Campbell .— The Embryo-sac of Pandamts . 783 
demonstrations made of the presence of a male generative nucleus within 
the egg, or its fusion with the egg nucleus. 
The fusion of the polar nuclei takes place about the same time as the 
fertilization of the egg, but there is probably some variation in this respect. 
The fusing polar nuclei (Figs. 25, 26, PI. LX) are extremely conspicuous. 
Each one contains as a rule a single very large nucleolus and shows an 
evident reticulum, which does not stain at all strongly and is apparently 
rather deficient in chromatin. The nuclei become closely appressed and 
their cavities gradually fuse until there results a single very large nucleus, 
the primary endosperm nucleus, within which can still be clearly seen the 
separate nucleoli of the component nuclei. In the nucleus figured there 
were six large nucleoli, only two of which show in the figure. It is probable 
that the division of the primary endosperm nucleus follows quickly, as only 
one resting stage was found, while a number of cases were seen in which 
the nucleus was in process of division. In the resting nucleus which is 
figured the nuclear reticulum was more conspicuous than it is in the unfused 
polar nuclei, and there is much more chromatin, which shows in the form 
of distinct strongly staining granules. 
In Figs. 30-2 are shown the details from a very peculiar embryo-sac. 
At the upper end of the sac there was an imperfectly differentiated egg 
apparatus which showed four instead of three nuclei, and it was impossible 
to tell which of the four represented the egg. What looked like the end 
of the pollen-tube (p. t) could be seen at the apex, but if this structure 
really was the pollen-tube, it had not yet destroyed either of the synergidae. 
Near the egg apparatus there was a single cell (y) which looked very much 
like an egg-cell of the normal type. Near the middle of the sac there was 
a large mass of cytoplasm surrounding a group of about twelve large 
nuclei which were in process of fusion. Fig. 32 shows five of these. 
Near this group of nuclei there was a second cytoplasmic mass (x) attached 
to the wall of the embryo-sac and containing what looked like two nuclei, 
but these were not very distinct. What would have been the further 
history of this abnormal embryo-sac is impossible to conjecture. 
In other cases apparently otherwise normal it looked as if there were 
two primary endosperm nuclei. Thus in the embryo-sac from which the 
endosperm nucleus shown in Fig. 27 was taken, there was a second 
group of seven nearly completely fused nuclei. 
The few preparations that were secured showing the division of the 
primary endosperm nucleus were all rather advanced metaphases of mitosis, 
no examples of prophases being found. Fig. 28, a , shows the nuclear 
spindle of the dividing primary endosperm nucleus. The chromosomes 
form an undivided equatorial plate. The number of the chromosomes, as 
might be expected from a nucleus made up of the fusion of several, is 
extremely large, and their small size and crowded position made it prac- 
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