1 6 Campbell . — The Development of the Flower and 
distinct and bounded by a well-marked protoplasmic mem- 
brane. The two polar nuclei move toward the centre of the 
sac, where they finally fuse. There is usually no appreciable 
difference in the size or structure of the two, in which respect 
Lilaea agrees with Naias and Z annichellia. In his recent 
paper on the development of Sagittaria variabilis , Schaffner 
states 1 that the upper polar nucleus is by far the largest 
nucleus of the embryo-sac, and in the case figured in Fig. 24 
the upper polar nucleus is slightly larger, but this is probably 
not constant. 
The embryo-sac increases rapidly in size after the formation 
of the egg-apparatus and antipodal cells, and with this increase 
in size there is a change in the various nuclei, as well as 
marked growth in both the antipodal cells and the egg- 
apparatus. The former increase very much in size, and are 
usually arranged in a manner which often strongly suggests 
the arrangement of the cells of the egg-apparatus. The 
uppermost cell projects strongly into the cavity of the 
embryo-sac, and its nucleus becomes decidedly larger than 
those of the two lower cells (Fig. 28). In all of the cells 
the protoplasm is very granular, and there are often aggrega- 
tions which stain strongly, and look almost like nuclei. The 
nuclei stain readily, and possess a single large nucleolus. 
In the upper part of the embryo-sac the three nuclei of the 
egg-apparatus, which at first were nearly alike, soon show 
a decided difference in appearance. The two nearest the 
apex of the sac, the nuclei of the synergidae, increase very 
little in size, but remain clearly defined. The lower, or egg- 
nucleus, however, becomes many times larger than at first. 
The polar nuclei also increase very much in size, and the 
endosperm-nucleus resulting from the fusion (Fig. 27, en.) is 
the largest of all the nuclei in the embryo-sac. The syner- 
gidae, have a large vacuole, but the upper part, including 
the nucleus, is filled with granular protoplasm. The egg-cell 
extends some distance below the synergidae, and its granular 
1 Schaffner, The Life History of Sagittaria variabilis, Bot. Gazette, April, 1897. 
