WEATHERWAX: GAMETOGENESIS IN ZEA MAyYs 81 
In 1881, Focke (9, p. 511) coined the word xenia to apply to the 
immediate effect of foreign pollen upon maternal tissue. 
Nawaschin’s discovery (16) that in many plants, one of the 
sperm nuclei enters into the makeup of the endosperm, suggested 
an explanation of the mechanism of xenia in maize; and Guignard’s 
discovery of ‘“‘double fecundation”’ in maize, in 1901 (10), left no 
room for reasonable doubt as to the mechanism of xenia. 
The immediate effects of cross pollination, that is, such effects 
as may immediately be observed in the seed or fruit in which the 
hybrid embryo is borne, are probably not so common as has often 
been supposed; and by no means are all of them illustrations of 
xenia, in the true sense of the word. 
There is a common belief that pumpkins growing near water- 
melons will, by hybridization, impair the quality of the latter in 
the first generation; and numerous other instances have been 
cited of slight changes in the quality of fruits, supposed to be due 
to the immediate effects of cross pollination. The experimental 
demonstration of most of these, with races known to be genetically 
pure for the characteristics considered, has not been accomplished. 
Another type of the phenomenon is afforded by hybrids between 
varieties of peas and other plants, which are variable as to the 
color or physical character of the cotyledons. Here a dominant 
character may, through hybridization, appear in seeds borne on 
plants pure for the recessive character. But this is merely the 
early recognition of a hybrid by means of characteristics that are 
differentiated in the embryo. Bailey and Gilbert (1) must have 
had in mind such phenomena as these when they made the errone- 
ous statement (p. 327) that xenia occurred in peas. 
In contrast with these phenomena is the immediate effect 
upon the endosperm, so well known in maize. This has also been 
demonstrated in teosinte-maize hybrids (21), and has been re- 
ported in a few other crosses between different varieties of cereals. 
The primary essential for xenia is variability of endosperm in plants 
that will hybridize, and for this reason, maize when used for one 
of the parents, at least, furnishes the best-known illustration. 
In a recent review of the whole question of influences following 
fecundation, Waller (22) suggests that the term xenia be reserved 
for the phenomenon limited to the endosperm of angiosperms and 
