which gives a stimulus to development in correlation with the other.
If, on the other hand, the endosperm is the product of an act of
fertilization as definite as that giving rise to the embryo itself,
we have to recognize that twin-plants are produced within the
embryo-sac--one, the embryo, which becomes the angiospermous plant,
the other, the endosperm, a short-lived, undifferentiated nurse to
assist in the nutrition of the former, even as the subsidiary embryos
in a pluri-embryonic Gymnosperm may facilitate the nutrition of the
dominant one. If this is so, and the endosperm like the embryo is
normally the product of a sexual act, hybridization will 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