CHAPTER VII 

 HEREDITY 



ALL plants arise from parents more or less like them- 

 selves. This reproduction has a visible material basis in 

 the egg-cells and pollen-grains liberated from the parental 

 bodies. By inheritance is meant all the qualities which 

 have their physical basis in the fertilized egg-cell, the ex- 

 pression of which results in the organism. "Thus," says 

 Thomson, "heredity is no force, no principle, but a con- 

 venient term for the genetic relation between successive 

 organisms." 



The inheritance of plants may be studied by considering 

 parents and their offspring collectively or by studying 

 the separate characters and their modes of transmission. 

 The former is statistical, the latter, analytical. Studies 

 of heredity from both points of view are being extensively 

 conducted by the biometricians on the one hand and the 

 mendelians on the other. 



Heredity studied collectively. "To define heredity," 

 says Davenport, "as the direct and personal relation 

 between the individual parent and the individual offspring 

 is not only to restrict its meaning within too narrow limits, 

 but to destroy its significance to the breeder and deceive 

 him as to the actual facts of transmission during descent. 

 ' Heredity ' properly refers to the group that constitutes 



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