MENDEL'S TWO LAWS 59 



have had all white- or all red-flowering ancestors. 



Mendel's Law explains the results of this cross 

 as follows: 



The egg-cell from the white parent carries a fac- 

 tor for white, the pollen-cell from the red parent 

 carries a factor for red. The hybrid formed by their 

 union cames both factors. The results of their com- 

 bined action is to produce 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 (fig. 18) , but not 

 both. In other words, the two factors that have been 

 brought together in the hybrid separate in its germ- 



f<39S • O 

 Pollen 9-^6 



r. 





^9 • 



o 



o 

 o 



o 



Fig. 18. — Diagram illustrating the transmission of the 

 factors for red color (here black) and for white (here the 

 open circles) in a cross between red and white flowered 

 four o'clocks. 



