Considerable care has been bestowed upon the indication of the lacunae
in our knowledge of the subject and the methods by which they may be
filled. Many interesting observations bearing upon the little known
parts of the subject may be made with limited facilities, either in the
garden or upon the wild flora. Accuracy and perseverance, and a warm
love for Nature's children are here the chief requirements in such
investigations.

In his admirable treatise on Evolution and Adaptation (New York,
Macmillan & Co., 1903), Thomas Hunt Morgan has dealt in a critical
manner with many of the speculations upon problems subsidiary to the
theory of descent, in so convincing and complete a manner, that I think
myself justified in neglecting these questions here. His book gives an
accurate survey of them all, and is easily understood by the general
reader.

In concluding I have to offer my thanks to Dr. D.T. MacDougal and Miss
A.M. Vail of the New York Botanical Garden for their painstaking work in
the preparation of the manuscript for the press. Dr. MacDougal, by
[viii] his publications, has introduced my results to his American
colleagues, and moreover by his cultures of the mutative species of the
great evening-primrose has contributed additional proof of the validity
of my views, which will go far to obviate the difficulties, which are
still in the way of a more universal acceptation of the theory of
mutation. My work claims to be in full accord with the principles laid
down by Darwin, and to give a thorough and sharp analysis of some of the
ideas of variability, inheritance, selection, and mutation, which were
necessarily vague at his time. It is only just to state, that Darwin
established so broad a basis for scientific research upon these
subjects, that after half a century many problems of major interest