560 STRUCTURE AND LIFE HISTORIES 



true to white seeds (when selfed 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. Numer- 

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

 been unsolvable riddles except in the light of Mendelism. 



482. Inheritance and Environment. Emphasis should 

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

 the characters it manifests, are the result of the combined 

 influence of inheritance and environment. A bean seed- 

 ling is green, not merely because it has inherited chloro- 

 plastids, but because it develops in sunlight; without 

 sunlight the green color could not come into expression. 

 If we vary any factor of environment (temperature, mois- 

 ture, illumination, food) the expression of the inheritance 

 may be altered, just as truly as though the inheritance 

 were changed. The characteristics expressed by any plant 

 (or animal) are the result of the combined action of inherit- 

 ance and environment. It is of fundamental importance 

 to a man, not only to be "well-born" (eugenics), but also 

 to be "well-placed" (euthenics). 



483. Johannsen's Conception of Heredity. The con- 

 ception that inheritance, as previously noted, is not the 

 transmission of external characters from parent to off- 

 spring, but the reappearance, in successive generations, 



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

 another flower of the same plant, is called setting. 



