[Footnote 15: This paper was originally published in part in the _Proceedings of the American Academy of Arts and Sciences_, Vol. xxxviii, No. 18, January, 1903. It may be found complete in _Science_ for 25 September, 1903.] Professor Bateson, whose book on Mendel's "Principles of Heredity" is the best popular exposition in English of Mendel's work, says that an exact determination of the laws of heredity will probably produce more change in man's outlook upon the world and in his power over nature than any other advance in natural knowledge that can be clearly foreseen. No one has better opportunities of pursuing such work than horticulturists and stockbreeders. They are daily witnesses of the phenomena of heredity. Their success also depends largely on a knowledge of its laws, and obviously every increase in that knowledge is of direct and special importance to them. After thus insisting on the theoretic and practical importance of the subject, Professor Bateson says:-- As regards the Mendelian principles which it is the chief aim of this introduction to present clearly before the reader, it may be said that by the {200} application of those principles we are enabled to reach and deal in a comprehensive manner with phenomena of a fundamental nature, lying at the very root of all conceptions not merely of the physiology of reproduction and heredity, but even of the essential nature of living organisms; and I think that I use no extravagant words when, in introducing Mendel's work to the notice of the Royal Horticultural Society's Journal, I ventured to declare that his experiments are worthy to rank with those which laid the foundation of the atomic laws of chemistry. Professor L. H. Bailey, who is the Director of the Horticultural Department at Cornell University and the editor of the authoritative _Encyclopedia of Horticulture_, was one of the first of recent scientists to call attention to Mendel's work. It was, we believe, because of a reference to Mendel's papers by Bailey that Professor de Vries was put on the track of Mendel's discoveries and found that the Austrian monk had completely anticipated the work at which he was then engaged. In a recent issue of _The Independent_, of New York, Professor Bailey said:--