588 THE AMERICAN NATURALIST. [Vol. XXXIX. 



These experiments of De Vries, Correns, Webber, and others 

 have established experimentally the facts of xenia and Nawas- 

 chin's theory of double fertilization seems to offer the only 

 explanation of the phenomenon. But it was left to Guignard 

 (:oi) to make the concluding observation that a second sperm 

 nucleus does actually enter into the composition of the endo- 

 sperm of maize, and this fact clinched the argument which up 

 to this time had been a speculation. 



Webber has made a very important addition to the theory of 

 " double fertilization " as an explanation of xenia in some obser- 

 vations and speculations on a mottled condition which is some- 

 times present when white corns are pollinated by colored. He 

 found that the color was sometimes only transmitted in spots as 

 when Hickory King was pollinated by Cuzco, or perhaps only 

 half a kernel may be colored. Webber offers the hypothesis 

 that the second sperm nucleus may enter the embryo-sac but 

 instead of uniting with the two polar nuclei to form a triple 

 fusion may itself divide separately and thus gives rise to a 

 progeny very different from the other endosperm nuclei. 

 There might then be two sets of nuclei in the endosperm one of 

 which is composed of nuclei which would come directly from 

 the male parent. These latter then might become distributed 

 ^throughout the embryo-sac but would tend to remain in groups 

 as multiplication progressed and would certainly be expected to 

 influence the character of the tissue which is formed later when 

 the walls are developed around the free nuclei. As Webber 

 expresses it, there might be formed islands of tissue in the 

 endosperm whose cells contain nuclei derived directly from the 

 second sperm and such tissue would be expected to show char- 

 acters of the male parent in spots as xenia. Again, if the sperm 

 nucleus should unite with only one of the polar nuclei and the 

 other should give rise to an independent progeny we should 

 expect similar mixed conditions in the endosperm, with xenia 

 only expressed in the areas dominated by nuclei containing 

 material derived from the sperm. 



There have been reported illustrations of xenia in tissues out- 

 side of the endosperm but we are fully justified in awaiting 

 their confirmation before accepting them, especially since some 



