EXPERIMENT STATION REPORTS. 



299 



varieties that are not at present coinbined in any known strain. Cross- 

 inji; involves considerable work in the following generations before the new 

 type can be fixed and testeci. 



In open fertile or alloganious crops, one must not forget that vigor may 

 be lost through too raind in-br(>(Mling. 



THE SEGREGATION OF HYBRIDS. 



F(n- each alternative i)air of hereditaj-y characters in which the parents 

 of the hybrid differ, a geneplex results. This, no doubt, means that a pair 

 of chromosomes carry the determiner for these characters. One of these 

 are of maternal and the other of paternal origin. They exist together 

 in all the cells of the first generation hybrid. The two chromosomes of a 

 pair come to lie side by side at the metaphase of the heterotypic division 

 when the hybrid produce spores and eventually gametes. 



What is true in the case of one genoplex will be true for the others. 

 The resulting gametes will each carrj^ one of the alternative characters 

 of each genoplex. The various gametes will carry the chance combina- 

 tions of these alternative characters. Thus after fertilization, the result- 

 ing individuals of the second generation come by the chance combinations 

 of the resulting gametes. The second filial generation is thus composed of a 

 mixture of individuals possessing all combinations of the segregating paren- 

 tal characters. 



The seeds obtained from a cross are planted in a bed in the first filial 

 generation, and from this bed selections are made to become mothers of 

 the progenies of the secoiul generation. The centgener method is used in 

 planting progenies that are apt to segregate. 



Self pollinating wurk w itli curn. 



This is necessary to allow the classification of the plants into their 

 phenotypes and to make individual plant selections for the mothers of 

 the next generation. 



In the case of the self-fertile crops, plant selections are made and cent- 

 geners planted in each generation until races breed true to seed. In the 

 case of the allogamous (open fertile) crops th€ plants may need to be selfed 

 in order to gain the purity desired. 



