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TEXTBOOK OF BOTANY 



FLOWERS 



OF TWO 



PARENTS 



FLOWERS ON ALL 

 HYBRID PLANTS 

 F, GENERATION 



r ^ 



FLOWERS OF HYBRID PROGENY: F^ GENERATION 



Fig. 205. A diagrammatic representation of the color of flowers on plants of 

 snapdragon of the F^ and F2 generations following a cross between a red-Howered 

 and a white-flowered variety. 



If cross-fertilization occurs between the red-flowered and pink-flow- 

 ered plants, one-half of the progeny are red-flowered, the others are pink- 

 flowered. If cross-fertilization occurs between the white-flowered and 

 pink-flowered plants, one-half of the progeny are white-flowered, the 

 others are pink-flowered. 



Self-fertilization in the red-flowered plants results only in red-flowered 

 plants. Consequently all the red-flowered plants of this species of snap- 

 dragon are said to be a pure line with respect to flower color. Note, 

 however, that our attention is only on flower color. The plants may or 

 may not be a pure line with respect to certain other characters such as 

 height, shape of leaf, and immunity to rust. Self-fertilization in the white- 

 flowered plants results in only white-flowered plants. They constitute a 

 pure line of white-flowered plants. The pink-flowered plants are hybrids 

 with respect to flower color, but they may be pure-line plants with re- 

 spect to other characters that we are ignoring at the present. 



Red- and white-colored flowers are hereditary traits or characters in 

 snapdragon, but the flowers and the pigments are not actually inherited. 

 They develop as a result of something that is inherited. Anything that is 

 directly inherited must be in the egg or in the sperm, since these two 



