PEEFACE BY THE EDITOR 



Professor de Vries has rendered an additional service 

 to all naturalists by the preparation of the lectures on 

 mutation published in the present volume. A perusal of 

 the lectures will show that the subject-matter of "Die 

 Mutationstheorie " has been presented in a somewhat 

 condensed form, and that the time which has elapsed 

 since the original was prepared has given opportunity for 

 the acquisition of additional facts, and a re-examination 

 of some of the more important conclusions with the re- 

 sult that a notable gain has been made in the treatment 

 of some complicated problems. 



It is hoped that the appearance of this English version 

 of the theory of mutation will do much to stimulate in- 

 vestigation of the various phases of the subject. This 

 volume, however, is by no means intended to replace, as a 

 work of reference, the larger book with its detailed recital 

 of facts and its comprehensive records, but it may prove 

 a substitute for the use of the general reader. 



The revision of the lectures has been a task attended 

 with no little pleasure, especially since it has given the 

 editor the opportunity for an advance consideration of 

 some of the more recent results, thus materially facilitat- 

 ing investigations which have been in progress at the 

 New York Botanical Garden for some time. So far as 

 the ground has been covered the researches in question 

 corroborate the conclusions of de Vries in all important 

 particulars. The preparation of the manuscript for the 

 printer has consisted chiefly in the adaptation of oral 



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