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RailroadsandCommercialAgricultureinCenturyUnitedBy1850theUnitedStatespossessedroughly9,000ofrailroadtrack;tenyearslaterithadover30,000,morethantherestoftheworldcombined.Muchofthenewconstructionduringthe1850soccurredwestoftheAppalachianMountains—over2,000inthestatesofOhioandIllinoisalone.2，000多英里在俄亥俄州和伊利诺斯州。Theeffectofthenewrailroadlinesrippledoutwardthroughtheeconomy.Farmersalongthetracksbegantospecializeincorpsthattheycouldmarketindistantlocations.Withtheirprofitstheypurchasedmanufacturedgoodsthatearliertheymighthavemadeathome.BeforetherailroadreachedTennessee,thestateproducedabout25,000bushels(or640tons)ofwheat,whichsoldforlessthan50centsabushel.Oncetherailroadcame,farmersinthesamecountiesgrew400,000bushels(over10,000tons)andsoldtheircropatadollarabushel.25,000农民可出产400,000蒲式耳（超过10，000吨，并且每蒲式耳可一Thenewrailroadnetworksshiftedthedirectionofwesterntrade.In1840mostnorthwesterngrainwasshippedsouthdowntheMississippiRivertothebustlingportofNewOrleans.Butlowwatermadeboattravelhazardousinsummer,andiceshutdowntrafficinwinter.Productssuchaslard,tallow,andcheesequicklyspoiledifstoredinNewOrleans’hotandhumidwarehouses.Increasingly,trafficfromtheMidwestflowedwesttoeast,overthenewraillines.Chicagobecametheregion’shub,linkingthefarmsoftheupperMidwesttoNewYorkandothereasterncitiesbymorethan2,000 oftrackin1855.ThuswhilethevalueofgoodsshippedbyrivertoNewOrleans toincrease,theSouth’soverallshareofwesterntradedropped1840年大部分西北部的粮食沿着密西西AsharpriseindemandforgrainabroadalsoencouragedfarmersintheNortheastandMidwest emorecommerciallyoriented.Wheat,whichin1845$1.08abushelinNewYorkCity,fetched$2.46in1855;insimilarfashionthepriceofcornnearlydoubled.Farmersrespondedbyspecializingincashcrops,borrowingtopurchasemoreland,andinvestinginequipmenttoincreaseproductivity.化。小麦在1845年纽约城里只能卖到1.08每蒲式耳，在1855年就卖到than.AsrailroadlinesfannedoutfromChicago,farmersbegantoacquireopenprairielandinIllinoisandthenIowa,puttingthefertile,deepblacksoilintoproduction.Commercialagriculturetransformedthisremarkabletreelessenvironment.Tosettlersaccustomedtoeasternwoodlands,thethousandsofsquare oftallgrasswereanawesomesight. ngrass,Canadawildrye,andnativebigbluestemallgrewthan.prairiegrass,theearliestsettlerserectedfarmsalongtheboundaryseparatingthefromtheprairie.In1837,however,JohnDeerepatentedasharp-cuttingsteelplowthatslicedthroughthesodwithoutsoilstickingtotheblade.CyrusMcCormickrefinedamechanicalreaperthatharvestedfourteentimesmorewheatwiththesameamountoflabor.Bythe1850sMcCormickwasselling1,000reapersayearandcouldnotkeepupwithdemand,whileDeereturnedout10,000plowsannually.境对于适应了东部林地的者来说成千上万平方英里的茂盛草丛令人惊叹，草野麦和当地的大须芒草长得比人还要高。因为东部的耕犁不能穿1，00010，000台。，ThenewcommercialfarmingfundamentallyalteredtheMidwesternlandscapeandtheenvironment.NativeAmericanshadgrowncornintheregionforyears,butneverineast.Prairiefarmersalsointroducednewcropsthatwerenotpartoftheearlierecologicalsystem,notablywheat,alongwithfruitsandvegetables.Nativegrasseswererecedbyasmallnumberofntscultivatedascommodities.Cornhadthebestyields,butitwasprimarilyusedtofeedlivestock.BecausebreadyedakeyroleintheAmericanandEuropeandiet,wheatbecamethemajorcashcrop.Tamegrassesrecednativegrassesinpasturesformakinghay.Westernfarmersalteredthelandscapebyreducingtheannualfiresthathadkepttheprairiefromtrees.Intheabsenceofthesefires,treesreappearedonlandnotincultivationand,ifundisturbed,eventuallyformedwoodlots.Theearlierunbrokenlandscapegavewaytoindependentfarms,eachfencedoffinaprecise