4 Weiss, Researches on Heredity in Plants. 



Of these the first three contain the dominant character, 

 whether derived from the egg cell or the pollen grain, and 

 would consequently all appear alike and resemble the 

 dominant parent; while the fourth individual would receive 

 a double dose of the recessive character and be purely 

 recessive. Thus the simple numerical ratio of 3 to i 

 would be accounted for, and this explanation is in harmony 

 with the fact that during the development of the repro- 

 ductive cells of plants and animals, we have a remarkable 

 reduction in the complexity of the nucleus, generally 

 taken to be the carrier of hereditary character, which 

 might well correspond with the assumed segregation of 

 parental characters. 



Further consideration of the nature of the three 

 dominant forms produced by the four possible combina- 

 tions of unit character will show that only the first {Dd), 

 which obtained its dominant character from both its 

 parents, is a pure bred dominant (homozygous), while the 

 other two {Dr and Rd) are, like the first hybrid genera- 

 tion, impure, containing the recessive constituent derived 

 in one case from the male and in the other case from 

 the female parent. If fertilised with their own pollen 

 they would therefore in the next generation (_/3) segregate 

 out exactly as f i had done when self-fertilised. This, 

 too, was clearly proved by Mendel, and has been repeatedly 

 confirmed. Of the 75 % of dominants in the f2 genera- 

 tion, only 25 % are pure and breed true. 



The two laws of dominance of certain unit characters 

 in the first hybrid generation and of segregation of the 

 characters in the second hybrid generation Mendel found 

 to be true for a variety of racial characteristics in peas, 

 such as colour of the seed coat, colour of the cotyledons, 

 difference in the form of the ripe pods, etc. Since the 

 rediscovery of Mendel's work, they have been shown to 



