BREEDING 425 



characters depending upon a single factor, the work would be greatly 

 simplified, but it is likely that some of the most important characters 

 of apples depend upon the simultaneous presence of several distinct 

 factors. Thus, in the crosses given, there are indications that shape, 

 size, and color of fruit may depend on the presence or absence of 

 several factors. 



Another difficulty is that characters, if recessive, may not appear 

 in the F 1 generation. 1 This skipping of a generation will greatly 

 delay and complicate the breeding of plants that are propagated 

 vegetatively, for if the desired characters do not appear in the 

 intermediate generation, propagation cannot proceed at once. 



In the case of certain plants it has been found that some charac- 

 ters are linked together and are so transmitted, while others repel 

 one another and refuse to be transmitted together. This phenome- 

 non of coupling and repulsion is not yet understood, and if it appears 

 in apples will tend to complicate breeding processes. Then, too, 

 the bringing together of complementary factors, which somehow 

 in the past breeding of the fruit had become separated, may result 

 in reversions and thus produce unexpected characters. 



A breeder cannot obtain wholly new characters in apples by 

 making Mendelian combinations ; nor can he augment existing 

 characters, with the possible exception of size and vigor, by crossing. 



To perpetuate all the many characters of a species it is necessary 

 to work with large numbers of plants, which in the case of apples 

 is difficult and time-consuming. It is probable that disappointments 

 will most often come from the attempt to perpetuate variations 

 which are fluctuations dependent upon environment and not upon 

 the constitution of the gametes. 



There is likely to be some confusion, at least until we have more 

 knowledge on the subject, between what are known as " simple 

 Mendelian characters " and " blending characters," or those which 

 may be complex in composition, in which the offspring are seem- 

 ingly intermediate between the parents. 



Bud-selection. 2 It is held by many orchardists and experimenters 

 that such qualities as productiveness, vigor, and hardiness can be 

 reproduced by taking scions, or buds, from the plants possessing 



1 The intermediate generation. 



2 After Professor U. P. Iledrick, Geneva Experiment Station. 



