60 EVOLUTION AND GENETICS 



cells. Half of the egg-cells are white-bearing, half 

 red-bearing. Half of the pollen-cells are white- 

 bearing, half red-bearing. Chance combinations at 

 fertilization give the three classes of individuals of 

 the second generation. 



The white-flowering plants should forever breed 

 true, as in fact they do. The red-flowering j)lants 

 also breed true. The pink-flowering plants, having 

 the same composition as the hybrids of the first gen- 

 eration, should give the same kind of result. They 

 give, in fact, this result, i.e., one white-, to two 

 pink-, to one red-flowered offsj^ring (fig. 18). 



Another case of the same kind is known to breed- 

 ers of poultry. One of the domesticated breeds is 

 known as the Andalusian. It is a slate-blue bird 

 shading into blue-black on the neck and back. Poul- 

 try men have known for a long time that tliese blue 

 birds do not breed true but ^^roduce white, black, and 

 blue offspring. The explanation of the failure to 

 produce a pure race of Andalusians is that they are 

 like the pink flowers of the four o'clock, i.e., they 

 are a hybrid type formed by the meeting of the white 

 and the black germ-cells. If the whites produced by 

 the Andalusians are bred to the blacks, all the off- 

 spring will be blue (fig. 19) . 



When two such blue colored hvbrid birds are 

 bred to each other, chance fertilization of any egg 

 by any sperm (fig. 20) will give one pure white, to 

 two hybrid blues, to one pure black. 



