256 HEREDITY AND ENVIRONMENT 



parents, that is, when it is duplex; if derived 

 from one parent only, that is, if simplex, it is 

 diluted in appearance and is intermediate be- 

 tween the two parents. For example, when 

 white-flowered four o'clocks which are nulli- 

 plex are crossed with red-flowered ones which 

 are duplex the progeny, which are simplex, 

 bear pink flowers; in this case red flowers are 

 produced only when the factor for red is de- 

 rived from both parents, pink flowers when it 

 is derived from one parent, white flowers when 

 it is derived from neither parent (Fig. 50). 



5. Summary of Mendelian Principles. — 

 Since the rediscovery in 1900 of Mendel's work 

 many investigators have carried out similar ex- 

 periments on many species of animals and 

 plants and have greatly extended our knowl- 

 edge of the principles of inheritance discovered 

 by Mendel, but in the main Mendel's conclu- 

 sions have been confirmed again and again, so 

 that there is no doubt that they constitute an 

 important rule of inheritance among all 

 organisms. 



In brief the "Mendelian Law of Alternative 

 Inheritance" or of hereditary "splitting" con- 

 sists of the following principles : 



