How mechanisms explain interfield cooperation: biological–chemical study of plant growth hormones in Utrecht and Pasadena, 1930–1938


This article examines to what extent a particular case of cross-disciplinary research in the 1930s was structured by mechanistic reasoning. For this purpose, it identifies the interfield theories that allowed biologists and chemists to use each other’s techniques and findings, and that provided the basis for the experiments performed to identify plant growth hormones and to learn more about their role in the mechanism of plant growth. In 1930, chemists and biologists in Utrecht and Pasadena began to cooperatively study plant growth. I will argue that these researchers decided to join forces because they believed to rely on each other’s findings and methods to solve their research problems adequately. In the course of the cooperation, organic chemists arrived at isolating plant growth hormones by using a test method developed in plant physiology. This achievement, in turn, facilitated biologists’ investigation of the mechanism of plant growth. Researchers eventually believed to have the means to study the relation between a substance’s molecular structure and its physiological activity. The way they conceptualized the problem of identifying hormones and unraveling the mechanism of plant growth, as well as their actual research actions are compatible with the new mechanists’ account of mechanism research. The study illustrates that focusing on researchers’ mechanistic reasoning can contribute considerably to explaining the structure of cross-disciplinary research projects.

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  1. 1.

    See, for example, Otto Warburg’s letter to Friedrich Went, 29 April 1932: “All of us who aim to reduce life processes to physics and chemistry have been encouraged by the plain results of your studies.” Correspondence of F. A. F. C. Went, Museum Boerhaave, Leiden, a 79, file ‘Warburg, Otto’. Unless otherwise indicated, translations are mine.

  2. 2.

    Craver and Darden (2013, pp. 162–163).

  3. 3.

    MacLeod and Nersessian (2016, p. 402) diagnose the lack, at least in philosophy, of a close examination of interdisciplinary scientific practices.

  4. 4.

    For Went Jr.’s post-war research program, see Munns (2014). The history of plant hormone research in Utrecht has been studied by Höxtermann (1994) and Faasse (1994). Rasmussen (1999) has worked on James Bonner’s collaboration with Merck in the late 1930s.

  5. 5.

    See Emerson (2011, p. 5) and Kohler (1982, p. 321). On Emerson’s work with Chlorella, see Nickelsen 2017, this topical collection.

  6. 6.

    At least his former student Lourens M. G. Baas Becking was anticipating this when he wrote to Went Sr. in October 1928: “Let us hope for the best. If we succeed, Dolk will have the best opportunity to work of any botanist in this country.” Boerhaave Museum, Leiden, a 79, file “Baas Becking, L. G. M.” See also Faasse (1994, p. 39).

  7. 7.

    Went (1931, pp. 273–274); see also Morgan (1927b, p. 214): “[O]nly through an exact knowledge of the chemical and physical changes taking place in development can we hope to raise the study of development to the level of an exact science”.

  8. 8.

    See, for example, Aaserud (1990), Abir-Am (1982), Kay (1989, 1993, 1996), Kohler (1991), and Pauly (1987a, b). Morange (2008, p. 35), however, insists that “historical models that give one institution or one institute a major role in this story […] are obviously much too narrow in their perspectives.” See also Rheinberger (2009, p. 7).

  9. 9.

    Max Mason promised to support the eventual development of organic chemistry in cooperation with the biology division with $1,900,000 (see Kay 1993, p. 86).

  10. 10.

    See Darden and Maull (1977, p. 50), Bechtel (1988), and Bechtel (1993, p. 282). The idea corresponds with the notion of cooperation introduced by social psychologist Deutsch (1949).

  11. 11.

    Love (2008, p. 875). See also Nickles (1981, p. 113): “By their very function of defining what counts as a solution [problems] provide a kind of description of the solution. The set of constraints thereby determines the admissible solutions to the problem”.

  12. 12.

    This is the minimal definition of mechanisms, as presented by Illari and Williamson (2012, p. 120). See also Craver and Bechtel (2007, p. 549), or Bechtel and Abrahamsen (2007, p. 28): “to explain a phenomenon, researchers identify the component parts and operations of the mechanism and how they are organized so as to realize that phenomenon”.

  13. 13.

    Cf. Mc Manus (2012), who argues that developmental mechanisms are not adequately captured by current proposals on mechanistic explanation; and Allen (2005), who claims that Jacques Loeb, a prominent proponent of mechanistic biology in the early 20th century, did not aim at establishing step-by-step descriptions of mechanisms.

  14. 14.

    There are ongoing debates about the ubiquity, nature, and explanatory virtue of mechanisms in science. Although the case of phytohormone research might as well serve as a test for ontological and epistemological hypotheses discussed, the historical analysis presented here is not sufficiently fine-grained for such a purpose and does not attempt to contribute to the philosophical debates. My goal is to assess the descriptive adequacy of the new mechanists’ central ideas for plant hormone research in the 1930s, especially with respect to the strategies adopted in investigation how the mechanism of plant growth works.

  15. 15.

    See, for example, Nersessian and Patton (2009) and Andersen and Wagenknecht (2013).

  16. 16.

    I take theoretical integration to be the actual production of interfield theories by scientists. Further, plant physiologists and organic chemists involved in phytohormone research are seen as practitioners from different fields, insofar as they went through different trainings, tried to solve different problems, mastered different techniques, published in different journals, and presented their findings at different conferences.

  17. 17.

    Deichmann (2008, p. 102) refers to Emil Fischer, Richard Willstätter and Kögl’s mentor Heinrich Otto Wieland as members of the v. Baeyer-school, which established natural products chemistry between the wars. Natural products chemistry yielded a number of Nobel laureates in chemistry in the 1920s and 1930s: Adolf Windaus (1928), Walter N. Haworth and Paul Karrer (1937), Richard Kuhn (1938), and Adolf Butenandt (1939).

  18. 18.

    Kögl (1930) claimed it to be essential for the future of organic chemistry to look beyond its borders: The discipline will be advanced, on the one side, by chemists who interpret the findings established in physical chemistry, and, on the other side, by those who collaborate with biologists and study natural products (p. 79). Fischer (1907, p. 1751) argued that “the great chemical secrets of life are only to be unveiled by co-operative work” of biologists and organic chemists. For Fischer’s dream of “synthetic-chemical biology,” see Johnson (2015).

  19. 19.

    See Kögl (1930, p. 90). Fischer (1894, p. 2992) proposed that “chemical affinities are considerably influenced by geometrical shape. Unless enzyme and glucoside fit together like a lock and key, there is no chemical reaction”.

  20. 20.

    See Höxtermann (1994, pp. 316–324).

  21. 21.

    See Went (1928, pp. 33–45). The amount of growth substance could be varied by diluting portions of given sample with further agar.

  22. 22.

    Went (1928, pp. 51–52) estimated the growth substance’s molecular weight based on its diffusion coefficient.

  23. 23.

    Nielsen (1924) and Seubert (1925) both tried, without success, to isolate the growth-promoting substance.

  24. 24.

    Similar accounts can be found in Pisek (1929, p. 72) and Went (1930, p. 638).

  25. 25.

    Cf. Ramsey (2008).

  26. 26.

    See Went Jr. (1934, p. 446): “[T]he main difficulty in working out such a [test] method is that it has to be based on a broad knowledge of the phenomenon to be measured”.

  27. 27.

    Kögl was familiar with the practice of hormone isolation by means of physiological tests: His former colleagues in Göttingen, Butenandt and von Ziegner (1929) used the Allen-Doisy test to study the follicle-stimulating hormone.

  28. 28.

    He coined the phrase “no growth without growth substance,” see Went (1928, p. 65).

  29. 29.

    This assumption was not controversial. Botanist Peter Boysen Jensen (1928, p. 437), for example, agreed that “growth hormones can only be detected by means of alterations in coleoptile growth”.

  30. 30.

    Dolk and Thimann (1932, p. 46) defined a unit as the quantity of growth substance present in 1 cc of solution to give, after mixing with 1 cc of agar, an angle of 1°. Kögl defined 1 AE (Avena Einheit) as the amount of auxin present in one block of agar, 2 × 2 × 0.5 mm, causing a curvature of 10°.

  31. 31.

    See Craver (2002, p. S91). In the Avena-test, the decapitated oat coleoptile is the experimental model, the unilateral application of chemical substances the intervention technique, and the measuring of the resulting curvature the detection technique.

  32. 32.

    See Kögl and Haagen Smit (1931), Kögl et al. (1933), and Kögl and Erxleben (1934).

  33. 33.

    See Dolk and Thimann (1932), and Thimann and Dolk (1933). Later, it transpired that auxin-a and -b do not exist. See Wildman (1997), Troyer (2008), and Karlson (2013).

  34. 34.

    The substance produced by Rhizopus turned out to be Indole-3-acetic acid.

  35. 35.

    It was unclear whether the growth-promoting substance in human urine was identical with the one produced in oat tips. Kögl intended to test this by comparing the two substances’ chemical behavior once growth substance from urine was purified. See Kögl and Haagen Smit (1931) and Kögl et al. (1933).

  36. 36.

    Kögl and Haagen Smit (1931, p. 1412) and Kögl et al. (1933, p. 243).

  37. 37.

    Haagen-Smit (2000, pp. 4–5). Caltech’s biology students were taught by Dolk how to perform Avena-tests, see Bonner et al. (1981).

  38. 38.

    See Kögl and Erxleben (1934, p. 51). Chemists used the other 350 mg to study functional derivatives of the isolated substance.

  39. 39.

    Kögl et al. (1933). See also Kögl and Haagen Smit (1931, p. 1414); Kögl (1932, p. 317).

  40. 40.

    See, for example, Czaja (1932, p. 264) and Went Sr. (1934).

  41. 41.

    On additive strategies, see Craver (2002, p. S94).

  42. 42.

    Went and Thimann (1937, p. 2) emphasized that in analyzing the mechanism of growth, “knowledge of the chemical nature of the substances has played an essential part”.

  43. 43.

    For the notion of activity enabling properties, see Darden and Craver (2002, p. 22).

  44. 44.

    Namely at the sixth International Botanical Congress in Amsterdam in 1935 and at the first International Conference on phytohormones in Paris, 1937.

  45. 45.

    Kögl was awarded with the Emil-Fischer-medal in 1934, and with Scheele-medal for biochemical research in 1936. In the same year, Thimann received the Stephen Hales Prize.

  46. 46.

    Morgan to Went, 25 March 1932, Boerhaave Museum, Leiden, a 79, file ‘Morgan, T. H.’.

  47. 47.

    In summer 1935, only one year after his retirement, Went Sr. died in Wassenaar.

  48. 48.

    From Kögl to the biological working group of the faculty for mathematics and natural sciences, 20 April 1933, Boerhaave Museum, Leiden, a 79, file 1.

  49. 49.

    Heteroauxin, the third growth hormone, isolated in 1934, differed considerably from auxin-a and auxin-b in its composition, structure, and its physical and chemical properties.

  50. 50.

    See Thimann (1935a, b), Kögl and Kostermans (1935), and Haagen Smit and Went (1935).

  51. 51.

    Thimann (1935a, p. 896), see also Robin Snow (1935, p. 357), and Bonner (1936, p. 377).

  52. 52.

    A similar hypothesis was put forward by Dodds (1934, p. 988), who faced the same challenge in follicle hormone research.

  53. 53.

    Went and Thimann (1937, p. 118): “One [approach to investigate the mechanism] is to attempt to unravel the chain of physiological processes which ultimately results in growth. This we may call the physiological approach. The other […] consists in an attempt to identify those properties of the molecule which give it its activity. This we shall term the chemical approach; in its later stages it becomes interrelated with the physiological analysis”.

  54. 54.

    Darden (2002, p. 356); Darden and Craver (2002, p. 21): “Entities and a specific subset of their properties enable the activities in which they engage […]. Furthermore, activities require distinct types of entities and properties of those entities as the basis of such acts”.

  55. 55.

    It would thus be misleading to refer to this research as an episode of theory reduction in the Nagelian sense. For a comprehensive discussion on reduction and integration, see Bechtel and Hamilton (2007); on the difference between anti-reductionist and non-reductionist epistemologies, see Love (2008, p. 884).

  56. 56.

    See Bechtel (1988, p. 101).

  57. 57.

    See Craver and Bechtel (2007, p. 561).

  58. 58.

    Morgan, for his part, was eager to prove the feasibility of physico-chemical biology and he was looking for a problem that could be solved in cooperation with Caltech’s organic chemists. He heard in 1928 that Went Jr. and Dolk had demonstrated that a growth-promoting substance moves down oat coleoptiles. He employed Dolk, because his ideal candidate Went Jr. had just begun to work at the botanical garden in Bogor, Java (see Skoog 1994, p. 2).

  59. 59.

    Went and Thimann (1937, p. 27) referred to the Avena-test as the “basis of all phytohormone work”.

  60. 60.

    Went Sr. (1930, p. 643). See also Koepfli et al. (1938, p. 763): “[P]lants offer an exceptionally favorable field for study in that their structures—and possibly their physiological processes—are somewhat less complicated”.


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I am grateful to Kärin Nickelsen and Robert Meunier for their encouragement and helpful criticism of earlier versions of this article. I profited a lot from discussions with Christian Joas, Raphael Scholl, and Cora Stuhrmann. Finally, I would like to thank the two anonymous reviewers whose comments improved this paper significantly.

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Schürch, C. How mechanisms explain interfield cooperation: biological–chemical study of plant growth hormones in Utrecht and Pasadena, 1930–1938. HPLS 39, 16 (2017).

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  • Interfield cooperation
  • Mechanism modeling
  • Integration
  • Plant physiology
  • Natural products chemistry
  • Plant growth hormones
  • Structure-activity relationship