- : ~~ atk ' > ‘ 7 Pee ST : 2 fas : ' z , : of » ps . ‘ - aw 5 ¥ , wd , A 1 “4 ™ ‘ i es ee a te ah en ate etieennatitetom pie sensy ss sapmneperiere’ samen ae aa <4 a heen ete ne ip tna a : te Ae iim Vinnie weer ng ge ul aa SOUS IAUIIRTANT INAS TE RNP RAVE HEE ANNIE AWE REA Ch OMI MEMORNEEE A eM Re wu bP oe 1: eeP/ndnst ae en of etapa 4 on 9 me ANG He Voi 98 hay emit 08 teotem donc ip ema an aohu-xacteleits THIS BINDING No. SEE PENCIL MARKS ON TITLE PACE WARD BROTHERS, LIBRARY BOOK BINDERS IMPROVED METHOD JACKSONVILLE, ILL. SEND FOR PRICE LIST STAT- ING WHAT YOU HAVE FOR BINDING. Pe ‘lA » . Fi \) / \ oh ‘ ] oh =) { + ‘4 re pie Oe) Bde i rs et Py “a ' f j i i J 1, m) | ; | > A Ath A f ba My “ ; Ava 1 ee rae Bea ae , ] - , “J i a < Pe ‘ i \ ] 1 f b : spi t ie Hy A it i 7 } eal i] oO i ae fh iy i Ly | ital \\ BULLETIN OF THE ILLINOIS STATE LABORATORY OF NATURAL HISTORY Ursana, Iturois, U. S. A. VOLUME VI. 1901-1903 CONTRIBUTIONS TO THE NaTuRAL History SuRVEY OF ILLINOIs, MADE UNDER THE DIRECTION OF S. A. ForsBes GAZETTE PRESS CHAMPAIGN, ILLINOIS 1903 UNIVERSITY OF ILEINOIS BOAKD- OF TRUSTEES THE GOVERNOR OF ILLINOIS, RTS ETCAVERSID an AGU Ess pate fatavesel choters forrielal'e (ols aie letisisisletelshelateysteheverslstetarertepal=l=ieK Springfield THE PRESIDENT OF THE STATE BOARD OF AGRICULTURE, IVI SK eG RAMEE S ON iors role teimieisieie «ies cinta ststeietetaloeicia: | rain eoioiere Lawrenceville THE SUPERINTENDENT OF PUBLIC INSTRUCTION, JNIEISISIEIO) BYAWALIIS IS cmtorabeate upn Oot une DODmOUD Send oenEOs TOoere Springfield ANIEINCID, ANSISRONRNE INES OU MIDS cope doooon caste DRanoLdoBabecn aoNe copsoe caer Urbana ARES Es 1) IRS Serre UNG GEM creer tete et tevaie rakeleianavstelniatalclei ns s'nia’o\elwteraiefelaivislseleyese Spring Grove AMUCGUISINUIS). [Ae ISMG 8 MRINKEVNI UE poo oceoc nod doucOsOncpunndes Sercousgacn Chicago PAVE BENOAUN I Es ROSIN G IGPLAUN a aatemetsereistel sisisteterieigeors 2)elonni=-(ielateiciarsiae lam eos. LA COMP SVAMMUJ DIE AN, TULA Dea sso aopeorpeoobOOoUnnenn oC nocnooosbeacns Springfield (CAMISURUID, SES NIG GAIN DISIRUE 5 oc ooh cogosun oop ubbS cauopnanoocueon . Belleville AYLI GIEIUNIM INTs IM CCR CUM DIC 6 Commosnerenmopeecs boas ea EDUdOs eons Coa Champaign (ETE OMNPUOVAS Ib, GCI IR LENS A aomSoObeuoOOOonoLO olibncosocoos pote Bloomington PEAS UIRCAC IS Sa BL VAUN'S « ctici-yareis ise aires aYefetete ewes sic cistaeaeeversteiclotetere eieveisrsisreie oie Taylorville ANDREW S. DRAPER, LL.D., PRESIDENT OF THE UNIVERSITY STATE LABORATORY OF NATURAL HISTORY SCIEN TMFIC, STAPF, 1903 STEPHEN A. FORBES, Pu.D., DiRECTOR CHARLES A. HART, SysTEMATIC ENTOMOLOGIST E. S. G. TITUS, M. S., FigLD 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 CONTENTS ARTICLE I. THE DRAGON-FLIES (ODONATA) OF ILLINOIS, WITH DESCRIPTIONS OF THE IMMATURE STAGES. PART I, PETALURID#, AASCHNID#, AND GOMPHID#. BY JAMES CoN EOL AM AND: CEA RIE S VAL HART tii. 22. sana se derce ose s( PAI CDLON sarrveeie acess esos aiken ieee easel sels o vise) ansaiare ea sie eeraiaie atsraicieis we DORIDSR CHEN Ro 7a on dajoarenncs Oboe a SCOOCRED Cao AO SEMOee Oona UcGecacc Characteristics, Phylogeny, Gnd PAmitzes....- 2. 0s. 20> coae aces cose sees ETOP EEE ERE SE Noe Phakisis sale es ae Ress Onis afeaewing adie ss Bemerae ne 6 oe eine ILE CETIS TG he GO ABO ODS SOR See Coa OOE AGS SE Ce DEDAE SRC CG ai aac WLS, COGS po neeeabeeoned semenesae HO OUE Een oda nOe roa aencude PE VRP AGC PETIOGSatstalo see aioiss = wintaiaieielisiatorsss\eysiclhaidie sew cae ainon's Change of nymphal color at molting time... ................ 0000 seeeees RET AaSIOL DAMON rae secre eee ere neers ci aclcit iain wie Siatincins Wel atatoleees same OMT EESN OT SES Ss asa anode Sods Doce Gan nOs OnE anaso. aeIcE aa aie iaCaeOCe Relative abundance of nymph and imago.... ............ see sees eeees AGTH NADIES cc ace occas. actor Se salaeecieca meses wo ptaraslelare ahaoa Smmle EIstory, of OGonata Observed at Havana. oc. ssc.0< cece wasn cecies ee nce ae= Waters from which Collections were made .... 0.1... cece cece cece cee sone Nymphs inhabiting Various Kinds of Situationse .... 000.00 cece cence Living among submerged vegetation LENA ha eS, agree So don co eso sioth A Aor ECOG A SORES SarivOs HOAG GUCCI AS Living concealed in mud‘or sand bottom... 2 2... 2 sae ona dees cies cose Nymphs inhabiting the Various Illinois Waters...... 00. cece eee eee es LARS TAC Slab oe gasp aaan dso on ooeeh ban Sapoceddtcnobe Souacnsee SHAN SEISULE ALS co ale nyajaeee ne eve (atch sin ciel «ture el orate wisicraleisie Mone = ste sia eTaeie asics OR RCLALLONS 552 2 cae esses 5 « FUMIE MY LALA pe ete eee Ce en ae Nsom a (salons viele oisisiele Me es\ne as acces INROTPH OEE toler | oor, Ge oboe adeanonbeosc geese tania eek Cecio ots ietanic 's slo COTEPLAL ARE REATINE Sor oraciaia a aeiais sisisl.s = 0s) salou! ss/e'e Sbis's.cis,50 ba Ss asad o5m5,6 Collecting PLES CUM ID Meera chal aise erste utictove fe sian aicke Parasol orem ee ema aiaeleh osersclowe se eres AUNT Pree eee tera MS rete Ser Naialareiatalc: Slide, e/alcie a siosa@ariecete ewes) sivesleears s Characters used in Classification The nymph BITE NTA KON Me ara cine yo oslepaleny cre eiceien owisinicle ais since ieee ese caisleceSe Seenee PUA REISE EP SCR tma et aetna Sewechae te © stele oma ere es ele aaa cet e Sellars ses PAGE I-94 vi PAGE. IN yO PB S's. 'c10 crn ec eleie oie oie cieieiei s.c101n) olsinip inicio) sininisialensisieis lelria\cin\e)«|ejolsl= timninie Be 4 TMABOSs 4 nie stores eisiece clalsicps sists ererara eeeasle pie etare tetera gee tetisets siete efstanatato ete 26 Family PetaQlurtd 2... ccve ven cece cca cnee ence ses cen e cece snes cece eees 27 Family ALSCHNIAE....00. coc 00a vet wens nese cone cece sone eces cot nicinoe aes0e 27 Key to Genera... 2... 222. cece cone cee cone tone cece cers cons cane aerers 30 Ibtty sie JegrriAdba HOpo ron pOlaeboa Ao Oncpdn nootsrncc sei Heos Coe yob9 Hook 30 NES bese thee ener eeMnMne GRUB cad crabibcn bAtsanasdouumdnoqabSnoentct 656 33 IDyosek{el vee WARN A BaeeMAHn Oberon OObabooa O00 6 9s anor edhe dodn Obovedecoo. 35 Oy erence ocapaietain levels =Heretslaavatels felelsiofaiete atc tsretauieals top otetebtiehet iets) = keto tekae cateae 36 Basizeschma: te lictea cesses pavlneesncteoeposseaye ater rene oiay fetes eta cach ea ere 38 PO dE nee, Ha ee a Ga Ace oo anon doo qurcinmgacen iden sno ap syoo kN je 39 Key: tOlmy Maps ie aie spsre wieetete wlryetr) a rmcete ene re tine fof vcle cn ote gkn oi) chad taeoS 40 it qe ee ae IN RnR 26) Sin dcr orange MR e ne He ERO OOO ROG oc 46 1h) (COVA LUCE ARADO AOU AD OI5 40 cone meOsdOccenaBsoareomagernooouL: 50 Ne yGiite) CeOegdecanersvaacvac coodonssoneamacenesdeaseeedome sesuessh 52 Drea OSisyztere seve te 1cse/ ayers teyerete tetedate meee matee esata eye te pete) tape tetee te Nolete ee Tela ee 52 Ni gidlol eons Abdocano aso sbancoononsdese sonar adaadoatoaegansbed 70 53 Noy AlE@enenenpcenoeuenan woo dosh on adapcotneobasnonodosesbesder laces 54 Isdopdonja| Niewmrenosantos ondosnwosapochpogooSpgmovseccduacanseb one Boe, ys Diastatatomma and Herpetogomphus.............-..-.----.0-++ee0e 57 AA fehl kiganosaguadoausay conc sot soo SDen ru cdAnaBdbeAaosoHIAGS 58 LSEY tran ANA SnOSo BOE OUnne sohogundoDbasoouedany cogs ede aeabwIG - 60 LEE held Nu ee EAE nom OiaeG gitid pemconoc ac Ududcancomcmageno Gan bocssc 62 ID} Roh enloy-Kojono)UChAe soem nrAssAdgoorNcodadhodosGe 4” Aboonsnwnycnadosse 4 64 Gon p Buss score ersinrevete sa) atcicen)s ele sreteratiintor stoke ate le tei Fase fe ister sietiets tye eteretat tee siete 65 Key to) amy map ls p- reser erento misters ete neste eter eee eek erate 66 Sto paamenonada donoosdd qcudcccnnbs ovsbduocodsenbosteenanndaoc: 68 PET ih) ga PRG AO OSD OOO ED OA Onan TOD Ae AOR OTA DOE Os. go ARTICLE II._PLANKTON STUDIES. IV. THE PLANKTON OF THE ILLINOIS RIVER, 1894-1899, WITH INTRODUCTORY NOTES UPON THE HYDROGRAPHY OF THE ILLINOIS RIVER AND ITS BASIN. PART I. QUANTITATIVE INVES- PAGE TIGATIONS AND GENERAL RESULTS. BY C.A.KOFOID.... 95 629 INTRODUCTION PNA aon Aso fpelAeicinnda eh sugc oni daoonagoddoon tbo otAnea Aes med HAN eS ne 96 THE GEOLOGICAL AND HYDROGRAPHIC FEATURES OF THE ILLINOIS RIVER BASIN Somer Maca G aie. sah Gen einer Cone ROME o Rau ACNE 6 98-251 TRE OMUCLOTY Vira seicteteie cx, aloe eat ee a TEE RUTH erectete oes cee 98 LOC ALON. or5 ee Sr eis tases eee HR Re EL IEE ee BO Re eee feniete certo iere revere 99 Geological Features of the Illinois River Bastn.... +... cece cece ce ccc renee 99 FCT @ Via tL oi 5 :ch5.4 5 Sec kotare eas cto lee ote HAT one a elon oe eee emratetereisien cierer were terane 99 GlacialsandivalleysD rite: cece rer ieee eieete etait ieee re een 100 ING RAGES BEMA Dene np rmperand Goeswontiooooanod eb aTaDResaeseunSosasT 101 Lite LUMO RAVER SY SLEML detain 20 eae ne ee ee err 102 Length and area PAGE INTIS Gana ees Osa e dato eoheoe ee OrRtcat Onin Leo SoOC OSCE pO SeeICeDeee 103 MBCHTIDSE eretere ae esisicreorelere cree Prerers/e ainia trees as iavaratevertecleta a rejaiecinige a(e ere) s/aug ales iniers 104 DISH DULIONOL. tKIDULATIeS|e.<:2..1< 109 LGD GOS SOT ET AGG TA Irs DODO AC ORE IORIOD DAES OC DEC OS SS OCTEGE 110 Direct course and undeveloped flood-plain....................0.--e++s 110 Relation to river levels in the Mississippi River................-.----- 110 Dams and their relation to river levels at Havana.................... III Oe spare cssiahe'stefesoncsioieiatatsyc aiarsie nie ser etalsieunersiacs aieiec/idisisiehaera slaisve a eeeisiac ess 114 (CihtetStle bo so. Bo pan oine dopond CURIE OUD URIS OU SADE HERCSur 200 co aoaon 3 Beene 115 Welaettygat Wa ran ce tnigtidtats ssscanaceerser With seasonal changes in nitrates.. Pibeimaximam-oainMOAUM) CYCIEC:..c-cadecreccnccecsaecaosssseavirerenes> os sseers Relation to plankton maxima in the several localities... Whthyseasonaliichan ges) in DIfTiteS, -c..ccesusoesetsccnsaq <= 505 Is there a normal sequence in production?............... ......0.0. 506 Direction of movement in mean monthly production............... 507 Predominant seasonal changes in direction..................-....- 507 The cyclic movement of recurrent pulses..............-.....0-000-- 509 Necessity of brief interval of collection.....................--.+-+ 509 Suggestions of cyclic phenomena in data of other investigators..... 509 Evidence in, our, récords)....).2--m-reeiee ieee eee eee ee 510 Xvil PAGE Attectedibysenvironmentall factors... seers ees ee ee ieee ie tise ei 510 Approximation in time of pulses at different stations.............. 510 Normal regimen in our waters one of recurrent pulses of varying am- plitudes JORG HOOND DOU DOKI COAT SAE aE nberican fecal CHO ROAE OCH 51 Source and maintenance of potamoplankton...................2-02+2: 511 Broblemistated-tr.% reterelorc (ict isles «'s =-eteraete spereret sl aleletaialsielisteleteloleieleteels 537 Contrastsiimeautumnall plankton jor cece cere eect sieice 538 Applicability of conclusions to other streams...................-- 539 Effect of tributaries upon channel plankton......................- 539 Relation of backwaters to channel plankton.................-.+-.5-- 540 (Copnalessisy OUUNS joys oo qaeaoangoconode coon dosodnocongbccnon 540 Impounding action Offood-plain. .|..1. 1.) eres lees so cee s ele oe 541 ATMO UIMHO Tm OUMG CAhwaterye wapyesde tale ete tocate ote cleici=tesisietalevalel ola cleliete «te 541 Duration Gl WoIpPOUMGiM es we esiels seis ieteleicieel sie reiaiata claetvieleieie cies) 542 xvill PAGE Representative character of/ournidadtar..\. css seems ce eee eens oe cee 543 Predominantly higher production in backwaters.................4. 543 Causes of periods of low production in backwaters ................ 544 Summary of statistics of channel and backwater production........ 544 Indigenous) planktonvof chann eclenseenieeninien sales eee eiaecveneereciele 545 General: Summary asi! Sekt we nero aeons era See cee lee 546 Totali-annual' production®. ctr ea ceases ee eee eer 547 At lava a: cies sis aalaseie-s se cies eee Su ae nei ote aetoeesforcie ls eae pete 547 At mouth’ obrivienti.c2 si sere eae ec eerie meee eis eee tae 548 Variation ‘from iy ear'to years. was asmtos eee beeen hss eso ee 548 Total annual loss of organic matter from Illinois River.............. 549 Determination of total production as affected by leakage through silk 5 EON Sore MEANIN EOS BO apOn Dagon a dana CORaoroa ees Se 549 Volumetric determination by means of filter-paper catches.......... p Gharacter of silt iin theseicatchesererrenci1se eerie si aire 550 Filter-paper catches not suited for volumetric work................ 540 Confirmation of my results by the work of Lohmann ............... 550 Methods of making filter-paper catches....................00000-- 551 Statistical data of silk and filter-paper catches...................... 552 INASP adnonopApaenos oo on aoc Too Koco dNeosUoe HAR oNdesabIseSbooRORS 554 Seasonal changesiim ratios norco eee eects eee rector ee 555 Volumetric methods imperfect as a test of productivity.............. 556 Comparison with other bodies of water..................-.2.22..+-000 556 Atbsencerof, comparable (datate- ermree nm ene ee crenelaniet islet 557 Comparison) with Danube (Steven) ener cter eee tl amiss nt eet 557 Comparison with New England streams (Whipple).................. 557 Gomparison with, Elbe y(Seborben) ite eyercteeterayatetelat-eeetteue eres tceleraletel ete 558 Comparison with Oder (Zimmer and Schreeder)............-...-..--- 558 Omission of comparisons with lakes............ 0.2.0.2. eeee cess aces 558 Does geographical position determine planktograph?................ 559 Comparison of maximum production..............+++.1+ seer eee eee 559 Statistical datas 2... cin stein rsecie aise nus emia ieee eetetetere Peete ere 560 Relative productivity of Illinois waters..........+. esses eees eeeess 560 Location of Seasonal masiimalystayey-my etter te sie ene eile fenetelaletalieleteiep=tal=tere 561 EECONOMUGIN GONSTACTOLLONS viel tnteiatel fete eee eee eee ere 561 Illinois River as a source of wealth.... 0.0.0.0. eee cee cece eee ee eee ees 561 Value for sportand recreation> cy eccee ein erat eten acme 561 Are resources now utilized to advantage?................ 0-0 e--e ease 562 Relation of plankton to fisheries..........2..2-..0 2 0- ce ee een eee ers 563 ING Tools bovis es) Neo abnahoinade Hoounesh oo tuoore asc ubes SoUade mabe 563 Importance of knowledge of plankton in scientific aquiculture........ 564 Comparison of annual product of fisheries and plankton............... 505 Smale UGC inan a Hone pareipeaop boosts uec conoccdonsonb aspnpenacane 565 Gorrespondence inidatals nq science rue ee nein ey etree cree 566 Annual wastage and fish production ............ 61+ eeeeee cere eeee ee 567 Suggestions for utilization of resources.....-..-... 0... -.e+seeeeeeeee 567 NEON GLUSTIONS ii ites cfeietsie ie =) sreswie: ennai chal cole eltes fal ey Neate teks lassie otaoletstarelintotele 569-574 f BG oCh ORE oon cern TOD aaron Anse qos adatkinod LOntapameoeo 575-618 BIBLIOGRAPHY........ SAO OtoaenAc cdg Aona bose aaa dnbaar ",... 619-624 EXPLANA TIONIO“ PLATES: sae. + cchcelcrer isomer tateteh tier ralelete sete ance aiaetats 625-628 Dr. Charles A. Kofoid, the writer of the accompanying report on the plankton of the Illinois River, was appointed to the staff of the Illinois State Laboratory of Natural History as Superintendent of the Illinois Biological Station, July 1, 1895, and con- tinued in that relation until December 31, 1900. Elected Assistant Professor of Histology and Embryology in the University of California during the summer of the latter year, he received a virtual leave of absence from that University until the be- ginning of the January following to enable him to complete the collation and tabu- lation of the data of the Station studies, on which he was then engaged, and these materials were sent to him at Berkeley, California, early in 1901. His paper was thus mainly prepared after his formal connection with the State Laboratory had ceased, and during his residence in a distant state. Grateful acknowledgements are due to the University of California, and espe- cially to the successive heads of its Department of Zodlogy, Professor Joseph Le Conte and Professor William E. Ritter, for the privileges accorded in this connection. without which this report would necessarily have been prepared, under embarrassing disad- vantages, by another hand. S. A. FORBES, Director of Laboratory. Urbana, IIl., October 10, 1903.. BUELETIN OF THE ILLINOIS STATE LABORATORY OF NATURAL HISTORY Ursana, ILuinots. U.S.A. Wioits WAL NOVEMBER, 1903 ARTICLE II. * THE PLANKTON OF THE ILLINOIS RIVER, 1894-1899, WIE IN = TRODUCTORY NOTES UPON THE HYDROGRAPHY OF THE ILLINOIS RIVER AND ITS BASIN. PARTI. QUANTITATIVE INVESTIGATIONS AND GENERAL RESULTS. BY CA COEOID PAD. Peet hn eta oe h a, w ni % 4{ . ‘ { . . } < ArticLeE 1—The Dragon-flies (Odonata) of Illinois, with Descriptions of the Immature Stages. — Part 1. Petaluride, Aesch- nide, and Gomphide. By James G. NeEDHAM AND CHARLES A. Harr. INTRODUCTION. The present paper is the combined product of studies made by the authors upon the collections of the [linois 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.S. Fish Commission. Professor Needham’s pri- vate collection used in the preparation of this paper contains many Illinois 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 Illinois 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 Illinois 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- lies 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. The 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 Illinois the branch nearest the primitive stock is probably that of the “black-wings,” or Caloptery., of our smaller streams, representing the Calopterygide. 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, Aischnide, 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 familhes. The Petaluride is probably the oldest of the five. It has not as yet been found in Illinois. In this family and the schnide the ovipositor is well devel- oped and oviposition is endophytic, as in all the Zygoptera. The Petaluride, judging from Mr. Wilhamson’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 link in the evolution of the labium, being interme- diate in this respect between Aschnide 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 dvschnide. 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 schnide and Gomphide 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- idw, 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 Libellulide in having a spoon-shaped labium and a sym- metrically 4-toothed larval gizzard. The last family, Libe/lu- lide, comprises most of the commoner species. They are diversified in structure and habits, and may be grouped in three subfamiles. The first two of these (Synthemiinw and Cordu- liinw) 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 L/- belludine, 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 Aschnidw, and his third (’90) the Synthemiine and Cor- duliime 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 bibliography 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 (797). 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 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 (790). The numerous published lists of Odonata in this country contain much valuable information as to the life history of our ( 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 (91a) 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 Illinois. Among Illinois 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, IIl., 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, I1.” (°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. Epiwschna 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. dAnar, 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- 8 idly, and have been known to produce imagos before the close of the same season. Jvramea 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 Libellulidw, which contains most of our commoner Anisoptera, the eggs laid during midsummer hatching in latesummer,and thenymphs maturing in time forthe general emergence the following season. In late August there is asurprising number of very small nymphs,—tiny spider-lke youngsters,—and even in September and October the prepon- derance of young nymphs is still manifest. As the period of maximum emergence of their species 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- gling 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 limits 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 light 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 like, 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 occuratany time. The usual process will be fully described under T'ramea 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 Eschnid, 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, Cordulegasterida, and Libellulidw, 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 drift- 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 familiar sight everywhere about the Station. The species of Sympetrwm 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, Kpicordulia 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. Itis prob- ef 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 E'schnide 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 Zé schnide, 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 situatious, and there was consequently in * 1896 an excessive development of Pachydiplax longipennis and species of Sympetrum. A slight rise took place in the spring of 1896 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 am 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 im Ohio the warm rainy weather of April, 1896, following the drouth of 1594-95, caused emergence earlier 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 Illinois, 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 of Lake Michigan in Illinois 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 Arschnide, 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- 138 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 Cordulegasteride, 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 Anar are common everywhere in bodies of water with vegetation, from the small- est pool to considerable lakes. The other schnide 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 Calopterygide thrive in little rapid-flowing sandy rivulets like 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. LEpicordulia 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 Sympetrwm 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 [linois, 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 7x 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 in 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. Hach 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 Illinois 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 4schnidw@ may be looked for. In bottom-land lakes where vegetation is abundant, one may find Anax, Agrionide, 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 £schnide 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 Libellulide occur amongst vegetation, and Sympetrum in shallower parts, while Libellula 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 [llnois, a remarka- bly varied odonate life can be found. Among the vegetation and along shore, Agrionide, Anax, 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 occur, and, especially where it is clayey, the Synthemiinwe—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 likely to be found along the shores of waters inhabited by their nymphs, though many 17 forms, such as some Agrionide, most of the Aschnide, Libel- lula, Sympetrum, and Mesothemis scatter widely inland. Sym- petrum will be 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 Agrionidw 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 larvee, and even the younger or weaker members of their own order. Anax takes even the thicker-shelled univalves. like Amnicola. The deep-water Ep/- cordulia feeds principally on small mollusks, such as Amnicola and Physa, as well as on other life of the bottom. The A’sch- nide, especially Anar, 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. the course of Professor Forbes’s studies of the food of (88a, pp. 485, 524) he found odonate nymphs most ?' (twenty-five per cent.) in the food of the grass pic. vermiculatus), and forming ten to thirteen per cent of the crappie (Pomowis annularis), the pirate ner 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 life. 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-flies do not usually suffer seriously from natural enemies. They are frequently found infested by small ~ed mites. Some birds, such as the king-bird, possess sufficient ~tness to capture them as regular articles of their food. It to be the weaker forms, such as Agrion, that suffer thus »xtensively (Needham ’98). The females while oviposit- netimes captured by fishes. COLLECTING AND REARING. ~deration 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. It is 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 Agrionide, as in the E’:phemeride, 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 like 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 not so much as to overheat the water. Ifthe 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 larve, 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. Anar is especially unprincipled in this respect, and Gomphus is fond of libellulids. Recently emerged living 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 like, 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- tenn, 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. ‘he mentum itself is called the median lobe. Kach of the lateral lobes bears outwardly, near its tip, a strong movable hook. In the Petaluride, 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 sete, 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 Aschnide, 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 is 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. As the 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 Anisoptera 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- 25 ages. These are of considerable value in classification. The posterior lateral angles of some of the abdominal segments bear the /ateral spines, sometimes very small but distinct, as in L/- bellula, rarely entirely wanting asin 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 life 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 Avni- 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. i 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 is 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 posteubital 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. NDHDWHDDHDNHHONH NN NNN NNN IN IROOOOOOOO Ni! N zz eck a | NO OD NO tH OOM INO OMNINA MNO MN +000 iva | MOU st sh st sh sh st sh tO NN ENN A OL ent tt tt IMINOOO NN |] + heel (ners PREOP? a) | TULA IN SEEN EN ON et O O00 DOO ININns NO ONmINM ss OMNiInIn a) poke tcee tack dele | SAAB NRE RN ROOOOO MinineG § | oN av ie ee : % | HHO Cm NOFNOWMO TIO DOO OTNON +inINOw OHM val | MN NOOO OOOO NiNininin st tininoo RNIN NNR ROOD | eh 2 Ri as : as Co) | 00 DE DONO nt 09.09 SP Ln tn eb ste OO OO IO'O'0 O mt mt : ia = SAN RN NRA NNN RNR RNR RRR ROOOO RAIN INN [ ON LARS EE SEL ee ee ET FS ES SE | OHM AMMO DROW NOINSMHOONO TMAH O| SF Ss | PCVPADDDVADADDOODAAGDAAAAAARHOMDMHMMMMMO N fos a Dat (eee 2) Ga TN UN NO © P00 00 DOOM OCS Ninth OW} HH tDS00 OD : - | oO fy PDHWDWDWDNDNWD ANADAOWONNDNHDONHHWH ARAAG i) Gl PENS Bi ae > — [| OO MANN ODO HH OAMINMHOONTN ODO NINGTN AHH] A Sladadddddenntnodco00 0 annncnnnnnnwwn | o esas Pa Nea a Ns FR NL om Bs oe Be Ba) Epa g al i. evel ax B | TAO One OPEN OTL ER LRAR NTR ARR AD| F GrandIAVerdve youn ecnicee Jess cae sci care Onasch sem cee descemcseessn Seusevses 160 READINGS OF RIVER GAGE AT Havana, 1807. (Plane of reference, low water of 1873.) Day | Jan. | Feb.} Mar. April| May | June | July | Aug. | Sept.| Oct. | Nov. | Dec. I | 4.5 |11.8 | 11.9 15.7 | D1j2) || OSs 7a al eedeO 127)|\ la) se2abn lees AN Soy iiayle@ksop vcs) wis oll eek 2333 Hf. 7))|.UsO) | Zebu eae 8:17.01. GN TE. ON Ge ON Tteoy ly OnS \i7ese in 3. GNliitedile con |e ee acy 428-0 11.15) | Orleo7 1a Onn On4nleni7e an eegeis Deze |) 129) |) 2e4ulegeo bE | 8.6) |Th.4 | 125011) 15-6) O.O Ns ObZ ale 725 ens. gull taza Teo) | NezeAnl eae 6 | 9.5 |11.3 | 12.2 | 15.4 | 10.9 || 6.0) 7.4) 3.2 1.8 1.9 | 2.4 | 3.0 7 \10.3 |11.2 | 12.3 | 15.1 | 10.8} 5.8] 7.3] 2.8] 1.8] 1.9] 2.6] 3.0 8 /10°8) |1¥.2 | 12.3)) 14.9#|10.6)|) 566) | 722 | 2550\) Teo) | Teo! v2 ONlegeo Q j11.2 |II.1 | 12.4 | 14.6] 10.5] 5.4] 7.0] 2.3 | 2.0] 1.19] 2.6] 3.1 YO |11.6 |11.0 | 12.5 | 14.4 | 10.49 5.2) |) 6-9) 23) |) 20) T-o/)) s2een naar II |I2.0 |10.9 | 12.7 | 14.1 | 10.3] 5.0] 7.2] 2.3 2.0] 1.9] 3.0) 3.3 12) | 12.2 |10.7) |12.9) || 13-9) 10.25 |) 85-ONl a0 nl 2200|)2-0nl eI. o)|)2rouesed 13 |12.4 }10.6 | 13.2 | 13.7] 10.1] 4.8] 6.6; 2.0] 2.0) 1.9] 2.8} 3.5 14 |{2.5 |10.4 | 13.4 | 13.5] 9.9] 4.6] 6.3] 1.9] 2.0] -I.9] 2.8] 3.4 15 )12.6 |10.4 | 13.6] 13.2] 9.8] 4.4] 6.0] 1.9] 2.0] 1.9| 2.8] 3.4 16 |12.6 |10.4 | 13.8 | 13.1 | 9.6] 4.2] 5.9 LEQ) [2 Ou Zou 2eonlmoee 17 |12.6 |10.5 | 14.0] 12.9! 9.5 | 4.1 5-7 Ton zen 2.0| 2.8] 3.4 ASs|E2Z7\1O.7 | 14-25) 02.7 | TQ gu eed sOnlp be 5aluele oul Zein ll 2eOnlm2 eoMleams IQ) (12-7 |LO.8 4) 44) | 6125 Oe aa lea Ae zal eS SAS eet O)iiie 2a (neo "ONE eoM mame 207)|02.9) |1O!.9) 14.7)! 1203) 0 8-On| 4-350 Ge sa|e l-Onle 2elu\s 220) 1s 2rou| aging 21 |I2.9 |I1.0 | 14.9 | 12.1 | 8.7] 4.7] 5.2 TQ) | 220) |) 223) (Pe 2rouliaaes 22 |12.9 {11.1 | 15.2 | 11.9 | 8.6] 5.1 5.1 TOV be 2-O|) 220) 2rou lege 23) [259 (11.3) | 15G0| 10.9 9|h Sidulleusmaiii isan) Ml ou |iezeOn m2 cONlm2 non mame 24 |12.6 JI11.4 | 15.8] 11.9 | 8.2] 5.7] 5.5 LO ir2 Om |) e2aON | mee anna me 25 |12.6 |11.6 1 15.9 | 11.8] 8.0] 6.0] 5.3] 1.8] 2.0] 2.1] 2.9 | 3.2 26 |12.6 |11.7 | 16.0] 11.7| 7.9 | 6.4] 5.1 1 Su |) 2ONl 2a ba egeze eee Ap Werks PIS Ao | THES) FGA |) er |! Boy || wets |) BO | 8-2 |) 3 || 3.2 28 |12.4 |11.7 | 16.0] 11.5 | 7.5 | 6.9] 4.8 10) |p 2-00 | 225 ea omieaee ZQ) 12229 bees || 15.9) | LA) Pagal ake eas aeeldon|: 2cOn|eecean ese qmligmo! 30 |12.1 |. 15-0. j UNS ez y 72 a|0 e4eOulmleom |i 2 Onn 2een ian oom igre 31 |12.0 |. 15.7 sete Moxon te 4.4 | ists) |} tse Peds Noel Shoe Mean |11.28,11.13 13.89) 13.40, 9.41] 5.54] 6.05! 2.29' 2.01] 2.01] 2.82 we N N Grand Averages. hoc gsi obo eee EO Ee Eee Tee tae aoe 6.903 161 READINGS OF RIVER GAGE AT HAVANA, 1808. (Plane of reference, low water of 1873.) Day | Jan. | Feb.| Mar. | April | May | June | July | Aug. | Sept.| Oct. | Nov. Dec | 32a ese Lea ler 7eQ|ekNe 3] E3200} |) Oh. 3h A213? |) (8227 529 25-8) [1023 || 13-7) L2-9))}, 12s0 |!) 10,8! 4:0°|/ 4.8 | 4.05] 4.0 | °8.3) 15.9 22UeGe st |TOs7al CAake| SEZ 712937 FOrG)|| Boo) Ae) 4aNal aT. SoS) 5.8 235 Ow4 | 1028) TA) | 2abe | 13233| 1045 | 3-00 4.27) AsSel) gare! “8.59 )15.8 24 | 6.2 11.0 | 14.5 | 12.4 |] 13.6] 10.4 | 3.3] 4-0] 4.6] 4.2] 6.6] 5.9 25 ROs Oil Del | (040) eI2s20 13.8 sl MtO.A.)| BZUE4| SVS 428)" 4.3) 8271] seo 2OWNGR Ties ul Tae yal) L2eOn|"TSean|| 10.6) |= 2so) || At 4.9] 4.8] 8.61 6.1 27 hO.Ou| Lis 3e |) 25 40 ||| i0ea) || L42o0)) 1OL2 omg fad REMY Te Hl ee Heo) 5-4) (8251 6.5 28, 6:9 \0r-45|/ 05.8) |/1L.6 || 13:8 | 10.0 | 255 | 4.3/| 4.7] 5.6) 8.3 | 6.2 ON e7.O))| eee ALOe Sey LIne Eaton Osa a2. 5) |) | AAT 4265) 5.9 | “853 |) 6.2 30 | 7.0 Laz ele 4a PES On|ieQ.OiN) 2.0") 3-On ead Ih Ont 8.2 | 6.3 SHU Ree | Re a BG fall abe ANTS sy BG 2/6) 327 ame 6:2 pee Ord Mean) 5.08] 8.94] 12.99] 14.00] 11.55] 11.53] 5.70] 3.66 444 4.26] 7.44] 6.59 Roach dees Gonooomct Sher OOee 8.015 162 READINGS OF RIVER GAGE AT HAVANA, I899. (Plane of reference, low water of 1873.) Day | Jan. Feb.| Mar. | April} May | June | July | Aug. | Sept.| Oct. Nov. | Dec. I -5 | 8.0] 10.9} 12.8] 9.1 SETA ALON) ScOnll 2e2a| 20Gs|s ghcn ieee ZANGO N79 \p Ue3) | 02. 6y le Qnoal Woe Oul Ar Onl arses ame 2e2Nlle 2 Oui le oll aie 3 | 6.8] 7.8] 1109] 12.5] 9.4] 8.9] 3.9] 3-7] 2.3] 2.6] 3.6] 4.0 ANOLON 727 Nt2e2 2s nor On | mOnE AZO} |S 7ialhc2 3 2eO) 1) BON aee Sleek We i L2cOu ls D2 SSeS eosin) maly7ieeok ey laos lio On uCeic a ea | oe 7A ey SON SVN aShl lash | Gata Bes wel |e Bais || alae) TNF AN Feds) 12.9%) L2sO 7s 82201 Ons ALSy sess Oe\e2e3l ee 2a On lung ici ee Sul 7cOl7 2) | ol2,. Onli ¥2 Os Se On Gn si|enqasiiseon |i 2nd ul ey 2eOn| les eal ite ON 728) 7-3) |) W2eo8|| Uo RON | onze) agulled nol zea | ea RON eae ei TOM 729) 7. LISS Eta Sy 7S oe2H |" Aszellie 1820) || 2240) Po 2e7 a esealal eae PE 820) | 6.9) |) 13.00 Dele Zaza Oia | Sede lee Se Ou ie 2abh|| wera Aan |e 12 |Sal)|6.8>|| 13/ON TO 75a) QhOn|miAat) leg 7a 2m) |e) eae SeeAee) 13) |eSs2|Ont7: || 0329 110 Ure ee sae Onon | md ea ress ib gle 2esa meena Gell mr ea Git) ned ORCI ee SRA UA ais || eal) eh ll er) iron ei || al TS y Orde |) On5e) Selle Lye te7rau Om Oul| meAlsiiel| ests is|mn2eAe| ea tin Meme erie NOW| Sil Gage) 05/0 A Ls 7s 2 OnSe |e AON | ees ile ieziad |e sie (same |mAle U7))\18ie231| O53) ) 13.0 euler) 7/stell On 2| dee es Onli 2e4n ego) an ROnEARA TS HRGie3) |G. i 13. dal 110) S71 ASrOn| me ARO We RON ie 2. 4l\ p32) |heedete | eAG TQ) |(0S940|/ S29) 13. 30iT Olle 7eOnle 77a Anon nesZOF ees hOu eset 4.1 | 4:7 710) | edekyy MOAN NMSIor ah HOMO Zale |h MeO) SRO - Boule ior l) vl |) Aue Pt Mealy | Sey Gieriul LION AN ae Il Geet | Gixey || Waxy’ Buz | ire) PMILSY | al 6) PM oF || Gaal Wesae | MOR) 7/40) | a) KO |) 2x) || S52 | sau 4.3 | 5.0 230F8 On| Ont) 1365) AOA we 7O)l) Ora vin SiO) | (in 2son lies ei suse ere a ee) PHU SAOV | Mee Ve YaGy ssh ll ots aga Mave I ARG) Ih aay || eyed ya seh || ie 25 | 8.9 | 6.6] 13.4 | 10.0 | SEOs OPO BAe alee 7a tes eOn | mas ne An Au See 26/8585) 6 On 18 sil Os@i he Oe 2a Seize ae aon |e Salllm2aoy len eign) aA mal cm 27 | 8-5. |9-3)|| 13-1 || O-74 8.3) 5.4 | Ae Sil 2.42.8. |) 3.5 (eal aul tae! PAS} atdesy Ona liDeialse eC Oe tinal ASLAN || Wed esr |b a7 Weiss viey || Boe ZOW Sez Mees |) AZO R 4a ges Oi47all AO lianas 2h Dea i|lme2 7a ean MAO RG 30 | 8.0 TA.ON 0-2 Oza leedOn |i iad PRP \| - PALOY | Me hA 4.1] 5.6 31 | 80 14.0 ae 8.7 eb 4.0] 2.2 Beis 3.5 Bee Wellset7/ Mean| 7.99| 7.02, 13.05| 11.15 8.02 7.8| 4.38] 3.20] 2.63] 2.99] 3.88] 4.74 GrandfAverage: i...) icc nose de eek Soe oo eae ee oe aL ba ee eee 6.401 These gage-readings at Havana have been plotted in the hydrographs of Plates VIII. to XIII. on a seale large enough to show the minor fluctuations, and at the same time to serve as a basis for the graphic representation of temperatures of the water and the results of the quantitative study of the plank- ton. The hydrographs for 1894 and 1895 are based upon the records at Copperas Creek with such supplementary data as our incomplete records at Havana provide. For convenience in comparing the seasons in the several years the following tables have been prepared from the same data, to show the monthly and yearly means, extremes, range, and total movement. 163 MONTHLY AND YEARLY AVERAGES OF READINGS OF RIVER GAGE AT HAVANA, 1894-1899. (Plane of reference, low water of 1873.) Year Jan. | Feb. | Mar.|April| May | June| July | Aug.|Sept.| Oct. | Nov.| Dec. Yearly lstoy Lee areeg a 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 TOQGi dicta 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 ifslofehy aera bis 10.24| 8.83] 9.41] 7.28) 6.58] 7.38] 4.55] 7-42] 4.62] 6.04 5.80] 5-48} 6.08 TSO 7icraciayers s 11.28)11.13/13.89]13-40| 9.41] 5.54) 6.05] 2.29] 2.01 2.01 2.82] 3-22] 6.90 itsollaagarae 5-08) 5-94|12.99]14.00, 11.55|11.53| 5-70] 3.66] 4.44 4.86) 7.44| 6.59) 8.02 1899....---| 7-99) 7-02|13-O5]I1. 15 8.02 7.80 4.38 3.20 2.63] 2.99 3.88] 4-74] 6.40 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.) January February March April May June July | a B ® = | = = Allee Z| 2l¢ fl 2lelolel2leleolel#lel ol giz ]el ol Zl alelelg w{S] Ss] So}, os] h) eo) s/s) ale) a) so) me) se) 8] gs] & so) 2 | so) &) o] S] 3) ale S| MES o| | Slaelel|Plslale| @|slale! =! Sl a] 6] =] 3] 51S! S| 8] se PIB Alea ae) A ela Alea BAMA BAe) Sm Alea aime 1894] 4.4/3 5}0.9/2.0 4.3) 3.8) 1.0) 1.5)10.4) 4.5] 5.9] 7.2) 9.0) 6.9 2.1| 2.4| 7.9/6.4/1.5) 2.7) 6.3°3 & 2.5/3.4/3.8]1.9/1.9)2.1 1895] 3.8/2.8]1 0/1.0] 7.5) 2.9) 4.6] 4.6] 7.6] 5.0) 2.6] 2.9] 6.2] 4.6] 1.6] 3.1] 4.4°2.7]1.7| 2.1] 2.7]9.9 1.8 2.7/5.411.5 3.9/7.3 1896 12.6|8.1 4.5/4.6] 9.9) 8.0) 1.9] 3.9)10.2) 7.9] 2.3} 2.6) 7.8} 6.9) 0.9) 1.6) 8.3 5.0/3.4) 5.6] 8.5/5.3 3.2/3.4]7.3/2.5 4.8/7.8 1897/12.9/4.5/8.4/9.3|11.8) 10.4) 1.4) 3.1)16.0/11.8) 4.2) 4.8)15.8/11.3 4.5) 4.6)11.2 7.0}4.2) 4.3) 6.9]4.0 2.9'6.3)7.5/4.4 3.1/5.2 1898} 7.2 3.2}4.0/6.0 11.4) 7.0| 4.4] 5.2)17.7/10.8) 6.9] 7.8/18.0/11.4| 6.6) 6.8/13.5 9.7/4.1] 6.0) 13.6]9.6 4.0/4.0/9.4/2.5 6.9/7.4 1899] 8.9 6.5}2.4/3.6!10.2 5.5) 4.71 6.4114.0/10.9} 3.1! 6.0'12.8| 9.2! 3.6] 4.8! 9.8 7.0/2.8 5.1) 9.3]4.6 4.7 5.5 5,013.9 1.1/4.4 August September October November December Extremes Totals ~ v + j e 2 ~ =] | | =) =| a SlelolelalelolaleielelElBileleola|eizielel @ | z wf[S{e} si sles [Sl el sisi hls eis) s/s; e] s/h) 2) 2) gs] & | eg S(PEla Si Piel a si Pi eials|Blelelsi Pls ais) »| 6] & | & Rl |Ale SIP IAIMIS le /Ale ae Ale le] alae l/al we | Al ae! 1894] 2.9 | 1.5) 1.4 2.6] 5.8 3.0 2.8] 4.7] 4.7 | 2.7) 2.0] 3.1] 3.0 , 2.8] 0.2] 0.4 oe 0.8] 0.8) 10.4) 1.5 8.9 32.9 1895] 4.3 | 1 8] 2.5] 3.5] 5.8 | 2.2] 3.6] 8.8] 2.6 | 1.2) 1.4] 2.7] 2.6! 1.9] 0.7] 1.6) 13.1 2.5]10.6]11.5} 13.1 | 0.9 | 12.2 | 51.9 1896] 8.6 | 5.8} 2.8] 4.3] 5.6 | 4.0] 1.6] 3.7] 6.9 | 4.4) 2.5] 4.6) 6.5 | 5.0] 1.5) 1.9] 6.2]4.5) 1.7) 1.7) 12.6 | 2.5 | 10.1 | 45.7 1897] 4.0 | 1.8] 2.2] 2.6} 2.1 | 1.7| 0.4] 0.6] 2 4} 1.9} 0.5) 0.6] 3.5 | 2.4) 1.1) 2.2) 3.5/3.0) 0.5) 1.2) 16.0] 1.7 | 14.3 | 44.8 1898} 5.7 | 2.6] 3.1] 7.5} 5.1 | 3.5) 1.6] 6.2] 6.2 | 3.6) 2.6 3.9) 8.7 | 6.3] 2.4) 2.6] 8.2'5.8] 2.4] 3.8] 18.0] 2.5 | 15.5 | 67.2 1899! 4.0 | 2.2] 1.8] 2.4! 3.6 | 2.2] 1.4] 26 3.5 2.6 0.9 1.1' 4.4 | 3.4] 1.0 1.6) 5.7/4.0) 1.7] 3.8! 14.0 | 2.2 118 7.3 It is evident that the changes from year to year in the 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 (Pl. VIL.) shows that the years of our plankton work at Havana practi- cally include the extremes of conditions in the river; no two years present the same fluctuations, and both typical and aber- 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 4.638 feet respectively, are, however, much below the general aver- age (13.8 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, tothe 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. The 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 6.95 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) 1s 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 five months; the change to low water, during which the reservoir action of the more permanent and diversified 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 8 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 relative 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. We are 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 life 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 climatic 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 limits 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 24,1898, after which time a Hick’s self-recording maximum-mini- mum thermometer was used. Under stable conditions no appre- clable 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 five 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 like 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 wind which 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 III. 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 (32°) 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, 1598. The diurnal range in temperature is considerable at times, depending naturally upon that of the air. On August 3-5,1598, 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, 1[894-1899, ILLINOIS RIVER. | Ray Year | Jan. | Feb. Mar.|April] May |, June} July | Aug.|Sept.| Oct. | Nov.| Dec. sz > Pea ee al ee a eae aoe 80. 25/82.25|83.5 \77.5 |58 al Se see TOQ5 accis||e2-3' Qi a Wieossis 58 -. (80 79 — |80.51)78.87)54.26.42.5 |37-5 |..---- 1896... .|32-75]33.7 |39-52/64.54|72.7 |74-7 |80.7 |82 [65.75/56 |44 133-6 |56.66 133 ¥/eoba) bacor 32.25/43.8 |60 |66.3 |75 _ |81.02'80.9 |77.07/65.1 |45.7 |33-02)...... 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...-132-9 {32-6 135.2 |...-.|----- eae el (eae [otk jiitee [ee eee eet eek Monthly if average|32.78)32-73 40-45|60. 46/68. 27/77 .75|81 -03/81 . 49174 -21/57-55143-00 35 -22'57 .08* *Average 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 is 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- 175 cline is a gradual one; in others, as 1595 and 1595, 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 he 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, VITI.—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,asarule, but slight. 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 in the waters of this region toa degree 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 18, 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. At no 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 diseussed. 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 far as 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. IT.) 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 life 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 ict. 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 (PI, II.)—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 (PI. 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 lies 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 slighter 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, etc.) 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 life 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 III.-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 dise 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 I1l.-IX.) The extreme range of our records extends from 1.3 em., in a Spoon River flood, to 260 em., 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 em., in the flood of May, 1897, to 115 em., 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 cm. 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. 18] In Dogfish Lake (Table VI.) the conditions are essentially those of Quiver Lake, of which it is an arm. The principal difference hes in the fact that flood water entering Quiver Lake at low stages never moves as far up as our station in Dog- fish Lake (PI. 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 [X.) the silt conditions are peculiar. The high level at which the lake lies 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 majovity 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 it 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 larve—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 lghter 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 IIl.-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-XLIL. 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. cm. (per cubic meter), in declining water under the ice in December, to 5,416 cu. cm., 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 cubic 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 (1,301,990 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 Hntomostraca 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 les 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 Illinois 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, like 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 Ili- 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 didxid 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 Illnois 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 LIII.-L. CHEMICAL ANALYSES OF WATER FROM PLANKTON STATIONS, AVERAGEs OF ALL ANALYSES. PARTS PER MILLION. | | | | Residue on Bees Eieiomemaporation 3 7] Nitropen = | a a ve lly supe aca alle eee ee ee ieee ie 42) | Ignition = | Ammonia | 2 | *5 3) ra Y Z | as Se xe Locality on z = rele S BA | ae a 3 2| = eae S yale ay |? Be Sel esse 3 Oe eel gees |p ee a o 2 Y I) pe es fe ee |) seh fese MD 3] A BH} A|a!AH}A/;|O]/O] & < | |4/4a O Bm a 5 = =e | easel SA (Saar ee SS Falls Illinois River... 188/367. 5/304.1] 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) 1282.9! 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 Illinois and Spoon rivers (367.5 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, 0.884, 1.62, and 6.68 cm.> per m.3, 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 greater 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, 274.3, 25.1, and 44.6) is due to the great leakage of the finer suspended particles through the silk, especially in Spoon and Illinois 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 (.3884), and Quiver Lake has likewise less residue (248.2) and less plankton (1.62 ) than Thompson’s Lake (282.9 and 6.68). The Illinois 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 shght 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 River runs 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 iscompared 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 Illinois rivers are 1 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 produe- ing the contrasts in plankton production above noted. The oxygex 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 Ili- 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 zoé- 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 sult, and in plankton, while that stored in the larger plants and 195 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 includes 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 16.3) or of the plankton (1.91, .884, 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 [linois 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 (.048) 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, .884, and 1.62) in the other local- ities, where the nitrites are but a little less or even greater (.147, .039, and .023). Hither 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 inorganic 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 little 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 z06- 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) asin 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 furnishany 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 impor- 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. City Population in 1890 7 es ea Remarks. Illinois 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 9,855 1,503,835 Lemont — 600,000 |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 zs ss “s 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!l'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. 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| Daily Pumpage Remarks. : in gal. Lilinots Batavia 3,543 2,500 1,500— 3,500 gallons. Braidwood 4,641 5,500 1,000— 10,000 ss 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, E] 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 55,000 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 fact that the drainage of certain districts did not enter the Illi- 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 Illinois 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 1597 in Chicago was 265,530,910 gallons—an amount 50 per cent. less than the pumpage at Bridgeport. The amount discharged into the [linois 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. The 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 [linois 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, [linois 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.? Illinois River........ 3.617 1.91 Spoon River......... 2.586 384 Quiver Lake......... 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 (1.03), 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), nitrites (.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 (.384). As in the case of the main stream, the ex- planation of the slight production lies 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 [linois, 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 (.023), 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 (36.5), 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 Quiy- er and Thompson’s lakes, than it is in tributaries such as Spoon River, or in the Illinois 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 cyele of seasonal fluctuations (see Pl. XLIII.—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 Illinois River in 1896 (Pl. XLIII.) 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 growth 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 1898. 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 1597, 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, I 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 [linois 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. II. and hydro- 211 graphs on Pl. XLVIII. and XLIX.) 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 slight 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 spring 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 XLIX.), 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 slight 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 213 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. As in 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 XLVI.) 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 (Pl. 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 Illinois River in 1895-96 (Pl. XLIII.) 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 slight 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 (Pl. 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.- XLV.), averaging about .3 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 XLVII.) 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. XLVIITI.). In Thompson’s Lake (PI. 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 Illinois 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. XLII. and XLV.). The effect of sudden floods, presuma- bly those of tributaries but a short distance above Havana, appears in February, 1896 (Pl. XLIIL), 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. ‘l'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 albuminoid ammonia and organic nitrogen. This appears in the [linois with the pulses of April, 1896 (Pl. XLII. ), 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. XLII), in May, July, September, and October, 1897 (Pl. XLIV.), and in June, 1898 (Pl. XLV.). With the pulses of December, 1895 (Pl. XLIII.), 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, 1898 (Pl. XLVIT.). 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 30 the amounts of albuminoid ammonia (.382) 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 in suspension. It is not plankton, neither is it to any large extent sewage, which the tributary floods of Spoon River bring to the [linois 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 Illinois 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 increase appears with plankton pulses in cold months, as in December-January- and February, 1899. Some exceptions to these general tendencies appear here as in 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 increase 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,aslightripple of 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 XIIL., gives the amounts of plankton and of the several forms of nitrogen present before QUIVER LAKE. Date Free Albuminoid} Organic 1898 Ammonia | Ammonia | Nitrogen Nitrites | Nitrates | Plankton Aprile igs .046 44 1.01 .033 65 | 103 MESY Slesooneoat ,092 3 82 .022 | 35 | 42.14 IMMER 7 IO \gendaoe .05 .48 .98 O15 a | : 4.7 —_ —— — — — I — Per cent. of Change. April 19 to ior. | Pe Lene | SE cn = el as aS May 3...... +100 ee alg — 33% — 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 1.03 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 per cent. 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 eyi- denceas to the possible limits ofthe 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 .855 and .181 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 insolution, rarely equaling or surpas- sing it, 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 (Pl. 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 (.84), 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 XLIII.—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 lie 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 (799). 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 of the 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 Euglena, viz., viridis, sanguinea, deses, acus, spirogyra, and gracilis. I 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 light of 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 lies 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 (zodplankton) 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 light, 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 zodplankton, 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 XLVII.) and occasionally in the Illinois, as, for example, in February, 1896 (Pl. XLIIL.). 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. Illustrations 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. XLIII.) 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. XLIII.—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 Ihnois, 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. XLITI.-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 Decemes 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 (PI. 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 slight correlation in the chlorine and plankton curves appears, though the only relation between the two may lie 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 J | ee residue {loss on| Chlo- ple minoid| Organ-| Ni- Ni- Station. Chicaso.|°% evap-| igni- | rine |“fj2'°|Ammo-| ic Ni- | trites | trates 5°! oration. | tion nia. | trogen Lockport ..............-..-. 29 438.6 20.5 24. 092 417 84 .019 95 orris. .... 57 359.4 23.4 29.7 | 3.55 709 1.44 149 1.72 La Salle. 95 372.3 23.03 19.6 971 .612 1.26 +255 2.51 WPeOniaijecceseeete ee ee 58 376.7 21. 1.8 +254 516 1.06 +209 2.59 Havana.......... ratte 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 (’00), gives the seasonal changes in numbers of colonies of bacteria from May BACTERIOLOGICAL EXAMINATION OF ILLINOIS RIVER AT HAVANA. Chlorine | ‘ No. of colonies per cm*. Dae lt per mil, Stas of Temygatee| | lion) : | water, C. Havana Pekin May 30...... 13.6 8.7 21 4,500 542,000 PUNECSG aes wy 13. 9.3 26 18,450 129,000 13 3e-). 0s 13.5 8.8 25 15,900 205,000 ZO Wasser 12.1 a5 26 2,500 225,000 (1) 28 ates 14.9 5.2 25 4,500 2,030,000 (2) July 85socns 14.7 4.7 26 2,400 52,000 (3) D2eaciea 23. 4.1 26 7,300 1,435,000 Sisgncos 36. 4.9 27 5,700 470,000 (4) 200 en. 31. 4.8 30 850 980,000 (5) PIES OQ ee ces 27.5 4.1 26 1,550 985,000 (6) 3 peters 34. 3. 26 goo 10,000 (7) 80h ts 30. ray 29 9,800 30,000 (8) Sept, (Osesco. 40. 2.4 2 1,900 650,000 (9) NAV yaretele 46. 2.5 22 1,500 310,000 (10) ZO Fs.ccis= 35. 3.5 14 3,400 240,000 (It) 2 Mic ieeye 49. 3- 16 3,700 120,000 (12) OCU, Was aches 52. 3. 14.5 2,500 | 500,000 (13) Ieee 50. 3.2 16. 6,600 | 430,000 (14) Toceeece 58. 3.2 17. 8,800 BE ewes 60.5 3. 12. 3,900 30,000 (15) INOVeonloace ox 63. 3.5 9. 7,000 150,000 (16) Thiers SI. 3.7 10 »300 =| ~~ 30,000 Dea Feysis« 47.5 4.4 II 128,000 ~—|_ 1,650,000 Zarate ts 43. my 41,600 | 380,000 (17) Decy §Onsccts sty Bit wh 85,000 | 140,000 (18) DON een 35 4.8 I | 66,800 | 5,000 (1) June 21. (2) June 27. (3) July 6. (4) July 18. (5) July 25. (6) Aug. 8. (7) Aug. 22. (8) Aug. 29. (9) Sept.5. (10) Sept. 12. (11) Sept. 18. (12) Sept. 26. (13) Oct. 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 | ; 3 2 Chlorine (pts. | Number of col- Collecting Stations Preece per Saisan) onies per cm.® scala ove tiearanemAdaoonodcnoap.so5e fo) IIg.2 1,245,000 COCK POLE cic custeteiitele tere eel eae 29 117.4 650,000 aes EAN O Ren aera BEA Odes 0d 33 104.8 486,000 OLMIS Merny seisiets artery nei ieeoeeoiats 57 68.1 439,000 KO ETAW.AY cies csioscpovcis stsietseereaie eine ose efor 81 58.5 27,400 War Salles a: csvsrcssnien morc emcn ies 95 46.1 16,300 Jn GIN SeDAnOUOHEMOOea A nods bO0G cour 123 44.2 11,200 Nisa Seppo osancorscansoboooad 159 40.9 3,660 Wesley City ier s seceererieete creas 165 40.9 758,000 PEK F 515 0: saya ltue ete clatetertetstnerensieien 175 38.4 492,600 SEV EhiE eer oerogomaucocuacaGRdodlU 199 36.2 16,800 Beards foyer seas beset 231 29.3 14,000 Kampsville’ if... sis ciieictestetoieivetsl 2112 +3.58 Greatest + + .27 +8.6 Greatest — — .19 —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 22 — 3.4 to+ 3 6.4 26 a-c 3 5.5 6.1 —9.1 “+ 9.1 18.2 27 a-e 5 4.1 7.8 —14.6 “ +15.9 30.5 28 a,b 2 4.5 11.1 —Ir1.i “ +I0LI D2 30 a,b 2 g.12 1.3 Sag) Sa ita) 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 13.3 33 dye 2 15.5 BEz — 3.2 “ - 3.2 6.4 34 a,b 2 17. 8.8 — 8.8 “ + 8.8 17.6 37 a-c 3 2.43 8.6 — 7.4 “ +13.2 20.6 41 a,b 2 1.5 13.3 —13.3 “ +13.3 26.7 43 a-c 3 1.93 19.5 =17.1 “ —29-5 46.6 46 a,b 2 2. oO. Oo. oO. 65 a,e 2 3-3 7-7 Pop Oa sy 15.4 73 a,b 2 2.5 oO. oO. Oo. 45 a,b 2 1.2 8.3 — 8.3% + 8.3 16.7 47 b,c 2 I.1 Oo. Oo. oO. 63 a,g 2 1.23 2.5 —- 2.5 “+ 2.5 5: 68 a,b 2 O.1 oO. Oo. Oo. 69 a,b 2 --O.1 Oo. O. Oo. 70 a,b 2 0.16 oO. Oo. oO. 24 a-C 3 I. @); 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 /ess than that represented in the extremes of our test. The number of hauls did not, however, in any of his tests eyzeed four. I have 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 (Pl. 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 limnoplankton. 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. |Esti- |Esti- | | | | De- Av. | T’lr’ge mated mated | | Temp. | Stage Catch | parture depart.| of limit No. of|rateof|range | Date | (F.)at) of per from _|inper | in per group | cur- in bott’m | river m.* mean in| ct. of | ct. of rent | miles | per cent,|mean | mean 1895 5 ie I 4 ; uly 29 | 75-5 | 5.3 +47 22.3 3 ; ek 1| 77.8 | 4.20 74 —22.3 | =22-3| 44.6 2 36 Aug. 5 | 79. 3.13 -95 fo) : Ce ts Pao 2.63 95 fo) S © 6 Aug. 12} 82.5 2.40 5-94 —1.2 3 ° : | CEES || tee. |) Basis 6.08 +1.2 |= t-2 ane 3 Aug. a 78 2.35 tee age 5 4 Hu eZ6)|879 2.7 4. —18.5 2 3 “ 29] 80 2.58 3.92 —26 24.3] 74.5 i SOB 7 725) ||) 0205 5.08 4.1 Sept.5 | 72.5 | 5.70 1.48 a 2D j ao Wee 6.35 1.16 + 4.1 ree ae 5 .75 | 108 7 eye 5.88 .86 —28.9 | =!7- 51. 9) | 72.5.) 038 | E48 url) she.g eo | fe 4.25 | 1.06 | —12.4 Sept.12| 78. 3.90 2.92 -+-27 MR cae es |, hl eae ke e II aged 74- 3. 9 i) +29. I. : he OTS eas ele ghigc: 1.19 —48.3 a ae LY « 20] 78. 3.20 | 1.98 —13.9 | Sept. 23] 76.5 | 2.75 1.37 +15.1 7 25 2A 25) 725 2.63 1.05 —11.8 |+10.4] 26.9 1 se AN pet /2b 3.23 1.14 — 4.2 J 1896 } Jan. 6 | 32.2 | 12.20 51 ae 8 ; 2 Ces) 2.1 | 11.90 1.21 orale i “ 10 a rio 1.02 BEA £25 78.7 oly 32.4 | 10.80 83 19,7) j Jan. 15 gel 10.40 I Be —10.2 OG" 4 2. -50 1.01 —11. 9 2 720 ; a = a hes 2.36 ee +10.8] 26.8 “30 | 34.3 | 8.10 2.18 oh, 3) § Mar. g| 37-1 | 10.20 4.96 — 6.1 1) 2 720" ||) Se 35. Ca Oage ee Ees — 3-8 |+6.6 | 15.9 ) “ 24] 40.7 | 8.80 5.80 + 9.8 Apr. 1.8 | 6.90 | 17.07 Hoe : ; oh { ne By see ae 16.91 ea 0.5 I Apr. O. 7-10 9-93 28.1 ar : a Meas 738 7.10 | 5.00 eae +28.1| 56.2 SAug. 15 | 78. 7-40 2.32 + 1.1 13 75 Tes WO nit | 7S 7-50 | 2.72 | 118.8 |+12.8] 38.4 : 2T 7 7.10 1.84 —19.6 Aug. 26 | 77- 6.50 1.44 — 7.7 af 6 43.4 { eo 29 | 74- 6.00 1.68 tO agh Waele Le 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 14 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. | aa Vol. in cm.3 Departure from | 9 | ona: of catch mean in per cent. No. Location Time = |3alon ‘ = A ==) es) Erek | To- Total Plank- 2|n ton Silt | tal catch ton 1 j1m.above Hardin... 5:45-6:45 p.m. | .10) 72 | 60 , .18 +26 44 — 85 — 75 2 |Kampsville Dam......... 6:45-7:45p. m. -08 | 71 | 80 | .23 91 | 1.14 — 61 — 68 3 Jlm. aboveC. A. bridge} 4:30-4:45 a. m. .08 | 69 | 90 | lost 4 |Florence...... ......... 6:00-7:05 a. m. |) .03 | 68 | 99 | .02 |2.32 | 2.34 —wail — 97 5 \Mauvaise Terres Crk} 7:10-8:10 a. m 04] 68 | 98 | .05 |2,36 | 2.41 — 18 — 93 6 |Meredosia ......... ........| 8:10-9:15 a, m 04 | 69 | 95 | 11 |215 | 2.26 = 5%} — 85 7 |La Grange .... 10:00-11:00 a. m 04 97 | .07 |2.21 | 2.28 — 24 — 90 8 |Beardstown ...... . }11:00-12:00 a. m 04) 88 | .22 |1.61 | 1.83 = 38 — 69 9 |Browning. .. .. | 2:45-3:45 p.m 05 95 | 11 |2.15 | 2.26 7 — 85 10 |Holmes Wanding...... _| 3:45-4:45 p. m 05 10 |1.80 20 | 2.00 59) +153 11 |Havana........... -.... .....| 6:15-7:30 p. m 05 80 | .53 |2.13 | 2.66 =a) = 12 |Liverpool. -...... --...... 4:20-5:20 a. m 04 167.5) 50 2.12 | 2.12 | 4.24 + 44 +199 13 |2 m.above Copperas Creek ene 5:25-6:30 a. m 041 68 | g0 !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 18.59 | 9.54 +224 + 16 |7m. above Peoria... tanasabupceael 08 | 67 | 60 |2.19 3.29 |5.48| + 86 +209 17.‘ |Chillicothe Park.. 2:50-1:50 p. m. | .12} 66 | 15 92 16 | 1.08 — 63 + 30 18 |1m. below Lac 7:30-3:40 p. m. 15} 66 | 20 88 +22 =| 1.10 — 62 + 27 19 |Henry ....... :00-4:55 p. m. 20] 66 | 88 12 -90 | 1.02 — 61 — 20 |Hennepin .. :20-6:30 p. m. 20} 66 | 95 | .12 |2.20 12.32 — 21 — 8 Average | -T1 | 2.23 | 2.94] +57 | +89 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 809 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 slight clogging of the net and the uncertainty as to the precise distance, there is an error of undetermined proportions caused by the vertical movement of the planktonts and consequent possibility of uneven distribution at the 18-in. level between 4:30 a. m. and 7:45 p. m.—the extremes of our time of collection. Furthermore, an examination of the planktographs in the river and its backwaters for 1896 and 1898 (Pl. X., XIL, XXVII., XXIX.,XXXI., XXXII.) —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 .S6, 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. T’o 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 are apparently but slight in comparison with the effect of certain environmental factors which are local- ly dominant within certain sections of the river. Wecandistin- 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 —79to +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 +32 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 arange 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,+32, 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, +86, 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 Illinois 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 9-7 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. It is 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 (96) 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 r=1) in Lake St. Clair is 2.607, in the Illinois 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 of 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. The absence of great sinuosity in the 285 Illinois as compared with other streams, as shown by the 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, 1596, 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. < a Tempera- Centrifuge Enumeration Omitting Omitting 5 hie : ture > method method Nos. 1,9, 10} Nos, 1, 8, 9, 10 Slag i=) (F.) >ES 2 3) 5 7 Balis)-=| a RE BS > Sea | De: De- | Per m.3 |Under1sq.m. 5 => |Plank | Par- DAN ee apes | ae ase = 8 8 5 Sur- | Bot- 5 4.2] ton in ene ae | ture ae Biss Hot=|¢ j x eA é g a] Q |face | tom | os emis sets tonts per from Vol-| ture | Vol- | ture A a ae in + res in + ©\ in = pins in + JI per ct perct per ct. 1 10 1.68 82 77 .33 2.00 | +27.5 143,800 +318 3.36) 2 37.5 3.96 73 nF T7 33 1.34 | —14.5 110,000 + 0.8 |1.34 |_224 Gg 31 | —25.2 3 75 4.88 77.5 77 45 1.34 | —14.5 95,600 —12.4 |1.34 |—22.1 6.5 — 7.9 4 85 4.88 77.5 a7 45 1.52 | — 3.2 110,200 + 1.0 1.52 |—11.6 7.42 | + 4.5 5 | 95 [427 | m5] 77 | 45 | 144]— 86 | rox600 |+ 0.5 l144|—163 | 6.15 | tis 6 105 4.04 77.5 7 42 2.36 | +50.5 93,100 —14.7 |2.36 |+37.2 9.53 | +34.2 7 115 3.18 77.5 77.1) 40 2.40 | +53.1 112,500 J+ 3.1 |2.40 |4+39.5 | 7.63 | + 7.5 8 125 1.68 a7.5 77.5) .40 1.64 | + 4.8 110,300 \+ 1.1 |1.64 |— 4.7 [2.76] 9 135 1.22 77.75 77.5] .38 1.04 | —33.9 109,900 j+ 0.7 | 11.27] 10 146 0.56 77.75| 77.6) .30 -60 | —61.7 96,200 |—1L8 [ .34] Average | 1.57] 27.21 109120 | +78 11.72] 21.9] 710 | £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 is + 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 is 66.9 per cent., the range being from 1.17 to 5.54meters. In my test the range is from .56 to 4.88 m., the greatest departure being 81.5 per cent., 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 +38 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., —57.5 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 +7.8 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 (Pl. 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. Tur- Departure from mean Num-| Temperature ae Plankton per Plankton under ; bidity 3 in per cent. ber of (F.) Depth depth m.3, in cm.$ 1sq. meter (omitting Nos. land 2) 1 Jam] (init moe yan Sige en | = DOG EE | | a on Pal a dise Nok Hon meet wer en eee Per m.3 (isGles © . oh a ‘O . ace tom visible | ume in per cent. ume a per cent. sq.m 1 Tes} 76 66 35 2.40 —60 1.58 —83 2 71.5 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 70 1.58 30 6.32 +5 9.99) +4 — 6 —12 7 ae uy ne au 5.60 aot 8.85 —8 —17 —22 70.5 1.6 +2 7.64 +27 12.84 +34 +14 14 7 70 5 70 1.83 225 8.20 +37 15 00 +56 +22 13 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 + 2 +11 10 71.2 71 1.72 aie 6.28 = 5 9.55 1 6 15 Average | 6.00 |=:22.3 9.60] 338 | 121 | 20.2 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 cm.* 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 (i. e. after silt deduction), or 44, 5, 36, and 34 per cent. for the total catches, the averages for the two methods being + 48 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 1 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 conelu- 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 em.’ 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 61'z | fay S€z LL 1Z°0O} |gg°0} joZ-1] |oS-z} |gg€}] j€z°b) jzzZ g0°9 (oR 7 Lz'0 €z'o |€1z‘'o | yay €1 | gz'o |b |1g'0S | gr‘o | 66, zS | €1°z | Eorz |S |66o)S |Sz-olb |bz-olh |69'o|S |16-o\b |gS*olb |g6°E |S jo€-s1Ib lob t]S | £€-o |b “zof€ | sho | gO, PE | 69°€ | Lz€ |b [gS*ojS Joo1|S |S6°SIh |Eg-giS |Sq°E/S Jog" bx |Zz°o |x |zg’S |r jar‘Slx | g€-o Iz to°o} 6, gL | OIL | Sort jz |gZo1 |zo'olz |rr‘ijz |ge-olpijerr/Stlbh-1/g \zZo |6 jofr |S |Z9°S|S | Zo'o |b |zo'06 | 10°0 | 96, oS | zz°€ | 16°S jg [br'r|h |zo°€/S |ZS-o)S1\zSrlorj€o' bp |€E°6]r |zv-o€ z |gr€ I |10‘o $6, or | 6b-z | €S°z |r jorolr Jor‘ojr |tg‘o}z |g€*1]1 |Zg°6z |z1°Siz |pZ‘o +6, | Sy plc | > >" > > SFB PES Sil Zl cho alae Bl ate al ele Sl zie lao e [alo PB lale Slal oF pzto olele 2 OB a eheg s[o 1S s/F(S 2/98 2/918 2/P 1S (S19 <8 < Vers e1g 2/9 Be |f/S <1 S< | awa, Bois S|8@=Sia & Sis Fla “sis sje F sis Hisia& |sipe [sis Sie) aS |8iaFisi aS SS |45u cepts ea Sola Selis| Sos elas ta acl Se eo [Flo )=) oo. n* (= I s. . : . ty : . 4 i . — : : Arewuins ‘saq | ‘AON | 390 | ‘3dag] ‘sny | Ajnf aunf | Ae |pudy | yore | ‘qoq ‘uel *SUOI}DATTOO ITe FO} ‘sodvivae ATWIUOU JO, *66g1-P6gI—GaLONGAd LIIS—AAAIA SIONITII NI NOLUNVId JO NOILOAGOYd ATHINOW 293 revealing only a single midsummer pulse, culminating in the August maximum in a 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 decline 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.—XII.) 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 1897. 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 suhsequent 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 thecrest 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 the autumnal 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.* This is 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 (cf. 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 em.’ per m.° of water. 1895. (Table III.; Pl. 1X., XLUL., 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 em. 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 cm.*, 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?).......... il Epistylis sp., heads............... 3 Carchesium lachmanni, head....... 1 Ciliate, indeterminate............ 1 Heliozoan: :. fo Skee eee ea kee 1 297 Rotifera: ' Brachionus dorcas, female......... 1 Rotifer tardus, female............. 9 Polyarthra platyptera, female...... 2 Polyarthra platyptera, female with ec ea ae ee Oe 1 Indeterminate rotifer sp........... 1 Entomostraca: 3 Cyclops bicuspidatus, female, young, dead or moribund..... 1 Cyclops, yOUne g. < 8) | og ems tad! > + heres & a me - F Bom soem Lansi fe} FS $2neee Si Spook ss Scag? ~~. ae el 4 c2089 “et ar COMPARATIVE EXHIBIT OF PLANKTON PRODUCTION IN ILLINOIS RIVER AND IN \ “ [2 | seuaie on | oom-no ootano | Oe ore oo00N0| Ss : |Qw 2 SSS SS oan nN ray ae oS mn j,5| woryued | 2 :OFS:/™ a pegs, si a rr) mn aye asviaay Doo :|0 Co} payien 3 hh = = a aj) SIDI ON | = amano =m mo | = : |G.» | Ty ray eee = _ ~ + Ne) [Sa] uogued |(eoeas |=) seece : iol seeae sls al © JR a) adeaay | osama :| + Hata ilo womton ay nN ) j 5 gz = = = | sayaqeo oN) | OO mH +0 oomoro oonoHno = bow il | 5 7 |e “ . . ise} ES) uoryueyd & SRE a(S Seri S| 8 | aSeiaay oxy Seep sen | Ion Bin) eee lea 6 a { me 5 | 5 S| i lg | Seuoveo “on oanooo | + : See] : [=| uorqueyd 8 2S a il 3 ia aseiaay | 3 lees a + a | 3 = TA 5 s9y9qe89 "ON +auiunmo maaan 3 =| vo 4 Role o (Bs| uoryuerd A) RASRA IS) Setlee sis Qi oO aseioay io} oonoo ° aooo0o ° te to | Sayd}e29 *o oonnHo OoONHHO oonadHO ooaHHo «a : \a x joe re) maa = nO 8 a we = o aon = 1 | oO o> 2 B 3 me a | |B-5| uworyarid Q'| 6S 8 | 82 IR 358 en 8 8 = oi Be aseiaay ° tooo clo S Prevave) 6 Na ono ° ooo 3 | | | S94d}89 “ON +o +MmM0 awnatto =tHwnino | | moa tino Fa : et, sis 3 ct |oo \e > ise) - an ww |e | st £5) uoryued | SESSA 3/5) Baege sie SHAG TISIIMOSSae FIR" el) s =M| aBeioay + ate mo Gay 44000 cs) OomoHO 3 | o-o00 ° a a re 2 5 5 3 Silaee os : th iNO E00 : two ho a] - tino NO D> :| tun 00 nhac ri 2 We SoSsses Ag PDADDAA| - DODO) 5 POOROS) 5/50 5 322 = E EF Z |2| “(2381 ce 5 Car i) S Ayal ysnsny jaquiaidas JaquiarAoN | daquia3aqT [Gly < Bs Jw | sayaieo ‘on EX) q N vu peaes uo} que|d G3 (| | adeiaay | ae. \} - [2-4] sayoyeo ‘ON - 16 ol = a5. fs 5] uoj}yued | 3 | = |i @| aSeray | . 7 |S Ve a =| D| ] oo || | saqoied ‘on | = | poe | - > s | na i= g|Pa| spun s I Vv ° Sy la Sayo}ro * 2 lls | Sauczee on | |e s 28 uouneid | ‘ a | | 4 5 all aseiaay | : = Zz il |] gz | 8242382 “ON ooo0onH| Hiles 7 eee ws | | a lez uo}xue]d | 8 ° ul Dp ||? aselaay Galant ail Z ||.2 | seuss ‘oN | 00 comin a2 ara a VE = \23) A oC) Bere SITS Uc a =| | advic :i6 id6|o : 3 pa ee ae | =} atoll se) : q x DDO! 2S) il * | ees |< | = | Aienue[ | Aieniqga 345 (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 (3 em.) flood water of August 18 ; there is more (.032) in the clearer water (30 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 em. 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 mainstream. 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 IV., XI.; Pl. XXVIII., 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 3 (.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 cm.) 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, 26.35 em.*) contains but .27 em.’ 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 slight. As in the main stream, so also in the tributary there is a dropin production in August (.056) toabout a 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 cm.*, 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 21st and 29th of September production in the Illinois falls again to 3.00 and 4.04 em. re- spectively, while in Spoon River on the 30th 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. XLVL.) in which chlorine in Spoon River rises temporarily. The three collections of November-December, 1.551, 1.99, and .599 em.*, 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 em.* 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. XLVL, 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 seenin 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 5,180 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 AVERAGES—PARTS PER MILLION. November December Bg | 2S | meh ee Re Ba ceil ee | eee = S w + = = eG Po) om + veer Se | Ge] e Wee dgehee | ea) eee BE Oe | el ce ee ee |e TOQO sce resco .065 | .84 | .013 | 1.6] .005 | .o1 -52 | .008 | 1.3 | .002 PSO] Jearcani seater 052 | .76 | .008 56/1 .671 022| .68 | .005 | .63 | .599 1898 jects neni 026 | .37_ | .009 -58] .oor | .084| .89 | .o15 | .33 | .oor 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, Noy. 2 and 30, and Dee. 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 em.*) is 180 times that recorded in the last half of 1896, and 43 times that for 1898—as a result of the low-water con- ditions discussed above. 1898-1899. (Tables IV., XI.; Pl. XXIV., XLVII.) 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 in a year of consider- able flood and repeated access of storm water. In 1898 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 waters of Spoon 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 cm.’ of plankton in the Illinois 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 in Spoon River is at a minimum, there being but the merest trace of living 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 .38, 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 em.’ per m.* of water. In the Illinois it 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 Illinois 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 Illinois 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 Illinois an immediate diluent function upon its pro- duction, which, qualitatively, is approximately 10 per cent. STATION C, QUIVER LAKE. (Tables V., XI1.; Pl. IL, 1V., XV-XVII., XXV-XXIX., XLVIII., XLIX.) ENVIRONMENTAL CONDITIONS, This lake lies 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. 351 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. IIL.) 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- cated (Pl. II). It is simply a shifting path through the vegeta- tion, and is not generally marked by deeper waters than adja- 352 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, 13, 31, 24, 26, and 7 re- spectively. Their distribution by months is shown in the table between pages 342 and 343. In the earlier years the interval of collection was somewhat irregular, though with 6 exceptions every mouth 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 353 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 also serve 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 em.’ 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 (PI. 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 (.25) andthe Illinois (.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 384, 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 em.’ 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 V.; Pl. XXVL., XLVIII.) 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 ia 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. XX VI.) 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. XXVI.) 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. IX. 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 23 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 cm.’, Pl. IX.) 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 (PI. IX.) andthe 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 396 increases its impounding function. Whatever run-off from lake to channel occurs under such conditions will result in a slight 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 access 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. XXVII.) There are 31 collections in this year, with an average of 2.59 em.’ per m.* as compared with 1.16 in the Illinois. The maximum of 16.76 cm.’ occurs 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 357 year, as will be seen on a comparison of Plates X. and XXVII. 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 em.’ 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 (Pl. IL). Slight 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 (Pl. 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 16.52 em.* 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 that inthe river. The maximum (16.76) is almost twice that in the river (9.39). The large development (16.32) 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 398 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 rise of the August flood, production again assumes a pulse-like character, lagging throughout its development a few days behind that in the adjacent stream (cf. 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. Inthe 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 sequel 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 ampli- 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 Ilh- 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 | 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 that in 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 Quiy- 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- tions 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 to a 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 lie in fundamental factors common to the plankton of both areas or to their envi- ronment, 361 1897. (Tables V., XIII.; Pl. XXVIII, XLVIIL.) 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- imum 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 fallsnear 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) is 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 deeline 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 . 28. The parallelism in the movement of production can still be traced in the 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 ay- 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 andthe 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. XLVIIL.) 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, hes at the basis of the relatively small plankton production in this body of water in this year. 1898. (Tables V., XIII.; Pl. XXIX., XLIX.) * 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 3 coincidently with the vernal maximum in the channel (Pl. 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, is 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 slight 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 like 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 (.23) 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 cm.* 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 2.13 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, .92and .569; the albuminoid ammonia, .431 and .275; and the free ammonia, .95 and .1388. 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., XII; Pl. XXIX., XLIX.) 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. XLIX.) 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 em.’ 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, (Table VI.; Pl. XVIIL., XXX., XXXII.) ENVIRONMENTAL CONDITIONS, This so-called lake is only the westerm arm of Quiver Lake (Pl. IL.), 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. XVIII.) almost exclusively of Cer- atophyllum, Elodea, 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 VI.). 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 VI., Pl. XXX.) There were 12 collections in this year, from April to De- cember, averaging 3.25 cm.* per m.’ The average of the monthly averages (see table between pp. 342 and 348) is 3.3 em.* to .74 and 6.65—similar averages for the same period in Quiver Lake and the [Jlinois 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- duction. 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 (30.42), 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 Dee. 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 Allorchestes 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), a7 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 toenrich 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 n/. 1896. (Table VI., Pl. XXXI.) There are 30 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 20.35em.* per m.* on the 17th, though production is also large on the 24th (19.5). In Quiv- 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 17th 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 than 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., XX VIL, 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 303 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 is 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 les 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 23 out of the total num- ber. The amplitude of the change is rarely equivalent, but its direction is 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] May8 |May 16-19|May 21-22) July 3 | Aug. 15] Aug. 29 | Sept. 16 20.35 to | 13.39 to 18.40 | 18.40to “1.58 11.25 1.18 "3.06 a 19.50 13.06 | 13.06 to 36] 1.14 to | 3.88to | .75 to | 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 51 .51 to 49 3.42 BPs 55 In almost every case these exceptions to the precise simi- larity of movement in production in the two lakes can be cor- related directly with some disturbing environmental factor potent in one and not equally so in the other, that is, to local disturbance in the environmental similarity, as follows: The exception on April 24 is due to the earlier appearance of the summit of the vernal pulse of production in Dogfish Lake, and this in turn is correlated with the greater proportion of shoal waters in Dogfish and the greater access of spring water in Quiver, both factors favoring the more rapid and complete warming up of Dogfish waters. As has been repeatedly pointed out, the thermal rise deflects towards itself the vernal rise in production. Conditions on May 8, when Quiver Lake production doubles and that in Dogfish Lake falls slightly, are to be explained by the different effect which the hydrographic changes have at the two stations. At stages existing at the first of the month (7 ft.) there is not sufficient overflow to carry any considera- ble current of warm backwaters to the southward down through the lake to the river. The content is largely of local impound- ing. The slight rise at that time (Pl. XX XI.) would therefore tend to increase the local reservoir action, and creek and spring waters would most naturally be impounded along the usual line of their run-off, in which our Quiver Lake station lies (PI. II.), while the plankton-rich backwaters of Dogfish Lake are held back, hence the low production in Quiver Lake 375 on the 2d (4.24) and the larger one in Dogfish (13.59). On the Sth conditions are changed ; the decline in levels (.6 ft.) has in- creased the run-off, and the recent contributions of tributary wa- ter have brought down into Quiver Lake an increased proportion of plankton-rich impounded backwaters which increase the con- tent at that point to 8.14 em.*, this being, however, still below that of contributing and declining Dogfish Lake (13.59 to 13.06). On May 16-19 the collections were not quite coincident, but, such as they are, they form another exception to the simi- larity of movement in the two lakes. In Quiver on the 16th the decline of levels brings the proportion of tributary waters at that point into greater prominence, while on the 19th in Dog- fish the impounding function is greatly increased by the inter vening rise in levels (1 ft.). Examination of the collections also shows that the maximum of 18.4 em. in Dogfish Lake on the 19th is caused primarily by an extraordinary pulse, or possi- bly a local “swarm”, of Melosira with some Cladocera, whose apex and location the date of collection approximates. On the 2Ist the plankton content in the same locality fell to .86 em.’—a decline of 98 per cent. in 2 days. On the 21st and 22d a quantitative survey of the local distribution of the plank- ton in the whole area of Quiver and Dogfish lakes was made, with the result that no development commensurate with that on the 19th at this point was anywhere detected. Since a sim- ilar sudden decline is to be seen in Flag Lake inthis same week, I am inclined to the view that we are dealing here witha complex biological phenonenon in which the reproductive cycles of the organisms as well as external factors—such as possible tempo- rary decline of food supply, or encroachment of emerging veg- etation—are involved. This sudden decline is earlier and less marked in Quiver Lake than in Dogfish, possibly because of in- creasing differential environment, and thus occasions this tem- porary dislocation of the similarity in the movement of produc- tion on May 16-19, and again on May 21-22. On July 3 we again find lower levels reached and accom- panying decline in production in Quiver Lake when tributary 376 waters rise in proportion. The readjustment which this ne- cessitates so modifies production that its movement differs, though the difference is slight and consequently the less sig- nificant. On Aug. 15 and 29 we deal again with a phenomenon simi- lar to that of May 21, namely, a pulse of large production in Dogfish Lake with an accompanying one of lesser amplitude in Quiver. The pulse in Dogfish was again later, apparently, in reaching its culmination (on the 15th) than that in Quiver (on the 7th), and its decline (93 per cent.) on the 22d more complete than that which Quiver attains (63 per cent.) on that date from its maximum (4.36) on the 7th. The conditions in Quiver Lake are further complicated by the fact that on the 15th river water was just beginning a temporary invasion at the point of collection (see hydrograph, Pl. XXXI.). Save for this invasion the similarity of movement might perhaps have been preserved on the 15th. The abrupt and extreme decline in Dogfish Lake on the 22d, however, with the resulting inter- ruption of the similarity of movement on the 29th, is in some way related to the excessive development of the 15th, which may bring into operation again the factors above suggested in connection with the ike phenomenon in May. It seems not improbable that the sharper localization in Dogfish Lake due to absence of current and tributary waters and the presence of these factors in Quiver tends to intensify environmental in- fluences or inherent tendencies of the plankton in the one area, and to minimize some if not all of them in the other, and that this differentiating influence of these purely local factors is - fundamentally the cause of the dislocations and disturbances of the otherwise similar movement in production in the two lakes. These exceptions seem, however, to emphasize the es- sential similarity in the production in the two areas, a similar- ity founded on the common factors of the environment, shared equally by both, and on the identity, in the main, of the con- stituent organisms of the plankton. The general hydrographic conditions of this year affect 577 profoundly the plankton production in this lake and in Quiver also. Although the average height for this year (6.975 ft.) is almost the same as in 1897 (6.903 ft.), the distribution of high water is such that the impounding function is exercised not only during the winter months, when production is low, but, owing to the recurrent floods, it is in operation to an unusual extent during the period from June to October, when produc- tion is wont, as a rule, to run low in these waters. Thus levels (Pl. XX XI.) are above 6 ft. fully half of this timeand are at all times above 4 ft. with the exception of 10 days in July. Not only does this increase the impounding function of these waters, but it decreases the relative occupation by vegetation in addition to reducing its actual extent by uprooting and removal. It also decreases the proportion which creek and spring waters form of the total content of the area, or impounds them long enough for the plankton to breed therein. The distribution of high water is such in this year that it affords an opportunity for increased production in the lake. In comparison with 1895, when production averaged 3.25 cm.‘ per m.* from April to the end of the year, we have 5.01 in 1896 for the year asa whole. The average height of the river in 1895 was 3.61 ft. (p. 163), in 1896, 6.98—an increase of 3.37 ft., or the equivalent of almost doubling the volume of water in the lake. So not only is the amount per cubic meter greatly increased, but the total run-off of plankton into the channel is multiplied by some undetermined factor. The net result of the hydrographic conditions of 1596 in Dogtish Lake is therefore an increase in its impounding func- tion at a time of large production (5.01),and its discharge - tends to raise the plankton content alike of Quiver Lake (2.59) and the river (1.16), but data are lacking which might enable us to compute its quantitative effect upon the plankton con- tent of either. Not only is the average production of Dogfish Lake greater than that of Quiver, but individual collections here exceed coin- cident ones there with the exceptions only of those on May 21 378 and 22 and Aug. 15, when phenomenal declines appeared in Dogtish lake. In a similar way its production exceeds that in the river in every case but one, that of May 21. Thus produc- tion is prevalently higher here than in Quiver Lake and the river, to which it contributes its run-off, as a result of the im- pounding factor and, in this year, of the relative absence of veg- etation also. The impounding permits the growth of the plank- ton to utilize the nutriment derived from decay of vegetation and other sources before it is carried out of the lake. 1897. (Table VI., Pl. XXXII.) There are but 6 collections here in 1897, in the first six months of the year, at approximately a monthly interval. The average production for this period is 2.23 cm.’ per m.*, with a maximum of 8.18 on Apr. 27. Since the collections are coin- cident in the river, Quiver Lake, and this lake, a comparison of production is facilitated. The similarity noted in the previ- ous year may be traced here also, and the relationship of the three areas remains in the main unchanged during this half of 1897. Briefly, there is low production in all three under the ice in midwinter, with a slight increase in all in March, a ver- nal pulse in April followed by a decline in production in May in the lakes but not in the river, while in June the flood reduces the plankton content in the river but changes that in the lakes but little. The collections throughout the period show greater production in the lakes (Dogfish, 2.23, Quiver, 2.77) than in the river (average, 1.91) with the exception of the May collection (Dogfish, 1.94, Quiver, 1.29, river, 5.62). This drop in plankton content in the lakes below that of the stream occurs at the time of greatest increase in vegetation and rapid drop in levels, which increases the relative occupation by vegetation-—a factor from which the river is relatively free. The flood of June, flushing the stream, obscures the relationships of production at that season. In all collections but those of May and Feb. 26 Dogfish Lake contains a more abundant plankton that Quiver 379 by from 25 to 100 per cent. This is apparently due to the pre- ponderance of the impounding factor in the former. Thus in this season also the similarity in the movement of production noted in the previous year can be traced, and the excess of production in Dogfish over Quiver continues in the main. Its run-off therefore serves in this period to enrich the plankton alike of Quiver Lake and the river. This is correlated with the high levels and consequent increase in the impounding factor and the relative diminution of vegetation in this area. GENERAL SUMMARY, RELATIONS OF PRODUCTION IN DOGFISH AND QUIVER LAKES TO THAT IN THE ILLINOIS RIVER. The analysis of the data of production in these two lakes leads to the following conclusions. Plankton production is in a large degree a function of the time allowed for the breeding of the plankton. Thus at times of high water, when both lakes are filled principally with the impounded backwaters of overflow, production is greater, other things being equal, than at low water, when a greater proportion of water of the lake (Quiver) is of recent origin from tributary creeks and springs. So, also, areas such as Dog- fish Lake, in which by reason of absence of tributaries and springy shores the impounding function is greater, show a great- er plankton content than similar areas (Quiver) where by reason of access of tributary water the impounding function-is de- creased. Vegetation of the character of that found in these lakes seems to exercise an inimical effect upon plankton production. Thus the season of dominant vegetation is generally one of low production in these lakes. Also during this period, as levels fall and occupation of the lake by vegetation becomes relatively greater, production generally declines, and, conversely, produc- tion rises when levels rise. Years of greater dominance of veg- etation, other things being equal, are wont to exhibit a decline in production, and, conversely, with lessened vegetation pro- duction rises. 380 These factors, combined with changes in production in the river, vary the relation which these lakes bear to production in channel waters. In general, in times of low water and domi- nance of vegetation the outflow from these lakes isa diluent of channel plankton, but during the run-off of impounded back- waters or in years of higher levels and less vegetation it serves to enrich channel waters. The river and the two lakes exhibit in common a very marked similarity in the seasonal movement in production. The recurrent pulses, which may be traced whenever collections are of sufficient frequency, coincide closely in their location but exhibit considerable local differences in their amplitude. This similarity is greatest when local environmental factors, such as vegetation and tributary waters in the lakes and sewage contamination and recent flood water in the river, are least op- erative, and is diminished or obscured as these factors come more into action. The diversity, as shown in the differing am- plitudes of the pulses of production and in the divergences and interruptions in their rise and decline, can generally be traced to the preponderance of some local factor or factors above named. The similarity in the seasonal movement of production is allthe more marked when the striking differences of the three localities in question are considered and the general instability of the whole environment is borne in mind. The changes in the plankton content of the river,—turbid and fouled by sewage, traversed continuously by a considerable current, and scoured repeatedly by flood,—of Quiver Lake,—with gentle current,clear spring-fed waters, and greater or less, but always considerable, vegetation,—and of Dogfish Lake,—with tranquil, almost cur- rentless waters, without access of tributary contributions, and also with considerable vegetation,—all exhibit a harmony that compels us to admit the potency of those general factors of the environment common to all—their climatic and geographical surroundings, which determine the amount and distribution of the light and heat, and the chemical constituents of the medi- 381 um in which the plankton grows. The similarity in the move- ment of production must also be correlated with the fact that these common environmental factors are responded to in the three localities by a plankton composed of identical or closely re- lated species in varying proportions. It is in the main the re- sult of the response of similar organisms to the common fac- tors of an environment, factors, moreover, of fundamental sig- nificance. FLAG LAKE. (Table VII.; Pl. XIX., XXXIIL, XXXIV.) ENVIRONMENTAL CONDITIONS. This is the local name for a marsh in the western bottom- lands opposite the location of our plankton station in the river (Pl. II.). Together with its outlet, Flag Lake Slough, it ex- tends parallel to the river from north to south a distance of about 44 miles, and is generally less than ? of a mile in width. It has no precise boundaries, since the fringe of willows which borders it, save for 2 miles along its northwestern margin where it joins Thompson’s Lake, merges gradually with the marsh on the one hand and the bottom-land forest on the other. It con- tains about 24 square miles of permanent marsh, of which but a small area toward the lower end was free from vegetation. The depth depends upon the stage of the river or the extent of the run-off of the impounded water. Its bottom, if we may dig- nify the treacherous ooze from which the vegetation springs by this name, is generally, if not entirely, several feet above low- water mark in the river. In the autumn of 1897, during the prolonged low water of that season, the lake dried up anda road was opened across it to Thompson’s Lake. Generally, how- ever, it retains sufficient water to tide over ordinary periods of low levels. The hydrographic conditions are such as to make this marsh exempt from all current save at times of most general overflow. Owing to the somewhat elevated banks along Flag 382 Lake Slough and along the west bank of the river, no access of river water is possible from the north or east until bank height is exceeded by the flood. At all levels below this, water enters the lake by the slough, which forms its outlet, or backs in from Seeb’s Lake (Pl. IT.). Another line of access is the low margin to the northwest between it and Thompson’s Lake. The rank - growth of living or dead vegetation which at all times fills this region, effectually blocks any localized current here, and no channel has opened in this region. Probably much of the water, as indicated by the distribution of drift, enters the lake from its southern end. The same reasons which prevent access of water from the north also tend to restrict the flow through this area at times of general overflow, and the fact that Thompson’s Lake (Pl. II.) affords for backwaters impounded to the north a channel where resistance is much less than in the shoal, forest- begirt, and rush-filled Flag Lake, tends also to divert the mov- ing backwaters to that region. Consequently, Flag Lake is in the main an impounding area whence the impounded water is drawn off as levels decline, but which is not generally trav- ersed by the waters of general overflow as are Quiver and Thompson’s lakes. It is thus one of the most strongly localized of all plankton stations, and the unity of its environment is more continuously maintained than that of any of the localities thus far examined. Its vegetation has been described on pages 249-250, and it will suffice in this connection to call attention to the predom- inance of the emergent and succulent types in its waters, and to the fact that little, if any, of it is ever carried away by flood or currents as it is from Quiver and Dogfish Lakes. This is a large factor in maintaining the local fertility of this area. This is a favorite haunt of migrating water-fowl in fall and spring, and contains breeding grounds of the few summer residents. It isalso much resorted to by the German carp, now one of the most abundant fish in the Illinois. Fish enter the lake in numbers when levels rise, but leave again before low water in the slough (Pl. I,) prevents their departure. Evi- 383 dences of the destructive work of the carp are seen in their ac- tivity in uprooting great patches of Sagittaria. Such condi- tions were prevalent shortly after the August flood of 1896 (PI. XXXIII.), when the combined action of the change in levels and the invasion of fish destroyed not a little of the vegetation. COLLECTIONS. Systematic examination of the plankton in this area was begun Oct. 17, 1895, and continued until Aug. 16, 1897. Six summer collections were made in 1898 for the purpose of de- tecting Trochosphera. Owing to the surroundings of this region access to it ex- cept during high water was a matter of much time and con- siderable difficulty. Absence of roads and bridges made ap- proach by conveyance impracticable, and save at maximum overflow the elevation of the surrounding bottoms or the abun- dant vegetation prevented the entrance of the steam launch- The drift in the slough (PI. II.) and the matted, and in many places impenetrable, growth of Scirpus fluviatilis rendered ac- cess to the small areas of open water an arduous task. At low stages the only means of obtaining a collection was to wade out through the morass to a suitable place. The difficulties of approach in winter were even greater, when ice and the emer- gent vegetation combined to interfere with rapid transit of any considerable load. For these reasons this station, though one of much local biological interest, was early dropped from our list. These same difficulties have enforced some variation in the methods of collection (Table VII.) and in the locality at which collections. were made. In the autumn of 1895 they were made by dipping water in scattered areas in the vege- tation and in advance of the roiling of the water caused by wading. On Feb. 28, 1896, a measured quantity of water from successive levels was taken amid the standing but submerged vegetation with a pump. Other collections prior to May 23, 1895, were made by the oblique-haul method and thereafter by the plankton pump. 384 In the autumn of 1895 collections were made in the north- ern arm of the area marked as open water on Plate II., and occupied at that time by a considerable amount of submerged and floating vegetation, largely of Nymphea. During high water, when landmarks were submerged, this location was ap- proximated as nearly as possible, but in the following spring the location of the plankton station was shifted to the lower arm of this open area (Pl. II.), and as the vegetation emerged and blocked access the station was moved to the head of the slough in effluent waters. These changes in method and loca- tion, impair somewhat the value of this series of collections for comparisons inter sc, but they still serve to throw important and significant light upon the relationship of such marshes and of their vegetation to plankton production in their own con- fines and in the channel waters to which they may contribute. There are 38 collections, extending continuously over 22 months in 1895-1897, with an interval of collection in the greater part of 1896 sufficiently short to enable us to follow the course of production. The scattered collections of the remain- der of the period and the six additional collections in 1898 throw but little light upon the movement in production, though they are of interest for comparison with other locali- ties. PLANKTON PRODUCTION. 1895. (Table VII., Pl. XXXIII.) There are but four collections in this year, in October—De- cember, averaging 20.45 cm. per m.’ and having a maximum of 57.76 on Oct. 17, and declining to 6.38 on Dec. 19. This period was one of no marked changes in the hydrographic conditions, The lowered temperature and autumn rains had checked evap- oration and brought about a slight increase in the volume of water, as shown by the increase in depth from .25 to.45m. The lake was choked with decaying vegetation, the product of two 385 season’s growth without a flood exceeding 7 ft. Even the rise to 5.2 ft. Dee. 19 was only beginning to affect the conditions within the lake. In October the succulent vegetation, such as Nymphea, Nelumbo, and Sagittaria, was undergoing rapid decay, which was checked by falling temperatures, and we find plank- ton production declining (from 57.76 to 6.38), and the decline accelerated on Dee. 28 (3.26) with the invasion of flood waters. This large production, unsurpassed at any other station (cf. Pl. XXXII. with Pl. [X., XXVI., XXX., and XXXVI), is to be cor- related with the excess of decaying vegetation in this locality resulting both from the abundance and character of the vegeta- tion and its freedom from flushing by current due to access of tributary waters. The maximum in October is due almost wholly to Synura ubella, which declines in the later collections in which the Cladocera and later the Copepoda appear in in- creasing numbers. Throughout this period there was no run- off until flood levels were reached late in December, and even then, owing to reasons above cited, the run-off from the area is relatively slight. There was consequently no direct enrichment of the channel waters from this area. Unfortunately, no chem- ical analyses of water from this area are available, and the chemical basis for an estimate of the relative fertility of this marsh is lacking. The data of production illustrate the great _ fertility of waters impounded where decaying organic matter abounds. Both the impounding factor and the local enrich- ment factor are apparently at a maximum potency here at this season, and production is correspondingly great. 1896. (Table VII.,-Pl. XXXI1I1.) There are 27 collections in this year, with an average of 13.83 em.’ per m.*, and a maximum of 203.52 on May 2. The weekly interval of collection in April-June enables us to follow the course of production withsome detail, but the fortnightly, or longer, interval prevalent during the most of the remainder 386 of the year reduces greatly the value of the data for such pur- poses or for comparison with other localities. The hydrographic conditions are such in 1896 that this lake maintains, throughout, a connection with the river. This is owing to the relative absence and brief duration of low levels, the run-off not being completed before a new invasion occurs asa result of a recurrent flood. Since falling levels prevail during more than two thirds of the year, a run-off from the lake continues during this portion of the timeat least. The lake is therefore in this year a factor in the determination of production in channel waters, whose continuity is broken only when levels are such that no waters are draining off from the lake or passing through it during general overflow—which is the case in less than one fourth of the time. The average produc- tion in the lake for 1896 (18.83) is almost twelvefold greater than that in the stream (1.16), and the monthly averages also (see table between pp. 342 and 343) are from 24 to 218 times greater, while individual collections in the lake in all but three in- stances exceed coincident or approximate ones in the river. The exception on July 30 occurred, when the invasion of flood water was followed, as is usually the case in midsummer in vegetation- rich backwaters, by a semi-stagnation with great development of Oscillaria, and the formation of considerable gas with a strong odor of H.S beneath the felt of Oscillaria which covers the bot- tom. Under these presumably abnormal conditions the plank- ton content reached a lower level in the lake (1.62) than in the river (3.90), and this was at a time of influx rather than outflow of water. With the above exceptions the lake at all ob- served seasons contains a richer plankton than the channel, which its run-off directly enters,and under similar hydrographic conditions we are justified in predicting at other times a similar relationship, though the exact ratio of production would proba- bly vary according as the vegetation by its growth or decay affected the fertility of the water. In the absence of any satisfactory basis for determining the amount of the run-off from this lake, a quantitative expres- 357 sion of its effect in increasing the plankton of the channel can- not be given. Similar marshy regions are found, along the course of the river elsewhere, especially above higher bottoms which have been built up across the flood-plain by tributaries such as Spoon River, and such areas presumably share with Flag Lake this contributory function in the maintenance of channel plankton. In the discussion of production in Quiver and Dogfish lakes I have called attention to the similarity in the movement in production, these two lakes and in the river. In Flag Lake, we are dealing with a very different environment ; bottom, shores, vegetation, hydrographic relations, especially in the matter of tributary waters, are all diverse. Indeed, the lake it- self includes several distinet typesof environment. It is inter- esting to note that in so distinct a unit of environment as this marsh we find so large a degree of similarity in the movement of production as can be traced between its seasonal plankto- graph and that of the river and of the lakesthus far examined. It should, however, be stated that the similarity is less precise here and is more evident in 1896 than in other years, though this is probably in part due to the absence of sufficiently fre- quent collections. The degree of similarity may be seen in the following com- parisons. In 17 of the 27 possible comparisons between pro- duction in Quiver and Flag lakes (Pl. XXVIL. and XXXIIL.) the direction of the change in production coincides. Most of the 10 exceptions are due to slight differences in the location of apices of pulses, or occur at times of lowest water, that is, of most pronounced local differentiation—as, for example, at the drop in levelsin May and again inJuly. Thesame number of excep- tions similarly located occurs when production in Dogtish Lake (Pl. XXXI.) is compared with that in Flag Lake (Pl. XXXIIT.), and there are 11 exceptions in the possible 27 in the case of the river (cf. Pl. X. and XXXIII.). In general terms, the similarity consists in the rise in pro- duction, probably obscured in Flag Lake by an overestimation 388 of silt on March 30—with increase in temperatures in January— April, culminating in a vernal pulse in April-May, which in Flag Lake reaches a much higher level (203.52) than elsewhere, culminates later by 7 to 14 days and is not divided into two apices as in the other three localities, but in duration covers the period of two pulses elsewhere. It is further seen in the May-June and August pulses and in the fairly well sustained correspondence in direction of the changes in the September-— December period. The most marked disagreement appears with the declines in stage of the river in May and July, when local environmental factors are most potent, and when, also, vegetation is at the height of its relative occupancy of the lakes in question. One of the most striking features in the production of this lake, and one not without parallels elsewhere in our records (Pl. XXIX., XXXI.), is the very sudden decline in plankton content after the vernal pulse, namely, from 203.52 em.* per m. on May 2 to 47.7 on the 9th—a decline of 77 per cent. in 7 days. On the 15th it reached the low level of .72, a decline of 98 per cent. in 6 days or of 99.6 in 13 days. The attendant hydro- graphic conditions are not without significance. This pulse (Pl. XX XIII.) attains its growth between March 30 (1.02) and May 2 (203.52), in which period the net drop in levels in channel waters is only from 8.1 to 6.9 ft. and the total move- ment only 1.7 ft., while in this protected backwater the fluctu- ations are probably somewhat lessened, as will be seen in the fact that the depth in the lake changes only .5 ft. to 1.2 ft. in the channel. The pulse thus rises in stable conditions. The decline of the pulse takes place between May 2 and 23 from 203.52 em.* per m.* to .12. In this time levels fall from 7.1 to 4.9 (see p. 159) on the 17th and rise again to 7.2 on the 23d. The decline in production from the 15th (.72) to the 23d (.12) is so small a part of the total that its significance in the present connection is slight, and the rise in levels has probably not had time to materially affect the lake. The hydrographic influences potent in the decline in production have been operative prior 389 to this rise, and consist in a fall of 2.2 ft. in channel waters though the depth at the station of collection changes only 1.6 ft.—equivalent to a reduction in volume of 25 per cent. at the point of collection and 30-40 per cent. in the lake as a whole. It thus involves a considerable and rapid run-off of the rich plankton developed in these impounded waters. This factor alone is, however, quite insufficient to account for the total loss in plankton content in this period. Another factor which is correlated with this reduction in the plankton content is the increasing occupancy of the lake by vegetation. The decline in levels hastens the emergence of the emergent forms and in- creases the relative occupancy by submerged and floating spe- cies, while the vernal growth in all during these three weeks in May, more than any other factor, transforms the broad expanse of open water into a vegetation-clogged marsh in which but few stretches of open water are visible. This phase of the growth of the grosser forms of the aquatic flora robs the water of some of its store of nutriment and cuts off the free access of light— both of which might interfere with the growth of the competing phytoplankton. Limnetic diatoms such as Asterionl/a and Melo- sira are the principal synthetic organisms building up this re- markable pulse, and the Cladocera, principally Bosmina and Chy- dorus,appear in numbers with itsculmination. The composition of the plankton favors the inference that a temporary exhaus- tion of the food of the phytoplankton and zoéplankton alike con- tributes to the sudden reduction in plankton content, while the additional and perhaps related factor of reproductive cycles may also have a large causal relation to the phenomenon. 1897. (Table VII., Pl. XXXIV.) There are but 7 collections in this year, at approximately monthly intervals in January-July. Collections were suspend- ed on July 16, when decline in levels made access even to the foot of the lake by boat impossible. With the further decline (Pl. XI.) in river levels the run-off from the lake soon ceased, 390 and by the middle of September the water had practically dis- appeared within its boundaries. The 7 collections average 4.59 cm.’ per m.’—about double the average production in the adjacent river, and in Quiver, and Dogfish lakes on coincident dates. Individual collections also exhibit in every case a greater plankton content in the lake than in the river. This area in this season thus contrib- utes to the enrichment of the channel waters, which its run-off enters, and its contributions exceed those of the lakes on the eastern side of the river. This higher production in this local- ity is, I believe, a corollary of the greater impounding function of Flag Lake, resulting from its freedom from tributary waters of recent origin, from its somewhat sheltered location—which checks the downward movement through its area of the gener- al currents of overflow, and from the enrichment of its im- pounded waters during this period by the decay of the abun- dant vegetation of the previous season, which, for the reasons just mentioned, is not extensively carried away by flood wa- ters. The fact that production appears to be so much less in 1897 (4.59 cm.’ per m.*) than in the corresponding months of 1896 (11.21) may be due to several factors ; to the greater dilution in the greater volume of overflow (cf. Pl. XX XIII. and XXXIV.) in the winter and spring floods of the latter year, to the greater abundance in 1896 of decaying organic matter accumulated by the vegetation of two preceding low-water seasons, and, possi- bly, in a measure, to the infrequency of collections in 1897 and the probable omission of the maxima of pulses of production which would tend to raise the average. The similarity in the movement of production in this and other localities will appear at once on comparison of Pl. XXXIV. with Pl. XI, XXVIII, and XXXII. The coincidence in the direction of the changes is precise in all of the 7 instances in the case of the river, in all but one for Quiver Lake, and in all but two in the case of Dogfish Lake. This is a period of max- imum overflow, when the individuality of these several locali- 391 ties is submerged by the flood. It will be noted that the ex- ceptions lie at the close of this period, when low water brings local factors into prominence. It is at this time also that the differences in the amplitude of production are most in evidence. 1898. (Table VII., Pl. XXXIV.) Six collections made at the outlet of Flag Lake in this year in July-September for the purpose of detecting Trocho- sphera are introduced int» !:ble VIL, since they throw some additional ight on productio. :e _. The four collections in July exhibit a very low level of plankton content, the highest being .62 cm.’ per m.*; and the level is not raised in the single August collection. However, with the run-off of the slight rises of August and September we find a rise to 15.54. At this time water of overflow was making its way from across the bottoms at the southern end of Thompson’s Lake through the marshy swale into the foot of Flag, and thence out to the river. The similarity in the movement of production here and in other stations is seen in the general low level of production in July and the slight rise towards the end of the month. A de- cline early in August can also be traced, followed by a rise in the next month (cf. Pl. XX XIV., XII. and XXIX.). With the exception of the collection on September 6, the collections of this year indicate that the effluent of Flag Lake is a diluent of channel plankton. This may result from the low levels and consequent dominance of the vegetation in the lake at this time of low production there. SUMMARY. The data discussed in the preceding pages lead to the fol- lowing conclusions concerning Flag Lake. The average production of plankton in this lake, or, more properly speaking, marsh (11.46 cm.’ per m.*. or 9.23 on the basis of monthly averages), exceeds that in the river (2.19 or 2.71), This greater fertility appears not only in the averages 392 but in general throughout most of the seasonal changes. Its run-off therefore serves generally to enrich the channel waters. The greater production is due to the decay of the abun- dant vegetation which the lake contains, to the absence of trib- utary water of recent origin, to the relative freedom from the general current of overfow which largely takes the line of less resistance through Thompson’s Lake (PI. II.), and, consequent- ly, to the greater time afforded for breeding an abundant plank- ton in this impounding area. The dominance of the abundant vegetation is inimical to large plankton production. Other things being equal, plankton production is greater when the relative occupancy of the water by vegetation is decreased. The movement in plankton production in this area is in the main similar to that in the river and in Quiver and Dog- fish lakes. Pulses of production tend to coincide, though their amplitude may differ widely in the several localities. This sim- ilarity is least when local environmental factors such as vege- tation, stagnation, or local exhaustion of the food supply are most potent. Itis greatest when these are least, that is, during high water. STATION G, THOMPSON'S LAKE. (Table VIII., Pl. IL, XX., XXXV.—XXXIX.,, L.) ENVIRONMENTAL CONDITIONS. This body of water lies in the bottom-lands on the right bank of the [llinois, above Spoon River, midway between the bluff and the main stream. It trends in a northerly and then a northeasterly direction, following somewhat the curve of the Illinois. It is about five miles in length at low water, with a width in three fourths of the distance of about two thirds of a mile, while the northern end is less than one third of a mile in width. At this stage it contains about 1,400 acres. As levels rise, its margins spread rapidly—owing to the slight gradient of the shores—northward to Grass and Slim Lakes, westward, through Mud Lake, towards the. bluff, to the south, towards 393 Spoon River, while its connection with Flag Lake is early es- tablished over the low sandy bank which lies between them. At stages above six feet the “cut road” (PI. Il.) and the marshy swale above it fill, and connection with Flag Lake at its lower end and with the river is established. Its area is about doubled by the time the river reaches bank height and general overflow ensues. The lake is of somewhat uniform depth in the middle half, but shoals toward either end. In prolonged low water, when the slough at the northern end is practically cut off from the lake, extensive mud-flats are exposed in the northern area, and a portion of the southern end for about half a mile is also left bare except when prolonged and heavy winds drive the water towards one or the other end of the lake. The depth at lowest river levels in the central region, which includes about two thirds of the total area, is 3 ft. Laterally the water does not shoal until within 10 rods of the shore. There is thus a large area (about two square miles) of water with uniform condi- tions in this particular. With slight exception the bottom is of the softest alluvial mud, several feet in depth, overlying a sandy blue clay. The shores along the southern, western, northern, and northeastern margins are also of soft alluvium and of a marshy character. The eastern shore, for most of its extent, and limited stretches along the western one, together with the spit which makes out into the lake on that side, are of sand and of a firmer consist- ency. All of the shores are bordered by a belt of vegetation, which has been described on page 246. This lake is the largest of the reservoir backwaters exam- ined by us, and is one of the permanent type, resembling in all important particulars except that of submergence in times of general overflow and its reservoir relation to the river a typ- ical lake of an alluvial prairie country. Its position in the bottom-lands brings it into intimate connection with the river, the source of most of its water supply, while at times of flood 394 its position is such that the backwaters from the bottom-lands up-stream sweep through it and out to the river through the “eut road,” being deflected by the alluvial deposits of Spoon River (Pl. II.). Its relation to the river is a peculiar one in that its outlet, or slough, lies at its up-stream end. At stages above six feet the current enters through this slough, and the run-off takes place at the lower end through the cut road. Below this level all the run-off must take place through the, slough. The direction of the movement in the run-off of the lake is thus reversed as river levels pass this stage. There are no tributary waters of consequence which enter the lake, though a small rill and a few springs enter along the western margin. The main supply is drawn directly from channel waters through the slough, and when levels are stationary there is no in- terchange in either direction. The current sets in or out, at stages below 6 ft., according as the river rises or falls. The re- sult of this condition is that during the higher levels back- waters of overflow and the river water entering by the slough are impounded and drawn off slowly at the lower end of the lake. At stages below 6 ft. a run-off occurs only in the falling stages and in relatively smaller volume through the narrow and tortuous slough. The impounding function is accordingly more highly developed at lower levels, while at lowest levels all interchange ceases. This close and intimate dependence of this lake upon the river for its water supply in so far destroys the unity and inde- pendence of the lake as a separate unit of environment, and tends to eliminate the differences in plankton production be- tween it and channel waters. This tendency is counterbal- anced to a considerable degree by the large size of the lake and consequent increase in the time occupied in transit during over- flow, and by the impounding, at lower levels, of entering river water at the upper end of the lake, where it deposits its silt and soon permits the development of the lake plankton in its area. Here, as elsewhere, local factors are most potent at lower levels. The effect of the greater size of this lake is thus to equal- 395 ize environmental fluctuations and to obviate their catastrophic results, which may be seen in their maximum violence in channel waters, and in a lesser degree in the lakes thus far ex- amined, COLLECTIONS, This station was opened June 7, 1894, and collections were continued until the close of operations on March 28, 1599. In all, 99 collections were taken, distributed in the several years as follows: 5, 14, 27, 18, 25, and 7, with but few exceptions at approximately a monthly or fortnightly interval. It was only in the spring and summer of 1896, when an interval of 7-10 days was adopted, that the interval is brief enough to enable us to trace the movement in production with any degree of fullness. At other seasons the data are suggestive, but not conclusive, of its course. The relatively smaller number of collections made at this important station is due to its distance from our center of operations, the round trip from Havana to the lower station in low-water conditions exceeding 25 miles. The difficulties of access were greatly increased when at low water it was necessary to make the trip from the outlet of the slough by rowboat, and to drag or push this over the soft mud and through the dense vegetation at the upper end of the lake, and when, in winter, at low water, the boat and outfit had to be dragged across the frozen bottom-lands. The locations at which collections have been made are principally the two marked on the map (PI. II). The lower one was used exclusively in 1894 and 1895, and thereafter when access to the lake was had through the cut road. The location off Sand Point, at the upper end, was used when the lake was entered by way of the slough. Both were in the open central region, well out in the vegetation-free area, though in 1895 and 1896 the lower station was encroached upon some- what by shifting masses of Ceratophyllum. In a few instances, owing to high southwest winds and the dragging of the waves in the shallow lake, it was not possible to maintain an anchor- 396 age in the unstable bottom, and refuge was had under the lee shore, but still in usual depths and open water. In several in- stances in overflow stages, when the ice was too heavy to break and too light to carry our load, it was necessary to make the collection near the margin of the lake in effluent waters. These variations in the location of the point of collection introduce no error of consequence into the series, judging by the results of an examination of the local distribution of the plankton in this lake, the details of which cannot be given in the present paper. With the exception of the single pump collection on Feb- ruary 28, 1896, all collections prior to May 20 of that year were made by the oblique-haul method, and thereafter by the plank- ton pump. This lake is a type of the larger reservoir backwaters, such as Meredosia Lake, Clear Lake, and others found in the bottom- lands of the Illinois and maintaining a constant connection with that stream. An examination of its plankton content will therefore serve to throw light on the relation which lakes of this type bear to plankton production in channel waters. PLANKTON PRODUCTION. 1894. (Table VIII., Pl. XXXV.) There are but 5 collections in this year, from June to De- cember, at an interval of a month or more, with an average production of 8.89 cm.’ per m.* and a maximum of 24.92 on June 7. An inspection of the hydrograph (Pl. XX XV.) of this year reveals the fact that only the first two collections were taken under conditions which permitted any run-off from the lake to the river, and both of them at times—that is, in falling levels below 6 ft.—when the run-off was largely, if not wholly, through the tortuous slough at the up-stream end of the lake. The pro- duction in the lake (24.92 and 10.74) at these times was 33- to 397 4-fold that in the river (.74 and 2.39),so that the run-off at this season enriches channel plankton. With the exception of the August collection the plankton content in the other three col- lections in the lake exceeds that in the stream. The low con- tent in August (1.08) occurs at atime of lowest water, when vegetation by reason both of river stage and the season is at its maximum occupancy of the lake. At other times the effect of the reservoir function of the lake is seen in the relatively great- er production in its waters. The scattered data of this year are insufficient as a basis for any conclusions as to the correspondence in the movement of production in this and other waters. 1895. (Table VIII, Pl. XXXVI.) There are 14 collections in this year, between April 10 and the end of the year, averaging 9.67 cm.’ per m.*, and with a maximum of 61.44 on May 1—an amplitude nearly 11-fold that of this pulse in the channel. The average production (9.67) is 3-fold greater than that of the river in this year (3.22), and the monthly averages (see table between pp. 342 and 343) are in 5 of the 9 months from 1.6- to 12-fold greater in the lake than in the river. In the remain- ing four months, June, July, August, and December, the ratios are respectively 30.42, 9.33, 4.03, and 1.14 (river), to 9.42, 4.85, 3.09, and 1.00. The lower production in June-August occurs at atime when, with the exception of three weeks, levels were low and vegetation at its maximum occupancy of the lake, and when, moreover, the current was greatly slackened in the river, and channel plankton in the richly fertilized waters had more than the usual time to breed, while the less production in the lake in December is, owing to the distribution of collections, more apparent than real. In the matter of individual collections on coincident or approximate dates the lake shows a greater plankton content in 9 out of the 14 instances, and of the 9 there are 5 in which 398 hydrographic conditions favor a run-off of this richer plankton of the lake into channel waters. There are two instances in which run-off occurs when lake waters are poorer than the channel, but they are both at low levels and during slow de- cline, so that the discharge and resulting diluent effect is but slight. Considering the average production, the times when run-off occurred, and the hydrographic conditions when the lake waters contained less than the channel, it is probable that even in this year Thompson’s Lake, owing to its reservoir function, served predominantly to enrich the channel plankton. Though this relation predominated, the total contribution of the lake to the stream in this year was but slight owing to the hydro- graphic conditions. In the April-December period covered by our collections, the stage of river never exceeded 6 ft. until the December flood. There was, therefore, never any general cur- rent of overflow passing through the lake and carrying the im- pounded waters out from the southern end (PI. II.) into the riverand thus discharging a considerable volume of plankton-rich water into the channel—a condition possible in both rising and falling levels above 6 ft. At the levels below this point which prevailed throughout this period, influx and efflux both can take place only through the slough at the northern end, so that con- tributions to the stream from the lake occur only during falling levels, and, moreover, owing to the tortuous course and clogged condition of the outlet, the volume discharged at these lower levels is very much less than at higher ones, across the broad outlet at the other end of the lake. Falling levels occurred in less than one half of the time in April-December, so that the contributions of the lake to the river were not only slight in volume but limited in duration and discontinuous. Collections were too infrequent to trace the movement in production with fullness or certainty. There are, however, a few suggestions of a similarity in the course of production here and elsewhere. The direction of the changes in the course of production in this lake and in the river in coincident or ap- proximate collections is the same in 9 out of the possible 13 in- 399 stances (cf. Pl. IX. and XX XVI.);in the case of Quiver Lake the agreements number 7 out of a possible 12 (ef. Pl. XX VI. and XXXVI.); in the production in Dogtish Lake the correspondence is found in 9 out of a possible 12 (ef. Pl. XXX. and XXXVI.); while in Flag Lake there are 2 out of 3 (ef. Pl. XXXIIT. and XXXVI.). The agreement is lessened in this year, it seems, by the hy- drographie conditions. The low water affords less opportunity for a mingling of the waters of the stream and its backwaters, and also serves to bring out the local environments at each of the stations. Thus Thompson’s Lake has but little connection with other backwaters at any time during the year, and ingress oregress of channel waters was but very slight during six months of the twelve in this year. Vegetation also gained more ex- tended possession of this lake in this year than in other seasons of our operations. Low water also tends to make the channel plankton more directly affected by its peculiar factors, such as sewage. It is noticeable that the agreement in production is most marked between Thompson’s and Dogfish lakes, both back- waters of somewhat similar character in respect to tributary waters, relation to the channel, and vegetation. The most marked differences between production in this lake and the channel appear in the respective amplitudes of the pulses of production in April-May and June-July. In the lake the-rising vernal pulse attains the exceptional volume of 28.2 on April 10 to.52in the river on the 9th, a difference which may in part be due to the earlier warming up of the shoal- er lake waters. The maximum (61.44) in the lake is 12- fold that observed in the stream. The June-July production in the river, on the other hand, is 3- to 5- fold that in the lake, the contrast being due on the one hand, it seems, to the temporary exhaustion either of the chemical substances utilized by the plankton or of the reproductive capacities of the planktonts of the lake waters, and, on the other, to the increased sewage con- tamination in the stream as a result of low levels. The direc- tion of the changes in production, however, remains the same in 400 both localities (cf. Pl. IX. and XXXVI.) in the face of these contrasts in amplitude. 1896. (Table VIII., Pl. XX XVII.) There were 27 collections in this year, at monthly inter- vals until April, and then every 5-1] days until the end of Au- gust, and thereafter every fortnight. The average production in this year is 9 em.’ per m.’, with a maximum at the vernal pulse on May 2 of 48.99 em.’ The hydrographic conditions of this year are such as to bring Thompson’s Lake into intimate connection with chan- nel waters. The average height of the river for the year, 6.98 {t., is sufficient to maintain a run-off from the southern end of the lake to the river, submerging the bottom-lands between to the depth of a foot. Indeed a run-off of varying depths was maintained for 241 days, in which stages exceeded 6 ft. This was due to the recurrence of 6 floods, so distributed as to keep the lake discharging through the southern outlet for 241 days with only 5 interruptions between May and December. Of the 125 days in which water did not flow through the lake from the northern to the southern end, there were 29 of rising water in which no discharge to the river occurred, 28 of stationary levels in which the movement of the water, if any, was declin- ing, and 68 of falling water, in which the lake discharged through the slough at the northern end. Thus, during 309 days of the year this lake was discharging to the channel, waters which had been impounded for a varying length of time within its boundaries. The importance of this impounding area is best shown by rough calculations which show that the run-off of a single foot from the lake proper, not including the expand- ing areas which join it with every rise in levels, will fill the channel of the river at Havana to a depth of 8 ft. (low-water stage) for about three miles. In 1896 the total depth of the run-off for the year computed on a single discharge after each 401 rise is 26.9 feet—sufficient to fill the channel for 81 miles. When we add to this the consideration that at levels above 6 ft. water is continually passing through the lake with brief im- pounding, the length of channel filled by the run-off of this area must be considerably extended. The relationship of plankton production in this lake to the plankton content in channel waters in this year may be in- ferred from the yearly averages. Thompson’s Lake contained 9 em.’ per m.* to 1.16 em.* in the river. The net result would therefore be an enrichment of the channel plankton in a ratio dependent upon the relative volumes of the mingling waters. No quantitative statement of this ratio is possible in the absence of data as to the run-off of Thompson’s Lake. Not only is the net result an increase in the channel plankton, but the monthly averages (see table between pp. 342 and 343) and the coincident or approximate individual collections (Tables IIL. and VIII.) in every instance exhibit a higher plankton con- tent in this lake than in channel waters. The monthly aver- ages range from 2 to 251 times greater in Thompson’s Lake than in the river—ratios within which most, if not all, of those of individual collections fall. The data all indicate that this impounded water of the lake breeds a plankton whose run-off, without exception throughout this year, enriched channel waters. The effect of invading and plankton-poor river waters upon the plankton content of the lake is not conclusively apparent in the data, since we have also to deal with the phenomenon of pulse-like changes in plankton content which are combined with other factors in affecting the movements in production. It may be significant of the diluent action of invading river water that plankton content falls in the lake with the first en- trance of the May-June, the July-August, the October, and the November floods (Pl. XXXVII.). The recovery in production follows promptly in each case with the impounding of the en- tering waters. Since, however, declines in content, as in June, July,and August, occur also when flood waters are not enter- ing, we cannot conclude that the decline upon this entrance is 402 due solely and unequivocally to the diluent action of the in- vading waters, though their share in the phenomenon seems probable. I have previously called attention to the similarity in the movement in production in the several localities wherever col- lections were of frequency sufficient to permit the tracing of the fluctuations in production. The course of production in Thompson’s Lake in 1896 forms no exception to this similarity, though the parallelism is less precise than itis in some other in- stances. Thus the plankton content rises or falls together in Thompson’s Lake and the Illinois River in 18 out of 26 instances of coincident or approximate collections ; in Thompson’s and Dogfish lakes in 18 out of 26 instances ; in Thompson’s and Flag lakes in 16 out of 25 cases; and in Thompson’s and Quiver lakes in 12 out of 25. The direction of the change thus agrees in a total of 64 out of 104 possible instances in the data. This isa some- what greater proportion of instances in agreement than chance would demand, and its significance is enhanced by the fact that the agreement with Thompson's: Lake is greatest (64 and 69 per cent.) in the case of Flag and Dogfish lakes—impounding bodies similar to Thompson’s Lake—and of the river (also 64 per cent.), which is in a measure and especially in this year a sum- mation of impounded backwaters. Quiver Lake, on the other hand, where tributary waters increase the local differentiation, has an agreement in only 12 out of 25 instances. In hke manner months of high water, such as August, when local differences are to some extent submerged, exhibit greater agreement than months of low water, whenthey are emphasized. Thusin August (average river gage, 7.42 ft.) 92 per cent. of the changes in produc- tion are inagreement, while in July (average river gage, 4.55 ft. ) only 58 per cent. exhibit this relation. Again, since the above comparisons are based on coincidence of changes in production it resultsthat slight chronological dislocations of otherwise similar movements in production indicate a greater disagreement than really exists. This is especially true of the vernal pulses of April— June, where as a whole only 58 per cent. of the coincident or 403 approximate collections show this agreement. A comparison of Plates X., XXVII., and XXXI. with XXXVII., will ‘show that much of this disagreement is due to slight variations in the positions of the apices of the several pulses in the different localities. In each locality we can trace three diminishing pulses in this period, pulses, moreover, which have much in common, barring variations in amplitude and time of culmi- nation. Their similarity is greater than the 58 per cent. of agree- ment would seem to indicate. The most marked difference between the production in the river and in Thompson’s Lake, as has been shown, lies in the amplitude of the pulses, which in the river never attain the height that they do in the lake. A part of this contrast is due to the fact that pulses of production are sometimes flushed out by floods in the channel while they continue to a normal cul- mination in lake waters, as, forexample, the vernal pulse which culminates in the lake May 2. Similarly, in the flood of the last of Mayand July the plankton content is suddenly depleted in the channel waters, while the rising pulse continues to alaterand much higher culmination in the lake. 1897. (Table VIIL, XIII; Pl. XXXVIII., L.) There are 18 collections in this year,at monthly intervals till July, and thereafter approximately every fortnight. The average annual production this year, 10.43 cm. per m.* is the largest recorded for this body of water, and is due to the exces- sive development in the low-water period, August-November, which reached an amplitude (35.35) over threefold that de- tected in the vernal pulse (10.58). (Pl. XX XVIII.) The hydrographic conditions are very different from those of the previous year, and change profoundly the relationship of the lake and river. As will be seen on Plate XXXVIIL., the river levels were above 6 ft. from the beginning of the year until June 6, and thereafter from the 25th until July 15,a total of 175 days in which the lake received water through the 404 slough at the northern end, impounded it for some time, and maintained a run-off at the southern end (PI. II.) of its plank- ton-rich waters. There are in addition 35 days in June, July, and August in which falling levels below 6 ft. afforded an op- portunity for a run-off through the slough at the northern end. Of the remaining 155 days, 10 are of rising levels below 6 ft., when the lake receives water from the river but does not dis- charge any into it, and 145 belong to the low-water period of the last 5 months, in which there was little interchange be- tween lake and river though the run-off continued in diminish- ing volume for a few days after stable levels were reached, early in August. About August 16 the channel discharge was so slight as not to float a rowboat in the narrow channel at the northern end of the lake, and connection with the river was not reestablished as the river rose in October-November until the level of 2.8 ft. was reached, Nov. 10. The shght fluctuations during the remainder of the year practically amount only to the reception of .4 ft. of water by the lake. For the last five months of the year—months of heavy plankton production in lake waters—there was no run-off to the river. On the average the lake produced this year 10.43 cm.’ per m.*, about 3-fold that in channel waters (3.69 cm.’) and the net result of the run-off would be, it seems, an enrichment of chan- nel waters. The actual enrichment is, however, much less than these averages indicate. An examination of the monthly averages (see table between pp. 342 and 343) reveals the fact that the excessive production in the lake, when the plankton content rises to 5- to 16-fold that in the channel, appears in the low-water period when no run-off occurs. During the first 7 months, in which there is an almost continual run-off, the production in lake waters is but 1.5- to 2-fold that in the chan- nel except in February and June, when flood waters in the latter increase the ratio to 1 to 7 and 13 respectively. The in- sufficiency of the collections in this period leaves in doubt the amplitude of the vernal pulse. The April and May collec- tions indicate only a low level of production as compared with 405 that in other years, and this also tends to lower the relative productiveness in the lake. It is evident that the seasonal dis- tribution of the period of flood waters and the resulting im- pounding function of the lake affect greatly its contributions to channel plankton. In this year flood waters are largely confined to the colder and less productive season, when the run-off contains little plankton and its contributions are small, while in 1897 recurrent floods throughout the year afforded a run-off in seasons of Jarger production, and this tended to greatly increase the enrichment of channel waters in that year as compared with 1897. Plankton content in 1897 in Thompson’s Lake was in ex- cess of that in the river in the case of coincident or approxi- mate collections in 16 of the 15 instances, the two exceptions appearing in July and September, when pulses in channel plank- ton rise above the recorded production in the lake as a result of some undetermined factor. The similarity in the course of plankton production here and elsewhere is most marked in the first part of the year, and decreases in the time of low water. Thus, on comparison of the planktographs of Thompson’s Lake (Pl. XX XVIII.) and the Illinois River (Pl. XI.) we find 14 out of 18 changes in the course of production coincident in the two regions, the four ex- ceptions occurring in May (1), July (2), and September (1). The environmental differences between Thompson’s Lake and the river are much less than between this lake and Quiver, and we find a corresponding disagreement in their planktographs, only 10 out of 18 changes being in the same direction, and six of the ten are in the period of high water, when local differen- ces are submerged. In the cases of Flagand Dogtish lakes col- lections extend only to July, with agreement in 5 cases in each out of a possible 7 and 6 respectively. In the year as a whole and including all the above localities we find 54 agreements to 15 exceptions, in January—June the ratio being 3 to 21 for 4 lo- calities, and in July-December, in low water conditions, 12 to 13 for from 2 to 3 localities. The effect of the common elements 406 of the environment which high water introduces, in unifying the course of plankton production in their several areas, and of low water in diversifying it, is well demonstrated by these compar- isons. In the planktographs of Thompson’s Lake and the Illinois River there is a striking general agreement in the low vernal production and the increased and unusual autumnal production. There are also some indications of a pulse-like character of the planktograph in the lake, though the collections are too infre- quent to demonstrate it. 1898. (Table VIII., XII.; Pl. XXXIX., L.) There were 25 collections in this year, at fortnightly inter- vals, with an average of 5.71 cm.’ per m.* to 2.13 cm.’ in channel waters. The net result of the run-off from Thompson’s lake in this year is thus an enrichment of the plankton of channel waters. This is true for all of the monthly averages (see table between pp. 342 and 343) with the exception of April, and this exception is due solely to the distribution of collections on the rising vernal pulse, and is more apparent than real (ef. Pl. XII. and XXXIX.). The relative plankton content in the two areas, as will be seen on a comparison of the planktographs, is not subject to great variations in this year aside from January, when the ratio of the lake to the river is 1 to 17, and, as above noted, in April, when the ratio apparently falls to lto.6. With these exceptions, it ranges in the first six months from 1 to 2-3 and in the last six from 1 to 3-5. These figures express quanti- tatively the striking similarity in the planktographs of the two areas, which may also be recognized at once in the plates (XII. and XX XIX.) in the low winter production, in the meteoric ver- nal pulse followed by a minor one in June, and in a low level of production during the remainder of the year with fluctuations within rather narrow limits. The cause of this close resemblance lies in the hydro- graphic conditions, which throughout this year favor constant 407 interchange between lake and river. The average height for this year is 8.02 ft., the highest during our years of record. From Jan. 22 to July 15 river levels were above 6 ft., anda constant inflow of impounded water from bottom-lands above the lake, or through the slough when overflow ceased, continued with impounding in the lake and subsequent discharge from its southern end to the channel. The same conditions again prevailed from Oct. 30 till the end of the year, with an inter- ruption of 6 days in December. During the remaining parts of the year there was a constant wavering in levels which fa- vored frequent—in fact, no less than 21—reversals in the direc- tion of flow in the slough connecting the lake with the river. During the 134 days of low water there were 56 of falling levels in which the lake was discharging its plankton-laden water through the slough to the river, making a total of 287 in which it contributes to channel plankton to 78 in which, owing to low levels, it merely receives an inflow from the river. Moreover, the periods of greatest plankton production in the lake, during the vernal pulse, occur at times when the run-off from the lake is at its height, so that in this year all the hydrographic factors combine with the distribution of the plankton production to render this reservoir lake a feeder of the channel plankton. Though the differences in the plankton content are such that the actual enrichment per cubic meter may be less than in other years, the total run-off of plankton into the channel must com- pare favorably with that in any other year of our operations. The comparison of coincident collections shows in all cases but three, a greater plankton content in the lake than in river. The first of these is on April 5, at the height of the spring flood, when a considerable current sweeps through Thompson’s Lake and shortens the period of impounding, and thus reduces the time for the development of the plankton. The second instance is on June 21, on the decline of the acces- sory vernal pulse, which reaches a lower level in the lake (2.47) than in the river (2.88). This is one phase of a not un- common phenomenon in the plankton pulses of the backwaters. 408 They have greater amplitudes, but are frequently followed by more sudden and complete declines. Thus, in this case the apex of the pulse is at 18.39 and 6.99 cm.’ respectively in the lake and river on June 7 and 14, while the decline has reached 2.47 and 2.88 on the 21st in the two localities—a fall of 86 and 59 per cent. respectively. The third instance occurs on Aug. 16 (lake, .45, river, .61), when a large silt content in Thompson’s Lake, due to roiling of the water by heavy wind, obscures the actual quantity of the plankton. The similarity in the direction of the changes in plankton content in Thompson’s Lake and the other localities continues in this year even to a greater degree than formerly, owing in part at least to the hydrographic conditions above noted and to the more complete and uniform records. In the case of Thompson’s Lake and the river there are 21 agreements in the direction of the changes to 4 exceptions, and in the records of Quiver Lake 22 to 3 in the possible 25, This is so far in excess of the degree of agreement demanded by chance that we may look with confidence for an efficient cause in the common fac- tors of the environment, in the similar reproductive cycles of the constituents of the plankton found in common in the sey- eral localities, and in the uniformity in the reactions of at least a predominant portion of the total plankton assemblage to the factors of the environment. The river levels average 8.01 ft. for the year and stood above 6 ft. for 8 months of the 12. The high water increases the area of the “open water,” and causes a retreat of the shore-line and bottom, and a decrease in the relative occupancy of the bodies of water in question by the spheres of influence of the immediate environment. Thus the local differentiating char- acters of the several environments are in general progressively less potent as the open water increases in extent. The loca- tions of the 7 exceptions to the similarity in the direction of the movement in production are significant. All of them lie in the last five months, in the period of low water, and 2in the lowest water in August, when local influences are more potent, 409 1899. (Table VIII., XII.; Pl. XXXIX., L.) There are 7 collections at fortnightly intervals in the first 3 months of the year, with an average of 1.21 em.* per m.* to .41 in channel waters. With the exception of four days in Febru- ary, river levels were above 6 ft. throughout the period, and con- sequently the lake was continually receiving water at the north- ern end and discharging at the southern, and contributing throughout the whole time, in this way or through the slough, to channel waters. The average result is an enrichment of the plankton of channel waters. ‘The monthly averages (see table between pp. 342 and 343) in January and February in the lake exceed those in the channel by 9- and 2-fold respectively, while those of March, in highest flood waters, are respectively .28 and .21 em.*, owing, as will be seen on a comparison of Plates XIII. and XXXIX., to the distribution of the dates rather than toan actual smaller production. A comparison of all coinci- dent collections in lake and river exhibits lkewise a larger plankton content in every instance in lake waters. The lake thus tends continually during this period to enrich by its run- off the plankton content of channel waters. The similarity in the movement in production noted in 1598 is interrupted in these winter months by dislocations of the apices of the slight pulses of production, due in part to the flushing action of sudden floods and its unequal distribution in channel and backwaters. Of 7 possible agreements in the di- rection of movement in production there are but 3 realized in the case of both the river and Quiver Lake. A comparison of the three plates (XIII, XXIX., and XXXIX.) will, however, show that all, in common, exhibit evidences of a January and a February pulse and a common March decline. SUMMARY. The grand average of all the Thompson’s Lake collections shows a plankton content of 7.94 cm,’ per m,‘in comparison with 410 2.19 cm.’ for channel waters. The relative fertility of each is perhaps better expressed by the average of the monthly aver- ages, 8.26 and 2.71 respectively. The run-off of the impounded lake waters would thus tend to enrich the plankton content of the channel in some ratio dependent upon the relative vol- umes and plankton contents of the mingling waters. We have also seen that the enriching function of the contributions of this lake is continuous throughout a large part of the year, with a few interruptions dependent upon cessation of run-off in rising levels in low-water periods, and, rarely, to a lower plankton content in lake waters, due generally to increase of plankton in channel waters as the current slackens in low river stages. The following comparison of the averages of the monthly averages for the years of our operations, taken from the table between pages 342 and 343, is instructive in indicating the vary- ing relation of production in lake and channel waters. COMPARISON OF MONTHLY PRODUCTION IN THOMPSON'S LAKE AND ILLINOIS RIVER. > > 1D) Z ue ct D o iS ao | a | = a |é o |& & |v ee) E/E) 2/22] oes] sea dles 3) (e) . 2) ele Sea ee ee eee Illinois River..] .213| .23] .27| 4.59] 6.08] 7.22] 4.23] 3.88] 2.56] 1.70] .88) .71| 2.71 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........../1:18 | 0:5 | r:tt] 1:3 | 1:5 [:1.5)1:1.1) 1:1.6) 1:2 | 1:6 | 0:7 | 134 | 133 Average height of river in ft..17.77 | 7.89112.34!10.02! 9.181 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 em.’ 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 yolume and fre- quently interrupted. It is also the season of least plankton production, averaging 6.74 em.’ 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 by the 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 shght 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 1 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 func- 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 tlood-plain of the [li- nois and the consequent considerable area of sach 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 summary, which gives 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. Illinois River|Quiver Lake|Dogfish Lake] Flag Lake | Total er Sd lode] Sa lade! Sz lasz) Sz lea) 2 |ad2 tx = a oy = FR -u mn ee ae Amel Se Abe] fe APe] Se Reel Me ARs ASOS ectel eseieie ele 9 4 7 5 9 3 2 I 27 13 W8OO! 5.6.0 cases 18 8 12 13 I 38 16 9 64 TSO Pfiverstceseterctsiese 14 4 10 3 5 I 5 2 34 15 LSGO ieee eee 21 4 22 Ste || Incase Neico] |FeaaOs| Laooce 43 7 TOG isseys/crerere erase 3 4 3 Ae Wares lla ansreve alls areletesc| ears eve 6 8 STA) spaces boee OS eed: 54 33 32 12 23 12 | 174 81 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 —hecause 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 1X.; Pl. XXI., XL.-XLIL.) 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 400-690 feet, and a total area of 50-60 acres. Its bottom lies 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- let is 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 whick 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 alge, 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 algz 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 IX.) 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 inroads 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 Inks. 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 em. 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 IX., Pl. XL.) There are 29 collections in this year, extending from Jan. 8 to Noy. 17—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 em." 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 68.4° to-7L° (Apr. 17) and 62.6° (average) in Quiver Lake, and to 66.5° (Apr. 17) and 63.2° in the Lllinois 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 43 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 43 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, 1 to 7. These latter ratios are somewhat exceeded by those of the av- erage production for the year, 1.16 to 13.17 em., 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 16U0-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- ters and the wealth of this lake is due to the impounding func- 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 em.*). Not only is this general similarity between the movement in plankton production in Phelps Lake and the Illinois 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 S50 per cent.—between Phelps Lake and the Illinois 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 fac- 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. Itis 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 1X., 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 em.’ 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 em.*, 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 13, and the run-off of impounded waters continued until the 25th, a total of 159 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 (Pl. XXXVIII.), Quiver (Pl. XXVIII.), Dogfish (XX XII.), 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 if 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.; and in 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 8ft., when fluctuations have relatively but a shght 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 IX., Pl. XLII) 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 Dec. 13, averaging 63.54 em.*, 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 7instances by from 1,4- to 14- 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 our station for collections was located in the upper end of the lake (PI. 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 8, isnot accompanied by increased turbidity (.45) in the lake (Table IX.), 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 Mareh and April, owing doubtless to this diluent 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 11.80 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- 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, butalternate, weeks, and makes the the similarity or difference probable rather than precise. A comparison shows 16 agreements out of a possible 20, or SO per cent., in the case of Thompson’s Lake, and 17 out of 20, or $5 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. In 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. XLIL.) There are but6 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 (PI. XLIL.). Proof of this is seen in the sudden decline in production (from 93 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- 407 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 ofall 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, 139, 145, and 86 days respectively, or an average of 76 days. Asa rule 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 slight 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 428 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 tomake 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. Av. of all collections Natok | Av. of Station Year collections eae Plankton} Silt | Total 1804 10 2.53 2.49 -28 | 2.77 oe ge toe 1 Co) -gI 3.22 -72 | 3-94 Illinois River........ 1808 36 ae 1.16 | 2.55 | 3.71 1897 34 3.28 3-69 | 1.91 | 5.60 1898 52 2.03 2213" | 2-00 | 4 sea 1899 13 -42 41 -94 | 1.35 Grandiavaes st iecee are ae 2.71* 2.19f | 1.79 | 3.98 Loraleccesears: 235 itis 9 pee -007 | .349 | .36 : af 1897 13 F 1.257 |1.173 | 2.43 spoon River. ...- .2.. 1898 Il ae .029 -796 83 1899 3 -O1! -O1L |2.2:6 | 2.23 Grand ay.cn.s.> |Saee one ses 256 465 -939 | 1.41 Wotaltcnocc css 36 ak ‘7 1894 14 -gO 1.08 Boaz 2225 1808 13 -65 -78 .70 | 1.48 : I 31 2.19 2.59 .20 | 2.79 Quiver Lake......,.. 1897 34 mite "8 "62 1.50 1898 26 1.96 2.44 .40 | 2.85 1899 7 -66 .67 -43 | 1.11 Grand avicsSs..5|/cosecooes| | seectel tose ocean Noted Raced poooe fooondel) come) |yeodosl|! of? 4.36] 4.23} 3.56) 3.88] 3.82) 2.56/3.56/ 1.70) 4.26] .88 4.97 Al eet oBe 2.71 An inspection of the table shows at once the complexity of the problem, and yields the following generalizations. In January-February, a period of sustained minimum tem- peratures, high levels are attended by a small, and low levels by a larger, plankton content, with the exception of stagnation conditions in February, 1895. This contrast results from the 468 recent origin of the flood waters of these months, from the di- lution of sewage and increased rapidity of run-off, and from the reduction in time of impounding under these hydrographic con- ditions. March-May isa period of rising temperatures, maximum flood levels, and increasing plankton production. The data, in so far as they go, indicate that high levels tend to increase pro- duction and low levels to decrease it, in some instances at least. These months witness the maximum and the initial de- cline of the spring flood, as a rule, and the greatest volume and principal run-off of flood waters whose impounding has been more or less prolonged.- The proportion of impounded water is greater in higher than in lower levels, and we find, accordingly, production increased in the former and decreased in the latter, as a general rule. It is noticeable that levels in May slightly exceeding bank height, as in 1897 and 1898, yield much greater production (5.62 and 11.30) than levels not attended by overflow, as in 1896, when production falls to 1.30 at a level of 6.58 ft. The data of the June period are somewhat aberrant, in part as a result of insufficient data in some years, as 1895, and in part because of the relatively great irregularity of hydrographic conditions in this month in different years. The high produc- tion (30.42 cm.*) in low levels (1.88 ft.) in 1895 attends sewage concentration. The data for the remaining years conform in the main to the conclusions concerning production in the three prior months, namely, that high levels favor and low levels depress production, and for the same reasons above cited. A comparison of production in 1896 and 1898 in June yields con- firmatory evidence on this point. With July begins the low-water period proper, which con- tinues during the remainder of the year. Levels do not rise, in the means of the monthly averages, above 5 ft. in this period. The relation which existed between production and high water in March—June is reversed in the period of July-November. An inspection of the table shows that in 20 of the 25 months in- cluded in the table in this period this reversed relation obtains; 469 that is, levels above the average are accompanied by a fall in production to an amount below the average, and those below, by a rise in production above the average. Thus, in this period higher levels depress production and lower levels tend to in- crease it. Two of the 5 apparent exceptions are in October and November, 1894, when insufficient data are available, and one is in July 1897, when the customary vernal conditions (Pl. XI.) encroach upon the low-water period. The cause of this changed relationship of levels and produc- tion in these months of predominantly low water is to be found in the relation which summer rises in levels bear to the im- pounding function of the backwaters. These summer rises are rarely above bank height. They flush the channel, are not ex- tensively impounded in the backwaters, run off quickly, and accordingly depress production. The months of lower average levels are more stable, and, owing to slackened current, a more abundant plankton breeds, other things being equal, than in the more rapid current in the summer months of higher levels. The relations in December between production and levels are again reversed. Indeed, suggestions of this reversal appear in November. In this month minimum temperatures are again reached and higher levels prevail, and production now is higher in the years of high levels and falls below the monthly mean in every year of low levels. The cause of this relation does not seem to le in hydrographic conditions. It may possibly be in- volved in the changed sewage and bacterial content of the channel that accompany the increased current and the decline in temperatures. The submergence of the summer’s growth of vegetation in the margin of the river and its connecting back- waters in years of higher levels may also be a contributory factor. We thus find that in channel waters higher levels favor production only when they increase the impounding function and by long duration afford time for production and run-off of the plankton, and when they make available additional sources of nutrition. They depress production when they first appear, 470 and when they are of short duration and merely flush the chan- nel, as is predominantly the case during the low-water period. Lower levels depress production when they introduce stagna- tion conditions—as in the winter under the ice, and when they cut off contributory backwaters or otherwise reduce the run- off of impounded waters of long standing. They increase pro- duction when they lend stability to hydrographic conditions, increase the relative fertilization (sewage) of the stream, and by slackened current afford time for breeding. In general terms, production in the backwaters exhibits relations to levels similar to those we have described for chan- nel waters so long as the backwaters retain an intimate con- nection with the channel, that is, generally during high water, and for longest periods when, as in Thompson’s Lake, the con- nection with the channel is most intimate. The diversification, as levels fall, of the several regions examined by us, renders generalizations impossible with respect to all of the backwaters, since one or another local factor sooner or later comes in to modify conditions. Moreover, some of the backwaters, as Phelps Lake, are cut off from the channel early and are not affected by changes in river levels, and, in general, the effect of the changes in channel levels, especially the minor ones, is reduced, equalized, or even obliterated, before it reaches the backwaters. The season at which the initial stages of the major flood of the year occurs, affects the subsequent production. Thus in 1896 and 1897 floods begin early in the year. The result is the carrying away in the run-off of great quantities of organic matter in suspension (Table X.) before they have had time to decay and yield up in solution their nitrogenous and other con- stituents for the support of the plankton. Temperatures are low in these months, decay is not rapid, and the plankton is not produced in large quantities. The result is that the stream is locally impoverished by this early run-off of matters in sus- pension and to some extent in solution. In 1898, on the other hand, the flood does not reach overflow stages till late in Feb- 471 ruary and is continued well into the early summer. Thus, while in 1896 and 1897 the vernal pulses of plankton production (9.39 and 5.62) are not large, in 1898 the production in this season rises to 35.68. Late high water, with decay and solution of organic substances increased by higher temperatures, occurs at the season of rapid plankton increase, and food matters which run off in the winter floods are here utilized and increase the amplitude of the plankton pulse. Winter floods thus tend to locally impoverish the plankton, and spring floods to in- crease it. Enough has been said to indicate the supreme importance of hydrographic conditions in the fluviatile environment in de- termining the amplitude of plankton production and in differ- entiating local areas in our environment. It is the prime fac- tor which distinguishes the fluviatile from the lacustrine envi- ronment, stamping the former with an instability as character- istic of the river as stability is of the lake. TEMPERATURE AND PLANKTON PRODUCTION. On pages 168-177 will be found a discussion of the temper- ature conditions at the various plankton stations and their gen- eral relations to the larger phases of plankton production. In the present connection the more detailed comparison will be made. To facilitate this comparison of production and tempera- ture conditions I have prepared the accompanying table (see p. 472), which gives the monthly means of production and of sur- face temperatures recorded at the times of collection in the river. This table in conjunction with the one following page 342 suggests the cooperation of temperature in controlling in a large way the seasonal fluctuations in production. In general, in the colder months less plankton is produced than in warmer months. Thus in the river the mean production in the 5 months below 45° is but little more than 9 per cent. of that in the 7 months above this temperature, in Phelps Lake, only 40 per cent., and 472 PLANKTON PRODUCTION AND TEMPERATURE, 1897|81.02] 4.69] 80.9 | 3.65] 77.07 8.83 65.1 5.95|. 45.7 1898/82 .87| 0.58] 80.56) 0.91] 71.87] 0.69 54-37| 0.24) 41.42] oO. {clove REY (AE eee Meee Stone Renee onmon done nononoracllogeue clsooeenllesnoc. January February | March | April | May | June u oO © ' j 1 : 1 5 ' DH A, | a | 4 a | a | Oo, | a | 4 Bles| Bias] 8 ee) 6 ee | alee) |e eee BH }A fH Ay fH Ay H Ay HB AY ia AY 1:0) | erences | aemeteo| erecta orition secs sacwed|sodcHs) aod ot |Scioa te 80.25] 0.74 ito srillecone 32 OnOD|Reseaere leer 58. 2304 oeracralloaco oo 80. | 30.42 1896|32.75| 0.01] 33.7 | ©.02| 39.52] 0.07] 64.54) 5.67] 72.7 | 1.30] 74.7 | 9.72 1SQ7} attodl seer 32.25} 0.04] 43.8 | 0.38] 60. 5.11} 66.3 | 5.62) 75. 0.27 1898)32.7 | 0.45] 32.12] 0.27] 43.3 | 0.33] 53.32| 4.40] 65.8 | 11.30] 78.8] 3.96 18991329) | 0.18] 32.6 |) <0. 81/535 527 | O28 | prev mel eseicve retell eetetenstet| cami tste tele eeehenete eet July August September October November | December S eee pm | a | a | a | a | a | a | Bias § |e3s) 2 | ss oe eee eee | Ay i AY & AY fH | AY BR AY i Ay 1894|82.25| 5.12] 83.5 | 9.67] 77.5 1.36] 58. 0.61} 41 0.10} 39. 0.10 1895/79. 9.33} 80.51] 4.03} 78.87] 1.52] 54.26] 0.57) 42.5 | 3.02] 37.5 1.14 1896|/80.7 | 1.44] 82. 1.12] 65.75] 0.38] 56. I.1I| 44 0.02] 33.6 | 0.76 1.00] 33.02} 0.56 fo) 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 $7 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,and that temperature is only one of the factorsinvolved. 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 slight 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 33, 862, 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 18098 Temper- Temper- Temper- ature |Plankton| ature |Plankton| ature | Plankton (Fahr.) (Fahr.) (Fahr.) North section... 31.9 34.4 39.0 Central section. 36.4 41.1 44.4 March .|South’rnsection| 40.6 .07 46.8 38 48.7 33 State, average.. 35.6 39.5 43.4 Normal). sce... 37-6 | 37.6 37.6 North section. . 55.3 47.2 46.9 Central section 590.9 51.3 50.5 April ..|South’rn section} 63.6 5.67 BELO |) eSaht 53-0 4.40 State, average. 59.0 50.4 49.6 Normalliee si 51.8 51.8 51.8 North section. . 67.2 57-5 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 Normalizeeccs|) O0s8 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 1896 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 1596 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. 342) production is from 13 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 233 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 in a 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 (48.14) 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 (51.39) 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 our records. 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 swhen 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, rises 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 478 976 8t Sb Bl hb St ‘eueAry ye soinjeiadwia} we Ajiep-14} Jo sydeisowi1ag]—'d ‘SI lis 4 ala TP aq 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 ina number of instances in our records. The most noticeable case was the extermination of the plank- tonin 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 ‘bane 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 light 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 lies 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 light 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 light 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 VIII.—XIII. in the uppermost row of squares. NUMBER OF CLOUDY DAYS. = i Le i] ee | rea lsecall etal es 2|2/5/2/8|/—|~ ¢ |S/S/2 El elels|Slelslelelsle R a 5 aj || Se s o/s] t| oe Sloljo]o|]s mA s|ols < 2)S5|3)6, B 219 1m ta pA here = a bee | 1894 | 13] 13° 8} 12| 19] 5! 9) 7] 9) 9} ral 35]133] 5 1895 | 11 7} 11{ 13] 2] 9} 7) 4] 4] 4} 15) 18]105) 1 Serneeeld 1896 | 14| 12); 16} 8! 9] of 7| 2] 12| 7| 18! 15|120] 4 Seager aes te 1897 | 16] 15! 20] 17} 4) to} 5) 2] 1) 4] 12] 21/127] 3 1898 | 12] 12 16] 13] 11] 5] 3 8i 10} 15) o} 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) 391 42| 47| 84] o1|767 1894 | 7 8, 7| 6} 4} of of 3] 3] 6] ro] 7] 61) 1 1895 | 6] 3 10! o} 3) 4) 4] 3] 4} 2) 13] 13] 74] 3 Hayanaye screenees 1896; 7) 6 4] 3] 5] 6) 4] 2] 11) 3] 10] 9! 70] 2 1897 | 10] 10} 17] 13] 6! 6! o| 4, 2] 4} 12) 15) go] 6 1898 | 11] Io} 11 8) 4) 3) 8 2) 16} 5) 7] ot| 5 1899 | 7) §| 16 4) 5] 3] 5] 3) 3] 6] 10) 7| 75] 4 Total | 48) 43] 65] 41] 3t| 23] 16] 23] 25] 37] 60 381470]... 1894 | 11] 9] 6 8] 9] of 3] 5] 8] 6] 12] 11 88) 1 1895 | 10] 8 io 8] 4) 5) 6) 5] 4} 2] 18] 19} go} 2 Peoria erase cee 1896 | 17| 10 8 3} 6 8) 6 2) ro) ro} 16 14)r10) 4 1897 | 13] 14] 18) 16] 5s} 6} 1} 4} 3! 3] 15] 1olrI7| 5 1898 | 15 14; 14] Io} 13] 6} 2) 8) 4} 16) 11 13/126 6 1899 | 12] 12) 16| 10} 8] 2) 5) 5] 6) 6] 13] 11106] 3 Total ' 78! 6 | 721 55! 45! 27| 23! 29) 35) 43! 85 78.646)... 6g 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 3 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 II. of this paper still further serve to demonstrate the correlation of light and plankton pro- duction. The necessity of light 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 zodplankton 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 1. 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 in 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.’ per m.° 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 is 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 D fi h Thompson’s|n,.1..7 3... Ratio Quiver Lake eee ie tee S!Phelps Lake Jantany 2 2cs cecens ease .27 -53 3-79 3.29 1:9 Mebruany son cc cnscchren se .67 1.10 1.27 5.68 1:4 March) sc 05 /jeletrasvew see -77 1.96 2.96 5.68 1:3 AND TAL eiata ok wraieisiets esti 7.26 10.50 14.49 11.77 1:1.5 May 6.85 5-79 29.59 25.33 1:4 PUNE earache ew icperok omer 1.25 1.75 10.66 II.40 1:7 Jul yyeietae wes evarciareterets eye : -78 1.95 4.74 ~ 8.50 1:5 AU PUSS Saack eemeneceee Shy) 2.51 6.19 58.12 1:20 Seplembet pees snes aif 2.39 5-37 47.25 1:17 October re sc. seein 69 3.05 10.64 27.68 1:10 November.....-..-...:- -23 2.64 6.39 41.57 1:17 Decemberest.n secon 63 3.76 3.08 _ 21 .96 1:6 Gr’d av. of monthly av.. 1.75 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. em3 Quiver ig E Phelps Lake, 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. tion will be found in the individual collections recorded in Tables V. and IX. and VI. and VII., 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 1 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 1 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 486 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, etc., 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 problemin 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 PI. 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 1 am able to judge from field observations, the current conditions in Thompson’s Lake and the Dogfish-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 Dogtish 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 /” part for the barrenness of the waters of Quiver Lake (1.53 em. 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 (8.15) 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. 488 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, I899. AVERAGES OF ALL ANALYSES——PARTS PER MILLION. Thompson’s Lake |Quiver Lake BATES TANI OWA i.o setae ore steer cycvore eta siaaeh eee eters 422 .199 Al buminoid amma Onialient\atue/ejlertnyusetae eto eterna: .546 293 INTEEIEES Teo 3) ave-e ci sess gone pein cieaie kee SEE oe eee .048 .023 IND ET ALCS ctccre cy ks oeiemdene oieic peltererteerstenemiere aerate .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 shghtly in the two lakes. The plottings in Plates XLVIIL. 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 years of abundant and scant vegetation. ‘ 490 Matanzas Lake (Pl. 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 light 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 Gave race | Dogfish Lake Gea eee eal!) iss as as ASAP re TG cee be eo ee neh pie a ct ea ae Til ee an: oe a ee ele Sore 3.9! Fe eae re [lala “free ren ee eee eee wa hae ce tilveae. al aesenn tree cle ce (i eee ae a 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 1894, and still more in 1595, owing to low water in early summer, vegetation was very abundant in Quiver Lake. The growth of Cerato- phyllum 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 XVIIL., 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 eraphically 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 cm.’ 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 1896 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 493 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 VIII.—XIII. and XX V.-XLII. 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 Dogtish 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 Oscil/aria at a time of local stagnation consequent upon backwater. In 1595 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 cm.’ 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 growing period of vegetation, is only 2.87 cm.’ per m.*, while in spring and late autumn (April 1 to May 15 and October 1 to December 30) it is 82.89. 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 Elodea) 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 light 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 zodplankton. 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 Klodea 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- 6 497 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 zoéplankton, 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 zodplankton 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 1895. The appended table also gives the average AVERAGE OF ALL ANALYSES—PARTS PER MILLION, Station Free Ammonia Nitrates 2 ; | : June 1 to Octo-| Remainder \June 1 to Octo-| Remainder ber 1, 1808 of year ber 1, 1898 of year Thompson's Lake...... 154 -457 244 .684 Mover Lakes nce. omen | .024 199 222 -923 Illinois River........... -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 chlorophy]l-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 (.352 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 algae 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 life 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 shght 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, 1597, when surface waters were at $8.2°, the temperature was but 80° at 15 ecm. 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 Ceratophyllwm 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. XXXIII. and XXXIV.) and Dogfish Lake (Pl. XXX.-XXXIT.) 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 cm.’ to 0.72 in 13 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 oligocheetes, the smaller mollusks, Hyalella, and Hydra. They materially increase the volume of the 5O1 catches recorded in the tables, and show in the plates of the plankton of Quiver, Dogtish, and Flag lakes. The sessile or- ganisms above named, with the Bryozoa, which often occur on Ceratophyllum, avail themselves of the plankton asfood. 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 em.’ 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 303 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 light, 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. J therefore class this periodic growth, these serual 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 a normal 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 139.85 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 little 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. eas . 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RELATIVE NUMBER OF PLANKTONTS IN ILLINOIS RIVER AND SPOON RIVER. j ALGH DIATOMS RHIZOPODA MASTIGOPHORA INFUSORIA Date | 2 2 a 2 2 (s) q ° q 3° qd iS) c=] 3° g EU Bf ee PPB a cles mae cea 5 n = a) 5 n = 7) 5 n | 1896 5 18 VIII |} 83,200) 6,080] 8, 896, 000 11,280) 28,800) 5,960) 1,508, 000 3, 360 23,800) 8,540 25 VIII 4, 840) 576) 1, 025, 200 29, 876) 18, 080 768) 110, 000) 960, 11, 200 192 166 «IX 5,446) 1,200 350, 489 3, 360)| 16,850) 2, 880 75, 845) = 40, 106 240 30 IX | 10,840)..........- 682, 200 6,240) 14,280) 8,160) 175,000) .............. 27,672} 2,400 14 x 4,560} 2, ne 816, 400 ne Med 80, 400) Bs on 1,111, 200) ny 65, 200 b ae 29 ax = BON sees 19, 200). ........... all eee ore sense BO | nese oneeeeee 920 i eer 2, 800} 480) 1, 064, 500 480) 25,200) 3, 360 88, 800 480 44, 000 7,200 3 XII 396 480 963, 916 7, 200 873) 500) 179, 606 240 10, 083 480 28 XII Bh etell Penson cence 165, 960 soe 120 480 64, 880) 120 440 240 Average} 14,420) 1,495) 1, 745, 583 9,688] 16,825] 3,336) 414, 166) 680, 27,938} 1, 9385 1897 ee 3 I 231, 900 240 300) 720 42, 420) 160 3, 400 26 100) eases 339, 480]....... .......] 10,700) 37, 440 46, 600 3, 840 18, 800 Oo Lek 2 1,231,900} 240,000) 2,240) 105,600) 172, 100 9, 600) 18, 240 Si. -/ RENE 1, 600)............| 828,414,320) 102,000) 11,520) 379, 200)27, 987, 400) ..............| 515, 920 29 V | 68,400) 7,500) 79,827,200] 3,048,000] 25,760) 40, 900] 9, 029, 360) 43, 201) 29, 600 28 VI} 49,000} 2,500] 1,937, 600 85, 200) 232, 600) 13,200) 148, 006 3, T0012, 186, 000 10 VIIL | 74,680) 8,800) 2,318, 160 54,000) 8,400) 1,200) 439, 600 18, 000 27, 600 26 VIII | 166,760) 24,000 847, 320 4,800] 19,200). ........ 408, 160) 53,000) 180, 000 11 TX || 406, 400) 816, 000 282,440] 662, 400) 118, 000) 28, 800] 1, 624, 800) 5, 030, 400 12, 000} 2 2 XI |} 28.980) 145, 000 148,880} 744,000) 3,900) 2,400) - 1,100 33, 600 26, 500 30 XI EUW eecenace 90,725} 24,000 BOO eee 11,100] 116,400] 244) 420 28 XII 1,200) 3, 600 65, 400 36, 000) 16, 640}... 15, 400) 54, 000 45, 600 Averagr| 65,725) 85,584) 34,644,610| 416,920 37,505) 50, 788| 3,577,171) 447, 158| 1, 109, 007 1898 Y 25 I 387) 174, 901 16, 800) 66.338) 19, 200 22, 059 2,400) 190,017} 39,000 22 Il 3, 159) 211, 653, 4,800) 141,524) 21,600) 227, 448}... 69, 498] 14, 400 29 «TAT 5, 400}... -. 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, 680) 129,600) 11,520 7 _VI} 17,200) 2,400] 30, 803, 600 81,200) 23,600) 21,600) 597, 000) 7,400} 1,516,000) 63, 600 5 VII | 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] 16,800) 14,400] 252,400) 112,800) 129,600) 3, 600 12. IX} 57,060) 3,700) 1,217, 000 8,400} 28, 00U} 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 6 XII 520].----- Pe 251, 250 9,120) 1, 000 480) 1, 708, 000 4, 320 7,620) 3,480 Average] 50,373) 4,16] 32,087,762) 180,553] 35,678) 12, 260) 8, 084, 246) 23,422) 206,036) 26, 065 1899 3 I 20)... 10, 300 3, 840 220) 960) 143, 020 3,360) 108,940) 1,920 "f ED eee (HS YO) ey 1,125) 1,200) 117, 000) 7, 200 6,000] 1, 200 (unt 140) . 59, 120 800} 3,200) 38,400) 899, 200)..........-.... 30,820] ..... .-.-- Average! 53)....-..-.-- 45, 390 1,547) 1,515} 13,520) 386, 407 3, 520 48,586] 1, 040 Grand Ay....| 43,539) 30,513] 23,031,820]. 293, 788] 289,637) 23, 281| 3,921,328) 161,149] 468,051] 22,999 Ratio es EL 78 1 rE) 1 om 20 1 615 TABLE XIV.—Concluded. RELATIVE NUMBER OF PLANKTON?TS IN ILLINOIS RIVER AND SPOON RIVER. ROTATORIA | ENTOMOSTRACA |vseor ARV MISCELLANEOUS OTAL SPECI TOTAL PLANKTONTS Date 2 2 ae ee 2 ae ° Ss ° c & ° = ° Ss ° i= ‘3 § a eS a Sele A g = a i = a = a = a = a iad n - = nn - n = nn al n 18 VIII 361,680] 2,72 ‘ 25 VIIL| 185,720 765 1,520 2 388,120] 34, 704 16 «IX 45,5921 3, 60d 2, 607 19 600,005) 14,520 30 IX 48, 642 96 2,400 | 1,480) 85 20 | 977, 434) 20, 080 u4 x 131,600, 3,560 4640] “2 | 2 2,173, 440| 20, 920 2 5a) |e eee Te Se OLE ST peril Fae [acon apart ieee! 33 "| 30, 680 17 XI] 172,800 2, 80 5, 360 2, aay 63| 20] 5,408,460, 17, 880 Sain 86,7 8 1, 665 |.......- | 56| 12] 1,252/579| 9, 820 28 X11} 100,340 2 520 130 42] 9 362,720] 1,360 Average) 141, 634 1, 561] 2,854 | Gos] 77 | 24] 2,892,085] 20,492 1897 3 IT] 10,460 5 AK DAOH||:. 5. 44) 10 293,080} 1, 720 2 IT 26,200] 2, 88 6,400 | 5,280] 45) 16 450,280, 52, 800 2 ITI 47,180) 20, 000, 2,080 [19,200 Si} 11] 1,498,200} 423, 200 27 ~—«-IV || 1,276, 000 34, 80) 4,000 [28, 67 | 20 || 358,278) 080] 591. 600 95 _V | 2,287,160] 217, 400) 10,240 | 2,500) 90] 36 | 91,362, 440) 3, 460, 600 38 VI| 351,900} 27, 900 : 33 |) 14,968, 406] 136, 7 33 3, 667, 220) 93, 400 32 3, 782, 800) 1, 418, 000 u = < _ I - ¥ aa iw Ss a a == 11 TX | 1,744,250) 2, 362, 400 49) 4,832, 640/11, 467, 600 Depaul . 900) 1, 072, 800 29 239, 660) 2, 061, 000 30 XI} 109,840) 1,965, 600 19 520, 165) 2, 113, 900 040 00 5 | 13 160, 760) 1, 258, 800 082) 93,918] 3.987) 85 | 703) 11,757 | 4,898] 67 | 25) 40,004, 478) 1, 923, 277 | } 1898 25 I} 126,603 2,600} 4,788 7,661 | 5,000) 7. 18 | 2 IT 48, 649) $00) _3,285)......--. 3,285] 2 35 9 29 III] 115,880) 17,920] 22,180 1,940 | 720) 100} 31 10 V | 2,663,400] 24, 480 13, 200 7 | 40 7 _VIj 903,000 2, 900 23, 600 |. 67! 31 VII | 153, 000 8, 400, 5, 040 9% | 23 5 VILL | 1,294, 240 61, 200] 3, 360 |. si} 41 12 =IX! 197,960 oe 2,420 89| 20 4 Xf] 105,020 2, 2,700 79| 24 2 XI] 156,300 9, 4, 360 | 75| 241 1,275,380) 53,300 6 XII 64, 280 ie 680 |.......) 40] 17] 2,043,090] 24, 800 Average} 529, 848) 14, 6, 204 98 7 25) 41,071,067) 263, 560 "1899 3 I 47| 18 309,280 16, 840 ” Tt 29] 6 318,022} 10, $00 IE ; | 47} 6) 1,121,980] 52, 000 Average| 87,490| 2,507) 1,772) 2ia)......|_ 200........]...... “| 10 583, 094) 26,547 Grand Av...) 465,067| _238,828| 63,983 2,255 104 | 616] 6,805 | 2,430, 69 | 24 | 28,283,205) 750,429 Ratio... 1.9 1 in| Pele ala Mella sal> Gopal ck 38 1 616 TABLE XV. SOLIDS IN SUSPENSION AT STATION HE, BERKEFELD FILTER. 22702. 22705. 22711. . , Cu. em. | Cu.cm. Silt | River Accession number Date SarraeGl somite per cu. m.| gage 9, XI, 1897 5, 000 1.40 280 2.6 15, XJ, 1897 10, 000 1.53 153 2.8 23, XI, 1897 5, 000 1.50 300 2.8 30, XI, 1897 5,000 | 2.75 550 3.2 7, SLL, 1897 5, 000 6.56 1,312 3 14, XII, 1897 5, 000 1.28 256 ud 21, XII, 1897 5, 000 5.26 1, 052 3.2 28, XII, 1897 5, 000 93 186 3,2 11, J, 1898 5, 000 4,25 850. 3.7 21, T, 1898 5, 000 7. 60 1,520 5.8 25, I, 1898 5, 000 5. 01 1, 002 6.8 ‘3, II, 1898 5, 000 4.00 800 7.4 8, II, 1898 5, 000 2.71 542 (eat 15, Il, 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, III, 1898 5, 000 2.51 502 ib 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 12, IV, 1898 5. 000 4.40 880 14.8 19, IV, 1898 5, 000 1.81 362 13.1 26, IV, 1898 5, 000 2.04 408 12 By V, 1898 5, 000 2.07 414 11.1 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 31, V, 1898 5, 000 2.11 422 13.6 tio Aves EL BOS, 5, 000 1.98 396 12.5 14, WI, 1898 5, 000 1,43 286 11.9 Pt, Vi; 1898 5, 000 127 254 10.8 28, _WI, 1898 5, 000 2.80 560 10 5, WIT, 1898 5, 000 1.90 . 8.7 12, VII, 1898 5, 000 1.94 7 19, VII, 1898 5, 000 2.04 4.7 26, VII, 1898 5, 000 1.56 2.9 2, VIII, 1898 5, 000 1,58 2.7 9, VIII, 1898 5, 000 2.98 3.2 16, VIII, 1898 5, 000 1.69 aan 23, VILI, 1898 5, 000 3.08 4.2 30, VILI, 1898 5, 000 2.42 3.9 6, IX, 1898 5, 000 2.90 4.7 13, IX, 1898 5, 000 2.04 4.2 20, IX, 1898 5, 000 2.40 4.2 27, LX, 1898 os 0) | ener es 4.9 4, X, 1898 5, 000 2.30 4 i, X, 1898 5, 000 1.70 3} s) iy | ees 5, 000 1.26 . 3.8 25, X, 1898 5, 000 4.00 4.3 1, XI, 1898 5, 000 3.20 6.3 8, XI, 1898 5, 000 2.77 6.7 15, XI, 1898 5, 000 4.41 7.1 22, XI, 1898 5, 000 5. 82 8.5 29, XI, 1898 5, 000 1.48 8.3 6, XII, 1898 5, 000 Hee 7.2 13, XII, 1898 5, 000 3.74 6.7 15, XII, 1898 5, 000 ily 6.6 20, XII, 1898 5, 000 1,04 5.9 27, XII, 1898 5, 000 1.26 6.1 3, J, 1899 5, 000 4.20 6.8 10, T, 1899 5, 000 3.79 fhe) 17, 1, 1899 5, 000 6.30 8.2 24, I, 1899 5, 000 4.06 8.9 Bl, J, 1899 5, 000 3.06 “Bier ie If, 1899 5, 000 3.42 8 7. Il, 1899 5, 000 1.15 7.3 14, IT, 1899 5, 000 1.42 6.6 21, Ti, 1899 5, 000 1.80) 5.5 28; II, 1899 5, 000 27.08 10,2 7, ILI, 1899 5, 000 20. 30 1229) 14, IIT, 1899 5, 000 17.40 13.1 Pi, a0, 1899 5, 000 16.82 3, 864 13.7 28, IIT, 1899 5, 000 9,35 1,870 13.5 592. 22 617 TABLE XV.—Continued. ‘SOLIDS IN SUSPENSION AT STATION M, BERKEFELD FILTER. as less . Cu.em. | Cu.em., Silt | River Accession number Date strained| silt | percu.m.| gage 22639. 30, XI, 1897 5, 000 1.57 314 3.2 22648 28, XII, 1897 5, 000 220. 240 3.2 22655. 20, I, 1898 5, 000 13.11 2, 622 6.8 22664. 22, II, 1898 5, 000 5. 64 1,128 10.7 22677 29, TI, 1898 2,500 25.11 10, 044 16.5 22698 10, V, 1898 5, 000 5.10 1, 020 10.3 22712 7, VI, 1898 5, 000 3.38 676 12.5 22727 - 5, VII, 1898 5, 000 1.63 326 8.7 22761... 5, VIII, 1898 5, 000 3.58 716 2.8 22775 2, IX, 1898 5, 000 6. 62 1, 324 4.4 22786.. 4, X, 1898 5, 000 2.20 440 4 22797 2, _XI, 1898 5, 000 2.92 584 6.5 22811 6, XII, 1898 1,900 61 321 7.2 22823 3, T, 1899 5, 000 2.56 512 6.8 22839. iy II, 1899 5, 000 «94 188 (ee) 22851 7, IIT, 1899 5, 000 40.35 8, 070 12.9 PAN WOR Gul GNU OR ortes eee ccm eee ea re me Nn Son er eR Ss bana seco ss csben oaas eee 1, 745. 55) TABLE XV.—Continued. SOLIDS IN SUSPENSION AT STATION CO, BERKEFELD FILTER. - Cu.em. | Cu.em. Silt River ANSE) seiebeeL ee strained silt percu.m. | gage 15, 1, 1897 10, 000 98 2.8 30, XI, 1897 5, 000 294 3.2 14, XII, 1897 5, 000 300 3.4 28, XII, 1897 5, 006 116 3.2: as IT, 1898 5, 000 662 3.7 25, I, 1898 5, 000 42 6.8 8, TI, 1898 5, 000 (enh 22, II, 1898 5, 000 218 10.7 8, III, 1898 5, 000 rs 1 22. III, 1898 5, 000 : 14.1 4, LV, 1808 5, 000 = 17.6 19, IV, 1898 5, 000 P 13.1 Bs V, 1898 5, 000 6 11.1 ll, V, 1898 5, 000 c 10.1 24, V, 1898 5, 000 .d 13.6 7, VI, 1898 5, 000 “ 1255 21, WI, 1898 5, 000 2 10.8 5, VII, 1898 5, 000 : 8.7 19, VII, 1898 5, 000 1.10 4.7 2, VIII, 1898 5, 000 1.03 2.7 16, VIII, 1898 5, 000 1.65 3.7 30, VIII, 1898 5, 000 2.01 3.9 13, IX, 1898 5, 000 1.85 4.2 27, IX, 1898 1.62 4.9 ll, X, 1898 5, 000 1.06 3.9 25, X, 1898 5, 000 -89 4.3 8, XI, 1898 5, 000 1.14 6.7 22, XI, 1898 000 1.75 8.5 6, XII, 1898 000 -93 7.2 20, XII, 1898 5, 000 -78 0.9 ah T, 1899 5, 000 1.66 6.8 17, T, 1899 5, 000 5.48 8.2 31, T, 1899 5, 000 3.06 8 1, II, 1899 5, 000 2.15 8 14, TI, 1899 5, 000 1.12 6.6 ie 28, TI, 1899 5, 000 19.78 10.2 22854... 14, ITI, 1899 5, 000 12.99 13.1 22859_. 28, ITI, 1899 5, 000 8.82 13.5 VAS VOT AE BRD MUIR OS Se oad eee eeu ng Ul ers eee teen en pease BEND au tnsanes 618 TABLE XV.—Continued. SOLIDS IN SUSPENSION AT STATION G, BERKEFELD FILTER. ta aN Cu.cm.| ©u.em.} Silt | River Accession number Nate strained| silt | perou.m.| gage 15, XI, 1897 5, 000 7.85 1,570 2.8 30, XI, 1897 5, 000 5.36 1, 072 3.2 14, XII, 1897 5, 000 7.50 1,500 3.4 28, XII, 1897 5, 000 1.41 282 3.2 25, I, 1898 5, 000 2.10 20 6.8 8, II, 1898 5, 000 2.26 452 71 22, II, 1898 5, 000 1.92 10.7 . LIT, 1898 5, 000 3.23 6: 11 22, III, 1898 5, 000 4.01 802 14.1 , LV, 1898 5, 000 4.68 936 17.6 19, IV, 1898 5, 000 3.18 636 13.1 3, V, 1898 5, 000 1.66 332 11.1 11, V, 1898 5, 000 1.37 274 10.1 24, V, 1898 5, 000 3.10 620 13.6 7, WI, 1898 5, 000 96 192 12.5 21, VI, 1898 5, 060 1.25 250 10.8 5, WII, 1898 5, 000 1.48 296 8.7 9, VII, 1898 5, 000 2.42 484 4.7 1, VIII, 1898 5, 000 3. 80 760 2.6 16, VILLI, 1898 5, 000 4.14 828 3.7 30, VIII, 1898 5, 000 3.80 760 3.9 3, IX, 1898 5, 000 4.23 846 4.2 27, IX, 1898 5, 000 2.06 412 4.9 i, X, 1898 5, 000 6.86 1,372 3.9 25, X, 1898 5, 000 4,12 2. 4.3 8, XI, 1898 5, 000 2.85 570 6.7 22, XI, 1898 5, 000 1.45 290 8.5 6, XII, 1898 5, 000 1.08 216 7.2 20, XII, 1898 5, 000 1.55 310 5.9 fe , 1899 5, 000 2. 66 532 6.8 iG , 1899 5, 000 3.88 776 8.2 31, I, 1899 5, 000 3.52 704 8 14, T), 1899 5, 000 3.18 636 6.6 28, II, 1899 5, 000 8.91 1, 782 10.2 14, III, 1899 5, 000 13. 86 2, 712 13.1 28, III, 1899 5, 000 11. 65 , 330 13.5 Average tor 1808. 16 oto Sie cera re ee eee nn On Oye me Pees 556. 48) TABLE XV.—Concluded. SOLIDS IN SUSPENSION AT STATION F, BERKEFELD FILTER. : Cu.em, | Cu.cm. Silt River Accession number Date strained| silt | percu.m,| gage 3, IIT, 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 12, IV, 1898 5, 000 4.76 952 14.8 26, IV, 1898 . 4.95 990 12 17, V; 1898 5, 000 2.26 452 10.1 a; , 1898 5, 000 6.12 1,224 13.6 14, WI, 1898 5, 000 5. 63 1,126 11.9 28 VI, 1898 5, 000 2.09 418 10 12, VII, 1898 5, 000 3. 84 768 ff 26, VII, 1898 5, 000 7.16 1, 432 2.9 9, VIII, 1898 5, 0U0 10. 00 2, 000 3.2 23, VIII, 1898 5, 000 12.47 2, 494 4.2 i, X, 1898 5, 000 24.12 4, 824 47 20, X, 1898 4,500 16. 01 3, 558 4.2 4, X, 1898 5, 000 12.43 2, 486 4 18, X, 1898 5,.000 11.18 2, 236 3.8 2, XI, 1898 5, 000 24 1, 448 6.5 15, XI, 1898 5, 000 6.51 1, 302 ical 29, XI, 1898 5, 000 2.91 582 8.3 13, XII, 1898 5, 000 -70 140 6.7 27, XII, 1898 5, 000 2.23 446 6.1 10, I, 1899 5, 000 3.90 ‘780 7.9 24. , 1899 5, 000 2.34 468 8.9 is II, 1899 5, 000 4.44 888 7.3 pate II, 1899 5, 000 1,64 328 5.5 7, III, 1899 5, 000 9. 48 1, 896 12.9 21, III, 1899 5, 000 18,57 3, 714 13.7 we anstislsnaseiaiean (ealiivac cance tases ces cae ac ity Garett Dee Me ee ee 1,572 BIBLIOGRAPHY. 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Der grosse Waterneverstorfer Binnensee. Eine Biologische Studie. Forschungsber. Biol. Station zu Plén, Theil VI., pp. 166-204, Taf. V. 1 Karte und 4 Fig. im Text. Leverett, Frank. 96. The Water Resources of Illinois. Seventeenth Annual Re- port of the U. S. Geological Survey, Part II., pp. 645-849, Pl. CVIII.-CXIII.; also as separate. °97. Water Resources of Indiana and Ohio. Eighteenth Ann. Rep. U. S. Geol. Surv., Pt. IV., pp. 419-559, Pl. 33-37. Lockyer, Sir Norman, and Lockyer, W. J.S. 700. Sunspots and Rainfall. Science, N.S., Vol. XII., No. 311, pp. 915-918. 701. On Solar Changes of Temperature and Variations in Rain- fall in the Region surrounding the Indian Ocean. Proc. Roy. Soc., Vol. LXVII., pp. 409-431. Loew, O. °96. Das Asparagin in pflanzenchemischer Beziehung. Chem. Zeit., Jahrg. XX., pp. 143-147. Lohmann, H. : 701. Ueber das Fischen mit Netzen aus Miillergaze Nr. 20 zu dem Zweck quantitativer Untersuchungen des Auftriebs. 622 Wiss. Meeresuntersuch., Abth. Kiel, N. F., Bd. V., pp. 45-66. 1 Taf. 703. Neue Untersuchungen 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. VIL, 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 Iniprovement 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 Kugineers, 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, Ill. Pieters, A. W. 94. The Plants of Lake St. Clair. Bull. Mich. Fish Comm., No. 2. 12 pp., 1 map. 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 Illinois. 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. 700. Das Plankton der Elbe bei Dresden. Zeitschr. f, Gewasser- kunde, Bd. III., pp. 1-27. Schroder, 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. VII., pp. 43-89. 00. 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. 01. Die Entomostrakenfauna der ‘‘alten Donau” bei Wien. Eine ethologische Studie. Mit einem Anhang: Zur Frage iiber Ursprung und Verbreitung der Entomostrakenfauna des Siisswassers. Zool. Jahrb., Abth. f. Syst. Geog. u. Biol. d. Thiere, Bd. XV., pp. 1-156, Taf. 1-12. 20 Abb. im Text. Volk, R. ‘01. 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 Verhiiltnisse der Elbe bei Hamburg und iiber die Einwirkung der Sielwisser auf die Organismen des Stromes. Mitth. a. d. Naturhist. Mus. in Hamburg, Bd. XIX., pp. 65— 164, Taf. I.-VII. Ward, H. B. 96. A Biological Examination of Lake Michigan in the Trav- erse Bay Region. Bull. Mich. Fish Comm., No. 6. 100 pp., 5 pl. 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— XVII. 624 Whipple, G.C. 98. Classification of Lakes according to Temperatures. Am. Nat., Vol. XXXII., pp 25-33. 3 fig. 99. The Microscopy of Drinking-Water. XII+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. Tech. Quart., Vol. XIIL, 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 Plén, Th. III., pp. 97-117. 06. Quantitative Untersuchungen iiber das Limnoplankton. Forschungsber. a. d. Biol Station zu Plén, Th. 1V., 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 Jahrb. f. wiss. Botanik, Bd. XXIV., pp. 149-198, Taf. VI. EXPLANATION OF PLATES.* PLATE I, 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. PLATE II. 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 (Ks), Thompson’s Lake (G), and Phelps Lake (F). PLaTE III. Illinois River bottoms at high water in spring flood in March, 1898, 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 III. 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. PLATE V. 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 4oo feet in width. Prate, Vile 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 givenin 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. PuLaTe VIII. 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. PLATE IX. The same for 1895. Hydrogfaph 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 XI. The same for 1897. PLATE XII. The same for 1808. PLATE XIII. The same for 1899. PLATE XIV. 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. II.) 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. PLATE 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. PLatTe XVII. Western shore of upper end of Quiver Lake, looking northward, showing rich- 627 ness of vegetation. Emergent Ve/umbo lutea 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. PLATE XIX. Flag Lake in autumn of 1895 at plankton station (K), looking north-northeast- ward. Scattered dwarfed clumps of Scé7fus and an abundance of Vymphea consti- tute the principal vegetation in this open area. PLATE XX. 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 Cevafophy//um, along shore. Plankton station (G) in open water to the right (northward), 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 1 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 I[|linois 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 1898-1899. 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 Illi- 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. PLaTE XXVII. The same for 1896. Hydrograph from gage-readings in the Illinois River at Havana. 628 PLATE XXVIII. The same for 1897. PraTe 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 XXXIII. The same for Flag Lake (Station K) for 1895-1896. PLATE XXXIV. The same for 1897-1898. PLATE XXXYV. 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. PLave XL. ‘The same for Phelps Lake in 1896. PLATE XLI. ‘The same for 1897. PuaTE XLII. The same for 1898-1899. 629 PLATE XLIII. 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. PLATE XLIV. The same for 1897. PLATE XLV. 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. PLATE XLVII. The same for 1898-1899. Plankton scale at the left should read 0.1 to 0.4 in- stead of 1 to 4. PuatTE XLVIII. The same for Quiver Lake (Station C) for 1895 and 1897. PLATE XLIX. The same for 1898-1899. PLATE L. The same for Thompson's Lake for 1897, 1898, and 1899. Nitrite scale should read 0.1 instead of 1. at. ERRATA AND ADDENDA Page 99, line 6 from bottom, for (’87) read ('85); line 5 from bottom, after Rodfe, 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 7. read Tables [1/-—IX, Page 170, line 15 from bottom, for V//7/, 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 7899 read 7896. 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 fo 5 read 7 fo 75. 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 sode. Page 310, line 14 from bottom, for Z//. read XZ/V.; line 4 from bottom, for che read an. Page 323, line 9 from bottom, read z7 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 guadzfatively read quantitatively. Page 357, line 6 from bottom, after 76.76 read on the 24th. Page 358, line 18, after ad read decreases the. Page 367, after heading Dogfish Lake read Station L. Page 371, line 4, before decaying read /o. Page 372, live 16, after maximum read in Ouiver Lake. Page 381, after heading /ag Lake read Station K. Page 385, line 14, for wded/a read uzella. Page 403, line 17, for food read floods; line 18, before /zy read of. Page 405, line I, after re/ative read annua; line 8, for 7597 read 7890. Page 414, line 12 from bottom, for 7zver 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 em.); line 13, for (.95) read (5 cm.); line 16 from bottom, for food read floods. Page 429, line 4 from bottom, for 22,35 read 22.55. Page 439, line 2 from bottom, for ¢/e read ¢hezr. Page 440, line 8, for mean read means and for the read ¢hezr. 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 y. Page 510, line 9, add, azd Volk (’03). Page 546, line 15 from bottom, after zs read zm the main. Page 549, line 1 below heading, page 551, line 1, and page 556, line 3, for (970 read (97a). Page 556, line 7, before ’07 read 'os and. Page 560, table, second column, line 4 from bottom, for (’00) read (’oo),; line 6 from bottom, for /uuzg read Yung; line 16 from bottom, for (’95) read (’97), line 17 from bottom, for (’99) read (00); line 19 from bottom, for (’95) read (’96). Page 584, at head of second column, for 7897 read 7898 ; under remarks, line 4, for above read along. Pages 597 and 5098, below table, read *Bottom visible. Page 598, 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: v. d. = very decided. v. m. = very much. Decimal in color column=volume of standard ammonium chloride solution required to develop the same tint when diluted to fifty cu- -++ = rising river level. — = falling river level. + = stationary river level. c. = considerable. d. = distinct ; decided: f . = filtered. little: bic centimeters with ammonia- m. = much. free water and treated with the n. f. = not filtered. usual amount of nessler reagent s. = slight. ANWT UAAING) JO LOOM UVAN “AALVAA HOIFT LV UAADT SIONITIT +f | po fa sf fs pens hoped) / aie a maiaie oie Beas IXX Pid “ZEB Wes e* TODA fe] “§ ait | $1 UL HH i JS Suet == oss AN ann | L aS iI | ] | I_t } | —— ee — —s | pete wa (el [ <- iE ¢ | \ | |a ia +t 4 SJ a Be(edepe [ele . 1 = > } 4 ot si t T Ge TTT ‘aa ee [| GoEee = 4 Sasa AXX "ld Lierissssssssoeaa Veg omg ee UOJYUe/ +} 3G WONING).4S17] ToUOSCa, Wy Pq “CBS * DoS False Tasers jo u013NQ14451C) Touosoa; River Gage Ft. a, so Net ead jy My Bet, + " | fou laceal ceolcmal ™ Te PS (el cial (as i a (AT i ca en a 0 |. i b , 3 i é l HHESE i x i 4 | L HEE J | Si \ ft zi " a E | | 1 ; SIG CE I | | \ / Lt ao = SEAM) 2 =! + Peete 5 SSE SIN sia TNC eae mn ira i 1 [ \ ~ — — }—— + —i— — ilenlaealn Th f \ Uj + = 4 4 — , — $+ —t—4F-- 1 4 4 Jf — ir +4 fa} CE EE IASI sl | a i | a i i i BI NED CINE MSE \ [ JOE SUSE Se) TEE SS PAE Sale| \ ry i] N Ele nt Ob sd lemperatureF* Plankton Cm P) ~ i) ° Ww 0 SERIES UESSSES CE Wise 0 all eI HCL : SEER HEEEEL ‘ts | }_ |i | Se ees a Eie = - 3 —_ ie lies {Fry [nal alin iit is Al I | > 5 oe etel “CME ‘ | eK Se ESN Cd | eS Nd ed ad Le lat 5 aa T | > T | | i G } f | ali aS) jt f (SS JOSIE Ht Hee CHEE 2 SStGas San : : ~ 9] 09 ] 3} ]09 [ST [ ial E: if it - fl al Ni Et f maul t Ef Z mn al lt ae 4 iy rt 7 1 [os a [| my cE | - iff IE | ric a a ae ol ; | / [HIE sla ; PH ae IEE oo UES (Ea SES pt =a at : in f a el (el f all . | ial Ea — + 1. is a le | 4 fll " i u IN [ = JENA eis | i [ + miele Wt ¢| [ et |i | oS - a [ EE) il Fr e 9 iY # | Ans | a 1] 1 re) eto | JERE g| © | : He il WA '}\s) a < Leu "sae LEIS AXXX Pid “QBB)*} vanes 7° U0IMUl/ +f jo WoHNgLAyS I] jouosea = / BB) Plankton Cm? 5 oe Elerion me AXXX *Pid “VES OUNMIG B° UOIYUE/) 30: WORYNg1AYSI1C] TOUOSOa 2) Plankton Cm3 ! £ = Hl ad eS i g |_| | z is iE EINES ieee alae | \ 4-4] To | LZ i Z | wile —+—t = A a i +4 | Le | eb PS 5 Z ' cy | | ~ | he | ia K | wim I | ul | fa a ray | 2! 3}| 3 || 2 Tail eat u|| o! SI el} 2 "Sale. IAXXX Pld “SEB OuNMS * uozMyue/y W919Ng1.49S 17] ToUOSeaC; prlg _<« | Plankton Gm? 2 . or s ait P Deiat: ONS eM * oA Gant z sf i . ~4_ (7 as 1" J | | ] [ || a AES ale ESE Me Sie aE il e+ ; 7S Ss FE an aE EVES y ——— = ~ ——t a etl team el Sy 7, PSE aia au ea ae aia ae TINT INT CI Ny | \ = all | l f 4th | +—} —t—+ {-+—4+— +4] ae — — — — — — 7 + (ASIEN SITET NS Fi STA sry Z 0 | A ale ‘ \ — — T “tH | ay wl SEI IIE ig] eat \ a Lie NI | eee ete (Os IE Jat + ++ +— aa eee HOA a B Sees {Hr iy ie | I! ale ; al [ NI a lite ia + +. + ot | + ++. + a + CI | | Etats [ a | TAXXX "1d G68)°O wns P° uoqyue/_y W919Ng144S 1] TOUOSOGC River Gage Ft. Plankton Cm? 3 Temperature F* re) i I =. 4 } | a a a| i {tat eh HS — — {—4— 4 : N | y | oan : 3 bad z + = - 1 _ — a Na — — a + + | \ a) [ile mai | | al | Ae SHEESH Et alt 2 SIE = | | el ieee = \N =a an — —— at SS eS ee ~ ‘ ee ie 8 ats CATE [oot a WEE 4 = tt —\— eS a —}—| | Re 1 | Ae c z | a aioe 4—|}— - = ea ea ee = — a ant (SSS AE SEEEEHHRECH I aie [I elias jt) tt tH} t+ q + bed I. 4. LEH art ffl 4 1 \ A 7 — — he mb + See { b+ —+—H-+-HH— eee on | i nn i |} ot tt I sa) HIE | a “Al tal | it | ea eae eS | ne . ae Ae = 2 I 4 Vv I | ease ae Z Es are al vi +—t. +4 = nl re fe SEEN | (ela ASAE | i ne | tT] a iN + I Spee 4 4 ee 12 St il = TIAXXX “Pid “ZE8h"O wus m U0JYUe/_Y JO UWOHNG1AYS 17) Toussoe uw emperature F™ 2) Plank ton Cm? & 8 Sa 4+ Tal XIXXX Id 668} ‘BEES wag FF UOJHUL] Y x i 43510] Joussees, erature (3 a | RwerGage © x 8 2) Tem Plankton ‘ Tet? ce Oo oe ras SS SIE |g} iia = ee Ue dt ENS 1 belt eet ACSI 2 as 7 ; i te TACHI - tatcl + Lee Peg { Le \ iv ait y 7 7 Hes Chee 14} I \ —t 4 | \I Z S Le \ Wie 5 | a | = = HH aS Ie 1 ti 4} Le ITIL SIRE —— a4 | \ + = + Sao = et e T i | 1 ha Hh ie ah ] T +H = 4 | _" — SE Mest } B U AVE A “ = i i ‘a : al +; a IL A 47 I= } i 1 i 7 NH \ \ | 7 T pal i \ / \ nN I a rd | i St + y af H + “IX Pid ‘96 09 ‘jung m° Uozyuely jo 08bS 49S 1] ToUDSOSC 08 erature F* River Ca es wv j& x 3] S2 Plankton Cm3 Pata 2 Nemec TX Pid L684 eS 40944) 4 30 WORINgIA4S 1} TOUDSoEC, RiverGage Ft. ral Planicton Cm3 ” +—} —j—t. = = = | = = a dt ttt / | / it iL - - d | 2) eee / —|-++ + +—+— = +— }—} t+} —_} | — gaze ——s | / h te = Seat oe Hi 4 2 ; + on cee }—fjt 4 te 1 COCA Tt Sal iia tN E BS OS! 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GS Oe Os es 183 2) PateXL re i [| i S |_| AH i “ee at aca | fp l HH fa ial TI | Ash ‘Hine ea im Ht =e ae Cie Spas Unt Sunes oe SEaneee (sednuace BEE "uN Ser jowta fowta |ucqaw |/Leuwoy Ny ivajou)— — Uaboiiy | uo} ~~ | ~~ "$a4P4! ‘SaUqIN wuedig | plouuing)y |euewmpyeas) uabAx aUlsoyy, aaa IN ay heat | 0 N49 SEES SEIT PEERS EEE ie eee eS See = | —— =e aa _ (5) ay ea —j—_+—+ SAVE EERIE EEE HEH AIEEE EH \ leo ~ SINCE AERIS Coote 5 a NA DESC IN aa Hepvieemal vos HEREIN CKEE COCCI 1 CAGE CENT ani sae ora COENEN} | FERAL ECACC RCD SCECEEC CHICA CEC EE ACETIC TIEN SSCA EOIN SST Sescinsal ac SesaeaiiNcd ced VigaR (etee tae FAT MSPInGu gaa pOTGnGdNeauiate! ee | be I 1m Le +}. ain | ABE p= —| as — ~ BE = yi] E Zi} / tele aie \ } | = ++ =e ic — AS | = +E i = +t = —b H+ + eerie aig a [ry TL i THAN AI i i SS oh EEEEEE CHEECH EEE HEISE A ETE ee Sie bee IN 1X ld Z ESI W i FO “LOL YUE] PUP RIFT /PIWAY) yo UoWMALAASIE E] i: TFS os iS bs wopueyy WAY uabhvg euouuiy 2uPbID | Ploukung jy | ewouny aly NV soz $2424 IN XS rest wOD HUE} : | or aug) : Be i Biot Seosonal Distribution of Chemical Data and Plankton. ee ee SeeRCREr | [3 TS SI [et | | aw i a | | TEE ft ia a i ie i | Pals + «wo > = al = S S ME TS ts ‘ 9 i Saiz ae le 2 a I i rata = Sete a t ‘fot fel) fe om 5 9! IL - ane RII M a ; 9: & 2 7 “eI < 7 as lets ai = = TROD oe Sela ecisratslarisiattnes =) a 2 | A’ : AG fe le Iie o arn TN Se Fg 2 | 3 a AMS | : 5 Z ae Ie we /| ‘ 7 ie i | [ a] Coal ‘T eo | 3 A? ~ 9 z- St St = = mia = = Te] PS — = | I>5 ia aia Tia mee i ie tS + a + vi 7 i 7 =a sh SSNS a ze aS | i; i 3 ae Le site| tall fellas ~ | — oe |= ia | 7 N Tt a | al ~. 3] el ial & igs ai nial so a iJe gr MS 5 ah | at |= SE r Slap if = fetes |_| od ee) = B | ele 2) | SEN SAI BBE l/s fe BEE 1) SUS ep See ro a a ER RES : i TH = rai | : H = = ty i | i | [ bee: isi i Cottman 3 + + = 2 Fe Wied LAY YXUIXT\d 6 GSI ‘PBSI'D wowers re * wep yueypuerje7jeauay)§a woRAgyAyS1~] youDsoac, River Gage Ft. TL] tee | ejay —t th ge - - | +~4 4 4-4 + —H-t~ {+44 - tHe > tt = 3 to a Is. 4+ (ed —te 1! 4+} 4} + -+-H] 3 & — ae ~ - = = tet —}i yt —+—_}— 1-H e x FS a] as a 7] | famed [we ia el Roleelouttal a = mi = | b wos | alee ele ap TA nae a [ eal Et zs is Saal | rcs SU F CE an J EIS IU ey SN Se a Pa a 2 a i a a a 4 | tH \ tit cry i | 1 1 ! {:| 1] ira mot | yf til f | N i i I | i le i ] =D te | i TTT | ] + | i 22 u2bhg AY | | | Sey SES aye =i IL Es! ie ® IfSS mm if mE SSI at. i (s E 7 [3 Het ERIS EHEC ALVA = SOUT Sy ESTE ESE | LS ue S fi oi quebig | poulungyy | euowmyrrsy Halt af va ia! i) + i 1 a q | i 4 Q ae ua! t ine iD 5 a| (ia Tals lt BE ae | |_| u | & + + | | Tl il é x Reh ea bs 44 Pd 6BBI BEB 2 was Fe Uepuel meen euay po wens] Teves; Z68! INDEX A Acer dasycarpum, 108. Zéschna, 7, 31, 32, 33, 35» 38, 39-46. californica, 41, 45. clepsydra, 40, 41-42, 46. constricta, 40, 42-44. eremita, 42. eremitica, 41, 42. juncea verticalis, 46. verticalis, 41, 46. ZEschnide, 4, 5, 6, 9, 11, 12, 13, 15, 16, 17, 21, 22, 23, 25, 26, 27-50, 51. “Eshna, 6. Agrion, 3, 18, 39, 47. Agrionidz, 3, 4, 13, 15, 16, 17, 20, 25, 26, 50, SI. Algz, 152,225, 241, 245, 256, 415, 480, 516, 519, 523, 530, 531, 532, 535, 539 546, 555, 564, 592, 597, 614. Allorchestes, 17, 370. dentata, 47. Ameiurus, 153. Amia calva, 153. Amnicola, 17, 47. Amphipoda, 513. Amphora, 516. Anax, 7, 13, 15, 16, 21, 28, 31, 33, 39, 46-50. junius, 17, 23, 29, 35, 46-50. Angelica atropurpurea, 238. Anisoptera, 3, 4, 7, 8, 20, 25, 26, 29, 51. Aphredoderus sayanus, 17. Aphylla, 53, 54. producta, 54. Arcella angulosa, 516. discoides, 516. vulgaris, 516. Arigomphus, 67. Asellus, 17, 47. Asterionella, 225, 389, 532. Azolla, 153, 237. carolina, 241. B Bacillariacez, 519. Basizschna, 16, 31, 32, 38-39. janata, 38-39. Bdelloida, 500, 519, 535. Belostoma, 18. Bidens, 246, Bosmina, 256, 380, 500. Boyeria, 13, 16, 31, 32, 36-38, 46. vinosa, 36-38. Brachionide, 518. Brachionus, 263 (table), 297. dorcas, 297, 518. Brachytron, 33, 35. Bryozoa, 243, 501. Cc Calopterygide, 3, 12, 13, 16, 25, 26. Calopteryx, 3, 4, 46. maculata, 64. Caltha palustris, 237. Canthocamptus, 297. Carchesium, 297, 534. lachmanni, 296, 546. Cardamine hirsuta, 237. rhomboidea, 237. Carteria, 225. Carya oliveformis, 108. Cathypna luna, 516. Catostomidz, 564. Celithemis, 10, 12, 15, 16. eponina, Io, Centropyxis aculeata, 516. ecornis, 516. Cephalanthus occidentalis, 108, 245. Ceratophyllum, 152, 153, 170, 236, 238, 243, 244, 245, 246, 247, 248, 249, 251, 352, 356, 368, 370, 395, 499, 491, 495, 496, 498, 499, 501, 563, 582, 587, 588, 589, 591, 592, 594. demersum, 238, 242. 632 Chara, 38, 236, 251. Chironomus, 47, 516, 517, 536. Chlamydomonas, 178, 225, 546, 555. Chlorophycee, 519, 532. Chydorus, 256, 389. globosus, 297. Cicuta bulbifera, 238. maculata, 238. Ciliata, 296, 500, 518, 519, 531, 534, 546, 555. Cladocera, 256, 258, 369, 370, 375, 385, 389, 519. Cladophora, 245. Closterium, 537. acerosum, 516. gracile, 516. lunula, 516. Cocconeis communis, 516. Codonella, 263 (table ), 534, 555. Colurus obtusus, 516. Composite, 245, 246, 240. Conjugate, 5109. Conochilus, 516. Copepoda, 185, 256, 257, 263 (table) ,385, 500, 519, 536. Cordulegaster, 14, 16. Cordulegasteridz, 4, 5, 6, 9, 13, 14, 22, 26, 27, 28. Corduliine, 5, 6, 14. Corisa, 17. Corixa, 580. Crenothrix, 582. Cruciferz, 244. Crustacea, 17, 47, 370, 457, 519. Cybister, 46. Cyclops, 263 (table ), 297, 536. bicuspidatus, 297, 518. serrulatus, 516, 536, 537. Cyclotella, 516. Cymatopleura solea, 516. Cyperacez 236, Cyphoderia ampulla, 516. Cyprinus carpio, 153. D Dero vaga, 297. Desmidiacez, 517, 532. INDEX Diastatomma, 14, 15, 52, 53, 55, 57-60, 65. carolus, 58, 59-60. rupinsulensis, 59. severus, 58-59. Diatoma vulgare, 516. Diatomacez, 152, 181, 182, 225, 227, 256, 257, 263 (table), 389, 500, 513, 516, 517, 518, 523, 530, 531, 532, 535, 539, 555, 569, 614. Didymops, 5, 16. Difflugia, 263 (table ), 296, 297. acuminata, 516. acuminata bifida, 516. constricta, 516. globulosa, 516. Dinobryon, 225. Diplax, 5,9. Diptera, 6, II, 17, 537. Distyla, 516. Dixa, 536. Dorosoma, 563, 564. Dromogomphus, 16, 53, 54, 64, 65. spinosus, 64-65. Dulichium spathaceum, 240. E Eleocharis acicularis, 241. intermedia, 240. palustris, 240. tenuis, 240. Elodea, 236, 243, 244, 246, 247, 248, 368, 379; 491, 495, 496, 499, 597. canadensis, 239. Encyonema, 516. Entomostraca, 17, 185, 263 (table), 297, 461, 516, 519, 530, 536, 564, 615. Ephemerida, 3. Ephemeride, 20, 60. Epizeschna, 30, 32, 33, 35-36. debilis, 33. heros, 7) 34, 35-36, 39, 43. Epicordulia, 13, 15, 16, 17, 46. princeps, 7, 10. Epistylis, 296, 297, 534. Equisetum, 236. limosum, 241. Esox vermiculatus, 17. Etheostomide, 564. INDEX 633 Eudorina, 518. elegans, 516. Euglena, 154, 155, 178, 192, 210, 224, 225, 341. acus, 226. deses, 225. gracilis, 225. sanguinea, 225, 513. spirogyra, 225. viridis, 225, 513. F Flagellata, 225, 263 (table ), 480, 517, 531, 546, 555. Fonscolumbia vinosa, 36. Foresteria acuminata, 108. Fragilaria, 256, 532. virescens, 516. Fraxinus viridis, 108. G Gompheeschna, 31. furcillata, 36. Gomphide, 4, 5, 6, 7,8,9, 10, 12, 13, 21, 22, 26, 27, 28, 29-50, 89. Gomphonema constrictum, 516. Gomphus, 6, 10, 14, 15, 16, 21, 23, 46, 51, 53, 54, 62, 64, 65-89. abbreviatus, 66, 72. adelphus, 74, 76. amnicola, 68, 83. australis, 67, 77-78. consobrinus, 74. cornutus, 82, crassus, 74, 75. descriptus, 66, 70-71. dilatatus, 83. exilis, 68, 79, 81-82. externus, 7, 67, 73, 74-76, 84, 85, 87, fluvialis, 84, 86, 87. fraternus, 15, 72, 73, 74, 75, 87. fraternus walshii, 74. furcifer, 79. graslinellus, 79, 80. minutus, 82. notatus, 15,72, 74, 83, 84, 85, 86-87. olivaceus, 83. 14, 16, 66, 69-70, 76, Gomphus— Continued. pallidus, 14, 16, 67, 77, 79-81, 87. parvulus, 63. plagiatus, 68, 83, 84-86, 87. quadricolor, 71. scudderi, 83. segregans, 87. spiniceps, 14, 15, 68, 85, 87-80. vastus, 67, 72-73, 87. ventricosus, 73. villosipes, 66, 67, 78-79. Gregarinide, 18. Gromia, 516. i Hagenius, 10, 12, 13, 16, 50, 52, 53, 54, 60- 62, 65. brevistylus, 61-62. Heliozoa, 296, 519. Hemiptera, 20. Herpetogomphus, 53, 57, 65. Heteranthera, 243. graminea, 239. Holotricha, 555. Hyalella, 500. Hydra, 243, 256, 486, 500, sor. I Infusoria, 530, 534, 535, 555, 614. Insecta, 256, 486, 5c0, 530, 531, 563, 615. Isopoda, 513. J Juncacez, 236, 246. Juncus acuminatus, 239. L Lanthus, 52, 54, 62-64, 65. parvulus, 63-64. Lemna, 152, 249, 579, 580, 580. minor, 239, 242. trisulca, 239. Lemnacez, 152, 153, 237, 240, 242, 243, 246, 249, 581, 582, 584, 588, sor, 592, 596. Lepidoptera, 20, i183. Lepocinclis, 225. Leptodora, 263 (table). hyalina, 258. Lestes, 3. 634 INDEX Leucorhinia, 9, 13, 16. Libellula, 5, 13, 14, 16, 17, 23, 64, 79, 88. Libellulidz, 4, 5, 6, 8, 9, 12, 13, 16, 22, 25, 26, 27, 28, 20, 51. Libelluline, 5. Lippia, 246. Macrogomphus spiniceps, 87. Macromia, 5, 10, 16, 30. illinoiensis, 64. Macronema zebratum, 73. Mallomonas, 225. Mastigocerca, 516. Mastigophora, 516, 518, 519, 523, 530, 533, 534, 535, 614. Melosira, 225, 256, 375, 389, 493, 500, 518, 532. spinosa, 516. varians, 516. Meridion circulare, 516. Mesothemis, £2, 15, 16, 17, 23. collocata, 13. simplicollis, 75. Metopidia solidus, 516. Micropterus pallidus, 562. Moina, 369, 544, 546. micrura, 300. Mollusca, 17, 47, 154, 486, 500, 563. N Naias, 243, 246, 415, 597. flexilis var. robusta, 240, 245. Nasizeschna, 30, 32, 33-35. pentacantha, 7, 34-35, 36. Nasturtium palustre, 237. sessiliflorum, 237. Navicula, 516. Negundo aceroides, 108. Nelumbo, 385, 415. 494. lutea, 237. Neureschna furcillata, 36. Nitella, 236. Nitszchia sigmoides, 516. Notholca acuminata, 297. jugosa, 516, 518. Notonecta, 17, 18. Nympheea, 51, 251, 384, 385, 494. reniformis, 237. oO Odonata, I-94. Oligochzeta, 486, 500, 513. Ophiogomphus, 14, 57. carolus, 59. Oscillaria, 181, 182, 245, 256, 386, 415, 493, 500, 516, 592, 597- Ostracoda, 516, 519. P Pachydiplax, 13, 16. longipennis, 11. Pantala, 6,°13, 16. Pelocoris, 47. Perca flavescens, 18. Peridinide, 225. Perithemis, 16. domitia, 7. Petaluridz, 4, 21, 22, 25, 26, 27, 51. Phacus longicauda, 516. Phanerogamia, 415. Philodina megalotrocha, 516. Physa, 17. Planaria, 513. Platanus occidentalis, 108. Plathemis, 14, 16. Platydorina, 95. Pleodorina illinoisensis, 95. Pleurosigma angulatum, 516. Ploima, 500, 5109. Plumatella, 152. Polyarthra, 297. platyptera, 297, 518. Polygonum, 152, 237, 242, 246, 240. amphibium, 238, 246, 251. Polyodon, 196, 563, 568. Pomoxis annularis, 17. Pontederia, 494. cordata, 237, 239. Populus monilifera, 108. Potamogeton, 236, 238, 244, 246, 247, 248, 251, 368, 415, 582, 594, 595, 597, 598. natans, 240, 243, 245, 246, 251. pectinatus, 240, 242. pusillus, 240. Progomphus, 10, 14, 16, 52, 53, 55-56, 65. obscurus, 55-56. INDEX 635 Proserpinaca palustris, 237. Protophyta, 263 (table). Protozoa, 256, 263 (table), 296, 5109. Pterodina patina, 297. Q Quercus palustris, 108. R Ranatra, 18. Ranunculus multifidus, 237. Rhabdoceela, 297. Rhizopoda, 263 (table), 500, 513, 516, 517, 518, 519, 530, 532, 533, 535, 555 564, 614. Rhizota, 5109. Rhyacophila, 47. Rhynchospora alba, 241. Rotatoria, 530, 534, 615. Rotifer actinurus, 516. tardus, 297. Rotifera, 256, 257, 263 (table), 297, 461, 500, 516, 517, 519, 535, 536, 564. Ss Sagittaria, 88, 249, 383, 385, 4o4. variabilis, 237, 240, 242. Salix longifolia, 245, 266. nigra, 108, 245, 266. Schizophycez, 510. Scirpus, 251, 495, 592. atrovirens, 241. fluviatilis, 237, 241, 246, 249, 383. lacustris, 241, 246, pungens, 241. smithii, 241. Silurida, 564. Sium cicutefolium, 238. Somatochlora., 9, 14, 16. Sparganium eurycarpum, 88, 239. Spirodela, 152, 241. polyrrhiza, 239, 242. Spirogyra, 241, 245, 415. Stratiomyiide, 47. Stylurus, 83. Suctoria, 519. Surirella, 518, 537. ovata, 516. splendida, 516, 537. Sympetrum, 5, 10, II, 13, 15, 16, 17. Syncheta, 256, 263 (table ), 273, 493, 518. Synedra, 225, 532. acus, 513, 516. ulna, 516. Synthemine, 5, 6, 14, 16. Synura, 256, 263 (table ), 273, 518, 555. uvella, 385, 516. Tr Tachopteryx thoreyi, 63. Tanypus, 536. Tetrageneuria, 16. Tipula, 47. Trachelomonas, 225, 341, 518. hispida, 516. Tramea, 5, 6, 8, 12, 13, 15, 16. lac rta, 7, 9, 48. Triglochin palustris, 240. Trinema enchelys, 516. Trochospheera, 383, 391. Typha latifolia, 239. U Ulmus americana, 108. Umbellifera, 244. Unionide, 196, 266. Uropetala thoreyi, 63. Utricularia vulgaris, 238. Vi Vallisneria spiralis, 239, 244. Volvocide, 95. Volvox, 500. Ww Wolffia, 152, 240, 286, 580, 591, 594. braziliensis, 240, 242. columbiana, 239, 242. Z Zizania aquatica, 241. Zygnema, 241, 245, 415. Zygoptera, 3, 4, 5, 6, 8, 9, 11, 12, 22,25, 26. ih Haan WAT Ad } Wa i ' HK ; A EMITLI ih Hi segs aa . 3 Bete side” 58% ade a a wae 2 al ee eae pin arenes aes = 5% = a e = 5 emcee Saami ea ee 6,02 ae er ee Cafe ee eee ek = = a +, : . 3 7 “iy = eve : > a - a = ¢ 4 . S ; % ~ = Aa VO - / es . 4 Ls z A = 4. _