-roit] SHARP—PHYSOSTEGIA 219 
cells ie soon multiply to several, and two free polar nuclei 
(fig. 
eee before the division to form eight nuclei, a laterally 
directed lobe begins to develop from the antipodal region of the 
sac, and at the eight-nucleate stage is very conspicuous (fig. 6). 
It rapidly invades the integumentary tissue, forming what may for 
convenience be called the ‘‘endosperm lobe,” since it is soon to 
contain nearly all of the endosperm formed. During these early 
stages it probably serves in a haustorial capacity, as does the 
greatly enlarged antipodal portion of the embryo sac of Saururus 
(JOHNSON 7). 
Meanwhile the micropylar polar nucleus migrates to the narrow 
portion of the sac near the antipodals, where it meets and fuses 
with the polar nucleus of the antipodal group. The resulting 
fusion nucleus is invariably found in this position (fig. 7). 
At about this time the antipodal cell which lies nearest the sac 
cavity takes on an appearance different from that of the others. 
It becomes binucleate, the cytoplasm changes in character, stain- 
ing more deeply, and rapid enlargement causes its wall to become 
strongly convex (fig. 7). This enlargement continues until the 
cell bulges out conspicuously into the embryo sac cavity (fig. 10), 
and its wall thus partitions off the small pocket in which it lies 
_ with the other antipodals. In stages somewhat later it bears much 
resemblance to the first few cells of the endosperm, but the possi- 
bility that it also is of endospermous origin is precluded by the 
' fact that it has been observed side by side with an undoubted 
endosperm nucleus resulting from the triple fusion (fig. 9). 
The function of the cell in question is in all probability haus- 
torial, recalling the behavior of the basal antipodal in several genera 
of the Galieae (LLoyp 10), although in the sac under consideration 
the neighboring tissue is not actively invaded. It soon fills all 
the space formerly occupied by the other antipodals, which dis- 
organize and completely disappear (figs. 13, 14, 16), while in its 
general form and relation to the vascular supply it is especially 
well suited to the performance of a nutritive function during the 
rapid development of the endosperm. Later it disappears and the 
tissue of the region becomes irregularly broken down (figs. 18-20). 
