MUTATIONS IN PLANT BREEDING 373 



of the seedlings exhibiting the new characters. In cross-fertilized species, 

 in which individual plants are self-sterile, where a mutation appears 

 in only one plant, several successive crosses may be necessary in order 

 to produce a strain which breeds true for the new type. It must be 

 crossed back on the parental form to begin with. If the change from 

 the parental type is conditioned by a single factor the number of hybrid 

 generations to be raised will depend on whether that factor segregates as a 

 dominant or a recessive. In the latter case a true breeding strain should 

 be obtained in the second generation but in the former it will require 

 three or more hybrid generations depending on the extent to which the 

 new characters depend upon environmental conditions for their expression. 



