Asnewcharacterssometimesappearbybud—variation，whichdonotoccurintheparent—speciesorinanyalliedspecies，wemayreject，atleastinthesecases，theideathattheyareduetoreversion。Nowitiswellworthwhiletoreflectmaturelyonsomestrikingcaseofbud—variation，forinstancethatofthepeach。Thistreehasbeencultivatedbythemillioninvariouspartsoftheworld，hasbeentreateddifferently，grownonitsownrootsandgraftedonvariousstocks，plantedasastandard，trainedagainstawall，orunderglass;
yeteachbudofeachsub—varietykeepstruetoitskind。Butoccasionally，atlongintervalsoftime，atreeinEngland，orunderthewidelydifferentclimateofVirginia，producesasinglebud，andthisyieldsabranchwhicheverafterwardsbearsnectarines。Nectarinesdiffer，aseveryoneknows，frompeachesintheirsmoothness，size，andflavour;andthedifferenceissogreatthatsomebotanistshavemaintainedthattheyarespecificallydistinct。Sopermanentarethecharactersthussuddenlyacquired，thatanectarineproducedbybud—variationhaspropagateditselfbyseed。Toguardagainstthesuppositionthatthereissomefundamentaldistinctionbetweenbudandseminalvariation，itiswelltobearinmindthatnectarineshavelikewisebeenproducedfromthestoneofthepeach;and，reversely，peachesfromthestoneofthenectarine。Nowisitpossibletoconceiveexternalconditionsmorecloselyalikethanthosetowhichthebudsonthesametreeareexposed？Yetonebudalone，outofthemanythousandsbornebythesametree，hassuddenly，withoutanyapparentcause，producedanectarine。Butthecaseisevenstrongerthanthis，forthesameflower—budhasyieldedafruit，one—halforone—quarteranectarine，andtheotherhalforthree—quartersapeach。Again，sevenoreightvarietiesofthepeachhaveyieldedbybud—variationnectarines:thenectarinesthusproduced，nodoubt，differalittlefromoneanother;butstilltheyarenectarines。Ofcoursetheremustbesomecause，internalorexternal，toexcitethepeach—budtochangeitsnature;butI
cannotimagineaclassoffactsbetteradaptedtoforceonourmindstheconvictionthatwhatwecalltheexternalconditionsoflifeareinmanycasesquiteinsignificantinrelationtoanyparticularvariation，incomparisonwiththeorganisationorconstitutionofthebeingwhichvaries。
ItisknownfromthelaboursofGeoffroySaint—Hilaire，andrecentlyfromthoseofDaresteandothers，thateggsofthefowl，ifshaken，placedupright，perforated，coveredinpartwithvarnish，etc。，producemonstrouschickens。
Nowthesemonstrositiesmaybesaidtobedirectlycausedbysuchunnaturalconditions，butthemodificationsthusinducedarenotofadefinitenature。