In Pursuit of the Gene

OENOTHERA RECONSIDERED © 217
complementary gene-complexes that were passed on intact from one generation
to the next. As in the case of beaded Drosophila, the complementary
complexes were kept in heterozygous condition by means of a system of
balanced lethals, and over generations, as Muller had hypothesized, recessive
mutations accumulated and a line became increasingly heterozygous. It
also became clear that De Vries’s mutants were due to chromosome rearrangements,
by means of recombination or the failure of homologous
chromosomes to segregate, that resulted in previously heterozygous genes
breaking out into homozygous condition. Though the fully elaborated theory
took another decade to develop and would extend beyond Muller’s
original formulation, already in 1917 Muller had pointed the way by providing
the essential idea of balanced lethals.
In the meantime, De Vries was forced to watch his mutation theory
dwindle into irrelevance. By 1919 he had wholly retired from his position in
the university to spend the last seventeen years of his life working in the
private laboratory and experimental garden that he had built next to his
home in Luntern, a small village in central Holland. Following his long-established
practice, De Vries refused to engage in public debate, even though
he was convinced that he was being wronged. To Loeb, he now explained
that his Oenothera were “always true to their principles, despite the rather
curious and vague objections of Morgan and others.” 25 Until his death in
1935, De Vries, tall, thin and regal, with a great Darwinesque white beard,
actively tended to his beloved Oenothera, unshaken in his conviction that the
O. lamarckiana and its varieties were essentially pure species, homozygous for
most traits, and that their differences were to be accounted for by rare mutations
within species. 26
¨ AS WORK ON THE CYTOLOGY and genetics of Oenothera proceeded,
De Vries’s account of the origin of O. lamarckiana began to seem less probable.
De Vries had long maintained that the O. lamarckiana he had found in
Hilvershum had escaped from a local garden where it had been planted
by seeds purchased from a local seedsman who gotten them from the London
firm of Carter and Company, who in turn claimed to have imported
them from Texas. 27 In 1895 and in 1913 again, he had visited the Muséum