488 Report of the DEPAKTMEi^^T of Hokticulture. 



simultaneous presence of several distinct factors. Thus, in the 

 crosses under study, there are indications that shape, size, and 

 color of fruit, may depend upon the presence or absence of 

 several factors. 



Another difficulty is that characters, if recessive, may not 

 appear in the Fi generation. Now this skipping a generation, 

 when it occurs, will greatly delay and complicate the breeding of 

 plants that are propagated vegetatively, for, if the desired char- 

 acters do not appear in the Fi generation propagation cannot pro- 

 ceed at once. 



The phenomena of coupling and repulsion, which has been 

 worked out with several plants, though not yet understood, if it 

 appears in apples will tend to complicate breeding processes. That 

 is, some factors seem to be linked together and are so transmitted 

 while others rej)el one another and refuse to be transmitted 

 together. 



Again, 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 may want wholly new characters in apples. These 

 he cannot obtain by making Mendelian combinations. 



Existing characters, if we possibly except size and vigor, cannot 

 be augmented by crossing. 



To have all of the many characters represented in the offspring 

 it is necessary to work with large numbers of plants — difficult 

 to obtain and time-taking with apples. 



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, for a time 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 seemingly intermediate between the parents. 



