
218 BOTANICAL GAZETTE [SEPTEMBER 
When two races differ in a single visible endosperm character in which 
dominance is complete, xenia occurs only when the dominant parent is the 
male; when they differ in a single visible endosperm character in which domi- 
nance is incomplete or in two characters both of which are necessary for the 
development of the visible difference, xenia occurs when either is the male. 
It is evident that such a statement can be true only if the two 
male nuclei always carry the same hereditary factors and if a male 
nucleus always enters into the formation of the endosperm. The 
first requirement has been satisfied in every experiment thus far 
recorded; the second requirement will now be considered. 
In particular cases where xenia has followed the crossing of 
races differing in endosperm color, aleurone color, or ability to 
mature starch grains, the seeds are not uniform in appearance. 
One may be half starchy and half wrinkled; another may be half 
yellow and half colorless; still another may have half of the aleurone 
cells red or purple and the other half colorless. Examples of this 
kind are rarely found, although it is a common thing to find seeds 
with a mottled appearance affecting only the aleurone colors. 
CoRRENS and WEBBER suggested independently that in these 
cases the male nucleus may fail to unite with the fusion nucleus and 
each divide independently, forming either the half-and-half seeds 
or those which are mottled. WEBBER also suggested, as an alter- 
nate hypothesis, the fusion of the male nucleus with one of the polar 
nuclei, the other polar nucleus remaining independent and dividing. 
East and Hayes have shown that CorrENS and WEBBER were 
dealing here with two phenomena. The seeds that are mottled 
become so only from the development or non-development of color 
in the aleurone cells. They merely exhibit irregularity of Mende- 
lian dominance, since in some crosses practically all seeds hetero- 
zygous for one of the factors producing aleurone color are mottled, 
although homozygotes are fully colored. Furthermore, the 
mottling does not extend to the color or other character of the 
deeper endosperm tissue in case the parental varieties had such differ- 
ences, which necessarily would be the condition if the endosperm 
had been formed according to either of WrBBER’s independent 
development hypotheses. This criticism has also been made inde- 
pendently by Emerson (8). 



