remain to be taken up. The work now demanding our attention is
manifestly that of the experimental observation and control of the
origin of species. The principal object of these lectures is to secure a
more general appreciation of this kind of work.


HUGO DE VRIES.
Amsterdam, October, 1904.

[ix]

PREFACE BY THE EDITOR

PROFESSOR DE VRIES has rendered an additional service to all naturalists
by the preparation of the lectures on mutation published in the present
volume. A perusal of the lectures will show that the subject matter of
"Die Mutationstheorie" has been presented in a somewhat condensed form,
and that the time which has elapsed since the original was prepared has
given opportunity for the acquisition of additional facts, and a
re-examination of some of the more important conclusions with the result
that a notable gain has been made in the treatment of some complicated
problems.

It is hoped that the appearance of this English version of the theory of
mutation will do much to stimulate investigation of the various phases
of the subject. This volume, however, is by no means intended to
replace, as a work of reference, the larger book with its detailed
recital of facts and its comprehensive records, but it may prove a
substitute for the use of the general reader.