296 Retrograde Varieties 



ity and the other half ovules with the opposite 

 latent mark. 



Calling P pollen and ovules, and represent- 

 ing the active mark by P and 0, the latent qual- 

 ities by P' and 0', they would combine as fol- 

 lows : 



P -F giving uniform pairs with the active mark, 



P -|- O' giving unequal pairs, 



P' + O giving unequal pairs, 



P' + 0' giving uniform pairs with the latent mark. 



In this combination the four groups are ob- 

 viously of the same size, each containing one- 

 fourth of the offspring. Manifestly they corre- 

 spond exactly to the direct results of the 

 experiments, P + representing the indi- 

 viduals which reverted to the specific mark, 

 P'+O' those who reassumed the varietal 

 quality and P-fO' and P+0' those who hybrid- 

 ized for the second time. These considerations 

 lead us to the following form of Mendel's 

 formula : 



P -fO =l/4-Active or I A, 



P -1-0') 



P' + O = 1/2-Hybrid or 2 H, 



P' + O' = 1/4-Latent or I L, 



Which is evidently the same as Mendel's 

 empirical law given above. 



To give the proof of these assumptions Men- 

 del has devised a very simple crossing experi- 



