1 8 THE FAMILY AND THE NATION 



to hold for certain qualities in peas, and to follow 

 definite laws of inheritance. His results have been 

 extended to other species of plants and animals by 

 recent observers. 



As an example of Mendelian principles let us take 

 the case of the Andalusian fowl, studied by Bateson 

 and Punnett. Black and splashed white Andalusians 

 each breed true when mated together ; we possess then 

 a definite splashed white breed and a definite black 

 breed. If we cross a white bird with a black, the 

 resulting chicks are all blue. So far the result seems 

 simple, and we are inclined to regard blue in these 

 fowls as an intermediate hybrid colour between black 

 and white. But, if we breed further generations exclu- 

 sively from these blue birds, we find that they do not 

 breed true to type — no definite blue race can be estab- 

 lished. Of a large number of birds with two blue 

 parents, on the average, half will be blue, one quarter 

 will be white, and one quarter black. Now, these white 

 and black birds, though derived from blue ancestors, 

 will once more breed true, just as did the white and 

 black of the first generation. By mating together two 

 white birds, we can re-establish a pure splashed-white 

 strain, which shows no sign of its blue ancestry ; and 

 similarly we can recover a pure black strain, uncon- 

 taminated by blue to any number of generations. 



If we think what these phenomena must mean in the 

 hereditary process, we are led to conclude that the germ 

 cells of the blue birds are not hybrids like the birds 

 themselves. Half the germ cells of a blue bird must 

 be pure " white " in character, half pure " black." 

 Then, when two blue birds pair, it is an even chance 



