exterminated. Legal supervision over the dis- charge of such industrial wastes may soon become imperative for the [llinois River as it has for some European streams. With the legal status thus clearly defined, and with wise legis- 569 lation which should efficiently prevent pollution of the stream by deleterious industrial wastes, protect the most desirable food and game fishes from depletion, and, at the same time, per- mit the full utilization of the annual crop of matured and mar- ketable fish, there is no apparent reason why the Illinois River and its backwaters should not become an increasing source of wealth to the state, and the great waste which now occurs be utilized to a considerable extent in future development. CONCLUSIONS. The following are the more important conclusions arrived at from this examination of the plankton and its environment in the Illinois River and its backwaters, based upon the study of 645 collections made in 7 localities in 1894-1899. 1. There is little correlation between the seasonal flux in chemical conditions (as shown in data of sanitary analyses) and the seasonal course of plankton production (as shown in the catches of the silk net). The nitrogenous matters are in- fluenced by the plankton pulses, especially when diatoms are multiplying rapidly, but the changes are not uniform or pro- portional. | 2. The plankton in the [llinois River is distributed with a uniformity approximately equal to that found in German lakes and in Lake St. Clair. The average departure from the mean in short distances (3 miles) probably falls within + 10 per cent. Chronological catches in periods of 2 to 15 days in 14 series yield an average departure of + 14.1 per cent. In the river, in 205 miles of the course the average departure in flood conditions was + 51 per cent., or + 48 per cent. if the river is divided into four sections, or + 29.7 per cent. if computations are based on total catch of the net. 3. The average departure from the mean plankton con- tent in two tests in a cross-section of the river is + 27.2 or + 23.2, or, omitting marginal collections, + 21.9 or + 12.1 per cent. 4. The plankton method can be applied to a stream as legitimately as to a lake. 570 5. The mean of the monthly averages of 235 collections in the Illinois River is 2.71 cm.’ of plankton per m.* of water. 6. The plankton of the river channel is subject to great seasonal and annual variations. The monthly averages of all collections indicate a period of minimum production of plank- ton in January-February, of rising production in March, of maximum production for the year in April-June, usually cul- minating ina vernal maximum about the end of April and often declining rapidly to a low level in June. The average monthly production declines gradually during the remainder of the year to the winter minimum in December. 7. Individual years vary greatly from these averages as a result of hydrographic, climatic, and other environing con- ditions in varying combinations. 8. The waters of Spoon River contain but a very small amount of plankton (.465) except at very lowest stages, when the flow is at a minimum. Its production at other times (.044) is less than one fiftieth of that in channel waters which it joins. Chemical conditions in this tributary are apparently such as to support a large plankton. The recent origin of the water is the cause of the low production. Its diluent effect on the plank- ton content of the channel is about 10 per cent. 9. Quiver Lake produces less (1.75) than channel waters. At high stages its production is relatively larger, and most re- sembles that in channel waters, while at low levels, when sub- merged vegetation is dominant and access of tributary waters of recent origin relatively great, its production is both rela- tively and actually low. It is predominantly a diluent of channel plankton. 10. Dogfish Lake produces (3.16) more than channel waters, freedom from access of tributary waters permitting a higher production than in the contiguous waters of Quiver Lake. 11. Flag Lake also produces more (9.23) than channel waters, the freedom from access of tributary waters, the im- pounding function, and decaying vegetation favoring high pro- 571 duction. The plantographs of this lake are marked by extreme changes in brief time, and by depression in production with the emergence of vegetation. 12. Thompson’s Lake also produces more (8.26) than channel waters, and maintains its higher level of production more generally. Its impounding function and the freedom from access of tributary waters contribute to this result. 13. Phelps Lake produces the most abundant plankton (22.55) of all our localities, freedom from vegetation and from access of tributary waters, and the highly developed impound- ing function contributing to this result. The maximum pro- duction in our records, 224.5 cm.’ per m.*, was found in this lake on Aug. 23, 1898. This lake is marked by relatively and abso- lutely high production in summer and autumn. 14. The course of plankton production in channel and backwaters throughout the year exhibits a series of recurrent pulses, culminating in maxima and separated by minima, which give the planktograph the appearance of a series of “frequency of error” curves of varying amplitudes. These pulses generally have a duration of 3 to 5 weeks, and tend to coincide in their location in all localities coincidently exam- ined by us. This similarity in the direction of movement in production amounts quantitatively to 65 per cent. of the possi- ble comparisons in our records. This cyclic movement in pro- duction is plainly influenced, accelerated or retarded, or its amphtude extended or depressed, by environmental factors, but is not itself traceable to any one or any combination of them. A brief interval of examination—not more than one week—is essential to a demonstration of the existence of these pulses. 15. Area and depth, within limits of our environment, - show little relation to plankton production. 16. Age of the water is an important factor in determining production in streams. Young waters from springs and creeks have but little plankton, and even such tributaries as Spoon River (drainage basin 1,870 square miles) contain but little plankton, principally of more rapidly developing organisms. 572 This barren water, impounded for 10-30 days in backwater res- ervoirs such as Phelps Lake, develops an abundant plankton. The rate of run-off and replacement of impounded waters de- termines to some extent the amplitude of production. This is greatest where run-off is least and rate of renewal slowest. 17. Fluctuations in hydrographic conditions constitute the most immediately effective factor in the environment of the potamoplankton. Rising levels usually witness a sharp decline in plankton content (per m.’) as barren storm waters mingle with or replace plankton-rich waters of channel and reservoir backwaters. Falling levels are periods of recovery and increase in plankton. Stability in hydrographic conditions conduces to rise in production at all seasons of the year, and instability is always destructive. Winter floods tend to lower plankton production; spring floods increase it. 18. Temperature affects production profoundly. Below 45° the plankton content in the river is only about 9 per cent. of that present above this temperature, and in backwaters but 29 to 40 per cent. Minimum production is at times of mini- mum temperature. The vernal pulse in production attends the vernal rise in temperature and culminates at about 60°—70°. With the establishment of the midsummer temperatures (about 80°) production falls from 44 to 87 per cent. in channel and backwaters. It rises, however, 65 per cent. in Phelps Lake, so that other causes than temperature may be operative in pro- ducing the midsummer decline. The autumnal decline in tem- peratures 1s accompanied by decline in production in the channel and in Quiver Lake, but by an increase in other backwaters, which exhibit a tendency toward an autumnal pulse. The de- cline to winter minimum occurs in December. An early spring accelerates, and a late spring retards, the vernal pulse, and a late autumn prolongs the autumnal pro- duction. Summer heat pulses often attend plankton increases. Minimum temperatures are not prohibitive of large plankton production. The December production in Phelps Lake in 1898 (43.14 em.’) exceeds the vernal maximum elsewhere in all local- 573 ities but one, but falls much below the summer production in Phelps Lake. The ice-sheet is not inimical to a considerable plankton production unless stagnation conditions occur. 19. Light affects plankton production. The half year with more illumination and fewer cloudy days produces from 1.6 to 7 times as much plankton as that with less illumination and more cloudy days. Seasons of unusual cloudiness are accom- panied by depression in production. 20. Lakes rich insubmerged vegetation produce less plank- ton than those relatively free from it, in an annual ratio of 1 to 6and a monthly ratio varying from 1.5 to 20 to that of 1 to 20. The higher ratios generally prevail in periods of dominance of vegetation. Quiver Lake produces more plankton when free from vegetation than when it abounds in it. The emergent and rooted vegetation of Flag Lake conduces by its autumnal and vernal decay to large plankton production, but tends to de- press production in summer. 21. The normal regimen of the course of plankton pro- duction in the []linois River and its backwaters does not form a definite seasonal planktograph, but consists rather of a series of recurrent plankton pulses, whose varying amplitudes are largely determined by the fluctuating environmental factors of the unstable fluviatile environment. Hence planktographs of the same locality in different years and of the different sta- tions in the same year show resemblances only in such funda- mental features as the winter minimum and the vernal pulse. The relative productive rank of the several localities is gener- ally maintained, and more completely in the more stable en- vironments. | 22. The plankton of the Illinois River is largely autono- mous. Seepage and creek waters are diluents of its plankton and add little to its diversity. Even Spoon River is generally a diluent, reducing the plankton content 10 per cent. and add- ing but few diversifying species to its population. The reser- voir backwaters, on the other hand, generally contain a more abundant plankton than the channel, the amount, on the bases 574 of monthly averages, being from 1.3 to 17 times as great. At all levels, waters from impounding areas in the bottom-lands are drawn into the channel, mingled with the plankton-poor contri- butions of tributaries, and further enriched by the growth of in- digenous channel plankton. The reservoir backwaters are thus of great importance both as a source of the channel plankton of the [llinois River and in its maintenance. 24. The total annual production of plankton in the [llhi- nois River, on the basis of normal discharge and a plankton content at the mouth of the river equal to that of our average record at Havana, is 67,750 cubic meters. 25. Filter-paper catches indicate the presence, on an ay- erage, of a plankton 3.3 times the volume of that taken by the silk net. Leakage through the silk is therefore a matter of some volumetric importance. 26. The annual production of plankton and of the fisher- ies of the Illinois River show some correlation in their changes from year to year. 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RELATIVE NUMBER OF PLANKTONTS IN ILLINOIS RIVER AND SPOON RIVER. ALGA DIATOMS RHIZOPODA MASTIGOPHORA INFUSORIA Date | 2 2 2 2 ca) i) i=] ° | ° g ° i= ° a as § aS g # Ss aa 5 A 8 fe! ay = Q = = = 2 = a = mM = M lal mM onl oD) ll mM 1896 7 18 VIII |} 83,200) 6,080) 8,896, 000 11,280} 28,800} 5,960} 1,508, 000 3, 360 23,800) 3,540 2 VIII 4,840 576 1, 025, 200 29,876) 18, 080) 768 110, 000 960 11, 200 192 16 IX 5,446) 1,200 390, 489 3, 360] 16, 850) 2, 880 CEN oe hee. 40, 106 240 30 TeX) 105-840)... 2 682, 200 6,240} 14,280) 8, 160 TGR (00 Hare ee ae 27,672| 2,400 14 xX 4,560} 2, 160 816, 400 10,080] 80,400) 2,640) 1,111, 200 480 65,200} 1, 200 29 he ere AS || Pec veces. 1O)200) See D280) ee ee AS). wee 1, 920 17 XI 2, 800 480 1, 064, 500 480) 25,200) 3, 360 88, 800 480 44, 000 7, 200 oF aL 396 480 963, 916 7, 200 873 500 179, 606 240 10, 083 480 OS ap XOlli BH280 eevee 165, 960) -......-.-.- 120 480 64, 880 120 1, 440 240 Average] 14,420) 1,495) 1, 745, 583 9, 688}) 16,825) 3,336 414, 166 680 27, 938 1, 985 1897 ; 3 II AO) Seana es 231, 900 240 300 720 42, 420 160 Sy 400 |e eres 26 A AP Wikeeeetoecee Sense Ae SOON ASO eevee 10,700) 37, 440 46, 600 3, 840 18, 800 2, 880 22 en HOG bates sea - 1,231,900} 240,000} 2,240) 105, 600 172, 100 9, 600 18,240} 19,200 27 IV 13/6002 ...|| 328, 414, 820 102, 000} 11,520) 379, 200/27, 987, 400) _............. 515,920} 42, 000 25 V | 68,400) 7,500) 79,827,200] 3,048, 000) 25, 760| 40,900] 9,029, 360] 43, 200 29,600} 98, 400 28 WI] 49,000} 2,500] 1,937, 600 85, 200] 232, 600] 13,200) 148, 006 3, TO0|12, 186, 000] 1, 300 10 VIIL| 74,680) 3,800) 2,318,160] 54,000] 8,400) 1,200) 489,600) 18,000) 27,600} ........... 26 VIII | 166,760) 24, 000 847, 320 4,800) 19,200). -.......- 408, 160 53,000]; 180,000) — 5,000 i TX | 406, 400) 816, 000 282,440} 662,400] 118, 000) 28, 800} 1, 624, 800) 5, 030, 400 42, 000) 249, 600 2 XI] 28,980} 145, 000 148,880] 744,000] 3,900} 2, 400 1,100) 33,600], 26,500} 55, 200 Bit) Bt SEY eecck ences 90, 725 24, 000 800 ae 11,100] 116,400) 244,420) 4,900 28. XII 1,200) 3,600 65, 400 36, 000] 16, 640)....-.....-- 15, 400 54, 000 45,600) 19,200 Average] 66,725) 85,534!) 34,644,610} 416,920] 37,505) 50,788] 3,577,171) 447, 158] 1,109, 007| 41, 473 1898 25 I oth eee ee 174, 901 16,800) 66.338) 19, 200 22, 059 2,400] 190,017} 39,000 22 II Bal59 meee | 211, 653 4, 800} 141,524) 21,600) 227,448). .-........ 69,498} 14, 400 29 Ill AUK) | Pearce 132, 140 27, 320 1,400) 1, 760 324, 800 640 42,020! 18,880 10 V_ | 68,800) 6, 240) 314, 224, 400) 1,778,400] 49,800] 14, 880/84, 967, 600 55, GSO 129, 600} 11,520 7 VI} 17,200) 2,400) 30,803, 600 31,200) 23,600) 21,600) 597, 000 7,400) 1,516,000} 63, 600 5 WVII| 50,040) 18,000] 3%, 772, 000 7,200) 19,360) 10,800] 536, 800 51, 600 20, 440) 108, 000 5 VIII |) 308, 040) 16, 800 360, 240 50, 400), 16,8u0) 14, 400 252,400) 112, 800 129, 600 3, 600 12 IX 57,060) 3,700) 1,217,000 8, 400] 28, 006) 22.800 19, 500 2, 400 56, 640} — 6, 000 4 X | 25,000) 1, 440 837,200 37,440] 12,580) 4,840] 265,600) ~ 16,800 35,900} 1,440 2 XI 18.500) 5, 500) 981, 000 15, 000) 32,060) 2,500! 5, 500) 3, 600 69, 060} 16, 800 (> OE (|| Lewes | 251, 250 9,120|| 1, 000 480) 1, 708, 000 4, 320) 7, 620 8, 480 Average] 50,373) 4,916] 32,087,762) 180,553! 35, 678} 12, 260) 8, 084, 246 23,422) 206,036) 26, 065 1899 | 3 I 20| See eae | 10, 300 3, 840 220 960) 143, 020 3,360] 108,940) 1,920 7 NO) |e eee eee eee | 66; (50 |2a2ee 1,125) 1,200] 117,000 7, 200 6,000} 1,200 (ee LAO) 2ees aces | 59, 120 800) 3,200) 38,400) 899, 200).........._.... SONSZ0 | Poeseeees Average 33 45, 390 1,547] 1,515) 13,520 | 386, 407 3, 520) 48,586} 1, 040 Grand Av....|_ 43,539] 30,513] 23,031,820] 293, 788|| 289, 637|_ 23, 281| 3,921,328} 161,149], 468,051| 22, 999 Ratio... 1.4 1 78 i Se 1 2A 1 20 1 : 615 TABLE XIV.—Concluded. RELATIVE NUMBER OF PLANKTONTS IN ILLINOIS RIVER AND SPOON RIVER. ROTATORIA ENTOMOSTRACA \INSECT LARVA) MISCELLANEOUS |TOTAL spRoris TOTAL PLANKTONTS Date 2D n n n n n o a i) | te) =| i) g 9 | i) =} a 8 & i lines! S & Sratteces S iS S S| = = i ee 2 Sis | 4 = iy _ mM = NM fol mM i mM Lal mM Ll iv 9 1896 18 SVL 361, 680 2,720} 68,160) 600) 160 240) 4,120 680} 114 fi 34, 460 ae VU 185, 720 768) 31,480) 36 80 | 1,488) 1,520 216) 100 22 34, 704 16 LX 45, 592 3, 600] 63, 070) 3, 360) ...... 240) 2, 607 240) 85 19 14, 520 310) IID 48, 642 960} 16,400) 560)......... 280) 2,400 | 1,480} 85 20 20, 080 14 x 131, 600 3, 56) 9,120} 480} 320 80) 4, 640 24 68 22 20, 920 29 ENS || Aces es ASO ae ee 2,000)... 2s. PAN eee 2! i ae eect QS lillian ee eee 30, 680 NiGee a okcl 172, 800 2,88 4, 920 4 80 80] 5,360 | 2, 88 63 20 5, 408, 460 17, 880 ae aH 86, 700 84 ON 340 eccsee || eeeenes SOM GG eee 56 12 1, 252, 579 9, 820 2 a. @ OE 100, 340) 240) 26,140) 13 40 30 520 120} 42 9 362, 720 1, 360 Average] 141,634 1,561) 28,539) ney 85 309} 2, 854 655) 77 24 2, 892, 085 20, 492 1897 | 3 II 10, 460 500} 3,520 GOs 2 40} 1,040 |........ 44 10 293, 080 1, 720 26 It 26, 200 27880) 2-1 00] ee 2S) eee | ere 6,400 | 5,280} 45 16 450, 280 52, 800 re SOU 47,180 20, 000) 21,320] 9,600) 440 |.......- 2,080 {19,200} 8&1 11 1, 498, 200} 423, 200 27 V | 1,276, 000 34,800) 67,000) 4, 200 320 600) 4,000 |28,800) 67 20 || 358, 278, O80} 591. 600 25 V || 2,287,160) 217,400) 84,720) 600)..__... 2, 100} 10, 240 | 2,500) 90 36 || 91, 362, 440) 3, 460, 600 28 VI 351, 900 27,900) 22,700) 1,900) 100 £00} 40, 900 200) 71 33 || 14,968,406} 136, 700 10 VIII 658, 120 15, 300] 116,100, 700) 160 400 24, 400 |.......- 102 33 3, 667, 220 93, 400 26 VIII | 2, 059, 360} 1, 330,200] 86,240; 600) .__... 400] 15, 760 |......... 80 32 3, 782, 800} 1, 418, 000 11 =X |} 1, 744, 250) 2, 362, 400] 618, 750)10, 000). ______. 4, 006) 26, 000 |.-....-.. 32 49 4, 832, 640/11, 467, 600 Pe ok 8, 900) 1, 072, 800} 19,500} 7,900)... 100} 1,900 |........ 65 29 239, 660} 2, 061, 000 BOR kl 109, 840) 1, 965, 600) 55,340) 600) ........).....-.. 7,000 | 2,400) 46 19 520, 165) 2, 113, 900 28 XII 9, 040] 1,135,200) 5, 720/10, SET aes |e TOO eeeeee 48 13 160, 760} 1, 258, 800 Average] 715,701) 682, 082 93, 918) 3,987) 85 703) 11, 757 | 4,898) 67 25 || 40, 004, 478) 1, 923, 277 1898 ede 25 IT] 126, 603 2,600] 4,788) 600) 77 |.----.-- 7,661 | 5,000) 7 18 592, 831 85, 600 22 IT | 48, 649 800} _3, 285)....-.-- ee ope Wrael | 3,285 200} 35 9 708, 501 41, 800 29 Til 115, 880 17,920) 22,180) 3,160) 80 |.--..-.-- | 1,940 720) 100 31 70, 400 10 V | 2,663, 400 24, 480) 235, 400) 2,800} 400 400) 13, 200 960} 78 40 1, 895, 360 a VI 903, 000! 22, 900} 438, 800/14, 700} 400 | 2, 100) 23, 600 | -...... Gina 165, 900 sy AVAile 153, 000 8,400) 4,920) 1, 200) 760 | 3, 700) 5,040 200 96 23 209, 100 5 VIII | 1,294, 240 61,200] 22, 160)...... 80 | 2,000} 3,360 |.-...... 81 41 2,386,920) 261,200 29) IX 197, 960 2,400) 24,720) 100) __..... 1,400) 2,420 | 1,500! 89 20 1, 603, 300 48, 700 4 ».¢ 105, 020 2,880] 33, 880) ..-.... 40 160] 2,700 |........ 79 24 1, 287, 720 65, 000 2 XI 156, 300 9, 600) 8, 600 1 Laer aes eee ce 4, 360 200} 75 24 1, 275, 380 53, 300 (Hj DIM 64, 280 7, 280) 9,740) 120)........ ae GSO eee 40 17 2, 043, 090 24, 800 Average] 529,848 14,587) 73,498) 2,089) 167 887]| 6, 204 798] 7 25 || 41,071,067} 265,560 | 1899 || | | i 3 I 41, 300 GriZOln eeaS40l) 40s eee eee 2540s | eee eat: UG 18 309, 280 16, 840 if II TIES LOpeeeee see | 13,976 600) SOI eee 29 6 318, 022 10, 800 6 Til 108, 860 SOOM MS O00 aoe eee [fee aeoe 2,140 12,000) 47 | 6 1,121, 980 52, 000 Average 87, 490 2, 507| 11, 772 20a | eee 41 10 5x3, 094 26, 547 Grand Av....| 465,067} 238,828) 63, 983) 616) 6,805 | 2,430) 69 24 | 28,283,295) 750,429 Ratio .... 1.9 1 28 1 238) |e 2.9 1 38 i \ | 616 TABLE XV. SOLIDS IN SUSPENSION AT STATION EH, BERKEFELD FILTER. Cu. em. | Cu. em. Silt River Accession number Date strained| silt | percum.| gage OF PERC Iggy, 5, 000 1.40 280 2.6 15, XI, 1897 10, 000 1.53 153 2.8 2o5) Nel, 1897 5, 000 1.50 300 2.8 30, XI, 1897 5, 000 2.10 5d0 3.2 7%, XII, 1897 5, 000 6.56 1, 312 3 14,° XII, 1897 5, 000 1.28 256 3.4 20) xen 180% 5, 000 5. 26 1, 052 3.2 28, XIT, 1897 5, 000 - 93 186 32 1, I, 1898 5, 000 4.25 850 Sali 21, T, 1898 5, 000 7.60 1,520 5.8 25, I, 1898 5, 000 5. OL 1, 002 6.8 3, II, 1898 5, 000 4.00 800 7.4 8, II, 1898 5, 000 2.71 542 eal 15; II, 1898 5, 000 7.86 1,572 9 22, Il, 1898 5, 000 8.01 1, 602 10.7 1, III, 1898 5, 000 3. 60 720 11.4 8, ILI, 1898 5, 000 2.51 502 11 15, III, 1898 5, 000 3.71 742 12.1 22, ILI, 1898 5, 000 2.34 468 14.1 29, III, 1898 5, 100 4.90 961 16.5 4, IV, 1898 5, 000 3.91 782 17.6 125 Wit S08 5. 000 4.40 880 14.8 19, IV, 1898 5, 000 1.81 362 150 26, LV, 1898 5, 000 2.04 408 12 3, V, 1898 5, 000 2.07 414 atlhal 10, V, 1898 5, 000 2.29 458 10.3 17, V, 1898 5, 000 3.97 794 10.1 24, V, 1898 5, 000 3.0L 602 13.6 ale V, 1898 5, 000 2.11 422 13.6 7, VI, 1898 5, 000 1.98 396 12:5 14, VI, 1898 5, 000 1.43 286 11.9 A Ji, 1898 5, 000 ET 254 10.8 28, VI, 1898 5, 000 2.80 560 10 5, VII, 1898 5, 000 1.90 380 8.7 12, VII, 1898 5, 000 1.94 388 ii 19, VII, 1898 5, 000 2.04 408 4.7 26, VII, 1898 5, 000 1.56 312 2.9 2, VIII, 1898 5, 000 1.58 316 Pal 9, VIII, 1898 5, 000 2.58 516 3.2 16, VILT, 1898 5, 000 1.69 338 Built 23, VIII, 1898 5, 000 3.08 616 4.2 30, VIII, 1898 5, 000 2. 42 484 3.9 6, IX, 1898 5, 000 2.90 580 4.7 13, IX, 1898 5, 000 2.54 508 4.2 20, IX, 1898 5, 000 2.40 480 4.2 2%. 1X, 1898 5, 000 Sess ae Se 4.9 4, X, 1898 5, 000 2.30 460 4 i / X, 1898 5, 000 1.70 340, 3.9 18, X, 1898 5, 000 1.26 252 3.8 25. xX, 1898 5, 000 4.00 800 4.3 1, XI, 1898 5, 000 3.20 640 6.3 8, XI, 1898 5, 000 2.77 5a4 6.7 15, XI, 1898 5, 000 4.41 882 Meal 22, XI, 1898 5, 000 5, 82 1, 164 8.5 29, XI, 1898 5, 000 1.48 296 8.3 6, XII, 1898 5, 000 . 74 148 7.2 135 NonIG Sos 5, 000 3.74 748 6.7 15, XII, 1898 5, 000 hay 234 6.6 20, XII, 1898 5, 000 1.04 208 5.9 27, XII, 1898 5, 000 1.26 252 6.1 3, I, 1899 5, 000 4.20 840 6.8 10, TI, 1899 5, 000 3.75 750 7.9 iy T, 1899 5, 000 6.30 1, 260 8.2 24. I, 1899 5, 000 4.06 812 8.9 Sule T, 1899 5, 000 3.06 612 8 le If, 1899 5, 000 3.42 684 8 ie II, 1899 5, 000 1.15 230 105) 14, II, 1899 5, 000 1.42 284 6.6 21, II, 1899 5, 000 1.80 360 5.5 28, IT, 1899 5, 000 27.08 5, 416 10.2 ie MU e899 5, 000 20.30 4, 060 12.9 14, III, 1899 5, 000 7.40 3, 480 13.1 21, III, 1899 5, 00' 16. 82 3, 364 IB i/¢ 28, III, 1899 5. 000 9,35 1, 870 13.5 rie ON. a eet tC Fi OEE INT 592. 22 617 TABLE XV.—Continued. SOLIDS IN SUSPENSION AT STATION M, BERKEFELD FILTER. . Cu.cm. | Cu.cm Silt River Accession number Date strained| silt | percu.m,| gage 30, XI, 1897 5, 000 Rey 314 3.2 28, XII, 1897 5, 000 120 240 3.2 20, I, 1898 5, 000 13.11 2, 622 6.8 99 II, 1898 5, 000 5. 64 1,128 10.7 29, III, 1898 2,500 20. 11 10, 044 16.5 10, V, 1898 5, 000 5.10 1, 020 10.3 te Val 1898 5, 000 3.38 676 12.5 5, VII, 1898 5, 000 1.63 326 8.7 5, VIII, 1898 5, 000 3.58 716 2.8 12, IX, 1898 5, 000 6. 62 1, 324 4,4 4, X, 1898 5, 000 2.20 440 4 2, XI, 1898 5, 000 2.92 584 6.5 6, XII, 1898 1, 900 61 21 1.2 By I, 1899 5, 000 2.56 012 6.8 ub II, 1899 5, 000 94 188 7.3 qo) DEES 1899. 5, 000 40, 35 8, 070 12.9 NRO Ee ETM Ca) a hol) ae ee eee Reel ee alee a ee eee eee sees 1, 745. 55 TABLE XV.—Continued. SOLIDS IN SUSPENSION AT STATION C, BERKEFELD FILTER. ‘ Cu.em. | Cu.cem Silt River Accession number Date strained silt per cu.m. | gage 155) XG 1897, 10, 000 .98 98 2.8 30, XI, 1897 5, 000 1.47 294 3.2 14, XII, 1897 5, 000 1.50 300 3.4 28, XII, 1897 5, 006 58 116 3.2 iil I, 1898 5, 000 3.31 662 3.7 25, IT, 1898 5, 000 2.01 542 6.8 8, TI, 1898 5, 000 2.24 448 ol 22, If, 1898 5, 000 2.80 560 10.7 8, ITI, 1898 5, 000 2.04 408 ii 22, II, 1898 5, 000 1. 66 332 14.1 4, IV, 1898 5, 000 9.38 1, 876 17.6 19, IV, 1898 5, 000 2.68 536 13:1 3, V, 1898 5, 000 1.63 326 ileal ane V, 1898 5, 000 1.10 220 10.1 24, V, 1898 5, 000 1.58 316 13.6 te Nek, 1898 5, 000 1.02 204 12.5 21, Vi, 1898 5, 000 . 84 168 10.8 5, VII, 1898 5, 000 40 80 Sai 19, VII, 1898 5, 000 1.10 220 4.7 2, VIII, 1898 5, 000 1.03 206 2.7 16, VIII, 1898 5, 000 1.65 330 oat 30, VIII; 1898 5, 000 2.01 402 3.9 13, IX, 1898 5, 000 1.85 370 4.2 27, LX, 1898 5, 000 1.62 324 4.9 os X, 1898 5, 000 1.06 212 3.9 25, X, 1898 5, 000 . 89 178 4.3 8, XI, 1898 5, 000 1.14 228 6.7 22, XI, 1898 5, 000 1.75 350 8.5 6, XII, 1898 5, 000 93 186 hz 20, XII, 1898 5, 000 .78 156 5.9 3, I, 1899 5, 000 1. 66 332 6.8 aly JT, 1899 5, 000 5.48 1, 096 8.2 31, T, 1899 5, 000 3.06 612 8 ile II, 1899 5, 000 2.15 430 § 14, TJ, 1899 5, 000 1.12 224 6.6 28, IT, 1899 5, 000 19.78 3, 956 10.2 14, III, 1899 5, 000 12.99 2,598 epi le Osean 2d state Te SE Des Ay Lad) oa a 28, IIT, 1899 5, 000 8. 82 1, 764 13.5 AV ERAS CMOr COS eee ee eee es ee ae ee ey eee 378. 46 618 TABLE XV.—Continued. SOLIDS IN SUSPENSION AT STATION G, BERKEFELD FILTER. Cu.em. | Cu.em. Date strained silt 1897 5,000 |° 7.85 Accession number 2.8 1897 5, 000 5.36 39) 1897 5, 000 7.50 3.4 1897 5, 000 1.41 3.2 1898 5, 000 2.10 6.8 1898 5, 000 2.26 iipal 1898 5, 000 1.92 10.7 1898 5, 000 3.23 il 1898 5, 000 4.01 14.1 1898 5, 000 4,68 17.6 1898 5, 000 3.18 13.1 1898 5, 000 1.66 11.1 1898 5, 000 1.37 10.1 1898 5, 000 3.10 13.6 1898 5, 000 . 96 12.5 1898 5, 060 1.25 10.8 1898 5, 000 1.48 8.7 1898 5, 000 2. 42 4.7 1898 5, 000 3.80 2.6 1898 5, 000 4.14 oni 1898 5, 000 3.80 3.9 1898 5, 000 4,23 4,2 1898 5, 000 2.06 4.9 1898 5, 000 6. 86 3.9 1898 5, 000 4,12 4.3 1898 5, 000 2.85 6.7 1898 5, 000 1.45 8.5 1898 5, 000 1.08 ee 1898 5, 000 1.55 5.9 1899 5,000 |. ° 2.66 6.8 1899 5, 000 3.88 8.2 1899 5, 000 3.52 8 1899 5, 000 3.18 6.6 1899 5, 000 8. 91 10.2 1899 5, 000 13.86 13.1 1899 5, 000 11.65 13.5 A VOT ARC TOT TSOR i Ve ee eee eae ew ean aoc eae eae eae 556. 48 TABLE XV.—Concluded. SOLIDS IN SUSPENSION AT STATION F, BERKEFELD FILTER. . Cu. em. | Cu.em. Silt | River Accession number Date Rhanod silt per cu. m, | gage 3, III, 1898 5, 000 4,20 840 11.3 15, III, 1898 5, 000 9.08 1, 816 12.1 29, III, 1898 5, 000 15. 25 3, 050 16.5 DOGR IS Aor! Genie He ans 2 a a 12, IV, 1898 5, 000 4.76 952 14.8 26, IV, 1898 5, 000 4.95 990 12 tl V, 1898 5, 000 2.26 452 10.1 31, _V, 1898 5, 000 6.12 1, 224 13.6 14, VI, 1898 5, 000 5. 63 1, 126 11.9 ~28, VI, 1898 5, 000 2.09 418 10 2, WII, 1898 5, 000 3.84 768 ff 26, VII, 1898 5, 000 7.16 1, 432 2.9 9, VIII, 1898 5, 000 10.00 2, 000 3.2 23, VIII, 1898 5, 000 12. 47 2, 494. 4,2 6, IX, 1898 5, 000 24,12 4, 824 4.7 205) Xe 1898 4,500 16, 01 3, 558 4.2 dean eXeoe (808 5, 000 12. 43 2, 486 4 18, _X, 1898 5, 000 11.18 2, 236 3.8 2 OL, TES 5, 000 7.24 1, 448 6.5 15, XI, 1898 5, 000 6.51 1, 302 ral 29, XI, 1898 5, 000 2.91 582 8.3 13, XII, 1898 5, 000 . 70 140 6.7 Die eSoliIees G98 5, Q00 2.23 446 6.1 10, I, 1899 5, 000 3.90 780 7.9 24, I, 1899 5, 000 2.34 468 8.9 ike Sule 1899 5, 000 4.44 888 eS 21, II, 1899 5, 000 1. 64 328 5.5 He TT 809 5, 000 9. 48 1, 896 12.9 21, Ti 31899 5, 000 18.57 3, 714 13:7 — Average for 1808..-.--.-.-2-.-.- SS eee SSutelets Si le Sa ae = 1, Byes BIBLIOGRAPHY. 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V., pp. 45-66. iad: 03. Neue Ontersuchungen tiber den Reichthum des Meeres an Plankton und tber die Brauchbarkeit der Verschiedenen Fangmethoden. Zugleich auch ein Beitrag zur Kenntniss des Mittelmeerauftriebs. Wiss. Meeresuntersuchung., Abth. Kiel, N. F., Bd. VII., pp. 1-88, Taf. 1-4. 14 Tabellen. Magnin, A. 93. Recherches sur la Vegetation des Lacs duJura. Rev. gen. de Botan., T. 5, pp. 241-303. Marshall, W. L. 90. Annual Report upon the Improvement of the Harbor of Chicago and Calumet, and Illinois and Calumet Rivers. Lo- cation of Illinois and Mississippi Canal, and Operating and Care of LaGrange Lock on the Illinois River. Ann. Rep. Chief of Engineers, 1890, Appendix JJ, pp. i-viii+ 2399-2605. Maxwell, W. 96. * " * * Report of the Hawaiian Experiment Station, 1896. Palmer, A. W: 97. Chemical Survey of Water Supplies of Illinois. Prelimina- ry Report. 98pp., 3pl., 1 map. Champaign, III. Pieters, A. W. 94. The Plants of Lake St. Clair. Bull. Mich. Fish Comm., No. 2. 12 ppeiamaip: 01. Contributions to the Biology of the Great Lakes. The Plants of Western Lake Erie, with Observations on their Dis- tribution. Bull. U. S. Fish Comm., Vol. XXI., pp. 57-79, Pl. 11-20. Reighard, J. E. 94. A Biological Examination of Lake St. Clair. Bull. Mich. Fish Comm., No. 4. 60 pp., 2 pl., and 1 map. 98. Methods of Plankton Investigation in their Relation to Practical Problems. Bull. U. S. Fish Comm., Vol. XVII., pp. 169-175. . Rolfe, C. W: 94. List of Altitudes in the State of L[llinois. Bull. Ill. State Lab. Nat. Hist., Vol. IV., pp. 36-137. 625 Russell, I. C. 98. Rivers of North America. XV- 327 pp., 23 fig., 1 table. New York. Schorler, B. 00. Das Plankton der Elbe bei Dresden. Zeitschr. f. Gewasser- kunde, Bd. III., pp. 1-27. Schrider, B. 97. Ueber das Plankton der Oder. Berichte das deutsch. botan. Ges., Bd. XV., pp. 482-492, Taf. XXV. Seligo, A. 90. Hydrobiologische Untersuchungen. I. Schriften d. naturf. Ges. Danzig, N. F., Bd. VIL. pp. 43-89. 700. Untersuchungen in den Stuhmer Seen. Nebst einem An- hange: Das Pflanzenplankton preussischer Seen, von B. Schréder. 88 pp., 9 Tabellen, und 10 Taf. Danzig. Steuer, A. 701. Die Entomostrakenfauna der ‘‘alten Donau” bei Wien. Hine ethologische Studie. Mit einem Anhang: Zur Frage uber Ursprung und Verbreitung der Entomostrakenfauna des Susswassers. Zool. Jahrb., Abth. f. Syst. Geog. u. Biol. d. Thiere, Bd. XV., pp. 1-156, Taf. 1-12. 20 Abb. im Text. Volk, R. 701. Die bei der Hamburgischen Elbe-Untersuchung angewand- ten Methoden zur quantitativen Ermittelung des Planktons. Mitth. a d. Naturhist. Mus. in Hamburg, Bd. XVIII., pp. 137-182, Taf. I-III. 03. Hamburgische Elb-Untersuchung. I. Allgemeines tiber die biologischen Verhialtnisse der Elbe bei Hamburg und tuber die Kinwirkung der Sielwisser auf die Organismen des Stromes. Mitth. a. d. Naturhist. Mus. in Hamburg, Bd. XIX., pp. 65-— 164, Taf. I.-VIL. Ward, H. 5B; 96. +A Biological Examination of Lake Michigan in the Trav- erse Bay Region. Bull. Mich. Fish Comm., No. 6. 100 pp., 5 ple Ward, H.B., assisted by Graybill, H. W., and others. 700. A Comparative Study in Methods of Plankton Measurement. Trans. Am.Micr. Soc., Vol. XXI., pp. 227-247, Pl. XV.— XV IT. 624 Whipple, G.C. 98. Classification of Lakes according to Temperatures. Am. Nat, Voly Ren. pp 25-33. 93) ie. 99. The Microscopy of Drinking-Water. XI{-+300 pp., 20 pl. New York. Whipple, G. C., and Jackson, D. D. 700. A Comparative Study of the Methods used for the Measure- ment of the Turbidity of Water: “lech. Onarty, Volaaimi, pp. 274-294. Yung, E. 99. Des Variations Quantitatives du Plankton dans le Lac Léman. Arch. d. Sci. Phys. e. Nat., Ser. 4, T. VIII., pp. 344-364, Pl. II. Zacharias, O. °95. Ueber die wechselnde Quantitat des Plankton im Grossen Pléner See. Forschungsber. a. d. Biol. Station zu Pl6n, Th. i, pps oie U7. 06. Quantitative Untersuchungen uber das Limnoplankton. Forschungsber. a. d. Biol Station zu Plén, Th. IV., pp. 1-64. Zimmer, C., u. Schréder, B. 99, Das Plankton der Oderstromes. Forschungsber. a. d. Biol. Station zu Plén, Th. VII., pp. 1-24. Zumstein, H. 99. Zur Morphologie und Physiologie der Huglena gracilis Klebs. Inaug. Diss. 50 pp.,1 Taf. Leipzig. Also, in 1900, in Jarb. f. wiss. Botanik, Bd. XXIV., pp. 149-198, Taf. VI. ERE rN SONGOE Ee Ah ES PrAree ls Map of the Illinois River Basin, modified from a map in Cooley’s “ Lakes and Gulf Waterway,” facing p. 58. Boundary of catchment-basin of whole system shaded, those of individual tributaries marked by dotted lines. Ig AGI EO le Map of field of operations of the Illinois Biological Station at Havana, III, 1894-1899. Locations of plankton stations in Illinois River (E), Spoon River (M), Quiver Lake (C), Dogfish Lake (L), Flag Lake (K), Thompson’s Lake (G), and Phelps Lake (F). * PruAce EN: Illinois River bottoms at high water in spring flood in March, 1808, looking westward. River gage about fifteen feet above low-water mark. Taken from base of the eastern bluff, just below field headquarters (see Plate II.) on Quiver Chute. En-: tire bottoms submerged, Quiver Chute and Illinois River united, Seeb’s Lake show- ing dimly through the forest on west side, beyond this the broad expanse of Flag Lake, with low forest intervening between it and Thompson’s Lake. Western bluff visible. PLATE IV. Illinois River at low water during summer of 1894. Taken from same point as Plate II]. River gage about 2 {t. above low water, showing minimum levels since erection of dam at LaGrange. Mud spit between Quiver Chute and Illinois River exposed. Summer foliage and atmospheric conditions obscuring bottom-land waters to westward. RGAE Vi. West bank of Illinois River a short distance below plankton station, looking northeastward. Taken during low water in midsummer of 1894. Sloping shore of black alluvium covered by low vegetation. Narrow marginal belt of vegetation visi- ble. River about 400 feet in width. PraAre VI. Sun-spots, rainfall, and riverlevels. Upper section of figure taken from Lockyer (or). Middle section gives fluctuations in average rainfall in Illinois above and be- low the mean, as given in records of U.S. Weather Bureau. Lower section gives fluctuations in mean annual river levels, compiled from records at Copperas Creek dam, 1878-1899. Average of all annual means shown at the left. * Plates IV., XV., XVII., and XXI. are from the Biennial Report of the Director of this Laboratory for 1893 and 1894; plates II., V., VIII., XVIII., XIX., and XX., from that for 1895 and 1896; and plates III. and XVI., from that for 1897 and 1898. 626 PLATE VII. Hydrographs of Illinois River, 1879-1899, from records of State Canal Com- missioners published in reports U. S. Army Engineers, taken at lower gage on Cop- peras Creek dam, and from records of U. S. Army Engineers, taken at lower gage on LaGrange dam, 1883-1899. Mean hydrograph at the right based on means of monthly averages. Pie Nae: WOU Seasonal distribution of plankton in Illinois River, Station E, in 1894. Volume of plankton in cm.? per m.* of water shown by heavy black ordinants, the diagonal- lined apices of which indicate the estimated proportion which silt forms of the total catch. Thermograph in dotted lines, from records of surface temperatures made at the times of plankton collection. Hydrograph in continuous line, plotted from rec- ords at Copperas Creek. Heavy black areas at top of plate indicate the relative number of cloudy days per month at Havana, the vertical space equaling seven days. Pi Nate, IDX The same for 1895. Hydrograph from Jan.1to Aug. 8 is that at Copperas Creek, and thereafter in the main from Havana records. Relative thickness of ice- sheet indicated by black area at bottom of plate, 1 mm. equaling 6 cm. of ice. PLATE X. The same for 1896. Hydrograph entirely from Havana records. PLATE) ool, The same for 1897. iPoAwins STU, The same for 1808. PLatTeE XIII. The same for 1899. PEATE) OCvV, Spoon River near its mouth, looking toward southwest from first bend in the stream. Plankton station (M) located near trestle. Taken at moderately low water. PLATE XV. Quiver Lake in midsummer, 1894, at low-water levels, looking northward from Station C (see Pl. Il.) toward the mouth of Dogfish Lake. Littoral vegetation in foreground. Driftwood indicating high-water margin. Lake rich in vegetation. Plankton station located in narrow strip of open water in middle of lake. PEATE, XVI: Quiver Lake, from same location, in low water of 1897. Only a small amount of marginal vegetation visible. Dogfish Lake also largely free from vegetation. PraArEe xcViIL. Western shore of upper end of Quiver Lake, looking northward, showing rich- 627 ness of vegetation. Emergent Ve/umbo Zutea Pers., with leaves, flowers, and seed pods. Submerged Ceratophyllum demersum L. Taken in low water of summer of 1894. PLATE XVIII. Dogfish Lake, looking northeastward, in low-water summer conditions. Lake full of Ceratophyllum, Elodea, and Potamogeton. Plankton station (L) near center of lake. PrarEe XCxXc Flag Lake in autumn of 1895 at plankton station (K), looking north-northeast- ward. Scattered dwarfed clumps of Scz7fus and an abundance of Vymphea consti- tute the principal vegetation in this open area. PEATE SOG Thompson’s Lake from shore station (G), looking southwestward, in low-water conditions of midsummer. Lotus bed in distance, and broad belt of submerged veg- etation, principally Ceratophyl/um, along shore. Plankton station (G) in open water to the right (northward), e PLATE XXI. Phelps Lake, looking southwestward from plankton station (F), in midsummer in 1894, just as the lake was drying up. PLATE XXII. Seasonal distribution of plankton in Spoon River (Station M) in 1896. Scale of plottings of plankton o.1 cm.* per vertical unit, instead of I cm.*, as in case of all other stations. Dotted portion of ordinant indicates estimated proportion of silt in total catch. Thermograph plotted from surface temperatures of water at times of collection of plankton, and hydrograph from gage-readings in the adjacent IIlinois River at Havana. Ice indicated by black areas below diagram, I mm. equaling 6 cm. of ice. PLATE XXIII. The same for 1897. The excess of plotted plankton-silt ordinants over limits of diagram is indicated by figures at top. PLATE XXIV. The same for 1898-1890. PLATE XXV. Seasonal distribution of plankton in Quiver Lake (Station C) in 1894. Scale of plotting of plankton-silt is 0.4 cm.’ per vertical unit. Hydrograph is that of the IIli- nois River at Copperas Creek. Thermograph is that of surface temperatures at times of plankton collections. PLATE XXVI. } The same for 1895. Hydrograph from Jan. 1 to Aug. 8 is that of the Illinois River at Copperas Creek, and thereafter, from river gage-readings at Havana. 1D Aa a RO AVAUIE The same for 1896. Hydrograph from gage-readings in the Illinois River at Havana. 628 PLATE XXVIII. The same for 1897. PLATE XXIX. The same for 1898-1899. PLATE XXX Seasonal distribution of plankton in Dogfish Lake in 1895. Hydrograph from Jan. 1 to Aug. 8 is that of the Illinois River at Copperas Creek, and thereafter, at Havana. PLATE XXXI. The same for 1896. Hydrograph is that of the Illinois River at Havana, PLATE XXXII. The same for 1897. PLATE XXXII. The same for Flag Lake (Station K) for 1895-1896. PLaTE XXXIV. The same for 1897-1808. PLATE XXXV. Seasonal distribution of plankton in Thompson’s Lake (Station G) in 1894. Hydrograph is that of the Illinois River at Copperas Creek. PLATE XXXVI. The same for 1895. Hydrograph from Jan. 1 to Aug. 8 is that of the Illinois River at Copperas Creek, and thereafter, at Havana. PLATE XXXVII. The same for 1896. Hydrograph is that of the Illinois River at Havana. PLATE XXXVIII. ‘The same for 1897. PLATE XXXIX. The same for 1898-1899. Prag ck, The same for Phelps Lake in 1896. PEATE Sclele The same for 1897. PLATE XLII. The same for 1898-1899. 629 BVArE Xe lit Seasonal distribution of chemical data and plankton in Illinois River in 1895- 1896. Chlorine, oxygen consumed, free ammonia, albuminoid ammonia, total or- ganic nitrogen, nitrites, and nitrates, in parts per million, plotted according to scales specified at the left, and plankton in cm.’ per m.’, according to scale at the left, in the form of a continuous planktograph. The hydrograph, with scale at the right, is plotted in the usual form as a continuous curve. The planktograph, and the chlo- rine and nitrite plots are also in continuous lines, but, owing to distribution of data are more angular, Nitrite scale should read 0.1 to 0.3. PEATE SceiVe The same for 1897. PEATE XLY. The same for 1898-1899. PLATE XLVI. The same for Spoon River (Station M), for 1896-1897. Nitrite scale should read 0.1 instead of Io. PEATE Oe Ville The same for 1898-1899. Plankton scale at the left should read 0.1 to 0.4 in- stead of 1 to 4. PLATE XLVIII. The same for Quiver Lake (Station C) for 1895 and 1897. PEATE SLX The same for 1898-1899. Jeney Naess 1Le The same for Thompson’s Lake for 1897, 1898, and 1899. Nitrite scale should read 0.1 instead of 1. : ni t Hts ) Py ca ae ae i i chy yi t, r - a, Vweiroe eal ERRATA AND ADDENDA Page gg, line 6 from bottom, for (’87) read (’85); line 5 from bottom, after Rod, read, (’94). Page 100, line 3, page 132, line 10, page 264, line 11 from bottom, page 457, lines 7 and 15 from bottom, page 458, line 14, and page 541, line 8, for Ward (95) read Ward (°96). Page 159, Feb. 18, for 6.8 read 8.8; June 30, for 3.5 read 5.5. Page 160, Oct. 9, for 7.79 read 7.9. Page 161, Nov. 24, for 6.6 read 8.6. Page 169, line 14, for Zable /. read Tables [1I.-—1X, Page 170, line 15 from bottom, for V///, read V//. Page 202, line 9, for (’96) read (’97). Page 253, line 15 from bottom, for (97) read (’97a). Page 263, line 12, for 7599 read 7890. Page 282, line 11 from the bottom, for—43 per cent. read + 43 per cent. Page 288, line 2 from bottom, transpose 37.8 and 28.8. Page 290, line 2, for 2 ¢o 5 read 7 Zo 25. Page 295, line 18, omit the first eight words; line 20, for 2.72, 7.08, and 4.07, read respectively, 7, 22, 0.72, and 3.94. Page 311, line 14, and last line page 313, for zode read mode. Page 310, line 14 from bottom, for 7//. read XZ/V.; line 4 from bottom, for the read am. Page 323, line 9 from bottom, read zz 7897 after catches. Page 332, lines 16 and 17, for exceeded read Preceded. Page 343, line 14, for cm. read cm.*. Page 350, line 17, for guaditatively read quantitatively. Page 357, line 6 from bottom, after 76.76 read on the 24th. Page 358, line 18, after azd read decreases the. Page 367, after heading Dogfish Lake read Station L. Page 371, line 4, before decaying read Zo. Page 372, live 16, after maximum read in Quiver Lake. Page 381, after heading lag Lake read Station K. Page 385, line 14, for wbe//a read uvella. Page 403, line 17, for food read floods; line 18, before /uly read of. Page 4o5, line 1, after ve/ative read annual; line 8, for 7597 read 7596. Page 414, line 12 from bottom, for szver read area, and for drains to read reaches. Page 416, line 12 from bottom, for zs read was. Page 422, line 7 from bottom, for 5 read 3-5. Page 424, line 12, for (.¢5) read (45 cm.); line 13, for (.05) read (5 cm.); line 16 from bottom, for food read floods. Page 429, line 4 from bottom, for 22,35 read 22.55. Page 430, line 2 from bottom, for ¢he read ¢hezr. Page 440, line 8, for mean read means and for ¢he read their. Page 463, line 4, for Zo read zm} line 5, for peculiar zz read peculiar Zo. Page 484, in table, transpose Vegetation-poor and Vegetation-rich. Page 501, line 1, for show read shown. Page 505, last line of table, column 4, for .4 read 4. Page 510, line 9, add, axd Volk (’03). Page 546, line 15 from bottom, after zs read zn the main. Page 540, line 1 below heading, page 551, line 1, and page 556, line 3, for (‘974 read (97a). Page 556, line 7, before ’0? read ’oz and. Page 560, table, second column, line 4 from bottom, for (’00d) read (’oo),; line 6 from bottom, for /umg read Yung; line 16 from bottom, for (’95) read (’g?),; line 17 from bottom, for (99) read (’oo); line 19 from bottom, for (’95) read (’96). Page 584, at head of second column, for 7597 read 7898 ; under remarks, line 4, for above read along. Pages 597 and 508, below table, read *Bottom visible. Page 508, eighth column, line 7 from bottom, for 0.76 read 0.28. Pages 599-603, 606-610, 612, and 613, below table, read *Plankton not collected on same date as sample for water analysis. Pages 599-613, columns 2-4, meaning of symbols, abbreviations, etc., as follows: -++ = rising river level. v. d. = very decided. — = falling river level. v.11. = Very much, + = stationary river level. Decimal in color column=volume c. = considerable. of standard ammonium chloride d. = distinct ; decided. solution required to develop the fe htened: same tint when diluted to fifty cu- bic centimeters with ammonia- free water and treated with the usual amount of nessler reagent l= little: m. = much. n. f. = not filtered. s. = slight. ESE > i. i . NgOsS 2 ing tenn a : : i FIELD OF BIOLOGICAL STATION OPERATIONS. Low water. Drawn ty LYDIA M. HART. AFTER U. S. GOVERNMENT SURVEYS, REVISED BY MEMBERS OF THE STATION STAFF. 2 Q aed 2220 2 Oe OPO D0 eee NY Cue. ee RR @ Q -! ror Aentel Ces 5 OP g Loee Minors River eP So OPS THAD ENS @ 4\o Nes N\20,2 2 et Marsh Re Foresi ‘ie Sandbar. ; Wagon Road =e AN —— — sation Seale of Milas. WSubstation. Re RR eRe @NV] YAAING AO LOOT YVAN ‘AALVAA HOIFL LV AFAIY SIONITT]T loowaIHo ZNVW. a A. it ail is gs : Ml FF ld @AVT YAAING) AO LOOT YVAN “YALVAA MOT LV AFANT SIONITIT foes ieee ae Al ®8\d BA OTE NOLLVIS “INV ISH WOW ‘AALVAA MOTT LV UAANYT SIONITIT ees hee VL Plate MEAN#PULSE MEAN -PULSE 1884 /885 /886 1/887 /888 /889 MEAN+PULSE —-PULSE inn AI aoatenee Bee i a a plamier Peis pina Bre es Se 1a =o a EST Sr Aue sec ea a CT La ES ES SS 71 Ue |e a SECRET vz 220 ieee Nae? CE aaa | RRSSRee ees =iRESEGRSLESaS fe | LE =NMERNERREREED bale A a 2 | =HRUR) LE EEEEEER Ral ee Seeeeeeee 4/893 189% 1896 (896 1897 /898 /899 /900 | WALLA | ia ca SS Bae ia eC ae iB ear espa Gea. UN EA 4 Heal [| --4 nae i || a3 at cit Nari iV il 489/ 1892 7 BRR SH Pi SSRSesees=. REBRAeE ees Gage ears: BEBSEee see RSs lee (ca ales ee ea je ESE aa ia acca ia ie ime ales a ei Hi? oe BN Ni T INZ| ga / H Pa A bas || JAE ww eS ae IE] el ie ei a el @ See a al ES NX Fes 4, “pe ste 7 eA BA ee "at aeeae ZA se A En 2 le Es ala aes cis xi = ed ica = |_| Ne IN |i SRA: SSB mi ac 1862 /883 tae Wages es gs pac | V7 sa SEEGER EeSeereHac Ud ta = Po| d 7 LZ = /877 1878 /879 /88O /88/ ZZ Pleat Bee Soeee sc GRBESE EGeS | SURVES OF RIVER LEVEL, RAINFALL AND SUNSPOTS i : ‘ 1882 LOWER GAGE AT COPPERAS ORBEK DAM. 1807 1888 18890 1890 1891 1892 1893 1894 1895 1896 FEE oe sels e ash le! EM pelle sitll], BIE ie ARS LOWER GAGE AT LAGRANGE DAM i. - q } a [ : [ Sonceseueus Ja Generar Hyprocrari or Intrnois River, 1879 To 1899 tt 1898 18090 E BEESESESREE! aut a ch TH 2 Coo { a | Tt EEE t sane T TH CON f ty { ia qa Plate vil 20% | Mean.1870-1809 | iff is] ha 15 20f Mean, 1883-1899 E co CHIC | ! coaneeatiee! i ea >I \ Hl ! | : Re I + + HoH : : SEEHEEC HERE aeolian | NS | (ao if ira + ‘TIP L EE Cope on oe Sete eS a | SS) oe ee Fo ae | ! - SP 3 " cit | | Conc 7 coo | HEH FH ECE : mim TH Hels eal | ie 444 | é ae Sa] IG TA ®d PSB) JUNG Pe UOIHUe/ 4 3B: WONINADAYSIy ToUDsOaC, Plankton Cm3 UoIHue/y yO woTyNg1445 17] ToUDSoAC, 7 RELuuELE Lk sce [TZATT VIII AT Ty (ITTTAITLITITY BAU Ser aanas: Uozyue// JO u019NQ1A9S1] TOUOSCAG G River Gage Ft. 222202, —— ra RUBE WZLLLL mE: "hs Bn nak. W7777 77242 vous @. a 77777) | eee SINE ~ AaMTOTERTCA STU IL ass (TAT TIT BELLE LI Ts LAT TT AT TT, jt —_} —— ; Hi s : s b : Ny + | I : / 11+ i” : i 8 : mh [estan = 5 Tempratwel| a a LPF} 4 fs tt zi TX Pid “BBB Jug von yueyy 0 wonbedysiqy ous; Temperatu | Plankton Cm? T ea } 1 «| River Gage Ft. ] = IX ld fe 014 uel JO WO1WNGI.4SIC] JoUDSvAa River Gage Ft 7 Plankton Cm3 G 2 % J ip) “HLAOW SLI YVAN ‘WAANT NOOdS Ms Fo. a fr re ONiKeor ici NOILVLANGA AO TINT “ANW] AAAINC) AX 82ld NOILVIGOU A HO AWay “AAV T MHALNAC) OO¥aIHO ZNVW TAX Pld adaq SoLoyT “Avay, LV aavy MAAN) HIAX 838 \d aANV] HSIAD0(] SUNITA, GS Fs wary. pong eK sani, pbtetgy a aIV] OVI a SSSR aANW] S,NOSdWOH] re 8) "XX Bte|d STUSSAW GNV HSIq Gvaq ‘AY ATAVAN ‘ANW]T SdTAHYG “IXX 938d ~~ ime ee eh See WwW wns ee U0pyUe/_Y JO W01yNg1YS1P] ToUNSoA River Gage Ft. emperature F.* lankton Cm! “9/295 et ee BRae aa TS ~ ate Av CATT TITTY fe ee eee eee SEs zie SS BS Bs es Bs ee ee BERR Site EEE Temperature F* Plankton Cm DX ld Ler WS coe Samos = | 0 SSS = al ¢ ZZZZZ2A1 aera (a a Sd ed OD a a 5 a a a Ha OS a es ~ BEBI oak ad Se = ce nin “Ate Uo,HUe/-{ jo Uo Sle Plankton Cm? 7) 2x % 3S n F1IS I] youosoa AXX Pid “PEBP* QuumgG Fw UO,4Ue/—} YB UBHRALYSIC] TouosBAC 6 RiverGage Ft. s 091 SI | tu! nm. 2! S ail § 2 | gi] © €/ & oo Bers pits 2 kek: SEB} Oo wus per [se eA | a zs IS ra U0734UC/-7 38 WOIYNgL.YS1C] yoUDseAC, eds Gogh 7 MS P” U0QyUe/_Y JO wo1yNg1A4S17] JoUDSVAC on 2 K ! \ — H Ni : if: t \ rh ; Wy | \ \ / | ; x \ | EEE lease \ “| pa ales) ||] et fe a 4 } | =k A \ mel | (nal | r i L \ ip ie ta IN a | ah | Ih 2 is \ Aalto wat |} | +9 \ r - \ N U — _ - eet nina i ag = IT ahaa lia | 6 Woh Ht Bn vt ee ea | in | YEN fal = _|\ ne | : ho | \ SNe } {Ay} = il eae lal ie | \ 01 |08 [Se Neale =. | IL att al nin iT | || | ila esis 7 3 j | eilssire| el Ge ETE I A 4 4+ — 4——}-—++ —— +—+—_+- + +— oye { | | Sal | al 812 oI oie ea 1 | = S 5 el See §|| Bi] 2 f jel is : c 2 | | LS §|| &} 3 \|. Toa aS SSeS el ealalul eye |i $9/89S <«l 0 = ease 2 = | =F = a4~< u He < Mee a +4 / \ Ob |S | | | | ; t ase Sie PA [ é i | | | A He ' / 0. | » | + : ; 4 C \ 7 i++ iY } + mel LI z i ‘2 4 im esi i Ma |_| { t | [ \ ie | 7 i || Z | ‘I iP “neal if ic \ /\ | | LAE L oe Beat 14 < \ 0, | | | : | h vi + ee \ 7 =I T 6 T | ie IE Stlainvie = aT | si) + Tr i | to Ap Ta t—+ \ [Mi \ \ 1 \ iI | l 4 | fl Pare ite A &§ | c Ol] Bi) 8 o ers a >}} El] ss eye yo "83/B9C ee Cer: J mers U0JYUL] 4 3: WATANAIAYSI] ToUosoAC; ae (668) 0 _4-- | | NIDA z Naa | | \ / | Flas: E j £ SS i \ NI 1 i] +--+ ; aa Es es \ al | [ \ g Aes u Be LL = ==! A 9} |09 ft L KS eae : A. 4 [S \ = . T ay 7 1 | 6 a el z a va * / \|4 al id iT 1 2! |0 ie | i T ry ale a IL | hind fo eS L allie } e2'|8 Hegeseeeaiees ae 1 = esata PES Cosel | (Le ee il [Sd us a = = ane) ES = >] El) ala SaeIS BBP NSB 1070e/,7 fo umn asicy uoeeT; a. ESP y “ = = [ ea a \ as + 4 x i HAR 7 EEO \ \ y ie | Siem Poet oat [ f [| \ 4 th r — — + ia T =|: le Et Nt | | eRe A | i Sa Ie He 5 et Ur ts | 4} : 3 La CI am | AL - i +—+-—+ =a nae feraseleiaiate | | 1 ia) [ Ett Fe ++ = tt 1 +— J 1 PEA | TIE |v eee A Poo ae) emg UOIYUL/_Y JO waIYNGIAySIC] yoUosoIG _| River Gage Fi eraturef. P Plankton Cm? em, ve) a) % S ee) DXX Pid “OBB oS U014UL/_Y JO woTyNgI.YSI] ToUDSoAC EAICLARS Av. Plankton Cm? -| River Gage Ft. Temperature F.? G au % yy ” TXXX Pid 268) 7 AS Pas Sis as SCANS SER ee | JIS RaYe Soid esei secon oevtast ate ates artneiaehs tia BERG rece SQ SS ct ee ee eee im Toe : Shae sae beeel ND Beee aaa FEE teSeiraa geet depeifectons EE sue dostlatantort (Zon) cutateed intastane tpestiandi eed! Et Ea ieee UI aged eae SUPE isestscete PNCEEEN EE ECIEPR, BESS ‘Sannin Serr (ae ea | KT TT Th aps SN | ||4 Seep se C#e#ttfl fas C20 aoe nee GEESE CM Gi a a Sa Sees ieeahevoatocevacttatts (tas au ctaced ineelaatenOm ECHR ECE Breanna tase PN | ate cis oa es EEE eo SCENE ee eee 7) 1 SSE WS A Da SsES ion! ccacseetistel fest asfaitant EEE ude ee} Besreeeecaeslae Ea | P| HHH | || ml | VE HH es Ss ee alk Soeaievalisoeyaeue (adel deed foedieved deg tiraeususiigeee(| BSERIIEERIIGES SESGaaee)'Sua0 SU8\'VSeileeetaeeet eee eee eee cee eS ee ee | ee ee es yo * UOIHUL/_Y 38 WETINALAYSI] JOUOSAG oy re hein ~> WIA ye N vx 0 01 a et ay Bae Beale LC ~ ETA ELEALT TIA TET ETA Bowe BEA ame mi B4aa0 Cane ES —— Pa q J 2 a se Baues Sh Sees | | ro PEE eee ToMae aan BE Ee ee ees es ee ee Ee es ee en es a ____.___ Bee A PL pepe at i el abe EEE peaesuiae Zoe Bee aa SS SR SS SS SD eS ee estes waa aca pada seGke EEE sas a seeeeeer (=a SRS je a fa = a | and {Plankton Cm? ' f i ; 2) @ 2 % S River Gage Ft Plankton Cm3 2 | |0r ; FA —_}—_}—_}— —t—- Al jp ht et —}— —}+—+ if 4 SL Hee ea We be id { eal £ : : ee See ees = tt 4 4 fo 4 } = OL 4 | OL \0 = bile { = ral + | “ie i lel ‘ 6 aa eae cial ee LUT le + = T = i Ian ae = 5 =I ra al come] saa = = i= lin T + ft} a ah yale — - =i 4 hn Ht Ne | Gi River Gage Ft. Temperature. F. ag Ol Plantcton Cm 4 - | | River Gage rate Plantxton Cm? *sgjeo MOO Pd BEB) NAS me VOIHUe/_7 30 WERMATSIC] Tous, FBI . ot Station G , 1894. Plate XXXV LTE TS i Fea LER sa USS ETE OPP ON Fc eT ARS Ss SESE ahh Sees as LL = ez2Zee BREESE Sa i ee ee ae p ee Se eS a eee = SS SS i es [es nee ESE EES=== e777 P= a aS Sao AEE EEE = BERRA SEER EE es } | Raheee ae ics |_| Seosonal Distribution of /ankrton 7 7 Sea ee 3 co 4 = ai ware aes < it eg err e | ee ME +i u reat i ae ts 3 eat ae \ all | | \ | |_| eal ¢ \ je CI 7 L [ MI iSiSiaiel zs | [ \ | Be a | DEReee Che CHA zi mai Bina We | | ol a tz | sal ia l | Yi} basal | | iL cl | et | Ss a 4 5 i al Ilo O]| § | | | E Gipalil ietesl SBS elt! "Saye IAXXX Pld “SEBO usveIG FP 4YOI4UE/ + UoHNg1.13S 1] ToUosoaS pr19 ®| Plankton Cm? -4- pb TD dda) 7 MS uozyue/_} U91INg1AYS 1] yoUCSvACS Ob Plankton Cm? | RiverGage Ft. Temperature F-° ” a © iS) Ce) W77 a = P. sities rT Let | (pete Bam UT ATT ia - a [oils oae BERRRES So cohmoee BREEDS aaae UZ 77 77 TVA TIAXXX Pid ‘ZE8I°O veg m° | YOJYUe/{ w uonnaLsIC] Toussoa IES Stee } | : + it iL | = 5 |B | : a 1] id e oO i-*) yA River Gage-Ft. > a %, 3 3 “te | Temperature 3 R 3 + oe) O|--7==-===== = ‘| Plankton Cm3 a & | — Fc] >< +3 =a | lA lA, LE i ik AT | SIE i aN eH / / LAS Th We INT ur \ \) ‘i IN| \ +f | | \ y \ \ | POOR Cea eT RSNA ee AN ana Pel ae NEL Late ie 7K “ies | (eB, IN | NS \ ATA HTS MST TST SSRN SUN ease |S Sh / aa Saeco! Ch atrivetien of Chemical Data and Plankton, ot Station £, 1896, - RiverGageort[ JY J J 4 Sue aR Reae a) eee = See |S ta : : (a ro a a : Bene Bie ‘ i oP Beue ie Ba EI PAI pan |_| R Vv oH a 5 es = |_| ae Ae he