For their encouragement and helpful comments I thank Ernst Homburg, Dick van Lente, Robert C. Olby, Piet de Rooy, Rienk Vermij and my colleagues at the Utrecht Institute for the History of Science. I also thank Lian Hielkema for her indispensable bibliographic assistance, and Enid Perlin for her correction of the English text.

¹ Letter to F. Went, A. F. C., 14 09 1922Google Scholar; Museum Boerhaave, Leiden. The relevant passage runs as follows: ‘The glorification of Mendel is a fashionable article in which everyone, even those without much understanding, can join; this fashion will surely pass. The celebration in Brünn is nationalistic and anti-English, directed especially against Darwin and therefore unsympathetic to me, yet for these reasons also very popular.’

² Meijer, O. G., ‘Hugo de Vries no Mendelian?’, Annals of Science (1985), 37, 189–232, especially 220–4CrossRefGoogle Scholar; references to the earlier literature on the ‘rediscovery’ of Mendel may also be found here. While Meijer has provided the most convincing arguments so far that de Vries did not ‘rediscover’ Mendel independently, he has misunderstood de Vries' position with regard to Mendelism after the rediscovery, in my view; see Theunissen, B., ‘Closing the door on Hugo de Vries' Mendelism’, Annals of Science (1994), 51, 225–48.CrossRefGoogle ScholarPubMed A discussion of the problematic notion of ‘rediscovery’ is provided by Olby, Robert C., ‘Rediscovery as an historical concept’, in New Trends in the History of Science (ed. Visser, R. P. W., Bos, H. J. M., Palm, L. C. and Snelders, H. A. M.), Amsterdam and Atlanta, 1989, 197–208Google Scholar; see also his Origins of Mendelism, revised edn, Chicago, 1985.Google Scholar

³ Allen, Garland E., ‘Hugo de Vries and the reception of the mutation theory’, Journal of the History of Biology (1969), 2, 55–87, especially 64.CrossRefGoogle Scholar For de Vries' supposed essentialism and typological concept of species, see for instance Mayr's ‘Prologue’ in The Evolutionary Synthesis. Perspectives on the Unification of Biology (ed. Mayr, E. and Provine, W. B.), Cambridge, Mass., 1980, 4–5 and 20–1CrossRefGoogle Scholar; Mayr, E., The Growth of Biological Thought. Diversity, Evolution and Inheritance, Cambridge, Mass, and London, 1982, 546–8.Google Scholar

⁴ Sapp, Jan, ‘The struggle for authority in the field of heredity, 1900–1932: new perspectives on the rise of genetics’, Journal of the History of Biology (1983), 16, 311–42, quotation on 311.CrossRefGoogle ScholarPubMed

⁵ Sapp, , op. cit. (4), 312.Google Scholar

⁶ Allen, , op. cit. (3)Google Scholar; Bowler, Peter J., ‘Hugo de Vries and Thomas Hunt Morgan: the mutation theory and the spirit of Darwinism’, Annals of Science (1978), 35, 55–73CrossRefGoogle Scholar and, by the same author, The Eclipse of Darwinism. Anti-Darwinian Evolution Theories in the Decades Around 1900, Baltimore, 1983, 197–212.Google Scholar

⁷ de Vries, Hugo, Die Mutationstheorie. Versuche und Beobachtungen über die Entstehung von Arten im Pflanzenreich, 2 vols., Leipzig, 1901–1903Google Scholar. It is important here to distinguish between our post-synthesis view of de Vries' position with respect to Darwin's work and the perspective from which de Vries saw the matter. In his Species and Varieties. Their Origin by Mutation (Chicago and London, 1905, p. ix) de Vries wrote, for instance: ‘My work claims to be in full accordance with the principles laid down by Darwin, and to give a thorough and sharp analysis of some of the ideas of variability, inheritance, selection and mutation, which were necessarily vague at this time. It is only just to state, that Darwin established so broad a basis for scientific research upon these subjects, that after half a century many problems of major interest remain to be taken up’ (see also Bowler, , The Eclipse, op. cit. (6), 200)Google Scholar. Further, de Vries composed an essay on variation honouring Darwin in Seward, A. C., Darwin and Modern Science, Cambridge, 1909, 66–84.Google Scholar J. Heimans has noted that de Vries took great pains to present his theory of intracellular pangenesis as an updated version of Darwin's ‘provisional hypothesis of pangenesis’, while de Vries' version would in fact be more adequately described as a refutation of the original (Zeventig jaar pangenenleer, Amsterdam and Djakarta, 1959, passim). Moreover, de Vries would have died rather than ‘make fun’ of Darwin's views, as Ernst Mayr has recently made him do (One Long Argument. Charles Darwin and the Genesis of Modern Evolutionary Thought, Harlow, 1992, 46)Google Scholar. De Vries revered and emulated Darwin all his life; see for instance van der Pas, Peter W., ‘The correspondence of Hugo de Vries and Charles Darwin’, Janus (1970), 57, 173–213.Google Scholar

⁸ Theunissen, , op. cit. (2).Google Scholar

⁹ The bare fact that de Vries deemed his hereditary research to be of practical relevance for agriculture and horticulture has of course been noted by de Vries' biographers (cf. note 22), and de Vries' social views have been mentioned by Noordman, Jan, Om de kwaliteit van het nageslacht. Eugenetica in Nederland 1900–1950, Nijmegen, 1989, 59–60.Google Scholar However, the ideology underlying de Vries' views on the relation between science and practice and its cultural and social backgrounds remains to be analysed.

¹⁰ See, for instance, Kimmelman, Barbara A., ‘A Progressive Era Discipline. Genetics at American Agricultural Colleges and Experiment Stations, 1900–1920’, Ph.D. dissertation, University of Pennsylvania, UMI, Ann Arbor, Michigan, 1987Google Scholar; Paul, Diane B. and Kimmelman, Barbara A., ‘Mendel in America. Theory and practice’, in The American Development of Biology (ed. Rainger, R., Benson, Keith R. and Maienschein, Jane), Philadelphia, 1988, 281–310Google Scholar; Fitzgerald, Deborah, The Business of Breeding. Hybrid Corn in Illinois, 1890–1940, Ithaca, New York, 1989.Google Scholar

¹¹ Kingsland, Sharon, ‘The battling botanist: Daniel Trembley MacDougal, mutation theory, and the rise of evolutionary biology in America, 1900’, Isis (1991), 82, 479–509.CrossRefGoogle Scholar

¹² Teich, Mikuláš and Porter, Roy (eds.), Fin de Siècle and its Legacy, Cambridge, 1990, Introduction, 1.Google Scholar

¹³ Romein, Jan's classic study of the fin de siècle, Op het breukvlak van twee eeuwen, 2 vols., Leiden and Amsterdam, 1967Google Scholar (teanslated as The Watershed of Two Eras, Middletown, Conn., 1978) has recently been evaluated with respect to the situation in the Netherlands in a special issue on the Dutch fin de siècle of the Bijdragen en Mededelingen betreffende de Geschiedenis der Nederlanden (1991), 106/4.Google Scholar See especially the contribution by N. C. F. van Sas, ‘Fin-de-siècle als nieuw begin. Nationalisme in Nederland rond 1900’, 595–609.

¹⁴ See de Rooy, P., Darwin en de strijd langs vaste lijnen, Nijmegen, 1987Google Scholar; Stuurman, Siep, ‘Het einde van de produktieve deugd’, Bijdragen en Mededelingen betreffende de Geschiedenis der Nederlanden (1991), 106, 610–24Google Scholar, and, by the same author, Wacht op onze daden. Het liberalisme en de vernieuwing van de Nederlandse staat, Amsterdam, 1992, ch. 8.Google Scholar Despite differences in the political landscape and differences of motive, there is a clear parallel with the shift from Gladstonian liberalism toward Social Imperialism and Lloyd George's New Liberalism in the United Kingdom (see, for instance, Freeden, M., The New Liberalism. An Ideology of Social Reform, Oxford, 1978Google Scholar, and Gilbert, Bentley B., David Lloyd George, a Political Life. The Architect of Change 1863–1912, London, 1988)Google Scholar, and also with the Progressive Movement in the USA. See, for instance, Wiebe, Robert, The Search for Order, 1877–1920, New York, 1965Google Scholar; Hofstadter, Richard, Age of Reform. From Bryan to F.D.R., New York, 1955.Google Scholar

¹⁵ Prominent among this group were the Society's secretary, A. Kerdijk, and H. P. G. Quack, member of the central board. For a general history of the society, see: Mijnhardt, W. W. and Wichers, A. J., Om het algemeen volksgeluk. Twee eeuwen particulier initiatief 1784–1984. Gedenkboek ter gelegenheid van het tweehonderdjarig bestaan van de Maatschappij tot Nut van 't Algemeen, Edam, 1984.Google Scholar The development of the Society's ideology is discussed in detail in the chapter by Mijnhardt, W. W., ‘Het nut en de genootschapsbeweging’, 187–220, especially 197–202.Google Scholar See also Kruithof, Bernard, Zonde en deugd in domineesland. Nederlandse protestanten en problemen van opvoeding, zeventiende tot twintigste eeuw, Groningen, 1990, 60–95, 182–6.Google Scholar

¹⁶ See Helsloot, P., ‘De nutsbeweging’Google Scholar, in Mijnhardt, and Wichers, , op. cit. (15), 3–186, especially 79–81Google Scholar; de Rooy, , op. cit. (14), 14, 25–6.Google Scholar

¹⁷ De Rooy, , op. cit. (14).Google Scholar

¹⁸ Kelly, A., The Descent of Darwin. The Popularization of Darwinism in Germany 1860–1914, Chapel Hill, 1981.Google Scholar

¹⁹ Noordman, , op. cit. (9), 25–9Google Scholar and ‘Darwinisme en sociale selectie. Sociaal-darwinistische visies op evolutie en geschiedenis’, Wijsgerig Perspectief op Maatschappij en Wetenschap (1991/1992), 32, 104–10.Google Scholar

²⁰ De Rooy, , op. cit. (14), 18–19.Google Scholar

²¹ As far as de Vries is concerned, there is again a clear parallel here with the views of the new liberals in the UK and the USA (see note 14). Within the realm of the biological sciences, the changing attitude towards government-supported research in the UK is illustrated in Olby, Robert C.'s ‘Scientists and bureaucrats in the establishment of the John Innes Horticultural Institution under William Bateson’, Annals of Science (1989), 46, 497–510CrossRefGoogle Scholar, and in his ‘Social Imperialism and state support for agricultural research in Edwardian Britain’, Annals of Science (1991), 48, 509–26Google Scholar; an apt example of the American situation is Kimmelman, , op. cit. (10)Google Scholar. The impact of the views of progressive scientists such as de Vries on the Dutch government's science policy remains to be explored, yet Bastiaan Willink has broken important new ground in his analysis of the factors involved in bringing about the remarkable period of Dutch science in the last quarter of the nineteenth century: Willink, B., Burgerlijk sciëntisme en wetenschappelijk toponderzoek. Sociale grondslagen van nationale bloeiperioden in de negentiende eeuwse bètawetenschappen, Rotterdam, 1988.Google Scholar

²² The only available full biography of de Vries (which leaves much to be desired) is de Veer, P. H. W. A. M.'s Leven en werk van Hugo de Vries, Groningen, 1969.Google Scholar Useful shorter biographies are Peter J. van der Pas' entry in the Dictionary of Scientific Biography; Smit, P., ‘Hugo de Vries (1848–1935)’, in Van Stevin tot Lorentz. Portretten van Nederlandse natuurwetenschappers (ed. Kox, A. J. and Chamalaun, M.), Amsterdam, 1980, 163–76Google Scholar; Visser, R. P. W., ‘Hugo de Vries (1848–1935). Het begin van de experimentele botanic in Nederland’, in Een brandpunt van geleerdheid in de hoofdstad. De Universiteit van Amsterdam rond 1900 in vijftien portretten (ed. Kooijmans, L.), Hilversum, 1992, 159–78.Google Scholar

²³ Theunissen, , op. cit. (2).Google Scholar

²⁴ See Theunissen, B., ‘De beheersing van mutaties. Hugo de Vries’ Werdegang van fysioloog tot geneticus’, Gewina, Tijdschrift voor de Geschiedenis der Geneeskunde, Natuurwetenschappen, Wiskunde en Techniek (1992), 15, 97–115.Google Scholar

²⁵ On Sachs see Pringsheim, E. G., Julius Sachs, der Begründer der neueren Pflanzenphysiologie 1832–1897, Jena, 1932Google Scholar; Gimmler, H., Julius Sachs und die Pflanzenphysiologie heute, Würzburg, 1984.Google Scholar See also Pauly, Philip J., Controlling Life. Jacques Loeb and the Engineering Ideal in Biology, New York and Oxford, 1987, 34–8.Google Scholar

²⁶ See note 15. De Vries contributed to the publications of the Society by writing a treatise on the improvement of plant cultures: de Vries, Hugo, Over veredelde landbouwplanten, Amsterdam, 1899.Google Scholar

²⁷ de Vries, Hugo, ‘Pieter Harting’, Het Nieuws van den Dag, 7 12 1885, 3.Google Scholar Harting expressed his pertinent views in, for instance, his ‘Natuurkennis als opvoedingsmiddel; een afscheidswoord’, Album der Natuur (1985), 393–8.Google Scholar Contrary to the progressive liberals, Harting, a typical representative of classical liberalism was rather pessimistic about the future of Dutch culture and society; see te Velde, Henk, Gemeenschapszin en plichtsbesef. Liberalisme en nationalisme in Nederland, 1870–1918, Ph.D. dissertation University of Groningen, Den Haag, 1992, 67–8.Google Scholar

²⁸ Album der Natuur (1852), ‘Voorberigt’.Google Scholar

²⁹ de Vries, Hugo, ‘Eenheid in veranderlijkheid’ (Rectorial Address, Amsterdam University, 1898) in Zaaien en planten, Haarlem, 1899, 3–25, quotation on 25.Google Scholar

³⁰ Thus de Vries gave his warm support to the nature movement that was gaining momentum in the Netherlands in the 1890s, for the study of nature made people ‘more content and happier [and] nobler in thoughts and intentions’ (‘Herleven’, Album der Natuur (1905), 367–72, quotation on 371)Google Scholar. See Theunissen, B., ‘Natuursport en levensgeluk: Hugo de Vries, Eli Heimans en Jac. P. Thijsse’, Cewina, Tijdschrift voor de Geschiedenis der Geneeskunde, Natuurwetenschappen, Wiskunde en Techniek (1993), 16, 287–307.Google Scholar

³¹ de Vries, Hugo, ‘Over Nägeli's conserven’, Eigen Haard (1879), 145–6, 154–7.Google Scholar

³² de Vries, Hugo, ‘Over het zoet worden van aardappelen in den winter’, Eigen Haard (1883), 320–1.Google Scholar

³³ Unless otherwise mentioned these articles (and others of a similar nature) can be found in the collection Zaaien en planten, op. cit. (29).

³⁴ de Vries, Hugo, ‘Aardbeziën onder glas’Google Scholar, in de Vries, , Zaaien en planten, op. cit. (29), 254–60.Google Scholar De Vries was referring here to the experiment station extension work led by Liberty Hyde Baily at Cornell University. For the Nixon act, see True, A. C., A History of Agricultural Education in the United States 1785–1925, US Department of Agriculture Miscellaneous Publication No. 36, Washington, DC, 1929, 44–5.Google Scholar

³⁵ de Vries, Hugo, ‘Proeftuinen voor selectieproeven’, Album der Natuur (1896), 65–74, quotation on 67.Google Scholar

³⁶ de Vries, Hugo, Naar Californië. Reisherinneringen, 2 vols., Haarlem, 1906, i, 478.Google Scholar

³⁷ de Vries, Hugo, ‘The evidence of evolution’, Science, NS (1904), 20, 395–401, quotation on 395.CrossRefGoogle Scholar

³⁸ De Vries, , op. cit. (35), 67.Google Scholar See also de Vries, Hugo, ‘Beiträge zur Physiologie landwirtschaftlicher Kulturpflanzen. Keimungsgeschichte der Kartoffelknollen’Google Scholar, in de Vries, Hugo, Opera e periodicis collata (henceforth Opera), 7 vols., Utrecht, 1918–1927, iii, 200–46, especially 201–2.Google Scholar

³⁹ de Vries, Hugo, Die Mutationstheorie. Versuche und Beobachtungen über die Entstehung von Arten im Pflanzenreich, vol. 2, Elementare Bastardlehre, Leipzig, 1903, 53–4.Google Scholar

⁴⁰ De Vries, , op. cit. (37), 396.Google Scholar

⁴¹ See, for instance, Allen, Garland E., Life Science in the Twentieth Century, 2nd edn, Cambridge, 1978, 10–17Google Scholar, where de Vries' case is presented as a paradigmatic example of the rising experimentalism in biology.

⁴² See, for instance, de Vries, Hugo, De voeding der planten, Haarlem, 1876.Google Scholar

⁴³ de Vries, Hugo, ‘Ueber die Aufrichtung des gelagerten Getreides’Google Scholar, in Opera, op. cit. (38), iii, 523–88.Google Scholar

⁴⁴ de Vries, Hugo, ‘De Peel’, Onzen Tijd. Studiën en Berichten (1874), 9, 88–124.Google Scholar

⁴⁵ de Vries, Hugo, ‘Over de invloed der temperatuur op de kieming van zaden’Google Scholar, in Opera, op. cit. (38), iv, 251–63.Google Scholar

⁴⁶ These studies were collected in vol. 3 of de Vries, ' Opera, op. cit. (38).Google Scholar

⁴⁷ De Vries' growing interest in the problem of variability and in the practices of breeders in this area can also be gleaned from his Het leven der bloem, Haarlem, 1877, 129ffGoogle Scholar. De Vries mentions his first breeding experiments and his earliest visits to plant breeders in ‘Sur la fécondation hybride de l'endosperme chez le Maïs’ in Opera, op. cit. (38), vi, 270–7, especially 274Google Scholar, and in ‘Die Svalöfer Methode zur Veredelung landwirtschaftlicher Kulturgewächse und ihre Bedeutung für die Selektionstheorie’, in Opera, vi, 380–420, especially 423.Google Scholar

⁴⁸ der Pas, Van, op. cit. (7)Google Scholar; among other things, Darwin and de Vries talked, and later corresponded, about the mechanism of several physiological adaptations.

⁴⁹ Visser, , op. cit. (22), 169.Google Scholar

⁵⁰ A passing reference – the only one that I have been able to find – to the ultimate practical aim of de Vries' hereditary investigations is contained in a footnote to an article by Meijer, O. G., ‘Hugo de Vries und Johann Gregor Mendel: die Geschichte einer Verneinung’, Folia Mendeliana (1986), 21, 69–90, on 86.Google Scholar

⁵¹ For more details, see Theunissen, , op. cit. (2).Google Scholar

⁵² de Vries, Hugo, ‘Beschouwingen over het verbeteren der rassen van onze cultuurplanten XI’, Maandblad Hollandsche Maatschappij van Landbouw (1887), 9Google Scholar (unpaginated reprint of a series of nineteen articles in the Maandblad, present in the Artis Library, Amsterdam).

⁵³ de Vries, Hugo, Die Mutationstheorie: Versuche und Beobachtungen über die Entstehung von Arten im Pflanzenreich, vol. 1, Die Entstehung der Arten durch Mutation, Leipzig, 1901, pp. v and 131.Google Scholar

⁵⁴ de Vries, Hugo, ‘Over het ontstaan van soorten door mutatie’, Album der Natuur (1901), 193–206, quotation on 204.Google Scholar

⁵⁵ de Vries, Hugo, Van amoebe tot mensch, Utrecht, 1918, 16–17.Google Scholar

⁵⁶ De Vries, , op. cit. (53), 366.Google Scholar

⁵⁷ De Vries, , op. cit. (53), 353–4.Google Scholar

⁵⁸ de Vries, Hugo, Gruppenweise Artbildung, Berlin, 1913, 339–41.Google Scholar

⁵⁹ de Vries, Hugo, Die Mutationen in der Erblichkeitslehre, Berlin, 1912, 6Google Scholar; Ueber die Abhängigkeit der Mutationskoeffizienten von äusseren Einflüssen’, in Opera, op. cit. (38), vii, 72–7Google Scholar; ‘Die latente Mutabilität von Oenothera biennis L.', in Opera, vii, 633–81, especially 675–8.Google Scholar

⁶⁰ De Vries, , Opera, op. cit. (38), viiGoogle Scholar, ‘Vorwort’: ‘Die ursprüngliche Entstehung der Neuheiten oder die Prämutation blieb einstweilen der Forschung unzugänglich’.

⁶¹ Kingsland, , op. cit. (11); cf. note 21.Google Scholar

⁶² Pauly, , op. cit. (25).Google Scholar

⁶³ De Vries, , op. cit. (35), i, 135, 150, 184.Google Scholar Pauly (op. cit. (25), 113) provides another example of Loeb's and de Vries' shared interests: on his second visit to the USA de Vries contributed his mite to Loeb's attempts at producing mutations experimentally. For this, a sample of radium lent by Rutherford was transported personally from Canada to California by de Vries.

⁶⁴ Pauly, , op. cit. (25), 35.Google Scholar Interesting though it is, the evidence Pauly adduces for this suggestion is inconclusive, in my view. In any case, Sachs definitely deserves more attention than he has received so far.

⁶⁵ de Vries, Hugo, ‘Intracellulare pangenesis’ [1889], in Opera, op. cit. (38), v, 1–149Google Scholar, quotation on 9. De Vries' reductionisric stance is clearly expressed by one of his favourite dicta, a saying of Goethe that crops up in his publications from the beginning until the end of his career: ‘Dich im Unendlichen zu finden / Musst unterscheiden und dann verbinden’ (To reach the infinite, one should first divide and then combine). For further details, see Theunissen, , op. cit. (24), 113–14.Google Scholar Robert Olby, in a review of Pauly's Controlling Life (op. cit. (25)), Nature (1988), 332, 756–57Google Scholar, points out that Loeb's preoccupation with control does not necessarily imply that he opposed reductionism; it seems more likely that, for Loeb, the opposites were not control and reductionism, but dynamic and structural explanation.

⁶⁶ Theunissen, , op. cit. (2).Google Scholar

⁶⁷ A third category consisted of ‘degressive’ mutations, which were introduced to explain the hereditary behaviour of ‘monstrosities’. This category, however, is immaterial to our discussion here.

⁶⁸ See for example de Vries, , op. cit. (55), 8Google Scholar: ‘[The] investigations of Morgan have, in a completely unexpected manner, resulted in a splendid confirmation of the theory of pangenesis.’

⁶⁹ See for example de Vries, Hugo, ‘Die Svalöfer Methode zur Veredelung landwirtschaftlicher Kulturgewächse und ihre Bedeutung für die Selektionstheorie’Google Scholar, in Opera, op. cit. (38), vi, 380–420Google Scholar; and de Vries, , Plant Breeding. Comments on the Experiments of Nilsson and Burbank, London, 1907.Google Scholar

⁷⁰ Yet not all agricultural stocks were of this mixed composition, according to de Vries. Some, for instance sugar beets, were more or less ‘pure’. In this case, only a limited improvement of the stock was to be achieved by acting on the plant's fluctuating variability, and constant selection was needed to prevent regression to the mean value of the population. See de Vries, , op. cit. (53), 52–90, 368–411, especially 72–7Google Scholar; de Vries, , Species and Varieties, op. cit. (7), Lectures XXV and XXVII, passim.Google Scholar

⁷¹ See de Vries, Hugo, ‘Wetenschap in dienst der praktijk’, Landbouwkundig Tijdschrift (1893), 9, 217–30Google Scholar; ‘De proefstations voor suikerriet op Java’, De Gids (1895), 13, 283–303Google Scholar; ‘Kapitaal en wetenschap’, Album der Natuur (1898), 353–66Google Scholar; ‘Vooruitzichten in de plant- en dierkunde’, Album der Natuur (1900), 210–15.Google Scholar

⁷² De Vries, , op. cit. (37), quotation on 395.Google Scholar For a discussion of the idea of ‘social control’ in American social science in the period, see, e.g. Ross, Dorothy, The Origins of American Social Science, New York, 1991, ch. 7Google Scholar, and Lash, Christopher, The New Radicalism in America, 1889–1863, New York, 1965Google Scholar, ch. 5. Cf. notes 14 and 21.

⁷³ De Vries, , ‘Vooruitzichten in de plant- en dierkunde’ op. cit. (71), 212.Google Scholar

⁷⁴ De Vries, , op. cit. (29), 14.Google Scholar

⁷⁵ de Vries, Hugo, Afstammings- en mutatieleer, Baarn, 1907, 36.Google Scholar

⁷⁶ De Vries, , op. cit. (53), 108–12.Google Scholar

⁷⁷ De Vries, , op. cit. (53), 109.Google Scholar

⁷⁸ De Vries, , op. cit. (75), 31–6.Google Scholar De Vries did believe that the intensity of expression of some fluctuating characters was to a certain extent hereditary (cf. note 70). In all such cases quantitative characters were involved, which reacted in an identical way to selection and to improved breeding conditions (‘la sélection, c'est la sélection des mieux nourriées’, as de Vries put it). The mental capacities, however, did not rank among these ‘hereditary’ fluctuating characters, according to de Vries (ibid., 35–6). See also note 80.

⁷⁹ De Vries, , op. cit. (75), 36.Google Scholar

⁸⁰ In 1898, in his ‘Eenheid in veranderlijkheid’ (op. cit. (29), 9ff) de Vries was still in doubt as to whether or not humankind's intellectual abilities might be ‘artificially’ improved. The situation of the American blacks, which he studied with great interest during his trips to the USA, provided him with one of the arguments to conclude negatively on this point: ‘the unchangeability of the negroes in America hopelessly thwarts all well-meaning attempts at political and social emancipation’ (op. cit. (75), 31).

⁸¹ De Vries, , op. cit. (75), 35–6.Google Scholar

⁸² de Vries, Hugo, ‘Herleven’, Album der Natuur (1905), 367–72, quotation on 371Google Scholar. De Vries’ conviction of the central role of individual development is also evident from his involvement with the educational system of Maria Montessori; see Kramer, Rita, Maria Montessori. A Biography, Oxford, 1976, 267–9.Google Scholar Montessori cited de Vries' ideas on individual development as confirmation of her pedagogical views (see for instance her Pedagogical Anthropology, London, 1913, 47, 255 and 455).Google Scholar

⁸³ De Vries, , op. cit. (75), 36.Google Scholar

⁸⁴ De Vries, , op. cit. (75), 36.Google Scholar

⁸⁵ Treub, W., ‘Darwinisme en socialisme’, Sociaal Weekblad (1894)Google Scholar, 9 June – 4 August; ‘Liberaal/sociaal anarchist of vrijzinnig/sociaal democraat’, Sociaal Weekblad (1899), 20 May – 1 July.Google Scholar A comparable view was defended by Treub's pupil D. van Embden in his Darwinisme en democratie. Maatschappelijke vooruitgang en de hulp aan het zwakke, 's Gravenhage, 1901; see de Rooy, , op. cit. (14), 17–19.Google Scholar

⁸⁶ De Veer, , op. cit. (22), 3.Google Scholar