MENDEL'S EXPLANATION 163 



duction of the character represented by that factor 

 in the germ cell. 



Now, what happens when a germ cell bearing the 

 factor for tallness unites with a germ cell bearing 

 the factor for dwarfness ? We know the answer to 

 this question. A tall pea is produced. The fertilised 

 egg contains in this case, as in the others, two factors ; 

 but one is the factor for dwarfness, and the other 

 that for tallness. But the latter seems to dominate 

 completely over the former, and allows it no share in 

 determining the stature of the plant ; for the hybrid 

 tall pea which is produced is indistinguishable from 

 its pure tall parent, except that it possesses the 

 exceptional vigour which is characteristic of hybrids, 

 and is often a little taller than its pure tall parent. It 

 should be noted that the result of crossing " female 

 dwarf " with " male tall " is the same as that of cross- 

 ing " male dwarf " with " female tall." In technical 

 parlance, the reciprocal crosses are identical. We have 

 now to consider the condition in which these factors 

 exist in the germ cells produced by the hybrid tall. And 

 in so doing we get to the kernel of Mendel's theory. 

 It might be expected that one kind of factor occurred 

 in all the germ cells, and that this factor represented 

 a mixture between tallness and dwarfness ; or it 

 might be concluded from the fact that the hybrid 

 itself was tall that all its germ cells contained the 

 factor for tallness, and that the dwarf factor had 

 been eliminated altogether. Neither of these views 

 were held by Mendel. He supposed that half of the 

 germ cells, produced by the hybrid, contained the 



