18 MENDELISM chap. 



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 fail- 

 ure he was careful to avoid, and throughout his experi- 

 ments he crossed plants presenting sharply contrasted 

 characters, and devoted his efforts to observing the be- 

 haviour of these characters in successive generations. 

 Thus in one series of experiments he concentrated his at- 

 tention on the transmission of the characters tallness and 

 dwarfness, 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 ij feet. Previous testing had 

 shown that each strain bred true to its peculiar height. 

 These two strains were artificially crossed * with one an- 

 other, 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 



1 Cf. note on p. 171. 



