298 PLANT HYBRIDIZATION BEFORE MENDEL 



fertilization. The algebraic multiplication of these two series sim- 

 ply represents the fact that both B and b unite with A, lAa and 

 a and so on. 



Since the segregation of the offspring of a self-fertilized hybrid 

 involving one pair of characters, a dominant D and recessive r, 

 gives us a total of 3 apparent D's to 1 r, or the familiar ratio 

 of 3:1, then two pairs of opposing characters, thus segregating, 

 would give a ratio of 9:3:3:1, which is plainly the result of 

 the combination of two 3 : 1 ratios, this being the result obtained 

 by multiplying together the ratios in w'hich each of the character- 

 combinations separately occurs. Taking, for example, the charac- 

 ters round (D) and wrinkled (r) : and yellow (D) and green (r) : 



In the F2 generation, there are 3 yellows to 1 green in every 4, 

 and there are 3 round to 1 wrinkled in every 4. 



Where both of these two sets of character-pairs are united in 

 the same hybrid, the numerical proportions of the character- 

 combinations, so far as appearances go, will necessarily then be 

 as follows : 



Yellow and round 3X3 — 9 



Yellow and wrinkled 3 X ' = 3 



Green and round 1 X 3 — 3 



Green and wrinkled 1 X 1 -— 1 



In the detailed analysis we will have : 



1. Yellow round 



(1) pure as to color and form l 



(2) pure as to color but not as to form 2 



(3) pure as to form but not as to color 2 



(4) hybrid in both respects 4 



Yellow wrinkled 



(1) pure as to color and form l 



(2) pure as to form but not as to color 2 



Green round 



(1) pure as to both color and form 1 



(2) pure as to color but not as to form 2 



