THEORY OF EVOLUTION 43 



history it would be quite impossible to state 

 what the ancestry of the white or of the red 

 had been, for they might just as well have come 

 from pure white and pure red ancestors respec- 

 tively as to have emerged from the pink hy- 

 brids. Moreover, when we test them we find 

 that they are as pure as are white or red flower- 

 ing plants that have had all white or all red 

 flowering ancestors. 



Mendel's Law explains the results of this 

 cross as shown in figure 14. 



The egg cell from the white parent carries 

 the factor for white, the pollen cell from the red 

 parent carries the factor for red. The hybrid 

 formed by their union carries both factors. 

 The result of their combined action is to pro- 

 duce flowers intermediate in color. 



When the hybrids mature and their germ 

 cells (eggs or pollen) ripen, each carries only 

 one of these factors, either the red or the white, 

 but not both. In other words, the two factors 

 that have been brought together in the hybrid 

 separate in its germ cells. Half of the egg 

 cells are white bearing, half red bearing. Half 

 of the pollen cells are white bearing, half red 



