PHENOMENA OF INHERITANCE 235 



A single germ cell can carry the factors, or 

 causes, for red flowers or white flowers, for 

 green seeds or yellow seeds, for tall stem or 

 short stem, etc., but not for both pairs of these 

 contrasting characters. The hybrids formed 

 by crossing white and red four o'clocks carry 

 the factors for both white and red, but the in- 

 dividual germ cells formed by such a hybrid 

 carry the factors for white or red, but not for 

 both ; these factors segregate or separate in the 

 formation of the germ cells so that one-half of 

 all the germ cells formed carry the factor for 

 white and the other half that for red. 



This is the most important part of Mendel's 

 Law, the central doctrine from which all 

 other conclusions of his radiate. It explains 

 not only the segregation of dominant and re- 

 cessive characters from a hybrid in which both 

 are present, but also the relative numbers of 

 pure dominants, pure recessives and mixed 

 dominant-recessives in each generation. For 

 if all germ cells are pure with respect to any 

 particular character the hybrid offspring of 

 any two parents with contrasting characters 

 will produce in equal numbers two classes of 



