82 WEATHERWAX: GAMETOGENESIS IN ZEA MAys 
due to the entrance of a sperm into the constitution of the primary 
endosperm nucleus. It is a direct result of the introduction of 
hereditary factors into the endosperm and not to be attributed to 
enzymatic action or other stimulating influence. To include 
“those influences which follow fertilization but are remote from 
it’’ (p. 282) and are ‘‘due to the developing zygote”’ (p. 284), he 
proposes the term ectogony. 
Whether or not the new term is applicable, is not a question 
to be decided in this connection; but the distinction between 
xenia and other influences less directly connected with fecundation 
isa timely one. Xenia may be defined, then, as any effect that may 
bé produced upon the endosperm of an angiosperm by pollination 
with pollen from a plant having a different kind of endosperm. 
Of course, it is not to be expected that xenia will occur in all 
such crosses. Correns (3, pp. 411-414) has outlined a number of 
cases in which xenia will or will not occur in maize, and East and 
Hayes (7, p. 103) have condensed all the available data into a law 
of xenia. For our purpose, it may be said that xenia will occur in 
any cross in which the male parent possesses the dominant and 
the female the recessive of an allelomorphic pair of endosperm 
characters, or when the two parents possess respectively two 
characters whose interaction is necessary for the production of a 
visible effect. When dominance is incomplete, or when inhibiting 
factors are present, complications are introduced which need not 
be discussed here. 
THE ENDOSPERM OF ANGIOSPERMS 
The variability of the maize endosperm, with the accompanying 
phenomenon of xenia, gives it a prominent place in any explana- 
tion of the endosperm of angiosperms. This tissue has been ex- 
plained in many ways, but its true significance still offers an un- 
solved problem. The correct explanation, if it is ever found, will 
probably develop from researches on the phylogenetic origin of 
the angiosperms. 
In most of the plants in which fecundation has been studied, 
one sperm has been found to enter into the constitution of the 
endosperm, and the phenomenon is believed to be of general oc- 
currence. But there are many exceptions which serve to com- 
