61 EVOLUTION AND GENETICS 



were three such kinds of second generation indi- 

 viduals by following them into the next (third) gen- 

 eration. Had he been fortunate enough to have 

 worked with a form like the four o'clock where the 

 1:2:1 ratio is apparent in the second generation 

 this relation would probably have been seen without 

 carrying the experiment one generation further. 



T.ll Tall 



Fig. 22. — Diagram illustrating the results of self-pollination of the 

 F^ plants of fig. 31, The results show that one of the tall F., plants is 

 pure for tall (tall-tall), that two of them are hybrid or heterozygous, 

 and that one is pure for short (short-short). 



Mendel also crossed yellow and green peas (fig. 

 23 ) . He crossed a plant belonging to a race having 

 yellow peas with one having green peas. The hybrid 

 plants had yellow seeds. These hybrids inbred gave 

 three yellows to one green seed. The explanation of 

 the results with peas is the same as that given for the 



