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lished that there at least xenia occurs. When the white-grained 

 variety {Zea alba) is poUinated from the blue-grained variety 

 {Zea cyanea), the majority of the seeds have white endosperm 

 around the embryo, but a few have blue endosperm. The con- 

 verse is likewise the case. It must be noted that the effect is 

 only on the so-called " endosperm," or nutritive layer around 

 the embryo ; the envelope of the seed, for instance, is never 

 affected. 



What happens seems to be this. The pollen-tube arising from 

 the pollen-grain contains two generative nuclei, which arise by 

 the division of one. Of these two nuclei, one fertilises the egg- 

 cell, the other fuses with what are called the polar-nuclei (a fact 

 discovered by Nawaschin and Guignard). Thus there is a sort of 

 double fertilisation within the embryo-sac ; the one results in the 

 embryo, the other gives origin to the endosperm. 



Thus we see that xenia (in the well-authenticated case of 

 maize) is no mysterious influencing of maternal tissue by the 

 pollen-tube, and that it does not require Darwin's hypothesis of 

 a migration of " gemmules " from the fertilised ovum into the 

 surrounding tissue. It is a phenomenon sui generis, due to the 

 very peculiar " double fertilisation." As Weismann points out, 

 it corroborates the view that the nuclei are the vehicles of the 

 hereditary qualities. 



Many of the alleged cases of xenia are cited in Prof. Delage's 

 great work (1903, p. 252), the most picturesque being that of an 

 apple-tree of Saint Valery. " This tree was sterile through the 

 abortion of its stamens. Every year the young girls gathered 

 branches from other apple-trees in flower, and shook them over 

 the flowers of the non-staminate tree to fertilise them. Tillet 

 De Clermont-Tonnerre (1825) relates that the resulting fruits 

 recalled in their size, colour, and taste, those of the trees which 

 had furnished the pollen." 



It is to be feared, however, that many of the alleged cases of 

 xenia will not stand examination. Thus the records in regard 



