First z's. Second Hybrid-Generation 253 



matter naturally gets the equivalent inactive unit as an 

 antagonist. With this it must therefore be exchanged. 

 We assume that in this the latent condition is without 

 significance, that hence the exchange comes about in the 

 same manner as in normal fertilization. 



Over this, however, the crossings of varieties have the 

 great advantage that there the origin of the characteris- 

 tic in question can always be clearly and positively rec- 

 ognized. Both units of a pair of antagonists are other- 

 wise distinguished only by a more or less of development, 

 here by a sharp contrast. And for this reason it is experi- 

 mentally much easier to discover the laws with varieties 

 than with purely individual differences. 



In doing this, two points have to be distinguished ; the 

 consequences of fertilization and the consequences of the 

 exchange of the units. The former we see in the hybrid 

 itself, the latter in its descendants.^ And since fertiliza- 

 tion and exchange are two such fundamentally different 

 things, we must not wonder that there exist such decided 

 differences between a hybrid and its descendants. These 

 differences show themselves essentially by the fact that 

 the hybrids of a mother-species with a variety of the same 

 are alike, even if they are obtained in great numbers, 

 while their descendants always display a certain variety. 



Let us first consider the first generation of variety- 

 hybrids. How do the two pronuclei, notwithstanding 



^In the fertilized egg, resulting from the crossing, the chromatin 

 from the male and female parents is not completely fused. As pointed 

 out in a preceding footnote (p. 240), this fusion, called synapsis, 

 occurs as almost the last step preceding the nuclear and cell-divisions 

 that give rise to the reproductive cells. The characters of the first 

 hybrid generation are a result of fertilization. Following synapsis, 

 the pure bred offspring of this generation differ from their parents 

 and also among themselves. Tr. 



