CHAPTER VIII 

 THEORY AND PRACTICE 



I HAVE all along attempted to make it clear 

 that the fundamental principles of plant 

 breeding are simple, and that the amateur 

 may begin experiments and even carry them to 

 interesting conclusions with comparative ease. It 

 is desirable now to supplement what has previ- 

 ously been said by calling attention to some of the 

 complications that are sure to arise as the work 

 of plant breeding progresses ; and in so doing, of 

 course, to point out clearly how these complica- 

 tions may be met. 



Let us first recall what has been outlined in the 

 previous articles as to Mendelian heredity. We 

 saw that when the flower of a tall pea vine is 

 fertilized with pollen from the flower of a short 

 pea vine the progeny will all be tall; but that in 

 the second generation one vine in four will be 

 short, like one of the grandparents. Thus in the 

 vine of the first filial generation the hereditary 

 factors for tallness may be said to be " dominant, " 

 since they make themselves manifest, and the 

 factors for shortness may be said to be "re- 

 cessive," since they are submerged and for the 

 time being inoperative. But these recessive fac- 

 tors come to the surface, as it were, in one in 



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