20 INTRODUCTION 



experience of practical breeders ; only the elucida- 

 tion of one simple rule of inheritance has brought into 

 order a host of phenomena, which were previously quite 

 incapable of a coherent explanation. 



The experimental results with which it is the pro- 

 vince of this book to deal are, then, firstly those of 

 biometry, or the statistical study of variations, and 

 particularly of continuous variations ; secondly, the 

 results of direct observations bearing upon the origin 

 of species by the discontinuous method ; and thirdly, 

 the results of experimental observations on heredity 

 by the methods of scientific breeding. By these 

 methods results of the utmost moment to mankind 

 have been, and are being, arrived at, quite apart from 

 their interest as bearing upon the problems of evolu- 

 tion. From a biologist's point of view, however, the 

 latter is, of course, paramount. And so it has been 

 thought fitting to begin with a brief discussion of the 

 problems of evolution, and of the various solutions of 

 them which have been from time to time suggested. 



In a later chapter some of the more prominent recent 

 results of the kindred science of cytology the micro- 

 scopic study of the minute constituent parts of organ- 

 isms will be briefly described, on account of the very 

 close connection which recent progress in this subject 

 bears to the experimental study of the inheritance of 

 the grosser characters. 



