86 
IOWA ACADEMY OF SCIENCES. 
it being impossible to identify the o ie which is to become 
abortive. The seed coats soon grow nearly even with the 
tip of the nucellus. The latter is relatively large. At this 
time great difficulty was found in studying the earliest 
appearance of the archesporium. Development appears 
to be perfectly normal, except that the embryo sac, instead 
of being formed near the apex of the nucellus is formed 
near the center, as many as ten or twelve rows of cells be- 
ing between it and the apex. Mitosis could be observed in 
some cases, but was not studied owing to the minute size 
of the cells. 
The macrospore is formed normally, and increases rapidly 
in size. When it reaches the length of about 25 microns its 
nucleus divides, one daughter cell giving rise to the antipodal 
cells, and the other to the egg cell and the synergids. The 
antipodal cells disappear almost immediately, being indis- 
tinguishable very shortly after formation. The endosperm 
nucellus is formed by the conjugation of the nuclei from 
either end of the sac. This stage of formation is shown in 
figure c, Plate II. The cells in the lower part of the n ucellus 
increase rapidly in number and size, the embryo sac elongates 
in the direction of the micropyle, breaking down those cells 
in this portion of the nucellus, and coming ultimately to 
occupy a position just below the micropyle. At the stage 
shown in figure c, Plate II, the embryo sac is oval in shape, 
and rather small in comparison with the size of the egg cells 
and the synergids. These extend nearly half the length of 
the embryo sac. 
The embryo sac continues to increase rapidly in size, espe- 
cially in length. For a period neither the oosphere nor the 
definitive nucleus changes the synergids and the oosphere 
remaining in their place, and the endosperm nucleus mov- 
ing and keeping approximately in the center of the sac. 
After the lapse of several days to a week, the latter begins 
to divide rapidly, and soon fills the entire sac with small 
nuclei. These do not surround themselves with a definite 
cell wall. At this time the embryo sac has reached a 
length of .525mm. 
