Heredity 191 



was found in the fact that two plants, each totally devoid 

 of color in the flowers and stems and each breeding true 

 to albinism may, when crossed together, give purple 

 flowers in FI. The two white parents each contain a 

 factor which, alone, is incapable of forming color. Each 

 of these factors is independently transmitted in gameto- 

 genesis, and thus in F 2 the ratio of colored individuals to 

 whites is 9:7. This proportion depends on the fact that 

 a series of 16 individuals is necessary to exhibit all the 

 possible combinations of germ cells, for, as in any example 

 of hybridization involving two pairs of allelomorphs, 

 there will be four types of female cells and four types of 

 male cells produced by FI. Of these sixteen individuals, 

 9 will contain both the dominant or present factors, while 

 of the remaining seven individuals, 3 will contain one 

 dominant, 3 will contain the other, and 1 will contain 

 neither. There will, therefore, be 9 which are colored 

 and 7 which are albino. In the diagram (p. 192) C 

 and R are the symbols representing the two comple- 

 mentary factors, c and r being their respective allelomor- 

 phic absences. 



Absence factors. It may be well for us in this connection 

 to touch upon the different conceptions of several investiga- 

 tors on such characters as cannot be seen without resorting 

 to breeding tests. Tschermak considers the appearance of 

 mottling in FI between a white and self-colored varieties 

 due to the presence of mottling in a latent condition in 

 the self-colored variety. Latency in his view is inactivity. 

 Shull often speaks of latent characters, but latency, 

 according to him, means invisibility and not dormancy or 

 inactivity. 



