Campbell . — The Embryo-Sac of Peperomia. 109 
embryo-sac at other places. This group of endosperm-nuclei 
may be either at the base of the sac, or at the side, even 
close to the fertilized egg. Shortly after fertilization is com- 
pleted, the cytoplasm within the embryo-sac increases greatly 
in amount, and the central vacuole disappears. At this 
stage (Fig. 6) the cytoplasm is usually densest in the centre 
of the sac, and surrounding this central mass are numerous 
smaller vacuoles separated by thick layers of granular 
cytoplasm. The group of endosperm-nuclei usually occupies 
the central part of the cytoplasm (Fig. 6). 
The fusion of the group of endosperm-nuclei, to form the 
definitive nucleus, which has been followed in detail by 
Johnson 1 , could only be found in its earlier phases (Fig. 7); 
but there seems no reason to doubt the accuracy of his 
observations, as the single endosperm-nucleus resulting from 
the fusion of the group was found, and its division observed. 
According to Johnson’s account, two of the nuclei first fuse, 
and this is followed by the gradual absorption of the whole 
group into one very large nucleus, in which the nucleoli are 
more or less completely fused. 
Fig. 9 shows the large endosperm-nucleus, apparently in 
the early prophase of division. The form was somewhat 
irregular, showing evidences of its compound structure. The 
nucleoli had quite disappeared, and the very numerous chromo- 
somes were plainly evident and showed an almost complete 
separation into two groups, almost suggesting a direct division 
of the nucleus. It is certain, however, that a typical mitosis 
occurs in some cases, and it is not likely that a direct 
division of the primary endosperm-nucleus ever takes place, 
although the possibility of such a division is not to be denied. 
The first division-wall in the endosperm is usually vertical 
(Fig. 10), but it may be more or less inclined, or even almost 
horizontal. The resting nuclei after the first division (Fig. 10) 
are very large and contain numerous nucleoli, each of which, 
in stained specimens, shows a clear area about it : they have 
loc. cit., pp. 4, 5. 
