66 HEREDITY AND EVOLUTION IN PLANTS 



56. Applications of Mendel's Law. Over 100 pairs 

 of structural and color characters have been found, in 

 plant breeding, to behave more or less closely in accord- 

 ance with the Mendelian conception. In peas alone over 

 20 pairs of characters are expressed in successive genera- 

 tions, in accordance with this law. Among the more 

 striking results which are explainable upon Mendelian 

 theory are the following : 



1. Mottled beans have been produced in the FI genera- 

 tion by crossing two varieties, neither of which had mottled 

 seeds. Various types appeared in the F 2 generation. 



2. Jet black beans have appeared in the FI generation 

 from a cross between two varieties, one of which had pure 

 white seeds, the other light yellow. Various shades and 

 colors appeared in the F 2 generation. 



3. In one case three distinct varieties of beans, breed- 

 ing true to white seeds (when self ed 1 ), were crossed with the 

 same variety of red bean. In the FI generation each cross 

 gave a different color one blue, another black, and the 

 third brown. A varied assortment of colors appeared in 

 each case in the F 2 generations. 



4. Two varieties of sweet peas, each breeding true to 

 white flowers, when crossed gave, in the FI generation, 

 nothing but purple-flowered offspring, resembling the 

 wild sweet pea. A medley of white, pink, purple, and 

 red-flowered plants appeared in the F 2 generation. Num- 

 erous other cases might be cited, all of which would have 

 been unsolvable riddles except in the light of Mendelism. 



57. Inheritance and Environment. Emphasis should 

 be laid on the fact that the behavior of any plant, and the 



1 The pollination of a flower with its own pollen, or with pollen from an- 

 other flower of the same plant, is called selfing. 



