PLANT-BREEDING 339 



splitting appears in each succeeding generation. In propa- 

 gating a hybrid by seed, therefore, one may expect that in 

 ordinary conditions only about one-half the progeny will 

 show the desired combination. 



It follows, therefore, that hybridization is most useful with 

 those plants that are not propagated by seed, but by some 

 vegetative method, as by tubers, bulbs, cuttings, layering, 

 grafting, etc. ; for in these cases one hybrid individual is 

 continued directly in its progeny, without bringing in another 

 plant as a parent. It is evident that the method can be used 

 with great efficiency among the fruits, which are so largely 

 propagated vegetatively ; but that it is by no means so 

 efficient among the cereals, which must be propagated by 

 seeds. 



A few illustrations will fix the method in mind. Seedless 

 apples of poor quality have long been known, but by crossing 

 seedless apples with those of good quality, a hybrid was pro- 

 duced which combined the two desired characters. It is 

 evident that in this case vegetative propagation is necessary, 

 so that there would be no danger of the hybrid splitting in the 

 ordinary way. 



The ordinary cultivated blackberry is large and black, 

 but there is a small wild blackberry that is whitish or cream 

 color. By crossing the two, a hybrid was secured that pro- 

 duced berries of the large size and light color, so that " white 

 blackberries " could be grown. 



The possibilities of such combinations are endless and many 

 of them have been made, some more curious than useful, 

 but many of them very useful. 



Enough has been said to show that the operations of plant- 

 breeding are exceedingly varied, and that by the use of various 

 methods, either singly or in combination, almost any desired 

 result may be obtained. It is becoming almost literally true 

 that one may order almost any kind of plant and expect to 

 have the order filled. 



