214 BOTANICAL GAZETTE [SEPTEMBER 
The actual mitosis resulting in the binucleate embryo sac was 
not observed, but binucleate sacs were found March 11 (fig. 25), in 
which the spindle fibers between the nuclei had not yet disappeared. 
By March 16 these nuclei had again divided, showing a great varla- 
tion in the arrangement of the resulting four nuclei (jigs. 26, 27, 60). 
On March 17 the third mitosis (fig. 28) shows one nucleus dividing 
parallel to the main axis and three at right angles to it. Figs. 29-31 
are even more perplexing than the foregoing, showing that rapid 
divisions have occurred in various planes. 
After reaching the eight-nucleate stage there are, in a majority of 
cases, no further nuclear divisions; the egg apparatus begins to 
organize, the antipodals take their proper place, and the polar nuclei 
move toward each other preparatory to fusion (fig. 30). However, 
in very many cases, there is further nuclear division without any 
indication of polarity, the nuclei being distributed promiscuously 
throughout the cytoplasm of the sac and all apparently alike (jigs. 
31-55). 
Mitotic figures were not found in the sac after the eight-nucleate 
stage was reached, but many sacs were examined containing as hig 
as twelve (occasionally more) free nuclei very evenly distributed and 
very similar in appearance. Later a number of embryo sacs were 
found having more than eight nuclei and showing polarity. In these 
four nuclei were in the micropylar and eight or more in the antipodal 
end of the sac (fig. 32). Fig. 54 shows the only observed exception 
to the above rule. (These numbers include also the nuclei which are 
to function as polars at a later date.) _ 
The antipodals, excepting two or three, soon disintegrate. The 
remaining ones enlarge rapidly, sometimes rivaling the egg in their 
prominenee (jigs. 53-54). They seem, however, to be of the passive 
type common among Archichlamydeae. 
The embryo sac of Ulmus americana, therefore, shows 4 condi- 
tion intermediate between the regular eight-nucleate angiosperm 
type and the sixteen-nucleate sac of the Peperomia described by 
CAMPBELL (3) and JoHNSON (11). 
The fusion of the eight nuclei to form the endosperm nucleus 1” 
Peperomia has its parallel in the fusion of several nuclei in Ulmus 
for the same purpose. NawascHINn (16) has reported an instance 
