范文一:孟德尔遗传规律的发现和假说演绎法
假说演绎法四个步骤:发现问题―→构想假说―→演绎假说―→实验验证
假说演绎法是科学家为了获得对某一未知问题的答案,往往要通过自己的知识、经验和想象力提出一种假说,来解释这一未知的问题。从知识和经验上看,这种假设似乎是正确的,但要成为能被人们广泛接受的理论,还必需根据假说进行演绎推理得到一定的预期结果,再通过实验检验演绎推理的预期结果。如果实验结果与假说预期的结果一致,则说明假说是正确的,可以上升为理论;如果实验结果与假说预期的不一致,则还需要继续研究。
下面以孟德尔对基因的分离定律的探究加以说明,孟德尔的探究过程是:
一、发现问题
(1)提出问题 在孟德尔以前,人们对生物的遗传也进行了探索。但这些探
索都没有用实验的方法进行,大多是猜想和臆断,所以不能对生物的遗传作出科学的解释。孟德尔设想,对生物的遗传规律用实验的方法进行探究,可能从中找出遗传的科学规律。
(2)设计实验 豌豆是自花授粉植物,后代一般是纯种;豌豆的相对性状区别比较明显,易于观察和分析。孟德尔运用豌豆作实验材料,设计了具有相对性状的豌豆作为亲本进行杂交,得到杂交子一代,让杂交子一代自交,得到了杂交子二代。
(3)分析数据? 孟德尔观察和分析了杂交子一代和子二代性状表现和不同性状表现的个体的数据。在分析数据以前,孟德尔对实验中出现的各种现象进行概念规范,建立了一套杂交实验知识的概念体系。 孟德尔概念体系如下:
基因―――――――――――――――――――――――――――――性状
| |
等位基因 显性基因―――――――――――――――显性性状 相对性状
| 隐性基因―――――――――――――――隐性性状 |
| | | |
| (纯合子与杂合子) (显性类型与隐性类型)|
基因分离―――――――――――――――――――――――――性状分离
孟德尔假设的概念体系
孟德尔在分析杂交子二代的数据时,运用当时数学领域的最新成果----------统计学。所以他对数据分析的规律性和科学性都比较强。孟德尔发现,用具有一对相对性状的豌豆杂交,杂交子一代都表现为显性性状;子二代都表现出3∶1的性状分离比。
二、构想假说 孟德尔对豌豆杂交实验中出现的杂交子一代都表现为显性性状,子二代都表现出3∶1的性状分离比的实验结果作出了解释性的假设。“孟德尔假设”的主要内容有:
1.生物的性状遗传是由基因(孟德尔当时称遗传因子)控制的。 2.根本原因(后来的分离定律):控制某个性状遗传的基因在体细胞中成对存在,在生殖细胞中成单个存在。
3.必要因素:雌雄配子受精机会均等。
4.重要条件:个体发育(基因的表达)必须具有适宜的环境条件。
以上就是“孟德尔假设”的主要内容。用孟德尔假设能够圆满地解释植物杂交实验中出现的各种实验结果。
三、演绎假说 “孟德尔假设”能圆满地解释植物杂交实验的实验结果。他进一步设想,如果他的假设是正确的,则他的假设不仅能够解释以上相同类型的杂交实验结果,还要能够解释并预期其他不同类型的杂交实验结果。因此,孟德尔根据“孟德尔假设”设计了测交实验,即把杂交子一代与隐性类型相交,根据“孟德尔假设”的预期,测交后代会出现1∶1的性状分离结果。
四、验证假说 孟德尔做完测交实验,并对其结果进行统计分析,果然与“孟德尔假设”预期的结果完全相符。
五、被实践检验是正确的假说可以上升为理论
“孟德尔假设”是从实践中得出的,现在又被测交实验检验是正确的。所以,孟德尔假设可以上升为理论,即基因的分离定律(课本上对分离定律指强调了在形成配子时,等位基因分离这一核心问题)。
六、孟德尔成功的原因。
(1)运用了假说演绎法: 孟德尔通过对具有一对相对性状的豌豆进行杂交实验,并从实验结果中发现了豌豆遗传的普遍问题――杂交后代的性状分离比为3∶1。并通过严谨的和富于创造性的思维,提出了能圆满解释杂交实验结果(杂交后代性状分离比为3∶1)的“假说”。孟德尔又把他的“假说”进行演绎,预期了测交后代性状分离比应为1∶1的结果,并运用测交实验来验证他预期的结果。
(2)探究方法的划时代性:在孟德尔以前,人们对生物学的研究主要是运用观察、调查、类比等方法进行研究,这些方法难以取得重大突破。孟德尔用实验的方法研究生物的遗传,取得了重大成果。自1900年,孟德尔的遗传定律被人们重新发现后,人们认识到用实验的方法研究生物学,比较容易取得重大成果,用实验的方法研究生物学在生物学研究领域蔚然成风,从此,生物学研究走上实验生物学时代。同时人们还认识到孟德尔理论是现代遗传学的奠基性成就,孟德尔被誉为“遗传学之父”。
(3)实验材料选择得好:用豌豆作实验材料的优点是,豌豆是严格的自花传粉植物,后代一般是纯种。豌豆的相对性状之间区分明显,不易混淆。
(4)注重运用当时的最新科学成果,孟德尔运用了当时数学统计学方面的最新成果,对杂交后代中出现的性状分离现象进行统计学分析,而这一点正是被前人忽视的问题。
(5)锲而不舍的精神:孟德尔成果的取得,经过了8年时间持之以恒的探索。
范文二:孟德尔对假说—演绎法的运用
孟德尔对假说—演绎法的运用
三亚一中 陈彬
假说—演绎法是指首先通过实验或其他方法观察到现象,然后通过分析这个现象后提出问题,再运用推理和想像的方法提出解释这个问题的假说,然后再根据假说进行演绎推理得出有关结论,最后是通过实验检验这个结论。如果检验结果与假说的预期结果相符,就证明假说是正确的,反之,说明假说不正确。
下面是孟德尔对假说—演绎法的运用:
首先孟德尔通过豌豆杂交实验,
亲本P 纯种高茎 × 纯种矮茎
?
子一代F1 全为高茎
子一代F1自交 ?
子二代F2 高茎 矮茎
子二代F2比例 3 : 1
观察到的现象:F1都表现出显性性状、F2出现了性状分离、F2中出现3:1的性状分离比。
然后分析这个现象并提出问题:为什么子一代中只表现一个亲本的性状(高茎),而不表现另一个亲本的性状或不高不矮的性状,另一个亲本的性状是永远消失了还是暂时隐藏起来,F2中的3:1是不是巧合,
第三、运用推理和想像的方法提出解释这个问题的假说:
1、生物的性状是由遗传因子决定的。这些遗传因子就像一个个独立的颗粒,既不会相互融合、也不会在遗传中消失。每个因子决定着一种特定的性状,其中决定显性性状的为显性遗传因子,用大写字母(如D)表示;决定隐性性状的为隐性遗传因子,用小写字母(如d)表示。
2、体细胞中遗传因子是成对存在的。例如,纯种高茎豌豆的体细胞中有成对的遗传因子DD,纯种矮茎豌豆的体细胞中有成对的遗传因子dd。像这样,遗传因子组成相同的个体叫做纯合子。因为F1自交的后代中出现了隐性性状,所以在F1的体细胞中必然含有隐性遗传因子,而F1表现的是显性性状,因此F1的体细胞中的遗传因子应该是Dd。像这样,遗传因子组成不同的个体叫做杂合子。
3、生物体在形成生殖细胞-----配子时,成对的遗传因子彼此分离,分别进入不同的配子中。配子中只含有每对遗传因子中的一个。
1
4、受精时,雌雄配子的结合是随机的。例如,含遗传因子D的配子,既可以与含遗传因子D的配子结合,又可以与含遗传因子d的配子结合。
第四,根据假说进行演绎推理得出有关结论:
P 纯种高茎 × 纯种矮茎
DD dd
? ?
配子 D d
? ?
F1 Dd
高茎
F1 高茎 × 高茎
Dd Dd
? ? ? ?
配子 D d D d
?? ? ? ? ? ??
F2 DD Dd Dd dd
表现型 高茎 高茎 高茎 矮茎
表现型比例 3 : 1
第五、通过测交实验检验这个结论。如果检验结果与假说的预期结果相符,就证明假说是正确的,反之,说明假说不正确。
孟德尔的测交实验结果:
用杂种子一代F1高茎豌豆(Dd)与隐性纯合子矮茎豌豆(dd)杂交,在所得到的64株后代中,有30株是高茎,34株是矮茎,这两种性状的分离比接近1:1。
假说的预期结果:
杂种子一代F1高茎 × 隐性纯合子矮茎
测交 Dd dd
? ? ?
配子 D d d
? ? ? ?
测交后代 Dd dd
高茎 矮茎
比例 1 : 1
检验结果与假说的预期结果相符,证明孟德尔的假说是正确。
2
范文三:孟德尔的故事
孟德尔的故事
孟德尔的故事
2011年10月17日
孟德尔(Gregor Johann Mendel) (1822年7月22日-1884年1月6日)是“现代遗传学之父(father of modern genetics)”,是遗传学的奠基人。1865年发现遗传定律。
1822年7月22日,孟德尔[1]出生在奥地利西里西亚(现属捷克)海因策道夫村的一个贫寒的农民家庭里,父亲和母亲都是园艺家(外祖父是园艺工
。孟德尔童年时受到园艺学和农学知识的熏陶,对植物的生长和开花非常感人)
兴趣。
1840年他考入奥尔米茨大学哲学院,主攻古典哲学,但他还学习了数学和物理学。
当时,在欧洲,学校都是教会办的。学校需要教师,当地的教会看到孟德尔勤奋好学,就派他到首都维也纳大学去念书。
1843年大学毕业以后,年方21岁的孟德尔进了布隆城奥古斯汀修道院,并在当地教会办的一所中学教书,教的是自然科学。他由于能专心备课,认真教课,所以很受学生的欢迎。后来,他又到维也纳大学深造,受到相当系统和严格的科学教育和训练,也受到杰出科学家们的影响,如多普勒,孟德尔为他当物理学演示助手;又如依汀豪生,他是一位数学家和物理学家;还有恩格尔,他是细胞理论发展中的一位重要人物,但是由于否定植物物种的稳定性而受到教士们的攻击。这些为他后来的科学实践打下了坚实的基础。孟德尔经过长期思索认识到,理解那些使遗传性状代代恒定的机制更为重要。
1856年,从维也纳大学回到布鲁恩不久,孟德尔就开始了长达8年的豌豆实验。孟德尔首先从许多种子商那里,弄来了34个品种的豌豆,从中挑选
出22个品种用于实验。它们都具有某种可以相互区分的稳定性状,例如高茎或矮茎、圆料或皱科、灰色种皮或白色种皮等。
孟德尔通过人工培植这些豌豆,对不同代的豌豆的性状和数目进行细致入微的观察、计数和分析。运用这样的实验方法需要极大的耐心和严谨的态度。他酷爱自己的研究工作,经常向前来参观的客人指着豌豆十分自豪地说:“这些都是我的儿女~”
8个寒暑的辛勤劳作,孟德尔发现了生物遗传的基本规律,并得到了相应的数学关系式。人们分别称他的发现为“孟德尔第一定律”和“孟德尔第二定律”,它们揭示了生物遗传奥秘的基本规律。
孟德尔开始进行豌豆实验时,达尔文进化论刚刚问世。他仔细研读了达尔文的著作,从中吸收丰富的营养。保存至今的孟德尔遗物之中,就有好几本达尔文的著作,上面还留着孟德尔的手批,足见他对达尔文及其著作的关注。
起初,孟德尔豌豆实验并不是有意为探索遗传规律而进行的。他的初衷是希望获得优良品种,只是在试验的过程中,逐步把重点转向了探索遗传规律。除了豌豆以外,孟德尔还对其他植物作了大量的类似研究,其中包括玉米、紫罗兰和紫茉莉等,以期证明他发现的遗传规律对大多数植物都是适用的。
从生物的整体形式和行为中很难观察并发现遗传规律,而从个别性状中却容易观察,这也是科学界长期困惑的原因。孟德尔不仅考察生物的整体,更着眼于生物的个别性状,这是他与前辈生物学家的重要区别之一。孟德尔选择的实验材料也是非常科学的。因为豌豆属于具有稳定品种的自花授粉植物,容易栽种,容易逐一分离计数,这对于他发现遗传规律提供了有利的条件。
孟德尔清楚自己的发现所具有的划时代意义,但他还是慎重地重复实验了多年,以期更加臻于完善、1865年,孟德尔在布鲁恩科学协会的会议厅,将自己的研究成果分两次宣读。第一次,与会者礼貌而兴致勃勃地听完报告,孟德尔只简单地介绍了试验的目的、方法和过程,为时一小时的报告就使听众如坠入云雾中。
第二次,孟德尔着重根据实验数据进行了深入的理论证明。可是,伟大的孟德尔思维和实验太超前了。尽管与会者绝大多数是布鲁恩自然科学协会的会员,中既有化学家、地质学家和生物学家,也有生物学专业的植物学家、藻类学家。然而,听众对连篇累续的数字和繁复枯燥的论证毫无兴趣。他们实在跟不上孟德尔的思维。孟德尔用心血浇灌的豌豆所告诉他的秘密,时人不能与之共识,一直被埋没了35年之久~
豌豆的杂交实验从1856年至1864年共进行了8年。孟德尔将其研究的结果整理成论文发表,但未引起任何反响。其原因有三个。
第一,在孟德尔论文发表前7年(1859年),达尔文的名著《物种起源》出版了。这部著作引起了科学界的兴趣,几乎全部的生物学家转向生物进化的讨论。这一点也许对孟德尔论文的命运起了决定性的作用。
第二,当时的科学界缺乏理解孟德尔定律的思想基础。首先那个时代的科学思想还没有包含孟德尔论文所提出的命题:遗传的不是一个个体的全貌,而是一个个性状。其次,孟德尔论文的表达方式是全新的,他把生物学和统计学、数学结合了起来,使得同时代的博物学家很难理解论文的真正含义。
第三,有的权威出于偏见或不理解,把孟德尔的研究视为一般的杂交实验,和别人做的没有多大差别。
孟德尔晚年曾经充满信心地对他的好友,布鲁恩高等技术学院大地测
教授尼耶塞尔说:“看吧,我的时代来到了。”这句话成为伟大的预言。量学
直到孟德尔逝世16年后,豌豆实验论文正式出版后34年,他从事豌豆试验后43年,预言才变成现实。
随着20世纪雄鸡的第一声啼鸣,来自三个国家的三位学者同时独立地“重新发现”孟德尔遗传定律。1900年,成为遗传学史乃至生物科学史上划时代的一年。从此,遗传学进入了孟德尔时代。
今天,通过摩尔根、艾弗里、赫尔希和沃森等数代科学家的研究,已经使生物遗传机制——这个使孟德尔魂牵梦绕的问题建立在遗传物质DNA的基础之上。
随着科学家破译了遗传密码,人们对遗传机制有了更深刻的认识。现在,人们已经开始向控制遗传机制、防治遗传疾病、合成生命等更大的造福于人类的工作方向前进。然而,所有这一切都与圣托马斯修道院那个献身于科学
的修道士的名字相连。
诗评:
八年耕耘源于对科学的痴迷,
一畦畦豌豆蕴藏遗传的秘密。
实验设计开辟了研究的新路,
数学统计揭示出遗传的规律。
孟德尔遗传规律
任何一门学科的形成与发展,总是同当时热衷于这门科学研究的杰出人物紧密相关,遗传学的形成与发展也不例外,孟德尔就是遗传学杰出的奠基人。他揭示出遗传学的两个基本定律——分离定律和自由组合定律。
孟德尔
1822年出生于当时奥地利海森道夫地区的一个贫苦农民家庭,他的父亲擅长于园艺技术,在父亲的直接熏陶和影响之下,孟德尔自幼就爱好园艺。1843年,他中学毕业后考入奥尔谬茨大学哲学院继续学习,但因家境贫寒,被迫中途辍学。1843年10月,因生活所迫,他步入奥地利布隆城的一所修道院当修道士。从1851年到1853年,孟德尔在维也纳大学学习了4个学期,系统学习了植物学、动物学、物理学和化学等课程。与此同时,他还受到了从事科学研究的良好训练,这些都为他后来从事植物杂交的科学研究奠定了坚实的理论基础。1854年孟德尔回到家乡,继续在修道院任职,并利用业余时间开始了长达12年的植物杂交试验。
在孟德尔从事的大量植物杂交试验中,以豌豆杂交试验的成绩最为出色。经过整整8年(1856-1864)的不懈努力,终于在1865年发表了《植物杂
交试验》的论文,提出了遗传单位是遗传因子(现代遗传学称为基因)的论点,并揭示出遗传学的两个基本规律——分离规律和自由组合规律。这两个重要规律的发现和提出,为遗传学的诞生和发展奠定了坚实的基础,这也正是孟德尔
名垂后世的重大科研成果。
孟德尔的这篇不朽论文虽然问世了,但令人遗憾的是,由于他那不同于前人的创造性见解,对于他所处的时代显得太超前了,竟然使得他的科学论文在长达35年的时间里,没有引起生物界同行们的注意。直到1900年,他的发现被欧洲三位不同国籍的植物学家在各自的豌豆杂交试验中分别予以证实后,才受到重视和公认,遗传学的研究从此也就很快地发展起来。
范文四:孟德尔的论文
孟德尔的论文——植物杂交试验(1865)
资料来源:
Experiments in Plant Hybridization (1865)
by Gregor Mendel
Introductory Remarks
of artificial fertilization, such as is effected with plants in order to obtain new variations in color, has led to the experiments which will here be discussed. The striking regularity with which the same hybrid forms always reappeared whenever fertilization took place between the same species induced further experiments to be undertaken, the object of which was to follow up the developments of the hybrids in their progeny.
To this object numerous careful observers, such as K?lreuter, G?rtner, Herbert, Lecoq, Wichura and others, have devoted a part of their lives with inexhaustible perseverance. G?rtner especially in his work Die Bastarderzeugung im Pflanzenreiche [The Production of Hybrids in the Vegetable Kingdom], has recorded very valuable observations; and quite recently Wichura published the results of some profound investigations into the hybrids of the Willow. That, so far, no generally applicable law governing the formation and development of hybrids has been successfully
formulated can hardly be wondered at by anyone who is acquainted with the extent of the task, and can appreciate the difficulties with which experiments of this class have to contend. A final decision can only be arrived at when we shall have before us the results of detailed experiments made on plants belonging to the most diverse orders.
Those who survey the work done in this department will arrive at the conviction that among all the numerous experiments made, not one has been carried out to such an extent and in such a way as to make it possible to determine the number of different forms under which the offspring of the hybrids appear, or to arrange these forms with certainty according to their separate generations, or definitely to ascertain their statistical relations.
It requires indeed some to undertake a labor of such far-reaching extent; this appears, however, to be the only right way by which we can finally reach the solution of a question the importance of which cannot be overestimated in connection with the history of the evolution of organic forms.
The paper now presented records the results of such a detailed experiment. This experiment was practically confined to a small plant group, and is now, after eight years' pursuit, concluded in all essentials. Whether the plan upon which the separate experiments were conducted and carried out was the best suited to attain the desired end is left to the friendly decision of the reader. Selection of the Experimental Plants
The value and utility of any experiment are determined by the fitness of the material to the purpose for which it is used, and thus in the case before us it cannot be immaterial what plants are subjected to experiment and in what manner such experiment is conducted.
The selection of the plant group which shall serve for experiments of this kind must be made with all possible care if it be desired to avoid from the outset every risk of questionable results. The experimental plants must necessarily:
1. Possess constant differentiating characteristics.
2. The hybrids of such plants must, during the flowering period, be protected from the
influence of all foreign pollen, or be easily capable of such protection.
The hybrids and their offspring should suffer no marked disturbance in their fertility in the successive generations.
Accidental impregnation by foreign pollen, if it occurred during the experiments and were not recognized, would lead to entirely erroneous conclusions. Reduced fertility or entire sterility of certain forms, such as occurs in the offspring of many hybrids, would render the experiments very difficult or entirely frustrate them. In order to discover the relations in which the hybrid forms stand towards each other and also towards their progenitors it appears to be necessary that all member of the series developed in each successive generations should be, without exception, subjected to observation.
At the very outset special attention was devoted to the Leguminosae on account of their peculiar floral structure. Experiments which were made with several members of this family led to the result that the genus Pisum was found to possess the necessary qualifications.
Some thoroughly distinct forms of this genus possess characters which are constant, and easily and certainly recognizable, and when their hybrids are mutually crossed they yield perfectly fertile
progeny. Furthermore, a disturbance through foreign pollen cannot easily occur, since the fertilizing organs are closely packed inside the keel and the anthers burst within the bud, so that the stigma becomes covered with pollen even before the flower opens. This circumstance is especially
important. As additional advantages worth mentioning, there may be cited the easy culture of these plants in the open ground and in pots, and also their relatively short period of growth. Artificial fertilization is certainly a somewhat elaborate process, but nearly always succeeds. For this purpose the bud is opened before it is perfectly developed, the keel is removed, and each stamen carefully extracted by means of forceps, after which the stigma can at once be dusted over with the foreign pollen.
In all, 34 more or less distinct varieties of Peas were obtained from several seedsmen and subjected to a two year's trial. In the case of one variety there were noticed, among a larger number of plants all alike, a few forms which were markedly different. These, however, did not vary in the following year, and agreed entirely with another variety obtained from the same seedsman; the seeds were therefore doubtless merely accidentally mixed. All the other varieties yielded perfectly constant and similar offspring; at any rate, no essential difference was observed during two trial years. For
fertilization 22 of these were selected and cultivated during the whole period of the experiments. They remained constant without any exception.
Their systematic is difficult and uncertain. If we adopt the strictest definition of a species, according to which only those individuals belong to a species which under precisely the same circumstances display precisely similar characters, no two of these varieties could be referred to one species. According to the opinion of experts, however, the majority belong to the species Pisum sativum; while the rest are regarded and classed, some as sub-species of P. sativum, and some as independent species, such as P. quadratum, P. saccharatum, and P. umbellatum. The
positions, however, which may be assigned to them in a classificatory system are quite immaterial for the purposes of the experiments in question. It has so far been found to be just as impossible to draw a sharp line between the hybrids of species and varieties as between species and varieties themselves.
Division and Arrangement of the Experiments
If two plants which differ constantly in one or several characters be crossed, numerous experiments have demonstrated that the common characters are transmitted unchanged to the hybrids and their progeny; but each pair of differentiating characters, on the other hand, unite in the hybrid to form a new character, which in the progeny of the hybrid is usually variable. The object of the experiment was to observe these variations in the case of each pair of differentiating characters, and to deduce the law according to which they appear in successive generations. The experiment resolves itself therefore into just as many separate experiments are there are constantly differentiating characters presented in the experimental plants.
The various forms of Peas selected for crossing showed differences in length and color of the stem; in the size and form of the leaves; in the position, color, size of the flowers; in the length of the flower stalk; in the color, form, and size of the pods; in the form and size of the seeds; and in the color of the seed-coats and of the albumen [cotyledons]. Some of the characters noted do not permit of a sharp and certain separation, since the difference is of a "more or less" nature, which is often difficult to define. Such characters could not be utilized for the separate experiments; these could only be applied to characters which stand out clearly and definitely in the plants. Lastly, the result must show whether they, in their entirety, observe a regular behavior in their hybrid unions, and whether from these facts any conclusion can be reached regarding those characters which possess a subordinate significance in the type.
The characters which were selected for experiment relate:
1. To the difference in the form of the ripe seeds. These are either round or roundish, the depressions, if any,
occur on the surface, being always only shallow; or they are irregularly angular and deeply wrinkled (P. quadratum).
2. To the difference in the color of the seed albumen (endosperm). The albumen of the ripe seeds is either
pale yellow, bright yellow and orange colored, or it possesses a more or less intense green tint. This
difference of color is easily seen in the seeds as their coats are transparent.
3. To the difference in the color of the seed-coat. This is either white, with which character white flowers are
constantly correlated; or it is gray, gray-brown, leather-brown, with or without violet spotting, in which
case the color of the standards is violet, that of the wings purple, and the stem in the axils of the leaves is of a reddish tint. The gray seed-coats become dark brown in boiling water.
4. To the difference in the form of the ripe pods. These are either simply inflated, not contracted in places; or
they are deeply constricted between the seeds and more or less wrinkled (P. saccharatum).
5. To the difference in the color of the unripe pods. They are either light to dark green, or vividly yellow, in
which coloring the stalks, leaf-veins, and calyx participate.*
6. To the difference in the position of the flowers. They are either axial, that is, distributed along the main
stem; or they are terminal, that is, bunched at the top of the stem and arranged almost in a false umbel; in this case the upper part of the stem is more or less widened in section (P. umbellatum).
7. To the difference in the length of the stem. The length of the stem is very various in some forms; it is,
however, a constant character for each, in so far that healthy plants, grown in the same soil, are only
subject to unimportant variations in this character. In experiments with this character, in order to be able to discriminate with certainty, the long axis of 6 to 7 ft. was always crossed with the short one of 3/4 ft. to 1 and 1/2 ft.
Each two of the differentiating characters enumerated above were united by cross-fertilization. There were made for the
1st trial 60 fertilizations on 15 plants.
2nd trial 58 fertilizations on 10 plants.
3rd trial 35 fertilizations on 10 plants.
4th trial 40 fertilizations on 10 plants.
5th trial 23 fertilizations on 5 plants.
6th trial 34 fertilizations on 10 plants. 7th trial 37 fertilizations on 10 plants.
*One species possesses a beautifully brownish-red colored pod, which when ripening turns to violet and blue. Trials with this character were only begun last year. From a larger number of plants of the same variety only the most vigorous were chosen for
fertilization. Weakly plants always afford uncertain results, because even in the first generation of hybrids, and still more so in the subsequent ones, many of the offspring either entirely fail to flower or only form a few and inferior seeds.
Furthermore, in all the experiments reciprocal crossings were effected in such a way that each of the two varieties which in one set of fertilizations served as seed-bearer in the other set was used as the pollen plant.
The plants were grown in garden beds, a few also in pots, and were maintained in their natural upright position by means of sticks, branches of trees, and strings stretched between. For each experiment a number of pot plants were placed during the blooming period in a greenhouse, to serve as control plants for the main experiment in the open as regards possible disturbance by insects. Among the insects which visit Peas the beetle Buchus pisi might be detrimental to the
experiments should it appear in numbers. The female of this species is known to lay the eggs in the flower, and in so doing opens the keel; upon the tarsi of one specimen, which was caught in a
flower, some pollen grains could clearly be seen under a lens. Mention must also be made of a
circumstance which possibly might lead to the introduction of foreign pollen. It occurs, for instance, in some rare cases that certain parts of an otherwise normally developed flower wither, resulting in a partial exposure of the fertilizing organs. A defective development of the keel has also been observed, owing to which the stigma and anthers remained partially covered. It also sometimes happens that the pollen does not reach full perfection. In this event there occurs a gradual
lengthening of the pistil during the blooming period, until the stigmatic tip protrudes at the point of the keel. This remarkable appearance has also been observed in hybrids of Phaseolus and Lathyrus. The risk of false impregnation by foreign pollen is, however, a very slight one with Pisum, and is quite incapable of disturbing the general result. Among more than 10,000 plants which were
carefully examined there were only a very few cases where an indubitable false impregnation had occurred. Since in the greenhouse such a case was never remarked, it may well be supposed that Brucus pisi, and possibly also the described abnormalities in the floral structure, were to blame. The Forms of the Hybrids
Experiments which in previous years were made with ornamental plants have already affording evidence that the hybrids, as a rule, are not exactly intermediate between the parental species. With some of the more striking characters, those, for instance, which relate to the form and size of the leaves, the pubescence of the several parts, etc., the intermediate, indeed, is nearly always to be seen; in other cases, however, one of the two parental characters is so preponderant that it is difficult, or quite impossible, to detect the other in the hybrid.
This is precisely the case with the Pea hybrids. In the case of each of the 7 crosses the
hybrid-character resembles that of one of the parental forms so closely that the other either escapes observation completely or cannot be detected with certainty. This circumstance is of great
importance in the determination and classification of the forms under which the offspring of the hybrids appear. Henceforth in this paper those characters which are transmitted entire, or almost unchanged in the hybridization, and therefore in themselves constitute the characters of the hybrid, are termed the dominant, and those which become latent in the process recessive. The expression "recessive" has been chosen because the characters thereby designated withdraw or entirely disappear in the hybrids, but nevertheless reappear unchanged in their progeny, as will be demonstrated later on.
It was furthermore shown by the whole of the experiments that it is perfectly immaterial whether the dominant character belongs to the seed plant or to the pollen plant; the form of the hybrid remains identical in both cases. This interesting fact was also emphasized by G?rtner, with the
remark that even the most practiced expert is not in a position to determine in a hybrid which of the two parental species was the seed or the pollen plant.
Of the differentiating characters which were used in the experiments the following are dominant:
1. The round or roundish form of the seed with or without shallow depressions.
2. The yellow coloring of the seed albumen [cotyledons].
3. The gray, gray-brown, or leather brown color of the seed-coat, in association with violet-red
blossoms and reddish spots in the leaf axils.
4. The simply inflated form of the pod.
5. The green coloring of the unripe pod in association with the same color of the stems, the
leaf-veins and the calyx.
6. The distribution of the flowers along the stem.
7. The greater length of stem.
With regard to this last character it must be stated that the longer of the two parental stems is
usually exceeded by the hybrid, a fact which is possibly only attributable to the greater luxuriance which appears in all parts of plants when stems of very different lengths are crossed. Thus, for instance, in repeated experiments, stems of 1 ft. and 6 ft. in length yielded without exception hybrids which varied in length between 6 ft. and 7 [and] 1/2 ft.
The hybrid seeds in the experiments with seed-coat are often more spotted, and the spots sometimes coalesce into small bluish-violet patches. The spotting also frequently appears even when it is absent as a parental character.
The hybrid forms of the seed-shape and of the [color of the] albumen are developed immediately after the artificial fertilization by the mere influence of the foreign pollen. They can, therefore, be observed even in the first year of experiment, whilst all the other characters naturally only appear in the following year in such plants as have been raised from the crossed seed.
The First Generation From the Hybrids
In this generation there reappear, together with the dominant characters, also the recessive ones with their peculiarities fully developed, and this occurs in the definitely expressed average proportion of 3:1, so that among each 4 plants of this generation 3 display the dominant character and one the recessive. This relates without exception to all the characters which were investigated in the
experiments. The angular wrinkled form of the seed, the green color of the albumen, the while color of the seed-coats and the flowers, the constrictions of the pods, the yellow color of the unripe pod, of the stalk, of the calyx, and of the leaf venation, the umbel-like form of the inflorescence, and the dwarfed stem, all reappear in the numerical proportion given, without any essential alteration. Transitional forms were not observed in any experiment.
Since the hybrids resulting from reciprocal crosses are formed alike and present no appreciable difference in their subsequent development, consequently these results can be reckoned together in each experiment. The relative numbers which were obtained for each pair of differentiating characters are as follows:
Expt. 1. Form of seed. -- From 253 hybrids 7324 seeds were obtained in the second trial year. Among them were 5474 round or roundish ones and 1850 angular wrinkled ones. Therefrom the ratio 2.96:1 is deduced.
? Expt. 2. Color of albumen. -- 258 plants yielded 8023 seeds, 6022 yellow, and 2001 green;
their ratio, therefore, is as 3.01:1. ?
In these two experiments each pod yielded usually both kinds of seed. In well-developed pods which contained on the average 6 to 9 seeds, it often happened that all the seeds were round (Expt.
1) or all yellow (Expt. 2); on the other hand there were never observed more than 5 wrinkled or 5
green ones on one pod. It appears to make no difference whether the pods are developed early or later in the hybrid or whether they spring from the main axis or from a lateral one. In some few plants only a few seeds developed in the first formed pods, and these possessed exclusively one of the two characters, but in the subsequently developed pods the normal proportions were maintained nevertheless.
As in separate pods, so did the distribution of the characters vary in separate plants. By way of illustration the first 10 individuals from both series of experiments may serve.
Experiment 1 Experiment 2
Form of Seed Color of Albumen
Plants Round Angular Yellow Green
1 45 12 25 11
2 27 8 32 7
3 24 7 14 5
4 19 10 70 27
5 32 11 24 13
6 26 6 20 6
7 88 24 32 13
8 22 10 44 9
9 28 6 50 14
10 25 7 44 18
As extremes in the distribution of the two seed characters in one plant, there were observed in Expt. 1 an instance of 43 round and only 2 angular, and another of 14 round and 15 angular seeds. In Expt. 2 there was a case of 32 yellow and only 1 green seed, but also one of 20 yellow and 19 green. These two experiments are important for the determination of the average ratios, because with a smaller number of experimental plants they show that very considerable fluctuations may occur. In counting the seeds, also, especially in Expt. 2, some care is requisite, since in some of the seeds of many plants the green color of the albumen is less developed, and at first may be easily overlooked. The cause of this partial disappearance of the green coloring has no connection with the
hybrid-character of the plants, as it likewise occurs in the parental variety. This peculiarity is also confined to the individual and is not inherited by the offspring. In luxuriant plants this appearance was frequently noted. Seeds which are damaged by insects during their development often vary in color and form, but with a little practice in sorting, errors are easily avoided. It is almost superfluous to mention that the pods must remain on the plants until they are thoroughly ripened and have become dried, since it is only then that the shape and color of the seed are fully developed.
Expt. 3. Color of the seed-coats. -- Among 929 plants, 705 bore violet-red flowers and
gray-brown seed-coats; 224 had white flowers and white seed-coats, giving the proportion
3.15:1.
? Expt. 4. Form of pods. -- Of 1181 plants, 882 had them simply inflated, and in 299 they
were constricted. Resulting ratio, 2.95:1.
? Expt. 5. Color of the unripe pods. -- The number of trial plants was 580, of which 428 had
green pods and 152 yellow ones. Consequently these stand in the ratio of 2.82:1.
? Expt. 6. Position of flowers. -- Among 858 cases 651 had inflorescences axial and 207
terminal. Ratio, 3.14:1. ?
? Expt. 7. Length of stem. -- Out of 1064 plants, in 787 cases the stem was long, and in 277
short. Hence a mutual ratio of 2.84:1. In this experiment the dwarfed plants were carefully lifted and transferred to a special bed. This precaution was necessary, as otherwise they
would have perished through being overgrown by their tall relatives. Even in their quite
young state they can be easily picked out by their compact growth and thick dark-green
foliage.
If now the results of the whole of the experiments be brought together, there is found, as between the number of forms with the dominant and recessive characters, an average ratio of 2.98:1, or 3:1. The dominant character can have here a double signification; namely, that of a parental character, or a hybrid-character. In which of the two significations it appears in each separate case can only be determined by the following generation. As a parental character it must pass over unchanged to the whole of the offspring; as a hybrid-character, on the other hand, it must maintain the same behavior as in the first generation.
The Second Generation From the Hybrids
Those forms which in the first generation exhibit the recessive character do not further vary in the second generation as regards this character; they remain constant in their offspring.
It is otherwise with those which possess the dominant character in the first generation. Of these two-thirds yield offspring which display the dominant and recessive characters in the proportion of 3:1, and thereby show exactly the same ratio as the hybrid forms, while only one-third remains with the dominant character constant.
The separate experiments yielded the following results:
Expt. 1. Among 565 plants which were raised from round seeds of the first generation, 193 yielded round seeds only, and remained therefore constant in this character; 372, however, gave both round and wrinkled seeds, in the proportion of 3:1. The number of the hybrids,
therefore, as compared with the constants is 1.93:1.
? Expt. 2. Of 519 plants which were raised from seeds whose albumen was of yellow color in
the first generation, 166 yielded exclusively yellow, while 353 yielded yellow and green
seeds in the proportion of 3:1. There resulted, therefore, a division into hybrid and constant forms in the proportion of 2.13:1. ?
For each separate trial in the following experiments 100 plants were selected which displayed the dominant character in the first generation, and in order to ascertain the significance of this, ten seeds of each were cultivated.
Expt. 3. The offspring of 36 plants yielded exclusively gray-brown seed-coats, while of the offspring of 64 plants some had gray-brown and some had white.
? Expt. 4. The offspring of 29 plants had only simply inflated pods; of the offspring of 71, on
the other hand, some had inflated and some constricted.
? Expt. 5. The offspring of 40 plants had only green pods; of the offspring of 60 plants some
had green, some yellow ones. ?
Expt. 6. The offspring of 33 plants had only axial flowers; of the offspring of 67, on the
other hand, some had axial and some terminal flowers.
? Expt. 7. The offspring of 28 plants inherited the long axis, of those of 72 plants some the
long and some the short axis. ?
In each of these experiments a certain number of the plants came constant with the dominant character. For the determination of the proportion in which the separation of the forms with the constantly persistent character results, the two first experiments are especially important, since in these a larger number of plants can be compared. The ratios 1.93:1 and 2.13:1 gave together almost exactly the average ratio of 2:1. The sixth experiment gave a quite concordant results; in the others the ratio varies more or less, as was only to be expected in view of the smaller number of 100 trial plants. Experiment 5, which shows the greatest departure, was repeated, and then in lieu of the ratio of 60:40, that of 65:35 resulted. The average ratio of 2:1 appears, therefore, as fixed with certainty. It is therefore demonstrated that, of those forms which posses the dominant character in the first generation, two-thirds have the hybrid-character, while one-third remains constant with the dominant character.
The ratio of 3:1, in accordance with which the distribution of the dominant and recessive characters results in the first generation, resolves itself therefore in all experiments into the ratio of 2:1:1, if the dominant character be differentiated according to its significance as a hybrid-character or as a parental one. Since the members of the first generation spring directly from the seed of the hybrids, it is now clear that the hybrids form seeds having one or other of the two differentiating characters, and of these one-half develop again the hybrid form, while the other half yield plants which remain constant and receive the dominant or the recessive characters in equal numbers.
The Subsequent Generations From the Hybrids
The proportions in which the descendants of the hybrids develop and split up in the first and second generations presumably hold good for all subsequent progeny. Experiments 1 and 2 have already been carried through 6 generations, 3 and 7 through 5, and 4, 5, and 6 through 4, these experiments being continued from the third generation with a small number of plants, and no departure from the rule has been perceptible. The offspring of the hybrids separated in each generation in the ratio of 2:1:1 into hybrids and constant forms.
If A be taken as denoting one of the two constant characters, for instance the dominant, a the recessive, and Aa the hybrid form in which both are conjoined, the expression
A + 2Aa + a
shows the terms in the series for the progeny of the hybrids of two differentiating characters. The observation made by G?rtner, K?reuter, and others, that hybrids are inclined to revert to the parental forms, is also confirmed by the experiments described. It is seen that the number of the hybrids which arise from one fertilization, as compared with the number of forms which become constant, and their progeny from generation to generation, is continually diminishing, but that nevertheless they could not entirely disappear. If an average equality of fertility in all plants in all generations be assumed, and if, furthermore, each hybrid forms seed of which one-half yields hybrids again, while the other half is constant to both characters in equal proportions, the ratio of
numbers for the offspring in each generation is seen by the following summary, in which A and a denote again the two parental characters, and Aa the hybrid forms. For brevity's sake it may be assumed that each plant in each generation furnishes only 4 seeds.
Ratios
Generation A Aa a A : Aa : a
----------------------------------------------------
1 1 2 1 1 : 2 : 1
2 6 4 6 3 : 2 : 3
3 28 8 28 7 : 2 : 7
4 120 16 120 15 : 2 : 15
5 496 32 496 31 : 2 : 31
. ............ ........
n n
n 2 - 1 : 2 : 2 - 1
In the tenth generation, for instance, 2En - 1 = 1023. There result, therefore, in each 2048 plants which arise in this generation 1023 with the constant dominant character, 1023 with the recessive character, and only two hybrids.
The Offspring of Hybrids in Which Several Differentiating Characters are Associated.
In the experiments above described plants were used which differed only on one essential character. The next task consisted in ascertaining whether the law of development discovered in these applied to each pair of differentiating characters when several diverse characters are united in the hybrid by crossing. As regards the form of the hybrids in these cases, the experiments showed throughout that this invariably more nearly approaches to that one of the two parental plants which possesses the greater number of dominant characters. If, for instance, the seed plant has a short stem, terminal white flowers, and simply inflated pods; the pollen plant, on the other hand, a long stem, violet-red flowers distributed along the stem, and constricted pods; the hybrid resembles the seed parent only in the form of the pod; in the other characters it agrees with the pollen parent. Should one of the two parental types possess only dominant characters, then the hybrid is scarcely or not at all
distinguishable from it.
Two experiments were made with a considerable number of plants. In the first experiment the
parental plants differed in the form of the seed and in the color of the albumen; in the second in the form of the seed, in the color of the albumen, and in the color of the seed-coats. Experiments with seed characters give the result in the simplest and most certain way.
In order to facilitate study of the data in these experiments, the different characters of the seed plant will be indicated by A, B, C, those of the pollen plant by a, b, c, and the hybrid forms of the characters by Aa, Bb, and Cc.
First Experiment: AB Seed parents, abc Pollen parents,
A form round a form wrinkled
B albumen yellow b albumen green
The fertilized seeds appeared round and yellow like those of the seed parents. The plants raised therefrom yielded seeds of four sorts, which frequently presented themselves in one pod. In all, 556 seeds were yielded by 15 plants, and of these there were:
315 round and yellow,
? 101 wrinkled and yellow,
? 108 round and green,
? 32 wrinkled and green. ?
All were sown the following year. 11 of the round yellow seeds did not yield plants, and 3 plants did not form seeds. Among the rest:
38 had round yellow seeds ........ AB
? 65 round yellow and green seeds..........ABb
? 60 round yellow and wrinkled yellow seeds........AaB
? 138 round yellow and green, wrinkled yellow
and green seeds...... ..... AaBb ?
From the wrinkled yellow seeds 96 resulting plants bore seed, of which:
28 had only wrinkled yellow seeds................aB
? 68 wrinkled yellow and green seeds .............aBb ?
From 108 round green seeds 102 resulting plants fruited, of which:
35 had only round green seeds ...............Ab
? 67 round and wrinkled green seeds ..........Aab ?
The wrinkled green seeds yielded 30 plants which bore seeds all of like character; they remained constant ab.
The offspring of the hybrids appeared therefore under 9 different forms, some of them in very unequal numbers. When these are collected and coordinated we find:
38 plants with the sign AB
35 " " " Ab
28 " " " aB
30 " " " ab
65 " " " ABb
68 " " " aBb
60 " " " AaB
67 " " " Aab
138 " " " AaBb
The whole of the forms may be classed into 3 essentially different groups. The first includes those with the signs AB, Ab, aB, and ab : they possess only constant characters and do not vary again in the next generation. Each of these forms is represented on the average 33 times. The second group includes the signs ABb, aBb, AaB, Aab : these are constant in one character and hybrid in another,
and vary in the next generation only as regards the hybrid-character. Each of these appears on any average 65 times. The form AaBb occurs 138 times : it is hybrid in both characters, and behaves exactly as do the hybrids from which it is derived.
If the numbers in which the forms belonging to these classes appear be compared, the ratios of 1:2:4 are unmistakably evident. The numbers 33, 65, 138 present very fair approximations to the ratio numbers of 33, 66, 132.
The development series consists, therefore, of 9 classes, of which 4 appear therein always once and are constant in both characters; the forms AB, ab, resemble the parental forms, the two others
present combinations between the conjoined characters A, a, B, b, which combinations are likewise possibly constant. Four classes appear always twice, and are constant in one character and hybrid in the other. One class appears four times, and is hybrid in both characters. Consequently, the offspring of the hybrids, if two kinds of differentiating characters are combined therein, are represented by the expression
AB + Ab + aB + ab + 2ABb + 2aBb + 2AaB + 2Aab + 4AaBb
This expression is indisputably a combination series in which the two expressions for the characters
A and a, B and b are combined. We arrive at the full number of the classes of the series by the combination of the expressions:
A + 2Aa + a
B + 2Bb + b
Second Experiment: ABC Seed parents, abc Pollen parents,
A form round a form wrinkled
B albumen yellow b albumen green
C seed-coat gray-brown c seed-coat white
This experiment was made in precisely the same way as the previous one. Among all the
experiments it demanded the most time and trouble. From 24 hybrids 687 seeds were obtained in all: these were all either spotted, gray-brown or gray-green, round or wrinkled. From these in the following year 639 plants fruited, and as further investigation showed, there were among them:
8 plants ABC 22 plants ABCc 45 plants ABbCc
14 " ABc 17 " AbCc 36 " aBbCc
9 " AbC 25 " aBCc 38 " AaBCc
11 " Abc 20 " abCc 40 " AabCc
8 " aBC 15 " ABbC 49 " AaBbC
10 " aBc 18 " ABbc 48 " AaBbc
10 " abC 19 " aBbC
7 " abc 24 " aBbc
14 " AaBC 78 " AaBbCc
18 " AaBc
20 " AabC
16 " Aabc
The whole expression contains 27 terms. Of these 8 are constant in all characters, and each appears on the average 10 times; 12 are constant in two characters, and hybrid in the third; each appears on
the average 19 times; 6 are constant in one character and hybrid in the other two; each appears on the average 43 times. One form appears 78 times and is hybrid in all of the characters. The ratios 10:19:43:78 agree so closely with the ratios 10:20:40:80, or 1:2:4:8 that this last undoubtedly represents the true value.
The development of the hybrids when the original parents differ in 3 characters results therefore according to the following expression:
ABC + ABc + AbC + Abc + aBC + aBc + abC + abc +
2ABCc + 2AbCc + 2aBCc + 2abCc + 2ABbC + 2ABbc +
2aBbC + 2aBbc + 2AaBC + 2AaBc + 2AabC + 2Aabc +
4ABbCc + 4aBbCc + 4AaBCc + 4AabCc + 4AaBbC +
4AaBbc + 8AaBbCc.
Here also is involved a combination series in which the expressions for the characters A and a, B and b, C and c, are united. The expressions
A + 2Aa + a
B + 2Bb + b
C + 2Cc + c
give all the classes of the series. The constant combinations which occur therein agree with all combinations which are possible between the characters A, B,C,a,b,c; two thereof, ABC and abc, resemble the two original parental stocks.
In addition, further experiments were made with a smaller number of experimental plants in which the remaining characters by twos and threes were united as hybrids: all yielded approximately the same results. There is therefore no doubt that for the whole of the characters involved in the experiments the principle applies that the offspring of the hybrids in which several essentially different characters are combined exhibit the terms of a series of combinations, in which the
developmental series for each pair of differentiating characters are united. It is demonstrated at the same time that the relation of each pair of different characters in hybrid union is independent of the other differences in the two original parental stocks.
If n represent the number of the differentiating characters in the two original stocks, 3En gives the number of terms of the combination series, 4En the number of individuals which belong to the series, and 2En the number of unions which remain constant. The series therefore contains, if the original stocks differ in four characters, 3E4 = 81 classes, 4E4 = 256 individuals, and 2E4 = 16 constant forms: or, which is the same, among each 256 offspring of the hybrids are 81 different combinations, 16 of which are constant.
All constant combinations which in Peas are possible by the combination of the said 7
differentiating characters were actually obtained by repeated crossing. Their number is given by 2E7 = 128. Thereby is simultaneously given the practical proof that the constant characters which appear in the several varieties of a group of plants may be obtained in all the associations which are possible according to the laws of combination, by means of repeated artificial fertilization. As regards the flowering time of the hybrids, the experiments are not yet concluded. It can, however, already be stated that the time stands almost exactly between those of the seed and pollen parents, and that the constitution of the hybrids with respect to this character probably follows the rule
ascertained in the case of the other characters. The forms which are selected for experiments of this class must have a difference of at least 20 days from the middle flowering period of one to that of the other; furthermore, the seeds when sown must all be placed at the same depth in the earth, so that they may germinate simultaneously. Also, during the whole flowering period, the more important variations in temperature must be taken into account, and the partial hastening or
delaying of the flowering which may result therefrom. It is clear that this experiment presents many difficulties to be overcome and necessitates great attention.
If we endeavor to collate in a brief form the results arrived at, we find that those differentiating characters, which admit of easy and certain recognition in the experimental plants, all behave
exactly alike in their hybrid associations. The offspring of the hybrids of each pair of differentiating characters are, one-half, hybrid again, while the other half are constant in equal proportions having the characters of the seed and pollen parents respectively. If several differentiating characters are combined by cross-fertilization in a hybrid, the resulting offspring form the terms of a combination series in which the combination series for each pair of differentiating characters are united.
The uniformity of behavior shown by the whole of the characters submitted to experiment permits, and fully justifies, the acceptance of the principle that a similar relation exists in the other characters which appear less sharply defined in plants, and therefore could not be included in the separate experiments. An experiment with peduncles of different lengths gave on the whole a fairly
satisfactory results, although the differentiation and serial arrangement of the forms could not be effected with that certainty which is indispensable for correct experiment.
The Reproductive Cells of the Hybrids
The results of the previously described experiments led to further experiments, the results of which appear fitted to afford some conclusions as regards the composition of the egg and pollen cells of hybrids. An important clue is afforded in Pisum by the circumstance that among the progeny of the hybrids constant forms appear, and that this occurs, too, in respect of all combinations of the associated characters. So far as experience goes, we find it in every case confirmed that constant progeny can only be formed when the egg cells and the fertilizing pollen are of like character, so that both are provided with the material for creating quite similar individuals, as is the case with the normal fertilization of pure species. We must therefore regard it as certain that exactly similar factors must be at work also in the production of the constant forms in the hybrid plants. Since the various constant forms are produced in one plant, or even in one flower of a plant, the conclusion appears logical that in the ovaries of the hybrids there are formed as many sorts of egg cells, and in the anthers as many sorts of pollen cells, as there are possible constant combination forms, and that these egg and pollen cells agree in their internal compositions with those of the separate forms. In point of fact it is possible to demonstrate theoretically that this hypothesis would fully suffice to account for the development of the hybrids in the separate generations, if we might at the same time assume that the various kinds of egg and pollen cells were formed in the hybrids on the average in equal numbers.
In order to bring these assumptions to an experimental proof, the following experiments were designed. Two forms which were constantly different in the form of the seed and the color of the albumen were united by fertilization.
If the differentiating characters are again indicated as A, B, a, b, we have:
AB Seed parents, ab Pollen parents,
A form round a form wrinkled
B albumen yellow b albumen green
The artificially fertilized seeds were sown together with several seeds of both original stocks, and the most vigorous examples were chosen for the reciprocal crossing. There were fertilized:
1. The hybrids with the pollen of AB
2. The hybrids with the pollen of ab
3. AB with the pollen of the hybrids.
4. ab with the pollen of the hybrids.
For each of these 4 experiments the whole of the flowers on 3 plants were fertilized. If the above theory be correct, there must be developed on the hybrids egg and pollen cells of the forms AB,Ab,aB, ab, and there would be combined:
1. The egg cells AB, Ab, aB, ab with the pollen cells AB.
2. The egg cells AB, Ab, aB, ab with the pollen cells ab.
3. The egg cells AB with the pollen cells AB, Ab, aB, and ab.
4. The egg cells ab with the pollen cells AB, Ab, aB, and ab.
From each of these experiments there could then result only the following forms:
1. AB, ABb, AaB, AaBb
2. AaBb, Aab, aBb, ab
3. AB, ABb, AaB, AaBb
4. AaBb, Aab, aBb, ab
If, furthermore, the several forms of the egg and pollen cells of the hybrids were produced on an average in equal numbers, then in each experiment the said 4 combinations should stand in the same ratio to each other. A perfect agreement in the numerical relations was, however, not to be expected since in each fertilization, even in normal cases, some egg cells remain undeveloped or subsequently die, and many even of the well-formed seeds fail to germinate when sown. The above assumption is also limited in so far that while it demands the formation of an equal number of the various sorts of egg and pollen cells, it does not require that this should apply to each separate hybrid with mathematical exactness.
The first and second experiments had primarily the object of proving the composition of the hybrid egg cells, while the third and fourth experiments were to decide that of the pollen cells. As is shown by the above demonstration the first and third experiments and the second and fourth experiments should produce precisely the same combinations, and even in the second year the result should be partially visible in the form and color of the artificially fertilized seed. In the first and third
experiments the dominant characters of form and color, A and B, appear in each union, and are also partly constant and partly in hybrid union with the recessive characters a and b, for which reason they must impress their peculiarity upon the whole of the seeds. all seeds should therefore appear round and yellow, if the theory be justified. In the second and fourth experiments, on the other hand,
one union is hybrid in form and in color, and consequently the seeds are round and yellow; another is hybrid in form, but constant in the recessive character of color, whence the seeds are round and green; the third is constant in the recessive character of form but hybrid in color, consequently the seeds are wrinkled and yellow; the fourth is constant in both recessive characters, so that the seeds are wrinkled and green. In both these experiments there were consequently four sorts of seed to be expected; namely, round and yellow, round and green, wrinkled and yellow, wrinkled and green. The crop fulfilled these expectations perfectly. There were obtained in the
?
? 1st Experiment, 98 exclusively round yellow seeds; 3rd Experiment, 94 exclusively round yellow seeds.
In the 2nd Experiment, 31 round and yellow, 26 round and green, 27 wrinkled and yellow, 26 wrinkled and green seeds.
In the 4th Experiment, 24 round and yellow, 25 round and green, 22 wrinkled and yellow, 27 wrinkled and green seeds.
There could scarcely be now any doubt of the success of the experiment; the next generation must afford the final proof. From the seed sown there resulted for the first experiment 90 plants, and for the third 87 plants which fruited: these yielded for the
1st Exp. 3rd Exp.
20 25 round yellow seeds ..................... AB
23 19 round yellow and green seeds ............. ABb
25 22 round and wrinkled yellow seeds .......... AaB
22 21 round and wrinkled green and yellow seeds.. AaBb
In the second and fourth experiments the round and yellow seeds yielded plants with round and wrinkled yellow and green seeds, AaBb.
From the round green seeds plants resulted with round and wrinkled green seeds, Aab.
The wrinkled yellow seeds gave plants with wrinkled yellow and green seeds, aBb.
From the wrinkled green seeds plants were raised which yielded again only wrinkled and green seeds, ab.
Although in these two experiments likewise some seeds did not germinate, the figures arrived at already in the previous year were not affected thereby, since each kind of seed gave plants which, as regards their seed, were like each other and different from the others. There resulted therefore from the
2nd. Exp. 4th Exp.
31 24 plants of the form AaBb
26 25 plants of the form Aab
27 22 plants of the form aBb
26 27 plants of the form ab
In all the experiments, therefore, there appeared all the forms which the proposed theory demands, and they came in nearly equal numbers.
In a further experiment the characters of flower-color and length of stem were experimented upon, and selection was so made that in the third year of the experiment each character ought to appear in half of all the plants if the above theory were correct. A,B,a,b serve again as indicating the various characters.
A, violet-red flowers;
? a, white flowers;
? B, axis long;
? A, axis short. ?
The form Ab was fertilized with ab, which produced the hybrid Aab. Furthermore, aB was also fertilized with ab, whence the hybrid aBb. In the second year, for further fertilization, the hybrid Aab was used as seed parent, and hybrid aBb as pollen parent.
Seed parent,Aab;
? Pollen parentaBb;
? Possible egg cells, Ab,ab;
? Pollen cells, aB, ab. ?
From the fertilization between the possible egg and pollen cells four combinations should result, namely:
? AaBb + aBb + Aab + ab
From this it is perceived that, according to the above theory, in the third year of the experiment out of all the plants
half should have violet-red flowers (Aa) Classes 1, 3
" " " white flowers (a) " 2, 4
" " " a long axis (Bb) " 1, 2
" " " a short axis (b) " 3, 4
From 45 fertilizations of the second year 187 seeds resulted, of which only 166 reached the flowering stage in the third year. Among these the separate classes appeared in the numbers following:
Class Flower color Stem
---------------------------------------------
1 violet-red long 47 times
2 white long 40 "
3 violet-red short 38 "
4 white short 41 "
There subsequently appeared
?
?
?
? the violet-red flower color (Aa) in 85 plants, the white flower-color (a) in 81 plants, the long stem (Bb) in 87 plants, the short stem (b) in 79 plants.
The theory adduced is therefore satisfactorily confirmed in this experiment also.
For the characters of form of pod, color of pod, and position of flowe\ rs, experiments were also made on a small scale and results obtained in perfect agreement. All combinations, which were possible through the union of the differentiating characters duly appeared, and in nearly equal numbers.
Experimentally, therefore, the theory is confirmed that the pea hybrids form egg and pollen cells which, in their constitution, represent in equal numbers all constant forms which result from the combination of the characters united in fertilization.
The difference of the forms among the progeny of the hybrids, as well as the respective ratios of the numbers in which they are observed, find a sufficient explanation in the principle above deduced. The simplest case is afforded by the developmental series of each pair of differentiating characters. This series is represented by the expression A+2Aa+a, in which A and a signify the forms with constant differentiating characters, and Aa the hybrid form of both. It includes in 3 different classes 4 individuals. In the formation of these, pollen and egg cells of the form A and a take part on the average equally in the fertilization; hence each form [occurs] twice, since four individuals are formed. There participate consequently in the fertilization
o the pollen cells A+A+a+a,
o the egg cells A+A+a+a.
It remains, therefore, purely a matter of chance which of the two sorts of pollen will become united with each separate egg cell. According, however, to the law of probability, it will always happen, on the average of many cases, that each pollen form A and a will unite equally often with each egg cell form A and a, consequently one of the two pollen cells A in the fertilization will meet with the egg cell A and the other with the egg cell a, and so likewise one pollen cell a will unite with an egg cell A, and the other with the egg cell a.
Pollen cells A A a a
| \ / |
| X |
| / \ |
Egg cells A A a a
The result of the fertilization may be made clear by putting the signs for the conjoined egg and pollen cells in the form of fractions, those for the pollen cells above and those for the egg cells below the line. We then have
A A a a
----- + ----- + ----- + -----
A a A a
In the first and fourth term the egg and pollen cells are of like kind, consequently the product of their union must be constant, namely A and a; in the second and third, on the other hand, there again results a union of the two differentiating characters of the stocks, consequently the forms resulting from these fertilizations are identical with those of the hybrid from which they sprang. There occurs accordingly a repeated hybridization. This explains the striking fact that the hybrids are able to produce, besides the two parental forms, offspring which are like themselves;
A a
----- and -----
a A
both give the same union Aa, since, as already remarked above, it makes no difference in the result of fertilization to which of the two characters the pollen or egg cells belong. We may write then
A A a a
--- + --- + --- + --- = A + 2Aa + a
A a A a
This represents the average result of the self-fertilization of the hybrids when two differentiating characters are united in them. In individual flowers and in individual plants, however, the ratios in which the forms of the series are produced may suffer not inconsiderable fluctuations. Apart from the fact that the numbers in which both sorts of egg cells occur in the seed vessels can only be regarded as equal on the average, it remains purely a matter of chance which of the two sorts of pollen may fertilize each separate egg cell. For this reason the separate values must necessarily be subject to fluctuations, and there are even extreme cases possible, as were described earlier in connection with the experiments on the forms of the seed and the color of the albumen. The true ratios of the numbers can only be ascertained by an average deduced from the sum of as many single values as possible; the greater the number the more are merely chance effects eliminated.
The developmental series for hybrids in which two kinds of differentiating characters are united contains among 16 individuals 9 different forms,AB + Ab + aB + ab + 2ABb + 2aBb + 2AaB + 2Aab + 4AaBb. Between the differentiating characters of the original stocks Aa and Bb 4 constant combinations are possible, and consequently the hybrids produce the corresponding 4 forms of egg and pollen cells AB, Ab,aB,ab, and each of these will on the average figure 4 times in the
fertilization, since 16 individuals are included in the series. Therefore, the participators in the fertilization are
Pollen cells: AB+AB+AB+AB+Ab+Ab+Ab+Ab+aB+aB+aB+aB+ab+ab+ab+ab.
? Egg cells: AB+AB+AB+AB+Ab+Ab+Ab+Ab+aB+aB+aB+aB+ab+ab+ab+ab. ?
In the process of fertilization each pollen form unites on an average equally often with each egg cell form, so that each of the 4 pollen cells AB unites once with one of the forms of egg cell AB,Ab aBab. In precisely the same way the rest of the pollen cells of the forms AbaBab unite with all the other egg cells. We obtain therefore AB AB AB AB Ab Ab Ab Ab
---- + ---- + ---- + ---- + ---- + ---- + ---- + ----
AB Ab aB ab AB Ab aB ab
aB aB aB aB ab ab ab ab
+ ---- + ---- + ---- + ---- + ---- + ---- + ---- + ----
AB Ab aB ab AB Ab aB ab
or
? AB + ABb + AaB + AaBb + ABb + Ab + AaBb + Aab + AaB + AaBb
+ aB + aBb + AaBb + Aab + aBb + ab
= AB + Ab + aB + ab + 2ABb + 2aBb + 2AaB + 2Aab + 4AaBb
In precisely similar fashion is the developmental series of hybrids exhibited when three kinds of differentiating characters are conjoined in them. The hybrids form 8 various kinds of egg and pollen cells: ABC, ABc, AbC, Abc, aBC, aBc, abC, abc; and each pollen form unites itself again on the average once with each form of egg cell.
The law of combination of different characters which governs the development of the hybrids finds therefore its foundation and explanation in the principle enunciated, that the hybrids produce egg cells and pollen cells which in equal numbers represent all constant forms which result from the combinations of the characters brought together in fertilization.
Experiments with Hybrids of Other Species of Plants
It must be the object of further experiments to ascertain whether the law of development discovered for Pisum applies also to the hybrids of other plants. To this end several experiments were recently commenced. Two minor experiments with species of Phaseolus have been completed, and may be here mentioned.
An experiment with Phaseolus vulgaris and Phaseolus nanus gave results in perfect agreement. Ph. nanus had together with the dwarf axis, simply inflated, green pods. Ph. vulgaris had, on the other hand, an axis 10 ft. to 12 ft. high, and yellow colored pods, constricted when ripe. The ratios of the numbers in which the different forms appeared in the separate generations were the same as with Pisum. Also the development of the constant combinations resulted according to the law of simple combination of characters, exactly as in the case of Pisum. There were obtained
Constant Axis Color of the Form of the
combinations unripe pods ripe pods
---------------------------------------------------------
1 long green inflated
2 " " constricted
3 " yellow inflated
4 " " constricted
5 short green inflated
6 " " constricted
7 " yellow inflated
8 " " constricted
The green color of the pod, the inflated forms, and the long axis were, as in Pisum, dominant characters.
Another experiment with two very different species of Phaseolus had only a partial result.
Phaseolus nanus, L, served as seed parent, a perfectly constant species, with white flowers in short recemes and small white seeds in straight, inflated, smooth pods; as pollen parent was used Ph. multiflorus, W, with tall winding stem, purple-red flowers in very long recemes, rough, sickle-shaped crooked pods, and large seeds which bore black flecks and splashes on a
peach-blood-red ground.
The hybrids had the greatest similarity to the pollen parent, but the flowers appeared less intensely colored. Their fertility was very limited; from 17 plants, which together developed many hundreds of flowers, only 49 seeds in all were obtained. These were of medium size, and were flecked and splashed similarly to those of Ph. multiflorus, while the ground color was not materially different. The next year 44 plants were raised from these seeds, of which only 31 reached the flowering stage. The characters of Ph. nanus, which had been altogether latent in the hybrids, reappeared in various combinations; their ratio, however, with relation to the dominant plants was necessarily very
fluctuating owing to the small number of trial plants. With certain characters, as in those of the axis and the form of pod, it was, however, as in the case of Pisum, almost exactly 1:3.
Insignificant as the results of this experiment may be as regards the determination of the relative numbers in which the various forms appeared, it presents, on the other hand, the phenomenon of a remarkable change of color in the flowers and seed of the hybrids. In Pisum it is known that the characters of the flower- and seed-color present themselves unchanged in the first and further generations, and that the offspring of the hybrids display exclusively the one or the other of the characters of the original stocks. It is otherwise in the experiment we are considering. The white flowers and the seed-color of Ph. nanus appeared, it is true, at once in the first generation in one fairly fertile example, but the remaining 30 plants developed flower-colors which were of various grades of purple-red to pale violet. The coloring of the seed-coat was no less varied than that of the flowers. No plant could rank as fully fertile; many produced no fruit at all; others only yielded fruits from the flowers last produced, which did not ripen. From 15 plants only were well-developed seeds obtained. The greatest disposition to infertility was seen in the forms with preponderantly red flowers, since out of 16 of these only 4 yielded ripe seed. Three of these had a similar seed pattern to Ph. multiflorus, but with a more or less pale ground color; the fourth plant yielded only one seed of plain brown tint. The forms with preponderantly violet-colored flowers had dark brown, black-brown, and quite black seeds.
The experiment was continued through two more generations under similar unfavorable
circumstances, since even among the offspring of fairly fertile plants there came again some which were less fertile and even quite sterile. Other flower- and seed-colors than those cited did not
subsequently present themselves. The forms which in the first generation contained one or more of the recessive characters remained, as regards these, constant without exception. Also of those plants which possessed violet flowers and brown or black seed, some did not vary again in these respects in the next generation; the majority, however, yielded together with offspring exactly like
themselves, some which displayed white flowers and white seed-coats. The red flowering plants remained so slightly fertile that nothing can be said with certainty as regards their further development.
Despite the many disturbing factors with which the observations had to contend, it is nevertheless seen by this experiment that the development of the hybrids, with regard to those characters which concern the form of the plants, follows the same laws as in Pisum. With regard to the color
characters, it certainly appears difficult to perceive a substantial agreement. Apart from the fact that from the union of a white and a purple-red coloring a whole series of colors results, from purple to pale violet and white, the circumstance is a striking one that among 31 flowering plants only one received the recessive character of the white color, while in Pisum this occurs on the average in every fourth plant.
Even these enigmatical results, however, might probably be explained by the law governing Pisum if we might assume that the color of the flowers and seeds of Ph. multiflorus is a combination of two or more entirely independent colors, which individually act like any other constant character in the plant. If the flower-color A were a combination of the individual characters A(1) + A(2) + ..... which produce the total impression of a purple coloration, then by fertilization with the
differentiating character, white color, a, there would be produced the hybrid unions A(1)a + A(2)a + ..... and so would it be with the corresponding coloring of the seed-coats. According to the above
assumptions, each of these hybrid color unions would be independent, and would consequently develop quite independently from the others. It is then easily seen that from the combination of the separate developmental series a complete color-series must result. If, for instance, A = A(1) + A(2), then the hybrids A(1)a and A(2)a form the developmental series:
A(1) + 2A(1)a + a
A(2) + 2A(2)a + a
The members of this series can enter into nine different combinations, and each of these denotes another color:
1 A(1)A(2) 2 A(1)aA(2) 1 A(2)a
2 A(1)A(2)a 4 A(1)aA(2)a 2 A(2)aa
1 A(1)a 2 A(1)aa 1 aa
The figures prescribed for the separate combinations also indicate how many plants with the
corresponding coloring belong to the series. Since the total is 16, the whole of the colors are on the average distributed over each 16 plants, but, as the series itself indicated, in unequal proportions. Should the color development really happen in this way, we could offer an explanation of the case above described, namely that of the white flowers and seed-coat color only appeared once among 31 plants of the first generation. This coloring appears only once in the series, and could therefore also only be developed once in the average in each 16, and with three color characters only once even in 64 plants.
It must, nevertheless, not be forgotten that the explanation here attempted is based on a mere
hypothesis, only supported by the very imperfect result of the experiment just described. It would, however, be well worth while to follow up the development of color in hybrids by similar experiments, since it is probable that in this way we might learn the significance of the
extraordinary variety in the coloring of our ornamental flowers.
So far, little at present is known with certainty beyond the fact that the color of the flowers in most ornamental plants is an extremely variable character. The opinion has often been expressed that the stability of the species is greatly disturbed or entirely upset by cultivation, and consequently there is an inclination to regard the development of cultivated forms as a matter of chance devoid of rules; the coloring of ornamental plants is indeed usually cited as an example of great instability. It is, however, not clear why the simple transference into garden soil should result in such a thorough and persistent revolution in the plant organism. No one will seriously maintain that in the open country the development of plants is ruled by other laws than in the garden bed. Here, as there, changes of type must take place if the conditions of life be altered, and the species possesses the capacity of fitting itself to its new environment. It is willingly granted that by cultivation the origination of new varieties is favored, and that by man's labor many varieties are acquired which, under natural conditions, would be lost; but nothing justifies the assumption that the tendency to formation of varieties is so extraordinarily increased that the species speedily lose all stability, and their offspring diverge into an endless series of extremely variable forms. Were the change in the conditions the sole cause of variability we might expect that those cultivated plants which are grown for centuries under almost identical conditions would again attain constancy. This, as is well known, is not the case since it is precisely under such circumstances that not only the most varied but also the most variable forms are found. It is only the Leguminosae, like Pisum, Phaseolus, Lens, whose organs of fertilization are protected by the keel, which constitute a noteworthy exception. Even here there
have arisen numerous varieties during a cultural period of more than 1000 years under most various conditions; these maintain, however, under unchanging environments a stability as great as that of species growing wild.
It is more than probable that as regards the variability of cultivated plants there exists a factor which so far has received little attention. Various experiments force us to the conclusion that our cultivated plants, with few exceptions, are members of various hybrid series, whose further development in conformity with law is varied and interrupted by frequent crossings inter se. The circumstance must not be overlooked that cultivated plants are mostly grown in great numbers and close together,
affording the most favorable conditions for reciprocal fertilization between the varieties present and species itself. The probability of this is supported by the fact that among the great array of variable forms solitary examples are always found, which in one character or another remain constant, if only foreign influence be carefully excluded. These forms behave precisely as do those which are known to be members of the compound hybrid series. Also with the most susceptible of all characters, that of color, it cannot escape the careful observer that in the separate forms the inclination to vary is displayed in very different degrees. Among plants which arise from one spontaneous fertilization there are often some who offspring vary widely in the constitution and arrangement of the colors, while that of others shows little deviation, and among a greater number solitary examples occur which transmit the color of the flowers unchanged to their offspring. The cultivated species of Dianthus afford an instructive example of this. A white-flowered example of Dianthus caryophyllus, which itself was derived from a white-flowered variety, was shut up during its blooming period in a greenhouse; the numerous seeds obtained therefrom yielded plants entirely white-flowered like itself. A similar result was obtained from a sub-species, with red flowers somewhat flushed with violet, and one with flowers white, striped with red. Many others, on the other hand, which were similarly protected, yielded progeny which were more or less variously colored and marked.
Whoever studies the coloration which results in ornamental plants from similar fertilization can hardly escape the conviction that here also the development follows a definite law which possibly finds its expression in the combination of several independent color characters.
Concluding Remarks
It can hardly fail to be of interest to compare the observations made regarding Pisum with the results arrived at by the two authorities in this branch of knowledge, K?reuter and G?rtner, in their investigations. According to the opinion of both, the hybrids in outward appearance present either a form intermediate between the original species, or they closely resemble either the one or the other type, and sometimes can hardly be discriminated from it. From their seeds usually arise, if the fertilization was effected by their own pollen, various forms which differ from the normal type. As a rule, the majority of individuals obtained by one fertilization maintain the hybrid form, while some few others come more like the seed parent, and one or other individual approaches the pollen parent. This, however, is not the case with hybrids without exception. Sometimes the offspring have more nearly approached, some the one and some the other of the two original stocks, or they all incline more to one or the other side; while in other cases they remain perfectly like the hybrid and continue constant in their offspring. The hybrids of varieties behave like hybrids of species, but they possess greater variability of form and more pronounced tendency to revert to the original types.
With regard to the form of the hybrids and their development, as a rule an agreement with the observations made in Pisum is unmistakable. It is otherwise with the exceptional cases cited.
G?rtner confesses even that the exact determination whether a form bears a greater resemblance to one or to the other of the two original species often involved great difficulty, so much depending upon the subjective point of view of the observer. Another circumstance could, however, contribute to render the results fluctuating and uncertain, despite the most careful observation and
differentiation. For the experiments, plants were mostly used which rank as good species and are differentiated by a large number of characters. In addition to the sharply defined characters, where it is a question of greatly or less similarity, those characters must also be taken into account which are often difficult to define in words, but yet suffice, as every plant specialist knows, to give the forms a peculiar appearance. If it be accepted that the development of hybrids follows the law which is valid for Pisum, the series in each separate experiment must contain very many forms, since the number of terms, as is known, increases with the number of the differentiating characters as the powers of three. With a relatively small number of experimental plants the results therefore could only be approximately right, and in single cases might fluctuate considerably. If, for instance, the two
original stocks differ in 7 characters, and 100-200 plants were raised from the seeds of their hybrids to determine the grade of relationship of the offspring, we can easily see how uncertain the decision must become since for 7 differentiating characters the combination series contains 16,384 individuals under 2187 various forms; now one and then another relationship could assert its
predominance, just according as chance presented this or that form to the observer in a majority of cases.
If, furthermore, there appear among the differentiating characters at the same time dominant
characters, which are transmitted entire or nearly unchanged to the hybrids, then in the terms of the developmental series that one of the two original parents which possesses the majority of dominant characters must always be predominant. In the experiment described relative to Pisum, in which three kinds of differentiating characters were concerned, all the dominant characters belonged to the seed parent. Although the terms of the series in their internal composition approach both original parents equally, yet in this experiment the type of the seed parent obtained so great a preponderance that out of each sixty-four plants of the first generation fifty-four exactly resembled it, or only differed in one character. It is seen how rash it must be under such circumstances to draw from the external resemblances of hybrids conclusions as to their internal nature.
G?rtner mentions that in those cases where the development was regular among the offspring of the hybrids the two original species were not reproduced, but only a few individuals which approached them. With very extended developmental series it could not in fact be otherwise. For 7
differentiating characters, for instance, among more than 16,000 individuals -- offspring of the
hybrids -- each of the two original species would occur only once. It is therefore hardly possible that these should appear at all among a small number of experimental plants; with some probability, however, we might reckon upon the appearance in the series of a few forms which approach them. We meet with an essential difference in those hybrids which remain constant in their progeny and propagate themselves as truly as the pure species. According to G?rtner, to this class belong the remarkably fertile hybrids Aquilegia atropurpurea canadensis, Lavatera pseudolbia thuringiaca, Geum urbanorivale, and some Dianthus hybrids; and, according to Wichura, the hybrids of the Willow family. For the history of the evolution of plants this circumstance is of special importance, since constant hybrids acquire the status of new species. The correctness of the facts is guaranteed
by eminent observers, and cannot be doubted. G?rtner had an opportunity of following up Dianthus Armeria deltoides to the tenth generation, since it regularly propagated itself in the garden. With Pisum it was shown by experiment that the hybrids form egg and pollen cells of different kinds, and that herein lies the reason of the variability of their offspring. In other hybrids, likewise, whose offspring behave similarly we may assume a like cause; for those, on the other hand, which remain constant the assumption appears justifiable that their reproductive cells are all alike and agree with the foundation-cell of the hybrid. In the opinion of renowned physiologists, for the purpose of propagation one pollen cell and one egg cells unite in Phanerogams* into a single cell, which is capable by assimilation and formation of new cells to become an independent organism. This development follows a constant law, which is founded on the material composition and
arrangement of the elements which meet in the cell in a vivifying union. If the reproductive cells be of the same kind and agree with the foundation cell of the mother plant, then the development of the new individual will follow the same law which rules the mother plant. If it chance that an egg cell unites with a dissimilar pollen cell, we must then assume that between those elements of both cells, which determine opposite characters some sort of compromise is effected. The resulting compound cell becomes the foundation of the hybrid organism the development of which necessarily follows a different scheme from that obtaining in each of the two original species. If the compromise be taken to be a complete one, in the sense, namely, that the hybrid embryo is formed from two similar cells, in which the differences are entirely and permanently accommodated together, the further result follows that the hybrids, like any other stable plant species, reproduce themselves truly in their
offspring. The reproductive cells which are formed in their seed vessels and anthers are of one kind, and agree with the fundamental compound cell.
* In Pisum it is placed beyond doubt that for the formation of the new embryo a perfect union of the elements of both reproductive cells must take place. How could we otherwise explain that among the offspring of the hybrids both original types reappear in equal numbers and with all their peculiarities? If the influence of the egg cell upon the pollen cell were only
external, if it fulfilled the role of a nurse only, then the result of each fertilization could be no other than that the developed hybrid should exactly resemble the pollen parent, or at any rate do so very closely. This the experiments so far have in no wise confirmed. An evident proof of the complete union of the contents of both cells is afforded by the experience gained on all sides that it is immaterial, as regards the form of the hybrid, which of the original species is the seed parent or which the pollen parent.
With regard to those hybrids whose progeny is variable we may perhaps assume that between the differentiating elements of the egg and pollen cells there also occurs a compromise, in so far that the formation of a cell as the foundation of the hybrid becomes possible; but, nevertheless, the
arrangement between the conflicting elements is only temporary and does not endure throughout the life of the hybrid plant. Since in the habit of the plant no changes are perceptible during the whole period of vegetation, we must further assume that it is only possible for the differentiating elements to liberate themselves from the enforced union when the fertilizing cells are developed. In the formation of these cells all existing elements participate in an entirely free and equal arrangement, by which it is only the differentiating ones which mutually separate themselves. In this way the production would be rendered possible of as many sorts of egg and pollen cells as there are combinations possible of the formative elements.
The attribution attempted here of the essential difference in the development of hybrids to a
permanent or temporary union of the differing cell elements can, of course, only claim the value of an hypothesis for which the lack of definite data offers a wide scope. Some justification of the opinion expressed lies in the evidence afforded by Pisum that the behavior of each pair of
differentiating characters in hybrid union is independent of the other differences between the two original plants, and, further, that the hybrid produces just so many kinds of egg and pollen cells as there are possible constant combination forms. The differentiating characters of two plants can finally, however, only depend upon differences in the composition and grouping of the elements which exist in the foundation-cells of the same in vital interaction.
Even the validity of the law formulated for Pisum requires still to be confirmed, and a repetition of the more important experiments is consequently must to be desired, that, for instance, relating to the composition of the hybrid fertilizing cells. A differential may easily escape the single observer, which although at the outset may appear to be unimportant, yet accumulate to such an extent that it must not be ignored in the total result. Whether the variable hybrids of other plant species observe an entire agreement must also be first decided experimentally. In the meantime we may assume that in material points an essential difference can scarcely occur, since the unity in the developmental plant of organic life is beyond question.
In conclusion, the experiments carried out by K?lreuter, G?rtner, and others with respect to the transformation of one species into another by artificial fertilization merit special mention. Particular importance has been attached to these experiments and G?rtner reckons them "among the most difficult of all in hybridization."
If a species A is to be transformed into a species B, both must be united by fertilization and the resulting hybrids then be fertilized with the pollen of B; then, out of the various offspring resulting, that form would be selected which stood in nearest relation to B and once more be fertilized with B pollen, and so continuously until finally a form is arrived at which is like B and constant in its
progeny. By this process the species A would change into the species B. G?rtner alone has effected 30 such experiments with plants of genera Aquilegia, Dianthus, Geum, Lavatera, Lynchnis , Malva, Nicotiana, and Oencthera. The period of transformation was not alike for all species. While with some a triple fertilization sufficed, with others this had to be repeated five or six times, and even in the same species fluctuations were observed in various experiments. G?rtner ascribes this difference to the circumstance that "the specific power by which a species, during reproduction, effects the change and transformation of the maternal type varies considerably in different plants, and that, consequently, the periods with which the one species is changed into the other must also vary, as also the number of generations, so that the transformation in some species is perfected in more, and in others in fewer generations". Further, the same observer remarks "that in these transformation experiments a good deal depends upon which type and which individual be chosen for further transformation".
If it may be assumed that in these experiments the constitution of the forms resulted in a similar way to that of Pisum, the entire process of transformation would find a fairly simple explanation. The hybrid forms as many kinds of egg cells as there are constant combinations possible of the characters conjoined therein, and one of these is always of the same kind as that of the fertilizing pollen cells. Consequently there always exists the possibility with all such experiments that even from the second fertilization there may result a constant form identical with that of the pollen parent.
Whether this really be obtained depends in each separate case upon the number of the experimental plants, as well as upon the number of differentiating characters which are united by the fertilization. Let us, for instance, assume that the plants selected for experiment differed in 3 characters, and the species ABC is to be transformed into the other species abc by repeated fertilization with the pollen of the latter; the hybrids resulting from the first cross form 8 different kinds of egg cells, namely: ABC, ABc, AbC, aBC, Abc, aBc, abC, abc
These in the second year of experiment are united again with the pollen cells abc, and we obtain the series AaBbCc + AaBbc + AabCc + aBbCc + Aabc + aBbc + abCc + abc
Since the form abc occurs once in the series of 8 terms, it is consequently little likely that it would be missing among the experimental plants, even were these raised in a smaller number, and the transformation would be perfected already by a second fertilization. If by chance it did not appear, then the fertilization must be repeated with one of those forms nearest akin, Aabc, aBbc, abCc. It is perceived that such an experiment must extend the farther the smaller the number of experimental plants and the larger the number of differentiating characters in the two original species; and that, furthermore, in the same species there can easily occur a delay of one or even of two generations such as G?rtner observed. The transformation of widely divergent species could generally only be completed in 5 or 6 years of experiment, since the number of different egg cells which are formed in the hybrid increases as the powers of 2 with the number of differentiating characters.
G?rtner found by repeated experiments that the respective period of transformation varies in many species, so that frequently a species A can be transformed into a species B a generation sooner than can species B into species A. He deduces therefrom that K?lreuter's opinion can hardly be
maintained that "the two natures in hybrids are perfectly in equilibrium". Experiments which in this connection were carried out with two species of Pisum demonstrated that as regards the choice of the fittest individuals for the purpose of further fertilization it may make a great difference which of two species is transformed into the other. The two experimental plants differed in 5 characters, while at the same time those of species A were all dominant and those of species B all recessive. For mutual transformation A was fertilized with pollen of B, and B with pollen of A, and this was repeated with both hybrids the following year. With the first experiment, B/A, there were 87 plants available in the third year of experiment for selection of the individuals for further crossing, and these were of the possible 32 forms; with the second experiment, A/B, 73 plants resulted, which agreed throughout perfectly in habit with the pollen parent; in their internal composition, however, they must have been just as varied as the forms in the other experiment. A definite selection was consequently only possible with the first experiment; with the second the selection had to be made at random, merely. Of the latter only a portion of the flowers were crossed with the A pollen, the others were left to fertilize themselves. Among each 5 plants which were selected in both
experiments for fertilization there agreed, as the following year's culture showed, with the pollen parent:
1st Expt 2nd Expt
---------------------------------
2 plants ----- in all characters
3 plants ----- in 4 characters
---- 2 plants " 3 "
---- 2 " " 2 "
---- 1 " " 1 character
In the first experiment, therefore, the transformation was completed; in the second, which was not continued further, two more fertilizations would probably have been required.
Although the case may not frequently occur in which the dominant characters belong exclusively to one or the other of the original parent plants, it will always make a difference which of the two possesses the majority of dominants. If the pollen parent has the majority, then the selection of forms for further crossing will afford a less degree of certainty than in the reverse case, which must imply a delay in the period of transformation, provided that the experiment is only considered as completed when a form is arrived at which not only exactly resembles the pollen parent in form, but also remains as constant in its progeny.
G?rtner, by the results of theses transformation experiments, was led to oppose the opinion of those naturalists who dispute the stability of plant species and believe in a continuous evolution of
vegetation. He perceives in the complete transformation of one species into another an indubitable proof that species are fixed with limits beyond which they cannot change. Although this opinion cannot be unconditionally accepted we find on the other hand in G?rtner's experiments a
noteworthy confirmation of that supposition regarding variability of cultivated plants which has already been expressed.
Among the experimental species there were cultivated plants, such as Aquilegia atropurpurea and canadensis , Dianthus caryophyllus, chinensis , and japonicus , Nicotiana rustica and paniculata, and hybrids between these species lost none of their stability after 4 or 5 generations.
范文五:孟德尔的生平
孟德尔的生平(1)
一、孟德尔的青少年时期
孟德尔(Gregor Johann Mendel, 1822—1884)祖籍德国,出生于奥地利西里西亚地区的海钦道夫(现属捷克斯洛伐克的海恩西斯村)。他父亲是个贫苦农民,母亲是个园林工人的女儿。孟德尔出生时,奥地利正处于哈登斯堡王朝统治时期。由于家中田地很少,父亲不得不靠打短工和租种地主的土地来维持全家生活。少年时期的孟德尔就勤奋好学,聪明过人。4年就读完小学全部课程,被称为“乡村中学的高材生”。1833年,孟德尔进入中学。当时生活十分艰苦,常常忍饥挨饿。1840年,他结束了中学生活,全部课程成绩都是优秀。此后,他十分想望进入大学,到奥尔莫茨现称奥洛穆茨哲学学院学习。由于家境贫困,他本人的种种努力也都未成功。失望和对前途的焦虑使他病了一年。后来是他妹妹特蕾西亚(Tresia)拿出了部分嫁妆费,才使他进入大学。在奥尔莫茨大学哲学学院中,孟德尔除了学习自然科学外,主要攻读德国古典哲学。在大学学习期间,孟德尔还找到一个家庭教师的工作,经济上的困难尽管有所减少,但由于工作劳累,健康趋向恶化。1843年,由于他父亲丧失了从事农业的能力,使他增加了新的困难。
二、修道院中的学生和工作
1843年10月,孟德尔在物理学老师弗朗茨(F. Franz)教授的推荐下进入布尔诺(即布隆)奥古斯丁教派修道院。他取名为“格里戈”,并充当该院的一名见习修道士。孟德尔在《自传》中说,由于生活所迫,是环境决定了他“职业的选择”。
但是,孟德尔不久就觉察到,修道院不仅可以解决生活问题,还可以学习、研究学问。布尔诺修道院位于现在捷克的摩拉维亚(Moravia)地区,当时是奥地利的属地。该院负有的使命之一是通过学术研究,发展摩拉维亚的工业和文化。因此,修道院中大多是科学家或技术人员。其中主教纳普(Napp)是大学教授,对哲学、神学、语言学、数学、生物学都有相当的研究。有的神父如特勒(A. Thaler)、克拉塞尔(Klacel)还是著名的植物学家。摩拉维亚是个农业昌盛的地区,所以在修道院的研究活动中,也包括杂交试验。在纳普主教的支持下,修道院内建立了植物标本室和植物园。孟德尔当时只是一个生物学的爱好者,在克拉塞尔等人的支持和影响下,使他酷爱生物学,从而不遗余力地通过自学和请教知名学者来弥补自己知识上的缺陷。1847年,孟德尔被任命为副主祭司,一年后提升为神父,负责教会医院的传教工作。1849年,主教派他当大学预科的代理教员,讲授物理学和博物学。由于他出色地完成教学任务,受到国家社会道德教育部的通报表扬。
三、维也纳时代
1
孟德尔的教学工作虽很出色,但毕竟仍是个代理教员,为取得正式教员的资格,他参加了1850年在维也纳大学举行的教师转正考试。可惜没有录取,后几经周折,总算在1851年进入维也纳大学深造。到维也纳后,孟德尔发奋地学习着。他读书以物理学为主,但也聆听数学、化学、植物学、动物学、昆虫学和古生物学等课程。此外,凡是与自然科学有关的学术报告和讨论会,他都争取参加。维也纳时代对孟德尔从事科学事业极其重要。这所大学是奥地利的最高学府,也是欧洲最古老的大学之一,校内集中一大批优秀的科学家。例如,大学理学院院长、物理学教授多普勒(C. Doppler),是“多普勒效应”的发现者。他的研究方法不是按培根的方式先进行许多观察后归纳出基本规律,而是首先分析问题,提出假设,然后通过实验加以验证。孟德尔曾听过多普勒的实验物理学课,并在他的实验室作过实习实验员。著名物理学家兼数学家埃廷豪森(A. von Ettinghausen)是孟德尔的数学老师,他曾培养出马赫(E. Mach)这样的杰出物理学家。埃廷豪森在科学研究方法上有一个很大的特点,就是喜爱用数学方法研究所探讨的问题。他相信数学方法可以应用于各门自然科学。孟德尔后来在植物杂交试验中应用的精密实验技术和数理统计学知识,都是在大学中打下的基础。当时的化学,以道尔顿(J. Dalton)的原子论为基础,借微小质粒(原子)的聚合离散,说明物质的性质和化学反应,以致于孟德尔从这里引出将原子置换成遗传因子来看待生物的想法。教授植物学的昂格尔(F. Unger,1800,1870)是孟德尔最崇拜的老师。昂格尔以研究细胞学著称,他在课上常滔滔细述有关植物生殖的最新知识。他还经常向学生讲述生物的变异和进化的观念。他在1852年出版的《植物学通信》一书中,否定物种的不变性,并断言植物界“是一步一步逐渐发展而来的”。关于细胞起源的问题,书中写道:“(细胞的起源)在于这样的事实,即作为植物生长发育基础的每个细胞都来自先前已存在的细胞。”昂格尔有关植物受精过程的全部最新的研究工作(1855年以前),在他同年出版的教科书中也作了论述,其中较多涉及到格特纳的工作。在教科书的参考书目中,昂格尔全部引用格特纳和科尔罗伊德的著作。可见孟德尔在大学中有可能已了解他前辈的科学研究。昂格尔当时也已描述过有关杂种方面的已知事实即在F1代杂种的一致性和在F2代又倾向于亲本的现象。孟德尔后来的豌豆杂交实验项目正是从这种观点出发来选题的。 1853年,正是孟德尔结束维也纳大学生活回到布尔诺的那一年,他的第一篇论文“一种有害的昆虫——豌豆蟓”发表了。从论文题目可见,在维也纳时代,孟德尔就开始对豌豆植物产生了兴趣。
孟德尔的生平(2)
四、植物杂交的实验
孟德尔回到修道院后,仍当过代课教师,讲授物理和博物学。有时因身体虚弱,医生称他患有一种“不稳定的心理状态”症,多少也妨碍了工作。1856年夏天,孟德尔已完全恢复
2
健康,并开始从事豌豆杂交实验。他从事这一研究,主要是“为了获得新的颜色变异对于观赏植物进行人工受精的经验”。
正如前面提到的,在19世纪,尽管奈特、格特纳、诺丁等人做了大量的植物杂交试验,但在所有这许许多多试验中,没有一个试验就其规模和方法来说,能确定杂种后代出现的不同类型的数目,或者按照不同世代把这些类型予以可靠性归类,或者明确地查明它们在统计学上的关系。要从事一项如此规模巨大的工作,的确需要一些勇气;但看来是我们最终解决这个问题的唯一正确的途径,这个问题的重要性对有机类型的进化历史方面是难以过分估计的”。这是孟德尔在他的著名论著《植物杂交的试验》(1865年)绪言中的一番话。他本人就创造性地做了这样的工作。1857年,孟德尔从市场上购买了34个豌豆品种,他将经过精心选择的22个品种种在修道院的后院内,并确定7对稳定可区分的性状作为研究对象,即茎的长短和颜色;叶的大小和形状;花的位置、颜色和大小;花柄的长短;荚的颜色、形状和大小;种子的形状和大小;以及种皮和子叶的颜色。有人认为,孟德尔的“性状”和拉瓦锡(A. L. Lavoisier)的“化学元素”相类似,孟德尔也由此被称为“植物学上的拉瓦锡。”
在分别对这些性状稳定的品种进行系统正反交的基础上,孟德尔精细地计算杂种后代表现相对性状的株数,从而分析它们的比例关系。他证明,一对相对性状杂交的结果有两个共同点:第一,杂交一代所有植株的性状都只表现为一个亲本的性状,另一亲本性状则隐而不见。孟德尔称这一对性状中的前者为“显性”,后者为“隐性”。第二,杂交二代的植株有性状分离的现象,即一部分植株表现一个亲本的性状,其余植株表现另一亲本的性状,在第二代群体中相对性状的分离值大致总是3比1。孟德尔对某些植物的试验继续了5代或6代。在所有世代中,杂交种都呈现3与1之比。上述结果表明,控制豌豆性状的遗传物质是以自成单位的因子(即现在的“基因”)存在着,它们可以隐而不显,但不会消失。孟德尔认为,因子作为遗传单位在体细胞中是成双的,它在遗传上具有高度的独立性。因此,在减数分裂形成配子时,成对因子能互不干扰,彼此分离并通过因子重组表现出来。
此后,孟德尔同时观察两对或数对性状的后代中出现的情况。如把圆形黄色种子的豌豆与皱皮绿色种子的豌豆进行杂交,结果杂交一代都是圆形黄色种子。再将这些种子经过单独培育,自花传粉,第二代则有4种类型的种子:圆形黄色、圆形绿色、皱皮黄色、皱皮绿色。它们的比例约为9?3?3?1,恰好是3?1的平方。同时观察3对性状,则第二代有8种类型的种子,其比例约为27?9?9?9?3?3?3?1,正好是3?1的立方。由此可推出(3?1)n的遗传规律,n代表相对性状的数目。为了解释上述现象,孟德尔进一步提出,不同的相对性状的遗传因子在遗传过程中,这一对因子与另一对因子的分离和组合也互不干扰,独自分到配子中去。孟德尔的发现表明,性状的分离和自由组合是造成豌豆变异的原因。
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孟德尔在豌豆植物中的这个发现,被许多学者在其他植物、动物和人类的研究中得到证实。后来,德国植物学家柯灵斯(C. Correns)将这一发现概括为“孟德尔定律”,即性状分离和自由组合定律。孟德尔定律开创了遗传学的新纪元。
尽管孟德尔有多么重要的成就,但是他的工作在当时并未引起学术界的重视。1865年2月,当他在布尔诺召开的奥地利自然科学学会会议上报告自己的研究工作时,据说到会的约50人,其中有博物学、天文学、物理学、化学等方面的工作者。孟德尔花了一个小时介绍他的豌豆杂交试验,与会者除了对数学统计进入遗传学感到惊讶外,对其他内容则毫无兴趣。他们耐心地听完报告,有礼貌地鼓掌后,都默默地拂袖而去。孟德尔对此也有感触,他在给耐格里(K. n geli)的信中说:“我料想会遇到分歧意见的,然而就我所知,迄今还没有一个人重复过我的这些实验。”
第二年,孟德尔把自己的研究成果写成论文,题为“植物杂交的试验”,刊登在奥地利自然科学学会年刊上。这篇论文虽然分送欧美城市的约120个图书馆,也曾被多次引用过,如德国植物学家福克(W. O. Focke)的论文中曾提到过15次,在他的《植物杂种》(1881年)一文中,记载了孟德尔在豌豆上的实验和在其杂交类型中发现的恒定比例;俄国植物学家施马里高践(J. F. Schmalhausen)在他的学位论文“论植物杂种——圣彼得堡植物区系的观察”中提到了孟德尔的论文;贝利(L. H. Bailey)在演讲“杂交育种和杂种生成”(1891年)所开的书目中、皇家学会的《科学论文目录》(1864—1873年)中以及英国生物学家罗曼斯(G. J. Romanes)为《植物学百科全书》第9版关于植物杂交的条目中也都分别提到孟德尔的论文。但是孟德尔论文的意义,在他1884年逝世及此后的一段时间内,却始终没有被学术界所认识。在当时的科学家中,耐格里是最了解孟德尔的。他们通信的时间达7年以上。有大量信件往来。但是,他也未认识到孟德尔成就的价值。唯有施马里高践认识到孟德尔学说的巨大意义,但当时俄国并未重视他对孟德尔的评价。直到1900年,孟德尔的工作才分别由三位著名的植物学家重新发现,这位避世而居的僧侣在很久以前所揭示的生物遗传普遍规律,终于得到了学术界的公认。
五、孟德尔的晚年
孟德尔晚年担任修道院的主教,工作极为繁忙,但仍然坚持自己的植物杂交试验。1868年5月,他在给耐格里的信中说:“最近,我的生活发生了意外的变化,3月30日我这个无足轻重的人被我所隶属的修道院牧师会选为终身主教(院长)。这样,我由一个普通的实验物理学教师转到了一个对我来说是相当陌生的领域。在我熟识这种工作前,我将付出相当的时间和精力。但这不会阻止我继续我所喜爱的杂交试验;一旦我熟识了新的岗位工作后,我甚至希望能用更多的时间和精力去从事这种试验”。孟德尔的愿望也有所实现。如他晚年确实
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作过许多杂交试验,并进行气象学、园艺学的研究。在杂交试验中,最重要的是山柳菊的研究。为此他用了5年(1866—1871)的时间和精力,但实验结果使他失望。山柳菊属杂种行为完全不同豌豆属,大多数杂种都可纯一传代。这种反常现象使孟德尔困惑不解。其原因现在很清楚,由于山柳菊属某些品种是“无融合生殖”,即雌雄配子不发生核融合,杂种后代当然不会有分离现象。关于山柳菊属的这种生殖特点,直到1910年,才被瑞典植物学家奥斯特菲尔德(Ostenfeld)和劳恩基亚尔(Raunki r)所揭示。由此也说明,山柳菊的特点,在植物界是个例外,豌豆的特性倒是普遍现象。当时的植物学权威学者耐格里是山柳菊属的专家,而他也不知他的研究对象所表现的生理特点是一种例外。正是在耐格里的劝说下,孟德尔晚年集中注意山柳菊的研究。可是这一工作为孟德尔带来许多困难,山柳菊植物的花既小又难以交配,使孟德尔的眼疾越发恶化;更重要的是得出的结果与豌豆属明显不一致。这不能不影响他对原有工作的信心,造成不必要的麻烦。难怪有人说,孟德尔碰到了耐格里,是一个很大的“不幸”。
孟德尔晚年有两个方面的因素,使他过早地结束了科学工作。一是1874年奥地利政府向修道院征收一笔庞大的税款,孟德尔拒绝缴纳,与政府对抗。这场冲突几乎延续了10年之久,到孟德尔去世仍未圆满解决;二是孟德尔的健康逐步下降。由于他学术上的不得志,山柳菊实验的失败,与政府关系的恶化,促使他常常闷郁和忧愁。1883年圣诞节后,他的慢性肾炎再次复发。他经常忍受失水的折磨,但却很少呻吟。他大部分时间坐在沙发上,只有感到困倦时才上床睡觉。1884年1月4日,当他作完最后一次气象学观察和记录后,心脏病又一次打击了他。1月6日凌晨,当修女整理他的床褥时,发现他靠在沙发上与世长辞了。布尔诺日报对孟德尔写下这样的颂词:“他的死使穷人失去了一位恩人,使人类失去了一位品质高尚的人,一位热情的朋友,一位自然科学的促进者和一位模范的牧师??。”1月9日,布尔诺修道院为孟德尔举行了葬礼,有数以千计的人们为他送葬,大家为失去这样一位敬爱的院长而悲伤,但谁也不了解他在遗传学上的伟大贡献。不过,孟德尔深信他的研究会对人类产生影响。在他逝世前几个月曾说过:“我一生充满辛酸,但也有过美好的时光,因而我得感恩。毕竟我可以尽情地完成自然科学的研究。也许没多久,世人就会承认这项研究成果吧。”
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