38 The Third and Fourth Generation 



9 yellow smooth peas, 3 yellow wrinkled, 3 

 smooth green, and i green wrinkled. This 

 proportion obtained only when large numbers 

 were produced. These results of Mendel's have 

 been repeatedly verified since. 



Mendel could hardly have achieved such 

 very definite results without devising some 

 theory to account for them. He conceived that 

 a pea plant producing yellow peas has some- 

 thing in its every cell that determines the color 

 of the peas to be produced, even in the germ 

 cells which fuse at the time of fertilization. 

 Each character is determined by the presence 

 of a definite substance that acts to produce it. 

 When then the egg of a pea plant normally 

 producing yellow peas is fertilized by the sperm 

 (product of the growth of the pollen grain) of 

 such a plant, the fusion in fertilization might be 

 represented somewhat thus : 



(V) + ® = hry\ 



Egg Sperm Fertilized Egg 



When a pea plant producing yellow peas is 

 crossed with one producing green peas, Mendel 



