Introduction. 7 



The experiments to this end were begun in the autmnn 

 of 1886 and are now at least in one particular direction 

 almost complete. A description of them will constitute 

 most of the contents of the second part. 



The critical revision to which I have referred will 

 form the substance of the first section. 



I shall confine my critique to the facts of selection 

 and to the material, afforded by variability, on which 

 selection operates. It will be shown that artificial selec- 

 tion is, as already mentioned, a twofold process. On the 

 one hand it consists in the isolation of constant strains 

 from their neighbors and, inasmuch as the best are chosen, 

 in their improvement. On the other hand it improves 

 races and is the source of those superior fruits which we 

 can only propagate by grafting and other vegetative 

 methods. But this selection, so far as our experience 

 goes, never leads to the origin of new and independent 

 types. 



In this first section then it will be our object to 

 render the difference between these two types of varia- 

 bility as clear as possible. A correct apprehension of the 

 nature of this difference will make clear the overwhelm- 

 ing importance of Mutability, as opposed to individual 

 variation, in the production of new species. In connec- 

 tion with this critical treatment I have tried, by experi- 

 ments on numerous examples of individual variation, to 

 discover the limits to the amount of alteration that can 

 be attained in this way. And we shall see that these are 

 much narrower than a belief in the theory of Selection, 

 as commonly entertained, would lead us to expect. 



For the main experiment I have chosen a plant in 

 which I was enabled to follow in detail the phenomenon 

 of Mutation through a number of years. This was 



