PLANT HYBRIDIZATION BEFORE MENDEL 



299 



4. Green wrinkled 



(1) pure as to both color and form 



Total number of types 



1 



I 



16 



We may now use the customary table of squares to represent 

 the possible number of zygote forms that are derived from a 

 given number of characters carried by the gametes. 



Let us continue to take round and wrinkled, and yellow and 

 green as the character-pairs. We may then represent the F^ gen- 

 eration as being formed in the following way, where a plant bear- 

 ing the characters green and wrinkled is fertilized by pollen from 

 a plant bearing the yellow and round characters in its germ cells. 



Male gametes 

 AB 



Female 

 gametes 



Likewise, let us suppose the reciprocal cross, where a plant 

 bearing yellow and round characters, is fertilized by pollen from 

 a plant bearing the characters green and wrinkled. We then have : 



Male gametes 

 ab 



Female 



gametes 



AB 



In both cases, as is plain, the zygote will theoretically have the 

 same character and appearance, AaBb. If we wish to show the 

 actual condition of things in the zygote, we may use the custom- 

 ary four-square table, indicating the dominant and recessive char- 

 acters by D and r. 



