59 



BY X BY 

 " X By 

 " X bY 



" X 

 X 

 X 

 X 



By 



by 

 BY 



By 



by 



b Y 



by 



X by = 



X B Y = 



X By 



X b Y = 



X by = 



X B Y = 



X By 



X b Y = 



X by = 



Black ( + Yellow but yellow hidden) 



Black ( + yellowish) 



Black (+ yellow) 



Black (+ yellowish) 



Black (+ yellowish) 



Black (pure) 



Black (+ yellow) 



Black . 



Black (+ yellow) 



Black (+ yellowish) 



Yellow 



Yellowish 



Black (+ yellowish) 



Black 



Yellowish 



White 



F 2 : 12 B; 3 Y. Yellowish; 1 white. 



Constant B 

 Constant B. 

 3 B: 1 y. 

 12 B: 3 y. 1 w. 

 Constant B. 

 Constant B. 

 12 B; 3 y; 1 w. 

 3 B.; 1 w. 

 3 B; 1 w. 

 12 B. 3 y. 1 w. 

 Constant Y. 

 3 Y; 1 w. 

 12 B; 3 Y. 1 w. 

 3 B., 1 w. 

 3 Y; 1 w. 

 Constant W. 



Twelve out of the 16 zygotes contain "B" but not "Y" and are thus 

 pure Blacks. Three contain "Y" but not "B" and are thus pure Yellow. 

 Nine contain "B" and "Y," but since "B" is dominant over "Y" they are 

 all Black or Blackish. Finally one contains neither Black nor Yellow, and 

 is White. The above scheme illustrates clearly the manner in which new and 

 strange forms may arise either under domestication or in nature. 



When the white-kernelled sort No. 0315 was crossed with the Black 

 Moss variety (No. 0670), there were obtained not only Blacks and Whites 

 but Greys as well. The proportions obtained moreover corresponded with 

 those peculiar to a dihybrid combination. The actual proportion in this case 

 was 187 black, 38 grey and 17 white, or 11 black, 2 .2 grey, 1 white (49, p. 25). 

 The assumption here is that this particular sort possesses not only a unit for 

 Black color but also a unit for grey, although the grey is hidden until brought 

 into certain combinations when it appears as a new character. The following 

 dihybrid scheme is submitted as explaining the situation: 



Sort No. 0315 



O (white) 



(absence of black) b 

 (absence of grey) g 



Sort No. 0670$ (black) 

 B (Presence of Black) 

 G (Presence of Grey) 



Here we have represented four possible combinations which may go 

 to form four different kinds of pollen cells and four of egg-cells, viz.: 6 G, 

 b g, B G, B g. Whenthese four kinds of pollen cells and four kinds of egg-cells 

 are brought together the sixteen combinations peculiar to a dihybrid cross- 

 ing are made, the combinations bGXbG, bGXbg and b g X b G 

 representing the "new" grey forms. 



