Disjunction of Hybrids 255 



course, presuppose self-fertilization. At the formation 

 of the sexual cells the two pronuclei separate ; this happens 

 at the origination of the egg-cells as well as of the sperms. 

 Through exchange, the active units of our differing pair 

 combine partly with new units of the other pairs, and 

 thereby new combinations originate as in ordinary fertili- 

 zation. But if we consider only the differing pair, exactly 

 one-half of the egg-cells must obviously have the pater- 

 nal, and the other half the maternal character. Or, in 

 other words, in one-half of the egg-cells the given charac- 

 ter occurs in the active, in the other in the latent state. 

 Exactly the same is true of the male sexual cells, the 

 sperms, in animals as well as in plants, and independently 

 from the circumstance that in the higher plants the sperm- 

 cells are conducted to the egg-cells in the pollen-tube. 



The male sexual products of a hybrid are therefore 

 unlike each other, and the same holds true of the female. 

 In the simplest case selected both groups consist of two 

 types, in the more complicated cases this number will ob- 

 viously become greater. The paternal and maternal fac- 

 tors of the hybrid become, in its progeny, grandpaternal 

 and grandmaternal. Hence, in regard to the point of 

 difference, one-half of its egg-cells and one-half of its 

 sperm-cells have grandpaternal factors, while the other 

 halves possess grandmaternal ones. 



By means of this principle the composition of the pro- 

 geny in the simple as well as in the complex cases, and for 

 constant as well as for inconstant varieties can be calcu- 

 lated. Thus we obtain the formulae which are now uni- 

 versally known as MendeTs law. 



They indicate, foranygiver!* number of points of dif- 

 ference between two parents, how many children corres- 

 pond to every individual combination of the respective 



