148 Outline of Genetics 



cuss all of the Mendelian situations in which xenia may 

 occur. An understanding of the underlying mechanism 

 should enable us to analyze such cases and reach a con- 

 clusion as to the expected results. 



A law which East (i) has formulated in reference to 

 xenia is pertinent: ''When two races differ in a single 

 visible endosperm character, in which dominance is com- 

 plete, xenia occurs only when the dominant parent is 

 male (pollen parent). When the two races differ in a 

 single endosperm character, in which dominance is incom- 

 plete, or when they differ in two characters (factors), 

 both of which are necessary for the development of the 

 visible difference, in both of these cases xenia occurs 

 when either parent is male." This may be called the 

 law of ''normal" xenia. What may be called "abnor- 

 mal" xenia should now be considered. 



In connection with some of his work on sweet and 

 starchy corn, East (i) was able to distinguish two distinct 

 races of starchy corn. In one race the starch occurred 

 in a loose powdery or floury condition, while in the 

 other race it was compacted into a hard, flinty, or so-called 

 corneous condition. The two races, therefore, may be 

 spoken of as floury and corneous races of starchy corn. 



East made various crosses between these two races 

 to discover the method of inheritance of the two endo- 

 sperm characters. Naturally such characters would be 

 expected to show xenia. In the following description, 

 therefore, when the Fi generation is referred to, both the 

 hybrid embryo and the hybrid endosperm surrounding 

 it will be included. 



When East used the floury race as the pollen parent 

 and the corneous race as the ovule parent, the Fi genera- 



