vi PREFACE 



dominant-recessive character relations. For a discussion of the 

 extended development of theory and investigation based upon the 

 Mendelian discovery, reference must naturally be made to the va- 

 rious general text-books and handbooks in genetics, and to the 

 multitude of papers in the journals of biological science. 



It has been necessary to make frequent use of the resources of 

 various libraries. Appreciation is particularly due the libraries of 

 the University of Chicago, Harvard, the Crerar Library of Chi- 

 cago, and the library of the Missouri Botanical Garden, for liberal 

 access to works of reference. Especial thanks are due the library 

 of the University of Manitoba for affording every possible means 

 for obtaining material, and for securing the loan of important 

 books. 



The writer desires to express especial thanks to Dr. Geo. H. 

 Shull and Dr. E. G. Conklin of Princeton University, for most 

 thorough editorial reading given the manuscript in an earlier draft. 

 Their many constructive suggestions have been largely utilized. 

 For the manuscript in its present form, however, together with any 

 imperfections that may appear, the author is solely responsible. 



The subject-matter of portions of the first four chapters has 

 appeared in past issues of the Journal of Heredity, to which 

 acknowledgments are due for the privilege of their reproduc- 

 tion in their present form, and for the use of the accompanying 

 illustrations. The Gartner material has appeared in part in the 

 American Naturalist. The portrait of Darwin is reproduced by 

 permission of the Cambridge University Press, from Volume I 

 of Professor Karl Pearson's "Life, Letters and Labours of Francis 

 Galton." The portraits of Mendel and of Bateson, and the 

 illustration of the Konigskloster in Briinn, are reproduced from 

 the Report of the Royal Horticultural Conference on genetics, 

 1906, by permission of the President and Council of the Royal 

 Horticultural Society. The portraits of MM. Louis and Henry 

 de Vilmorin are furnished by the courtesy of Messrs. Vilmorin 

 & Co. of Paris. The portrait of Galton is reproduced by per- 

 mission from Vol. II of Biometrika. A copy of Sir Thomas Mil- 

 lington's portrait was obtained by consent from the original in 

 the Royal College of Physicians in London. The copies of the 

 Assyrian bas-reliefs in Plates VIII, IX, and X, are photographed 



