"discontinuous variations," or "mutations," as De Vries has called
them. Darwin, in the first four editions of the "Origin of Species,"
attached more importance to the latter than in subsequent editions;
he was swayed in his attitude, as is well known, by an article of the
physicist, Fleeming Jenkin, which appeared in the North British
Review. The mathematics of this article were unimpeachable, but they
were founded on the assumption that exceptional variations would only
occur in single individuals, which is, indeed, often the case among
those domesticated races on which Darwin especially studied the
phenomena of variation. Darwin was no mathematician or physicist,
and we are told in his biography that he regarded every tool-shop
rule or optician's thermometer as an instrument of precision: so he
appears to have regarded Fleeming Jenkin's demonstration as a
mathematical deduction which he was bound to accept without
criticism.

Mr. William Bateson, late Professor of Biology in the University of
Cambridge, as early as 1894 laid great stress on the importance of
discontinuous variations, collecting and collating the known facts in
his "Materials for the Study of Variations"; but this important work,
now become rare and valuable, at the time excited so little interest
as to be 'remaindered' within a very few years after publication.

In 1901 Hugo De Vries, Professor of Botany in the University of
Amsterdam, published "Die Mutationstheorie," wherein he showed that
mutations or discontinuous variations in various directions may
appear simultaneously in many individuals, and in various directions.
In the gardener's phrase, the species may take to sporting in various
directions at the same time, and each sport may be represented by
numerous specimens.