356 BOTANICAL GAZETTE [MAY 
Immediately after the organization of the egg apparatus, the 
polar nuclei move toward one another. The lower nucleus 
travels much faster than the upper one, so that they meet com- 
paratively near the oosphere. The two take a position just 
beneath the egg, but in contact with it, and there fuse to form 
the endosperm nucleus. An early stage of fusion is illustrated 
by fig. 6, in which one polar nucleus appears closely pressed 
against the other. In fig. 7 the membranes between the two 
fusing nuclei have already disappeared. The endosperm nucleus 
is very large, almost spherical in outline, and is furnished with a 
rather open reticulum and one large densely staining nucleolus. 
The fusion of the polar nuclei may be delayed, in some instances 
until the time of fertilization (fig. g), but ordinarily the forma- 
tion of the endosperm nucleus has taken place before the pollen 
tube discharges its contents into the embryo sac. 
When the embryo sac is mature, it occupies about one-half 
the entire length of the nucellus. The lower two-thirds of the 
embryo sac consists of the narrow elongated antipodal cells. 
As a rule, the cells of the nucellus immediately surrounding the 
antipodals are empty and more or less irregular in outline. A 
general conception of the structure and position of the parts of 
the ovule at the time of the maturity of the embryo sac is given 
in fig. ro. 
LATER HISTORY OF THE ANTIPODALS. 
The antipodal portion of the embryo sac in dicotyledons has 
been found to vary greatly in the number, structure, and position 
of its cells. Chamberlain (1895) finds that the number of antip- 
odals in A. Novae-Angliae ranges from two to thirteen, six oF 
seven being the usual number. The lower antipodal was found 
to differ from the others in size, in the density of its cytoplasm, 
and in the appearance of its nuclei. He observes, however, 
that in one instance the contents of this cell bear a superficial 
resemblance to an egg and believes that it represents an 
antipodal oosphere. The number of nuclei in an antipodal cell 
was found to vary from one to over twenty. In my study of 
Aster I find that the antipodals in the species examined, 
although showing in no instance as many as thirteen cells, agree 
