PLANT BREEDING A.ND EVOLUTION 183 



habit of the American daisy. This favorable chance combination 

 was selected as the Shasta daisy, a well-known garden variety. 



The most marked results from the hybridization of cultivated 

 varieties have been obtained among the ornamental plants, which 

 are most highly protected from competition and from the adverse 

 effects of soil and climate. The brilliant effects due to the colors 

 of flowers and foliage among such plants as the common phlox, 

 pansies, tulips, and foliage plants are in most instances due to 

 the mixing of races and varieties by a long series of hybridiza- 

 tions similar to those recounted above in the production of the 

 Shasta daisy by Burbank. Among fruits and vegetables there 

 are fewer successful hybrids than among ornamental plants. 

 Almost no important hybrids are recorded among garden 

 vegetables. Among the fruits there are some hybrid grapes 

 and pears, but in apples, peaches, plums, cherries, and cur- 

 rants there are no important recognized commercial hybrids. 

 Among blackberries there are hybrids between blackberries and 

 dewberries, and between the black and white blackberries already 

 indicated. Among raspberries there are hybrids between the red 

 and the black varieties. Perhaps the most notable hybrids are 

 those obtained among citrous fruits, such as the tangelo (which 

 is a hybrid between the pomelo and the tangerine) and the 

 citranges (which are hybrids between the sweet orange and the 

 hardy hedge orange (Citrus trifoliata)). 



In crosses between plants which are too distantly related the 

 unfavorable effect of infertility is often partially obviated in culti- 

 vation by propagating the offspring vegetatively. The various 

 methods were discussed earlier under vegetative reproduction, 

 and need not be repeated here. It is sufficient to repeat that by 

 budding, grafting, and propagation by means of bulbs, tubers, 

 and runners favorable varieties obtained by hybridization are 

 now perpetuated for long periods of time. Hybridization, there- 

 fore, is one of the most potent of the methods available to the 

 modern breeder for the production of new kinds of ornamental 

 and useful plants. 



