ON CORN BREEDING 151 



in our last chapter, I have pointed out how ignorance of 

 the real nature of the variability of cereals has deluded its 

 originator. It made him assume that a slow improvement 

 was the effect of his twenty years of selection, but in reality 

 he simply gradually isolated by it one of the constituents of 

 his initially selected but mixed group of ears. 



According to the experience of the Svalof Station, no 

 such slow improvement really occurs, and a single choice of 

 an ear followed by a separate culture of its grains is always 

 sufficient to secure a pure and uniform strain, provided that 

 cross-pollinations do not interfere with the result. 



These principles must be applied to corn breeding also. 

 Any selected ear will give, in its progeny, a pure and uni- 

 form race within the limits of its fluctuating variability, 

 provided that it has not been contaminated by crossing. 

 Here we meet with the main difference in the breeding of 

 corn and of other cereals. With the latter cross-fertilization 

 is an exception; with corn it is the rule. This explains the 

 necessity of repeated selection of corn without having to 

 assume the hypothesis of slow improvement. Repeated 

 selection is the only practical means of eliminating the effects 

 of previous crosses. It is only apparently a fixation of the 

 characters of the young family; in reality it is only its puri- 

 fying from vicinistic impurities. It is enforced because of 

 the conviction of the detrimental effects of self-fertilization 

 in corn, but if experience should prove that one year's self- 

 fertilization is sufficiently harmless, the process of corn 

 breeding could be shortened in the same way as the Svalof 

 method may be considered as a shortening of the older pro- 

 cesses of breeding of cereals. An experimental test of the 

 value of the Swedish principles in their application to corn 

 breeding would, no doubt, elucidate many as yet doubtful 

 points, and probably lead to some essential changes in the 

 practical work. 



