Application of Biological Principles to Plant Breeding 123 



differ in several transmissible characters. The first hybrid 

 generation may be as uniform as one of the pure varieties, 

 but in the second hybrid generations all possible combina- 

 tions of the characters of the two parents are obtained 

 provided a sufficient number of individuals have been 

 grown. Among these combinations many new and desir- 

 able types may be found. Some of them are pure types; 

 some are heterozygous and will again segregate. Since 

 homozygous and heterozygous types are found which are 

 exactly alike in appearance, the only way to determine 

 which plants are pure is to self-fertilize desirable individuals 

 and raise a third generation. For example, N. alata, 

 a species with large white flowers, when crossed with 

 ~N. forgetiana, a species with small red flowers, gives 

 hybrids that are very uniform in all their characters. The 

 flowers are intermediate between those of the parents in 

 size, and are red in color. In the second hybrid generation, 

 there are 16 visibly different color types. x\mong these 

 there are really 81 classes, including those both pure and 

 hybrid. It is therefore necessary to grow seed from many 

 self-fertilized plants for another generation to be certain 

 of getting pure strains of each type. But having done this, 

 the pure types continue to breed true in spite of the mixed 

 ancestry. 



This method is tj^Dical of the manner in which floral 

 novelties are produced. So many varieties carry latent 

 characters that one is always likely to obtain new things 

 in crosses. Results of greater economic worth, however, 

 are probably obtained by combinations made for a definite 

 purpose. A beautiful example of such work is afforded by 

 the experiments of Biff en. English wheats have long been 

 known as highly productive varieties, but they are very 



