In Pursuit of the Gene

NOTES TO PAGES 112–114 © 309
15. As it happened, the Oenothera varieties not only failed to obey the standard
Mendelian splitting of hybrids, but they also violated the fundamental Mendelian
principle of the equivalence of the role of the two sexes in crosses. For example,
when O. lamarckiana was used as the seed plant and O. biennis as the pollen plant, the
hybrids were constant, but when the roles of the male and female were reversed
(that is, O. biennis was pollinated by O. lamarckiana) the hybrids split into the twin hybrids.
Though it would turn out that De Vries had indeed stumbled on a new principle,
neither Hieracium nor Oenothera operated according to entirely novel laws of
heredity. In fact, the explanation for the strange behavior of the Oenothera mutants
would ultimately be found in an ingenious application of orthodox Mendelism,
but it would take another decade before the true nature of the mutants would be
revealed by the American geneticist H. J. Muller.
16. De Vries, “On Crosses,” 249.
17. William Bateson, “Problems of Heredity as a Subject of Horticultural Investigation,”
Journal of the Royal Horticultural Society 25 (1901): 55–61.
18. B. Bateson, William Bateson, 179–180.
19. A. G. Cock, “William Bateson, Mendelism and Biometry,” Journal of the History of
Biology 6 (1973): 4.
20. On Oct. 31, 1901, De Vries wrote Bateson, “I am very anxious to know your
doubt as to the purity of Lamarckiana” (Bateson MSS, reel C, no. 15).
21. Bert Theunissen, “Closing the Door on Hugo de Vries’ Mendelism,” Annals of
Science 51 (1994): 247.
22. De Vries laid out his hereditary theory in the final hundred pages of the second
volume of Die Mutationstheorie: Versuche und Beobachtungen über die Entstehung von Arten
im Pflanzenreich (Leipzig: Veit, 1901–1903), as well as in a short article in the Revue
genérale de botanique, the journal in which he’d published one of his three rediscovery
papers. Regressive and degressive mutations, which arose from normal and regressive
pangenes, respectively, were always paired in the nucleus with their normal
counterparts, and as a result they were capable of undergoing normal Mendelian
segregation during sex cell formation, but the all-important progressive mutations
had no partner with which to pair. It was the species-forming pangene’s inability to
find a matching partner that disrupted the normal process of segregation. Instead
the species-forming pangene underwent a division into two identical copies, which
were in turn distributed to the two daughter cells. This, De Vries believed, was the
explanation for the constancy of crosses between new mutant races.
23. William Bateson and E. R. Saunders, Royal Society, Reports to the Evolution Committee,
Report 1 (London: Harrison and Sons, 1902), 126.