382 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 
the total, or almost total, exclusion of the other. No intermediate 
forms appeared. 
Mendel called the character that prevailed dominant, and the 
character that was suppressed, or apparently suppressed, recessive. 
And the first big result was that crosses between a plant with the 
dominant character and a plant with the recessive character yielded 
offspring all resembling the dominant parent as regards the character 
in question. Let us for shortness call the parents D and R, and the 
first result may be expressed thus: DXR=D. 
It must be carefully noted that the complete dominance which 
Mendel observed has been shown in other cases to be the exception 
rather than therule. Thusa cross between a “Chinese” primula with 
wavy crenated petals and a “star” primula with flat simply notched 
petals is intermediate between the two parents; and yet, as the next 
generation shows, the case is one of Mendelian inheritance. 
In many cases the hybrid, while on the whole dominant, may show 
some influence of the recessive character but not nearly enough to 
warrant us in speaking of a blend. Thus, when white (dominant) 
Leghorn poultry are crossed with brown (recessive) Leghorn, most of 
the offspring have some “ticks” of colour. When these are inbred 
they produce a quarter brown (extracted recessives) and three- 
quarters pure white or white with a few ticks. The dominance is not 
quite perfect. 
The Law of Splitting or Segregation.—In the next generation the 
cross-bred plants (products of D and R, or R and D, but all apparently 
like D) were allowed to fertilise themselves, with the result that their 
offspring exhibited the two original forms, on the average three domi- 
nants to one recessive. Out of 1,064 plants, 787 were tall, 277 were 
dwarfs. 
When these recessive dwarfs were allowed to fertilise themselves 
they gave rise to recessives only, for any number of generations. The 
recessive character bred true. 
When the dominants, on the other hand, were allowed to fertilise 
themselves, one-third of them produced “pure” dominants, which in 
subsequent generations gave rise to dominants only; and two-thirds 
of them produced once again the characteristic mixture of dominants 
and recessives in the proportion of 3:1. 
The general results may be expressed in the scheme. The 
result of the hybridisation is a generation (F,) like the dominant 
parent. They may be represented by the symbol D(R), for they 
