8 APPLICATION OF PRINCIPLES OF HEREDITY TO BREEDING. 



that is, imperfect horns. Hence, we say that horns are recessive 

 and the poll character dominant. Many other cases might be cited 

 to illustrate dominance and recessiveness of hereditary characters, 

 but the above examples will serve to illustrate the principles suffi- 

 ciently here. 



While it is not uncommon for a character to be dominant or reces- 

 sive in a cross, it is seldom that dominance is absolute. The presence 

 of the recessive character can usually be detected, and in some cases 

 very easily. Thus, in the cross between bearded and smooth wheat 

 the hybrids usually show a slight tendency to be bearded. Likewise, 

 as already stated, the cross between horned and polled cattle may 

 have scurs. It frequently happens that instead of either of two 

 opposite characters being dominant we get a form intermediate be- 

 tween the two parent forms. Thus, in the cross between ordinary 

 long-headed wheat and the short-headed club wheats of the Pacific 

 coast the hybrid has heads of intermediate length, though they are 

 much more like club wheat than they are like the ordinary kinds, so 

 that the club character is at least partially dominant. In certain 

 crosses between red-flowered and white-flowered ornamental plants 

 the hybrids are pink. 



In not a few instances a hybrid is altogether different in some 

 characters from either of its parents. Thus, in the case of the cross 

 between a certain red primrose and a certain nearly related white 

 variety the hybrid is purple. 



We thus have every gradation between perfect dominance of a 

 character over its opposite and cases in which the hybrid is unlike 

 either parent. 



SEGREGATION. 



We have seen that when two naturally opposite characters meet 

 in the same individual one of them may be completely dominant, 

 as the poll character in many individuals of the cross between polled 

 and horned cattle, or the crossbred individual may exhibit a char- 

 acter intermediate between the opposed characters of its parents, 

 as the pink color of certain hybrids between red-flowered and white- 

 flowered plant varieties, or the hybrid may exhibit a character 

 different from the corresponding characters of either of its parents, 

 as the purple color of hybrid primroses produced by crossing cer- 

 tain red and white varieties. 



In a pure race of plants having red flowers we may assume that 

 each individual which bears seed transmits to all its seed the tend- 

 ency to produce red flowers. Likewise, in a pure wliite-flowered 

 race, each individual transmits to its progeny the tendency to pro- 

 duce white flowers. But what of the hybrid between two such 



165 



