INHERITANCE— IMPROVEMENT BY BREEDING 175 



the gametes. Nevertheless the phenomena are very definite, chap. 

 and it is not unlikely that a further study of them may throw 

 important light on the architecture of the living cell." 



East and Hayes report a case in which perfect coupling 

 occurred between red cobs and red pericarp colour in their 

 R L red (If 144), and another case in which the red pericarp colour 

 of R 3 (IT 144) was completely coupled with red silks; "Coup- 

 ling is proved by the fact that red silks occur without red 

 pericarp in other combinations". Emerson has reported (cf. 

 East and Hayes, 1) cases in which certain red colours of maize 

 are absolutely coupled in their inheritance, while in other cases 

 spurious allelomorphism occurs. 



133. Xenia. — When an ear of pure-bred white-grained 

 maize is crossed with pollen of a pure-bred yellow-grained 

 breed, the resulting grain is yellow, and the same result is 

 obtained with the reciprocal cross. As this is the F 1 seed 

 generation, and as all the cross-bred grains are yellow, this is 

 not a case of segregation of a unit-character (IT 128), but is the 

 visible effect of the second male nucleus on the endosperm ; it 

 is called xenia. The term was originally proposed by Focke 

 (i) to express the supposed influence of foreign pollen on 

 maternal tissue. But Guignard' (1) and Nawaschin (1) found 

 that the endosperm is in reality a part of the filial generation, 

 formed by the development of the endosperm nucleus after 

 fusion with the second male nucleus of the pollen cell ; this 

 disposed of the only authentic examples of xenia as originally 

 defined, and there is no further reason to use the word in that 

 sense. But as the phenomena remain the same, the term is 

 still used to express them. 



Xenia, in the modified sense of the word, affects not only 

 the colour, but also the chemical composition, of the endo- 

 sperm ; if wrinkled sugar maize is crossed with pollen of a 

 starchy breed, the resulting grain is starchy (whether flint or 

 dent). East and Hayes (1) find that when a flint (starchy) 

 breed is crossed with a dent breed (also starchy) the resulting 

 grain is intermediate, i.e. partial xenia shows in that the re- 

 sulting grain may carry a slight, though often almost indis- 

 tinguishable, crease. 



It will be noticed that in the cases cited it is the dominant 

 factor, whether carried by the male or the female parent, 



