INHERITANCE- IMPRO VEMENT /»' I ' BREEDING i 7 7 

 It is clear that when a female flower carrying a dominant CHAP. 



character such as flintness, or colour of the endosperm, is 

 crossed with pollen from a breed carrying the recessive allelo- 

 morph, it may be impossible to detect that a cross has taken 

 place. 



There are cases, however, in which the recessive allelomorph 

 does modify the dominant, behaving as xenia. In some breeds 

 of dent maize, where there is a large area of crown starch (see 

 chapter XIII. If 608), the yellow when crossedwith white becomes 

 somewhat lighter, xenia appearing as a cap of lighter colour 

 than the homozygous yellow. In some breeds, e.g. Chester 

 County, the modification of colour varies in degree ; some 

 grains have a distinct white cap, others are quite unchanged, 

 and among the remainder numerous intermediate shades 

 occur (Fig. 781;). Where the crown starch is plentiful in the 

 white-grained female parent, xenia may only affect the body 

 of the grain, leaving the white crown-starch unchanged 

 (Fig. 78A). 



When yellow-grained breeds of flour corn (var. amy laced) 

 are crossed with pollen of white-grained breeds of the same 

 variety, the lighter colour of the heterozygote is not confined 

 to the cap, but extends throughout the endosperm. " In this 

 case difference in colour is always great enough to be noticed 

 by a careful observer, in either cross" (East and Hayes, 1). 



In the flint and pop varieties, having corneous endosperm, 

 colour occurs as xenia, as a rule, only when the female parent 

 carries the recessive character. But even here, East and Hayes 

 have found exceptional cases in which a few heterozygous 

 yellows were distinguishable from homozygous yellows when 

 the female parent bore the dominant character. 



Both red and purple colour of the aleurone layer are com- 

 pletely dominant, and xenia occurs only when they are trans- 

 mitted by the male parent. 



East and Hayes also find that in the case of Be or pC, 

 as described in 1T 131, purple appears as xenia when 

 either of them is the female parent. The writer has found 

 what appears to be a similar case, in the second (i.e. paler) 

 yellow colour which occurs in some breeds of maize, but fur- 

 ther evidence is required to demonstrate the actual facts of the 

 case. 



12 



v. 



