Ch. VI, 9] METHODS OF PLANT BREEDING 321 



segregation (page 312), which applie.s in full force to hj'brids, 

 where indeed it was discovered. Fourth, two, or more, de- 

 sirable qualities belonging to different varieties may be 

 brought together and permanently combined in a single 

 variety. Theoreticall}' this is the highest utihty of hy- 

 bridization, and its practice the highest form of plant breed- 

 ing. 



Hj'bridization is, however, bj^ no means so simple in 

 practice as in principle. It is often very difficult to accom- 

 plish mechanically ; manj- plants which one desires to 

 hybridize fail to set seed with one another's pollen ; new 

 features are as likely to be useless as desirable ; hybrids 

 designed to combine certain good qualities are as likely to 

 combine others which are bad ; the reproductive power of 

 hybrids is usuallj' poor ; and many other difficulties make 

 hybridization a slow and difficult method of effecting de- 

 sired improvements in plants. Nevertheless, in the hands 

 of skilled breeders, it is the most important of the three 

 methods of plant improvement, and is actually yielding most 

 valuable results, especially in the breeding of grains. 



It was earlier said that cultivation, though it makes better 

 plants and crops, does not produce new varieties. Indi- 

 rectly, however, it helps to that end : for under cultivation 

 plants vary and sport far more profusely and widely than 

 when wild, — apparently because of their better nutritive 

 conditions, in conjunction with the stimulative effect of new 

 surroundings, and perhaps the removal of old restraints. 

 Further, it is possible, by devices of cultivation, to intensify 

 the rapidity and degree of variation, though not to direct its 

 character : and skilled breeders can thus "break the type," in 

 their phrase, as a foundation for new varieties. It is also 

 of course true that the greater the number of plants grown, 

 the greater the chance for the appearance of new and de- 

 sirable variations ; and this method of growing plants in vast 

 quantities is one of the "secrets of success" of the best 

 known of present-day plant breeders, Luther Burbank. 



