252 Fertilisation and Hybridisation 



stant varieties to the species from which they are derived, 

 is therefore quite different from that of the constant 

 varieties. 



Nevertheless, the two crossings behave in the same 

 manner in regard to their mother-species. From the lat- 

 ter they are distinguished, for the most part, only in one 

 point, though sometimes in several. But we have always 

 to deal with the distinction between active as contrasted 

 with latent, be it that the given character is active in the 

 variety and latent in the mother-species, or latent in the 

 former and active in the species itself. 



If to this we apply the conception of the arrangement 

 of the units in rows on the nuclear threads, as explained 

 above, it is quite evident that everything will follow ex- 

 actly the same course as in normal fertilization. Every 

 unit in the paternal pronucleus corresponds to the repre- 

 sentative of the same peculiarity in the maternal one. 

 The nuclear threads fit as nicely into each other as in a 

 pure species, and all the units which do not directly bring 

 about the point of difference behave quite normally. Co- 

 operation in vegetative life, and exchange during the 

 formation of the sexual cells need not be disturbed. We 

 may confine our whole consideration to the point of dif- 

 ference, and we shall select, for the purpose, as simple 

 an illustration as possible, one in which there is only one 

 difference between the species and the variety, for exam- 

 ple, the color of the flower. 



The material bearer of the color-characteristic is situ- 

 ated in the mother-species so that it can display its full 

 activity while in the variety it is unable to do so. If the 

 paternal and maternal nuclear threads of the hybrid come 

 into contact for the purpose of exchange, and with the 

 same sequence of units in both, the active unit of coloring 



