m MENDEL'S WORK 21 



conceived of the gametes as bearers of something capable 

 of giving rise to the characters of the plant, but he re- 

 garded any individual gamete as being able to carry one 

 and one only of any alternative pair of characters. A 

 given gamete could carry tallness or dwarfness, but not 

 both. The two were mutually exclusive so far as the 

 gamete was concerned. It must be pure for one or the 

 other of such a pair, and this conception of the puritv of 

 the gametes is the most essential part of Mendel's theory. 

 We may now proceed with the help of the accompany- 

 ing scheme (Fig. i) to deduce the results that should flow 

 from Mendel's con- ^^^ □„„, 



ception of the nature P"^"* J|_ JJ^-p.rent 



of the gametes, and to ^^"^'^^i"^ O O^^""'"" 



see how far they are \ >.'' 



in accordance with ^ -^J-^ ' 



the facts. Since the _^'' ^"=';:_._^ 



original tall plant fc»— -^^^— -©fc 



belonged to a strain 1^ — s- O "^ O -^ 



which bred true, all <? „ ^^ _ § 



the gametes produced % ^ 



by it must bear the tall I O— -^ Q)^----0'S, 



F 

 character. Similarly generltion 



all the gametes of the Fig- i- 



. . 1 J r 1 . Scheme of inheritance in the cross of tall with dwarf 



original UWari plant p^^ Gametes represented by small and zygotes 



must bear the dwarf "y wger circles. 



character. A cross between these two means the union of 



