12 IOWA STUDIES IN NATURAL HISTORY 
into the placenta and broadens into a rounded structure. A 
membrane for a time surrounds the haustorium, separating its 
protoplasm from the adjacent placental tissue (Figs. 11-14). 
Digestion of the special receptive placental tissue continues 
until most of its walls have broken down, leaving a cavity filled 
with a coenocytic mass. Commonly a small volume of the re- 
ceptive tissue is left on the funicular side with walls intact. 
With the disappearance of walls from this portion of the pla- 
cental tissue the nuclei are set free in the common-cytoplasm 
and present a wide range of sizes and shapes. They may en- 
large somewhat, and apparently some of them unite to form 
tuber-like nuclei many times their normal size (Fig. 14). 
Midway in the embryo development one or both of the en- 
dosperm nuclei of the micropylar haustorium may be seen ap- 
parently breaking through the limiting membrane. These en- 
dosperm nuclei, measuring 28x15 micra, are very different from 
those of the placental tissue being larger and having great 
splotches of darkly staining chromatin. They develop lobes 
which may in turn become dissociated amitotically into separ- 
ate masses. These with the placental nuclei lying in the fluids 
of the haustorium, offer a most peculiar assemblage of nuclear 
structures (Fig. 14). 
At a later stage the haustorium shrivels, leaving an empty 
pit in the placenta and also a companion cavity in the base of 
the seed. As suggested by Merz (7) the endosperm adjacent 
to the haustorium forms a plug which closes this opening into 
the seed. The placenta, after seeds are shed, is pitted all over 
its surface, marking the positions of the haustoria. 
The endosperm about the seed offers no peculiarities. It 
forms a spindle-shaped mass which entirely surrounds the em- 
bryo except at the base of the long and slender suspensor, which 
remains until late in the development anchored to the funicular 
wall of the embryo-sac. 
THE MATURE SEED 
During later development of the embryo the seeds are pressed 
together in a compact layer between placenta and ovary wall. 
Under dissection of living material it was noted that the seeds 
