LECTURE XXI 



MUTATIONS IN HORTICULTURE 



It is well known that Darwin based his theory 

 of natural selection to a large extent upon the 

 experience of breeders. Natural and artificial 

 selection exhibit the same general features, yet 

 it was impossible in Darwin 's time to make a 

 critical and comparative analysis of the two 

 processes. 



In accordance with our present conception 

 there is selection of species and selection within 

 the species. The struggle for life determines 

 which of a group of elementary species shall sur- 

 vive and which shall disappear. In agricultural 

 practice the corresponding process is usually 

 designated by the name of variety-testing. 

 Within the species, or within the variety, the 

 sieve of natural selection is constantly eliminat- 

 ing poor specimens and preserving those that 

 are best adapted to live under the given condi- 

 tions. Some amelioration and some local races 

 are the result, but this does not appear to be of 

 much importance. On the contrary, the selec- 



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