ill give a hybrid
endosperm as it does a hybrid embryo, and herein (it is suggested) we
may have the explanation of the phenomenon of xenia observed in the
mixed endosperms of hybrid races of maize and other plants, regarding
which it has only been possible hitherto to assert that they were
indications of the extension of the influence of the pollen beyond the
egg and its product. This would not, however, explain the formation
of fruits intermediate in size and colour between those of crossed
parents. The signification of the coalescence of the polar nuclei is
not explained by these new facts, but it is noteworthy that the second
male-cell is said to unite sometimes with the apical polar nucleus,
the sister of the egg, before the union of this with the basal polar
one. The idea of the endosperm as a second subsidiary plant is no new
one; it was suggested long ago in explanation of the coalescence of
the polar nuclei, but it was then based on the assumption that these
represented male and female cells, an assumption for which there
was no evidence and which was inherently improbable. The proof of a
coalescence of the second male nucleus with the definitive nucleus
gives the conception a more stable basis. The antipodal cells aid more
or less in the process of nutrition of the developing embryo, and may
undergo multiplication, though they ultimately disintegrate, as do
also the synergidae. As in Gymnosperms and other groups an interesting
qualitative change is associated with the process of fertilization.
The number of chromosomes (see PLANTS: _Cytology_) in the nucleus of
the two spores, pollen-grain and embryo-sac, is only half the number
found in an ordinary vegetative nucleus; and this reduced number
persists in the cells derived from them. The full number is restored
in the fusion of the male and female nuclei in the process of
fertilization, and remains until the formation of the cells from which
the spores are derived in the new generation.

In several natural orders and genera departures from the course of
development just described have been noted. In the natural order
Rosaceae, the series Querciflorae, and the very anomalous genus
_Casuarina_ and others, instead of a single macrospore a more or less
extensive sporogenous tissue is formed, but only one cell proceeds to
the formation of a functional female cell. In _Casuarina_, _Juglans_
and the order Corylaceae, the pollen-tube does not enter by means
of the mic