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The Ohio Naturalist. 
[Vol. Ill, No. 4 , 
which degenerate for the enlargement of the sac which occupies 
the entire inner zone in the eight-celled stage (Fig. 7). The 
walls of this inner zone were so delicate that it was difficult to 
get good preparations of the eight-celled stage. The outer zone 
is made up of thicker walled cells, which are more permanent and 
which are in more or less regular rows, which radiate from the 
inner zone. The inner zone is connected with the micropolar end 
of the ovule by two or three rows of elongated cells, which 
degenerate to form the path for the pollen tube ( Figs. 5 and 23). 
After fertilization the part of the nucellus projecting through the 
micropyle degenerates and the integuments come together at that 
point . 
Lyon* describes an enlargement of the ovule similar to that in 
Euphorbia corollata, except that there is no zone-like structure, 
and the cells which break down for the passage of the pollen tube 
are larger and looser than the surrounding tissue. 
After the conjugation of the polar nuclei the sac enlarges on 
one side and at right angles to its long axis (Fig. 24). The 
endosperm nucleus passes down into this pocket, divides and event- 
ually forms a peripheral endosperm (Fig. 18). One case was 
observed where the endosperm nucleus had failed to divide, 
although the embryo was in its five-celled stage. At the lower 
end of this newly formed pocket a mass of endosperm is formed, 
which probably hastens the absorption of the nucellus at that 
point (Fig. 19). At this time the egg has enlarged considerably ; 
the synergids remain about the same size and disappear very 
early ; in only one case was a syuergid observed to persist until 
after the formation of the first transverse wall in the embryo. 
By the enlargement of the sac in the new direction the antipodals 
are left in a small pocket (Fig. 24 a); they degenerate, sometimes 
by fragmentation, and eventually disappear. 
The pollen tube was observed a number of times, always fol- 
lowing the canal formed by the absorption of the cells previously 
described, but in no case was I able to observe the act of fertili- 
zation. 
EMBRYO. 
The fertilized egg divides by transverse wall, the lower cell 
enlarging into a large basal cell (Fig. 8). The upper cell now 
divides by transverse division (Fig. 9). This is followed by a 
series of transverse divisions, the order of which I could not 
determine, resulting in a filamentous embryo of five, six or seven 
cells, with one large basal cell (Figs. 19, 11, 12). When the 
embryo has reached this condition the cell next to the upper cell 
divides by a longitudinal wall (Fig. 13). The cell next below 
now divides in a similar manner, while the two cells next to the 
Florence May Lyon. A Contribution to the Life History of Euphorbia corollata. 
Bot. Gaz. 25, 6. i 89 S.’ pp. 418-426. 
