Withthevarietiesofmanyplants，theadaptationtoclimateisoftenveryclose。Thusithasbeenprovedbyrepeatedtrials"thatfewifanyoftheEnglishvarietiesofwheatareadaptedforcultivationinScotland"（24/54。
’Gardener’sChronicle’1851page396。）;butthefailureinthiscaseisatfirstonlyinthequantity，thoughultimatelyinthequality，ofthegrainproduced。TheRev。M。J。Berkeleysowedwheat—seedfromIndia，andgot"themostmeagreears，"onlandwhichwouldcertainlyhaveyieldedagoodcropfromEnglishwheat。（24/55。Ibid1862page235。）Inthesecasesvarietieshavebeencarriedfromawarmertoacoolerclimate;inthereversecase，as"whenwheatwasimporteddirectlyfromFranceintotheWestIndianIslands，itproducedeitherwhollybarrenspikesorfurnishedwithonlytwoorthreemiserableseeds，whileWestIndianseedbyitssideyieldedanenormousharvest。"
（24/56。OntheauthorityofLabatquotedin’Gardener’sChronicle’1862page235。）Hereisanothercaseofcloseadaptationtoaslightlycoolerclimate;akindofwheatwhichinEnglandmaybeusedindifferentlyeitherasawinterorsummervariety，whensownunderthewarmerclimateofGrignan，inFrance，behavedexactlyasifithadbeenatruewinterwheat。（24/57。MM。EdwardsandColin’Annal。desSc。Nat。’2ndseriesBot。tome5page22。）
Botanistsbelievethatallthevarietiesofmaizebelongtothesamespecies;
andwehaveseenthatinNorthAmerica，inproceedingnorthward，thevarietiescultivatedineachzoneproducetheirflowersandripentheirseedwithinshorterandshorterperiods。Sothatthetall，slowlymaturingsouthernvarietiesdonotsucceedinNewEngland，andtheNewEnglishvarietiesdonotsucceedinCanada。Ihavenotmetwithanystatementthatthesouthernvarietiesareactuallyinjuredorkilledbyadegreeofcoldwhichthenorthernvarietiescanwithstandwithimpunity，thoughthisisprobable;buttheproductionofearlyfloweringandearlyseedingvarietiesdeservestobeconsideredasoneformofacclimatisation。Henceithasbeenfoundpossible，accordingtoKalm，tocultivatemaizefurtherandfurthernorthwardsinAmerica。InEurope，also，aswelearnfromtheevidencegivenbyAlph。DeCandolle，thecultureofmaizehasextendedsincetheendofthelastcenturythirtyleaguesnorthofitsformerboundary。（24/58。’Geograph。Bot。’page337。）OntheauthorityofLinnaeus（24/59。’SwedishActs’Englishtranslation1739—40volume1。Kalminhis’Travels’volume2page166givesananalogouscasewithcotton—plantsraisedinNewJerseyfromCarolinaseed。），Imayquoteananalogouscase，namely，thatinSwedentobaccoraisedfromhome—grownseedripensitsseedamonthsoonerandislessliabletomiscarrythanplantsraisedfromforeignseed。
WiththeVine，differentlyfromthemaize，thelineofpracticalculturehasretreatedalittlesouthwardsincethemiddleages（24/60。DeCandolle’Geograph。Bot。’page339。）;butthisseemsduetocommercebeingnoweasier，sothatitisbettertoimportwinefromthesouththantomakeitinnortherndistricts。Neverthelessthefactofthevinenothavingspreadnorthwardshowsthatacclimatisationhasmadenoprogressduringseveralcenturies。Thereis，however，amarkeddifferenceintheconstitutionoftheseveralvarieties，——
somebeinghardy，whilstothers，likethemuscatofAlexandria，requireaveryhightemperaturetocometoperfection。AccordingtoLabat（24/61。’Gardener’sChronicle’1862page235。），vinestakenfromFrancetotheWestIndiessucceedwithextremedifficulty，whilstthoseimportedfromMadeiraortheCanaryIslandsthriveadmirably。
GallesiogivesacuriousaccountofthenaturalisationoftheOrangeinItaly。
Duringmanycenturiesthesweetorangewaspropagatedexclusivelybygrafts，andsooftensufferedfromfrosts，thatitrequiredprotection。Aftertheseverefrostof1709，andmoreespeciallyafterthatof1763，somanytreesweredestroyed，thatseedlingsfromthesweetorangewereraised，and，tothesurpriseoftheinhabitants，theirfruitwasfoundtobesweet。Thetreesthusraisedwerelarger，moreproductive，andhardierthantheoldkinds;andseedlingsarenowcontinuallyraised。HenceGallesioconcludesthatmuchmorewaseffectedforthenaturalisationoftheorangeinItalybytheaccidentalproductionofnewkindsduringaperiodofaboutsixtyyears，thanhadbeeneffectedbygraftingoldvarietiesduringmanyages。（24/62。Gallesio’TeoriadellaRiproduzioneVeg。’1816page125;and’TraiteduCitrus’1811page359。）
ImayaddthatRisso（24/63。’Essaisurl’Hist。desOrangers’1813page20
etc。）describessomePortuguesevarietiesoftheorangeasextremelysensitivetocold，andasmuchtendererthancertainothervarieties。
ThepeachwasknowntoTheophrastus，322B。C。（24/64。Alph。deCandolle’Geograph。Bot。’page882。）AccordingtotheauthoritiesquotedbyDr。F。
Rolle（24/65。’Ch。Darwin’sLehrevonderEntstehung’etc。1862s。87。），itwastenderwhenfirstintroducedintoGreece，andevenintheislandofRhodesonlyoccasionallyborefruit。Ifthisbecorrect，thepeach，inspreadingduringthelasttwothousandyearsoverthemiddlepartsofEurope，musthavebecomemuchhardier。Atthepresentdaydifferentvarietiesdiffermuchinhardiness:someFrenchvarietieswillnotsucceedinEngland;andnearParis，thePaviedeBonneuildoesnotripenitsfruittillverylateintheseason，evenwhengrownonawall;"itis，therefore，onlyfitforaveryhotsouthernclimate。"（24/66。Decaisnequotedin’Gardener’sChronicle’1865page271。）
Iwillbrieflygiveafewothercases。AvarietyofMagnoliagrandiflora，raisedbyM。Roy，withstandsatemperatureseveraldegreeslowerthanthatwhichanyothervarietycanresist。Withcamelliasthereismuchdifferenceinhardiness。OneparticularvarietyoftheNoisetterosewithstoodtheseverefrostof1860"untouchedandhaleamidstauniversaldestructionofotherNoisettes。"InNewYorkthe"Irishyewisquitehardy，butthecommonyewisliabletobecutdown。"Imayaddthattherearevarietiesofthesweetpotato（Convolvulusbatatas）whicharesuitedforwarmer，aswellasforcolder，climates。（24/67。ForthemagnoliaseeLoudon’s’Gardener’sMag。’volume13
1837page21。Forcamelliasandrosessee’Gardener’sChronicle’1860page384。Fortheyew’JournalofHort。’March3，1863p174。ForsweetpotatoesseeCol。vonSieboldin’Gardener’sChronicle’1855page822。）]
Theplantsasyetmentionedhavebeenfoundcapableofresistinganunusualdegreeofcoldorheat，whenfullygrown。Thefollowingcasesrefertoplantswhilstyoung。InalargebedofyoungAraucariasofthesameage，growingclosetogetherandequallyexposed，itwasobserved（24/68。TheEditor’Gardener’sChronicle’1861page239。），aftertheunusuallyseverewinterof1860—61，that，"inthemidstofthedying，numerousindividualsremainedonwhichthefrosthadabsolutelymadenokindofimpression。"Dr。Lindley，afteralludingtothisandothersimilarcases，remarks，"Amongthelessonswhichthelateformidablewinterhastaughtus，isthat，evenintheirpowerofresistingcold，individualsofthesamespeciesofplantsareremarkablydifferent。"NearSalisbury，therewasasharpfrostonthenightofMay24，1836，andalltheFrenchbeans（Phaseolusvulgaris）inabedwerekilledexceptaboutoneinthirty，whichcompletelyescaped。（24/69。Loudon’s’Gardener’sMag。’volume121836page378。）Onthesamedayofthemonth，butintheyear1864，therewasaseverefrostinKent，andtworowsofscarlet—
runners（P。multiflorus）inmygarden，containing390plantsofthesameageandequallyexposed，wereallblackenedandkilledexceptaboutadozenplants。Inanadjoiningrowof"Fulmer’sdwarfbean"（P。vulgaris），onesingleplantescaped。Astillmoreseverefrostoccurredfourdaysafterwards，andofthedozenplantswhichhadpreviouslyescapedonlythreesurvived;thesewerenottallerormorevigorousthantheotheryoungplants，buttheyescapedcompletely，withnoteventhetipsoftheirleavesbrowned。Itwasimpossibletobeholdthesethreeplants，withtheirblackened，withered，anddeadbrethrenallaround，andnotseeataglancethattheydifferedwidelyinconstitutionalpowerofresistingfrost。
Thisworkisnottheproperplacetoshowthatwildplantsofthesamespecies，naturallygrowingatdifferentaltitudesorunderdifferentlatitudes，becometoacertainextentacclimatised，asisprovedbythedifferentbehaviouroftheirseedlingswhenraisedinanothercountry。Inmy’OriginofSpecies’Ihavealludedtosomecases，andIcouldaddmanyothers。
Oneinstancemustsuffice:Mr。Grigor，ofForres（24/70。’Gardener’sChronicle’1865page699。Mr。G。Mawgives（’Gardener’sChronicle’1870page895）anumberofstrikingcases;hebroughthomefromsouthernSpainandnorthernAfricaseveralplants，whichhecultivatedinEnglandalongsidespecimensfromnortherndistricts;andhefoundagreatdifferencenotonlyintheirhardinessduringthewinter，butinthebehaviourofsomeofthemduringthesummer。），statesthatseedlingsoftheScotchfir（Pinussylvestris），raisedfromseedfromtheContinentandfromtheforestsofScotland，differmuch。"Thedifferenceisperceptibleinone—year—old，andmoresointwo—year—
oldseedlings;buttheeffectsofthewinteronthesecondyear’sgrowthalmostuniformlymakethosefromtheContinentquitebrown，andsodamaged，thatbythemonthofMarchtheyarequiteunsaleable，whiletheplantsfromthenativeScotchpine，underthesametreatment，andstandingalongside，althoughconsiderablyshorter，areratherstouterandquitegreen，sothatthebedsoftheonecanbeknownfromtheotherwhenseenfromthedistanceofamile。"Closelysimilarfactshavebeenobservedwithseedlinglarches。
[HardyvarietieswouldalonebevaluedornoticedinEurope;whilsttendervarieties，requiringmorewarmth，wouldgenerallybeneglected;butsuchoccasionallyarise。ThusLoudon（24/71。’ArboretumetFruticetum’volume3
page1376。）describesaCornishvarietyoftheelmwhichisalmostanevergreen，andofwhichtheshootsareoftenkilledbytheautumnalfrosts，sothatitstimberisoflittlevalue。Horticulturistsknowthatsomevarietiesaremuchmoretenderthanothers:thusallthevarietiesofthebroccoliaremoretenderthancabbages;butthereismuchdifferenceinthisrespectinthesub—varietiesofthebroccoli;thepinkandpurplekindsarealittlehardierthanthewhiteCapebroccoli，"buttheyarenottobedependedonafterthethermometerfallsbelow24degFahr。;"theWalcherenbroccoliislesstenderthantheCape，andthereareseveralvarietieswhichwillstandmuchseverercoldthantheWalcheren。（24/72。Mr。Robsonin’JournalofHorticulture’1861
page23。）CauliflowersseedmorefreelyinIndiathancabbages。（24/73。Dr。
Bonavia’ReportoftheAgri。—Hort。Soc。ofOudh’1866。）Togiveoneinstancewithflowers:elevenplantsraisedfromahollyhock，calledtheQueenoftheWhites（24/74。’CottageGardener’1860April24page57。）werefoundtobemuchmoretenderthanvariousotherseedlings。Itmaybepresumedthatalltendervarietieswouldsucceedbetterunderaclimatewarmerthanours。Withfruit—trees，itiswellknownthatcertainvarieties，forinstanceofthepeach，standforcinginahot—housebetterthanothers;andthisshowseitherpliabilityoforganisationorsomeconstitutionaldifference。Thesameindividualcherry—tree，whenforced，hasbeenobservedduringsuccessiveyearsgraduallytochangeitsperiodofvegetation。（24/75。’Gardener’sChronicle’
1841page291。）Fewpelargoniumscanresisttheheatofastove，butAlbaMultiflorawill，asamostskilfulgardenerasserts，"standpine—appletopandbottomheatthewholewinter;withoutlookinganymoredrawnthanifithadstoodinacommongreenhouse;andBlancheFleurseemsasifithadbeenmadeonpurposeforgrowinginwinter，likemanybulbs，andtorestallsummer。"
（24/76。Mr。Beatonin’CottageGardener’March20，1860page377。QueenMabwillalsostandstoveheat。See’Gardener’sChronicle’1845page226。）TherecanhardlybeadoubtthattheAlbaMultiflorapelargoniummusthaveawidelydifferentconstitutionfromthatofmostothervarietiesofthisplant;itwouldprobablywithstandevenanequatorialclimate。
WehaveseenthataccordingtoLabatthevineandwheatrequireacclimatisationinordertosucceedintheWestIndies。SimilarfactshavebeenobservedatMadras:"twoparcelsofmignonette—seed，onedirectfromEurope，theothersavedatBangalore（ofwhichthemeantemperatureismuchbelowthatofMadras），weresownatthesametime:theybothvegetatedequallyfavourably，buttheformeralldiedoffafewdaysaftertheyappearedaboveground;thelatterstillsurvive，andarevigorous，healthyplants。""Soagain，turnipandcarrotseedsavedatHyderabadarefoundtoanswerbetteratMadrasthanseedfromEuropeorfromtheCapeofGoodHope。"（24/77。
’Gardener’sChronicle’1841page439。）Mr。J。ScottoftheCalcuttaBotanicGardens，informsmethatseedsofthesweet—pea（Lathyrusodoratus）importedfromEnglandproduceplants，withthick，rigidstemsandsmallleaves，whichrarelyblossomandneveryieldseed;plantsraisedfromFrenchseedblossomsparingly，butalltheflowersaresterile;ontheotherhand，plantsraisedfromsweet—peasgrownnearDarjeelinginUpperIndia，butoriginallyderivedfromEngland，canbesuccessfullycultivatedontheplainsofIndia;fortheyflowerandseedprofusely，andtheirstemsarelaxandscandent。Insomeoftheforegoingcases，asDr。Hookerhasremarkedtome，thegreatersuccessmayperhapsbeattributedtotheseedshavingbeenmorefullyripenedunderamorefavourableclimate;butthisviewcanhardlybeextendedtosomanycases，includingplants，which，frombeingcultivatedunderaclimatehotterthantheirnativeone，becomefittedforastillhotterclimate。Wemaythereforesafelyconcludethatplantscantoacertainextentbecomeaccustomedtoaclimateeitherhotterorcolderthantheirown;althoughthelattercaseshavebeenmorefrequentlyobserved。]
Wewillnowconsiderthemeansbywhichacclimatisationmaybeeffected，namely，throughtheappearanceofvarietieshavingadifferentconstitution，andthroughtheeffectsofhabit。Inregardtonewvarieties，thereisnoevidencethatachangeintheconstitutionoftheoffspringnecessarilystandsinanydirectrelationwiththenatureoftheclimateinhabitedbytheparents。Onthecontrary，itiscertainthathardyandtendervarietiesofthesamespeciesappearinthesamecountry。Newvarietiesthusspontaneouslyarisingbecomefittedtoslightlydifferentclimatesintwodifferentways;
firstly，theymayhavethepower，eitherasseedlingsorwhenfull—grown，ofresistingintensecold，aswiththeMoscowpear，orofresistingintenseheat，aswithsomekindsofPelargonium，ortheflowersmaywithstandseverefrost，aswiththeForellepear。Secondly，plantsmaybecomeadaptedtoclimateswidelydifferentfromtheirown，fromfloweringandfruitingeitherearlierorlaterintheseason。Inboththesecasesthepowerofacclimatisationbymanconsistssimplyintheselectionandpreservationofnewvarieties。Butwithoutanydirectintentiononhispartofsecuringahardiervariety，acclimatisationmaybeunconsciouslyeffectedbymerelyraisingtenderplantsfromseed，andbyoccasionallyattemptingtheircultivationfurtherandfurthernorthwards，asinthecaseofmaize，theorangeandthepeach。
Howmuchinfluenceoughttobeattributedtoinheritedhabitorcustomintheacclimatisationofanimalsandplantsisamuchmoredifficultquestion。Inmanycasesnaturalselectioncanhardlyhavefailedtohavecomeintoplayandcomplicatedtheresult。Itisnotoriousthatmountainsheepresistsevereweatherandstormsofsnowwhichwoulddestroylowlandbreeds;butthenmountainsheephavebeenthusexposedfromtimeimmemorial，andalldelicateindividualswillhavebeendestroyed，andthehardiestpreserved。SowiththeArrindysilk—mothsofChinaandIndia;whocantellhowfarnaturalselectionmayhavetakenashareintheformationofthetworaces，whicharenowfittedforsuchwidelydifferentclimates？Itseemsatfirstprobablethatthemanyfruit—treeswhicharesowellfittedforthehotsummersandcoldwintersofNorthAmerica，incontrastwiththeirpoorsuccessunderourclimate，havebecomeadaptedthroughhabit;butwhenwereflectonthemultitudeofseedlingsannuallyraisedinthatcountry，andthatnonewouldsucceedunlessbornwithafittingconstitution，itispossiblethatmerehabitmayhavedonenothingtowardstheiracclimatisation。Ontheotherhand，whenwehearthatMerinosheep，bredduringnogreatnumberofgenerationsattheCapeofGoodHope——thatsomeEuropeanplantsraisedduringonlyafewgenerationsinthecoolerpartsofIndia，withstandthehotterpartsofthatcountrymuchbetterthanthesheeporseedsimporteddirectlyfromEngland，wemustattributesomeinfluencetohabit。WeareledtothesameconclusionwhenwehearfromNaudin（24/78。QuotedbyAsaGrayin’Am。Journ。ofSc。’2ndseriesJanuary1865page106。）thattheracesofmelons，squashes，andgourds，whichhavelongbeencultivatedinNorthernEurope，arecomparativelymoreprecocious，andneedmuchlessheatformaturingtheirfruit，thanthevarietiesofthesamespeciesrecentlybroughtfromtropicalregions。Inthereciprocalconversionofsummerandwinterwheat，barley，andvetchesintoeachother，habitproducesamarkedeffectinthecourseofaveryfewgenerations。Thesamethingapparentlyoccurswiththevarietiesofmaize，which，whencarriedfromtheSouthernStatesofAmerica，orintoGermany，soonbecameaccustomedtotheirnewhomes。Withvine—plantstakentotheWestIndiesfromMadeira，whicharesaidtosucceedbetterthanplantsbroughtdirectlyfromFrance，wehavesomedegreeofacclimatisationintheindividual，independentlyoftheproductionofnewvarietiesbyseed。
Thecommonexperienceofagriculturistsisofsomevalue，andtheyoftenadvisepersonstobecautiousintryingtheproductionsofonecountryinanother。TheancientagriculturalwritersofChinarecommendthepreservationandcultivationofthevarietiespeculiartoeachcountry。Duringtheclassicalperiod，Columellawrote，"Vernaculumpecusperegrinolongepraestantiusest。"（24/79。ForChinasee’MemoiresurlesChinois’tome11
1786page60。ColumellaisquotedbyCarlierin’JournaldePhysique’tome24
1784。）
Iamawarethattheattempttoacclimatiseeitheranimalsorplantshasbeencalledavainchimera。Nodoubttheattemptinmostcasesdeservestobethuscalled，ifmadeindependentlyoftheproductionofnewvarietiesendowedwithadifferentconstitution。Withplantspropagatedbybuds，habitrarelyproducesanyeffect;itapparentlyactsonlythroughsuccessiveseminalgenerations。Thelaurel，bay，laurestinus，etc。，andtheJerusalemartichoke，whicharepropagatedbycuttingsortubers，areprobablynowastenderinEnglandaswhenfirstintroduced;andthisappearstobethecasewiththepotato，whichuntilrecentlywasseldommultipliedbyseed。Withplantspropagatedbyseed，andwithanimals，therewillbelittleornoacclimatisationunlessthehardierindividualsareeitherintentionallyorunconsciouslypreserved。Thekidney—beanhasoftenbeenadvancedasaninstanceofaplantwhichhasnotbecomehardiersinceitsfirstintroductionintoBritain。Wehear，however，onexcellentauthority（24/80。Messrs。HardyandSonin’Gardener’sChronicle’1856page589。）thatsomeveryfineseed，importedfromabroad，producedplants"whichblossomedmostprofusely，butwerenearlyallbutabortive，whilstplantsgrownalongsidefromEnglishseedpoddedabundantly;"andthisapparentlyshowssomedegreeofacclimatisationinourEnglishplants。Wehavealsoseenthatseedlingsofthekidney—beanoccasionallyappearwithamarkedpowerofresistingfrost;butnoone，asfarasIcanhear，haseverseparatedsuchhardyseedlings，soastopreventaccidentalcrossing，andthengatheredtheirseed，andrepeatedtheprocessyearafteryear。Itmay，however，beobjectedwithtruththatnaturalselectionoughttohavehadadecidedeffectonthehardinessofourkidney—
beans;forthetenderestindividualsmusthavebeenkilledduringeveryseverespring，andthehardierpreserved。Butitshouldbeborneinmindthattheresultofincreasedhardinesswouldsimplybethatgardeners，whoarealwaysanxiousforasearlyacropaspossible，wouldsowtheirseedafewdaysearlierthanformerly。Now，astheperiodofsowingdependsmuchonthesoilandelevationofeachdistrict，andvarieswiththeseason;andasnewvarietieshaveoftenbeenimportedfromabroad，canwefeelsurethatourkidney—beansarenotsomewhathardier？Ihavenotbeenable，bysearchingoldhorticulturalworks，toanswerthisquestionsatisfactorily。
Onthewholethefactsnowgivenshowthat，thoughhabitdoessomethingtowardsacclimatisation，yetthattheappearanceofconstitutionallydifferentindividualsisafarmoreeffectiveagent。Asnosingleinstancehasbeenrecordedeitherwithanimalsorplantsofhardierindividualshavingbeenlongandsteadilyselected，thoughsuchselectionisadmittedtobeindispensablefortheimprovementofanyothercharacter，itisnotsurprisingthatmanhasdonelittleintheacclimatisationofdomesticatedanimalsandcultivatedplants。Weneednot，however，doubtthatundernaturenewracesandnewspecieswouldbecomeadaptedtowidelydifferentclimates，byvariation，aidedbyhabit，andregulatedbynaturalselection。
[ARRESTSOFDEVELOPMENT:RUDIMENTARYANDABORTEDORGANS。
Modificationsofstructurefromarresteddevelopment，sogreatorsoseriousastodeservetobecalledmonstrosities，arenotinfrequentwithdomesticatedanimals，but，astheydiffermuchfromanynormalstructure，theyrequireonlyapassingnotice。Thusthewholeheadmayberepresentedbyasoftnipple—likeprojection，andthelimbsbymerepapillae。Theserudimentsoflimbsaresometimesinherited，ashasbeenobservedinadog。（24/81。Isid。GeoffroySaint—Hilaire’Hist。Nat。desAnomalies’1836tome2pages210，223，224，395;
’Philosoph。Transact。’1775page313。）
Manylesseranomaliesappeartobeduetoarresteddevelopment。Whatthecauseofthearrestmaybe，weseldomknow，exceptinthecaseofdirectinjurytotheembryo。Thatthecausedoesnotgenerallyactatanextremelyearlyembryonicperiodwemayinferfromtheaffectedorganseldombeingwhollyaborted，——arudimentbeinggenerallypreserved。TheexternalearsarerepresentedbymerevestigesinaChinesebreedofsheep;andinanotherbreed，thetailisreduced"toalittlebutton，suffocatedinamanner，byfat。"（24/82。PallasquotedbyYouatton’Sheep’page25。）Intaillessdogsandcatsastumpisleft。Incertainbreedsoffowlsthecombandwattlesarereducedtorudiments;intheCochin—Chinabreedscarcelymorethanrudimentsofspursexist。WithpolledSuffolkcattle，"rudimentsofhornscanoftenbefeltatanearlyage"（24/83。Youatton’Cattle’1834page174。）;andwithspeciesinastateofnature，therelativelygreatdevelopmentofrudimentaryorgansatanearlyperiodoflifeishighlycharacteristicofsuchorgans。
Withhornlessbreedsofcattleandsheep，anotherandsingularkindofrudimenthasbeenobserved，namely，minutedanglinghornsattachedtotheskinalone，andwhichareoftenshedandgrowagain。Withhornlessgoats，accordingtoDesmarest（24/84。’Encyclop。Method。’1820page483:seepage500，ontheIndianzebucastingitshorns。SimilarcasesinEuropeancattleweregiveninthethirdchapter。），thebonyprotuberancewhichproperlysupportsthehornexistsasamererudiment。
Withcultivatedplantsitisfarfromraretofindthepetals，stamens，andpistilsrepresentedbyrudiments，likethoseobservedinnaturalspecies。Soitiswiththewholeseedinmanyfruits;thus，nearAstrakhanthereisagrapewithmeretracesofseeds，"sosmallandlyingsonearthestalkthattheyarenotperceivedineatingthegrape。"（24/85。Pallas’Travels’EnglishTranslat。volume1page243。）Incertainvarietiesofthegourd，thetendrils，accordingtoNaudin，arerepresentedbyrudimentsorbyvariousmonstrousgrowths。Inthebroccoliandcauliflowerthegreaternumberoftheflowersareincapableofexpansion，andincluderudimentaryorgans。IntheFeatherhyacinth（Muscaricomosum）initsnaturalstatetheupperandcentralflowersarebrightlycolouredbutrudimentary;undercultivationthetendencytoabortiontravelsdownwardsandoutwards，andalltheflowersbecomerudimentary;buttheabortivestamensandpistilsarenotsosmallinthelowerasintheupperflowers。IntheViburnumopulus，ontheotherhand，theouterflowersnaturallyhavetheirorgansoffructificationinarudimentarystate，andthecorollaisoflargesize;undercultivation，thechangespreadstothecentre，andalltheflowersbecomeaffected。Inthecompositae，theso—
calleddoublingoftheflowersconsistsinthegreaterdevelopmentofthecorollaofthecentralflorets，generallyaccompaniedwithsomedegreeofsterility;andithasbeenobserved（24/86。Mr。Beatonin’JournalofHorticulture’May21，1861page133。）thattheprogressivedoublinginvariablyspreadsfromthecircumferencetothecentre，——thatis，fromtherayflorets，whichsooftenincluderudimentaryorgans，tothoseofthedisc。Imayadd，asbearingonthissubject，thatwithAsters，seedstakenfromthefloretsofthecircumferencehavebeenfoundtoyieldthegreatestnumberofdoubleflowers。
（24/87。Lecoq’DelaFecondation’1862page233。）Intheabovecaseswehaveanaturaltendencyincertainpartstoberudimentary，andthisunderculturespreadseitherto，orfrom，theaxisoftheplant。Itdeservesnotice，asshowinghowthesamelawsgovernthechangeswhichnaturalspeciesandartificialvarietiesundergo，thatinthespeciesofCarthamus，oneoftheCompositae，atendencytotheabortionofthepappusmaybetracedextendingfromthecircumferencetothecentreofthediscasintheso—calleddoublingoftheflowersinthemembersofthesamefamily。Thus，accordingtoA。deJussieu（24/88。’AnnalesduMuseum’tome6page319。），theabortionisonlypartialinCarthamuscreticus，butmoreextendedinC。lanatus;forinthisspeciesonlytwoorthreeofthecentralseedsarefurnishedwithapappus，thesurroundingseedsbeingeitherquitenakedorfurnishedwithafewhairs;
andlastlyinC。tinctorius，eventhecentralseedsaredestituteofpappus，andtheabortioniscomplete。
Withanimalsandplantsunderdomestication，whenanorgandisappears，leavingonlyarudiment，thelosshasgenerallybeensudden，aswithhornlessandtaillessbreeds;andsuchcasesmayberankedasinheritedmonstrosities。Butinsomefewcasesthelosshasbeengradual，andhasbeeneffectedpartlybyselection，aswiththerudimentarycombsandwattlesofcertainfowls。Wehavealsoseenthatthewingsofsomedomesticatedbirdshavebeenslightlyreducedbydisuse，andthegreatreductionofthewingsincertainsilk—moths，withmererudimentsleft，hasprobablybeenaidedbydisuse。]
Withspeciesinastateofnature，rudimentaryorgansareextremelycommon。
Suchorgansaregenerallyvariable，asseveralnaturalistshaveobserved;for，beinguseless，theyarenotregulatedbynaturalselection，andtheyaremoreorlessliabletoreversion。Thesamerulecertainlyholdsgoodwithpartswhichhavebecomerudimentaryunderdomestication。Wedonotknowthroughwhatstepsundernaturerudimentaryorganshavepassedinbeingreducedtotheirpresentcondition;butwesoincessantlyseeinspeciesofthesamegroupthefinestgradationsbetweenanorganinarudimentaryandperfectstate，thatweareledtobelievethatthepassagemusthavebeenextremelygradual。Itmaybedoubtedwhetherachangeofstructuresoabruptasthesuddenlossofanorganwouldeverbeofservicetoaspeciesinastateofnature;fortheconditionstowhichallorganismsarecloselyadaptedusuallychangeveryslowly。Evenifanorgandidsuddenlydisappearinsomeoneindividualbyanarrestofdevelopment，intercrossingwiththeotherindividualsofthesamespecieswouldtendtocauseitspartialreappearance;sothatitsfinalreductioncouldonlybeeffectedbysomeothermeans。Themostprobableviewis，thatapartwhichisnowrudimentary，wasformerly，owingtochangedhabitsoflife，usedlessandless，beingatthesametimereducedinsizebydisuse，untilatlastitbecamequiteuselessandsuperfluous。Butasmostpartsororgansarenotbroughtintoactionduringanearlyperiodoflife，disuseordecreasedactionwillnotleadtotheirreductionuntiltheorganismarrivesatasomewhatadvancedage;andfromtheprincipleofinheritanceatcorrespondingagesthereductionwillbetransmittedtotheoffspringatthesameadvancedstageofgrowth。Thepartororganwillthusretainitsfullsizeintheembryo，asweknowtobethecasewithmostrudiments。Assoonasapartbecomesuseless，anotherprinciple，thatofeconomyofgrowth，willcomeintoplay，asitwouldbeanadvantagetoanorganismexposedtoseverecompetitiontosavethedevelopmentofanyuselesspart;andindividualshavingthepartlessdevelopedwillhaveaslightadvantageoverothers。But，asMr。Mivarthasjustlyremarked，assoonasapartismuchreduced，thesavingfromitsfurtherreductionwillbeutterlyinsignificant;sothatthiscannotbeeffectedbynaturalselection。Thismanifestlyholdsgoodifthepartbeformedofmerecellulartissue，entailinglittleexpenditureofnutriment。Howthencanthefurtherreductionofanalreadysomewhatreducedpartbeeffected？ThatthishasoccurredrepeatedlyunderNatureisshownbythemanygradationswhichexistbetweenorgansinaperfectstateandthemerestvestigesofthem。Mr。Romanes（24/89。Isuggestedin’Nature’（volume8
pages432，505）thatwithorganismssubjectedtounfavourableconditionsallthepartswouldtendtowardsreduction，andthatundersuchcircumstancesanypartwhichwasnotkeptuptoitsstandardsizebynaturalselectionwould，owingtointercrossing，slowlybutsteadilydecrease。Inthreesubsequentcommunicationsto’Nature’（March12，April9，andJuly2，1874），Mr。Romanesgiveshisimprovedview。）has，Ithink，thrownmuchlightonthisdifficultproblem。Hisview，asfarasitcanbegiveninafewwords，isasfollows:
allpartsaresomewhatvariableandfluctuateinsizeroundanaveragepoint。
Now，whenaparthasalreadybegunfromanycausetodecrease，itisveryimprobablethatthevariationsshouldbeasgreatinthedirectionofincreaseasofdiminution;forthepreviousreductionshowsthatcircumstanceshavenotbeenfavourableforitsdevelopment;whilstthereisnothingtocheckvariationsintheoppositedirection。Ifthisbeso，thelongcontinuedcrossingofmanyindividualsfurnishedwithanorganwhichfluctuatesinagreaterdegreetowardsdecreasethantowardsincrease，willslowlybutsteadilyleadtoitsdiminution。Withrespecttothecompleteandabsoluteabortionofapart，adistinctprinciple，whichwillbediscussedinthechapteronpangenesis，probablycomesintoaction。
Withanimalsandplantsrearedbymanthereisnosevereorrecurrentstruggleforexistence，andtheprincipleofeconomywillnotcomeintoaction，sothatthereductionofanorganwillnotthusbeaided。Sofar，indeed，isthisfrombeingthecase，thatinsomefewinstancesorgans，whicharenaturallyrudimentaryintheparent—species，becomepartiallyredevelopedinthedomesticateddescendants。Thuscows，likemostotherruminants，properlyhavefouractiveandtworudimentarymamma;butinourdomesticatedanimals，thelatteroccasionallybecomeconsiderablydevelopedandyieldmilk。Theatrophiedmammae，which，inmaledomesticatedanimals，includingman，haveinsomerarecasesgrowntofullsizeandsecretedmilk，perhapsofferananalogouscase。Thehindfeetofdogsnaturallyincluderudimentsofafifthtoe，andincertainlargebreedsthesetoes，thoughstillrudimentary，becomeconsiderablydevelopedandarefurnishedwithclaws。InthecommonHen，thespursandcombarerudimentary，butincertainbreedsthesebecome，independentlyofageordiseaseoftheovaria，welldeveloped。Thestallionhascanineteeth，butthemarehasonlytracesofthealveoli，which，asIaminformedbytheeminentveterinarianMr。G。T。Brown，frequentlycontainminuteirregularnodulesofbone。Thesenodules，however，sometimesbecomedevelopedintoimperfectteeth，protrudingthroughthegumsandcoatedwithenamel;andoccasionallytheygrowtoafourthorevenathirdofthelengthofthecaninesinthestallion。WithplantsIdonotknowwhethertheredevelopmentofrudimentaryorgansoccursmorefrequentlyunderculturethanundernature。
Perhapsthepear—treemaybeacaseinpoint，forwhenwilditbearsthorns，whichconsistofbranchesinarudimentaryconditionandserveasaprotection，but，whenthetreeiscultivated，theyarereconvertedintobranches。
CHAPTER2。XXV。
LAWSOFVARIATION，continued。——CORRELATEDVARIABILITY。
EXPLANATIONOFTERMCORRELATION。
CONNECTEDWITHDEVELOPMENT。
MODIFICATIONSCORRELATEDWITHTHEINCREASEDORDECREASEDSIZE
OFPARTS。
CORRELATEDVARIATIONOFHOMOLOGOUSPARTS。
FEATHEREDFEETINBIRDSASSUMINGTHESTRUCTUREOFTHEWINGS。
CORRELATIONBETWEENTHEHEADANDTHEEXTREMITIES。
BETWEENTHESKINANDDERMALAPPENDAGES。
BETWEENTHEORGANSOFSIGHTANDHEARING。
CORRELATEDMODIFICATIONSINTHEORGANSOFPLANTS。
CORRELATEDMONSTROSITIES。
CORRELATIONBETWEENTHESKULLANDEARS。
SKULLANDCRESTOFFEATHERS。
SKULLANDHORNS。
CORRELATIONOFGROWTHCOMPLICATEDBYTHEACCUMULATEDEFFECTSOFNATURAL
SELECTION。
COLOURASCORRELATEDWITHCONSTITUTIONALPECULIARITIES。
Allpartsoftheorganisationaretoacertainextentconnectedtogether;buttheconnectionmaybesoslightthatithardlyexists，aswithcompoundanimalsorthebudsonthesametree。Eveninthehigheranimalsvariouspartsarenotatallcloselyrelated;foronepartmaybewhollysuppressedorrenderedmonstrouswithoutanyotherpartofthebodybeingaffected。Butinsomecases，whenonepartvaries，certainotherpartsalways，ornearlyalways，simultaneouslyvary;theyarethensubjecttothelawofcorrelatedvariation。Thewholebodyisadmirablyco—ordinatedforthepeculiarhabitsoflifeofeachorganicbeing，andmaybesaid，astheDukeofArgyllinsistsinhis’ReignofLaw’tobecorrelatedforthispurpose。Again，inlargegroupsofanimalscertainstructuresalwaysco—exist:forinstance，apeculiarformofstomachwithteethofpeculiarform，andsuchstructuresmayinonesensebesaidtobecorrelated。Butthesecaseshavenonecessaryconnectionwiththelawtobediscussedinthepresentchapter;forwedonotknowthattheinitialorprimaryvariationsoftheseveralpartswereinanywayrelated:
slightmodificationsorindividualdifferencesmayhavebeenpreserved，firstinoneandtheninanotherpart，untilthefinalandperfectlyco—adaptedstructurewasacquired;buttothissubjectIshallpresentlyrecur。Again，inmanygroupsofanimalsthemalesalonearefurnishedwithweapons，orareornamentedwithgaycolours;andthesecharactersmanifestlystandinsomesortofcorrelationwiththemalereproductiveorgans，forwhenthelatteraredestroyedthesecharactersdisappear。Butitwasshowninthetwelfthchapterthattheverysamepeculiaritymaybecomeattachedatanyagetoeithersex，andafterwardsbeexclusivelytransmittedtothesamesexatacorrespondingage。Inthesecaseswehaveinheritancelimitedbybothsexandage;butwehavenoreasonforsupposingthattheoriginalcauseofthevariationwasnecessarilyconnectedwiththereproductiveorgans，orwiththeageoftheaffectedbeing。
Incasesoftruecorrelatedvariation，wearesometimesabletoseethenatureoftheconnection;butinmostcasesitishiddenfromus，andcertainlydiffersindifferentcases。Wecanseldomsaywhichoftwocorrelatedpartsfirstvaries，andinducesachangeintheother;orwhetherthetwoaretheeffectsofsomecommoncause。Correlatedvariationisanimportantsubjectforus;forwhenonepartismodifiedthroughcontinuedselection，eitherbymanorundernature，otherpartsoftheorganisationwillbeunavoidablymodified。
Fromthiscorrelationitapparentlyfollowsthatwithourdomesticatedanimalsandplants，varietiesrarelyorneverdifferfromoneanotherbyasinglecharacteralone。
Oneofthesimplestcasesofcorrelationisthatamodificationwhicharisesduringanearlystageofgrowthtendstoinfluencethesubsequentdevelopmentofthesamepart，aswellasofotherandintimatelyconnectedparts。IsidoreGeoffroySaint—Hilairestates（25/1。’Hist。desAnomalies’tome3page392。
Prof。Huxleyappliesthesameprincipleinaccountingfortheremarkable，thoughnormal，differencesinthearrangementofthenervoussystemintheMollusca，inhispaperontheMorphologyoftheCephalousMolluscain’Phil。
Transact。’1853page56。）thatthismayconstantlybeobservedwithmonstrositiesintheanimalkingdom;andMoquin—Tandon（25/2。’ElementsdeTeratologieVeg。’1841page13。）remarks，that，aswithplantstheaxiscannotbecomemonstrouswithoutinsomewayaffectingtheorganssubsequentlyproducedfromit，soaxialanomaliesarealmostalwaysaccompaniedbydeviationsofstructureintheappendedparts。Weshallpresentlyseethatwithshort—muzzledracesofthedogcertainhistologicalchangesinthebasalelementsofthebonesarresttheirdevelopmentandshortenthem，andthisaffectsthepositionofthesubsequentlydevelopedmolarteeth。Itisprobablethatcertainmodificationsinthelarvaeofinsectswouldaffectthestructureofthematureinsects。Butwemustbecarefulnottoextendthisviewtoofar，forduringthenormalcourseofdevelopment，certainspeciespassthroughanextraordinarycourseofchange，whilstotherandcloselyalliedspeciesarriveatmaturitywithlittlechangeofstructure。
Anothersimplecaseofcorrelationisthatwiththeincreasedordecreaseddimensionsofthewholebody，orofanyparticularpart，certainorgansareincreasedordiminishedinnumber，orareotherwisemodified。Thuspigeonfanciershavegoneonselectingpoutersforlengthofbody，andwehaveseenthattheirvertebraearegenerallyincreasednotonlyinsizebutinnumber，andtheirribsinbreadth。Tumblershavebeenselectedfortheirsmallbodies，andtheirribsandprimarywing—feathersaregenerallylessenedinnumber。
Fantailshavebeenselectedfortheirlargewidely—expandedtails，withnumeroustail—feathers，andthecaudalvertebraeareincreasedinsizeandnumber。Carriershavebeenselectedforlengthofbeak，andtheirtongueshavebecomelonger，butnotinstrictaccordancewiththelengthofbeak。Inthislatterbreedandinothershavinglargefeet，thenumberofthescutellaeonthetoesisgreaterthaninthebreedswithsmallfeet。Manysimilarcasescouldbegiven。InGermanyithasbeenobservedthattheperiodofgestationislongerinlargethaninsmallbreedsofcattle。Withourhighly—improvedbreedsofallkinds，theperiodsofmaturityandofreproductionhaveadvancedwithrespecttotheageoftheanimal;and，incorrespondencewiththis，theteetharenowdevelopedearlierthanformerly，sothat，tothesurpriseofagriculturists，theancientrulesforjudgingoftheageofananimalbythestateofitsteetharenolongertrustworthy。（25/3。Prof。J。B。SimondsontheAgeoftheOx，Sheep，etc。quotedin’Gardener’sChronicle’1854page588。）
CORRELATEDVARIATIONOFHOMOLOGOUSPARTS。
Partswhicharehomologoustendtovaryinthesamemanner;andthisiswhatmighthavebeenexpected，forsuchpartsareidenticalinformandstructureduringanearlyperiodofembryonicdevelopment，andareexposedintheeggorwombtosimilarconditions。Thesymmetry，inmostkindsofanimals，ofthecorrespondingorhomologousorgansontherightandleftsidesofthebody，isthesimplestcaseinpoint;butthissymmetrysometimesfails，aswithrabbitshavingonlyoneear，orstagswithonehorn，orwithmany—hornedsheepwhichsometimescarryanadditionalhornononesideoftheirheads。Withflowerswhichhaveregularcorollas，allthepetalsgenerallyvaryinthesamemanner，asweseeinthecomplicatedandsymmetricalpattern，ontheflowers，forinstance，oftheChinesepink;butwithirregularflowers，thoughthepetalsareofcoursehomologous，thissymmetryoftenfails，aswiththevarietiesoftheAntirrhinumorsnapdragon，orthatvarietyofthekidney—bean（Phaseolus）
whichhasawhitestandard—petal。
IntheVertebratathefrontandhindlimbsarehomologous，andtheytendtovaryinthesamemanner，asweseeinlongandshortlegged，orinthickandthinleggedracesofthehorseanddog。IsidoreGeoffroy（25/4。’Hist。desAnomalies’tome1page674。）hasremarkedonthetendencyofsupernumerarydigitsinmantoappear，notonlyontherightandleftsides，butontheupperandlowerextremities。Meckelhasinsisted（25/5。QuotedbyIsid。
Geoffroyibidtome1page635。）that，whenthemusclesofthearmdepartinnumberorarrangementfromtheirpropertype，theyalmostalwaysimitatethoseoftheleg;andsoconverselythevaryingmusclesofthelegimitatethenormalmusclesofthearm。
Inseveraldistinctbreedsofthepigeonandfowl，thelegsandthetwooutertoesareheavilyfeathered，sothatinthetrumpeterpigeontheyappearlikelittlewings。Inthefeather—leggedbantamthe"boots"orfeathers，whichgrowfromtheoutsideofthelegandgenerallyfromthetwooutertoes，have，accordingtotheexcellentauthorityofMr。Hewitt（25/6。’ThePoultryBook’
byW。B。Tegetmeier1866page250。），beenseentoexceedthewing—feathersinlength，andinonecasewereactuallynineandahalfincheslong！AsMr。
Blythhasremarkedtome，theseleg—feathersresembletheprimarywing—
feathers，andaretotallyunlikethefinedownwhichnaturallygrowsonthelegsofsomebirds，suchasgrouseandowls。Henceitmaybesuspectedthatexcessoffoodhasfirstgivenredundancytotheplumage，andthenthatthelawofhomologousvariationhasledtothedevelopmentoffeathersonthelegs，inapositioncorrespondingwiththoseonthewing，namely，ontheoutsideofthetarsiandtoes。Iamstrengthenedinthisbeliefbythefollowingcuriouscaseofcorrelation，whichforalongtimeseemedtomeutterlyinexplicable，namely，thatinpigeonsofanybreed，ifthelegsarefeathered，thetwooutertoesarepartiallyconnectedbyskin。Thesetwooutertoescorrespondwithourthirdandfourthtoes。（25/7。Naturalistsdifferwithrespecttothehomologiesofthedigitsofbirds;butseveralupholdtheviewaboveadvanced。SeeonthissubjectDr。E。S。Morsein’AnnalsoftheLyceumofNat。Hist。ofNewYork’volume101872page16。）Now，inthewingofthepigeonorofanyotherbird，thefirstandfifthdigitsareaborted;thesecondisrudimentaryandcarriestheso—called"bastard—wing;"whilstthethirdandfourthdigitsarecompletelyunitedandenclosedbyskin，togetherformingtheextremityofthewing。Sothatinfeather—footedpigeons，notonlydoestheexteriorsurfacesupportarowoflongfeathers，likewing—feathers，buttheverysamedigitswhichinthewingarecompletelyunitedbyskinbecomepartiallyunitedbyskininthefeet;andthusbythelawofthecorrelatedvariationofhomologouspartswecanunderstandthecuriousconnectionoffeatheredlegsandmembranebetweenthetwooutertoes。
AndrewKnight（24/8。A。Walkeron’Intermarriage’1838page160。）hasremarkedthatthefaceorheadandthelimbsusuallyvarytogetheringeneralproportions。Compare，forinstance，thelimbsofadrayandracehorse，orofagreyhoundandmastiff。Whatamonsteragreyhoundwouldappearwiththeheadofamastiff！Themodernbulldog，however，hasfinelimbs，butthisisarecently—selectedcharacter。Fromthemeasurementsgiveninthesixthchapter，weseethatinseveralbreedsofthepigeonthelengthofthebeakandthesizeofthefeetarecorrelated。Theviewwhich，asbeforeexplained，seemsthemostprobableis，thatdisuseinallcasestendstodiminishthefeet，thebeakbecomingatthesametimeshorterthroughcorrelation;butthatinsomefewbreedsinwhichlengthofbeakhasbeenaselectedpoint，thefeet，notwithstandingdisuse，haveincreasedinsizethroughcorrelation。Inthefollowingcasesomekindofcorrelationisseentoexistbetweenthefeetandbeak:severalspecimenshavebeensenttoMr。Bartlettatdifferenttimes，ashybridsbetweenducksandfowls，andIhaveseenone;thesewere，asmightbeexpected，ordinaryducksinasemi—monstrouscondition，andinallofthemtheswimming—webbetweenthetoeswasquitedeficientormuchreduced，andinallthebeakwasnarrowandill—shaped。
Withtheincreasedlengthofthebeakinpigeons，notonlythetongueincreasesinlength，butlikewisetheorificeofthenostrils。Buttheincreasedlengthoftheorificeofthenostrilsperhapsstandsinclosercorrelationwiththedevelopmentofthecorrugatedskinorwattleatthebaseofthebeak，forwhenthereismuchwattleroundtheeyes，theeyelidsaregreatlyincreasedorevendoubledinlength。
Thereisapparentlysomecorrelationevenincolourbetweentheheadandtheextremities。Thuswithhorsesalargewhitestarorblazeontheforeheadisgenerallyaccompaniedbywhitefeet。（25/9。’TheFarrierandNaturalist’
volume11828page456。Agentlemanwhohasattendedtothispoint，tellsmethataboutthree—fourthsofwhite—facedhorseshavewhitelegs。）Withwhiterabbitsandcattle，darkmarksoftenco—existonthetipsoftheearsandonthefeet。Inblackandtandogsofdifferentbreeds，tan—colouredspotsovertheeyesandtan—colouredfeetalmostinvariablygotogether。Theselattercasesofconnectedcolouringmaybedueeithertoreversionortoanalogousvariation，——subjectstowhichIshallhereafterreturn，——butthisdoesnotnecessarilydeterminethequestionoftheiroriginalcorrelation。Mr。H。W。
Jacksoninformsmethathehasobservedmanyhundredwhite—footedcats，andhefindsthatallaremoreorlessconspicuouslymarkedwithwhiteonthefrontoftheneckorchest。
Theloppingforwardsanddownwardsoftheimmenseearsoffancyrabbitsseemspartlyduetothedisuseofthemuscles，andpartlytotheweightandlengthoftheears，whichhavebeenincreasedbyselectionduringmanygenerations。