.90 .1 ' 



The unusual simplicity, directness and beauty of the language 

 used, the purity of its Anglo-Saxon English, in connection with 

 the largeness of its theme, renders the new book at once a classic, 

 and although " Die Mutationstheorie " must always stand as the 

 epoch-making work, it is " Species and Varieties " that will be 

 found most frequently back to back with Darwin's " Origin of 

 Species " on the shelves of the general libraries, and that will 

 make the name of de Vries known as Darwin's is to every man 

 and woman of intelligence regardless of vocation. 



As compared with " Die Mutationstheorie," the new book 

 shows many evidences that the author has profited by the dis- 

 cussions which have been aroused by that work, and he has very 

 carefully defined his position in regard to points in which he has 

 been misconstrued. Ardent Darwinians immediately attacked 

 the new theory because it appeared to be offered as a substitute 

 for the theory of " Natural Selection." In evident response to 

 these attacks, the author has joined his views in a masterful way 

 to those of Darwin, showing that there is no conflict, and making 

 the reader feel that the theory of mutation was the next step 

 logically, as it certainly has been the next important step histori- 

 cally in the development of a satisfactory conception of the 

 origin of specific and varietal differences. 



The basis of the author's views is the conception of character- 

 units as the ultimate bearers of heredity, a conception that, 

 though seemingly too simple and inelastic to be entirely satisfy- 

 ing to the physiologist, has been brought into the greatest promi- 

 nence and furnished support amounting at least to partial demon- 

 stration in the work of Mendel and of those who have since 

 confirmed and extended Mendel's results, in the renaissance and 

 extension of which Professor de Vries himself had such promi- 

 nent part. 



Recognizing as did Darwin that by far the greater part of our 

 knowledge of evolutionary processes is necessarily based upon 

 the results of economic practice, Professor de Vries has made a 

 careful experimental analysis of horticultural and agricultural 

 processes, and it is this part of his work which commends itself 

 especially to the thinking scientist. 



