MUTATION THEORY IN PRACTICAL BREEDING. 05 



rendered nearly inaccessible to the breeders of other countries by being 

 printed exclusively in the Swedish language. 



In the last five or six years, careful pedigreed cultures of a large 

 number of these isolated elementary forms have been made at Svalof, 

 and a number of mutants have been seen to originate in purebred, 

 carefully guarded lines, so that there can be no doubt that the ele- 

 mentary species of the various grains are the products of mutuation 

 either directly or through the combination and resolution of the 

 characters of two or more other elementary species by means of 

 hybridization. Indeed, every logical consideration as well as all the 

 experimental data now available lead conclusively to the view that the 

 very existence of distinct elementary species differing from each other 

 by unit characters is indubitable evidence that they originated by 

 mutation. 



In discussing the importance of the mutation theory, it is not to 

 be forgotten that mutation and Mendelism are counterparts of each 

 other and both depend for their validity, upon the existence of unit 

 characters. These three mutation, Mendelism, and unit characters 

 are all part and parcel of one consistent view of the world of living 

 matter. Together they constitute the new biological knowledge which 

 has revolutionized the discussion of breeding problems, and which has 

 already entered in large measure into the methods employed by the 

 breeder. Of the supreme importance of this new discipline as a whole 

 nothing need be said, and it would be futile to attempt to dissociate 

 the theory of mutation from the conception of unit characters and 

 Mendelian inheritance in order to weigh the importance each would 

 have for practical breeding when standing alone. Neither Mendelian 

 inheritance nor the mutation theory could have assumed by itself the 

 sudden importance they have now attained; but the appearance of 

 both at the same time, both telling the same story of the existence 

 of character-determining units, have wrought so great a change in 

 biological thought as to amount practically to a revolution. 



Always in revolutionary times the sane, conservative man guards 

 himself against being carried too far afield, and it may not be out of 

 place to say here, that although we must recognize the great value of 

 the new theories, they are not everything that the breeder needs to keep 

 in mind. There are many characters that are not unit characters, 

 variations that are not mutations, and inheritance that is non-Men- 

 delian, and such characters, such variations, and such inheritance are 

 also important to the breeder. Indeed, another great advantage the 

 breeder gains through recognition of the mutation theory comes from 

 the strong emphasis that theory places upon the fact that variations 

 are not all alike. A sharp distinction is drawn between mutations and 

 fluctuations and the breeder who would derive the greatest possible 

 benefit from the mutation theory will carefully keep this distinction 

 in mind to serve as a guide to the technique that may be expected to 

 best meet the requirements of each particular case. 



In the selection of a permanent seed-strain, mutation must be the 



