i8o PLANT-BREEDING 



to come into existence. This proposition can be proved, and 

 in fact has been proved, independently of the question con- 

 cerning the details of that origin. 



This broad principle of evolution by means of natural 

 laws having been established, the question naturally arose, 

 how far the breeder's experience could be considered as a re- 

 liable guide in evolutionary problems. On this point, how- 

 ever, many difficulties have arisen, all owing to the simple 

 fact that practical breeding and scientific experimenting are 

 things of altogether different purpose and method. Of late 

 it has been contended that the discussion of the scientific side 

 of the question should abstain from the use of the breeders' 

 results. There can be no doubt that in the end this will prove 

 the right way, since only then it will be possible to submit all 

 arguments to the most severe criticism. 



At present, however, the purely scientific investigations 

 concerning variability and inheritance are only in their 

 beginning. Some fields have been more or less thoroughly 

 explored, and definite laws have been discovered. But the 

 more complicated cases are as yet hardly accessible to our 

 analysis, and the breeders' experience often covers so long a 

 series of years that the science of evolution is still quite inade- 

 quate to be compared with it. Moreover, the practical re- 

 sults contain so many indications and hints for the starting 

 of investigations, and so many details which otherwise could 

 easily be overlooked, that they are still contributing a most 

 valuable support to evolutionary science. 



In estimating the value and reliability of the breeders' 

 work for theoretical discussions, its methods and aims should 

 clearly be understood. The practical work chiefly consists 

 in the selection of those specimens which are most suitable 

 for the purpose under consideration. But selection requires 

 material to choose from. This material, in some rare in- 

 stances, may be directly afforded by nature, but in the larger 



