304 PLANT HYBRIDIZATION BEFORE MENDEL 



hybrids, according to a fixed and unalterable ratio, with the re- 

 sult that by the tenth generation, there will be a practical elimina- 

 tion of the hybrid condition in most cases, all of the progeny 

 having been segregated into various combinations of dominants 

 and recessives. 



Hybrids in which tzuo pairs of characters are concerned : results of 

 MendeV s experiments, 



Mendel next undertook to determine the behavior of hybrids in 

 which more than one differentiating pair of characters was con- 

 cerned. To determine what would happen in such a case, he under- 

 took two experiments ; in the one, the parents differed in the form 

 and in the color of the seed (i.e., of the cotyledons within the seed 

 coat), involving therefore two differentiating characters in each 

 cross. In the second experiment, the seeds of the two parents dif- 

 fered in form^ in color ^ and in the color of the seed coats : thus 

 involving three pairs of differentiating characters in each cross. 



For convenience' sake, in the first experiment, Mendel used the 

 following symbols : 



A. round seed form a. wrinkled seed form 



B. yellow seed color b. green seed color 



In the F^ generation all the seeds produced were round and 

 yellow, as would have been expected from the fact that round 

 when taken singly is dominant over wrinkled, and yellow when 

 taken singly is dominant over green. 



The fifteen plants raised from these yellow round seeds, yielded, 

 however, four kinds of seeds^ 556 in all, distributed in the follow- 

 ing way : 



Ratio (^approximate) 



315 round and yellow AB 9 



101 wrinkled and yellow aB 3 



108 round and green Ab 3 



32 wrinkled and green ab 1 



All of these 556 seeds were sown in the following year. The 

 plants that came to maturity, were distributed with regard to the 

 kinds of seeds they bore, as follows : 



