xiv ECONOMICAL 155 



ber is raised, and of all these different varieties a certain 

 proportion of each is already fixed. Heredity is a ques- 

 tion of individuals, and the recognition of this will save 

 the breeder much labour, and enable him to fix his varie- 

 ties in the shortest possible time. 



Such cases as these of the sweet pea throw a fresh light 

 upon another of the breeder's conceptions, that of purity 

 of type. Hitherto the criterion of a " pure-bred" thing, 

 whether plant or animal, has been its pedigree, and the in- 

 dividual was regarded as more or less pure bred for a given 

 quality according as it could show a longer or shorter fist 

 of ancestors possessing this quality. To-day we realise 

 that this is not essential. The pure-bred picotee appears 

 in our F 2 family though its parent was a purple bicolor, 

 and its remoter ancestors whites for generations. So also 

 from the cross between pure strains of black and albino 

 rabbits we may obtain in the F 2 generation animals of the 

 wild agouti colour which breed as true to type as the pure 

 wild rabbit of irreproachable pedigree. The true test of 

 the pure breeding thing lies not in its ancestry but in the 

 nature of the gametes which have gone to its making. 

 Whenever two similarly constituted gametes unite, what- 

 ever the nature of the parents from which they arose, the 

 resulting individual is homozygous in all respects and 

 must consequently breed true. In deciding questions of 

 purity it is to the gamete, and not to ancestry, that oui 

 appeal must henceforth be made. 



