184 BREEDING CROP PLANTS 



Xenia may result from crossing varieties which differ in a 

 single visible endosperm character. When a character difference 

 is dependent on a single dominant factor, xenia occurs only when 

 the factor is carried by the male parent, or, when dominance is 

 incomplete, xenia results when either variety is the male. When 

 a character difference is dependent on more than one factor, all 

 located in one parent, and dominance appears complete, xenia 

 occurs only when these differential factors are located in the 

 male; when dominance is incomplete, xenia occurs if the factors 

 are located in either parent. When two varieties have a similar 

 character or a different character expression but contain between 

 them endosperm factors necessary for the production of a new 

 character, xenia occurs when either variety is the male. 



The inheritance of an intermediate starchy-sweet (called 

 pseudo-starchy) condition, which is often present in some sweet 

 corn ears, has been studied by Jones (1919). Three factors were 

 shown to explain the results: (1) a plant factor, A, necessary for 

 complete expression of the so-called pseudo-starchy character; 

 (2) an endosperm factor, B, which prevents the characteristic 

 shrinking of sweet seeds; (3) an endosperm factor, C, determining 

 opaqueness. C gives complete dominance, while A and B give an 

 intermediate condition when heterozygous, and B in addition 

 shows a cumulative effect in proportion to the number of factors 

 involved. C and c give the greatest differential effect only 

 in the presence of the homozygous condition for A and B. From 

 this brief discussion it is easy to see that reciprocal crosses 

 between AABBcc X aabbCC will not give like results. AABBcc 

 fertilized with aabbCC will give an endosperm condition ABBbcC, 

 while the reciprocal cross will give abbBCc. As A is necessary 

 for recognizable expression of pseudo-starchiness, one cross 

 will show xenia while its reciprocal will not. 



The following endosperm characters have been studied and 

 the results are briefly summarized. (See Table XXXIX.) 



The cross between the waxy variety of Chinese maize and 

 American sweet varieties is of interest, as in FI maize with a 

 corneous endosperm was obtained, while in F% a ratio of 9 

 horny to 4 sweet to 3 waxy seeds was obtained. Many starchj^- 

 sweet crosses have been studied and as yet no case has been 

 obtained which showed more than a single main factor difference. 

 Apparently the sub-species, Z. mays saccharata, differs by only 

 a single main factor from the starchy subspecies. 



