280 THE CONTINUITY OF THE RACE 



were grown, all the plants were fully as tall as the tall parent and none 

 resembled the dwarf parent. These tall offspring were allowed to self- 

 fertilize and produce seed without interference. 



The F 2 ("grandchildren") of the monohybrid cross. When the seeds 

 from the F\ generation were planted, they produced an F 2 (or grandchild) 

 generation that consisted of both tall and dwarf plants. When Mendel 

 counted the number of tall and of dwarf individuals in this generation, he 

 found that approximately % were tall and approximately 34 were dwarf. 



Repetition of the same experiment gave the same results. Mendel 

 found that it made no difference whether he took the pollen from the 

 dwarf variety and placed it on the stigmas of the tall variety or took 

 pollen from the tall variety and placed it on the stigmas of the dwarf 

 variety. In all cases the immediate offspring, the Fi, were all tall, and 

 the grandchildren, the F 2 , were approximately 3 ^ tall and 34 dwarf. Fur- 

 ther, he discovered that if he planted all the seed produced by the dwarf 

 plants of the F 2 , they would produce only dwarf plants. When, however, 

 he planted the seeds produced by the tall plants of the F 2 , he found that 

 the seeds from approximately one-third of these tall plants produced only 

 tall plants but that the seeds from the other two-thirds produced, on the 

 average, % tall plants and 34 dwarfs. 



Mendel then made similar crosses between other varieties that showed 

 contrasted qualities. A cross between the yellow-seeded and green-seeded 

 varieties produced only yellow-seeded individuals in the F\ generation 

 and a ratio of % yellow-seeded and 34 green-seeded, in the F 2 generation. 

 Another cross, that between the wrinkled-seeded and round-seeded 

 varieties, produced an F\ that were all round-seeded and an F 2 that were 

 % round-seeded and 34 wrinkled-seeded. 



In all, seven sets of contrasted characters were found and crossed, and 

 all the crosses showed a number of features in common : 



1. In all crosses the original parents were from varieties that, until 

 crossed, invariably bred true to the quality in question. 



2. The crosses were all between varieties that differed from each other 

 in regard to one particular pair of characters: tall versus dwarf, yellow 

 versus green, round versus wrinkled, etc. 



3. The members of the F x generation were all alike and resembled one 

 of the parents to the exclusion of the other. 



4. The members of the F 2 generation were always of two sorts, ap- 

 proximately 3 4 like the F\ and the parent that the F\ resembled, approxi- 

 mately 34 like the other member of the original parent cross. 



5. The smaller group (the 34) of the F 2 generation would breed true 

 if allowed to self-fertilize; approximately one-third of the larger group 

 (the %) of the F 2 would breed true, the other two-thirds again giving a 

 ;4 : 34 ratio of the same contrasted qualities. 



