of mutation assumes that new species and varieties are produced from
existing forms by sudden leaps. The parent-type itself remains unchanged
throughout this process, and may repeatedly give birth to new forms.
These may arise simultaneously and in groups or separately at more or
less widely distant periods.

The principal features of the theory of mutation have been dealt with at
length in my book "Die Mutationstheorie" (Vol. I., 1901, Vol. II., 1903.
Leipsic, Veit & Co.), in which I have endeavored to present as
completely as possible the detailed evidence obtained from trustworthy
historical records, and from my own experimental researches, upon which
the theory is based.

The University of California invited me to deliver a series of lectures
on this subject, at Berkeley, during the [vii] summer of 1904, and these
lectures are offered in this form to a public now thoroughly interested
in the progress of modern ideas on evolution. Some of my experiments and
pedigree-cultures are described here in a manner similar to that used in
the "Mutationstheorie," but partly abridged and partly elaborated, in
order to give a clear conception of their extent and scope. New
experiments and observations have been added, and a wider choice of the
material afforded by the more recent current literature has been made in
the interest of a clear representation of the leading ideas, leaving the
exact and detailed proofs thereof to the students of the larger book.

Scientific demonstration is often long and encumbered with difficult
points of minor importance. In these lectures I have tried to devote
attention to the more important phases of the subject and have avoided
the details of lesser interest to the general reader.