PHENOMENA OF INHERITANCE 231 



ation is indicated by the letter P, and the suc- 

 cessive filial generations by F lt F 2 , F 3f etc. 



In the case of the peas studied by Mendel 

 the hybrids of the Fi generation show only the 

 dominant character, the contrasted recessive 

 character being present but not expressed. 

 However in certain cases it has been found 

 that the hybrids differ from either parent and 

 in successive generations split up into both 

 parental types and into the hybrid type; thus 

 Correns found that when a white-flowered va- 

 riety of Mirabilis., the four o'clock, was crossed 

 with a red-flowered variety all of the hybrids 



D R D R 



Parent Generation ^^O X O Homozygotes 



D(]g# Heterozygotc* . 



FIG. 49. Diagram showing results of Mendelian splitting 

 where the parents are pure dominants and pure recessives 

 (homozygotes). All pure dominants are represented by black 

 circles, all pure recessives by white ones, while mixed domi- 

 nant-recessives (heterozygotes) are represented by circles half 

 white and half black. Successive generations are marked F l5 

 F 2 , F,, etc. 



