216 



BOTANY: PRINCIPLES AND PROBLEMS 



Fi hyl)ri(l, though only the purple expresses itself visibly in the 

 plant. Out of this purple hybrid, when self-fertilized, come some 

 perfectly pure white plants which exhibit no trace of purple in their 

 descendants and some purples which exhibit no trace of white, 



Parents 



PP 



(Purple) 



WW 



(White) 



Gametes 



All^V 



Fig. 124. — Diagram showing genotype (in letters), and appearance, of parents 

 of the Fi, and of the F-i in a cross between a purple-flowered and a white-flowered 



thus proving that the factors for these characters, which for a 

 generation have been existing together in every cell of the hybrid 

 plant, have now (in one-half of the individuals) become com- 

 pletely separated and have not produced the slightest effect on 

 one another. 



carry the factor for purple and half for white, and that none are ''light purple". 

 In the second hybrid generation or F2, derived by self-fertilization of the F\, 

 about one fourth of the plants are purple, with all their gametes carrying the 

 factor for purple; one half light purple, with about half their gametes carrying 

 purple and half white; and one fourth white, all their gametes carrying white. 

 The purple-flowered plants breed true to purple in the F3, the white-flowered ones 

 to white, and the light purple ones behave as did the light purple Fi, producing 

 about one fourth purple, one half light purple, and one fourth white. 



