Thepaperswhichonthissubjectprecededandcontributedto’FormsofFlowers’werethefollowing:——
\"OnthetwoFormsorDimorphicConditionintheSpeciesofPrimula，andontheirremarkableSexualRelations。\"Linn。Soc。Journal，1862。）
\"OntheExistenceofTwoForms，andontheirReciprocalSexualRelations，inseveralSpeciesoftheGenusLinum。\"Linn。Soc。Journal，1863。
\"OntheSexualRelationsoftheThreeFormsofLythrumsalicaria，\"Ibid。
1864。
\"OntheCharacterandHybrid—likeNatureoftheOffspringfromtheIllegitimateUnionsofDimorphicandTrimorphicPlants。\"Ibid。1869。
\"OntheSpecificDifferencesbetweenPrimulaveris，Brit。Fl。（var。
Officinalis，Linn。），P。vulgaris，Brit。Fl。（var。acaulis，Linn。）andP。
elatior，Jacq。;andontheHybridNatureoftheCommonOxlip。WithSupplementaryRemarksonNaturallyProducedHybridsintheGenusVerbascum。\"Ibid。1869。
Thefollowinglettershowsthathebegantheworkonheterostyledplantswithanerroneousviewastothemeaningofthefacts。]
CHARLESDARWINTOJ。D。HOOKER。
Down，May7[1860]……Ihavethismorningbeenlookingatmyexperimentalcowslips，andIfindsomeplantshaveallflowerswithlongstamensandshortpistils，whichI
willcall\"maleplants，\"otherswithshortstamensandlongpistils，whichIwillcall\"femaleplants。\"ThisIhavesomewhereseennoticed，IthinkbyHenslow;butIfind（afterlookingatmytwosetsofplants）thatthestigmasofthemaleandfemaleareofslightlydifferentshape，andcertainlydifferentdegreeofroughness，andwhathasastonishedme，thepollenoftheso—calledfemaleplant，thoughveryabundant，ismoretransparent，andeachgranuleisexactlyonly2/3ofthesizeofthepollenoftheso—calledmaleplant。Hasthisbeenobserved？Icannothelpsuspecting[that]thecowslipisinfactdioecious，butitmayturnoutallablunder，butanyhowIwillmarkwithstickstheso—calledmaleandfemaleplantsandwatchtheirseeding。Itwouldbeafinecaseofgradationbetweenanhermaphroditeandunisexualcondition。Likewiseasortofcaseofbalancementoflongandshortpistilsandstamens。Likewiseperhapsthrowslightonoxlips……
Ihavenowexaminedprimrosesandfindexactlythesamedifferenceinthesizeofthepollen，correlatedwiththesamedifferenceinthelengthofthestyleandroughnessofthestigmas。
CHARLESDARWINTOASAGRAY。
June8[1860]……Ihavebeenmakingsomelittletriflingobservationswhichhaveinterestedandperplexedmemuch。Ifindwithprimrosesandcowslips，thataboutanequalnumberofplantsarethuscharacterised。
SO—CALLED（byme）MALEplant。Pistilmuchshorterthanstamens;stigmarathersmooth，——POLLENGRAINSLARGE，throatofcorollashort。
SO—CALLEDFEMALEplant。Pistilmuchlongerthanstamens，stigmarougher，POLLEN—GRAINSSMALLER，——throatofcorollalong。
Ihavemarkedalotofplants，andexpectedtofindtheso—calledmaleplantbarren;butjudgingfromthefeelofthecapsules，thisisnotthecase，andIamverymuchsurprisedatthedifferenceinthesizeofthepollen……Ifitshouldprovethattheso—calledmaleplantsproducelessseedthantheso—calledfemales，whatabeautifulcaseofgradationfromhermaphroditetounisexualconditionitwillbe！Iftheyproduceaboutequalnumberofseed，howperplexingitwillbe。
CHARLESDARWINTOJ。D。HOOKER。
Down，December17[1860？]……Ihavejustbeenorderingaphotographofmyselfforafriend;andhaveorderedoneforyou，andforheaven’ssakeobligeme，andburnthatnowhangingupinyourroom。——Itmakesmelookatrociouslywicked……InthespringImustgetyoutolookforlongpistilsandshortpistilsintherarerspeciesofPrimulaandinsomealliedGenera。ItholdswithP。Sinensis。YourememberallthefussImadeonthissubjectlastspring;
well，theotherdayatlastIhadtimetoweightheseeds，andbyJovetheplantsofprimrosesandcowslipwithshortpistilsandlargegrainedpollen（Thustheplantswhichheimaginedtobetendingtowardsamaleconditionweremoreproductivethanthesupposedfemales。）arerathermorefertilethanthosewithlongpistils，andsmall—grainedpollen。Ifindthattheyrequiretheactionofinsectstosetthem，andIneverwillbelievethatthesedifferencesarewithoutsomemeaning。
Someofmyexperimentsleadmetosuspectthatthelarge—grainedpollensuitsthelongpistilsandthesmall—grainedpollensuitstheshortpistils;butIamdeterminedtoseeifIcannotmakeoutthemysterynextspring。
Howdoesyourbookonplantsbrewinyourmind？Haveyoubegunit？……
RemembermemostkindlytoOliver。Hemustbeastonishedatnothavingastringofquestions，Ifearhewillgetoutofpractice！
[ThePrimula—workwasfinishedintheautumnof1861，andonNovember8thhewrotetoSirJ。D。Hooker:——
\"IhavesentmypaperondimorphisminPrimulatotheLinn。Soc。Ishallgoupandreaditwheneveritcomeson;Ihopeyoumaybeabletoattend，forIdonotsupposemanywillcareapennyforthesubject。\"
Withregardtothereadingofthepaper（onNovember21st），hewrotetothesamefriend:——
\"IbynomeansthoughtthatIproduceda\"tremendouseffect\"intheLinn。
Soc。，butbyJovetheLinn。Soc。producedatremendouseffectonme，forI
couldnotgetoutofbedtilllatenextevening，sothatIjustcrawledhome。IfearImustgiveuptryingtoreadanypaperorspeak;itisahorridbore，Icandonothinglikeotherpeople。\"
ToDr。Grayhewrote，（December1861）:——
\"Youmayrelyonit，IwillsendyouacopyofmyPrimulapaperassoonasIcangetone;butIbelieveitwillnotbeprintedtillApril1st，andthereforeaftermyOrchidBook。IcaremoreforyourandHooker’sopinionthanforthatofalltherestoftheworld，andforLyell’songeologicalpoints。BenthamandHookerthoughtwellofmypaperwhenread;butnoonecanjudgeofevidencebymerelyhearingapaper。\"
TheworkonPrimulawasthemeansofbringingmyfatherincontactwiththelateMr。JohnScott，thenworkingasagardenerintheBotanicGardensatEdinburgh，——anemploymentwhichheseemstohavechoseninordertogratifyhispassionfornaturalhistory。Hewroteoneortwoexcellentbotanicalpapers，andultimatelyobtainedapostinIndia。（WhileinIndiahemadesomeadmirableobservationsonexpressionformyfather。）Hediedin1880。
AfewphrasesmaybequotedfromletterstoSirJ。D。Hooker，showingmyfather’sestimateofScott:——
\"Ifyouknow，dopleasetellmewhoisJohnScottoftheBotanicalGardensofEdinburgh;Ihavebeencorrespondinglargelywithhim;heisnocommonman。\"
\"Ifhehadleisurehewouldmakeawonderfulobserver;tomyjudgmentI
havecomeacrossnoonelikehim。\"
\"Hehasinterestedmestrangely，andIhaveformedaveryhighopinionofhisintellect。Ihopehewillacceptpecuniaryassistancefromme;buthehashithertorefused。\"（HeultimatelysucceededinbeingallowedtopayforMr。Scott’spassagetoIndia。）
\"Iknownothingofhimexceptingfromhisletters;theseshowremarkabletalent，astonishingperseverance，muchmodesty，andwhatIadmire，determineddifferencefrommeonmanypoints。\"
SohighlydidheestimateScott’sabilitiesthatheformedaplan（whichhoweverneverwentbeyondanearlystageofdiscussion）ofemployinghimtoworkoutcertainproblemsconnectedwithintercrossing。
Thefollowingletterreferstomyfather’sinvestigationsonLythrum（Hewasledtothis，hisfirstcaseoftrimorphismbyLecoq’s’GeographieBotanique，’andthismusthaveconsoledhimforthetrickthisworkplayedhiminturningouttobesomuchlargerthanheexpected。HewrotetoSirJ。D。Hooker:\"Hereisagoodjoke:IsawanextractfromLecoq，’Geograph。Bot。，’andordereditandhopedthatitwasagoodsizedpamphlet，andninethickvolumeshavearrived！\"），aplantwhichrevealsevenamorewonderfulconditionofsexualcomplexitythanthatofPrimula。
ForinLythrumtherearenotmerelytwo，butthreecastes，differingstructurallyandphysiologicallyfromeachother:]
CHARLESDARWINTOASAGRAY。
Down，August9[1862]。
MydearGray，Itislateatnight，andIamgoingtowritebriefly，andofcoursetobegafavour。
TheMitchellaverygood，butpollenapparentlyequal—sized。IhavejustexaminedHottonia，granddifferenceinpollen。Echiumvulgare，ahumbug，merelyacaselikeThymus。ButIamalmoststarkstaringmadoverLythrum（Onanotheroccasionhewrote（toDr。Gray）withregardtoLythrum:\"I
mustholdhard，otherwiseIshallspendmylifeoverdimorphism。\"）;ifI
canprovewhatIfullybelieve，itisagrandcaseofTRIMORPHISM，withthreedifferentpollensandthreestigmas;Ihavecastratedandfertilisedaboveninetyflowers，tryingalltheeighteendistinctcrosseswhicharepossiblewithinthelimitsofthisonespecies！Icannotexplain，butI
feelsureyouwouldthinkitagrandcase。IhavebeenwritingtoBotaniststoseeifIcanpossiblygetL。hyssopifolia，andithasjustflashedonmethatyoumighthaveLythruminNorthAmerica，andIhavelookedtoyourManual。Fortheloveofheavenhavealookatsomeofyourspecies，andifyoucangetmeseed，do;Iwantmuchtotryspecieswithfewstamens，iftheyaredimorphic;NesaeaverticillataIshouldexpecttobetrimorphic。Seed！Seed！Seed！IshouldratherlikeseedofMitchella。Butoh，Lythrum！
Yourutterlymadfriend，C。DARWIN。
P。S。——Thereisreasoninmymadness，forIcanseethattothosewhoalreadybelieveinchangeofspecies，thesefactswillmodifytoacertainextentthewholeviewofHybridity。（AlettertoDr。Gray（July，1862）
bearsonthispoint:\"AfewdaysagoImadeanobservationwhichhassurprisedmemorethanitoughttodo——itwillhavetoberepeatedseveraltimes，butIhavescarcelyadoubtofitsaccuracy。IstatedinmyPrimulapaperthatthelong—styledformofLinumgrandiflorumwasutterlysterilewithitsownpollen;IhavelatelybeenputtingthepollenofthetwoformsonthestigmaoftheSAMEflower;anditstrikesmeastrulywonderful，thatthestigmadistinguishesthepollen;andispenetratedbythetubesoftheoneandnotbythoseoftheother;norarethetubesexserted。Or（whichisthesamething）thestigmaoftheoneformactsonandisactedonbypollen，whichproducesnottheleasteffectonthestigmaoftheotherform。Takingsexualpowerasthecriterionofdifference，thetwoformsofthisonespeciesmaybesaidtobegenericallydistinct。\"）
[OnthesamesubjecthewrotetoSirJosephHookerinAugust1862:——
\"IsOliveratKew？WhenIamestablishedatBournemouthIamcompletelymadtoexamineanyfreshflowersofanyLythraceousplant，andIwouldwriteandaskhimifanyareinbloom。\"
AgainhewrotetothesamefriendinOctober:——
\"IfyouaskOliver，IthinkhewilltellyouIhavegotarealoddcaseinLythrum，itinterestsmeextremely，andseemstomethestrangestcaseofpropagationrecordedamongstplantsoranimals，viz。anecessarytriplealliancebetweenthreehermaphrodites。IfeelsureIcannowprovethetruthofthecasefromamultitudeofcrossesmadethissummer。\"
Inanarticle，’DimorphismintheGenitaliaofPlants’（’Silliman’sJournal，’1862，volumexxxiv。page419），Dr。GraypointedoutthatthestructuraldifferencebetweenthetwoformsofPrimulahadalreadybeendefinedinthe’FloraofNorthAmerica，’asDIOECIO—DIMORPHISM。Theuseofthistermcalledforththefollowingremarksfrommyfather。Theletteralsoalludestoareviewofthe’FertilisationofOrchids’inthesamevolumeof’Silliman’sJournal。’]
CHARLESDARWINTOASAGRAY。
Down，November26[1862]。
MydearGray，Theverydayaftermylastletter，yoursofNovember10th，andthereviewin’Silliman，’whichIfearedmighthavebeenlost，reachedme。Wewereallverymuchinterestedbythepoliticalpartofyourletter;andinsomeoddwayoneneverfeelsthatinformationandopinionspaintedinanewspapercomefromalivingsource;theyseemdead，whereasallthatyouwriteisfulloflife。Thereviewsinterestedmeprofoundly;yourashlyaskformyopinion，andyoumustconsequentlyendurealongletter。FirstforDimorphism;IdonotATPRESENTliketheterm\"Dioecio—dimorphism;\"forIthinkitgivesquiteafalsenotion，thatthephenomenaareconnectedwithaseparationofthesexes。CertainlyinPrimulathereisunequalfertilityinthetwoforms，andIsuspectthisisthecasewithLinum;and，thereforeIfeltboundinthePrimulapapertostatethatitmightbeasteptowardsadioeciouscondition;thoughIbelievetherearenodioeciousformsinPrimulaceaeorLinaceae。ButthethreeformsinLythrumconvincemethatthephenomenonisinnowaynecessarilyconnectedwithanytendencytoseparationofsexes。ThecaseseemstomeinresultorfunctiontobealmostidenticalwithwhatoldC。K。Sprengelcalled\"dichogamy，\"andwhichissofrequentintrulyhermaphroditegroups;namely，thepollenandstigmaofeachflowerbeingmatureatdifferentperiods。IfIamright，itisveryadvisablenottousetheterm\"dioecious，\"asthisatoncebringsnotionsofseparationofsexes……IwasmuchperplexedbyOliver’sremarksinthe’NaturalHistoryReview’
onthePrimulacase，onthelowerplantshavingsexesmoreoftenseparatedthaninthehigherplants，——soexactlythereverseofwhattakesplaceinanimals。Hookerinhisreviewofthe’Orchids’repeatsthisremark。Thereseemstobemuchtruthinwhatyousay（\"Formswhicharelowinthescaleasrespectsmorphologicalcompletenessmaybehighinthescaleofrankfoundedonspecialisationofstructureandfunction。\"——Dr。Gray，in’Silliman’sJournal。’），anditdidnotoccurtome，aboutnoimprobabilityofspecialisationinCERTAINlinesinlowlyorganisedbeings。Icouldhardlydoubtthatthehermaphroditestateistheaboriginalone。ButhowisitintheconjugationofConfervae——isnotoneofthetwoindividualshereinfactmale，andtheotherfemale？Ihavebeenmuchpuzzledbythiscontrastinsexualarrangementsbetweenplantsandanimals。Cantherebeanythinginthefollowingconsideration:ByROUGHESTcalculationaboutone—thirdoftheBritishGENERAofaquaticplantsbelongtotheLinneanclassesofMonoandDioecia;whilstofterrestrialplants（theaquaticgenerabeingsubtracted）onlyone—thirteenthofthegenerabelongtothesetwoclasses。Isthereanytruthinthisfactgenerally？Canaquaticplants，beingconfinedtoasmallareaorsmallcommunityofindividuals，requiremorefreecrossing，andthereforehaveseparatesexes？Buttoreturntoourpoint，doesnotAlph。deCandollesaythataquaticplantstakenasawholearelowlyorganised，comparedwithterrestrial;andmaynotOliver’sremarkontheseparationofthesexesinlowlyorganisedplantsstandinsomerelationtotheirbeingfrequentlyaquatic？Oristhisallrubbish？……Whatamagnificentcomplimentyouendyourreviewwith！YouandHookerseemdeterminedtoturnmyheadwithconceitandvanity（ifnotalreadyturned）andmakemeanunbearablewretch。
Withmostcordialthanks，mygoodandkindfriend，Farewell，C。DARWIN。
[Thefollowingpassagefromaletter（July28，1863），toProf。Hildebrand，containsareferencetothereceptionofthedimorphicworkinFrance:——
\"IamextremelymuchpleasedtohearthatyouhavebeenlookingatthemanneroffertilisationofyournativeOrchids，andstillmorepleasedtohearthatyouhavebeenexperimentingonLinum。Imuchhopethatyoumaypublishtheresultoftheseexperiments;becauseIwastoldthatthemosteminentFrenchbotanistsofParissaidthatmypaperonPrimulawastheworkofimagination，andthatthecasewassoimprobabletheydidnotbelieveinmyresults。\"]
CHARLESDARWINTOASAGRAY。
April19[1864]……IreceivedalittletimeagoapaperwithagoodaccountofyourHerbariumandLibrary，andalongtimepreviouslyyourexcellentreviewofScott’s’Primulaceae，’andIforwardedittohiminIndia，asitwouldmuchpleasehim。IwasverygladtoseeinitanewcaseofDimorphism（I
forgetjustnowthenameoftheplant）;Ishallbegratefultohearofanyothercases，asIstillfeelaninterestinthesubject。IshouldbeverygladtogetsomeseedofyourdimorphicPlantagos;forIcannotbanishthesuspicionthattheymustbelongtoaverydifferentclasslikethatofthecommonThyme。（Inthispredictionhewasright。See’FormsofFlowers，’
page307。）Howcouldthewind，whichistheagentoffertilisation，withPlantago，fertilise\"reciprocallydimorphic\"flowerslikePrimula？Theorysaysthiscannotbe，andinsuchcasesofone’sowntheoriesIfollowAgassizanddeclare，\"thatnatureneverlies。\"IshouldevenbeverygladtoexaminethetwodriedformsofPlantago。Indeed，anydrieddimorphicplantswouldbegratefullyreceived……
DidmyLythrumpaperinterestyou？Icrawlonattherateoftwohoursperdiem，with’VariationunderDomestication。’
CHARLESDARWINTOJ。D。HOOKER。
Down，November26[1864]……YoudonotknowhowpleasedIamthatyouhavereadmyLythrumpaper;I
thoughtyouwouldnothavetime，andIhaveforlongyearslookedatyouasmyPublic，andcaremoreforyouropinionthanthatofalltherestoftheworld。IhavedonenothingwhichhasinterestedmesomuchasLythrum，sincemakingoutthecomplementalmalesofCirripedes。IfearthatIhavedraggedintoomuchmiscellaneousmatterintothepaper……Igetlettersoccasionally，whichshowmethatNaturalSelectionismakingGREATprogressinGermany，andsomeamongsttheyounginFrance。I
havejustreceivedapamphletfromGermany，withthecomplimentarytitleof\"DarwinischeArten—Enstehung—Humbug\"！
Farewell，mybestofoldfriends，C。DARWIN。
CHARLESDARWINTOASAGRAY。
September10，[1867？]……TheonlypointwhichIhavemadeoutthissummer，whichcouldpossiblyinterestyou，isthatthecommonOxlipfoundeverywhere，moreorlesscommonlyinEngland，iscertainlyahybridbetweentheprimroseandcowslip;whilsttheP。elatior（Jacq。），foundonlyintheEasternCounties，isaperfectlydistinctandgoodspecies;hardlydistinguishablefromthecommonoxlip，exceptbythelengthoftheseed—capsulerelativelytothecalyx。Thisseemstomeratherahorridfactforallsystematicbotanists……
CHARLESDARWINTOF。HILDEBRAND。
Down，November16，1868。
MydearSir，IwrotemylastnoteinsuchahurryfromLondon，thatIquiteforgotwhatIchieflywishedtosay，namelytothankyouforyourexcellentnoticesinthe’Bot。Zeitung’ofmypaperontheoffspringofdimorphicplants。ThesubjectissoobscurethatIdidnotexpectthatanyonewouldhavenoticedmypaper，andIamaccordinglyverymuchpleasedthatyoushouldhavebroughtthesubjectbeforethemanyexcellentnaturalistsofGermany。
OfalltheGermanauthors（buttheyarenotmany）whoseworksIhaveread，youwritebyfarthecleareststyle，butwhetherthisisacomplimenttoaGermanwriterIdonotknow。
[Thetwofollowinglettersrefertothesmallbud—like\"Cleistogamic\"
flowersfoundinthevioletandmanyotherplants。Theydonotopenandarenecessarilyself—fertilised:]
CHARLESDARWINTOJ。D。HOOKER。
Down，May30[1862]……WhatwillbecomeofmybookonVariation？Iaminvolvedinamultiplicityofexperiments。IhavebeenamusingmyselfbylookingatthesmallflowersofViola。IfOliver（Shortlyafterwardshewrote:\"Oliver，theomniscient，hassentmeapaperinthe’Bot。Zeitung，’withmostaccuratedescriptionofallthatIsawinViola。\"）hashadtimetostudythem，hewillhaveseenthecuriouscase（asitseemstome）whichIhavejustmadeclearlyout，viz。thatintheseflowers，theFEWpollengrainsarenevershed，orneverleavetheanther—cells，butemitlongpollentubes，whichpenetratethestigma。To—dayIgottheantherwiththeincludedpollengrain（nowempty）atoneend，andabundleoftubespenetratingthestigmatictissueattheotherend;Igotthewholeunderamicroscopewithoutbreakingthetubes;Iwonderwhetherthestigmapourssomefluidintotheanthersoastoexcitetheincludedgrains。Itisaratheroddcaseofcorrelation，thatinthedoublesweetvioletthesmallflowersaredouble;i。e。，haveamultitudeofminutescalesrepresentingthepetals。Whatqueerlittleflowerstheyare。
HaveyouhadtimetoreadpoordearHenslow’slife？ithasinterestedmefortheman’ssake，and，whatIdidnotthinkpossible，hasevenexaltedhischaracterinmyestimation……
[Thefollowingisanextractfromthelettergiveninpartabove，andreferstoDr。Gray’sarticleonthesexualdifferencesofplants:]
CHARLESDARWINTOASAGRAY。
NOVEMBER26[1862]……YouwillthinkthatIaminthemostunpleasant，contradictory，fractioushumour，whenItellyouthatIdonotlikeyourtermof\"precociousfertilisation\"foryoursecondclassofdimorphism[i。e。forcleistogamicfertilisation]。IfIcantrustmymemory，thestateofthecorolla，ofthestigma，andthepollen—grainsisdifferentfromthestateofthepartsinthebud;thattheyareinaconditionofspecialmodification。ButuponmylifeIamashamedofmyselftodiffersomuchfrommybettersonthishead。TheTEMPORARYtheory（Thisviewisnowgenerallyaccepted。）whichIhaveformedonthisclassofdimorphism，justtoguideexperiment，isthatthePERFECTflowerscanonlybeperfectlyfertilisedbyinsects，andareinthiscaseabundantlycrossed;butthattheflowersarenotalways，especiallyinearlyspring，visitedenoughbyinsects，andthereforethelittleimperfectself—fertilisingflowersaredevelopedtoensureasufficiencyofseedforpresentgenerations。Violacaninaissterile，whennotvisitedbyinsects，butwhensovisitedformsplentyofseed。IinferfromthestructureofthreeorfourformsofBalsamineae，thattheserequireinsects;atleastthereisalmostasplainadaptationtoinsectsasintheOrchids。IhaveOxalisacetosellareadyinpotsforexperimentnextspring;andIfearthiswillupsetmylittletheory……Campanulacarpathica，asIfoundthissummer，isabsolutelysterileifinsectsareexcluded。Speculariaspeculumisfairlyfertilewhenenclosed;andthisseemedtometobepartiallyeffectedbythefrequentclosingoftheflower;theinwardangularfoldsofthecorollacorrespondingwiththecleftsoftheopenstigma，andinthisactionpushingpollenfromtheoutsideofthestigmaontoitssurface。Nowcanyoutellme，doesS。perfoliatacloseitsflowerlikeS。speculum，withangularinwardfolds？ifso，Iamsmashedwithoutsomefearful\"wriggling。\"
AretheIMPERFECTflowersofyourSpeculariatheearlyorthelaterones？
veryearlyorverylate？ItisratherprettytoseetheimportanceoftheclosingofflowersofS。speculum。
[’FormsofFlowers’waspublishedinJuly;inJune，1877，hewrotetoProfessorCaruswithregardtothetranslation:——
\"Mynewbookisnotalongone，viz。350pages，chieflyofthelargertype，withfifteensimplewoodcuts。AlltheproofsarecorrectedexcepttheIndex，sothatitwillsoonbepublished。
\"……IdonotsupposethatIshallpublishanymorebooks，thoughperhapsafewmorepapers。Icannotendurebeingidle，butheavenknowswhetherIamcapableofanymoregoodwork。\"
Thereviewalludedtointhenextletterisatpage445ofthevolumeof’Nature’for1878:]
CHARLESDARWINTOW。THISELTONDYER。
Down，April5，1878。
MydearDyer，Ihavejustreadin’Nature’thereviewof’FormsofFlowers，’andIamsurethatitisbyyou。Iwishwithallmyheartthatitdeservedonequarterofthepraiseswhichyougiveit。Someofyourremarkshaveinterestedmegreatly……Heartythanksforyourgenerousandmostkindsympathy，whichdoesamanrealgood，whenheisasdog—tiredasIamatthisminutewithworkingallday，sogood—bye。
C。DARWIN。
CHAPTER2。XIII。
CLIMBINGANDINSECTIVOROUSPLANTS。
[Myfathermentionsinhis’Autobiography’（volumei。）thathewasledtotakeupthesubjectofclimbingplantsbyreadingDr。Gray’spaper，\"NoteontheCoilingoftheTendrilsofPlants。\"（’Proc。Amer。Acad。ofArtsandSciences，’1858。）Thisessayseemstohavebeenreadin1862，butIamonlyabletoguessatthedateoftheletterinwhichheasksforareferencetoit，sothattheprecisedateofhisbeginningthisworkcannotbedetermined。
InJune1863hewascertainlyatwork，andwrotetoSirJ。D。Hookerforinformationastopreviouspublicationsonthesubject，beingtheninignoranceofPalm’sandH。v。Mohl’sworksonclimbingplants，bothofwhichwerepublishedin1827。]
CHARLESDARWINTOJ。D。HOOKER。
Down[June]25[1863]。
MydearHooker，Ihavebeenobservingprettycarefullyalittlefactwhichhassurprisedme;andIwanttoknowfromyouandOliverwhetheritseemsneworoddtoyou，sojusttellmewheneveryouwrite;itisaverytriflingfact，sodonotansweronpurpose。
IhavegotaplantofEchinocystislobatatoobservetheirritabilityofthetendrilsdescribedbyAsaGray，andwhichofcourse，isplainenough。
Havingtheplantinmystudy，Ihavebeensurprisedtofindthattheuppermostpartofeachbranch（i。e。thestembetweenthetwouppermostleavesexcludingthegrowingtip）isCONSTANTLYandslowlytwistingroundmakingacircleinfromone—halftotwohours;itwillsometimesgoroundtwoorthreetimes，andthenatthesamerateuntwistsandtwistsinoppositedirections。Itgenerallyrestshalfanhourbeforeitretrogrades。Thestemdoesnotbecomepermanentlytwisted。Thestembeneaththetwistingportiondoesnotmoveintheleast，thoughnottied。
Themovementgoesonalldayandallearlynight。Ithasnorelationtolightfortheplantstandsinmywindowandtwistsfromthelightjustasquicklyastowardsit。ThismaybeacommonphenomenonforwhatIknow，butitconfoundedmequite，whenIbegantoobservetheirritabilityofthetendrils。Idonotsayitisthefinalcause，buttheresultispretty，fortheplanteveryoneandahalfortwohourssweepsacircle（accordingtothelengthofthebendingshootandthelengthofthetendril）offromonefoottotwentyinchesindiameter，andimmediatelythatthetendriltouchesanyobjectitssensitivenesscausesitimmediatelytoseizeit;aclevergardener，myneighbour，whosawtheplantonmytablelastnight，said:\"Ibelieve，Sir，thetendrilscansee，forwhereverIputaplantitfindsoutanysticknearenough。\"Ibelievetheaboveistheexplanation，viz。thatitsweepsslowlyroundandround。Thetendrilshavesomesense，fortheydonotgraspeachotherwhenyoung。
Yoursaffectionately，C。DARWIN。
CHARLESDARWINTOJ。D。HOOKER。
Down，July14[1863]。
MydearHooker，Iamgettingverymuchamusedbymytendrils，itisjustthesortofnigglingworkwhichsuitsme，andtakesupnotimeandratherrestsmewhilstwriting。Sowillyoujustthinkwhetheryouknowanyplant，whichyoucouldgiveorlendme，orIcouldbuy，withtendrils，remarkableinanywayfordevelopment，foroddorpeculiarstructure，orevenforanoddplaceinnaturalarrangement。IhaveseenorcanseeCucurbitaceae，Passion—flower，Virginian—creeper，Cissusdiscolor，Common—peaandEverlasting—pea。Itisreallycuriousthediversificationofirritability（Idonotmeanthespontaneousmovement，aboutwhichIwrotebeforeandcorrectly，asfurtherobservationshows）:forinstance，IfindaslightpinchbetweenthethumbandfingerattheendofthetendriloftheCucurbitaceaecausespromptmovement，butapinchexcitesnomovementinCissus。Thecauseisthatonesidealone（theconcave）isirritableintheformer;whereasbothsidesareirritableinCissus，soifyouexciteatthesametimebothOPPOSITEsidesthereisnomovement，butbytouchingwithapencilthetwobranchesofthetendril，inanypartwhatever，youcausemovementtowardsthatpoint;sothatIcanmould，byameretouch，thetwobranchesintoanyshapeIlike……
CHARLESDARWINTOASAGRAY。
Down，August4[1863]。
Mypresenthobby—horseIowetoyou，viz。thetendrils:theirirritabilityisbeautiful，asbeautifulinallitsmodificationsasanythinginOrchids。
AbouttheSPONTANEOUSmovement（independentoftouch）ofthetendrilsandupperinternodes，Iamrathertakenabackbyyoursaying，\"isitnotwell—
known？\"IcanfindnothinginanybookwhichIhave……Thespontaneousmovementofthetendrilsisindependentofthemovementoftheupperinternodes，butbothworkharmoniouslytogetherinsweepingacircleforthetendrilstograspastick。Sowithallclimbingplants（withouttendrils）asyetexamined，theupperinternodesgoonnightanddaysweepingacircleinonefixeddirection。ItissurprisingtowatchtheApocyneaewithshoots18incheslong（beyondthesupportingstick），steadilysearchingforsomethingtoclimbup。Whentheshootmeetsastick，themotionatthatpointisarrested，butintheupperpartiscontinued;sothattheclimbingofallplantsyetexaminedisthesimpleresultofthespontaneouscirculatorymovementoftheupperinternodes。
Praytellmewhetheranythinghasbeenpublishedonthissubject？Ihatepublishingwhatisold;butIshallhardlyregretmyworkifitisold，asithasmuchamusedme……
CHARLESDARWINTOASAGRAY。
May28，1864……AnIrishnoblemanonhisdeath—beddeclaredthathecouldconscientiouslysaythathehadneverthroughoutlifedeniedhimselfanypleasure;andIcanconscientiouslysaythatIhaveneverscrupledtotroubleyou;soheregoes。——HaveyoutravelledSouth，andcanyoutellmewhetherthetrees，whichBignoniacapreolataclimbs，arecoveredwithmossorfilamentouslichenorTillandsia？（HesubsequentlylearnedfromDr。
GraythatPolypodiumincanumaboundsonthetreesinthedistrictswherethisspeciesofBignoniagrows。See’ClimbingPlants，’page103。）Iaskbecauseitstendrilsabhorasimplestick，donotmuchrelishroughbark，butdelightinwoolormoss。Theyadhereinacuriousmannerbymakinglittledisks，liketheAmpelopsis……Bytheway，Iwillenclosesomespecimens，andifyouthinkitworthwhile，youcanputthemunderthesimplemicroscope。Itisremarkablehowspeciallyadaptedsometendrilsare;thoseofEccremocarpusscaberdonotlikeastick，willhavenothingtosaytowool;butgivethemabundleofculmsofgrass，orabundleofbristlesandtheyseizethemwell。