Distribution and persistence of Amanita muscaria genotypes in Australian Pinus radiata plantations

高三英语统计学分析单选题60题及答案1.The average score of a class is calculated by adding all the scores and dividing by the number of students. This is an example of _____.A.meanB.medianC.modeD.range答案：A。

本题考查统计学基本概念。

A 选项mean（平均数）是通过将所有数据相加再除以数据个数得到的，符合题干描述。

B 选项median（（中位数）是将数据从小到大排列后位于中间位置的数。

C 选项mode（众数）是数据中出现次数最多的数。

D 选项range（极差）是数据中的最大值与最小值之差。

2.In a set of data, if there is a value that occurs most frequently, it is called the _____.A.meanB.medianC.modeD.range答案：C。

A 选项mean 是平均数。

B 选项median 是中位数。

C 选项mode 众数是出现次数最多的值，符合题意。

D 选项range 是极差。

3.The middle value in a sorted list of data is called the _____.A.meanB.medianC.modeD.range答案：B。

A 选项mean 是平均数。

B 选项median 中位数是排序后位于中间的数，符合题干描述。

C 选项mode 是众数。

D 选项range 是极差。

4.The difference between the highest and lowest values in a set of data is known as the _____.A.meanB.medianC.modeD.range答案：D。

100句激励自己的英文名言100句激励自己的英文名言1、Formanismanandmasterofhisfate.人就是人，是自己命运的主人。

2、Alazyyouth,alousyage.少壮不努力，老大徒伤悲。

3、Doonethingatatime,anddowell.一次只做一件事，做到最好！4、Youthmeanslimitlesspossibilities.年轻就是无限的可能。

5、Knowledgemakeshumble,ignorancemakesproud. 博学使人谦逊，无知使人骄傲。

6、Goforit!Justdoit！加油！向前冲！做了再说！7、Amanisonlyasgoodaswhatheloves.一个人要用他所爱的东西有多好来衡量。

8、Ifwintercomes,canspringbefarbehind?冬天来了，春天还会远吗？9、Sharptoolsmakegoodwork.工欲善其事，必先利其器。

10、Badtimesmakeagoodman.艰难困苦出能人。

11、Journeyofathousandmilesbeginswithsinglestep.千里之行，始于足下。

12、Thefirststepisasgoodashalfover.第一步是最关键的一步。

13、Failureisthemotherofsuccess.失败乃成功之母。

14、Geniusisaninfinitecapacityfortakingpains.所谓的天才是不断地承受痛楚。

15、Difficultcircumstancesserveasatextbookoflifeforpeople.困难坎坷是人们的生活教科书。

16、Amanisonlyasgoodaswhatheloves.一个人要用他所爱的东西有多好来衡量。

17、Iknowthatmyfutureisnotjustadream.我知道我的未来不是梦。

英语励志名言格言摘抄1.whohasnevertastedbitter,knowsnotwhatissweet.不尝黄连苦，怎知蜂蜜甜。

2.everyhousehasaskeleton.每座房子都有骨架。

3.worktoday,foryouknownothowmuchyoumaybehinderedtomorrow.今天有事今天做，明天可能事受阻。

4.oldfriendsarethebestmirror.老朋友是的镜子。

5.loveisthetouchstoneofvirtue.爱情是美德的试金石。

6.makelovegoeswitheachother.相爱相生。

7.hethatliveswellislearned.生活好者，博学多才。

8.sayingisonething,doingisanother.说是一回事，做是另一回事。

9.stepbystep.按部就班，循序渐进。

10.helivestwicewholiveswell.生活得好的等于生活了两次。

11.standonyourowntwofeet.自立更生，自食其力。

13.everycoinhasitsreverse.事物都有它的反面。

14.agreattalkerisagreatliar.说大话者多谎言。

15.praiseyourfriends,notyourenemies.要赞美朋友，莫提及敌人。

16.askanoldmanforadvice.如要忠告向老人请教。

17.lieuponroseswhenyoung,uponthornswhenold.年青时躺在玫瑰上，老年时就会躺在荆棘上。

18.wefirstmakeourhabits,andthenourhabitsmakeus.我们先养成习惯，然后习惯又左右我们。

19.earlyripe,earlyrotten.早熟早烂。

20.afriendiseasierlostthanfound.得朋友难，失朋友易。

英语励志短语原文翻译2017-03-181、sweatisthelubricantofsuccess.汗水是成功的润滑剂。

2、truemasteryofanyskilltakesalifetime.对任何技能的掌握都需要一生的刻苦操练。

3、ifyouaredoingyourbest,youwillnothavetoworryaboutfailure.如果你竭尽全力，你就不用担心失败。

4、energyandpersistenceconquerallthings.能量和坚持可以征服一切事情。

5、braverynevergoesoutoffashion.勇敢永远不过时!6、properpreparationsolves80percentoflife'sproblems.适当的准备能解决生活中80%的问题。

7、thosewhoturnbackneverreachthesummit.回头的人永远到不了最高峰!8、winnersdowhatlosersdon'twanttodo.胜利者做失败者不愿意做的事!9、everynobleworkisatfirstimpossible.每一个伟大的工程最初看起来都是不可能做到的!10、weimproveourselvesbyvictoriesoverourselves.theremustbecontests,andwe mustwin.我们通过战胜自己来改进自我。

那里一定有竞赛，我们一定要赢!11、neverunderestimateyourpowertochangeyourself!永远不要低估你改变自我的能力!12、givingisarewardinitself.给予本身就是一个奖赏。

13、amanisnotoldaslongasheisseekingsomething.amanisnotolduntilregretstake theplaceofdreams.(j.barrymore)只要一个人还有追求，他就没有老。

简短英语座右铭1.简单英语名言警句·Allthingsintheirbeingaregoodforsomething.·天生我才必有用。

·Difficultcircumstancesserveasatextbookoflifeforpeople.·困难坎坷是人们的生活教科书。

·Failureisthemotherofsuccess.-ThomasPaine·失败乃成功之母。

·Formanismanandmasterofhisfate.·人就是人，是自己命运的主人。

·Theunexamined lifeisnotworthliving.--Socrates·混混噩噩的生活不值得过。

--苏格拉底·Noneisoffreedomoroflifedeservingunlesshedailyconquersit anew.-Erasmus·只有每天再度战胜生活并夺取自由的人，才配享受生活的自由。

·Ourdestinyoffersnotthecupofdespair,butthechaliceofopp ortunity.Soletusseizeit,notinfear,butingladness.--R.M.Nixon ·命运给予我们的不是失望之酒，而是机会之杯。

因此，让我们毫无畏惧，满心愉悦地把握命运-尼克松·Livingwithoutanaimislikesailingwithoutacompass.--JohnRu skin·生活没有目标，犹如航海没有罗盘。

--罗斯金·Whatmakeslifedrearyisthewantofmotive.--GeorgeEliot·没有了目的，生活便郁闷无光。

--乔治·埃略特·Toweringgeniusdisdainsabeatenpath.Itseeksregi onshithert ounexplored.--Lincoln·卓越的天才不屑走旁人走过的路。

1.It all depends on human effort事在人为2.Man can conquer natur e人定胜天3.Heaven will always leave a door open天无绝人之路4.Willing t o help but unable t o do so爱莫能助5.Have seen much of the changes in human life饱经沧桑6.T each fish t o swim班门弄斧7.Two hearts are better than one一人技短，二人技长8.Work mak es the workman勤工出巧匠9.A light heart lives long豁达者长寿10.Nothing down,nothing up天下无上,不经历风雨怎么见彩虹11.Seeing is believing百闻不如一见12.No discord,no concord不打不成交13.Harmony brings wealth和气生财14.Gold can’t be pur e and man can’t be perfect金无赤足，人无完人15.A slow sparrow should mak e an early start笨鸟先飞16.Y ou can’t always get what you what天不从人愿17.All things must come t o an end天下没有不散的宴席18.Shooting two bird s with one st one一言为定19.It’s a deal一言为定20.What a gossip流言蜚语，闲言碎语21.All secrets may eventually come t o light水落石出22.All we hear is words,but there is no action雷声大，雨点小23.With honey on one’s lip and mur der in one’s heart口蜜腹剑，笑s 里藏刀24. Learning seems like rowing upstream, if one does n ot advance, onewill fall back学如逆水行舟，不进则退25. Have a clear demarcation between whom t o love and whom t o hat e爱憎分明26. Bad news has wings坏事传千里27. All is fair in war兵不厌诈28. A man may dig his grave with his t eeth 祸从口出29. It ’no usecrying over spilt milk 覆水难收30. Wine is mirror of the mind 酒后真言31. Y ou mind your business, and I will mind mine 井水不犯河水32. There is no such thing as a free lunch 天下没有白吃的午餐33. T ake it for grant ed 身在福中不知福34. It takes two t o tango 一个巴掌拍不响35. Great minds think alike英雄所见略同36. The pr oper function of man is t o live but n ot t o exist人应该生活，而非单纯生存37. T o err is human, t o forgive divine人皆犯错，能原谅别人，你就是圣人38. The only thing we have t o fear is fear itself我们唯一不得不害怕的就是害怕本身39. The man who has never made a mistake will never mak e anythingelse从不犯错误的人将一事无成40.Without confidence there is no friendship没有信任就没有友谊41.Every family has a black sheep家家有本难念的经42.Give a dog a bad name and hang him欲加之罪，何患无辞43.After a storm comes a calm否极泰来44.While the waters can k eep a boat a float they can also overturn it水能载舟，亦能覆舟45.Promises must be kept,and action must be resolute言必行，行必果46.For man is man and master of his fate人就是人，是自己命运的主人47.As long as the gr een hills last,ther e will always be wood t o burn留得青山在，不怕没柴烧48.Ask no questions and be told no lies不问就听不见假话49.Blood is thicker than water血浓于水50.Custom is a second natur e习惯成自然51.Well begin is half done好的开始是成功的一半52.A little of everything is nothing in the main每事浅尝辄止，事事都告无成53.Creep before you walk循序渐进54.A single spark can start a prairie fire星星之火，可以燎原55.Never leave that until t omorr ow which you can do today今日事，今日毕56.Nothing seek,nothing find无所求则无所获57.While there is life ther e is hope一息若存，希望不及58.The good seaman is known in bad weather惊涛骇浪，方显英雄本色59.Energy and persistence conquer all things能量加毅力可以征服一切60.An aim in life is the only worth finding生活的目标是唯一值得寻找的财富61.There is no royal r o ad o learning书山有路勤为径，学海无涯苦作舟62.It takes three generations t o mak e a gentleman十年树木，百年树人63.Never too old t o learn,never too late t o turn亡羊补牢，为时不晚64.A common danger comes action同舟共济65.The eye is bigger than belly心有余而力不足66.Fire and water have no mercy水火无情67.A few are no mat ch for the many寡不敌众68.He dances well t o whom fortune pipes时来运转百事顺69.He who helps others helps himself与人方便，与己方便70.No one can do two things at once一心不得二用71.No one is wise all times聪明一世，糊涂一时72.Nothing brave,nothing have不入虎穴，焉得虎子s 73. Old sin mak es new sh a me一失足成千古恨74. Once bitten, twice shy一朝被蛇咬，十年怕井绳75. T o a wise man one word is enough 对智者，一言已足76. T o be head and shoulders taller一枝独秀77. The milk is spilled覆水难收78. Laugh before breakfast you will cry before supper 乐极生悲79. Golden words offend the ear 忠言逆耳80. Gold ’in his heaven, all right with上帝就在天堂，时间一切美好81. Plan the whole year in the spring 一年之计在于春82. Y ears know m or e than books经验胜于书本83. Wisdom and virtue are like the two wheels of a cart智慧与美德兼备才好84. Thinks are ways, bu t acts another表里不一85. Time and tide wait for no man时不我待86. Good advice is the best gift for a friend忠告是朋友最好的礼物87. Victory and tear , that is life 胜利和眼泪，这就是人生88. Spring is beautiful, and early spring is charming, you are such anearly spring sending ou t the light of hope 春天是美好的，初春是迷人的，你如初春一样闪着希望之光89. A little knowledge is a danger ous thing一知半解，自欺欺人90. A little body often harbors a gr eat soul 浓缩的都是精品91.All rivers run into sea海纳百川92.All that glitters is n ot gold闪光的不一定都是金子93.A straight foot is n ot afraid of a crook ed shoe身正不怕影子歪94.No man is born wise or learned没有生而知之者95.Nothing is impossible t o willing heart心之所愿，无事不成96.T ruth nee ds no color beauty no pencil真理不需色彩，美丽不需涂饰97.Fish and visitors smell in three days鱼放三天发臭，客住三天嫌烦98.T o speak like a book咬文嚼字99.Every minute of the wedding might is precious春宵一刻值千金100.Two heads are always better than one三人行必有我师101.A crow is never beautiful,be it looked in the mirror or not猪八戒照镜子，里外不是人102.Y ou walk on your bright way,I stay in my narrow bridge你走你的阳光道，我过我的独木桥103.A bold att em pt is half success勇敢地尝试是成功的一半104.From small beginning come gr eat things伟大始于渺小105.Do what you say,say what you do做你说过的，说你能做的106.Do n ot for one repulse give up the purpose that you resolved t o effect不要只因为一次次失败就放弃你原来想要达到的目的107.Don’part with you illusions when they are gone you may still texist b ut you have ceased t o live不要放弃你的幻想，当幻想没有了今后，你还可以生存，但虽生犹死108.Hom e is the place where,when you have t o go there,it has t o take in无论何时何地家永远是向游子敞开大门的地方109.The family is one of natures masterpieces家庭是大自然创造的杰作之一110.the house of every one is t o him as his castle and fortress每个人的家对自己都像是城堡和要害111.Hom e is where the heart is心在哪里，哪里就是家112.Faith can move mountains精诚所至，金石为开113.Adversity mak es a man wise not rich逆境出人才114.A good conscience is a soft pillow不做亏心事，不怕鬼叫门115.A good hu sb and mak es a good wife夫善则妻贤116.A man is known by his friends什么人交什么朋友117.An apple a day k eeps the doctor away一天一苹果，不用请医生118.A tree is known by its fruit观其行而知其人119.A friend is never known till a man has need需要之时方知友120.Be slow t o promise and quick t o perform不轻诺，诺必果121.A single flower does n ot mak e a spring一花独放不是春，百花齐放春满园122.Genius was1percent inspiration and99percent perspiration天才是1%的灵感加99%的汗水123.Goals determine what you are going t o be目标决定你成为什么样的人124.Living without an aim is like sailing without a comp ass生活没有目标，就像航海没有罗盘125.One should eat t o live,no live t o eat人应该为生而食，不应为食而生126.Y outh is n o t a time of life;it is a state of mind青春不是生命的某一时段，而是一种精神状态127.Y ou can’t mak e an omelet without breaking eggs巧妇难为无米之炊128.What goes ar ound comes ar ound你怎么待人，人就怎么待你129.It’s no t over until the fat lady sings最后见输赢130.Once swallow doesn’t mak e a summer一燕不成夏131.The early bird catches the worm早起的鸟有虫吃132.Hundr eds schools of t ho ug ht c ont end ed百家争鸣133.T ouch pitch,and you’ll be defiled常在河边走，哪有不湿鞋134.T o hold court in place of the young emper or from behind a screen垂帘听政135.Throw a sprat t o catch a whale抛砖引玉136.Not pleased by external gains not saddened by personal losses 不以物喜，不以己悲137.T o a person in the world,the m ost important thing is t o be ablet o love n ot t o be loved人活在世上，最重要的是有爱人的能力，而不是被爱138.The unexamined life is n o t worth living浑浑噩噩的生活不值得过139.A snow year,a rich year瑞雪兆丰年placency is the enemy of study学习的敌人是自己的满足141.Courtesy on one side only lasts n ot long来而不往非礼也142.Energy and persistence conquer all things能量和毅力可以征服一切143.Keep trying no matt er how har d it seems it will get easier坚持不懈，难也变易144.Y ou’re unique nothing can replace you你举世无双，无人可以替代145.A t o Z从头到尾146.Everything comes t o him who waits功夫不负有心人147.Jack shall have Jill,all shall be well有情人终成眷属148.Such kindness of warm sun can’t be paid by grass谁言寸草心，报得三春晖149.No matt er the ending is perfect or not,you can’t disappear from my world我的世界不允许你的消失，不管结局是否完美150.Thinking can give men enjoyment and pleasure思考给人以享受和乐趣s 151. Books are the best thing, well used, abused, among the worse用之得当，书是最好的东西，用之不当，书是最坏的东西152. Know something of everything and everything of something通百艺而一长153. Knowledge advances by steps, and n ot by adv ance学知识只宜循序渐进，不可突飞猛进154. No man is wise at all time智者千虑，必有一失155. Birds of a feather flock t ogether 物以类聚，人以群分156. No matt er how high the mountain is, its name will spr ead farand wide. It there is a fairy 山不在高，有仙则名157. One boy is a boy , two boys half a boy , thr ee boys no boy一个和尚挑水喝，两个和尚抬水喝，三个和尚没水喝158. T aking thing as they come 既来之，则安之159. Advance with times与时俱进160. No cross, no crown无苦即乐161. A bad man always blame his tools 拙匠常怪工具差162. One good true deserves another 以德报德163. All things come t o those who wait 苍天不负有心人164. Y ou have t o believe in yourself . That ’ t he secret of success人必须要相信自己，这是成功的秘诀165. Life is n ot fair, get used t o it 生活是不公平的，要去适应它166. Books and friends should be few b ut good读书如交友，应求少而精167.A mother’s love never changes母爱永恒168.A bad beginning mak es a bad ending不善始者不善终169.Love is ever the beginning of knowledge as fire is of light 知识总是从爱好开始，犹如光总是从火开始一样170.F ading is true while flowering is p ast凋谢是真实的，盛开只是一种过去171.Life is a palette,you p ut colors on it生活是调色盘，每个人自己在上面加上颜色172.Life isn’t about waiting for the storm t o pass,it’s about learning t o dance in the rain生活部是等待暴风雨来的过程，而是学会在风雨中跳出最没的舞姿173.It’s the tears of the earth that k eep her smiles in bloom是大地的眼泪使她的微笑保持青春不谢174.Only when our eyes have been wished by tears can we have a br o ader field of vision只有泪水洗过的眼睛，才有更开阔的视野175.Life is like a cup of tea,carefully taste,t o reward ou t really taste人生像一杯清茶，仔细品味才能品出真味道176.Life is a no return one-way traffic,everyone with all of our time and move on人生是一条没有回程的单程线，每个人都用自己所有的时光前行177.A thousand friends are few,one enemy is too many朋友千人犹嫌少，仇敌一人犹嫌多178.Promises are often like the butterfly,which disappear beautifulrehover 承诺就像是蝴蝶，美丽的盘旋然后不见179. Y ou can always be a worse version of him, or better vision ofuseful 不要做一个单纯优秀的人，而要做一个不可替代的人180. Live from paycheck t o paycheck 月光族181. The lesser of two evils 两害相权取其轻182. Fine feathers mak e fine birds 人要衣装，佛要金装183. Who has never tasted bitter , knows n ot what is sweet不常黄连苦，怎知蜜蜂甜184. Old friends and old wines are best 陈酒味醇，老友情深185. Early sow, early mow 早动手，早收获186. One is never too old t o learn 患难之交才是真正的朋友187. Haste does not, bring success欲速则不达188. What mak es like dreary is the want of motive没有了目的，生活便郁闷无光189. Gods determine what you ’ going t o be 人生的奋斗目标决定你要成为怎样的人190. Cease t o struggle and you cease t o live 生命不止，奋斗不息191. Once one shore, one prays on m or e 好了伤疤忘了疼192. Harmony brings wealth 和气生财193. W orse off than some, better off than many 比上不足，比下有余194. Bid farewell t o the old, usher in the new 辞旧迎新195. Going t o far is as bad as n ot going far enough过犹不及196.Joy puts heart into a man人逢喜事精神爽197.Practice is the sole criterion for testing truth时间是检验真理的唯一标准198.W ater without a source,and a tree without roots无源之水，无本之木199.If you don’t leave,I will in life and death你若不离不弃，我必生死相依200.In order t o be irreplaceable,one must always be different要做到不可替代，就要与众不同201.Forgive,at the sa m e time,let yourself原谅别人，同时也放过自己202.Catch one’s heart,never be apart愿得一心人白首不相离203.Life’s gr eatest regret than the wr ong insist and easily give up 人生最大的遗憾莫过于错误的选择和轻易地放弃204.May all your wish come true心想事成205.Catch the ball before the bound先下手为强206.P our oil on tr oubled water息事宁人207.Haste doesn’t bring success欲速则不达208.Fortune knocks once at least at every man’s gat e风水轮流转209.Nobody can go back and start a new beginning b ut anyone can start now and mak e a new ending没有人能让时光倒流，然后重新出发。

一句话英语经典语录1、Formanismanandmasterofhisfate.译文：人就是人，是自己命运的主人。

2、Ablessingindisguise.译文：因祸得福3、Afriendinneedisafriendindeed.译文：患难中的朋友才是真正的朋友。

4、Agoodbeginningmakesagoodending.译文：善始善终5、Alightheartlivelong.译文：心情开朗寿命长。

不恼不愁，活到白头。

6、Astrongmanwillstrugglewiththestormsoffate.译文：强者能同命运的风暴抗争。

7、Athousand-lijourneyisstartedbytakingthefirststep.译文：千里之行，始于足下8、Acceptwhatwasandwhatis,andyou’llhavemorepositiveenergytopursuewhatwillbe.译文：接受过去和现在的模样，才会有能量去追寻自己的未来。

9、AllroadsleadtoRoma.译文：条条大道通罗马10、Allthatglittersisnotgold.译文：闪光的东西并非都是金子11、Allthingsaredifficultbeforetheyareeasy.译文：凡事必先难后易。

12、Yourhappypasser-byallknows,mydistressedthereisnoplacehides.译文：你的幸福路人皆知，我的狼狈无处遁形。

13、Allthingsintheirbeingaregoodforsomething.译文：天生我才必有用。

14、Althoughthesunshine，leavenotyourcloakathome.译文：未雨绸缪。

15、Anappleadaykeepsthedoctoraway.译文：日吃苹果一只，身体健康不求医。

Chapter 11 Geographical Distribution Present distribution cannot be accounted for by differences in physical conditions. Importance of barriers. Affinity of the productions of the same continent. Centres of creation. Means of dispersal, by changes of climate and of the level of the land, and by occasional means. Dispersal during the Glacial period co-extensive with the world.In considering the distribution of organic beings over the face of the globe, the first great fact which strikes us is, that neither the similarity nor the dissimilarity of the inhabitants of various regions can be accounted for by their climatal and other physical conditions. Of late, almost every author who has studied the subject has come to this conclusion. The case of America alone would almost suffice to prove itstruth: for if we exclude the northern parts where the circumpolar land is almost continuous, all authors agree that one of the most fundamental divisions in geographical distribution is that between the New and Old Worlds; yet if we travel over the vast American continent, from the central parts of the United States to its extreme southern point, we meet with the most diversified conditions; the most humid districts, arid deserts, lofty mountains, grassy plains, forests, marshes, lakes, and great rivers, under almost every temperature. There is hardly a climate or condition in the Old World which cannot be paralleled in the New--at least as closely as the same species generally require; for it is a most rare case to find a group of organisms confined to any small spot, having conditions peculiar in only a slight degree; for instance, small areas in the Old World could be pointed out hotter thanany in the New World, yet these are not inhabited by a peculiar fauna or flora. Notwithstanding this parallelism in the conditions of the Old and New Worlds, how widely different are their living productions!In the southern hemisphere, if we compare large tracts of land in Australia, South Africa, and western South America, between latitudes 25 deg and 35 deg, we shall find parts extremely similar in all their conditions, yet it would not be possible to point out three faunas and floras more utterly dissimilar. Or again we may compare the productions of South America south of lat. 35 deg with those north of 25 deg, which consequently inhabit a considerably different climate, and they will be found incomparably more closely related to each other, than they are to the productions of Australia or Africa under nearly the same climate. Analogous facts could be givenwith respect to the inhabitants of the sea.A second great fact which strikes us in our general review is, that barriers of any kind, or obstacles to free migration, are related in a close and important manner to the differences between the productions of various regions. We see this in the great difference of nearly all the terrestrial productions of the New and Old Worlds, excepting in the northern parts, where the land almost joins, and where, under a slightly different climate, there might have been free migration for the northern temperate forms, as there now is for the strictly arctic productions. We see the same fact in the great difference between the inhabitants of Australia, Africa, and South America under the same latitude: for these countries are almost as much isolated from each other as is possible. On each continent, also, we see the same fact; for on the opposite sides of lofty andcontinuous mountain-ranges, and of great deserts, and sometimes even of large rivers, we find different productions; though as mountain chains, deserts, etc., are not as impassable, or likely to have endured so long as the oceans separating continents, the differences are very inferior in degree to those characteristic of distinct continents.Turning to the sea, we find the same law. No two marine faunas are more distinct, with hardly a fish, shell, or crab in common, than those of the eastern and western shores of South and Central America; yet these great faunas are separated only by the narrow, but impassable, isthmus of Panama. Westward of the shores of America, a wide space of open ocean extends, with not an island as a halting-place for emigrants; here we have a barrier of another kind, and as soon as this is passed we meet in the eastern islands of the Pacific, with another and totallydistinct fauna. So that here three marine faunas range far northward and southward, in parallel lines not far from each other, under corresponding climates; but from being separated from each other by impassable barriers, either of land or open sea, they are wholly distinct. On the other hand, proceeding still further westward from the eastern islands of the tropical parts of the Pacific, we encounter no impassable barriers, and we have innumerable islands as halting-places, until after travelling over a hemisphere we come to the shores of Africa; and over this vast space we meet with no well-defined and distinct marine faunas. Although hardly one shell, crab or fish is common to the above-named three approximate faunas of Eastern and Western America and the eastern Pacific islands, yet many fish range from the Pacific into the Indian Ocean, and many shells are common to the eastern islands of the Pacificand the eastern shores of Africa, on almost exactly opposite meridians of longitude.A third great fact, partly included in the foregoing statements, is the affinity of the productions of the same continent or sea, though the species themselves are distinct at different points and stations. It is a law of the widest generality, and every continent offers innumerable instances. Nevertheless the naturalist in travelling, for instance, from north to south never fails to be struck by the manner in which successive groups of beings, specifically distinct, yet clearly related, replace each other. He hears from closely allied, yet distinct kinds of birds, notes nearly similar, and sees their nests similarly constructed, but not quite alike, with eggs coloured in nearly the same manner. The plains near the Straits of Magellan are inhabited by one species of Rhea(American ostrich), and northward the plains of La Plata by another species of the same genus; and not by a true ostrich or emeu, like those found in Africa and Australia under the same latitude. On these same plains of La Plata, we see the agouti and bizcacha, animals having nearly the same habits as our hares and rabbits and belonging to the same order of Rodents, but they plainly display an American type of structure. We ascend the lofty peaks of the Cordillera and we find an alpine species of bizcacha; we look to the waters, and we do not find the beaver or musk-rat, but the coypu and capybara, rodents of the American type. Innumerable other instances could be given. If we look to the islands off the American shore, however much they may differ in geological structure, the inhabitants, though they may be all peculiar species, are essentially American. We may look back to past ages, as shown in the last chapter, and wefind American types then prevalent on the American continent and in the American seas. We see in these facts some deep organic bond, prevailing throughout space and time, over the same areas of land and water, and independent of their physical conditions. The naturalist must feel little curiosity, who is not led to inquire what this bond is.This bond, on my theory, is simply inheritance, that cause which alone, as far as we positively know, produces organisms quite like, or, as we see in the case of varieties nearly like each other. The dissimilarity of the inhabitants of different regions may be attributed to modification through natural selection, and in a quite subordinate degree to the direct influence of different physical conditions. The degree of dissimilarity will depend on the migration of the more dominant forms of life from one region into another having been effectedwith more or less ease, at periods more or less remote;--on the nature and number of the former immigrants;--and on their action and reaction, in their mutual struggles for life;--the relation of organism to organism being, as I have already often remarked, the most important of all relations. Thus the high importance of barriers comes into play by checking migration; as does time for the slow process of modification through natural selection. Widely-ranging species, abounding in individuals, which have already triumphed over many competitors in their own widely-extended homes will have the best chance of seizing on new places, when they spread into new countries. In their new homes they will be exposed to new conditions, and will frequently undergo further modification and improvement; and thus they will become still further victorious, and will produce groups of modified descendants.On this principle of inheritance with modification, we can understand how it is that sections of genera, whole genera, and even families are confined to the same areas, as is so commonly and notoriously the case.I believe, as was remarked in the last chapter, in no law of necessary development. As the variability of each species is an independent property, and will be taken advantage of by natural selection, only so far as it profits the individual in its complex struggle for life, so the degree of modification in different species will be no uniform quantity. If, for instance, a number of species, which stand in direct competition with each other, migrate in a body into a new and afterwards isolated country, they will be little liable to modification; for neither migration nor isolation in themselves can do anything. These principles come into playonly by bringing organisms into new relations with each other, and in a lesser degree with the surrounding physical conditions. As we have seen in the last chapter that some forms have retained nearly the same character from an enormously remote geological period, so certain species have migrated over vast spaces, and have not become greatly modified.On these views, it is obvious, that the several species of the same genus, though inhabiting the most distant quarters of the world, must originally have proceeded from the same source, as they have descended from the same progenitor. In the case of those species, which have undergone during whole geological periods but little modification, there is not much difficulty in believing that they may have migrated from the same region; for during the vast geographical and climatal changes which will have supervened since ancient times, almost any amount ofmigration is possible. But in many other cases, in which we have reason to believe that the species of a genus have been produced within comparatively recent times, there is great difficulty on this head. It is also obvious that the individuals of the same species, though now inhabiting distant and isolated regions, must have proceeded from one spot, where their parents were first produced: for, as explained in the last chapter, it is incredible that individuals identically the same should ever have been produced through natural selection from parents specifically distinct.We are thus brought to the question which has been largely discussed by naturalists, namely, whether species have been created at one or more points of the earth's surface. Undoubtedly there are very many cases of extreme difficulty, in understanding how the same species could possibly havemigrated from some one point to the several distant and isolated points, where now found. Nevertheless the simplicity of the view that each species was first produced within a single region captivates the mind. He who rejects it, rejects the vera causa of ordinary generation with subsequent migration, and calls in the agency of a miracle. It is universally admitted, that in most cases the area inhabited by a species is continuous; and when a plant or animal inhabits two points so distant from each other, or with an interval of such a nature, that the space could not be easily passed over by migration, the fact is given as something remarkable and exceptional. The capacity of migrating across the sea is more distinctly limited in terrestrial mammals, than perhaps in any other organic beings; and, accordingly, we find no inexplicable cases of the same mammal inhabiting distant points of the world. No geologistwill feel any difficulty in such cases as Great Britain having been formerly united to Europe, and consequently possessing the same quadrupeds. But if the same species can be produced at two separate points, why do we not find a single mammal common to Europe and Australia or South America? The conditions of life are nearly the same, so that a multitude of European animals and plants have become naturalised in America and Australia; and some of the aboriginal plants are identically the same at these distant points of the northern and southern hemispheres? The answer, as I believe, is, that mammals have not been able to migrate, whereas some plants, from their varied means of dispersal, have migrated across the vast and broken interspace. The great and striking influence which barriers of every kind have had on distribution, is intelligible only on the view that the great majority of species have been produced on one sidealone, and have not been able to migrate to the other side. Some few families, many sub-families, very many genera, and a still greater number of sections of genera are confined to a single region; and it has been observed by several naturalists, that the most natural genera, or those genera in which the species are most closely related to each other, are generally local, or confined to one area. What a strange anomaly it would be, if, when coming one step lower in the series, to the individuals of the same species, a directly opposite rule prevailed; and species were not local, but had been produced in two or more distinct areas!Hence it seems to me, as it has to many other naturalists, that the view of each species having been produced in one area alone, and having subsequently migrated from that area as far as its powers of migration and subsistence under past andpresent conditions permitted, is the most probable. Undoubtedly many cases occur, in which we cannot explain how the same species could have passed from one point to the other. But the geographical and climatal changes, which have certainly occurred within recent geological times, must have interrupted or rendered discontinuous the formerly continuous range of many species. So that we are reduced to consider whether the exceptions to continuity of range are so numerous and of so grave a nature, that we ought to give up the belief, rendered probable by general considerations, that each species has been produced within one area, and has migrated thence as far as it could. It would be hopelessly tedious to discuss all the exceptional cases of the same species, now living at distant and separated points; nor do I for a moment pretend that any explanation could be offered of many such cases. But after somepreliminary remarks, I will discuss a few of the most striking classes of facts; namely, the existence of the same species on the summits of distant mountain-ranges, and at distant points in the arctic and antarctic regions; and secondly (in the following chapter), the wide distribution of freshwater productions; and thirdly, the occurrence of the same terrestrial species on islands and on the mainland, though separated by hundreds of miles of open sea. If the existence of the same species at distant and isolated points of the earth's surface, can in many instances be explained on the view of each species having migrated from a single birthplace; then, considering our ignorance with respect to former climatal and geographical changes and various occasional means of transport, the belief that this has been the universal law, seems to me incomparably the safest.In discussing this subject, we shall be enabled at the same time to consider a point equally important for us, namely, whether the several distinct species of a genus, which on my theory have all descended from a common progenitor, can have migrated (undergoing modification during some part of their migration) from the area inhabited by their progenitor. If it can be shown to be almost invariably the case, that a region, of which most of its inhabitants are closely related to, or belong to the same genera with the species of a second region, has probably received at some former period immigrants from this other region, my theory will be strengthened; for we can clearly understand, on the principle of modification, why the inhabitants of a region should be related to those of another region, whence it has been stocked. A volcanic island, for instance, upheaved and formed at the distance of a few hundredsof miles from a continent, would probably receive from it in the course of time a few colonists, and their descendants, though modified, would still be plainly related by inheritance to the inhabitants of the continent. Cases of this nature are common, and are, as we shall hereafter more fully see, inexplicable on the theory of independent creation. This view of the relation of species in one region to those in another, does not differ much (by substituting the word variety for species) from that lately advanced in an ingenious paper by Mr. Wallace, in which he concludes, that "every species has come into existence coincident both in space and time with apre-existing closely allied species." And I now know from correspondence, that this coincidence he attributes to generation with modification.The previous remarks on "single and multiple centres ofcreation" do not directly bear on another alliedquestion,--namely whether all the individuals of the same species have descended from a single pair, or single hermaphrodite, or whether, as some authors suppose, from many individuals simultaneously created. With those organic beings which never intercross (if such exist), the species, on my theory, must have descended from a succession of improved varieties, which will never have blended with other individuals or varieties, but will have supplanted each other; so that, at each successive stage of modification and improvement, all the individuals of each variety will have descended from a single parent. But in the majority of cases, namely, with all organisms which habitually unite for each birth, or which often intercross, I believe that during the slow process of modification the individuals of the species will have been keptnearly uniform by intercrossing; so that many individuals will have gone on simultaneously changing, and the whole amount of modification will not have been due, at each stage, to descent from a single parent. To illustrate what I mean: our English racehorses differ slightly from the horses of every other breed; but they do not owe their difference and superiority to descent from any single pair, but to continued care in selecting and training many individuals during many generations.Before discussing the three classes of facts, which I have selected as presenting the greatest amount of difficulty on the theory of "single centres of creation," I must say a few words on the means of dispersal.MEANS OF DISPERSAL.Sir C. Lyell and other authors have ably treated this subject. I can give here only the briefest abstract of the moreimportant facts. Change of climate must have had a powerful influence on migration: a region when its climate was different may have been a high road for migration, but now be impassable;I shall, however, presently have to discuss this branch of the subject in some detail. Changes of level in the land must also have been highly influential: a narrow isthmus now separates two marine faunas; submerge it, or let it formerly have been submerged, and the two faunas will now blend or may formerly have blended: where the sea now extends, land may at a former period have connected islands or possibly even continents together, and thus have allowed terrestrial productions to pass from one to the other. No geologist will dispute that great mutations of level have occurred within the period of existing organisms. Edward Forbes insisted that all the islands in the Atlantic must recently have been connected with Europe orAfrica, and Europe likewise with America. Other authors have thus hypothetically bridged over every ocean, and have united almost every island to some mainland. If indeed the arguments used by Forbes are to be trusted, it must be admitted that scarcely a single island exists which has not recently been united to some continent. This view cuts the Gordian knot of the dispersal of the same species to the most distant points, and removes many a difficulty: but to the best of my judgment we are not authorized in admitting such enormous geographical changes within the period of existing species. It seems to me that we have abundant evidence of great oscillations of level in our continents; but not of such vast changes in their position and extension, as to have united them within the recent period to each other and to the several intervening oceanic islands. I freely admit the former existence of many islands,now buried beneath the sea, which may have served as halting places for plants and for many animals during their migration. In the coral-producing oceans such sunken islands are now marked, as I believe, by rings of coral or atolls standing over them. Whenever it is fully admitted, as I believe it will some day be, that each species has proceeded from a single birthplace, and when in the course of time we know something definite about the means of distribution, we shall be enabled to speculate with security on the former extension of the land. But I do not believe that it will ever be proved that within the recent period continents which are now quite separate, have been continuously, or almost continuously, united with each other, and with the many existing oceanic islands. Several facts in distribution,--such as the great difference in the marine faunas on the opposite sides of almost every continent,--theclose relation of the tertiary inhabitants of several lands and even seas to their present inhabitants,--a certain degree of relation (as we shall hereafter see) between the distribution of mammals and the depth of the sea,--these and other such facts seem to me opposed to the admission of such prodigious geographical revolutions within the recent period, as are necessitated on the view advanced by Forbes and admitted by his many followers. The nature and relative proportions of the inhabitants of oceanic islands likewise seem to me opposed to the belief of their former continuity with continents. Nor does their almost universally volcanic composition favour the admission that they are the wrecks of sunken continents;--if they had originally existed as mountain-ranges on the land, some at least of the islands would have been formed, like other mountain-summits, of granite, metamorphic schists, oldfossiliferous or other such rocks, instead of consisting of mere piles of volcanic matter.I must now say a few words on what are called accidental means, but which more properly might be called occasional means of distribution. I shall here confine myself to plants. In botanical works, this or that plant is stated to be ill adapted for wide dissemination; but for transport across the sea, the greater or less facilities may be said to be almost wholly unknown. Until I tried, with Mr. Berkeley's aid, a few experiments, it was not even known how far seeds could resist the injurious action of sea-water. To my surprise I found that out of 87 kinds, 64 germinated after an immersion of 28 days, and a few survived an immersion of 137 days. For convenience sake I chiefly tried small seeds, without the capsule or fruit; and as all of these sank in a few days, they could not be floatedacross wide spaces of the sea, whether or not they were injured by the salt-water. Afterwards I tried some larger fruits, capsules, etc., and some of these floated for a long time. It is well known what a difference there is in the buoyancy of green and seasoned timber; and it occurred to me that floods might wash down plants or branches, and that these might be dried on the banks, and then by a fresh rise in the stream be washed into the sea. Hence I was led to dry stems and branches of 94 plants with ripe fruit, and to place them on sea water. The majority sank quickly, but some which whilst green floated for a very short time, when dried floated much longer; for instance, ripe hazel-nuts sank immediately, but when dried, they floated for 90 days and afterwards when planted they germinated; an asparagus plant with ripe berries floated for 23 days, when dried it floated for 85 days, and the seeds afterwardsgerminated: the ripe seeds of Helosciadium sank in two days, when dried they floated for above 90 days, and afterwards germinated. Altogether out of the 94 dried plants, 18 floated for above 28 days, and some of the 18 floated for a very much longer period. So that as 64/87 seeds germinated after an immersion of 28 days; and as 18/94 plants with ripe fruit (but not all the same species as in the foregoing experiment) floated, after being dried, for above 28 days, as far as we may infer anything from these scanty facts, we may conclude that the seeds of 14/100 plants of any country might be floated by sea-currents during 28 days, and would retain their power of germination. In Johnston's Physical Atlas, the average rate of the several Atlantic currents is 33 miles per diem (some currents running at the rate of 60 miles per diem); on this average, the seeds of 14/100 plants belonging to one country might be floatedacross 924 miles of sea to another country; and when stranded, if blown to a favourable spot by an inland gale, they would germinate.Subsequently to my experiments, M. Martens tried similar ones, but in a much better manner, for he placed the seeds in a box in the actual sea, so that they were alternately wet and exposed to the air like really floating plants. He tried 98 seeds, mostly different from mine; but he chose many large fruits and likewise seeds from plants which live near the sea; and this would have favoured the average length of their flotation and of their resistance to the injurious action of the salt-water. On the other hand he did not previously dry the plants or branches with the fruit; and this, as we have seen, would have caused some of them to have floated much longer. The result was that 18/98 of his seeds floated for 42 days, and werethen capable of germination. But I do not doubt that plants exposed to the waves would float for a less time than those protected from violent movement as in our experiments. Therefore it would perhaps be safer to assume that the seeds of about 10/100 plants of a flora, after having been dried, could be floated across a space of sea 900 miles in width, and would then germinate. The fact of the larger fruits often floating longer than the small, is interesting; as plants with large seeds or fruit could hardly be transported by any other means; and Alph. de Candolle has shown that such plants generally have restricted ranges.But seeds may be occasionally transported in another manner. Drift timber is thrown up on most islands, even on those in the midst of the widest oceans; and the natives of the coral-islands in the Pacific, procure stones for their tools, solely from theroots of drifted trees, these stones being a valuable royal tax.I find on examination, that when irregularly shaped stones are embedded in the roots of trees, small parcels of earth are very frequently enclosed in their interstices and behind them,--so perfectly that not a particle could be washed away in the longest transport: out of one small portion of earth thus COMPLETELY enclosed by wood in an oak about 50 years old, three dicotyledonous plants germinated: I am certain of the accuracy of this observation. Again, I can show that the carcasses of birds, when floating on the sea, sometimes escape being immediately devoured; and seeds of many kinds in the crops of floating birds long retain their vitality: peas and vetches, for instance, are killed by even a few days' immersion in sea-water; but some taken out of the crop of a pigeon, which had floated on artificial salt-water for 30 days, to my surprise。