Of late, a thorough and detailed discussion of the opposing views has
been given by Morgan in his valuable book on evolution and adaptation.
He has subjected all the proposed theories to a severe criticism both on
the ground of facts and on that of their innate possibility and logical
value. He decides in favor of the mutation theory. His arguments are
incisive and complete and wholly adapted to the comprehension of all
intelligent readers, so that his book relieves me entirely of the
necessity of discussing these general questions, as it could not be done
in a better or in a clearer way.

I intend to give a review of the facts obtained from plants which go to
prove the assertion, that species and varieties have originated by
mutation, and are, at present, not known to originate in any other way.
This review consists of two parts. One is a critical survey of the facts
of agricultural and horticultural breeding, as they have accumulated
since the time of Darwin. This body of evidence is to be combined with
some corresponding experiments [10] concerning the real nature of
species in the wild state. The other part rests on my own observations
and experiments, made in the botanical garden of the University of
Amsterdam.

For many years past I have tried to elucidate the hereditary conditions
of species and varieties, and the occasional occurrence of mutations,
that suddenly produce new forms.

The present discussion has a double purpose. On one side it will give
the justification of the theory of mutations, as derived from the facts
now at hand. On the other hand it will point out the deficiencies of
available evidence, and indicate the ways by which the lacunae may
gradually be filled. Experimental work on heredity does not require vast