CHAPTER X 



PLANT BREEDING AND EVOLUTION 

 CROSSING AND HYBRIDIZING 



Pollination, in order to be effective in the production of new 

 and better kinds of plants, must be followed by the union of the 

 gametes in fertilization and by the production of seed. It is a 

 common usage, therefore, in practical work, to substitute the 

 terms self-fertilization, close-fertilization, and cross-fertilization 

 for the corresponding terms already denned, which are used to 

 designate different kinds, or degrees, of pollination. It is of 

 course understood in each case that pollination has preceded the 

 union of the gametes in fertilization. 



Inbreeding is a term usually employed by horticulturists and 

 practical breeders of plants to include all cases of self- and close- 

 pollination and self- and close-fertilization, since it has been found 

 that self-fertilization and close-fertilization are essentially the 

 same in their effect upon the offspring. In other words, it makes 

 very little difference in the character of the offspring whether 

 the pollen from a given flower falls upon the stigma of the same 

 flower or upon that of a different flower on the same plant. 



Crossing is the term applied to the processes of pollination 

 and fertilization where the pollen and the male gametes derived 

 from a flower on one plant effect pollination of the stigma and 

 fertilization of a female gamete borne by a flower of a different 

 plant of the same kind, or species. Thus, if pollen derived from 

 a locust flower on one tree is transferred to the stigma of a 

 flower on another locust tree of the same kind, or species, both the 

 transfer of pollen and the resultant fertilization are designated 

 by the term crossing. The term crossing, therefore, includes both 

 cross-pollination and cross-fertilization. 



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