x PREFACE 



de Vries for the present of an excellent portrait ; and 

 Mr. Francis Galton for the loan of a photograph well 

 known from earlier reproductions. The portrait of 

 Mendel is reproduced from the frontispiece to Mr. 

 Bateson's ' Defence/ by the permission of the Syndics 

 of the Cambridge University Press. Messrs. Macmillan 

 and Co. have kindly allowed the reproduction of the 

 diagram which occupies p. 80, and of the table and 

 figure on pp. 82 and 83. The figures facing pp. 136 

 and 143 are from de Vries' ' Mutationstheorie,' pub- 

 lished by Messrs. Veit. 



The attempt has been made to render the following 

 pages intelligible to the general reader, as well as to 

 the more scientific public, to which they are primarily 

 addressed. A short glossary has been added, which 

 may be found useful by those who have no previous 

 acquaintance with biological terms. 



CAMBRIDGE, 



October 23, 1906. 



