'Versuche über Pflanzen-Hybriden': segregation of characters and numerical ratios

1865–1866 Life and health theory

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Experiments on crossing peas in which characters with two distinguishable states were counted one by one and the ratios of the numbers were recorded. Segregation in the second generation at about three to one, and the independent behaviour of different characters, turned talk of a 'capacity of inheritance' into arithmetic.

The experiments were made by the Czech Augustinian monk Gregor Mendel and printed in 1866 as 'Versuche über Pflanzen-Hybriden'. He took from the earlier hybridizers both the design of the experiment and the very matter in dispute, the reversion of hybrids to parental forms, but added what they did not have: the choice of two-state characters and the counting one by one.

The paper went almost unnoticed until 1900. Historians still argue about what the paper was actually about: heredity, or the origin of species through hybridization.

Why this date

The lectures were read to the Natural History Society in Brno on 8 February and 8 March 1865; the paper was printed in 1866: Verhandlungen des naturforschenden Vereines in Brünn, vol. 4 (Abhandlungen), pp. 3-47. The axis takes the year of printing, the label both years. The bibliographic details were checked against Zhang, Chen and Sun in Genetics (2017).

What it grew from

• The Sheep Breeders' Society in Brno: heredity becomes a subject in its own right

  influenced · Confidence: medium

  The question of heredity was posed in Brno by sheep breeders half a century before Mendel, and historians call their work outright a prelude to his experiments: Mendel came into the monastery of Napp, the man who formulated that question, and attended Diebl's course on agriculture.

  Dispute: Two different things are disputed. First: there is no direct documentary evidence that Mendel read Festetics, and the proponents of continuity admit as much, hedging 'whether or not Mendel was aware of Festetics's ideas' (Poczai et al., 2014); only the link through Napp and Diebl, that is through people rather than through a text, is firmly documented. Second: Olby, in 'Mendel no Mendelian?' (1979), argued that Mendel was not working on heredity at all but on the origin of species through hybridization, in which case Napp's question was not his question. Van Dijk and Ellis (Genetics, 2023) state the thesis thus: 'One of the conclusions of Olby (1979), which we investigated here, was that Mendel was not primarily interested in inheritance but in speciation', and reject it: 'little of Olby's views can hold'. A caution: Poczai and Wood with Orel are not fully independent, Orel being a co-author of both lines of work, and Poczai with co-authors published the continuity thesis three times.

  Link sources

  • Roger J. Wood, Vítězslav Orel, Scientific Breeding in Central Europe during the Early Nineteenth Century: Background to Mendel's Later Work, Journal of the History of Biology 38 (2), 239-272 (abstract) (2005) Verified 20 Sep 2026

    Efforts to bring science into early 19th century breeding practices in Central Europe, organised from Brno, the Hapsburg city in which Mendel would later turn breeding experiments into a body of timeless theory, are here considered as a significant prelude to the great discovery.

  • Roger J. Wood, Vítězslav Orel, Scientific Breeding in Central Europe during the Early Nineteenth Century: Background to Mendel's Later Work, Journal of the History of Biology 38 (2), 239-272 (abstract) (2005) Verified 20 Sep 2026

    Major figures in this development included Abbot Napp, the one who asked this question and who was due to receive Mendel into the monastery in 1843, and Professor Diebl whose lectures on agriculture and natural science at the Brno Philosophical Institute Mendel would attend in 1846.

  • Péter Poczai, Jorge A. Santiago-Blay, Jiří Sekerák, A. T. Szabó, How Political Repression Stifled the Nascent Foundations of Heredity Research before Mendel in Central European Sheep Breeding Societies, Philosophies 6 (2), 41 (2021)

    Research carried out by members of the SBS provided questions for centuries of experimental analysis and was a perfect prelude to Mendel.

  • Péter Poczai, Neil Bell, Jaakko Hyvönen, Imre Festetics and the Sheep Breeders' Society of Moravia: Mendel's Forgotten "Research Network", PLoS Biology 12 (1), e1001772 (2014) Verified 20 Sep 2026

    When Mendel turned his attention to inheritance in peas he was not an isolated monk, but rather the latest in a line of Moravian researchers and agriculturalists who had been thinking about inheritance for half a century.

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

• Artificial plant hybridization as a repeatable experiment

  influenced · Confidence: high

  Mendel worked inside the research tradition of the hybridizers opened by Kölreuter: he took from him both the subject (the reversion and transformation of hybrids in later generations) and the design of the experiment, and himself acknowledged the part his work played in his own research.

  Dispute: The continuity of technique and subject is not in dispute; what is in dispute is the meaning of the borrowing. For Olby and for Müller-Wille with Orel, Mendel's naming of Kölreuter and Gärtner in the introduction and again in the discussion of the 1866 paper is an argument that he belonged to the tradition of the hybridizers and was working on the origin of species through hybridization. Van Dijk and Ellis (2023) contest that reading and hold the link to the hybridizers to be methodological, Mendel's own problem being a different one. Separately: the Olby quotation 'Mendel, Sprengel, and Darwin owed him a debt' is taken from the electronic reprint of the Dictionary of Scientific Biography at encyclopedia.com; the volume and pages of the printed edition could not be verified.

  Link sources

  • Hui Zhang, Wen Chen, Kun Sun, Mendelism: New Insights from Gregor Mendel's Lectures in Brno, Genetics 207 (1), 1-8 (2017)

    Mendel admitted that the work of the German scientist Kölreuter on plant hybridization had played an important role in the development of his own research (Mendel 1866).

  • Hui Zhang, Wen Chen, Kun Sun, Mendelism: New Insights from Gregor Mendel's Lectures in Brno, Genetics 207 (1), 1-8 (2017)

    It is clear that Mendel had the same research interest as his predecessor Kölreuter in hybrid fertility and in the tendency of hybrids to revert or transform in subsequent crosses.

  • Robert Olby, Koelreuter, Joseph Gottlieb, Complete Dictionary of Scientific Biography (1973) Verified 20 Sep 2026

    Mendel, Sprengel, and Darwin owed him a debt.

  • Peter J. van Dijk, T. H. Noel Ellis, Gregor Mendel and the theory of species multiplication, Genetics 224 (2), iyad046 (2023)

    An important argument for Olby (1979), Brannigan (1979), and Müller-Wille and Orel (2007) to place Mendel in the tradition of the hybridizers, who were concerned with the question of whether species could arise through hybridization, was that Mendel explicitly mentioned these hybridists in the introduction and again in the discussion of the 1866 article.

  • David Kopecký, Antonio Martín, Petr Smýkal, Interspecific hybridization and plant breeding: From historical retrospective through work of Mendel to current crops, Czech Journal of Genetics and Plant Breeding 58 (3), 113-126 (2022) Verified 20 Sep 2026

    He also showed that F1 hybrids are usually morphologically intermediate relative to their parents and that successive generations tend to revert back to the parental forms.

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

What grew out of it

• Three papers of 1900: de Vries, Correns and Tschermak bring back Mendel's laws

  prerequisite for · Confidence: high

  The papers of 1900 exist as a 'rediscovery' only in relation to the paper of 1866: they name the rule after Mendel and give the location of his paper, and according to Olby neither de Vries nor Tschermak reached the theory independently, while de Vries reorganised his data around Mendel only after reading him.

  Dispute: The dispute is over the very word 'rediscovery'. The traditional version (Fisher 1936, 'Has Mendel's work been rediscovered?', and Tschermak's own recollections in the Journal of Heredity, 1951) treats the three discoveries as independent. The revision: Meijer (1985) and Corcos and Monaghan (1985) showed that de Vries began writing 3:1 only after 1900; Monaghan and Corcos (1986-1987) deny Tschermak the title of rediscoverer altogether, 'he did not understand Mendel when he had read it'; Rheinberger (Isis 1995) established that Correns had read Mendel in 1896. Olby (1997) sums up: 'The label rediscoverer is a slippery one', and adds that Mendel as founder was convenient because he removed any quarrel over precedence among the three living men. Brannigan (1981), whom Olby summarises, goes further: the status of discovery is attributed by society after the fact; in 1866 the work was a contribution to the normal science of hybrid reversion and became a 'discovery' only in the context of 1900. This also answers the question of the 34 silent years: the paper was read and cited (Hoffmann 1869, Focke 1881, eleven references according to Olby and Gautrey 1968), but read as a paper on hybrids, not on heredity.

  Link sources

  • Robert Olby, William Bateson's Introduction of Mendelism to England: A Reassessment, The British Journal for the History of Science 20 (4), 399-420 (extract) (1987) Verified 20 Sep 2026, quotation assembled from fragments

    The recognition of Gregor Mendel's achievement in his study of hybridization was signalled by the 'rediscovery' papers of Hugo de Vries, Carl Correns and Erich Tschermak. ... The rest, led by De Vries' Berichte paper, were in German and mentioned Mendel, giving the location of his paper.

  • Robert C. Olby, Mendel, Mendelism and Genetics, MendelWeb (1997) Verified 20 Sep 2026

    We now possess evidence that neither Hugo de Vries nor Erich Tschermak arrived independently of Mendel at his theory, although Tschermak did perceive the 3:1 ratio in his F2 data in 1900. Not till De Vries had read Mendel (possibly for the second time) did he reorganize his data and from them select those experiments which confirmed Mendel.

  • Alain Corcos, Floyd Monaghan, Role of de Vries in the recovery of Mendel's work: 1. Was de Vries really an independent discoverer of Mendel?, Journal of Heredity 76 (3), 187-190 (abstract) (1985)

    Arguments are based on de Vries' own writings that showed the F2 data of his numerous crosses are reported as 3:1 ratios only after 1900. They also show that his theory of inheritance becomes quasi Mendelian only after 1900.

  • Daniel J. Fairbanks, Demystifying the mythical Mendel: a biographical review, Heredity 129 (1), 4-11 (2022) Verified 20 Sep 2026

    No one, including Mendel, recognised the importance of his theory in his day; it languished mostly unnoticed until its dramatic rediscovery founded the science of genetics at the beginning of the twentieth century.

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong. "Assembled from fragments" means the words do not stand together on the page: we found each fragment separately and joined them with an ellipsis.

• Bateson gives the science of heredity a name: 'genetics'

  influenced · Confidence: high

  Bateson read Mendel's paper in 1900, at once accepted the hypothesis of germinal segregation, and found in it support for his long-held idea of discontinuous variation; genetics as the science he named grew out of the reading of this very paper, which he also translated into English.

  Dispute: Olby (1987) questions the family legend of reading the paper on the train on 8 May 1900 and examines whether Bateson learnt of Mendel earlier through de Vries's Berichte paper; either way his source was the 1866 paper, not experiments of his own.

  Link sources

  • Robert C. Olby, Mendel, Mendelism and Genetics, MendelWeb (1997) Verified 20 Sep 2026

    When Bateson read Mendel's paper in 1900 he gladly accepted the hypothesis of germinal segregation expressed therein. The determinants for differing character pairs separated and passed into different germ cells.

  • Robert C. Olby, Mendel, Mendelism and Genetics, MendelWeb (1997) Verified 20 Sep 2026

    Mendel thus supplied Bateson with further ammunition for his near decade-long campaign to convince biologists that it is the non-blending variations that are significant for evolution.

  • Robert Olby, William Bateson's Introduction of Mendelism to England: A Reassessment, BJHS 20 (4), 399-420 (1987) Verified 20 Sep 2026

    He had already prepared this paper, but in the train on his way to town to deliver it, he read Mendel's actual paper on peas for the first time. As a lecturer he was always cautious, suggesting rather than affirming his own convictions. So ready was he however for the simple Mendelian law that he at once incorporated it into his lecture.

  • Robert C. Olby, Mendel, Mendelism and Genetics, MendelWeb (1997) Verified 20 Sep 2026

    Explaining to the uninitiated what the Mendelian hybridists were doing had proved difficult and cumbrous, he remarked, yet the new science born of Mendel's work was still nameless. Therefore he offered the conference the term 'Genetics'

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

• The biometric-Mendelian debate: continuous or discontinuous heredity

  influenced · Confidence: high

  The data of Mendel's paper itself became the matter of the dispute: in 1902 Weldon applied Pearson's chi-squared test to them and was the first to raise the question of a fit with theory that was 'too good', a question later inherited by Fisher.

  Dispute: The question of Mendel's 'too good' data itself (Fisher 1936 and the forty-year controversy after 1965) belongs to the statistics theme and is not treated here; Fairbanks, following Franklin (2008), holds that the suspect experiments can be explained without fraud, while the 'too-good-to-be-true' aspect remains as a statistical fact.

  Link sources

  • Daniel J. Fairbanks, Demystifying the mythical Mendel: a biographical review, Heredity 129 (1), 4-11 (2022) Verified 20 Sep 2026

    Weldon was the first to raise questions, privately writing to Pearson in 1901 that Mendel had "cooked his figures, but that he was substantially right" (Mangello 2004, p. 23, italics in original). After applying Pearson's newly developed chi-squared test to Mendel's data, Weldon (1902) did not overtly claim in print that Mendel manipulated the data but dangled the possibility in several statements, one of which reads, "the odds against a result as good as this or better are 20 to 1" (p. 235).

  • Daniel J. Fairbanks, Demystifying the mythical Mendel: a biographical review, Heredity 129 (1), 4-11 (2022) Verified 20 Sep 2026

    Fisher, probably influenced by Weldon's paper, famously stated in a 1911 lecture, "It may just have been luck, or it may be that the worthy German abbot, in his ignorance of probable error, unconsciously placed doubtful plants on the side which favoured his hypothesis" (Norton and Pearson 1976, p. 160).

  • Robert Olby, William Bateson's Introduction of Mendelism to England: A Reassessment, BJHS 20 (4), 399-420 (reference 40) (1987) Verified 20 Sep 2026

    Weldon, W.F.R., 'Mendel's laws of alternative inheritance in peas', Biometrika, (1902), 1, pp. 228–254.

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

• 'The Chromosomes in Heredity': chromosome behaviour as the physical basis of Mendel's laws

  influenced · Confidence: high

  The chromosome hypothesis was born as an attempt to put a visible mechanism under Mendel's numbers: Sutton set the behaviour of paired chromosomes in the maturation of the germ cells beside the segregation and independent assortment of Mendelian factors.

  Dispute: Martins observes that Sutton's trust in Mendel was stronger than in his own cytology: he revised his earlier observations on the separateness of the paternal and maternal sets not because of new preparations but because otherwise the recombination of characters would not come out. The influence thus ran not only from Mendel to the chromosomes but back as well, from the Mendelian scheme to what Sutton was willing to see under the microscope.

  Link sources

  • Lilian Al-Chueyr Pereira Martins, Did Sutton and Boveri propose the so-called Sutton-Boveri chromosome hypothesis?, Genetics and Molecular Biology 22 (2), 261-272 (1999) Verified 20 Sep 2026

    The "Sutton-Boveri chromosome hypothesis" attempted to establish a parallel between cytological chromosome behavior and the principles followed by Mendelian factors.

  • Jane Oppenheimer, Boveri, Theodor, Complete Dictionary of Scientific Biography, 1902 (1970) Verified 20 Sep 2026, quotation assembled from fragments

    Walter Sutton called attention to “the probability that the association of paternal and maternal chromosomes in pairs and their subsequent separation during the reduction division… may constitute the physical basis of the Mendelian law of heredity.”

  • Lilian Al-Chueyr Pereira Martins, Did Sutton and Boveri propose the so-called Sutton-Boveri chromosome hypothesis?, Genetics and Molecular Biology 22 (2), 261-272 (1999) Verified 20 Sep 2026

    If one accepts the independent segregation of chromosomes, it is possible to associate them to Mendelian factors and explain the independent segregation of characters. That was what Sutton did; he associated one factor to each chromosome (Sutton, 1903, p. 234).

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong. "Assembled from fragments" means the words do not stand together on the page: we found each fragment separately and joined them with an ellipsis.

• The correlation between relatives on the supposition of Mendelian inheritance: biometry and Mendelism reconciled

  influenced · Confidence: high

  Fisher showed that the 'pea vs. height debate' is removed if a trait is determined by many factors, each obeying Mendelian rules and segregation ratios. Mendel's experiments of 1866 enter the paper of 1918 not as something cited but as the model of inheritance from which the observed correlations between relatives are derived.

  Dispute: Fisher's attitude to Mendel is double, and this is a well known dispute. In the 1936 paper 'Has Mendel's work been rediscovered?' the same Fisher asserted that the data of most of Mendel's experiments had been falsified to agree with expectation, and in private called the finding 'abominable' and 'shocking'. Hartl and Fairbanks go through both series of experiments and conclude that there is no factual basis for the allegation of falsification, the discrepancy being explained by which character Mendel actually scored and how many seedlings he examined. The dispute over data that are 'too good' continues, but it does not affect the 1866 to 1918 link: Fisher's 1918 paper rests on the Mendelian mechanism regardless of how Mendel himself counted.

  Link sources

  • Peter M. Visscher, Michael E. Goddard, From R.A. Fisher's 1918 Paper to GWAS a Century Later, Genetics 211 (4), 1125-1130 (2019)

    In his paper, Fisher showed that this “pea vs. height debate” could be reconciled by postulating that multiple genes contribute to variation in the population, each of them obeying Mendelian rules and segregation ratios.

  • Peter M. Visscher, Michael E. Goddard, From R.A. Fisher's 1918 Paper to GWAS a Century Later, Genetics 211 (4), 1125-1130 (2019)

    A century ago, a paper from R.A. Fisher reconciled Mendelian and biometrical genetics in a landmark contribution that is now accepted as the main foundation stone of the field of quantitative genetics.

  • Churchill Eisenhart, «Pearson, Karl», Complete Dictionary of Scientific Biography (2008) Verified 20 Sep 2026

    he improved upon the kinds of models that Pearson, Weldon, and Yule had been considering 10–20 years before, and showed clearly that the correlations observed between human relatives not only could be interpreted on the supposition of Mendelian inheritance, but also that Mendelian inheritance must lead to precisely the kind of correlations observed.

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

Node sources

• Hui Zhang, Wen Chen, Kun Sun, Mendelism: New Insights from Gregor Mendel's Lectures in Brno, Genetics 207 (1), 1-8 (2017) Verified 5 Oct 2026

  Mendel delivered two lectures to report his work at the meeting of the local scientific society in Brno on February 8 and March 8, 1865

• Hui Zhang, Wen Chen, Kun Sun, Mendelism: New Insights from Gregor Mendel's Lectures in Brno, Genetics 207 (1), 1-8 (2017) Verified 5 Oct 2026

  Mendel used the same experimental framework as his predecessor, performing the self-crosses of hybrids in multiple generations that resulted in a tendency toward (trait) “Reversion” and also conducting backcrosses with parents that brought about (trait) “Transformation” in successive generations.

• G. Mendel, Versuche über Pflanzen-Hybriden, Verhandlungen des naturforschenden Vereines in Brünn 4 (Abhandlungen), 3-47 (1866)

  Versuche über Pflanzen-Hybriden

• Peter J. van Dijk, T. H. Noel Ellis, Gregor Mendel and the theory of species multiplication, Genetics 224 (2), iyad046 (2023)

  One of the conclusions of Olby (1979), which we investigated here, was that Mendel was not primarily interested in inheritance but in speciation.

"Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

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