INHERITANCE— IMPRO VEMENT B I ' PRE E DING i 79 



When a purple is crossed with white, the resulting grain CHAP, 

 may be white. Xenia results when an inhibiting factor (II 131) V ' 

 occurs to prevent the appearance of colour. East and Hayes's 

 explanation of this phenomenon shows that it does not, as 

 has been suggested, indicate dominance of whiteness. These 

 authors also found cases in which the purple is not fully in- 

 hibited, and then a light purple results, whichever parent 

 carries the colour. 



Our knowledge of xenia in maize may be summarized as 

 follows : — 



(1) When the parents of a heterazygote differ in a single 

 visible endosperm character in which dominance is complete, the 

 pollen only produces xenia when it carries the dominant allelo- 

 morph. 



(2) When the parents differ in a single visible endosperm 

 character in which dominance is incomplete, the pollen produces 

 a modifying effect on the visible strength of the dominant allelo- 

 morph. 



(3) When each parent carries one of tzuo characters the union 

 of both of which is necessary to render the other visible, the pollen 

 also produces xenia when it carries the factor necessary to render 

 visible the dominant allelomorph borne by the female parent. 



(4) When the pollen parent bears the recessive allelomorph, 

 full xenia does not result, though in some cases a partial effect 



may be produced. 



Xenia does not appear to affect the shape or size of the 

 grain, as these are plant characters; in crosses between two 

 dent breeds of the same colour, but which differ in shape and 

 size of grain, no difference has been detected in the first ear 

 produced. 



From the foregoing it is clear that though xenia, i.e. the 

 effect of pollen on the F r seed generation, may in some cases 

 be useful as an indication that crossing has taken place, the 

 absence of xenia cannot be relied upon to indicate that crossing 

 has not taken place ; in many cases, therefore, the hand-picking 

 of seed-grain is useless as a means of entirely eliminating the 

 effect of crossing. 



1 34. Splashed Purple Colour of Aleurone Layer. — The cause 

 of the occurrence of splashed purple colour in the aleurone 

 layer has long been a subject of speculation and investigation, 



