Heredity 179 



RTh ; 9 Red dwarf Hairy, RtH ; 9 yellow Tall Hairy, rTH ; 

 3 Red dwarf smooth, Rth ; 3 yellow Tall smooth, rTh ; 

 3 yellow dwarf Hairy, rtH ;' and 1 yellow dwarf smooth, 

 rth. Of course most of the visible types are multiple, 

 containing both pure and hybrid forms. The number of 

 actually different types is 27 (3 n ) . 



Incomplete dominance. It was stated previously that 

 dominance is due to an unequal potency between the 

 unit-characters associated in a cross, the dominant unit 

 being " stronger" and covering up the weaker unit in the 

 FI generation. 



This is not always the rule, by any means. There are 

 various degrees of equilibrium between the opposed 

 units : if one is much stronger than the other, complete 

 dominance occurs ; if they are of equal potency, we 

 have a form in the first generation which is intermediate 

 between the . two parents. This intermediacy may 

 lean to one parent or the other in proportion to their 

 strength. 



When intermediacy exists, the mendelian ratios are 

 somewhat modified. Instead of having 3 : 1 ratio, we 

 have a 1 : 2 : 1, in which the 2 represents the heterozygous 

 or intermediate forms and the 1's represent the homo- 

 zygous forms. 



If we are concerned with more than one allelomorphic 

 pair, complete dominance may occur in certain units and 

 intermediacy or incomplete dominance in others. 



The commercial carnation is a heterozygous form which 

 is an intermediate between a single type and a type 

 which in commerce is called a " bull-head" or a " buster." 

 This latter is exceedingly double. When the hybrid 



