ANDERSON: EMBRYOGENY OF MARTYNIA LOUISIANA 165i 
the sperm has been in direct contact withthe egg nucleus. 
This would seem to indicate that the pollen tube carries the 
sperm into the egg-cell. 
THE ENDOSPERM 
The primary endosperm nucleus, resulting from the union 
of the two polar nuclei, occupies a position near the center of 
the embryo-sac. Usually before the pollen tube enters the sac 
this endosperm nucleus divides and a transverse wall is formed 
between the two resulting nuclei, thus dividing the embry-sac 
into two chambers (Fic. 29). At this time, the cytoplasm in 
the embryo-sac has a frothy appearance due to the many small 
vacuoles present. This frothy character seems to appear after 
the fusion of the polar nuclei (Fic. 28). Very’ conspicuous, 
densely staining plastid primordia and granules are present in 
the cytoplasm. The synergids seem to have increased in length 
and to have become more vacuolate (FIG. 29). The egg-cell 
remains apparently unchanged. The antipodals are more 
elongated and sometimes contain a granular, densely staining 
cytoplasm (Fic. 29). After the wall dividing the embryo-sac 
into two chambers is formed, the nuclei move to a nearly central 
position in their respective cells. And, as one would infer, the 
endosperm cell at the micropylar end of the sac grows more 
rapidly than the one at the chalazal end (Fic. 31). The pollen 
tube usually reaches the embryo-sac when the endosperm is in 
a two-celled stage. In Fic. 31, it may be seen that fertilization 
has taken place. The outline of the tip of the pollen tube is shown 
by a dotted line in the lower part of the egg-cell, and the shading 
represents the relative density of the contents in different parts 
of the tube. Only the tip seems to have discharged its contents. 
A remnant of one synergid still shows. The synergids, if 
not crushed out by the entrance of the pollen tube, are soon ab- 
sorbed. The endosperm cell in the micropylar end of the sac 
is very large and contains a large nucleus with irregular outline 
and a prominent nucleolus. Many plastids are still seen in the 
frothy cytoplasm of both endosperm cells, and some are present 
in the antipodals, which continue to grow, especially in length 
(Fic. 31). The increase in size of the antipodals is better illus- 
trated in Fic. 32. Their cytoplasm is somewhat vacuolate at 
this stage and the large nuclei contain very prominent nucleoli. 
Usually the first division of the endosperm cell is transverse 
