1 6 MENDELISM chap. 



characters in which the various races of peas differ 

 from one another. 



In planning his crossing experiments Mendel 

 adopted an attitude which marked him off sharply 

 from the earlier hybridisers. He realised that their 

 failure to elucidate any general principle of heredity 

 from the results of cross fertilisation was due to 

 their not having concentrated upon particular 

 characters or traced them carefully through . a 

 sequence of generations. That source of failure 

 he was careful to avoid, and throughout his ex- 

 periments he crossed plants presenting sharply 

 contrasted characters, and devoted his efforts to 

 observing the behaviour of these characters in 

 successive generations. Thus in one series of ex- 

 periments he concentrated his attention on the 

 transmission of the characters tallness and dwarf- 

 ness, neglecting in so far as these experiments were 

 concerned any other characters in which the parent 

 plants might differ from one another. For this 

 purpose he chose two strains of peas, one of about 

 6 feet in height, and another of about i^ feet. 

 Previous testing had shown that each strain bred 

 true to its peculiar height. These two strains were 

 artificially crossed ^ with one another, and it was 

 found to make no difference which was used as the 

 pollen parent and which was used as the ovule 

 parent. In either case the result was the same. 

 The result of crossing tall with dwarf was in every 

 case nothing but tails, as tall or even a little taller 

 than the tall parent. For this reason Mendel 

 termed tallness the dominant and dwarfness the 

 ' Cf. note on p. 171. 



