Preface by the Author ix 



his publications, has introduced my results to his Ameri- 

 can colleagues, and moreover by his cultures of the muta- 

 tive species of the great evening-primrose has con- 

 tributed 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 ac- 

 cord 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 scien- 

 tific research upon these subjects, that after half a century 

 many problems of major interest remain to be taken up. 

 The work now demanding our attention is manifestly that 

 of the experimental observation and control of the origin 

 of species. The principal object of these lectures is to 

 secure a more general appreciation of this kind of work. 



HUGO DE YRIES. 

 Amsterdam, October, 1904. 



