426 THE STRUCTURE OF EVOLUTIONARY THEORY
p. 222): "Species and varieties have originated by mutation, but are, at present, not
known to have originated in any other way. Originally this conception has been
derived from the hypothesis of unit characters as deduced from Darwin's
Pangenesis, which led to the expectation of two different kinds of variability, one
slow and one sudden."
Whatever the intellectual roots, de Vries eventually centered his illustration
and defense of the mutation theory upon a single source, the evening primrose,
Oenothera Lamarckiana—so we can identify a particular empirical basis for the
defense of his views. (This strategy, as mentioned previously, ultimately backfired
when researchers explained the unusual mutability in O. Lamarckiana as a
peculiarity of the plant's hybrid nature and chromosomal system, and not as the
generality that de Vries required.) In 1886, de Vries found odd and distinct
mutational variations growing among a wild field of evening primroses at
Hilversum, near Amsterdam. He later described his mixture of good fortune and
conscious preparation (1905, p. 27):
Cultivated plants of course, had only a small chance to exhibit new
qualities, as they have been so strictly controlled during so many years.
Moreover, their purity of origin is in many cases doubtful... For this reason
I have limited myself to the trial of wild plants of Holland, and have had the
good fortune to find among them at least one species in a state of
mutability. It was not really a native plant, but one probably introduced
from America or at least belonging to an American genus. It was the great
evening primrose or the primrose of Lamarck. A strain of this beautiful
species is growing on an abandoned field in the vicinity of Hilversum, at a
short distance from Amsterdam. Here it has escaped from a park and
multiplied. In doing so it has produced, and is still producing quite a
number of new types... This interesting plant has afforded me the means
of observing directly how new species originate, and of studying the laws
of these changes.De Vries' method for finding and propagating Oenothera mutants included a
mixture of experimental care and hard work in the Burbankian mode. To find new
mutants, he sowed prodigious numbers of seeds. For example, in his 1888 sowing,
he tested 15,000 seedlings and found 10 mutations. To propagate and breed his
new forms, and to test for their purity in inheritance, de Vries stringently followed
the obvious rules for tracing pedigrees: fertilize each plant with known pollen,
prevent insect pollination, save and sow all seeds separately.
De Vries, in crisp summary, presented the essence of his theory as exhibited
by the Oenothera mutants—sudden, fully constituted, nonadaptive, observable,
experimentally ascertainable origin of new species: "They came into existence at
once, fully equipped, without preparation or intermediate steps. No series of
generations, no selection, no struggle for existence was needed. It was a sudden
leap into another type, a sport in the best acceptation of the word. It fulfilled my
hopes, and at once gave proof of the possibility of the direct