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1、ReferenceforTeachingⅠ.异域风情PlantsinDesertOnlyspecialplantscansurvivetheterribleclimateofadesert,fortheseareregionswheretheannualrangeofthesoiltemperaturecanbeover75℃.Furthermore,duringthesummertherearefewcloudsintheskytoprotectplantsfromthesun’sray.Anotherproblemi
2、sthefactthattherearefrequentlystrongwindswhichdrivesmall,sharpparticlesofsandintotheplants,tearinganddamagingthem.Themostdifficultproblemforallformsofplantlife,however,isthefactthattheentireannualrainfalloccursduringafewdaysorweeksinspring.Grassesandflowersindesert
3、survivefromoneyeartothenextbyexistingthroughthelong,hot,dryseasonintheformofseeds.Theseseedsremaininactiveunlesstherightamountofrainfalls.Ifnorainfalls,orifinsufficientrainfalls,theywaituntilthenextyear,orevenstillthenext.Anotherfactorthathelpstheseplantstosurviveis
4、thefactthattheirlifecyclesareshort.Bythetimethatthewaterfromthespringrainsdisappears—justafewweeksafteritfalls—suchplantsnolongerneedany.Theperennialshavespecialfeatureswhichenablethemtosurviveasplantsforseveralyears.Thus,nearlyalldesertperennialshaveextensiveroots
5、ystemsbelowgroundandasmallshootsystemaboveground.Thelargerootnetworkenablestheplanttoabsorbasmuchwateraspossibleinashorttime.Thesmallshootsystem,ontheotherhand,considerablylimitswaterlossbyevaporation.Anotherfeatureofmanydesertperennialsisthataftertherainyseasonthe
6、ylosetheirleavesinpreparationforthelong,dryseason,justastreesinwetterclimateslosetheirsinpreparationforthewinter.Thisreducestheirwaterlossbyevaporationduringthedryseason.Then,inthenextrainyseason,theycomefullyaliveoncemore,andgrownewbranches,leavesandflowers,justast
7、hegrassesandflowersindesertdo.Ⅱ.知识归纳1.accumulate用法归纳(1)积累(vt.)Thescientisthasaccumulatedawealthofexperience.这位科学家已经积累了丰富的经验。(2)堆积，越积越多(vi.）Ifyoudon’tclearawaytherubbishregularly,itwilljustaccumulate.如果你不定时清除垃圾，便会越积越多。Apileofworkaccumulatedonhisdesk.他桌子上有一大
8、堆文件要他处理。2.involve的用法归纳(v.)(1)牵涉，牵连ThiseventinvolvedourinterestsinEurope.这牵涉到我们在欧洲的股份。有时表示“有……参加”。Morethan4millionworkerswereinvolved
