i8o 



BREEDING 



No. 2 represents the true-breeding of pure recessives, 

 according to a precisely analogous scheme in which 

 R is substituted for D. No. 3 represents the cross- 

 ing of DD with RR, according to this scheme : — 



(J gametes 

 D D 



(J gametes 

 K K 



R 



Of 



R 



D 



05 



or § 



Of 



D 



and No. 4 represents the mating together of these 

 hybrids, which has abeady been represented in this 

 scheme on p. 177. Nos. 5 and 6 have not yet been 

 dealt with, and are very important for more reasons 

 than one. 



One feature which these two types of mating 

 possess in common is so simple that even when it 

 is noticed at all it is usually passed over with a 

 few words. Yet this feature has, in my opinion, a 

 very important bearing. Although these two types 

 of mating are usually considered last, as a not very 

 important corollary to the Mendelian theory, they 

 possess this feature in common, that of all the six 

 matings, in the above Table, in which the forms mated 

 differ from one another (i.e. in all except 1 and 2) 

 they are the only two in which the two parental 



