66 PLANT-BREEDING 



which new races are not created but simply isolated from 

 among a mixture. The alternative principle is, that a race 

 may be improved and educated in arbitrarily chosen direc- 

 tions. The original race is thereby assumed to be pure 

 and uniform, and thus there is no reason for beginning with 

 one single individual. It is even better to start from a 

 handful of ears, and to select in each generation a similar 

 number, in order to be sure that all characters which are 

 not consciously considered in the selection may remain in 

 the average condition which they held in the original variety. 



Concerning the causes of the improvement in this re- 

 peated selection, two contrasting views have been discussed. 

 Hallett assumed that variability was induced or at least in- 

 creased in the desired direction by his treatment. In Ger- 

 many the opposite view was held, and it was even assumed 

 that all changes induced by outer influences had no hered- 

 itary power at all. They were considered as delusive, and 

 the principle followed was to exclude them carefully. In- 

 ternal causes were the real source of variability, and these 

 had to be guided by selection. And since those internal 

 causes, from their very nature, were not accessible to man, 

 selection was considered the only real means of improvement. 

 It worked slowly and often did not work at all, but wherever 

 a success was obtained, it was ascribed to the influence of 

 this selection. 



As I have already stated, methodical selection was as- 

 sumed to produce races which could only be kept up to their 

 high standard by a continuation of the selection. This 

 point was of the highest practical interest for the breeder, 

 since it kept the production of the seed-grains of his race in 

 his own hands, at least for a long succession of years, and 

 thereby enabled him to secure very considerable profits. 

 On this account it is only natural that many breeders of cere- 

 als of the present time still adhere to these old convictions. 



