50 PLANT-BREEDING 



and the results of the Svalof station have a very deep signifi- 

 cance. They confirm the fact that the ordinary cultivated 

 varieties of cereals are by no means pure, but must be con- 

 sidered as mixtures of well defined types. Moreover, they 

 show that these types are far more numerous than was pre- 

 viously supposed, and include hundreds of forms within each 

 of the now prevailing sorts. They also show that the differ- 

 ences among these newly discovered elementary types are 

 far greater than might be suspected from the study of the 

 varieties isolated by other breeders. The range of variabil- 

 ity disclosed by these new studies is simply so wide that it 

 affords all the required material for almost all the selections 

 desirable at present, and will no doubt continue to be an 

 inexhaustible source of improvements for a long succession 

 of years. They are founded on the principle of single selec- 

 tions, and the range of application of this method is proven 

 to be so extensive as to make all ideas of repeated or con- 

 tinuous selection simply superfluous. It is even so rich in 

 its productiveness that there is scarcely any room left for 

 other methods of improvement; and especially should all 

 endeavors of winning ameliorated varieties of cereals by 

 means of hybridization simply be left out of consideration, 

 as compared with the immense number of more easily pro- 

 duced novelties which this method offers. 



Leaving the teachings which may be derived from this 

 work in the study of the evolution of the organic world for 

 another chapter, I shall now try to give an idea of the work 

 itself. This may be divided into two parts; the first com- 

 prising the use and criticism of the German method, and 

 the second embracing the discovery and application of the 

 principle of selecting elementary species. 



Some historical details may precede this discussion. 

 Svalof is a httle village in the Swedish province of Schonen, 

 situated in the neighborhood of Helsingborg, Lund and 



