Second Edition, thoroughly Corrected 

 and Revised, with Portrait. 



SPECIES AND VARIETIES 



Their Origin by Mutation 



By Hugo de Vries. 

 Professor of Botany in the University of Amsterdam. 



Price, postpaid $5.00 (21s.) net. xxiii+830 pages, 8vo., 



cloth, gilt top. 



The belief has prevailed for more than half a century 

 that species are changed into new types very slowly and 

 that thousands of years are necessary for the development 

 of a new type of animal or plant. After twenty years of 

 arduous investigation Professor de Vries has announced 

 that he has found that new species originated suddenly by 

 jumps, or by "mutations," and in conjunction with this dis- 

 covery he offers an explanation of the qualities of living 

 organisms on the basis of the conception of unit-characters. 

 Important modifications are also proposed as to the con- 

 ceptions of species and varieties as well as of variability, 

 inheritance, atavism, selection and descent in general. 



The announcement of the results in question has excited 

 more interest among naturalists than any publication since 

 the appearance of Darwin's Origin of Species, and marks 

 the beginning of a new epoch in the history of evolution. 

 Professor de Vries was invited to deliver a series of lectures 

 upon the subject at the University of California during the 

 summer of 1904, and these lectures are offered to a public 

 now thoroughly interested in modern ideas of evolution. 



The contents of the book include a readable and orderly 

 recital of the facts and details which furnish the basis for 

 the mutation-theory of the origin of species. All of the 

 more important phases of heredity and descent come in for 

 a clarifying treatment that renders the volume extremely 

 readable to the amateur as well as to the trained biologist. 

 The more reliable historical data are cited and the results 

 obtained by Professor de Vries in the Botaniwil Garden at 

 Amsterdam during twenty years of observation are de- 

 scribed. 



Not the least important service rendered by Professor 

 de Vries in the preparation of these lectures consists in the 



