iv Author s Preface to the Translation. 



that time, which even Focke in his standard work on 

 Plant-hybrids did not give the rank of a work of first-rate 

 importance. The work of Bateson and of his school, of 

 CuENOT, Webber and many others, but above all that of 

 Davenport, have since brought the principle of unit-char- 

 acters to its now prominent rank in the study of hybridi- 

 zation. 



There can be no doubt, that this principle of the unit- 

 characters opens up a wide range of questions and subsidiary 

 theories, which may now be subjected to experimental in- 

 quiry and critical study. The phenomena of inheritance 

 and hybridization constitute a wide field, which had scarcely 

 been explored hitherto. Half- and middle-races, with their 

 apparently incomplete heredity, constant hybrids, correlated 

 and associated characters, and many other most curious phe- 

 nomena afiford plenty of scope for future investigation. 



Under these circumstances I feel deeply indebted to Pro- 

 fessor Farmer and Mr. Darbishire for their painstaking 

 work in preparing an English translation of this book, as 

 well as to Dr. Paul Carus of the Open Court Publishing 

 Co. for his liberality and full confidence in the scientific and 

 practical value of the principles enunciated therein. Great 

 support has already been accorded to my ideas by many 

 English and American workers in this field, and it is con- 

 fidently hoped, that this translation will secure that uni- 

 versal cooperation without which no great scientific principle 

 can attain its full measure of usefulness to mankind. 



No essential changes have been made in the translation, 

 with the exception of those which have been made necessary 

 by the work of Hj. Nilsson on the selection and the im- 

 provement of cereals in Sweden. Corrections of minor 

 points have been introduced wherever necessary. 



It is proposed to publish this translation in two inde- 

 pendent volumes, the first dealing Avith the origin of spe- 

 cies by mutation, the second with the origin of varieties 

 and with the general considerations found at the end of the 



