Bisexual Crosses 295 



one differential unit in the parents, we may 

 give it in the following manner. In fertiliza- 

 tion, the characters of both parents are not uni- 

 formly mixed, but remain separated though 

 most intimately combined in the hybrid 

 throughout life. They are so combined as to 

 work together nearly always, and to have nearly 

 equal influence on all the processes of the whole 

 individual evolution. But when the time ar- 

 rives to produce progeny, or rather to produce 

 the sexual cells through the combination of 

 which the offspring arises, the two parental 

 characters leave each other, and enter sepa- 

 rately into the sexual cells. From this it may be 

 seen that one-half of the pollen-cells will have 

 the quality of one parent, and the other the qual- 

 ity of the other. And the same holds good for 

 the egg-cells. Obviously the qualities lie latent 

 in the pollen and in the egg, but ready to be 

 evolved after fertilization has taken place. 



Granting these premises, we may now ask as 

 to the results of the fertilization of hybrids, 

 when this is brought about by their own pollen. 

 We assume that numerous pollen grains fer- 

 tilize numerous egg cells. This assumption at 

 once allows of applying the law of probability, 

 and to infer that of each kind of pollen grains 

 one-half will reach egg-cells with the same qual- 



