16 Descent 



nature and in culture, leaving the question of 

 their origin to a subsequent experimental treat- 

 ment. 



The question of the experimental origin of 

 new species and varieties has to be taken up 

 from two widely separated starting points. This 

 may be inferred from what we have already 

 seen concerning the two opposing theories, de- 

 rived and isolated from Darwin's original 

 broad conception. One of them considers 

 mutations as the origin of new forms, while the 

 other assumes fluctuations to be the source of 

 all evolution. 



As mentioned above, my own experience has 

 led me to accept the first view. Therefore I 

 shall have to show that mutations do yield new 

 and constant forms, while fluctuations are not 

 adequate to do so. Eetrograde varieties and 

 elementary species may both be seen to be 

 produced by sudden mutations. Varieties have 

 often been observed to appear at once and quite 

 unexpectedly in horticulture and agriculture, 

 and a survey of these historical facts will be the 

 subject of one of my lectures. In some in- 

 stances I have succeeded in repeating these 

 observations in my garden under the strict con- 

 ditions of a scientific experiment, and these in- 

 stances teach us the real nature of the process 

 of mutation in all its visible features. New ele- 



