[BIRDS。
InthecaseoftheFOWLawholearrayofauthoritiescouldbegivenagainsttoocloseinterbreeding。SirJ。Sebrightpositivelyassertsthathemademanytrials，andthathisfowls，whenthustreated，becamelonginthelegs，smallinthebody，andbadbreeders。（17/31。’TheArtofImprovingtheBreed’page13。）HeproducedthefamousSebrightBantamsbycomplicatedcrosses，andbybreedingin—and—in;andsincehistimetherehasbeenmuchcloseinterbreedingwiththeseanimals;andtheyarenownotoriouslybadbreeders。IhaveseenSilverBantams，directlydescendedfromhisstock，whichhadbecomealmostasbarrenashybrids;fornotasinglechickenhadbeenthatyearhatchedfromtwofullnestsofeggs。Mr。HewittsaysthatwiththeseBantamsthesterilityofthemalestands，withrareexceptions，intheclosestrelationwiththeirlossofcertainsecondarymalecharacters:headds，"Ihavenoticed，asageneralrule，thateventheslightestdeviationfromfemininecharacterinthetailofthemaleSebright——saytheelongationbyonlyhalfaninchofthetwoprincipaltailfeathers——bringswithitimprovedprobabilityofincreasedfertility。"（17/32。’ThePoultryBook’byW。B。Tegetmeier1866page245。）
Mr。Wrightstates（17/33。’JournalRoyalAgricult。Soc。’1846volume7page205;seealsoFergusonontheFowlpages83，317;seealso’ThePoultryBook’
byTegetmeier1866page135withrespecttotheextenttowhichcock—fightersfoundthattheycouldventuretobreedin—and—in，viz。，occasionallyahenwithherownson;"buttheywerecautiousnottorepeatthein—and—inbreeding。"）thatMr。Clark，"whosefighting—cocksweresonotorious，continuedtobreedfromhisownkindtilltheylosttheirdispositiontofight，butstoodtobecutupwithoutmakinganyresistance，andweresoreducedinsizeastobeunderthoseweightsrequiredforthebestprizes;butonobtainingacrossfromMr。Leighton，theyagainresumedtheirformercourageandweight。"
Itshouldbeborneinmindthatgame—cocksbeforetheyfoughtwerealwaysweighed，sothatnothingwaslefttotheimaginationaboutanyreductionorincreaseofweight。Mr。Clarkdoesnotseemtohavebredfrombrothersandsisters，whichisthemostinjuriouskindofunion;andhefound，afterrepeatedtrials，thattherewasagreaterreductioninweightintheyoungfromafatherpairedwithhisdaughter，thanfromamotherwithherson。ImayaddthatMr。EytonofEyton，thewell—knownornithologist，whoisalargebreederofGreyDorkings，informsmethattheycertainlydiminishinsize，andbecomelessprolific，unlessacrosswithanotherstrainisoccasionallyobtained。SoitiswithMalays，accordingtoMr。Hewitt，asfarassizeisconcerned。（17/34。’ThePoultryBook’byW。B。Tegetmeier1866page79。）
Anexperiencedwriter（17/35。’ThePoultryChronicle’1854volume1page43。）
remarksthatthesameamateur，asiswellknown，seldomlongmaintainsthesuperiorityofhisbirds;andthis，headds，undoubtedlyisduetoallhisstock"beingofthesameblood;"henceitisindispensablethatheshouldoccasionallyprocureabirdofanotherstrain。Butthisisnotnecessarywiththosewhokeepastockoffowlsatdifferentstations。Thus，Mr。Ballance，whohasbredMalaysforthirtyyears，andhaswonmoreprizeswiththesebirdsthananyotherfancierinEngland，saysthatbreedingin—and—indoesnotnecessarilycausedeterioration;"butalldependsuponhowthisismanaged。Myplanhasbeentokeepaboutfiveorsixdistinctruns，andtorearabouttwohundredorthreehundredchickenseachyear，andselectthebestbirdsfromeachrunforcrossing。Ithussecuresufficientcrossingtopreventdeterioration。"（17/36。’ThePoultryBook’byW。B。Tegetmeier1866page79。）
Wethusseethatthereisalmostcompleteunanimitywithpoultry—breedersthat，whenfowlsarekeptatthesameplace，evilquicklyfollowsfrominterbreedingcarriedontoanextentwhichwouldbedisregardedinthecaseofmostquadrupeds。Moreover，itisagenerallyreceivedopinionthatcross—
bredchickensarethehardiestandmosteasilyreared。（17/37。’ThePoultryChronicle’volume1page89。）Mr。Tegetmeier，whohascarefullyattendedtopoultryofallbreeds，says（17/38。’ThePoultryBook’1866page210。）thatDorkinghens，allowedtorunwithHoudanorCreve—coeurcocks，"produceintheearlyspringchickensthatforsize，hardihood，earlymaturity，andfitnessforthemarket，surpassthoseofanypurebreedthatwehaveeverraised。"Mr。
Hewittgivesitasageneralrulewithfowls，thatcrossingthebreedincreasestheirsize。Hemakesthisremarkafterstatingthathybridsfromthepheasantandfowlareconsiderablylargerthaneitherprogenitor:soagain，hybridsfromthemalegoldenpheasantandfemalecommonpheasant"areoffarlargersizethaneitherparent—bird。"（17/39。Ibid1866page167;and’PoultryChronicle’volume31855page15。）TothissubjectoftheincreasedsizeofhybridsIshallpresentlyreturn。
WithPIGEONS，breedersareunanimous，aspreviouslystated，thatitisabsolutelyindispensable，notwithstandingthetroubleandexpensethuscaused，occasionallytocrosstheirmuch—prizedbirdswithindividualsofanotherstrain，butbelonging，ofcourse，tothesamevariety。Itdeservesnoticethat，whensizeisoneofthedesiredcharacters，aswithpouters（17/40。’A
TreatiseonFancyPigeons’byJ。M。Eatonpage56。）theevileffectsofcloseinterbreedingaremuchsoonerperceivedthanwhensmallbirds，suchasshort—
facedtumblers，arevalued。Theextremedelicacyofthehighfancybreeds，suchasthesetumblersandimprovedEnglishcarriers，isremarkable;theyareliabletomanydiseases，andoftendieintheeggorduringthefirstmoult;
andtheireggshavegenerallytobehatchedunderfoster—mothers。Althoughthesehighly—prizedbirdshaveinvariablybeensubjectedtomuchcloseinterbreeding，yettheirextremedelicacyofconstitutioncannotperhapsbethusfullyexplained。Mr。YarrellinformedmethatSirJ。Sebrightcontinuedcloselyinterbreedingsomeowl—pigeons，untilfromtheirextremesterilityheasnearlyaspossiblelostthewholefamily。Mr。Brent（17/41。’ThePigeonBook’page46。）triedtoraiseabreedoftrumpeters，bycrossingacommonpigeon，andrecrossingthedaughter，granddaughter，great—granddaughter，andgreat—great—granddaughter，withthesamemaletrumpeter，untilheobtainedabirdwith15/16oftrumpeter’sblood;butthentheexperimentfailed，for"breedingsoclosestoppedreproduction。"TheexperiencedNeumeister（17/42。
’DasGanzederTaubenzucht’1837s。18。）alsoassertsthattheoffspringfromdovecotesandvariousotherbreedsare"generallyveryfertileandhardybirds:"soagainMM。BoitardandCorbie（17/43。’LesPigeons’1824page35。），afterforty—fiveyears’experience，recommendpersonstocrosstheirbreedsforamusement;for，iftheyfailtomakeinterestingbirds，theywillsucceedunderaneconomicalpointofview，"asitisfoundthatmongrelsaremorefertilethanpigeonsofpurerace。"
Iwillreferonlytooneotheranimal，namely，theHive—bee，becauseadistinguishedentomologisthasadvancedthisasacaseofinevitablecloseinterbreeding。Asthehiveistenantedbyasinglefemale，itmighthavebeenthoughtthathermaleandfemaleoffspringwouldalwayshavebredtogether，moreespeciallyasbeesofdifferenthivesarehostiletoeachother;astrangeworkerbeingalmostalwaysattackedwhentryingtoenteranotherhive。
ButMr。Tegetmeierhasshown（17/44。’Proc。Entomolog。Soc。’August6，1860
page126。）thatthisinstinctdoesnotapplytodrones，whicharepermittedtoenteranyhive;sothatthereisnoaprioriimprobabilityofaqueenreceivingaforeigndrone。Thefactoftheunioninvariablyandnecessarilytakingplaceonthewing，duringthequeen’snuptialflight，seemstobeaspecialprovisionagainstcontinuedinterbreeding。Howeverthismaybe，experiencehasshown，sincetheintroductionoftheyellow—bandedLigurianraceintoGermanyandEngland，thatbeesfreelycross:Mr。Woodbury，whointroducedLigurianbeesintoDevonshire，foundduringasingleseasonthatthreestocks，atdistancesoffromonetotwomilesfromhishives，werecrossedbyhisdrones。InonecasetheLiguriandronesmusthaveflownoverthecityofExeter，andoverseveralintermediatehives。OnanotheroccasionseveralcommonblackqueenswerecrossedbyLiguriandronesatadistanceoffromonetothreeandahalfmiles。（17/45。’JournalofHorticulture’1861
pages39，77，158;and1864page206。）
PLANTS。
Whenasingleplantofanewspeciesisintroducedintoanycountry，ifpropagatedbyseed，manyindividualswillsoonberaised，sothatiftheproperinsectsbepresenttherewillbecrossing。Withnewly—introducedtreesorotherplantsnotpropagatedbyseedwearenothereconcerned。Withold—
establishedplantsitisanalmostuniversalpracticeoccasionallytomakeexchangesofseed，bywhichmeansindividualswhichhavebeenexposedtodifferentconditionsoflife，——andthis，aswehaveseenwithanimals，diminishestheevilfromcloseinterbreeding，——willoccasionallybeintroducedintoeachdistrict。
Withrespecttoindividualsbelongingtothesamesub—variety，Gartner，whoseaccuracyandexperienceexceededthatofallotherobservers，states（17/46。
’BeitragezurKenntnissderBefruchtung’1844s。366。）thathehasmanytimesobservedgoodeffectsfromthisstep，especiallywithexoticgenera，ofwhichthefertilityissomewhatimpaired，suchasPassiflora，Lobelia，Fuchsia。
Herbertalsosays（17/47。’Amaryllidaceae’page371。），"IaminclinedtothinkthatIhavederivedadvantagefromimpregnatingtheflowerfromwhichIwishedtoobtainseedwithpollenfromanotherindividualofthesamevariety，oratleastfromanotherflower，ratherthanwithitsown。"Again，ProfessorLecoqascertainedthatcrossedoffspringaremorevigorousandrobustthantheirparents。（17/48。’DelaFecondation’2ndedition1862page79。）
Generalstatementsofthiskind，however，canseldombefullytrusted:I
thereforebeganalongseriesofexperiments，continuedforabouttenyears，whichwillIthinkconclusivelyshowthegoodeffectsofcrossingtwodistinctplantsofthesamevariety，andtheevileffectsoflong—continuedself—
fertilisation。Aclearlightwillthusbethrownonsuchquestions，aswhyflowersarealmostinvariablyconstructedsoastopermit，orfavour，ornecessitatetheunionoftwoindividuals。Weshallclearlyunderstandwhymonoeciousanddioecious，——whydichogamous，dimorphicandtrimorphicplantsexist，andmanyothersuchcases。Iintendsoontopublishanaccountoftheseexperiments，andIcanheregiveonlyafewcasesinillustration。TheplanwhichIfollowedwastogrowplantsinthesamepot，orinpotsofthesamesize，orclosetogetherintheopenground;carefullytoexcludeinsects;andthentofertilisesomeoftheflowerswithpollenfromthesameflower，andothersonthesameplantwithpollenfromadistinctbutadjoiningplant。Inmanyoftheseexperiments，thecrossedplantsyieldedmuchmoreseedthantheself—fertilisedplants;andIhaveneverseenthereversedcase。Theself—
fertilisedandcrossedseedsthusobtainedwereallowedtogerminateinthesameglassvesselondampsand;andastheseedsgerminated，theywereplantedinpairsonoppositesidesofthesamepot，withasuperficialpartitionbetweenthem，andwereplacedsoastobeequallyexposedtothelight。Inothercasestheself—fertilisedandcrossedseedsweresimplysownonoppositesidesofthesamesmallpot。Ihave，inshort，followeddifferentplans，butineverycasehavetakenalltheprecautionswhichIcouldthinkof，sothatthetwolotsshouldbeequallyfavoured。Thegrowthoftheplantsraisedfromthecrossedandself—fertilisedseed，werecarefullyobservedfromtheirgerminationtomaturity，inspeciesbelongingtofifty—twogenera;andthedifferenceintheirgrowth，andinwithstandingunfavourableconditions，wasinmostcasesmanifestandstronglymarked。Itisofimportancethatthetwolotsofseedshouldbesownorplantedonoppositesidesofthesamepot，sothattheseedlingsmaystruggleagainsteachother;forifsownseparatelyinampleandgoodsoil，thereisoftenbutlittledifferenceintheirgrowth。
Iwillbrieflydescribetwoofthefirstcasesobservedbyme。Sixcrossedandsixself—fertilisedseedsofIpomoeapurpurea，fromplantstreatedinthemannerabovedescribed，wereplantedassoonastheyhadgerminated，inpairsonoppositesidesoftwopots，androdsofequalthicknessweregiventhemtotwineup。Fiveofthecrossedplantsgrewfromthefirstmorequicklythantheopposedself—fertilisedplants;thesixth，however，wasweaklyandwasforatimebeaten，butatlastitssounderconstitutionprevailedanditshotaheadofitsantagonist。Assoonaseachcrossedplantreachedthetopofitsseven—
footroditsfellowwasmeasured，andtheresultwasthat，whenthecrossedplantsweresevenfeethightheself—fertilisedhadattainedtheaverageheightofonlyfivefeetfourandahalfinches。Thecrossedplantsfloweredalittlebefore，andmoreprofuselythantheself—fertilisedplants。OnoppositesidesofanotherSMALLpotalargenumberofcrossedandself—fertilisedseedsweresown，sothattheyhadtostruggleforbareexistence;asinglerodwasgiventoeachlot:hereagainthecrossedplantsshowedfromthefirsttheiradvantage;theyneverquitereachedthesummitoftheseven—footrod，butrelativelytotheself—fertilisedplantstheiraverageheightwasassevenfeettofivefeettwoinches。Theexperimentwasrepeatedduringseveralsucceedinggenerations，treatedinexactlythesamemanner，andwithnearlythesameresult。Inthesecondgeneration，thecrossedplants，whichwereagaincrossed，produced121seed—capsules，whilsttheself—fertilised，againself—fertilised，producedonly84capsules。
SomeflowersoftheMimulusluteuswerefertilisedwiththeirownpollen，andotherswerecrossedwithpollenfromdistinctplantsgrowinginthesamepot。
Theseedswerethicklysownonoppositesidesofapot。Theseedlingswereatfirstequalinheight;butwhentheyoungcrossedplantswerehalfaninch，theself—fertilisedplantswereonlyaquarterofaninchhigh。Butthisdegreeofinequalitydidnotlast，for，whenthecrossedplantswerefourandahalfincheshigh，theself—fertilisedwerethreeinches，andtheyretainedthesamerelativedifferencetilltheirgrowthwascomplete。Thecrossedplantslookedfarmorevigorousthantheuncrossed，andfloweredbeforethem;
theyproducedalsoafargreaternumberofcapsules。Asintheformercase，theexperimentwasrepeatedduringseveralsucceedinggenerations。HadInotwatchedtheseplantsofMimulusandIpomoeaduringtheirwholegrowth，Icouldnothavebelieveditpossible，thatadifferenceapparentlysoslightasthatofthepollenbeingtakenfromthesameflower，orfromadistinctplantgrowinginthesamepot，couldhavemadesowonderfuladifferenceinthegrowthandvigouroftheplantsthusproduced。This，underaphysiologicalpointofview，isamostremarkablephenomenon。
Withrespecttothebenefitderivedfromcrossingdistinctvarieties，plentyofevidencehasbeenpublished。Sageret（17/49。’MemoiresurlesCucurbitacees’pages36，28，30。）repeatedlyspeaksinstrongtermsofthevigourofmelonsraisedbycrossingdifferentvarieties，andaddsthattheyaremoreeasilyfertilisedthancommonmelons，andproducenumerousgoodseed。
HerefollowstheevidenceofanEnglishgardener（17/50。Loudon’s’Gardener’sMag。’volume81832page52。）:"Ihavethissummermetwithbettersuccessinmycultivationofmelons，inanunprotectedstate，fromtheseedsofhybrids（i。e。mongrels）obtainedbycrossimpregnation，thanwitholdvarieties。Theoffspringofthreedifferenthybridisations（onemoreespecially，ofwhichtheparentswerethetwomostdissimilarvarietiesIcouldselect）eachyieldedmoreampleandfi...完整阅读请扫描二维码下载丁香书院APP免费看：