EVIDENCE FROM EXPERIMENT 159 



offspring, and that in each generation of hybrids a 

 process of segregation goes on, by which a definite 

 proportion of plants is separated out from the mass of 

 cross-bred individuals and returns to the character of 

 one or other original parent. When this segregation 

 has once been effected, all the subsequent progeny is 

 constant to type; the descendants of the segregated 

 white flowers are invariably white. 



The process is made simpler and more intelligible, 

 when the somewhat confusing effects of dominance 

 are absent, as they are in the Jalap, or Wonder of 

 Peru, experimented on by Correns. If the white- 

 flowered race of this plant is crossed with the red- 

 flowered race, all the plants of the first hybrid gener- 

 ation have uniformly pink flowers, because neither 

 color is dominant over the other and the two seem 

 to blend, though they do not actually do so. When 

 the second generation is produced, either by self- 

 fertilization or by crossing the hybrids with each 

 other, one-fourth of this second generation is red, 

 one-fourth white and one-half pink, and each suc- 

 ceeding generation acts in the same way. 



This behaviour is explained by assuming that 

 every unit character is represented in the reproduc- 

 tive cells, or germ, by something which causes the 

 development of that character in the full-grown 

 plant and this something is called the "factor" for 

 the character. If we symbolize the factor for the 

 red colour by R and that for the white by W, then 

 the germs of the red-flowering race contain the fac- 



