The Endosperm in InJieritance 145 



cal or physiological nature of endosperm, but he is much 

 concerned about its behavior in inheritance. J*erhaps 

 the phenomena of endosperm inheritance may help to 

 decide whether endosperm is gametophyte or sporophy te 

 or neither. 



Certain races of corn have yellow endosperm, while 

 in other races it is white (colorless). If a cross is made 

 with pollen from the yellow endosperm race on the silks 

 of the white endosperm race, what results would be 

 expected ? We could assume that yellow is dominant 

 over white, since yellow is probably due to the presence 

 of a factor which is absent in white. In making such a 

 cross, therefore, we should expect a hybrid embryo to be 

 formed which would show the dominant character of 

 yellow endosperm when this embryo becomes a plant 

 bearing ears the next season. On the contrary, we tind 

 the dominant yellow character appears the same year 

 that the cross is made. The cross, of course, puts the 

 yellow endosperm factor in the young hybrid embryo, 

 but we cannot imagine that this embryo passed the 

 character out into the endosperm that surrounds it. 

 The real mechanism is as follows. 



Some time after this phenomenon was discovered in 

 1872, it was named xenia (in 1881), the definition of the 

 term being the direct effect of foreign pollen upon the 

 endosperm. At the time of its discovery the mechanism 

 involved in xenia was not understcK>d. Later, double 

 fertilization was discovered, and this furnished the neces- 

 sary mechanism. A pollen grain from the yellow endo- 

 sperm race contains two male gametes, and each gamete 

 contains the factor for yellow endosjHTin. One of the 

 gametes fertilizes the egg and produces a hybrid embryo, 



