TRANSLATORS' PREFACE. 



The task of preparing' this translation has been made 

 Hghter by the knowledge that the need for it is urgent. 

 Professor De Vries's successful attempt to bring the pro- 

 cess of specific differentiation within the sphere of experi- 

 mental inquiry is now recognized as a landmark in the 

 history of our knowledge of these phenomena. But those 

 who take part in the discussion of evolutionary questions 

 are rarely equipped with even a superficial familiarity with 

 the broad features of Professor De Vries^s investigations 

 and ideas, and, still less, with (what should be a minimum 

 qualification for a participant in such discussions) a de- 

 tailed knowledge of the contents of Die Mutationstheorie. 



It is hoped that this translation will help to remedy this 

 state of affairs. This much, at any rate, is certain, that the 

 evidence, collected by De Vries up to 1901, bearing on the 

 question of the origin of species and varieties by mutation, 

 is now for the first time available to the student of evolution 

 who cannot read German. 



In the translation itself we have endeavored to convey 

 the author's meaning as faithfully as possible rather than 

 to provide a word for word translation of the German. 

 And to this end we have, wherever it seemed necessary, 

 split sentences into two, or run two into one, or made other 

 such additions and omissions as seemed desirable. All of 

 these alterations have been examined and approved by the 

 author. 



