in 



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 purity of 

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

 We may now proceecl 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 

 of the gametes, and to & ametes 

 see how far they are 

 in accordance with 

 the facts. Since the 

 original tall plant 

 belonged to a strain 

 which bred true, t all 

 the gametes produced 

 by it must bear the tall 

 character. Similarly 

 all the gametes of the 

 original dwarf plant 

 must bear the dwarf 

 character. A cross between these two means the union of 



\ 



CL 



Q gametei 



F, 



to 



F 2 



generation 

 FIG. i. 



Scheme of inheritance in the cross of tall with dwarf 

 pea. Gametes represented by small and zygotes 

 by larger circles. 



