Experimental Hybridizing 67 



heredity and evolution were being actively discussed during 

 that time. It was not until 1900 that de Vries, and simul- 

 taneously Correns and Tschermak, independently obtained re- 

 sults that brought to light again the long- forgotten discoveries 

 of Mendel. 



Mendel found that when the flowers of one race of peas are 

 fertilized artificially with pollen from another race, the hybrid 

 offspring {F^ of the first generation are like one of the parents 

 in each particular character, and not intermediate in character. 

 If, however, these hybrids were self-fertiKzed or inbred, both 

 grandparental types reappeared in their offspring (^2)' ^^^ 

 in definite proportions. The character of one of the parents 

 that appears in the first hybrid generation [F^ is called the 

 dominant^ and the contrasted character of the other parent that 

 disappears in the first hybrid generation is called the recessive- 

 When these first hybrids are inbred as stated above, there ap- 

 pears in the second generation of hybrids {F^ three individuals 

 showing the dominant character to one individual showing the 

 recessive. This, however, is by no means the whole discovery ; 

 for Mendel found that the recessives of this second generation, 

 if inbred, give always recessives and nothing else. Those that 

 show the dominant character, on the other hand, do not all 

 breed true. A third only are pure and give rise only to domi- 

 nants, while two- thirds of them produce both dominants and 

 recessives. The matter can be graphically expressed as fol- 

 lows : — 



If we call the dominant character A^ the recessive 5, then the 

 first generation {F^ of hybrids will be A{B). This means that 

 while the hybrids show outwardly only the dominant character 

 A, the recessive character {B) is also present in an undeveloped 

 condition. When these hybrids {F^ are inbred, the ^-char- 

 acter dominates in one fourth of the offspring, the ^-character 

 in one fourth, and the A{B) character in two fourths, i.e. in 

 the proportion of 1:2:1. Mendel showed by a simple 



^ In practice A{B') can only be distinguished from A by the kind of progeny 

 that each produces. 



